How Does A Frequency Converter Cause A "hard Short Circuit" In The Dc Bus?

The DC bus inside frequency converter 60hz to 50hz 3 phase is responsible for the energy transfer between rectification and inversion. If a power component in the DC loop experiences a severe fault, it can cause a state similar to a hard short circuit on the DC bus. This often manifests as a sudden drop in bus voltage and a surge in instantaneous current, impacting the power electronic equipment.

This hard short circuit is not a simple ground fault, but a direct conduction caused by the failure of internal components in the DC link. For example, insulation breakdown inside a filter capacitor or a short circuit in an internal switching element (such as an IGBT/diode) will cause the current to shift from a high-impedance path to a near-zero-impedance path. Once the short circuit occurs, the voltage on the DC bus is rapidly clamped to near zero, and the energy output from the rectifier bridge is almost instantaneously consumed by the internal short-circuit path.

Under fault conditions, current limiting mainly relies on the impedance on the power supply side and the series impedance of the components on the bus. When the internal path resistance of the DC link is negligible, the system short-circuit current will increase rapidly, which will generate great thermal and mechanical stress on the electrical connections, wires, DC capacitors and power semiconductor devices inside the frequency converter 60hz to 50hz single phase.