An Overlap-Time Compensation Method for Current-Source Space-Vector PWM Inverters

In voltage-source inverters, it is necessary to add the dead time between gating signals of the upper and lower switches to prevent short circuit in a phase leg. But in current-source inverters (CSI), due to the large series inductor in dc link, it is necessary to add the overlap time in gating signals of switches during the commutation process for avoiding voltage spikes generated by the intermittent dc current. However, the overlap time will cause negative influence in the output current waveform. In this paper, the current commutation process of CSI within a carrier period is investigated, which shows that the overlap time can cause output-current-vector errors. The output-current-vector errors are then analyzed, which are equivalent to a superposition and introducing additional low-order harmonics in the output current waveform. The relationship between harmonic distortion and the overlap time is derived. An overlap-time compensation method is then proposed, which compensates the dwell time of vectors according to the relations of voltages at the ac side of the inverter. The proposed overlap-time compensation method can effectively decrease the current harmonics introduced by the overlap time and improve the output current of the inverter. Simulation and experimental results are finally provided to verify the feasibility and validity of the proposed method.