Performance Analysis of a Direct Power Controlled VSC for PMSG based Wind Energy Conversion System

Abstract

Small-scale Permanent Magnet Synchronous Generator (PMSG) based Wind Energy Conversion System (WECS) widely uses diode rectifier for conversion from AC to DC due to their affordability and ease of use. But, this structure results in high current harmonics and poor power factor on the source side. Direct Power Control (DPC) is a well-established control approach for pulse width modulation (PWM) converter to obtain sinusoidal current waveform and unity power factor (UPF) at the source side. DPC for AC grid-connected converter is extensively reported in the literature, but its use for variable-speed AC machine is still relatively limited. DPC is particularly challenging to implement for machine-side converter (MSC) of variable-speed generator because it involves accurate measurement of instantaneous voltage, current, and phase angle under continuously changing frequency. Despite these difficulties, implementation of DPC for the MSC in WECS is very attractive as it provides stable DC-link control without the need for extra converter stages. In this research, the efficacy of table-based DPC, which is commonly used for constant source frequency, is tested for variable voltage source that emulates the output characteristics of variable speed generator. The converter’s performance is tested in two different ways: (1) by changing the source voltage/frequency in a linear way and (2) by changing source voltage/frequency randomly. Both cases are tested under two different conditions: one with a constant load and the other with stepwise load change for the performance of DC-link voltage regulation, rise time, ripple, and power factor. The simulation results confirm that the model effectively regulates DC-link voltage at 180 V and maintains sinusoidal source current with UPF during the changes in source voltage/frequency and load.