An Optimized Carrier Phase-Shifted Modulation Strategy for Cuk PV Inverter

There exists the problems of output voltage zero-point drift and high even harmonic content of the three-phase Cuk liftable voltage photovoltaic (PV) inverter when it adopts the conventional carrier modulation method. In view of these, a new optimized Phase-Shifted Pulse Width Modulation (PSPWM) strategy is proposed. Firstly, the optimal zero-sequence component is determined based on the inverter topology and control objectives. Next, the zero-sequence component is injected into the sinusoidal signal and used as the new modulating signal so that the carrier pulse width modulation is equivalent to the space vector pulse width modulation. Finally, the carrier and modulating waveforms are blended in a superior manner, and a new logical operation is applied to generate the required switching drive signals for the control of the inverter switching tubes. In order to verify the effectiveness of the strategy, simulation and experimental platforms were constructed, and numerous simulations and experiments were done. The results show that the modulation strategy can solve the output voltage zero drift problem effectively, and suppress the even harmonics effectively, meanwhile, the harmonics are mainly concentrated near the primary frequency, which significantly reduces the total harmonic content and greatly improves the output voltage waveform. In addition, the modulation can be achieved by reducing one carrier signal, thus simplifying the modulation process and the design of the digital signal system.