High-voltage power-on and power-off response principle of each control node

High-voltage power-on and power-off response principle of each control node

  1. General principles of high-voltage power-on and power-off response of each control node

The high-voltage power-on and power-off responses of each control node include a normal situation response and an abnormal situation response. The response action of each control node to the high-voltage power-on and off demand shall conform to the following general principles:
(1) Undesirable acceleration, deceleration, reversing and steering of the vehicle should be avoided or prevented.
(2) Personal casualties, equipment damage or environmental damage caused by high-voltage faults should be avoided or prevented.
(3) Meet the high-voltage power-on and power-off performance requirements.
(4) The performance requirements should be met on the premise of meeting the safety requirements, that is, the principle response priority of a and b should be higher than that of c;

  1. Principles of Response to Abnormal Situations

For any abnormal situation, there should be corresponding handling measures:
(1) If each control node has a response function corresponding to this abnormal situation and the function is normal, the response shall be performed according to the established function.
(2) If each control node has a response function corresponding to this abnormal situation but this function fails, it should consider adding the corresponding fail-safe function and respond according to the fail-safe procedure.
(3) If each control node has no feasible response plan for this abnormal situation, it shall take identification and explanatory measures for the residual danger.
(4) In the event of a vehicle accident, emergency high-voltage power-off should be performed.
(5) If Category I and Category II undesired personnel actions and vehicle high voltage faults occur at the same time, priority shall be given to dealing with vehicle high voltage faults. Unexpected personnel actions of Category III should be treated with emergency high-voltage power-off.

  1. Principles of Response to Undesired Human Actions

(1) For category I undesired human actions, if the vehicle has no fault, respond according to the Quick Key Cycle processing logic table shown in Table 1. Description: The vehicle speed condition is to consider that after the high-voltage power-on is completed, if the vehicle is still in a stationary state, it is considered that the current driver’s “driving” intention is still unclear, and the system should be in the original count state of Quick Key Cycle; if the vehicle starts to run, then Considering that the current driver’s “driving” intention is clear, the system should jump out of the original counting state of Quick Key Cycle, and the counter should re-count.

Table 1 - Quick Key Cycle processing logic table to respond
Table 1 – Quick Key Cycle processing logic table to respond
Quick Key Cycle processing logic
Quick Key Cycle processing logic

(2) For category II undesired human actions, because the actual driving intention cannot be judged, it is assumed that the driver has taken an abnormal operation under special circumstances, so each control node should respond according to the normal high-voltage power-off sequence.

(3) Emergency response to high-voltage power-off should be made for the undesired actions of Class III personnel.

  1. Response principles for vehicle high voltage fault conditions

When a high-voltage fault occurs in the vehicle, the high-voltage power-on and power-off response of each control node must meet the following principles:
(1) A high-voltage fault occurs in the vehicle during the normal high-voltage power-on process. If the fault is serious but the emergency high-voltage power-off conditions are not met, the power-on behavior should be stopped immediately and the motor should not be able to output (torque, electric energy), or DC/DC. There is power output, and the power-off is completed according to the normal power-off sequence.

(2) If a high-voltage fault occurs during the normal high-voltage power-off process, only the fault code is allowed to be recorded, and no response is made to the fault, and the power-off is completed according to the normal high-voltage power-off sequence.

(3) If the vehicle has a high voltage fault in any state (except the state that has entered or completed the high voltage power-off process), if the severity of the fault meets the conditions for emergency high-voltage power-off, each control node shall respond to emergency high-voltage power-off.

(4) For a fault that triggers an emergency high-voltage power-off, if the severity of the fault meets the condition that high-voltage power-on is not allowed, the vehicle is not allowed to be powered on again until the fault is manually eliminated.

Read more: How Lithium-Ion Power Batteries Work

Do you really understand the high-voltage power-on and power-off technology?

Do you really understand the high-voltage power-on and power-off technology?

High-voltage power-on and power-off technology is an important part of the power battery energy management system for electric vehicles. This section puts forward the principle requirements for the power-on and power-off behavior of each high-voltage control node of the electric vehicle electric system, and makes time mandatory requirements for the response behavior of each control node under the general principle. Each control node refers to the node on the HCAN, including the vehicle controller (VCU), integrated power unit (IPU), inverter (DC/DC) and battery management system (BMS). The contents of high-voltage power-on and power-off of electric vehicles include the normal high-voltage power-on sequence, the normal high-voltage power-off sequence, and the emergency high-voltage power-off sequence. These three power-on and power-off sequences are the core content of the high-voltage control of the electric vehicle power battery energy management system.

The following describes the related terms of high-voltage power-on and power-off technology:
High-voltage power-on means that each control node responds to the power-on demand. After the high-voltage battery pre-charges the load through the pre-charge circuit, the voltage difference across the high-voltage relay is less than the set threshold Vth, and then the total positive relay is closed. . The high-voltage power-on completion sign is that the total positive relay is closed. The voltage difference is equal to the total voltage value of the high-voltage battery minus the load voltage value at both ends of the DC bus. During the high voltage power-on process, the voltage difference setting threshold Vth should be set according to the impulse withstand voltage condition of the inductive load.

If the rated voltage is 360V, the voltage difference threshold of high-voltage power-on and power-off technology is Vth=360V×(1-90%)=36V[91]. High-voltage power-off is a process in which each control node responds to the power-off demand, disconnects the high-voltage battery, discharges the remaining power, and finally enters the sleep state according to the user’s power-off demand. The high-voltage power-off completion flag indicates that the VCU enters the sleep state. The power-off requirement can be the user’s requirement to “cut off the power”, which corresponds to the user’s “key off/Acc” action; it can also be the requirement of the electric system to automatically “cut off the power” in a dangerous situation.

The residual power discharge is to discharge the residual high electric energy in the high-voltage load after the high-voltage battery is disconnected, so that the DC bus voltage drops below the dangerous voltage or the electric energy drops below the dangerous energy level, so as to avoid the damage caused by the residual electric energy. a protective measure. Dangerous voltage refers to a voltage with a DC voltage greater than 60V or a peak AC voltage greater than 42.4V. Hazardous energy level means that the stored energy level is equal to or greater than 20J, or the continuous power level that can be given is equal to or greater than 240VA when the voltage is equal to or greater than 2V.

The abnormal situation of high-voltage power-on and power-off refers to the situation in which unexpected personnel actions occur, high-voltage faults occur in the vehicle, or an accident occurs in the vehicle. There are three types of undesired human actions:
(1) Category I Unexpected Person Action: The vehicle is in a stationary state, which occurs many times. When the high-voltage normal power-on is not completed, the user suddenly makes a “key off/Acc” power-off action, or when the high-voltage is normal When the power-off is not completed, the user suddenly performs the power-on action “key on/Crank”.

(2) Category II Unexpected Person Action: The vehicle is in a normal driving state, and the user suddenly makes a power-off action “key off/Crank”.

(3) Category III unintended personnel actions: when the DC bus carries dangerous voltage or dangerous energy, dismantling or removing the cover of the high-voltage device, the door of the box, or inserting and unplugging the high-voltage connector.

For the “multiple occurrences” referred to in Category I undesired human actions, the threshold of this number of times must be determined after comprehensive consideration. On the one hand, it must be considered to respect the intention of the user and respond accordingly to the limited number of rapid key-turning actions; The number of times its quickly turned the key. Therefore, considering the overall consideration, it is recommended that the threshold value of the pairing times be set to 3. Emergency high-voltage power-off means that the control node responds to the demand of the electric system to automatically “cut off the power supply”, emergency stops the motor output, emergency disconnects the high-voltage battery, and completes the residual power discharge within 2s according to GB4944-2001 [92], and finally according to the use of The power-off of personnel requires all control nodes to enter the sleep state. Stop the motor output, including stopping the power output in the motor generator mode and the torque output in the motor mode.

Optimization method of energy management system based on dynamic programming

Optimization method of energy management system based on dynamic programming

Based on the fuzzy logic energy management system, the use efficiency of the power battery of the pure electric vehicle with a single energy source is effectively improved, and the economic performance and dynamic performance of the whole vehicle are improved on the premise that the total energy of the power battery remains unchanged. On the basis of this control strategy, an optimization unit is added, which is guided by dynamic programming theory, extracts valuable control rules, and automatically adjusts the fuzzy controller according to the actual situation of the vehicle, so that the sum of the energy loss of the vehicle reaches minimum. Experiments show that:

Under the same driving conditions, the optimization method can further improve the economic performance of the whole vehicle.
Because the conventional fuzzy controller does not have the self-adjustment ability of rules and parameters, it cannot automatically adjust its parameters to adapt to the change of the object. When the robustness of the system needs to be analyzed, if the method of fuzzy control is adopted, the system cannot complete the analysis faster than using the control theory commonly used in the past. The system can also fluctuate if the quantifiers are poorly chosen, or if the control rules are poorly structured or covered.

Secondly, due to the limitations of the design itself, the fuzzy control designed by using experience is easily affected by subjective influence. Therefore, when applying fuzzy control strategy to solve complex multi-stage control problems, it is often easy to fall into local optimum. The dynamic programming can decompose the more complex problems, and then obtain the optimal solution of the whole problem by solving each problem one by one. For some difficult optimization problems, it can often reflect its superiority, especially for some discrete optimization problems. In this section, from the perspective of modifying and improving the fuzzy control principle, the optimization problem of the energy management system of pure electric vehicles is expressed as a dynamic programming theoretical optimization problem with the goal of minimizing the sum of the energy loss of the whole vehicle. The control effect of dynamic programming theory is verified by calculating the optimal control solution under specific cycle conditions.

  1. Description of the dynamic programming optimization problem

Let the allocable power of the energy management system at any time be Pe. The power relationship is as follows (1):

Due to the loss of the drive motor and the power devices of the thermal management system, the power provided by the energy management system cannot be used for effective work, that is, the efficiency of the two is not 1, and the relationship is as follows (2):

Among them, is the function of the thermal management system components on the ambient temperature T, and is the function of the motor speed N. The cycle conditions of the whole vehicle are divided into n stages, k∈n, and the following assumptions are made:
(1) State variable xk: represents the power allocated by the energy system to the thermal management system from the kth time period to the nth time period.
(2) Decision variable uk: represents the power allocated by the energy management system to the thermal management system in the kth time period.
Under the action of the decision uk, the state variable xk changes, and the state transition equation is (3)

Indicates the power allocated by the energy management system to the thermal management system from the k+1th time period to the nth time period. When the energy management system distributes according to the decision variable uk, the power flows through the drive motor and the thermal management system respectively, which will generate corresponding incentives for the two, so that the characteristic states of the two will change. Since the efficiency of the drive motor is a function of the motor speed, and the efficiency of the thermal management system is related to the ambient temperature, the energy Jsys lost by the system at time k is a function of the state variable xk and the decision variable uk. Let it be the dynamic optimization stage index function vk(xk, uk), then (4):

represents the system loss caused by the power allocation of decision uk in the kth time period.
In this way, according to the power demand of the whole vehicle, starting from time 0, different control rates U will generate different new states (state variables) x, and at the same time face the problem of selecting a new control rate (decision variable) U until the whole cycle works. situation is over. Since the initial conditions of the vehicle simulation will be given, the power optimization control problem of the pure battery vehicle energy management system can be summarized as: the initial state x(0)=x0 given, the terminal x(n)=0 optimal control The problem is shown in Figure (5):

Power Optimal Control of Energy Management System
Power Optimal Control of Energy Management System

In the process of vehicle driving, if the distribution of each control rate in all cycles is optimal, the sum of energy losses generated by the system at each moment can be minimized. In the case of the same total amount of energy system, that is It can be understood that the efficiency of the energy system in the cycle is the largest, and the economic performance of the vehicle is the best. From this, the optimization objective shown in Equation (6) can be set:

fk(xk, Wk) represents the sum of the system losses caused by the power allocation of the decision uk from the kth time period to the nth time period. In the process of vehicle cycle conditions, the power of the drive system and thermal management system and the energy of the power battery system must meet the following constraints (7):

In this way, the output of the energy management system can be adjusted by solving the optimal control rate under dynamic programming, and the energy management system can be further optimized. According to the principle of Bellman optimality, to solve the dynamic programming recursive equation with constraints, the steps are as follows:
①Using the boundary condition fN(xN, uN)=0, obtain the optimal control un in the Nth stage when the state is xn.
②According to the values ​​of the formula xk+1=xk-uk and fk(xk, uk), find the optimal control uk-1 and fk-1 (xk-1, uk- 1).
③ Let k=k-1, if 0≤k≤N-1 is satisfied, go back to step ②; if not, go to step ④. ④ Obtain the optimal control u0 and f0 (x0, u0) when the state is x0 at the initial moment, then the sequence {u0, 1…, uN-1} is the optimal control strategy, and f0 (x0, u0) is the optimal control strategy. The optimal performance index corresponding to the optimal control strategy.

  1. Validation of dynamic programming optimization method

Because the dynamic programming takes the minimum energy loss of the whole vehicle as the optimization goal, the energy consumption rate of the whole cycle process is lower than that of the fuzzy control strategy, and there is no under-power situation in the later cycle of the cycle. The control amount allocated by the optimization algorithm is smaller at the beginning of the cycle, because the initial temperature of the system is lower and the efficiency loss of the thermal management system is larger. As the cycle progresses, the system temperature gradually increases, the efficiency loss of the thermal management system becomes smaller, and the control amount allocated by the algorithm gradually increases. In addition, when the motor speed is low, the system energy loss is relatively large, and the algorithm will appropriately reduce the allocated control amount; when the motor speed increases to the high-efficiency working area, its guiding significance for the real vehicle is as follows:
(1) When the initial temperature is low, appropriately reduce the allocated control amount.
(2) When the temperature in the mid-term is high, increase the allocated control amount appropriately.
(3) When the motor speed is low, reduce the allocated control amount appropriately.
(4) The motor enters the high-efficiency area, and the allocated control amount is appropriately increased.

Energy Management System Based on Threshold Control Method and Fuzzy Logic

Energy Management System Based on Threshold Control Method and Fuzzy Logic

  1. Energy management system based on threshold control method

The control strategy of the energy management system usually adopts the threshold value control method, that is, a threshold value of the remaining energy is set:
If the remaining energy is higher than this threshold, the thermal management system is turned on; if the remaining energy is below this threshold, the thermal management system is turned off. Now introduce an energy management system power distribution coefficient KT-M, which represents the weight of the maximum power allocated to the thermal management system, and its definition domain is [0, 1]. The maximum power allocated to the thermal management system is then shown in Figure 1:

where PTM-MAx(t) is the peak power of the high-voltage components of the thermal management system. The maximum power allocated to the drive system is therefore Fig: 2:

When PT-M(t)=0, it is the way to reduce the energy usage rate: allocate the limited battery power to the drive system to the greatest extent.
In the energy management system threshold control method, KT-w(t) is the variation, and the control strategy is as shown in Figure 3:

Among them, SOCTH is the threshold value.
From the above mathematical description, it can be seen that the threshold value control process of the energy management system is shown in Figure 4:

The driver steps on the accelerator pedal, understands the driver’s driving intention through the accelerator pedal opening θ curve, and obtains the motor demand power PMR; the energy management system can allocate the power Pe, and distribute the power to the thermal management system and the drive system according to the threshold control strategy . When the system completes the work, the energy of the power battery becomes Ee’, the maximum distributable power becomes Pe’, and the temperature of the power battery becomes T’ and the state of charge becomes SOC’.

Figure 4 - Threshold value control process of energy management system
Figure 4 – Threshold value control process of energy management system

The optimization purpose of the energy management system is to reduce the energy consumption rate of the whole vehicle when the total rated energy of the power battery remains unchanged, and to minimize the ECR by distributing the power of the energy management system between the drive system and the thermal management system. Generally, the economic performance of pure electric vehicles is evaluated by energy consumption rate.

Among them, the mileage of the whole vehicle is S, the unit is km; E is the battery energy consumed by the whole vehicle when it travels, the unit is J; k is the unit conversion factor.
The optimization of the power battery energy management system is to add an optimization unit to the control strategy of the conventional energy management system, by dynamically adjusting KT-w(t) in the interval [0, 1] to minimize the ECR. In addition, during the driving time t of the vehicle, Pmotor(t) should be as large as possible larger than the required power PMR(t) of the drive motor. From the above analysis, the mathematical model of the optimization problem of the energy management system of pure electric vehicles can be established as shown in Figure 6:

It can be seen that this problem belongs to a typical constrained nonlinear optimization problem.

  1. Energy management system based on fuzzy logic

The main parameters of the control strategy design that affect the power distribution of the pure electric vehicle energy management system are:
SOC(t), battery SOC at time t;
dθ/dt, the rate of change of the accelerator pedal opening at time t;
△T, the temperature difference between the battery temperature and the battery optimal temperature working range at time t. Figure 7:

Among them, Topt-max is the upper limit of the optimal operating temperature range of the battery; Topt-min is the lower limit of the optimal operating temperature range of the battery; Tbat is the battery temperature. Due to the inconsistency of the temperature of the power battery body, it is taken in the actual calculation. average value.

Therefore, on the basis of the original control strategy, an optimized control process as shown in Figure 8 is established, and a fuzzy controller for power distribution in the energy management system is added, with SOC(t), dθ/dt and ΔT as the input parameters, and the output control parameter KT-M (t), after the thermal management system and the drive system do work according to the power distribution coefficient of KT-w(t), SOC(t) and ΔT change, and then feedback to the fuzzy controller as the next input to form a closed loop.

Figure 8-Optimal control flow of energy management system based on fuzzy logic
Figure 8-Optimal control flow of energy management system based on fuzzy logic

The working process of the fuzzy control of the pure electric vehicle energy management system is described as follows:
①When the vehicle starts, if the operating temperature Tbat of the power battery is low, PT-M is given priority.
②When the vehicle starts, if the working temperature of the power battery is normal, Pmotor is given priority.
③ When the car accelerates rapidly or runs on a hill, that is, dθ/dt is greater than a certain set threshold, the Pamr is started first to meet the high power demand of the drive motor, and then the PT-M is started.

④ When the car is running at a normal speed, that is, dθ/dt is less than a certain threshold, the priority is to meet the PT-w to improve the charging and discharging efficiency, and then meet the Pmotor to ensure the ordinary power demand of the drive motor.
⑤ If the battery SOC is low, Pmotor should be given priority.
⑥ If the battery SOC is high, PT-M should be given priority.

According to the above working process, the following basic principles are followed when formulating fuzzy control rules:
(1) When the remaining battery power SOC(t) is low, if the temperature difference ΔT is relatively small, and the accelerator pedal opening change dθ/dt is relatively large, the power allocated to the thermal management system is relatively small, namely KT-M(t) smaller.
(2) When the remaining battery power SOC(t) is high, if the temperature difference ΔT is relatively large, and the accelerator pedal opening change dθ/dt is relatively small, the power allocated to the thermal management system is relatively large, namely KT-M(t) bigger.

Read more: How Lithium-Ion Power Batteries Work

Energy system structure and power flow analysis of pure electric vehicle

Energy system structure and power flow analysis of pure electric vehicle

The power battery energy management system is one of the key technologies of electric vehicles. At present, the research on power battery energy management system mainly focuses on the energy management strategies of hybrid electric vehicles and pure electric vehicles. Due to the complex powertrain system of hybrid electric vehicles, there are many control strategies and a large space for development. For example, the commonly used control strategies for series hybrid electric vehicles include thermostat strategy, power tracking strategy and basic rule strategy; the commonly used control strategies for parallel hybrid electric vehicles include static logic threshold strategy, instantaneous optimal energy management strategy, and fuzzy logic control. strategy and global optimal energy management strategy, etc.; the commonly used control strategies for hybrid hybrid vehicles include engine constant operating point strategy, engine optimal working curve strategy, etc.

Pure electric vehicles can be divided into multiple energy source systems and single energy source systems according to the number of energy sources. The multi-energy source is mainly a dual-energy source system composed of a battery and a supercapacitor. The main feature of the supercapacitor’s large charge and discharge rate is used to make up for the shortcomings of the power battery by cutting peaks and filling valleys. At the same time, due to the existence of supercapacitors, which increases the complexity of the powertrain system, the available control strategies are also much more than that of single energy sources, such as threshold control strategies and fuzzy logic control strategies. For pure electric vehicles with a single energy source, because the powertrain system is simpler than that of hybrid and multi-energy source systems, there is less room for control strategies.

Combining the energy management and control strategies of pure electric vehicles of Chinese and foreign OEMs, the main control strategies are as follows: one is to reduce the energy usage rate of the entire vehicle, and only retain the high-voltage load necessary for the vehicle to travel, so as to minimize the energy consumption of the entire vehicle. The power consumption of the high-voltage system is to allocate all the limited power to the drive system; the second is to improve the efficiency of battery use. Through the use of the thermal management system, the battery has been controlled in the high-efficiency range. Although the first method can save the power consumption during driving to the greatest extent, due to the lack of the battery thermal management system, the long-term high temperature operation will accelerate the aging of the battery, which will sacrifice the economic performance of the vehicle; the second method is the most commonly used threshold. Although the control strategy is simple and stable, it cannot optimally solve the power distribution problem due to the fixed control rules, thus affecting the dynamic performance of the vehicle.

  1. Energy system structure and power flow analysis of pure electric vehicle

The high-voltage system components of pure electric vehicles are mainly divided into air-conditioning system components, drive system components, low-voltage power supply system components and charging system components. Among them, the low-voltage power supply system components convert high-voltage electricity into low-voltage electricity to support the entire vehicle electronic components , the operation of low-voltage equipment such as power steering, water pumps and fans. Charging system components replenish energy from the grid through chargers or other charging equipment. The air conditioning system components are mainly used to improve driver comfort and thermal management of the power battery. The high-voltage components are the electric heater (PTC) for heating and the air compressor (ACP) for cooling, and the drive system components are used to drive the motor to the outside. Doing work, you can also brake to recover part of the energy.

From the above-mentioned components of the power battery system and the high-voltage system, a schematic diagram of the power flow of the vehicle energy management system as shown in FIG. 1 can be obtained. It describes the input-output relationship of power flow between the power battery system and the high-voltage system of the vehicle.

Figure 1 - Power flow of vehicle energy management system
Figure 1 – Power flow of vehicle energy management system

In the figure, Pbat represents the maximum output power of the power battery system. PA-c represents the maximum power allocated by the energy management system to the air conditioning system. Since the comfort system and the thermal management system share power devices, in order to describe their functions intuitively, the air conditioning system is equivalent to a thermal management system, which is called PT-M. Pmotor represents the maximum power that the energy management system can allocate to the drive system. PL-p represents the required power of the low-voltage power supply system. Pm represents the maximum rechargeable power of the charging system.
During the driving process of the vehicle: Pcha(t)=0; PL-p(t) is a fixed value, which is equal to the DC/DC rated power in value and must be allocated; PT-M(t) and Pmotor(t) The size can be determined according to the power required by the power bus under different working conditions, and it is an amount that can be adjusted and allocated. Let the power that can be allocated by the vehicle energy management system be Pe(t), then:

Obviously, the purpose of the vehicle energy management system is to reasonably allocate Pe(t) to PT-M(t) and Pmotor(t), so as to maximize the energy utilization efficiency of the vehicle.

Read more: What is a Lithium-Ion Power Battery Pack

Power battery-battery energy management system hardware slave board design

Power battery-battery energy management system hardware slave board design

  1. System framework and overview

The battery management system mainly implements the collection and reporting of voltage and temperature signals on a single battery module from the board, and performs balancing operations on the cells on the module when the balancing function is executed.
Multiple battery modules are used in the pack system design, and each battery module uses a slave board. The slave board is mainly used for the collection, reporting and equalization functions of battery cell voltage and temperature. The slave board hardware generally includes a dedicated battery acquisition chip, an isolation chip, a single-chip microcomputer, and a communication circuit. The block diagram of the slave board system is shown in Figure 1.

Figure 1 Block diagram of the slave board system
Figure 1 Block diagram of the slave board system

The MCU main control unit is placed on the high-voltage battery side, only the CAN module is placed on the low-voltage side of the slave board, and a power chip is placed on the high-voltage side and the low-voltage side, which can reduce the isolation of one power supply and reduce the EMC problem of the entire board. The functional requirements of the slave board system are as follows:
(1) Slave board channel: Each slave board has 4 voltage acquisition channels and is compatible with 5-channel mode, and 5 temperature acquisition channels. Only 4 channels can be selected as the acquisition interface.
(2) Acquisition accuracy: single voltage accuracy ± 5mV, measurement range 0~5V, temperature measurement range -40°C~85°C, required accuracy at -30°C~60°C ≤±1°C, 60°C~85°C required Accuracy≤±1.5℃.
(3) Acquisition time: the single voltage reporting period is 50ms, and the temperature reporting period is 50ms.
(4) Communication mode: The communication between the slave board and the main board adopts high-speed fault-tolerant CAN, with a rate of 500kbit/s.
(5) Acquisition method: special acquisition chips are required to simplify system design and ensure scalability.
(6) Power supply mode: the power supply current of the high-voltage side does not exceed 50mA, and the power supply current of the low-voltage side does not exceed 30mA.

  1. Processor and chip and power supply

2.1. Processor
The slave board processor is used to monitor, process and report the battery voltage and temperature signals, and the functions can be realized by using the single chip microcomputer. The processor uses the freescale chip MC9S08DZ60. The processor must include at least ROM, RAM, and flash storage space, of which the EEPROM requirement is not less than 1K, the RAM requirement is not less than 2K, and the flash requirement is not less than 32K. Hardware watchdog function: The processor power-on completion time is required to be within 1s, and it can wake up and sleep through hard wires; the processor has the CAN interface function to communicate with the motherboard, and the SPI or I2C interface function to communicate with the internal chip.

2.2. Acquisition chip and isolation chip
The acquisition chip is used to manage the acquisition function of battery voltage and temperature. The function can be realized by using a special acquisition IC. The LTC6804HG-1 acquisition chip of Linear Technology is selected, which can provide the following resources: the single voltage acquisition channel is 12channel, 5 GPI0 ports (can be multiplexed into 5 temperature acquisition channels); multiple acquisition chips are allowed to be used in parallel, and a daisy-chain structure can be provided. The acquisition resolution of the voltage channel is 16bit, the total voltage acquisition accuracy (including analog front-end and back-end processing) meets -2.8~2.8mV, the acquisition time of the acquisition chip is 130us, the withstand voltage requirement of the acquisition chip is not less than 60V, and the voltage acquisition channel The measurement range is 0~5V, and the acquisition chip with hardware diagnosis function channel can perform hardware diagnosis on the undervoltage and overvoltage of the battery cell voltage, and report the fault status. The acquisition chip has the SPI interface function to communicate with the processor, and the chip temperature range is -40℃~125℃. The isolation chip is required to meet the electrical isolation of the battery side and the low-voltage side, and the electrical isolation meets the requirements of insulation and safety regulations. The electrical design defines the RMS voltage of 400V, and the minimum clearance and creepage distance of 4.00mm, which are mainly considered in the PCB layout. The isolation chip uses ADI’s I Coupler digital isolation chip ADuM12011.

2.3. Power supply
The slave board is powered by the low-voltage system and the high-voltage system, and the power supply system is designed as follows: the low-voltage power supply comes from the low-voltage battery of the whole vehicle (about the knowledge of the battery, I accidentally found an article before, and found that the author knows the knowledge of the battery Very thorough, if you are also interested, you can visit Tycorun Battery to read)
), the normal working voltage is 12V, the voltage range is 6~16V, and the working current does not exceed 50mA. Use the power management chip for power supply control, provide internal 5V or 3.3V, and supply power for CAN and isolation chips. The high-voltage power supply comes from the module of the high-voltage battery, and the voltage range is 8~25V. The high-voltage module directly provides power for the acquisition chip, and converts it into 5V through DC-DC or LDO to power the MCU and other chips on the high-voltage side. Power management can support power-on and power-off management of hard-wired Enable. Enable high level wakes up the power management chip and performs power-on initialization. It is required to complete initialization and start measurement within 120ms, and send a normal CAN signal; after Enable low level, the power management has a self-locking function, which supports the processor after the power-off management is completed. , go to sleep again.

  1. Interface definition and CAN communication

3.1. Interface Definition
The slave board is respectively connected to the battery terminal and the main board. The design requirements for the interface are as follows: the voltage input interface channel of the battery terminal is 4 channels, the temperature input interface channel is 4 channels, the connection terminals are designed separately, and the on-board connection terminals are used. The power supply terminal and the main board communication terminal have Redundant design to ensure the cascading of multiple acquisition sub-boards. The cascading method is shown in Figure 2.

Figure 2 Slave board cascade mode
Figure 2 Slave board cascade mode

3.2.CAN communication
The slave board has communication functions such as CAN. The communication follows the following requirements: the external port of the slave board needs to provide at least one high-speed CAN communication with the main board, the communication rate is 500kbit/s, and the CAN2.0 communication protocol. The acquisition chip and processor need to have communication functions such as SPI or I2C for internal communication; CAN needs to reserve a terminal resistance, and the CAN network ID can be configured independently. The voltage and temperature signals are collected from the board and reported to the main board through the CAN signal. At the same time, the equalization command of the main board is sent to the slave board through the CAN signal to realize the equalization function.

Read more: What are the characteristics of lithium-ion power batteries

What is the hardware motherboard design of power battery energy management system?

Power battery-battery energy management system hardware motherboard design architecture

As the core controller of the power battery system, the hardware main board of the battery energy management system mainly realizes the BMS strategy operation and execution functions, including information collection of total voltage / total current, real-time SOC estimation, fault diagnosis and storage, real-time control of the main relay, etc.

  1. System framework and overview

The hardware circuit block diagram of the designed motherboard system is shown in Figure 1, including power supply circuit, digital / analog input, high / low-end drive output, PWM input / output, can communication, etc.

System hardware circuit framework
System hardware circuit framework

The designed microprocessor adopts Infineon’s tricore32bit series tc1728, the main frequency is 133MHz, and the storage space is 1.5MB flash; Abundant peripheral IO resources can meet the design requirements.

Mainboard system framework
Mainboard system framework

1.1. working voltage

The working voltage range of the main board is 6 ~ 16V, and the static current of the main board shall not exceed 1mA.

1.2. Self programming and diagnosis ability

The motherboard can support self programming in the offline stage through UDS protocol. The mainboard is required to have hardware diagnosis functions, such as detecting the open circuit and open circuit status of the output IO port (including short circuit to ground and short circuit to power), and turning off the output function in time according to the fault status. The requirements for shutdown time are as follows: high voltage relay drives IO, acquisition board / high voltage board enable signal, and the response time after fault detection is 10ms; The rest output IO, and the response time after fault detection is 100ms.

1.3. Electrical interface and can communication interface

1.3.1 power interface

The power interface block diagram is shown in Figure 3, and the pin definition is shown in Table 4.

The designed maximum withstand voltage of the power supply is 65V and the maximum current is 5A; The designed maximum current resistance of the power supply ground is 25A, and the offset voltage to the ground shall not exceed ± 0.5V.

power interface block diagram
Power interface pin definition 1
Power interface pin definition 1
Power interface pin definition 2
Power interface pin definition 2
  1. Digital input and analog input

The high-level interlocking detection is designed to be effective at high level. It is required to pull down 1.2k Ω resistance to the ground, and the filtering time constant shall not exceed 1ms. The emergency diagnosis line is designed to be effective at high level. It is required to pull down 1.2k Ω resistance to the ground, and the filtering time constant shall not exceed 1ms. The fast charging wake-up line is designed to be effective at high level. It is required to pull down 3.3k Ω resistance to the ground, and the filtering time constant shall not exceed 1ms. The slow charging wake-up line is designed to be effective at high level. It is required to pull down 3.3k Ω resistance to the ground, and the filtering time constant shall not exceed 1ms.

Fast charge signal detection input port, the internal resistance is 4.64k Ω, pulled up to 5V, the connected effective signal is lower than 1V, and the non connected invalid signal is 5V; The temperature sensor adopts NTC, the typical value is 10K Ω, and the designed pull-up resistance is 3K Ω to 5V.

2.1. Digital output

Main board digital output pin pin, main positive relay control, main negative relay control and fast charging relay control. The design is equipped with small relay drive. The relay model is acb33401, the interface is active at low level, and the driving current does not exceed 300mA. Precharge relay control, slow charge relay control, design direct drive relay evr10-12s, the interface is low-level effective, and the drive current does not exceed 300mA. Accessory relay control, designed to directly drive relay acb33401, the interface is effective at low level, and the driving current does not exceed 300mA.

2.3. Communication interface, storage space and mechanical interface

Pin pin of the main board communication interface. The main board uses two-way can, in which hcan is used as the whole vehicle can to communicate with the whole vehicle controller; As an internal can, Ican communicates with acquisition slave board and high voltage board; Both channels of can adopt high-speed can, and the communication rate is 500kbit / s.

The flash storage space of the main board is 1.5MB, which is divided into application software area, calibration area, test area, production data retention area and boot loader area according to function. The external EEPROM storage space is 8KB, which is used to store vehicle data. The connector adopts Tyco series automotive connector, which is divided into a / B two parts, with a total of 121pins, as shown in Figure 6.

Main board contact structure
Main board contact structure

Read more: What is the cycle life of a lithium-ion power battery?

What are the principle and design functional requirements of power battery energy management system?

Power battery-principle and functional design requirements of power battery energy management system

  1. Principle of power battery energy management system

The function of power battery energy management system in electric vehicle is to control the energy flow of high-voltage electric energy between high-voltage electric equipment such as energy storage device, motor, inverter and air conditioning compressor, as well as the energy transfer between electronic power converter, control system and auxiliary devices, so as to make high-voltage electric energy use efficiently and safely [86].

The power battery energy management system takes the chip processor as the center and forms a system together with various sensors and actuators [87]. The energy management system obtains the voltage, current and temperature status information of the power battery through the sensor. These information, together with the monitored relay status, hvil status, insulation status and the status of each high-voltage component, are used as the basis for real-time judgment and calculation, and the corresponding processing actions are completed through the actuator. For example, the energy management system monitors the voltage, electric quantity and temperature information of each battery unit and performs calculation and processing, and the equalization unit completes the electric quantity equalization and temperature equalization of the battery pack [88, 89].

The following figure is a typical battery management system architecture, which includes daughter board module, measurement module, relay module, safety module, communication module, etc. with the motherboard as the core. The seven sub boards in the figure are used to detect the voltage, current and temperature of the battery module; The measurement module realizes the voltage measurement of the main board to the power line and low-voltage line; The relay module includes the action control of the main positive and negative relays, precharge relays, fast charge and slow charge relays; The safety module realizes the insulation detection of the total positive and negative ends of the power line and the high-voltage interlock safety circuit; The mainboard interacts with the sub board and insulation detection through can data communication, and the mainboard interacts with external communication and fast charging charger through can data communication.

Architecture principle of battery management system
Architecture principle of battery management system
  1. Functional requirements of power battery energy management system design

From the perspective of vehicle high-voltage control strategy, this content focuses on the management of energy management and safety protection of power battery system, that is, power battery energy management system. The functional requirements for the design of power battery energy management system include:

(1) Power on / off control. Strictly control the power on and power off sequence and process to meet the power on and power off requirements of the whole vehicle.

(2) Relay control and disconnect the relay in case of emergency. The high-voltage relay is controlled according to the instructions of the vehicle controller (VCU), and the control mode is low side drive. VCU shall be able to directly disconnect the high-voltage relay during emergency power down.

(3) Precharge control function. According to the power on and power off sequence requirements, the precharge time is ≤ 300ms, and the precharge time is the time from the beginning of closing the precharge relay to the time when the bus voltage outside the load reaches 90% of the total voltage of the power battery.

(4) Communication function. Meet can2 0b protocol, baud rate is 500kbit / s, BMS shall have 120 Ω terminal resistance, and the communication protocol between DC charging pile and battery energy management system meets the requirements of national standard GB / t27930.

(5) Fault diagnosis function. The fault diagnosis contents of battery energy management system shall include but not limited to: over temperature (including over temperature, under temperature and over temperature difference), over voltage (over voltage of single body or total voltage, under voltage of single body or total voltage and over voltage difference of single body), low insulation resistance, hvil status, relay status, communication status, over-current, etc.

(6) High voltage safety protection function. The battery energy management system shall have the following protection functions: overvoltage protection, low voltage protection, discharge overcurrent protection, charging overcurrent protection, high temperature protection, emergency power failure, high voltage interlock and collision protection.

(7) Insulation status detection, relay status detection and hvil status detection.

(8) Various signal acquisition, including current, total voltage, monomer voltage, temperature, etc.

(9) Charging control function. Realize the control of fast charge and slow charge according to the charging requirements.

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What is a related battery model study?

What is a related battery model study?

As shown in Figure 1, a battery pack consists of some interfaces (such as electrodes) and several battery modules consisting of several battery cells. In a battery module, all battery cells are all connected in parallel, thereby reducing the possibility of battery failure caused by the failure of a single battery cell. The battery modules of the same group are usually connected in series to provide high voltage and energy to the battery pack. The BMS is responsible for protecting hundreds of battery cells from damage and keeping the batteries working properly while driving a pure electric vehicle.

What is a related battery model study?
Figure 1 battery and battery pack model

1. Battery efficient management and scheduling
Rate capacity and recovery effects are the most important physical performance parameters for efficient battery management. The larger the battery discharge current, the smaller the effective capacity of the battery, this phenomenon is called the rate capacity effect; the output voltage of the battery does not decrease with the battery discharge, but rises, this phenomenon is called the recovery effect. We can increase battery capacity by minimizing the discharge rate of each cell and hibernating the battery cells.

The state of charge (SOC) of the battery is used to characterize the remaining power of the battery, and the value ranges from 0 to 1. When SOC=0, it does not discharge externally, and when SOC=1, it means it is fully charged. Because large battery pack performance depends on the electrical state of the aging cells within the pack, balanced state of charge is the most critical factor affecting the performance of large battery systems. In order to obtain better battery performance, a series of battery scheduling and discharge rate reduction measures based on SOC balance are taken to control the battery cells to release energy at a suitable discharge rate. For example, when the motor requires high power, the battery management system connects all battery cells to discharge to increase battery power; on the contrary, when the motor requires low power, the battery management system cuts off some cells with low remaining power to achieve output voltage recovery and Balance of state of charge.

2. Battery thermal characteristics
In addition to discharge behavior and SOC balance, battery thermal characteristics are also important for battery efficiency, operation, and safety. First, cell efficiency is temporarily improved at “immediate high temperature” due to increased chemical reaction rates and ion mobility, but cumulative exposure to high temperatures accelerates irreversible side reactions leading to a decrease in the permanent battery life. Therefore, most BMSs will require limiting each cell to a well-defined temperature range to achieve the desired performance. Every electric vehicle must therefore be equipped with a thermal management system that includes cooling and heating to keep the temperature of each battery cell within a reasonable operating range. When the temperature of the battery pack deviates from the operating temperature range, the thermal management system is activated to ensure the thermal stability of the battery.

In a high temperature environment, the radiator takes away the heat of the battery through the coolant and exchanges heat with the outside air to cool the battery; in a low temperature environment, the battery needs to be heated. For example, the GM Chevrolet Volt uses 144 fins to actively cool or heat 288 battery cells, and its radiator uses a coolant flow valve to control the flow of cooled or heated coolant. The Ford Focus also features an active liquid cooling and heating system for thermal management of its lithium-ion battery pack.

The simple method currently employed in battery cells can operate normally and efficiently during the shelf life of the car, but such a passive, extensive thermal control cannot take full advantage of the thermal management system. By understanding battery thermal characteristics, thermal management systems can be used to improve battery performance without sacrificing battery life: heating the battery cells at high power to improve instantaneous performance of the battery, and heating the battery cells when low power is required Cool down to delay battery life decay.

3. Relevant problem statement
The DC power generated by the battery pack of the electric vehicle is converted in the inverter to drive the electric motor of the electric vehicle. During the operation of the electric vehicle, the power inverter needs a suitable input voltage Vapp to drive the motor. After the battery pack is fully charged, the accumulated time to provide the required power Prep(t) within the output voltage range is defined as the running time top. Therefore, the BMS should ensure that its battery pack provides the required power to drive the motor, while keeping the output voltage not lower than the input voltage threshold during long-term operation, which is longer than the battery’s lifespan. Otherwise, EVs require a larger battery pack or frequent replacements.

By controlling the temperature of the battery cells to achieve a long enough operating time in the life, select the type of cooling liquid for each cooling fin to achieve the purpose of controlling the temperature of the battery each time it is cooled or heated, that is, the type of cooling liquid Used as a control knob for the BMS. Determine the type of coolant for each instant Cfin(t) to maximize the battery runtime top.

4. Overview of battery physical dynamic changes
The dynamic changes of the battery under stress conditions can affect the performance and safety of the battery system. For example, uncontrolled high temperatures can cause batteries to explode; extremely low temperatures can degrade battery performance and even make it impossible to drive electric vehicles. Therefore, the influence and interrelationship of control nodes and external conditions on battery dynamics should be analyzed to improve the safety and performance of battery systems. To this end, the factors affecting battery performance are first determined by bridging different abstract models of physical dynamic changes, and based on this unified abstract model, the dynamic changes of batteries under the influence of different temperatures are discussed.

What is a battery thermal management system?

What is a battery thermal management system?

As the main energy storage form of electric vehicles, the performance of power battery directly restricts the power, economy and safety of electric vehicles. Compared with other types of batteries, lithium-ion power batteries have great advantages in terms of energy density, power density and service life, making them the mainstream of current vehicle power batteries. But its performance, life and safety are closely related to temperature. As many studies have pointed out, temperature is one of the most important factors in battery design and operation. If the temperature is too high, the side reactions of the battery will be accelerated and the performance of the battery will be attenuated, and even lead to safety accidents. Therefore, it is very necessary to study the thermal management system (BTMS) of the battery.

The battery thermal management system obtains the temperature of battery cells at different locations through temperature measuring elements. Accordingly, the control circuit of the thermal management system needs to make the action decisions of the cooling actuators such as fans and water/oil pumps. At present, the temperature sensors of common power battery packs are mostly attached to the inner surface of the battery box or the outer surface of the battery cell. For example, in the third-generation Prius battery pack in 2010, part of the temperature sensor is arranged in the flow channel inside the battery pack; the other part is directly attached to the middle of the upper surface of the cells in some typical positions, and these cells are located in the front of the battery pack. top, middle and rear. The battery thermal management system usually performs hierarchical management according to the temperature region where the battery is located. Volt plug-in hybrid battery thermal management is divided into active (active), passive (passive) and non-cooling (bypass) three modes: when the power battery temperature exceeds a preset passive cooling target temperature, passive cooling mode starts ; and when the temperature continues to rise above the active cooling target temperature, the active cooling mode is activated. However, this is still an extensive control strategy, which leads to a larger safety margin of the battery and reduces the efficiency of the battery.

Next, an efficient and sophisticated battery thermal management system is investigated. The maximum operating time or accumulated time that the battery management system can provide the required power after being fully charged is used as the evaluation index of efficiency. as an indicator of reliability. The hardware and software relationship for integrating and coordinating battery temperature management is shown in Figure 1. For the hardware part, on the basis of understanding the influence of battery thermal properties and external temperature and pressure conditions on battery performance, by calculating these nonlinear physical properties and abstracting these features in cyberspace, an ideal solution to reduce the safety margin is developed accordingly. temperature management system, thereby improving the efficiency of the entire battery system of pure electric vehicles.

What is a battery thermal management system?
Figure 1 BTMS software and hardware relationship

Compared with the common temperature control system, the temperature is selected as the control node to realize dynamic control, and the influence of the thermal properties of the battery and the electrical state of the battery on the efficiency and reliability is analyzed. The cell-level thermal control is adopted as the control strategy of the battery thermal management system. Temporarily boost the performance of the cell layer when high power is required, while sleeping other layers to reduce stress, and the associated model is validated.

The main research contents include the following three points:
(1) Using cyberspace to summarize thermal properties to solve problems related to the efficiency and reliability of temperature management systems.
(2) Design the battery temperature management system, and systematically study the use of temperature as the control core of the temperature management system.
(3) The temperature management system used in the in-depth evaluation proves that it can effectively improve efficiency without sacrificing reliability.