Analysis and Control of the Injected Type-Adaptive Impedance (IT-AI) Inverter for Low-Capacity Requirement

In this article, an injected type-adaptive impedance (IT-AI) inverter is proposed for low inverter capacity requirement and wide reactive power compensation range. Different from the traditional coupling impedance, the IT-AI is not only used to reduce the voltage stress of the inverter but also to reduce current stress. Moreover, the adaptive impedance in the injection circuit can expand the reactive power compensation range without the additional harmonics. However, there is a risk of fundamental frequency resonance between the inverter and IT-AI. To overcome this challenge, the resonance phenomenon is analyzed through amplitude–frequency characteristics of the inverter current. Then, an additional damping control strategy is proposed to suppress resonance at the fundamental frequency, which is composed of a moving average filter (MAF) and virtual resistor–capacitor connected in series on the d-q coordinate system. Finally, representative simulations and experiments are carried out to verify the performance and effect of the proposed IT-AI inverter. The results show the proposed inverter has a lower capacity requirement compared to traditional coupling impedance inverter and the proposed control strategy has excellent damping control performance.