Electric vehicle on-board charger classification and requirements
(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 two-way DC-DC converter is a key technology for electric vehicles.
Hybrid fuel cell vehicle: Due to the current development level of fuel cells, fuel cells are generally used as the main power. In addition, super capacitors (UC) and power batteries (HVB, HVB, generally high pressure 100~500V) are used as auxiliary power to form a hybrid. Power 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 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 the power management unit of the vehicle battery (LowVoltage Battery, LVB, generally low voltage 12V or 24V). The function is: the fuel cell is cold-started to provide power for the fuel cell air compressor. When the vehicle accelerates, it assists in recovering energy during deceleration/braking, improving 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.
