Model predictive direct current control of DFIG at low switching frequency

Abstract

With the rapid development and growing capacity of wind power generation systems, high power converter technology is widely used and developed. However, the power converter adopting the conventional vector control (VC) methods presents high switching frequency which increases the loss of power output in the high-power drive system. Therefore reducing the high-power converter switching frequency is the main approach to reduce the loss of power converter, however, it will cause the increase of PWM outputs harmonic even affecting the control performance. In order to reduce switching frequency, based on the predictive model of DFIG, VC strategy is replaced by a model predictive direct current control (MPDCC) strategy, which directly regulates rotor current through an optimization function with selecting appropriate voltage vector. This optimization function mainly achieves two targets: The first objective is to track rotor current rapidly and the other is to reduce switching frequency. Compared to VC strategy combined with pulse-width modulation, it has several advantages. The most prominent one is that the switching frequency is reduced up sharply for the reason that proportion-integral regulator is replaced by predictive unit. Second, it achieves better dynamic characteristics and steady-state characteristics at low switching frequency. Simulation results verify the proposed control scheme for DFIG