Characteristic Harmonic Spectrum Relocating for Controlling Specific Inter-Harmonics of Inverters With New Phase-Shifted Rotating PWM

The problems of sub-synchronous oscillation and high-frequency oscillation related to inter-harmonics need to be solved in intermittent energy generation systems. The paper proposes a new Phase-Shifted Rotating Pulse Width Modulation (PSR-PWM) technique for specific inter-harmonics control, which can eliminate the specific inter-harmonic that may cause related inter-harmonic oscillations in power system. Based on the time-shift and phase-shift characteristic of signals, the initial phase angle of a characteristic harmonic is linearly modulated to realize the frequency control of moving the spectrum to the desired inter-harmonic spectrum. Therefore, the inverter controlled by the proposed PWM technique behaves as a controlled inter-harmonic voltage source, so as to suppress the specific inter-harmonics in the grid. The analysis of typical simulation cases shows that the maximum frequency offset range for any modulated output voltage characteristic harmonic of the inverter is from -50Hz to 50Hz theoretically. The amplitude of the inter-harmonic voltage combined with its phase angle and frequency can be continuously controlled over a wide frequency range simultaneously, and the suppression effect of other parasitic inter-harmonics is obviously better. Finally, the feasibility and correctness of proposed PSR-PWM techniques are verified by MATLAB simulations and experiments. This paper can be helpful for the study of new energy grid-connected inverters to damp sub-synchronous oscillations and high-frequency oscillation.