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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.

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.

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.

2. 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.

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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.

2. 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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