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

Circuit breakers (CBs) play an important role in distribution networks. According to IEC standards, protection characteristics need to be investigated to ensure reliability in the manufacturing process. It is required from IEC 60947 that the instantaneous release shall be verified with a test current at least 10 times greater than 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 complex programmable logic device (CPLD)-based logic control unit. To increase the current accuracy, an adaptive feedforward control strategy is developed to compensate for 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 CBs create 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 an error no greater than 2.2%.