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.