Chapter 14 - Integration of fixed-speed wind energy conversion systems into unbalanced and harmonic distorted power grids

Abstract

Under distorted and unbalanced grid voltage conditions, induction motors draw currents higher than their rated current values. This brings extra winding losses and torque pulsation problems to them. To avoid the overheating problem related to the extra winding losses under the distorted and unbalanced voltage conditions, their permissible loading ratio should be determined by reducing the highest phase current to the rated value. Likewise, the permissible penetration level (PPL) of fixed-speed wind energy conversion systems with induction generators should intentionally be reduced for unbalanced and nonsinusoidal distribution systems. On the other hand, their low penetration level prevents the provision of maximum benefits from them. Accordingly, in this paper, a compensator design, which consists of a Steinmetz compensator (SC) and a single-tuned harmonic filter (STF), was suggested for maximization of PPL and displacement power factor (DPF), and minimization of the average total voltage harmonic distortion (THDV) and voltage unbalance factor (VUF). The VUF and harmonic distortion limits, stated in the standards and the desired DPF and rms bus voltage ranges, were regarded as constraints of the optimal design problem. And then, for a typical two-bus distorted and unbalanced test system, particle swarm optimization algorithm was implemented to employ the proposed optimal compensator. Second, optimal STF, which has the problem formulation of the proposed compensator except the unbalanced voltage objectives and constraints, and optimal SC, which has the problem formulation of the proposed compensator except the voltage harmonic distortion objectives and constraints, were employed using the same optimization algorithm. Thus the results of all three compensators were comparatively evaluated. Finally, to show the performance of the proposed compensator design under variable system conditions, it was tested under different loading and utility voltage conditions.