Common Mode Power Control of Three-Phase Inverter for Auxiliary Load Without Access to Neutral Point

The purpose of this article is to investigate the potential of obtaining an auxiliary dc output from the common-mode switching harmonics of a three-phase inverter without access to the neutral point of the ac load. To achieve this, the control of common-mode (CM) switching harmonics with space vector modulation is proposed. With this control, CM switching harmonics can be regulated independently from the differential mode power flow to the main three-phase load. To physically implement the CM power flow, a harmonic extraction circuit is placed in parallel with the main three-phase load. The extraction circuit is formed by series-connected inductance and capacitance. Due to the LC series resonance and the mutual coupling of the inductance, only common-mode switching harmonics can pass through the extraction circuit. The extracted harmonics are then rectified and delivered to the auxiliary dc output. The control and topology are verified in both simulations and experiments. In the end, it is shown in experiments that there is no significant difference of the inverter efficiency after the auxiliary dc load is connected. This method can be used for instance to drive an ac machine while charging a low voltage battery or powering a compressor simultaneously.