Research On Detect And Compensation Control Strategy Of Unified Power Quality Controller

With the development of science and technology,nonlinear load, imbalance load, and impact of load are widely used in the power systems, which bring about many power quality problems, and seriously affect the security of power systems and power quality. Meanwhile, electricity consumers on the grid power quality and reliability requirements are increasing. These factors make the power grid suffer a severe test. Unified Power Quality Controller (UPQC) is a new type of multifunctional device and it can settle many power quality problems. UPQC is one of most important equipment among the custom power device. It can not only improve the power grid of the input current power quality problems, but also can enhance the load input voltage of power quality problems, which is considered as the most promising power quality controller. So many aspects of UPQC including the topology, detection algorithm and compensation control strategy are conducted extensively by electric power research workers in many countries.This paper expounds the UPQC main circuit topology and some basic derivative structures. The UPQC operation principle is deeply analyzed based on the ideal control system and its equivalent circuit model. The active power and reactive power flow among two converts are investigated under different working conditions. Several harmonic current detection methods based on the theory of instantaneous reactive power is compared, including their application, advantages and disadvantages. Combined with UPQC compensation strategy,integrated voltage and current detection method is analyzed and derived. The method is simple and real time. It can avoid a large number calculation, eliminate the distorted grid voltage on the PLL, and overcome the shortcomings and deficiencies of the existed detection methods of UPQC.Four compensation strategies are described in detail and they are in-phase compensation , pre-sag compensation , pure reactive power compensation and minimum-power compensation. They are compared by phasor diagram analysis, and pointed out their advantages and disadvantages. To solve this problem, this paper presents the optimal capacity compensation strategy. The optimal capacity compensation control strategy is based on not affecting the function of UPQC. The output voltage of series side active filter (SAPF) is optimally controlled, in order to achieve optimal capacity control UPQC. The simulation results show that the optimal UPQC energy control strategy can be well integrated power quality compensation, reducing the capacity of UPQC devices, energy storage capacity without increasing the compensation under the conditions of extended time, easy to practical application.