Power quality improvement and harmonic reduction in doubly fed induction generator-based wind systems using fuzzy-controlled static synchronous compensator
Abstract
The challenges of power quality are always present in wind energy integration into the modern grid, such as voltage sags and reactive power unbalances at point of common coupling (PCC), caused by stochastic wind speed variations. In this study, a unified control system for power quality enhancement of doubly fed induction generator-based wind energy conversion systems has been proposed which consists of a fuzzy-controlled static synchronous compensator, a sensorless maximum power point tracking (MPPT) using wind speed estimation (WSE), and a single-ended primary-inductance converter (SEPIC). The WSE-based MPPT eliminates mechanical anemometry for wind speed range of 4–15 m/s by estimating wind speed from electrical quantities of the generator, such as rotor current, active power, and angular speed. The SEPIC converter can control the injection of the fifth- and seventh-order harmonic currents from the rotor-side converter to reduce the direct current-link voltage ripple from 8.3% to 1.7%. The fuzzy logic controller controls the reactive current injection of the STATCOM with a 35-rule Takagi–Sugeno inference engine with Gaussian membership functions parameterized for wind speed variability, and performs the weighted average defuzzification in a single 10 kHz switching cycle without gain retuning. The proposed method reduces the total harmonic distortion (THD) from 7.09% to 4.2%, which is 40.8% and 30.6% better than THD of proportional–integral (PI)-controlled STATCOM (6.05%). MATLAB/Simulink simulations are conducted to confirm the effectiveness of the proposed method. The proposed system achieved harmonic reductions of 45%, 38%, and 32% for the third-, fifth-, and seventh-order harmonics, respectively. During a 30% voltage dip, the overshoot has been reduced from 14.3% to 8.5%, and the response time has been confirmed at 22 ms, compared with 48 ms in PI control, with a 37% settling time reduction. The PCC voltage is maintained in between 0.983 and 1.012 p.u. at all wind speeds, with a minimum power factor of 0.9998, thus proving the harmonic compliance of EN 50160.