1. Charger performance
(1) Security. When charging an electric car, how to ensure the personal safety of personnel and the safety of the battery pack is of utmost importance. The links involved are as follows:
① When the operator connects the battery pack of the electric car to the power supply network through the charger.
②After the charging is over, when the operator performs the disconnection operation.
③When a person touches the body of an electric car during the charging process.
④When the charger fails.
⑤The external environment is bad, such as rain and snow.
The charger must ensure that all links are normal, even if a link fails, the personnel and the battery pack are safe. Underwriters Laboratories Inc. has formulated the U12231 (Personnel Protection Systems for EV Supply Circuits) safety standard to regulate the safety performance of electric car chargers.
(2) Easy to use. When connecting or disconnecting between the power supply, the charger and the battery pack, the plug and socket operation are involved. This kind of plug is generally larger and heavier, and requires a certain amount of insertion and removal force. Plugs and sockets should have clear polarities to prevent incorrect connections. The charger should have high intelligence and does not require excessive intervention by the operator in the charging process.
(3) Cost economy. Cost-effective, low-priced chargers help reduce the cost of the entire electric car, improve operating efficiency, and promote the commercialization of electric cars.
(4) High efficiency. High efficiency is one of the most important requirements for modern chargers, and it has a huge impact on the energy efficiency of the entire electric car.
(5) Pollution to the power supply is small. The charger using power electronic technology is a non-linear device that will produce harmonic pollution that is harmful to the power supply network and other electrical equipment. Due to the low power factor of the charger, the impact on the power supply network cannot be ignored when the load of the charger increases.
2. Technical requirements
The charger needs to meet the following technical requirements in terms of safety and control:
(1) The charger should be able to communicate with the battery management system or battery management unit, and receive battery data. During the charging process, appropriate methods should be adopted to ensure that the voltage of the single battery in the series battery does not exceed the upper limit, and the battery management system should send a battery serious fault message After that, it should be able to automatically stop charging.
(2) The charger should have panel operation and remote operation functions, and should be able to be connected to the monitoring system, and all functions except closing and cutting off the input power supply can be completed on the monitoring computer.
(3) The charger should be able to transmit the data sent by the battery management system to the monitoring computer through the monitoring network.
(4) The charger should have a fault alarm function and be able to actively send fault information to the monitoring system.
(5) The charger should have protection functions such as input undervoltage, input overvoltage, output short circuit, battery reverse connection, output overvoltage, and over-temperature battery failure.
(6) The charger should stop charging when it is separated from the battery management system.
(7) The charger should provide a charging cable connection confirmation signal: on the one hand, during the charging period, after the charging plug is connected to the car, the car control logic can use this signal to prohibit the car drive system from working during the charging period to ensure charging safety; on the other hand, On the one hand, the confirmation line and the charging line form a lock to ensure the safety of the charging personnel.
(8) Provide a good man-machine interface to complete the closed-loop control of the charging process of the charger, display the type of failure, and provide certain troubleshooting instructions. Provide open charging process parameters (including charging mode, charging parameters, number of stages) setting function, and complete the automatic control of the charging process according to the parameters. When the charging process is interrupted due to the action of the charger’s protection system, it should be able to display the fault type and provide a simple treatment method for the faults that are easier to remove.
(9) When charging the whole car, it is necessary to provide the required DC power supply for the battery management system. Currently, 24V/50A is generally used.
(10) The monitoring system of the charger should have an event recording function to provide historical data for accident analysis and operational testing.
For charging stations with multiple chargers, the chargers also need to provide event record data for the charging station monitoring system.
(11) The reliability of the charger must meet certain indicators. Considering the cost and utilization rate, the charger must ensure a safe and reliable charging hours from 70,000 to 8,000.
(12) The design of the charger must fully ensure personal safety, and its live parts must not be exposed, and at the same time ensure that the car body and the ground are of equal potential. The charger should be grounded to the charging station, the charger should be connected to the car body shell, and the charging station grounding grid should be reliable and convenient.
3. The output requirements of electric car chargers
(1) Range of output voltage and current of electric car charger:
① Output voltage range. According to the range of the battery voltage level, the output voltage of the electric car charger is divided into three levels: 150 ~ 350V, 300 ~ 500V, and 450-700V.
②) Output current range. The output DC current of the electric car charger adopts 10A, 20A, 50A.
100A, 160A, 200A, 315A, 400A (500A).
(2) Accuracy of voltage stabilization. When the AC power supply changes within the range of ±15% of the nominal value, and the output DC current changes within the range of 0-100% of the rated value, the output DC voltage should remain stable at any value within the corresponding adjustment range of the specified value, and charge The accuracy of the output voltage of the machine should not exceed ±0.5%.
(3) Steady flow accuracy. When the AC power supply changes within ±15% of the nominal value, and the output DC voltage changes within the corresponding range of the specified value, the output DC current should remain stable at any value within the range of 20% to 100% of the rated value. Charge The accuracy of the output current of the machine should not exceed ±1%.
(4) Ripple coefficient. When the AC power supply changes within ±15% of the nominal value and the output DC current changes within the range of 0-100% of the rated value, the output DC voltage should remain stable at any value within the corresponding adjustment range of the specified value. The effective value coefficient of the output ripple should not exceed ±0.5%, and the peak value of the ripple should not exceed ±1%.
(5) Output current error. The electric car charger runs under constant current, and the output DC current is set within the range of 20%~100% of the rated value. When the set output DC current is greater than or equal to 30A, the output current setting error should not exceed ±1% ; When the set output DC current is less than 30A, the output current setting error should not exceed ±0.3A.
(6) Output voltage error. The electric car charger runs under constant voltage, the output DC voltage is within the corresponding range of the specified value, and the output voltage setting error should not exceed ±0.5%.
(7) Output current limiting and voltage limiting characteristics:
① When the electric car charger is operating under constant voltage, when the output DC voltage exceeds the voltage limit setting value, it should be able to enter the constant voltage charging operation immediately and automatically limit the increase of its output DC voltage.
②When the electric car charger is running under constant current state, when the output DC current exceeds the current limit setting value, it should be able to enter the current limit state immediately and automatically limit the increase of its output DC current.
(8) The efficiency and power factor of the charger. When the output power is 50%~100% of the rated power, the power factor of the charger should be no less than 0.90, and the efficiency should be no less than 90%.
(9) Unbalance of current sharing. When multiple high-frequency power modules of the same model work in parallel, each module of the charger should be able to share the load proportionally. When the average output DC current of each module is 50%-100% of the rated current value, the current sharing is unbalanced The degree should not exceed ±5%.
(10) Harmonic current. The harmonic current generated by the charger should not exceed the limit specified in GB/T19826-2005.
(11) Noise. Under the condition that the rated load and the ambient noise are not greater than 40dB, the maximum noise measured at 1m from the horizontal position of the charger should not be greater than 65dB (Class A).
(12) Reliability index. The mean time between failures (MTBF) should not be less than 8760 hours.