Waveform control method for mitigating harmonics of inverter systems with nonlinear load

DC power systems connecting to single-phase DC/AC inverters with nonlinear loads will have their DC sources being injected with AC ripple currents containing a low-frequency component at twice the output voltage frequency of the inverter and also other current harmonics. Such a current may create instability in the DC power system, lower its efficiency, and shorten the lifetime of the DC source. This paper presents a general waveform control method that can mitigate the injection of the low-frequency ripple current by the single-phase DC/AC inverter into the DC source. It also discusses the inhibiting ability of the waveform control method on other coexisting harmonics, while the DC source delivers AC power to a nonlinear load. With the application of the waveform control, the average DC output power is supplied by the DC source, while the other harmonics pulsation power can be confined to the AC side (between the capacitors and the AC load). Theoretical analyses and experiment results are provided to explain the operation and the inhibiting ability, and to showcase the performance of the approach in tackling the harmonics. Results validate that the proposed solution can achieve significant mitigation of harmonic component at DC side with nonlinear load as well as a high quality output voltage without the need for extra large capacitive energy storage element implementation.