Principles and Characteristics of Electric Vehicle Car Charger_Classification and Requirements for Electric Vehicle Car Charger

The car charger is also called an AC charger. It is installed on an electric car. It is connected to an AC outlet through a socket and a cable, and provides charging power to the electric car with a three-phase or single-phase AC power supply. The advantage of the car charger is that the car battery can be charged at any time and anywhere, as long as there is an AC outlet with the rated voltage of the charger. The disadvantage of the car charger is that it is limited by the space of the electric car, the power is small, the output charging current is small, and the battery is charged for a long time. Figure 6-1 shows the connection between the car charger and the charging power supply.

The car charger mainly supplements the electric energy of the small electric vehicle, and the charging power is small. The electric charging car built on the roadside, the community, etc. can be used to charge the electric vehicle, and the charging in the low valley period is fully utilized.

1, the principle structure

The input of the vehicle charger is based on the active power factor correction circuit. The electrical principle is shown in Figure 6-16, and the appearance is shown in Figure 6-17.

2, functional characteristics

(1) It has the ability to safely and automatically charge the electric vehicle battery. The charger can dynamically adjust the charging current or voltage parameters according to the data provided by the battery management system (BMS), and perform corresponding actions to complete the charging process.

(2) It has the function of high-speed CAN network and BMS communication, judging whether the battery connection status is correct, obtaining the battery system parameters and real-time data of the whole group and single battery before charging and during charging.

(3) It can communicate with the vehicle monitoring system through the high-speed CAN network, upload the working status, working parameters and fault alarm information of the charger, and accept the start charging or stop charging control commands.

(4) Complete safety protection measures.

1) AC input overvoltage protection function.

2) AC input under voltage alarm function.

3) AC input over current protection function.

4) DC output over current protection function.

5) DC output short circuit protection.

6) Output soft start function to prevent current surge.

7) During the charging process, the charger can ensure that the temperature, charging voltage and current of the power battery do not exceed the allowable value.

8) With single cell voltage limit function, the charging current is automatically adjusted according to the BMS battery information.

9) Automatically judge whether the charging connector and charging cable are properly connected. When the charger is properly connected to the charging post and the battery, the charger can start the charging process; when the charger detects that the charging pile or battery is not connected properly, the charging is stopped immediately.

10) The charging interlock function ensures that the vehicle cannot be started before the charger is separated from the electric vehicle power battery.

11) High-voltage interlock function, when there is a high voltage that is harmful to personal safety, the module locks no output.

12) Has a flame retardant function.

3. Technical indicators

(1) Environmental conditions.

1) Operating temperature: -30~70°C (the output power is limited to 50% of rated power above 50°C).

2) Relative humidity: 5%~95%.

3) Altitude: no more than 2000m.

(2) AC input.

1) AC working voltage: 220 & TImes; (1 ± 20%) V (single-phase three-wire).

2) AC working frequency: (50 ± 1) Hz.

3) Full load power factor: not less than 0.99.

4) Total distortion rate of harmonic current: no more than 5%.

4, DC output

(1) Steady flow accuracy: no more than ±0.5%.

(2) Voltage regulation accuracy: no more than ± 0.5%.

(3) Ripple coefficient: not less than 0.5%.

(4) Full load efficiency: not less than 94%.

(5) Voltage range: 140 to 350V.

(6) Current range: 1 to 8A.

(7) Maximum power: 2.5kW (output can be controlled by constant power).

5, structural protection

(1) Fully enclosed structure, enclosure protection class IP54.

(2) The metal casing and parts of the charger are treated with double-layer anti-rust treatment, and the non-metallic casing has an anti-oxidation protective film or anti-oxidation treatment.

(3) The printed circuit board and connector inside the charger are protected against moisture, mildew and smoke.

6, the average time between failures

Mean Time Between Failure (MTBF): no less than 50 000h.

(1) Vehicle DC-DC converter

The DC-DC converter is a technology that converts one type of direct current into another type of direct current. It mainly transforms voltage and current, and it plays the role of energy conversion and transmission in electric vehicles. The DC-DC converter is divided into a unidirectional DC-DC and a bidirectional DC-DC. The energy of the unidirectional DC-DC can only flow in one direction, while the bidirectional DC-DC refers to changing the direction of the current according to the need to keep the polarity of the DC voltage at both ends of the converter unchanged, thereby realizing the bidirectional flow of energy. Stream converter. Two-way DC-DC can realize energy recovery, and its application space is wider.

Electric vehicles include pure electric vehicles, hybrid vehicles and fuel cell electric vehicles. The vehicle-mounted bidirectional DC-DC converter is a key technology for electric vehicles.

Hybrid fuel cell vehicles: Due to the current development level of fuel cells, fuel cells are generally used as the main power. In addition, there are super capacitors (UC) and high voltage batteries (HVB, generally high voltage 100~500V) as auxiliary power. Form a hybrid fuel cell vehicle, as shown in Figure 6-14. The bidirectional DC-DC converter is used as the power management unit of the supercapacitor and the power storage battery. The function is to provide auxiliary energy when the vehicle accelerates, to provide peak power when the vehicle climbs, and to recover energy during deceleration/braking, thereby effectively improving energy utilization efficiency.

Pure fuel cell electric vehicle: The bidirectional DC-DC converter is used as a power management unit for a low voltage battery (LVB, generally low voltage 12V or 24V). The function is: cold start of fuel cell, providing fuel cell air compressor Power supply, assist when the vehicle accelerates, recover energy during deceleration/braking, and improve the acceleration and deceleration performance of the vehicle, as shown in Figure 6-16.

Pure electric vehicle: AC motor drive system: The bidirectional DC-DC converter adjusts the DC side voltage of the inverter, which makes the weak magnetic speed regulation and feedback braking easy to realize, expands the motor speed regulation range, and improves the system energy utilization efficiency, especially for Low-inductance motors commonly used in electric vehicles are more effective. The bidirectional DC-DC converter directly drives the four-quadrant operation of the DC motor.

Automotive electronics: The electricity consumption of electrical systems on modern cars is increasing, and the on-board electrical includes two levels of 12V and 42V. The bidirectional DC-DC converter can be used in a 12~42V dual power conversion system.

(2) Car Charger

The on-board Charger is a technology that converts alternating current into direct current, converting the electrical energy of the grid into the electrical energy of the vehicle's battery. The vehicle high-voltage charger is installed on an electric vehicle and connected to an AC outlet through a plug and a cable, so it can also be called an AC charger. The advantage of the car charger is that when the battery needs to be charged, as long as there is a power socket available, it can be charged. The disadvantage is that it is limited by the space on the car, so the power handling capacity is limited, and only a small current can be provided. Charging, charging time is generally longer.

The basic structure of the charger includes a power unit, a control unit, an electrical interface, and a communication interface. The electrical interface includes the charger power supply cable and connecting device, charging cable and charging connector. When the electric vehicle is being charged, the electric vehicle and the electric vehicle charging device are properly connected, so that the electric energy can be safely transmitted from the charging device to the electric vehicle under normal conditions. Even if it is negligent in normal use, it will not pose a danger to the surrounding environment and people (especially the charging operator). Basic functional requirements include:

1) The charger should be able to charge one or more of the following batteries: lithium ion batteries, nickel metal hydride batteries, lead acid batteries, etc.

2) During the charging process, the charger dynamically adjusts the charging parameters according to the data provided by the battery management system, performs corresponding actions, and completes the charging process.

3) The charger should have the function of communicating with the electric vehicle or battery management system. Communication purpose: determine the type of battery; determine whether the charger is properly connected to the battery system of the electric vehicle; obtain the parameters of the battery system of the electric vehicle, the status parameters of the battery before charging and during charging; the charger should also have the function of communicating with the monitoring system of the charging station .

The human-computer interaction function allows the charging personnel to obtain some information about the charger. The information that the charger should display: battery type, charging voltage, charging current, and electrical energy measurement information; in the event of a fault, there should be corresponding prompt information; and battery temperature, charging time, and so on. Table 6-1 and Table 6-2 show some technical requirements for the car charger.