How to suppress spikes in the RCD circuit of a frequency converter

Applying an RCD snubber circuit in a frequency converter is an effective method to suppress IGBT turn-off voltage spikes. The RCD circuit is typically connected in parallel between the collector and emitter of the IGBT, or across the DC bus. Its working principle is as follows: when the IGBT turns off, the voltage across its terminals rises rapidly. When the voltage exceeds the DC bus voltage, the snubber capacitor charges quickly through the diode, absorbing the energy stored in the parasitic inductance of the circuit, thus suppressing the voltage spike. Subsequently, the snubber capacitor discharges through the resistor, dissipating the absorbed energy as heat. Key parameters for designing the RCD circuit include: the capacitance value of the snubber capacitor, which needs to be calculated based on the parasitic inductance energy; the resistance value of the snubber resistor, which determines the discharge time constant and must ensure the capacitor voltage is below the bus voltage before the next switching cycle; and the selection of the diode, which must have fast recovery characteristics and sufficient current handling capability. The RCD circuit effectively reduces switching noise and device stress, but introduces additional losses. Optimization requires a trade-off between spike suppression effect and efficiency. For high-frequency applications, non-inductive capacitors with good high-frequency characteristics and fast recovery diodes should be selected. Eintech offers low-inductance capacitors and diodes suitable for buffer circuits, helping to design efficient spike suppression solutions.