Introduction to the design of electric compressor control principles for electric vehicles
The typical control principle of the electric compressor controller is shown in Figure 1. The hardware part of the electric compressor controller can be divided into a high-voltage power supply part, a low-voltage control part and a high-low pressure interlocking loop. When the compressor receives the low-pressure control signal, The IGBT conducts high-voltage power supply and drives the motor to drive the compressor to work.
1. High voltage power supply part
The high-voltage power supply part includes high-voltage connectors, high-voltage filter circuits and IGBTs. The high-voltage connector is connected to the vehicle wiring harness. The connector base is made of metal and is connected to the compressor housing through bolts. When leakage occurs at the connector connection, the current can be conducted to the vehicle through the compressor housing and then through The ground of the entire vehicle is transmitted to the earth. The high-voltage filter circuit generally consists of multiple filter capacitors connected in parallel. It has two main purposes: first, to filter out abnormal fluctuations in the bus voltage so that the voltage input to the compressor is stable and to avoid damage to the compressor caused by large voltage fluctuations; The second is to absorb the ripple voltage generated by the compressor itself due to power changes and prevent the ripples generated by the compressor from affecting the entire vehicle and other high-voltage parts. IGBT is a very important component in the air conditioning controller. Generally, an electric compressor is composed of 6 IGBTs. Its function is to conduct the high-voltage circuit through the on and off of IGBTs, thereby driving the motor compressor to start working. Because the IGBT will be connected to high voltage and will pull in frequently, its working environment is the worst among the entire controller. Common damage modes of IGBT include overcurrent, overvoltage and overheating. In order to ensure that the IGBT works within a suitable temperature range, generally electric The compressor controller will add a lot of protection logic.
2. Low voltage control part
The low-voltage control part includes low-voltage connectors, filter circuits, DCDC converters, LIN/CAN communication loops, sampling circuits and ECUs. The low-voltage connector is connected to the vehicle wiring harness to provide low-voltage electricity and LIN/CAN signal communication for the compressor controller. The filter circuit is mainly to ensure the stability of the low-voltage input voltage. The purpose of the DC-DC converter is to convert 12 V electricity into different voltages to provide power for different electrical appliances. For example, the IGBT drive circuit generally requires a 15 V regulated power supply, and the sampling circuit generally requires a 3.5 V regulated power supply. LIN/ CAN isolation and sleep require 5 V supply. LIN/CAN communication is the channel for interaction between the compressor and the vehicle. The vehicle issues various instructions to the compressor through LIN/CAN communication. At the same time, the compressor feeds back its actual status to the vehicle through LIN/CAN to determine the condition of the compressor. Operation status. The sampling circuit is used to detect the voltage, current temperature and hardware protection circuit of the compressor operation. ECU is the core of signal interaction and transmission and reception of electric compressor controller. ECU receives the vehicle LIN/CAN signal, and at the same time collects its own voltage, current, temperature and the status of feedback from each sampling circuit to determine whether the compressor meets the starting status. If it meets the starting status Condition, the ECU sends a start signal to the IGBT driver chip, driving the IGBT on and off to start the compressor motor. At the same time, the ECU constantly monitors the working status of each component. If there is any abnormality, it will immediately stop the compressor and feedback the fault mode to the entire vehicle.
3. High and low voltage interlock circuit
The purpose of the high and low voltage interlock circuit is to prevent electric compressor connectors from being disconnected or having poor contact, causing leakage and personal safety. The principle is to ensure that all high-voltage and low-voltage electrical circuits of the vehicle work normally through a low-voltage line circuit. Only When all the connectors are plugged in place, the high-voltage components can communicate normally. When it is detected that the interlock circuit current exceeds the normal value, the vehicle will report an interlock circuit fault, and the vehicle will not be able to receive high-voltage power.
