Online wavelet transform-based control strategy for UPQC control system

In this paper, a new algorithm is proposed to estimate amplitude and phase angle (and frequency) of load currents and source voltages in the presence of harmonics and frequency oscillation. Moreover, a comprehensive control strategy is introduced to extract the compensating signals for the control of series and shunt converters of the unified power-quality conditioner (UPQC). The basic approach used in this algorithm is to extract the fundamental component of load current and source voltage by using wavelet-transform decomposition. Then, the amplitude, phase angle, and frequency of fundamental component are calculated using the well-known LS algorithm, which is relatively simple and fast. The voltage and current references of UPQC active power filters are obtained using the positive sequence of three-phase system voltages and load currents. The proposed control strategy can extract the reference currents and voltages of UPQC fast and accurately in the presence of harmonics and/or frequency oscillation. Simulation results have been presented to show improvement of the UPQC performance in the presence of frequency and amplitude variation condition and various forms of current and voltage distortion.