Detailed explanation of power on and off for pure electric vehicles-Xinda Motor- electric motors and EV accessories supplier|INDEX--

Detailed explanation of power on and off for pure electric vehicles

Date：2023-03-28　　　Author：XINDA MOTOR

I. Introduction

In pure electric vehicles, the effective management of the power system is realized through the vehicle controller VCU. The VCU is responsible for the realization of key functions such as the vehicle power-on and power-off process, drive decision-making control, fault information diagnosis and processing, and energy management, which improves the driving performance of the vehicle. And the optimization of energy utilization has an important influence.

As one of the functions that the VCU is responsible for, power on and off is a necessary process to ensure the safe start and stop of pure electric vehicles, and it is also an important link in the design of the vehicle control strategy. For multiple devices such as pedals, the formulation of power-on and power-off control strategies needs to fully consider the working characteristics of these devices and their mutual interactions.

The power-on and power-on processes of different electric vehicles are similar, and the focus of this paper is to describe the power-on and power-on process of electric vehicles. This article is divided into 5 parts, which are described in terms of high-voltage power-on, high-voltage power-off, emergency high-voltage power-off, charging high-voltage power-on, and charging high-voltage power-off.

2. High voltage power on

According to the power mode signal represented by the key position, if the key position is in the Start position, the VCU will control the high-voltage power-on and continue to enter Ready; if the key position is only in the ON position, the VCU will control the high-voltage power-on, and the power-on is complete Then keep the power on and wait for the driver to operate.

The key position sends the corresponding power mode signal to the VCU. According to the signal, the driver's operation and the feedback status of each controller, the high-voltage battery relays are controlled to close, and the vehicle is powered on at high voltage and enters the Ready state.

In the case of three-stage BMS communication failure, high-voltage battery main-negative relay adhesion failure, and receiving a collision signal, the VCU will actively control the high-voltage battery main-negative relay to disconnect. Under normal circumstances, the main negative relay of the high-voltage battery is controlled to close after the VCU initialization is completed, and the main negative relay of the high-voltage battery is controlled to be disconnected after the power-off is completed and before the VCU goes to sleep.

The specific execution steps are as follows:

1. The VCU is awakened by the key ON gear and initialized; when the VCU is initialized, the VCU sends the high-voltage battery main negative relay closing command, and at the same time, after a certain delay time, sends the high-voltage battery main negative relay state to be closed;

2. The VCU detects that there is no failure to allow power-on of the vehicle, and at the same time receives the BMS, MCU and DCDC initialization success signals, the VCU sends a request to the BMS to close the main and negative relays of the high-voltage battery, and the BMS closes the main and negative relays of the high-voltage battery after receiving the request and gives feedback its status;

3. If the VCU sends a high-voltage battery main and negative relay closing request and does not receive the main and negative relay status closing signal within a certain period of time, it will go through the corresponding power-off process and record the high-voltage battery main and negative relay closure timeout fault; if it receives and detects the BMS feedback When the bus voltage of the battery is greater than the allowable pre-charging voltage threshold of the battery, a high-voltage battery non-power pre-charging relay 2 closing command is sent;

4. After the VCU controls the high-voltage battery non-power pre-charging relay 2 to close, it starts to detect the DCDC input voltage fed back by the DCDC, and detects whether it reaches the battery bus voltage signal fed back by the BMS (95% of the battery pack voltage) within the specified time. At the same time Detect whether the input voltage of DCDC is greater than the minimum voltage threshold of the pre-charged battery, if it is satisfied, execute 6 steps, if not, execute 5 steps;

5. The VCU controls the high-voltage battery non-power pre-charging relay 2 to be disconnected. After waiting for a certain period of time, it controls the high-voltage battery non-power pre-charging relay 2 to close again. The VCU starts to detect whether the DCDC input voltage of the DCDC feedback reaches the BMS feedback within the specified time. The battery bus voltage signal (95% of the battery pack voltage), and at the same time detect whether the DCDC input voltage is greater than the minimum voltage threshold voltage of the pre-charged battery, if it is satisfied, continue to the next step, if not, continue to repeat step 5 Operate until the number of precharge cycles reaches the calibrated number of precharge cycles. If the precharge completion condition is still not met, it will be judged that the precharge has failed, and a precharge fault will be sent, and continue to perform step 7 to enter the MCU power on. However, after power on , the vehicle power limit can only be in the creeping state (the instrument will prompt the system failure information at this time), and the pre-charge failure flag will not be cleared until the VCU is in sleep;

6. The VCU controls the DCDC relay to close, and after waiting for the DCDC relay to close, controls the high-voltage battery non-power pre-charging relay 2 to disconnect, and the VCU enables non-power high-voltage components such as DCDC/compressor/PTC;

7. The VCU controls the high-voltage battery power pre-charging relay 1 to close. After detecting that the high-voltage battery power pre-charging relay 1 is closed, the VCU sends a working mode request to the MCU to be in the pre-charging state, and then starts to detect the bus voltage fed back by the MCU to check whether it is Reach the BMS feedback battery bus voltage signal (95% of the battery pack voltage) within the specified time, and at the same time detect that the bus voltage of the motor is greater than the minimum voltage threshold voltage of the successfully pre-charged battery. If it is satisfied, perform step 9. If not, then Execute 8 steps;

8. The VCU controls the high-voltage battery power pre-charging relay 1 to be disconnected. After waiting for a certain period of time, it controls the high-voltage battery power pre-charging relay 1 to close again. The VCU starts to detect whether the bus voltage fed back by the MCU reaches the battery bus fed back by the BMS within the specified time. voltage (95% of the battery pack voltage), and it is detected that the bus voltage of the motor is greater than the minimum voltage threshold voltage of the pre-charged battery. If it is satisfied, continue to the next step. If the pre-charging times reach the calibrated pre-charging cycles, if the pre-charging completion condition is still not met, a pre-charging fault is sent, the MCU circuit is not allowed to be powered on at high voltage, and the PTC high-voltage power-on completion status is maintained, waiting for the effective operation of the driver. , the vehicle cannot be Ready, and the air conditioner can be used (at this time, the instrument prompts the system cannot drive fault information), and the pre-charge failure flag will not be cleared until the VCU sleeps;

9. The VCU controls the high-voltage battery main positive relay to close, and after waiting for a certain period of time, the high-voltage battery main positive relay closes and controls the high-voltage battery power pre-charging relay 1 to disconnect;

10. The VCU sends a Standby operation mode request to the MCU, and detects whether the MCU feedbacks that the motor’s operation mode is “Standby” within the specified time. If so, continue to the next step, otherwise enter the power-off process, and will not continue after power-off Power on until the VCU sleeps and wakes up again;

11. The VCU detects that the key position is in the Start position; detects that the charging gun is not connected; detects that the gear is in the P/N position; detects that the battery pack temperature is greater than or equal to the Ready temperature threshold, and then the VCU sends an enable signal to the MCU is "enable";

12. The VCU detects whether the MCU feedbacks that the MCU enable status is "Enable" within the specified time. If yes, execute the next step. If not, stop sending the enable signal and record the MCU enable fault, and control the power-off process;

13. When the system enters the driving state, the VCU sends a working mode request to the MCU, and controls according to the torque or speed;

14. The VCU starts timing, whether the MCU sends its working mode as "speed control" or "torque control" within the specified time, if so, sends a Ready signal to the meter, and the meter lights up the Ready light to remind the driver, The whole vehicle enters the Ready state, if not, the control goes through the power-off process.

3. Power off at high voltage

According to the power mode signal represented by the key position, if the key position is in the Off position or there is a high-voltage power-off fault or an emergency power-off request signal is received, the VCU controls each controller to stop working according to the signal, and then the VCU controls each high-voltage battery relay Disconnect to complete the vehicle high-voltage power-off process.

The specific workflow is as follows:

1. The VCU detects that the key position sends an OFF signal, or detects that the vehicle has a normal high-voltage power-off failure, or receives an emergency power-off request signal in the ON position;

2. The VCU turns off the Ready light, sends the requested torque to the MCU, and the requested speed is 0. If it is an emergency power-off request, the VCU will feedback the corresponding emergency power-off request;

3. VCU sends DCDC working mode to standby;

4. The VCU sends a signal to the TMS to order the compressor and the PTC to stop working, and at the same time sends a signal to the TMS to limit the power to 0;

5. The VCU detects whether the PTC, compressor and DCDC feedback are turned off or disabled within the specified time, that is, the DCDC working mode is not working, and the actual power of the compressor and PTC feedback is 0. If it is, continue to execute downward, otherwise report a fault and continue to execute downward;

6. The VCU judges whether the motor speed is lower than the threshold value of the power-off motor speed, and continues to execute downwards after meeting the conditions or waiting for a timeout;

7. The VCU judges whether the output current of the high-voltage battery pack is less than the threshold value of the battery current for power-off, and at the same time judges whether the compressor is allowed to power down the high-voltage power supply. If the conditions are met, it continues to execute downwards. After waiting for a timeout, it reports a fault and continues to execute downwards;

8. The VCU sends the motor working mode request to the MCU as "pre-power off", and after receiving the feedback from the MCU that the working mode is "pre-power off" or a timeout, the VCU controls the high-voltage battery main positive relay to disconnect, Proceed to step 10;

9. The VCU controls the main positive relay of the high-voltage battery to disconnect, and proceed to the next step;

10. The VCU judges whether the main positive relay of the high-voltage battery is normally disconnected by detecting whether the bus voltage of the MCU drops to 95% of the bus voltage of the battery within the specified time. If yes, perform step 13. If not, record the main positive relay of the high-voltage battery. Sticking failure, continue to the next step;

11. The VCU sends a request to the BMS to disconnect the main and negative relays of the high-voltage battery;

12. The VCU checks whether the state of the high-voltage battery main and negative relays fed back by the BMS is disconnected within the specified time. If yes, proceed to the next step. If not, report the disconnection timeout fault of the high-voltage battery main and negative relays and perform step 15. ;

13. The VCU sends a working mode request to the MCU as "discharge";

14. The VCU judges whether the bus voltage of the MCU drops below 60V within the specified time, and continues to execute the next step after meeting the conditions or overtime;

15. The VCU sends the motor enable request to the MCU as "disabled". At the same time, if the VCU detects that the MCU voltage is still higher than the discharge completion voltage at this time, it will record the MCU discharge fault;

16. The VCU judges whether the MCU feedback enable status is closed within the specified time, if yes, execute the next step, if not, record the MCU non-enabling fault, and continue to execute the next step;

17. The VCU controls the DCDC relay to disconnect, and after waiting for a certain period of time, proceed to the next step;

18. The VCU sends a request to the BMS to disconnect the main and negative relays of the high-voltage battery, and the BMS feedbacks that the main and negative relays are disconnected within the specified time or continues to execute the next step after a timeout;

19. Before sleep, the VCU controls the negative end of the main negative relay of the high-voltage battery to disconnect;

20. If there is no other wake-up source, the VCU enters sleep mode.

4. Emergency high voltage power off

The specific workflow is as follows:

1. The VCU detects that there is a fault in the vehicle that requires emergency high-voltage power-off;

2. The VCU turns off the Ready light, sends the requested torque to the MCU, the requested speed is 0, and at the same time sends the motor enable request as "disabled";

3. The VCU sends the DCDC working mode to standby, sends a signal to the TMS to order the compressor and the PTC to stop working, and at the same time sends the power limit to 0 to the TMS;

4. The VCU detects whether the PTC, compressor and DCDC feedback are turned off or disabled within the specified time, that is, the motor is not enabled, the DCDC working mode is not working, and the actual power of the compressor and PTC feedback is 0. If it is Then proceed to the next step, if not, wait for a certain period of time, and then proceed to the next step;

5. The VCU controls the main positive relay of the high-voltage battery to disconnect, and proceed to the next step;

6. The VCU judges whether the main positive relay of the high-voltage battery is normally disconnected by detecting whether the bus voltage of the MCU drops to 95% of the bus voltage of the battery within the specified time. If yes, execute step 13. If not, record the main positive relay of the high-voltage battery. Sticking failure, continue to the next step;

7. The VCU sends a request to the BMS to disconnect the main and negative relays of the high-voltage battery;

8. The VCU detects whether the state of the high-voltage battery main and negative relays fed back by the BMS is disconnected within the specified time. If yes, go to the next step. If not, report the disconnection timeout fault of the high-voltage battery main and negative relays and go to step 15 . ;

9. The VCU sends a working mode request to the MCU as "discharge";

10. The VCU judges whether the bus voltage of the MCU drops below 60V within the specified time, and proceeds to the next step after meeting the conditions or overtime;

11. The VCU sends a motor enable request to the MCU as "disabled". At the same time, if the VCU detects that the MCU voltage is still higher than the discharge completion voltage at this time, it will record the MCU discharge fault;

12. The VCU judges whether the MCU feedback enable status is closed within the specified time, if yes, execute the next step, if not, record the MCU non-enabling fault, and continue to execute the next step;

13. The VCU controls the DCDC relay to disconnect, and after waiting for a certain period of time, proceed to the next step;

14. The VCU sends a request to the BMS to disconnect the main and negative relays of the high-voltage battery, and the BMS feedbacks that the main and negative relays are disconnected within the specified time or continues to execute the next step after a timeout;

15. Before sleep, the VCU controls the negative end of the main negative relay of the high-voltage battery to disconnect;

16. If there is no other wake-up source, the VCU enters sleep mode.

5. Charging high-voltage power-on

After the charging gun is inserted, the BMS will be awakened, and the VCU will be awakened through the network at the same time. After the initialization of the VCU is completed, the high-voltage relays will be controlled to close according to the feedback status of each controller, and the high-voltage power-on of the vehicle charging mode will be completed, and the charging mode will enter.

The specific workflow is as follows:

1. The VCU is woken up. After the initialization is completed, the main negative relay of the sending high-voltage battery is closed. At the same time, after a certain period of delay, the state of the negative terminal of the main negative relay of the sending high-voltage battery is closed. If the self-test fails, stop the high-voltage power-on and record the relevant Fault;

2. If the VCU detects that the key signal is in the ON/Start position at the same time, and the charging gun is connected, and detects that the MCU is already in the MCU high-voltage power-on completion state, then directly execute step 7. If the key signal is in the ON/Start position and The charging gun is connected, but the MCU is not powered on, or the key signal is in the Off position and the charging gun is connected, then go to the next step;

3. The VCU receives DCDC initialization success, if so, proceed to the next step, otherwise prohibit high-voltage power-on;

4. The VCU detects that the charging gun status signal sent by the BMS is connected. At the same time, the VCU receives the BMS charging mode request as "on-board charging or off-board charging or inverter output" and the VCU receives the charging signal sent by the BMS as "ready for charging or inverting output". state change", and there is no fault that does not allow the vehicle to be powered on, the VCU sends a request to the BMS to close the main and negative relays of the high-voltage battery. If the BMS charging mode request is "abnormal" or if it detects that the charging gun status signal sent by the BMS is that there is no charging gun inserted, then stop the high voltage power-on;

5. If the VCU does not receive the high-voltage battery main-negative relay closing request within a certain period of time, it will go through the corresponding power-off process and record the high-voltage battery main-negative relay closing timeout fault; if received, it will send a high-voltage battery Battery non-power precharging relay 2 is closed;

6. The VCU controls the PTC power-on control. Specifically, step 4-6 in the high-voltage power-on, and then proceed to step 16. If the pre-charge fails when the PTC is powered on, it will directly enter the power-off process and power off After that, it will not be powered on again, unless the VCU has not been in sleep after the gun is drawn and the key signal gives the ON position, it can be controlled to directly enter the MCU to power on. After the power is completed, the power is limited and only crawling;

7. The VCU controls and enters the power-off process of the MCU circuit, turns off the Ready light, and sends the requested torque to the MCU, and the requested speed is 0;

8. VCU sends DCDC working mode to standby;

9. The VCU sends a signal to the TMS to order the compressor and the PTC to stop working, and at the same time sends a power limit to 0 to the TMS;

10. The VCU detects whether the PTC, compressor and DCDC feedback signals are turned off or disabled within the specified time, that is, the DCDC working mode is not working, and the actual power fed back by the compressor and PTC is 0. If yes, proceed to the next step, otherwise report a fault and proceed to the next step;

11. The VCU judges whether the motor speed is lower than the power-off motor speed threshold, and continues to execute downwards after meeting the conditions or waiting for a timeout;

12. The VCU judges whether the output current of the high-voltage battery pack is less than the threshold value of the battery current for power-off, and at the same time judges whether the compressor is allowed to power down the high-voltage power supply. If the condition is met, it continues to execute downwards. After waiting for a timeout, it reports a fault and continues to execute downwards;

13. The VCU controls the main positive relay of the high-voltage battery to disconnect;

14. The VCU checks whether the bus voltage of the MCU drops to 95% of the bus voltage of the battery within the specified time, and judges whether the main positive relay of the high-voltage battery is normally disconnected. If so, execute step 16, and if not, record the main positive relay of the high-voltage battery. Sticking failure, continue to the next step;

15. The VCU sends a request to the BMS to disconnect the main and negative relay of the high-voltage battery. After the BMS feedbacks that the main and negative relay of the high-voltage battery is disconnected or overtime, it enters the active discharge of the motor. After the discharge is completed, the MCU is not enabled. After the MCU circuit is powered off, Continue to control the power off of the PTC circuit. After the power off is completed, it will no longer respond to the high voltage in the charging mode;

16. The VCU detects that the vehicle status allows charging, sends a charging permission command to the BMS, and proceeds to the next step;

17. After power-on is completed, monitor the charging output process.

6. Charging under high voltage and power off

According to the charging information fed back by the BMS and the system status, the VCU controls each controller to stop working. Afterwards, the VCU controls each high-voltage battery relay to disconnect to complete the high-voltage power-off process in the vehicle charging mode.

The specific workflow is as follows:

1. When any of the following conditions are met, the VCU control system enters the charging mode high-voltage power-off process:

BMS feedback charging gun status is none or both AD/AC is connected or connection is abnormal, BMS has no charging request, BMS charging signal is charging end, high voltage interlock fault, charging system fault, VCU detects other faults that affect charging;

2. The VCU sends a DCDC working mode request to be Standby, and the VCU sends a signal to the TMS to command the compressor and the PTC to stop working, and at the same time sends a power limit to TMS to 0;

3. The VCU detects whether the DCDC enters the standby state within the specified time. The output power of the compressor and PTC is zero. If the condition is met, proceed to the next step. After waiting for a timeout, record the DCDC/compressor/PTC fault and proceed to the next step;

4. The VCU judges whether the bus current of the high-voltage battery pack is less than the threshold value of the battery current when the battery is powered off, and at the same time judges whether the compressor is allowed to power down the high-voltage power supply. If so, proceed to the next step; otherwise, after a timeout, record the fault and proceed to the next step;

5. The VCU sends a DCDC relay disconnection request. The VCU detects whether the DCDC relay is disconnected within the specified time. If it is disconnected, continue to the next step. If it is not disconnected, it will report a DCDC relay failure and continue to the next step;

6. The VCU sends an instruction to disconnect the main and negative relays of the high-voltage battery to the BMS;

7. The VCU detects whether the BMS feedbacks that the main negative relay of the high-voltage battery is disconnected within the specified time, and if so, execute the next step, otherwise record the fault and continue to execute the next step;

8. After the high-voltage power-off is completed in the charging mode, the VCU controls the main and negative relays of the high-voltage battery to disconnect before sleep;

9. If there is no other wake-up source, the VCU will enter sleep mode.

Detailed explanation of power on and off for pure electric vehicles

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