Dynamic Current Balancing for Paralleled SiC MOSFETs With Circuit Mismatches Considering Circulating Current in Drive Circuit

Parallel operation of silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) is necessary for high-power applications. However, the dynamic current sharing of paralleled devices is very sensitive to mis-matched circuit parasitic inductances due to their high switching speeds. Symmetric parasitic inductances are usually difficult to realize because of the limitation of circuit layout, especially when more than two devices are paralleled. In this paper, the effects of the circulating current in the drive circuit caused by the circuit mismatches, which result in dynamic current imbalance, are firstly analyzed in detail. The influences of related drive circuit parameters are presented, which reveal the mechanism of dynamic current sharing. Motivated by the analysis, a suppression method of the circulating current is proposed by inserting additional impedances in the drive circuit. Considering the coupling noises introduced by the additional impedances, the concept of blocking unit is proposed to guarantee the proper operation of the drive circuit. A simple circuit implementation and the operation principle are presented. Finally, the drive method is validated by both simulations and experiments. Experimental results show the peak current imbalance is reduced from 16.5% to 3.2% and the maximum switching loss imbalance is reduced by half.