Principles of Electric Vehicle Charging

Charging is an important part of the process of using electric vehicles. The experience of charging largely determines consumers’ purchasing decisions and car experience. Today, the old driver will talk to you about charging.

We know that electric vehicles are powered by on-board power batteries and powered by motors to achieve driving. The driving of an electric vehicle consumes the energy of the battery. After the battery is consumed, it needs to be supplemented. The process of transferring the electrical energy from the grid or other energy storage equipment to the vehicle’s battery is charging.

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The electric energy in the power grid or energy storage equipment needs to be converted by the charging equipment to match the technical characteristics of the electric vehicle power battery to complete the charging. The conversion process of charging equipment also needs to negotiate with the battery management system BMS (Battery Management System) on the electric vehicle to complete the charging with an appropriate voltage and current, and during the charging process, the charging current will decrease with the charging process , The high current can be charged faster in the early stage, and the lower current can be charged more slowly in the later stage.

A few terms

SoC: State of Capacity, the current capacity of the battery, generally expressed as a percentage, such as 60%.

BMS: BatteryManagement System, battery management system, monitors the status of the battery, uniformly manages the charging and discharging of the battery, protects the safety of the battery, and maintains the status of the battery to ensure the normal operation of the battery.

C: Current, battery charge-discharge rate. It is defined that a full charge of the battery in 1 hour will be charged at a rate of 1C. If the battery is charged at a rate of 2C, the battery can be fully charged in 0.5 hours. Therefore, the greater the magnification, the faster the charging. High-rate charging requires the support of battery materials and battery management systems. Generally, high-rate charging will reduce battery life to a certain extent.


Two main charging types

Slow charging

The AC charging pile does not have a power conversion module, and does not perform AC/DC conversion. It outputs AC power, which is connected to the car, and converted to DC power by the on-board charger before inputting the battery. The charging power depends on the power of the on-board charger. At present, there are 2Kw, 3.3Kw and 6.6Kw on-board chargers for mainstream models. Generally speaking, charging is slower. Generally, hybrid vehicles require 4-6 hours to fully charge, and pure electric vehicles require more than 8 hours to fully charge. The charging rate is basically below 0.5C.

DC fast charge

The DC charging pile has a built-in power conversion module, which can convert the AC power of the grid into DC power. It does not need to be converted by the on-board charger, and is directly connected to the battery in the car. The charging power depends on the battery management system and the output power of the charging pile, whichever is smaller.

At present, Tesla’s fast charging power on the market reaches 120Kw, which can charge 80% of the power in half an hour, and the charging rate is close to 2C. The BAIC Ev200 can reach 37Kw and the charging rate is 1.3C.

Public charging and private charging

From the perspective of ownership, there are two types of charging piles: public charging piles and private charging piles. Public charging piles provide charging services for the public in public places and charge charging service fees. Private charging stations only charge their own vehicles and are not open to the public.

Due to parking spaces, a large number of electric vehicle owners have not installed charging piles and need to charge on public charging piles.

It is estimated that private charging piles account for less than 30% of the total charging piles.

Mobile power bank

Similar to the power bank solutions for mobile phones and tablets, mobile power bank products and solutions for electric vehicles have also appeared. Power banks have different capacities and product forms, including trolley box types and mobile charging car types. Mobile power banks play an important supplementary role for emergency scenarios.

Post time: Feb-22-2021