Selection of residual current device in EV charging pile / module

With the explosive growth of the number of new energy vehicles in the past two years, the construction scale of its supporting facilities and charging piles has also expanded.

The growth of the new energy vehicle market is inseparable from the construction of basic charging facilities. How to ensure the safety of electricity used in the charging process, especially to prevent the leakage current from harming life and property, is a problem worthy of attention.

As a leakage protector, the residual current protector is widely used in low-voltage power distribution systems to prevent electric shock accidents, electrical equipment leakage damage and electrical fires. Also in the field of electric vehicle charging, RCD is also widely used as a basic electrical protection device.

Our zero phase current transformers Type A / Type B can be used for EV charing module.

There are four modes of electric vehicle charging, which are clearly stated in GB/T 18487.1-2015 "Electric Vehicle Conductive Charging System Part 1: General Requirements".

Mode one, the electric vehicle is connected to the AC grid using a charging connection cable. The residual current protection mainly depends on the residual current protection device (RCD) in the building distribution box. Since it is not guaranteed that all existing building devices are equipped with RCD, this kind of The method is very dangerous and has been banned

Mode two, the on-cable control and protection device (IC-CPD) is installed on the charging connection cable, and the IC-CPD has a residual current detection and protection function

Mode three,use special power supply equipment to directly connect the electric vehicle to the AC power grid, and install a control guide device on the special power supply equipment. The special power supply equipment is the AC charging pile

Mode four, when the electric vehicle is connected to the AC grid or the DC grid, a DC power supply device with a control guidance function, that is, a DC charging pile is used.

Here, we mainly discuss the selection of the residual current protector in the charging piles of mode three and mode four.

According to GB/T 18487.1-2015, the residual current protector of AC power supply equipment should adopt type A or type B, which meets the relevant requirements of GB 14084.2-2008, GB 16916.1-2014 and GB 22794-2008. As shown in Figure 1, it is the schematic diagram of the charging mode 3 control guide circuit, and the residual current protector is installed inside the power supply equipment.

What is type A or type B residual current protector? China's Residual Current Protection Device (RCD) Guiding Standard GB/Z 6829-2008 (IEC/TR 60755:2008, MOD) "General Requirements for Residual Current Action Protector" from the basic structure of the product, residual current type, trip Methods and other aspects have been divided.

According to the type of residual current, RCD can be divided into AC type, A type, and B type. AC type residual current protector: RCD that ensures tripping of residual sinusoidal AC current that is suddenly applied or slowly rising. Type A residual current protector: It includes AC type characteristics and superimposes 6mA of pulsating DC residual current and pulsating DC residual current to smooth the residual current to ensure tripping RCD.

Type B residual current protector: includes type A protection features, in addition, it can superimpose the sine AC residual current of 1000 Hz and below, the AC residual current superimposed smooth DC residual current, the pulsating DC residual current superimposed smooth residual current, two-phase or more The pulsating DC residual current and smooth DC residual current generated by the phase rectifier circuit ensure the tripped RCD.

At present, because the price of type B RCD is too expensive, most domestic AC charging piles are installed with type A residual current protectors. So can the type A residual current protector meet the leakage protection requirements of the charging pile? Let's analyze the type of residual current that may occur during charging.

During the charging process using the AC charging pile, the AC charging pile and the vehicle coupler are connected to the public power grid. If the insulation is damaged in the pile, power frequency AC leakage current may be generated.

In the electric vehicle part, the possible leakage current mainly comes from the leakage of the on-board charger. The general topology of the charger is mainly AC/DC and DC/DC.

The AC/DC part of the single-phase input AC power is first filtered by EMI, and then under the action of the Boost APFC circuit, the AC power of 85~265V is rectified into a stable output DC 400V voltage, and DC input is provided for the subsequent stage.

The DC/DC part uses a phase-shifted full-bridge LLC main circuit to convert the DC voltage of 400V into an acceptable voltage for the battery. When the insulation between the circuit board and the device casing is damaged, pulsating DC residual current may be generated in the rectifying part, and DC residual current with a small ripple factor may be generated in the Boost APFC circuit.

The following picture illustrates the generation and harm of DC residual current in detail (for reference)