DC-side Circuit Implementation of a Three-phase Inverter for Balancing Phase-leg Capacitor Currents

This paper proposes methods of balancing capacitor currents between phase legs in three-phase inverter circuits by changing the DC-side connection material or structure. The single-phase-leg unit consists of a half-bridge power module and DC-link capacitor that is connected directly to the module. Owing to this structure, it can be realized when there is a low stray inductance between the half-bridge module and DC-link capacitor. In the case of connecting a three-phase inverter, the stray inductance between the phase legs and the DC-link capacitor may lead to an imbalance in each capacitor current owing to DC-side resonance phenomena. The capacitor current imbalance may be due to the relationship between the switching and resonance frequencies. In order to balance the capacitor currents, this paper proposes two current balancing methods; applying (1) a graphite bus bar to increase the dumping resistance, and (2) a DC-side delta connection to geometrically balance the three phase legs. The experimental results obtained using a SiC MOSFET rated at 300 V, 4.6 A verify the suppression effectiveness of the DC-link capacitor current imbalance.