Study On The Detection And Control Method Of Unified Power Quality Conditioning Techniques

The popularity of power electronics brings convenience to energy conversion and utilization on one hand and also brings negative impact to power quality on the other hand, such as harmonic contamination, excessive reactive power consumption, unbalance, voltage fluctuation and voltage sag. Active power filter technique plays a major role in solving the problem. Unified power quality controller (UPQC) is one of the examples. It not only compensates the distortion of waveform, but also serves as dynamic voltage restorer. This paper discusses a new topology of UPQC, in which the conventional UPQC was divided into a voltage compensation section and a current compensation section respectively.The voltage compensation section comprises a voltage source inverter connected to grid in series by a single-phase step-up transformer. The current compensation section employs a three-phase switched capacitor connected in parallel to the grid. Such topology requires lower DC voltage, so the capacitance of the capacitor and then the total costs can be effectively reduced.This paper also developed a software-based synchronize method for determining the compensation signal according to the grid voltage. This software-based method, attempt to derive the unity fundamental component or positive sequence fundamental component of the phase voltage by using Fourier analysis and symmetric component method, helps to simplify the hardware design. Then the synchronizing signal can be calculated to realize the synchronization of voltage and current compensation. In the voltage compensation section, the reference signal is calculated according to the standard voltage signal which is determined by a preset desired RMS load. In the current compensation section, the standard current is calculated using the i_p-i_q calculation method in the instantaneous reactive power theory. Then the current compensation reference signal can be derived.The voltage compensation strategy is a renovated SVPWM method, which is more simple and faster. The current compensation strategy is a novel control method based on neural network hysteresis loop. All these control strategies were simulated using the Matlab, and fairly satisfactory results were showed in the simulation.