1. Types of electric car chargers
Since the first electric car came out in the 19th century, rechargeable batteries have been used as the power source. For an electric car, battery charging equipment is one of the indispensable subsystems. Its function is to convert the electrical energy of the power grid into the electrical energy of the on-board battery of an electric car. There are different ways to classify electric car chargers, which can be generally divided into on-board chargers and off-board chargers.
1) Car charger
On-board chargers refer to devices installed on electric cars that use ground AC power grids and on-board power sources to charge battery packs, including on-board chargers, on-board charging generator sets, and operating energy recovery chargers. car-mounted chargers usually use contact chargers with simple structure and convenient control, or inductive chargers, which are designed according to the type of car-mounted battery and are highly targeted.
On-board chargers are generally designed for low charging rate and long charging time (usually 5-8 hours). Due to the limitation of the quality and volume of electric cars, on-board chargers are required to be as small as possible and light in weight (generally less than 5kg). The on-board charger is specific to the battery to be charged, and the charging method of the battery is also pre-defined. Since the charger and the battery management system are both installed in the car, they can easily communicate with each other using the internal bus network of the electric car.
2) Off-board charger
Non-car chargers are ground chargers. The ground charger refers to a device fixed on the ground that rectifies and transforms AC power, and its DC output terminal charges the battery pack, so it can also be called a DC charger. According to different charging places and charging requirements, ground chargers are mainly used in homes, charging stations and various public places. In order to meet the various charging methods of various batteries, the power, volume and weight of the ground charger are usually relatively large, and are generally designed for a large charging rate. Since the ground charger and the battery management system are physically separate, they must communicate with each other via wired or wireless.
The charger also needs to have metering and charging functions. Generally, the charger should be able to charge at least one of the following three types of power batteries: lithium-ion batteries, lead-acid batteries, and nickel-metal hydride batteries. According to the information about the battery type, voltage, temperature and state of charge provided by the battery management system, the ground charger selects an appropriate charging method to charge the battery to avoid overcharging and overheating of the battery.
The ground charger consists of a rectifier that can convert the input AC power into DC power and a power converter that can adjust the DC power. By inserting the plug of the cable into the matching socket of the electric car , after the communication signal is shaken and confirmed, the ground The charger inputs DC power to the on-board battery of the electric car to charge it. The charger is equipped with a locking lever to facilitate the insertion and removal of the plug. At the same time, the lever can also provide a signal to confirm that it has been locked. If there is no signal, the charger will not charge the battery to ensure safety. According to the communication between the ground charger and the onboard battery management system, the power converter can adjust the DC charging power online, and the ground charger can display the charging voltage, charging current and charging power, and even the required charging fee.
2. Electric car charging method
1) Conductive charging method
The conductive charging method is also called the contact charging method. The contact charging method is usually controlled by a traditional contactor. The user connects the charging power connector (plug) to the car (socket), which uses metal contact to conduct electricity. The biggest advantage of the contact charging method is: mature technology, simple process and low cost. The disadvantage of the contact charging method is that it is not safe to expose the conductor to the outside, and it will cause mechanical wear due to multiple plugging operations, resulting in loose contact and ineffective transmission of electrical energy. The biggest problem of contact charging lies in its safety and versatility. In order to make it meet the strict safety charging standards, many measures must be adopted on the circuit to enable the charging equipment to be safely charged in various environments.
2) Wireless charging method
Research on the wireless charging method of electric cars is currently mainly focused on the inductive charging method, which can be charged without contact. The inductive charging method uses inductive coupling to charge, that is, the charging power supply and the car receiving device do not use direct electrical contact, but a combination of separate high-frequency transformers, through inductive coupling, non-contact transmission of energy. Using inductive coupling to charge can effectively solve the shortcomings of contact charging. The biggest advantage of inductive charging is safety, because there is no direct electrical contact between the charger and the car, and there is no risk of electric shock even when the car is charged in harsh weather, such as rain and snow.