A Novel Power-Voltage Control Strategy for the Grid-Tied Inverter to Raise the Rated Power Injection Level in a Weak Grid

The conventional power-current controlled grid-tied inverter suffers from interactive stability issues, including harmonic oscillations when connected to a weak ac grid, which limits the integrated power rating of distributed generators. To overcome preceding drawbacks, a novel power-voltage control strategy, based on the voltage feedback control of the inverter LCL filter capacitor, is proposed in this paper. A dynamic model of the inverter output impedance is developed in the rotating d-q frame. This model includes main circuit parameters, phase-locked loop (PLL) dynamics, and regulator parameters. Frequency characteristics of the output impedance, contrastive analysis between the conventional power-current strategy and proposed power-voltage strategy based on generalized Nyquist criterion are presented to show superiority of the latter in a weak grid. The impedance analysis proves the power-voltage controlled inverter can stably operate in a weak grid. The stability of the grid-tied inverter system remains unchanged with increasing PLL bandwidth and delivered power, thereby effectively raising the rated power injection level of the inverter in a weak grid. A low-power inverter prototype is built and tested in the laboratory. The simulation and experimental results verify the effectiveness of the proposed control strategy.