How does the PCS buffer circuit (RCD) of an energy storage system suppress spikes?

The RCD snubber circuit (also known as a snubber circuit) in the PCS is mainly used to suppress the spikes and ringing of the collector-emitter voltage (Vce) when the IGBT is turned off. Its working principle is as follows: when the IGBT is turned off and Vce rises rapidly, the snubber capacitor (Cs) is charged through the snubber diode (Ds), absorbing the energy stored in the parasitic inductance of the line, thereby limiting the voltage peak. Subsequently, the snubber resistor (Rs) dissipates the energy stored in Cs as heat, preparing for the next operation.

Design considerations:

1. Cs capacitance: Calculated based on the energy to be absorbed and the allowable voltage overshoot. The smaller the capacitance, the weaker the absorption effect; the larger the capacitance, the greater the loss.

2. Rs resistance: It needs to be small enough so that Cs can discharge completely before the next turn-off, but not too small to avoid excessive discharge current.

3. Layout: The RCD network must be as close as possible to the IGBT's C/E pins to minimize the parasitic inductance of the snubber circuit itself; otherwise, the effect will be greatly reduced.