Sensorless Virtual Flux Combined Control of Grid Connected Converters With High Power Quality Under Unbalanced Grid Operation

This paper presents a novel sensorless combined control for grid connected power electronic converters (GCCs) under both balanced and unbalanced grid operation. Under unbalanced grid conditions, output power quality of GCCs will be deteriorated by increased current harmonics and power oscillations injected to grids. To reduce current harmonics and power fluctuations, an improved sensorless combined control with a new switching logic based on instantaneous control of grid current components is presented. The simplicity and robustness of combined control is completely reserved due to a current reference vector, which is calculated using the virtual flux components in the grid voltage, and virtual flux reference frames without any positive and negative sequence extraction. The proposed method, in comparison with voltage oriented control, avoids problems of tuning current controller, PWM sub-system, and decoupling circuit. Compared to DPC, the method lacks active and reactive power calculation and voltage sensors and enjoys improved power ripples and current THD.