What is a controller for an electric car?

The car controller (EV ECU) is the most important controller on the electric car. It includes the control power management of the motor controller (MCU), self-diagnosis, data information sharing with other control nodes (ECU), electrical management, anti-theft device management and other functions.

1. control function of MCU
① Determine the torque data sent to the MCU according to the accelerator pedal position and the motor speed.
②For a transmission with a fixed gear ratio, the EV ECU determines the torque direction according to the position signal from the transmission shift lever.
③ For the transmission with two or three gear ratios, the EV ECU determines the torque direction and magnitude according to the position signal from the transmission shift lever.
④When the driver depresses the brake pedal, the EECU controls the MCU to turn off the signal of the drive circuit of the lane change bridge, from the positive signal to the all negative signal, and starts the regenerative braking and ABS friction braking functions, mainly to control the braking effect.

2. Power management functions
An electric car without a car controller needs to manually disconnect the DC bus when it is parked. If the bus is manually disconnected during driving, there will be a large current impact, and there will be potential safety hazards during repairs. When there is a car controller, the software in the car controller will power off the positive and negative DC buses differently. There are maintenance plugs or circuit breakers with fuses in the battery box, and the power-off method is to manually insert the maintenance plugs or disconnect the circuit breaker during maintenance. The position of the DC bus power-off relay should be designed near the output end of the battery pack. Generally, the three-relay control mode to slow down the current impact is adopted. A typical three-relay high-voltage power control system is shown in Figure 1.

What is a controller for an electric car?
Figure 1 Three-relay high-voltage power supply control system

SMR2 and SMR1 (system main relays) are positive main relays, SMR3 is system negative main relays, and the coils of the three relays are controlled by EV ECU. resistance. The working process is as follows.
①The power is turned on. When the circuit is connected, SMR and SMR3 are closed; then SMR2 ​​is closed and SMR1 is open, as shown in Figure 2. Because the current flowing through the resistor can be controlled in this way, the contacts in the circuit are protected from damage caused by high currents.

What is a controller for an electric car?
Figure 2 The EV ECU controls the three relays when the ignition switch (one-button start switch) is turned on

②The power is turned off. The circuit is disconnected as shown in Figure 3. SMRI is closed first, and SMR2 ​​is opened. EV ECU can judge whether SMR2 ​​is stuck by the current flowing through SMR1. If SMR1 has almost no current, it is determined that SMR2 ​​will output a fault prompt; if SMR1 has a large current, it is determined that SMR2 ​​has been disconnected, and then SMR3 is disconnected.

What is a controller for an electric car?
Figure 3 The EV ECU controls the three relays when the ignition switch (one-button start switch) is turned off

3. Self-diagnosis function
The car controller can monitor the sensors, actuators and other controllers connected to itself. The output data of the car controller to the detector includes the version of the car controller, the version of the motor controller, the version of the anti-theft electronic key, the fault code stored by the car controller, and the data stream. The car controller has the unit coding function for the input data of the detector and the self-adaptive function of the executive element diagnosis. The detector should also have the function of logging in to the Internet to facilitate the data update of the detector.

Sensor monitoring includes monitoring the temperature of the coolant in the motor, the relay coil circuit of the cooling fan motor, the electrical coil circuit of the water pump motor, and the presence or absence of the motor power supply. If there is a fault, a fault code will be generated, and the fault indicator will be lit when necessary. Actuator monitoring includes whether the relay can work, whether the reason is the coil or the switch, whether the solenoid valve can work, and a program for the diagnosis of the actuator is designed.

4. Data information sharing function with other control nodes (ECU)
Figure 4 shows the structure of a typical pure electric car control unit.
①Receive the motor controller (MCU) overheating, low voltage, overcurrent and other faults from the motor controller node, store the faults, and output them to the instrument after analysis to light the power system fault light.
②To deal with the total battery voltage and current from the battery management system (BMS), the voltage of each battery, the operation of the battery box temperature fan relay, the smoke sensor signal, the built-in temperature sensor, and the single block temperature of the battery, etc. Signal, output the battery box number and battery position number determined by the battery box BMS subsystem to the instrument, so as to facilitate the replacement of the battery during maintenance.
③ The EV ECU exchanges signals with the air conditioner ECU to control the heating and cooling of the air conditioner.
④ Receive the high-voltage leakage signal from the leakage protector unit, and start the function of automatically cutting off the main circuit switch for high-voltage leakage.

What is a controller for an electric car?
Figure 4 Typical pure electric car control unit

5. Appliance management functions
①Control lights and heaters.
②Control the priority of electrical power consumption.

6. Anti-theft function
The coded mechanical key (or induction key), the car controller and the motor controller are linked together, and the code-changing anti-theft technology is adopted..
The anti-theft technology of code-changing and code-transmitting mainly involves the coded mechanical key (or induction key), the car controller and the motor controller. Wired communication with the motor controller, confirmed by a password algorithm. Once the three-person identity authentication is passed, the motor controller works normally, otherwise the motor controller enters the control lock state, instead of simply not sending the torque signal, which can prevent thieves from stealing the car through the car’s own power. Because the three have been certified when they leave the factory, the most stolen by the thieves are both the car controller and the motor controller. Without the key, these two controllers cannot work, which can greatly reduce the thieves stealing the motor controller and the car controller. device idea. Once the key is lost, there is a program on the software to configure a new electronic key. The anti-theft control status can be seen through the data flow function of the detector.