Comparative study of voltage oriented and frequency coordinated control of grid connected doubly fed induction generator

Abstract

In this paper, a comparative study between voltage oriented control (VOC) and frequency coordinated control (FCC) of grid connected doubly fed induction generator (DFIG) is presented. The two method controls are deeply done on DFIG converter sides, grid side converter (GSC), and rotor side converter (RSC). The VOC method permanently maintains the DFIG reactive power to zero values to achieve stable voltage. This control is implemented by regulating the rotor direct axis reference current in RSC using grid reactive power. On the other hand, the FCC has employed the active power obtaining from the system frequency deviation to control the rotor quadrature axis reference current in the RSC. The GSC is the same in two studies, and its applied vector controlled method. The comparison study between the two methods is conducted at a steady and dynamic state under constant and variable wind speeds. The simulation results are carried out by using PSCAD/EMTDC electromagnetic transient program to validate the comparison study between two methods control of DFIG. The outcomes of the simulation show that the VOC is very convenient when the DFIG operated at transient mode and variable wind speeds while the FCC is feasible and effective for steady-state mode applications. Furthermore, the FCC method has an ability to reduce the active and reactive powers ripples as well as decreasing torque harmonics. Both of two methods had fewer transient recovery values of output parameters, which ensure safety dynamic response of DFIG and power system. This study contributes significantly to choose the suitable control of the DFIG converters according to electrical grid operation conditions. In addition, if a joint control has been applied to these two methods, the wind power gained strong and flexible control of the frequency and voltage for different operating conditions.