DC Fault Analytic Calculation and Fast Current Limiting Method for Hybrid Cascaded Converter Station

In the field of high-voltage, large-capacity, long-distance transmission, the hybrid converter topology has more technical advantages than the single converter. In order to cope with extremely hazardous DC short-circuit faults, the DC short-circuit fault traversal capability of the converter needs to be considered as a priority. First, this paper proposes a hybrid cascade topology with DC short-circuit fault ride-through capability based on line commutated converter (LCC) and modular multilevel converter (MMC). The DC short-circuit fault current limiting control method is then presented. Then, by analyzing the dynamic characteristics of the converter during a DC short-circuit fault, a mathematical model of the staged equation of state is constructed to realize the accurate analytical calculation of the DC short-circuit fault current. Next, the most serious DC short-circuit fault condition is selected, and the dynamic optimization calculation mechanism of forced triggering angle parameters is given by taking the maximum allowable current change as the criterion and combining with the proposed DC short-circuit fault current calculation method. Finally, a fast current-limiting control strategy is proposed based on the optimized design of the forced triggering angle, which ensures that the LCC avoids commutation failure during DC short-circuit fault ride-through, and reduces the fault current quickly.