Research on the design of intelligent charger for electric vehicles

Abstract: In the face of the rapid development of electric vehicles, the research on high-power power battery intelligent charger and charging algorithm is becoming more and more important. This paper develops an intelligent charger system, and develops constant current, constant voltage and intelligent charging algorithms. The test results show that the charger has achieved constant current and voltage limiting, constant voltage and current limiting, intelligent charging and discharging functions. The intelligent charger can provide stable and reliable energy conversion for electric vehicles, and will continue to develop with the widespread use of electric vehicles.
Keywords: electric vehicle intelligent charger microcomputer control

1 Introduction

Electric vehicles are currently the only motor vehicles in the world that can achieve zero emissions. Due to environmental protection requirements and the development of new materials and new technologies, electric vehicles have entered a climax of development. As a green means of transportation, electric vehicles will bring great changes to human society in the 21st century. In line with the current trend of international scientific and technological development, taking electric vehicles as the entry point for China's automobile industry to enter the 21st century is not only a strategic choice to achieve leapfrog development of China's automobile industry technology, but also an important choice to achieve sustainable development of China's automobile industry.

At present, China's research on electric vehicles has achieved phased results, and the development of electric cars, electric medium-sized buses and electric large buses has been completed. In China, large and medium-sized cities generally have very serious traffic problems and automobile exhaust emission pollution problems. Electric vehicles are an ideal medium-speed and short-distance daily public transportation tool, so they have unique development conditions and broad application prospects in China. According to the experience of advanced countries such as Europe, the United States and Japan, while developing and manufacturing electric vehicles, it is necessary to develop public charging stations for electric vehicles and carry out electric vehicle demonstration projects to accumulate experience for the promotion and use of electric vehicles. It is a very meaningful task to open up electric vehicle traffic lines in busy urban areas and promote and demonstrate electric vehicles. In order to do this well, it is necessary to develop electric vehicle chargers and their charging management systems.

With the deepening of electric vehicle research, there is a certain demand for battery chargers for electric vehicles. Because this is a relatively new application field, developers are mainly concentrated in some scientific research units or universities. Domestic production units are mainly oriented to applications such as battery vehicles, electric tour buses, and battery maintenance, so the power range of chargers is limited. From the above analysis, it can be seen that the development of high-power intelligent chargers for electric vehicles is of great significance.

2 Design and development of charger

2.1 Features of intelligent charger system

· Indication function:

Status indication: including low battery voltage, charging, and charging end;
Fault indication: overvoltage and undervoltage on the DC output side, abnormal temperature, and disconnection of the main circuit breaker. Abnormal battery temperature.

· Recording function:

AC input: record the input power (kW?h) for public chargers, and record the single charge value and daily cumulative value.
Temperature: battery temperature, charger temperature, and ambient temperature during charging.
Fault recording: overvoltage and undervoltage on the DC output side, abnormal battery or charger temperature;

· Automatic billing function:

The charger reserves an IC card interface and develops an IC card management system. The charger can be charged with an IC card, and the charger can automatically charge, display and print the billing results, or directly settle with an IC card.

· Monitoring function:

The battery temperature must be monitored during the charging process, and it must not exceed the maximum allowable value, otherwise it will damage the battery and reduce the battery life.

· The charger has reserved CAN bus interface and 485 interface, which are used to communicate with the equipment on the vehicle and to connect to the host computer to observe the charging curve and monitor the network microcomputer.

· The charger has the function of protecting data when the power is off; it has safety protection measures such as current, voltage, time and other parameters exceeding the range set by the operator and software fault prompts.

· It has perfect fault protection and alarm functions. It has automatic protection and sends out sound and light alarm signals for faults such as overvoltage and phase loss of input power supply, overcurrent and overheating of charger, short circuit, open circuit, reverse polarity and overtemperature of battery.

2.2 Design of main circuit of charger

According to analysis, it is suitable to use phase control mode for high-power (above 10kW) chargers, with mature control methods and stable and reliable performance. Figure 1 shows the main circuit of the designed intelligent charger.

1) The circuit form adopts a fully controlled rectifier circuit and an integrated control module, which has high integration, good multi-phase pulse symmetry, high linearity, automatic phase sequence recognition, no need for synchronous transformer, soft start and phase loss protection.
2) The sensor for detecting battery voltage and DC side current uses the LEM module to collect voltage and current signals.
3) A dummy load for self-test is designed, and the logic part is required to control the input and disconnection of the dummy load to ensure the self-test of the charger.
4) The temperature detection uses an AD590 integrated temperature sensor, which can transmit signals over long distances.

2.3 Design and implementation of microcomputer control system

The controller can be divided into a main control unit and an execution unit, among which the execution unit has the functions of parameter acquisition, output DC control signal and discharge control signal, fault display, etc. The main control unit has the functions of power metering, host computer communication, status and alarm display, keyboard scanning, LCD display control, and transmitting instructions to the execution unit.

(1) Microcomputer controller hardware design

The 89C52 microcontroller from ATMEL is used. The microcontroller has 8K FLASH, 256 bytes RAM, 32 programmable I/O lines, 3 16-bit timers/counters, 8-level interrupt sources, and a universal serial interface. The peripheral devices mainly include SD2000D, which has a built-in 64Kbit NVSRAM, crystal oscillator, battery, and clock. AD574 is selected as the A/D converter, and DAC0832 is used as the D/A converter.