Design and Adaptive Control of Matrix Transformer Based Indirect Converter for Large-Capacity Circuit Breaker Testing Application

Circuit breakers (CBs) have played important roles in the power distribution network. According to IEC standards, the protection characteristics need to be investigated in the manufacturing process to ensure high reliability. It is required from IEC 60947 that the instantaneous release shall be verified with a test current at least 10 times of the rated current. For large-capacity CB testing, converters with large output current, high accuracy and fast response are needed. A large current indirect converter including four converting units and a matrix transformer is proposed. The converting units are synchronized using a CPLD based logic control unit. To increase the current accuracy, an adaptive feedforward control strategy is developed to compensate the influences of CB-dependent resistances and inductances. The equivalent load impedance is adaptively identified from a robust identifier, which is then used to construct the feedforward compensator. Simulation and experimental results show that different circuit breakers bring in CB-dependent contact resistances and inductances in the testing circuit. The impedance change can be successfully identified by the robust identifier with limited errors. The proposed converter is capable of generating a wide range of current from 100 A to 40 kA with the error no more than 2.2%.