Research on Fault Ride Through Strategy of Power Unit of Cascaded H-Bridge Medium Voltage UPS

Cascaded H-bridge medium-voltage UPS is widely used in medium-voltage distribution networks. Because it uses a large number of power switching devices, its reliability cannot be ignored. Given the H-bridge's short-term failure, the traditional bypass method will cause the failed unit's permanent isolation and reduce the UPS's operating efficiency. In order to solve the above problems, for short-term full-bridge lock-up, this paper proposes an adaptive fault ride-through strategy based on fault voltage feedforward calculation. For short-term single component failure, this paper proposes a complementary electrical level fault ride-through strategy. It can prevent the faulted unit from being irreversibly isolated. Simultaneously, it optimizes the UPS output voltage and current during the fault period to achieve fault ride-through. The simulation results in PSCAD/EMTDC show that the proposed fault ride-through strategy has good feasibility and effectiveness.