Virtual Power Control and Sinusoidal Current Operation for Grid-Connected Inverter under Unbalanced Grid Voltages Conditions

ABSTRACT Power oscillation and current quality are the important performance targets for the grid-connected inverter under unbalanced and distorted grid voltages. In this work, the inherent reason for the current harmonic and power oscillations of the inverter are discussed. Then away from the positive and negative sequences analysis, novel strategy to determine the harmonic components of the grid currents during constant power control and to obtain relations for the power oscillations during sinusoidal current control are introduced. Based on the introduced analysis, a power control strategy is suggested. The proposed power control strategy uses a virtual power as a controlled variable. The virtual power depends on virtual grid voltages which can be extracted from actual grid voltages by using second ordergeneralized integrator. By controlling the virtual power, sinusoidal grid currents with minimum THD is obtained under unbalanced and distorted grid voltages. For constant power operations, the actual power is used as a controlled variable. Based on an adaptive parameter, flexible control technique is used to switch between sinusoidal current control and constant power control operations. Simulation studies are carried out to confirm the effectiveness of the proposed controller to obtain constant power/sinusoidal currentcontrol operation under unbalanced and distorted grid voltages and to confirm the correctness of the introduced equations to calculate the grid current harmonic components and the power oscillations under unbalanced grid voltages.