Type A and B RCD Leakage Detection Device for IC-CPD and Wall-Box applications
According to IEC 61851, it is clearly stipulated that the residual current protection in AC charging equipment shall adopt type B or type A and 6mA smooth DC RCD, which meets the requirements of IEC 60755-2017.
In IEC62752 < In-cable Control and protection device for mode 2 charging of electric road Vehicles ( IC-CPD)> A smooth DC 6mA or a Type-B Leakage current detection is required in the IC-CPD application. In IEC62955, A smooth DC 6mA or a Type-B Leakage current detection is required in the AC Charger/Wall-box application.
Why a type B or a smooth DC 6mA residual current protector been required?
Let’s do some basic analyze about the type of residual current that can be generated during charging.
During the charging process using the AC charger, the AC charger and the vehicle coupler are connected to the public grid. If insulation damage occurs when charging, power-frequency AC leakage current may occur. In electric vehicles, the possible leakage current mainly comes from the on-board charger (OBC). the general topology of the AC charger is mainly included in AC/DC and DC/DC.
The AC/DC part of the single-phase input AC power is filtered by EMI first. Then, under the action of the Boost type APFC circuit, the AC power from 85 V to 265V is rectified into a stable output DC voltage of 400V, and provides the DC input for the rear stage. The DC/DC part adopts the phase shift full bridge LLC main circuit to convert the DC voltage of 400V into an acceptable voltage of the battery. When the insulation between the circuit board and the device housing is damaged, a pulsating DC residual current may be generated in the rectifier section, and a DC residual current with a small ripple coefficient may be generated in Boost type APFC circuits. Here, Bender’s diagram is used to explain in detail the generation and harm of DC residual current.
The existing type A RCD can only detect the pulsating DC leakage current without being disturbed by the DC 6mA current, but cannot detect the pure DC leakage current and disconnect the protection. When the DC leakage current is more than 6 mA, due to the DC residual current will cause core magnetization in advance, make tripping value deviation, lead to type A RCD can’t normal movement. Therefore, type B RCD or A+6 protection must be used!
In the foreseeable future, with the electric vehicles into thousands of households, the EV charging will become an essential part of people’s life. Therefore, the replacement of the residual current protection in the EV charging is very necessary. Only a safe electricity environment can let everyone rest assured to enjoy the convenience of electric vehicles.
