Research On The Control Strategy Of Three-Phase Buck-Type Dynamic Capacitor

Because of the universality and importance, the problem of reactive power and harmonics in the power system has always been an essential part of the power electronics researching field. As an important aspect of power quality control, reactive power compensation and harmonic suppression has been the focus of research. The existing dynamic reactive power compensation and harmonic control device usually cannot balance high performance and low cost. People have also been exploring more efficient and reliable power quality regulating device. Traditional dynamic reactive power compensation and harmonic suppression devices are mostly based on the DC/AC inverter structure, of which the requirements of energy storage capacitor requirements on the DC side are higher, and the reliability and cost of the device is also partly constrained by the energy storage capacitor. Based on the traditional shunt capacitor which used for reactive power compensation and has been widely used, the dynamic capacitor do not use the traditional DC/AC inverter structure, but through direct AC/AC converter connects to the point of common coupling. As a new type of power quality regulating device, dynamic capacitor would have good dynamic reactive power compensation performance and harmonic suppression ability.In this paper, the main research object of the three-phase Buck type dynamic capacitor is presented,and the basic components of the Buck type dynamic capacitor are introduced in detail. Based on the principle of DC /DC chopping circuit, the basic control equation of dynamic capacitor is analyzed and deduced. On this basis, the principle of reactive power compensation and harmonic suppression of the dynamic capacitor is explored. Through the appropriate regulation of the duty ratio, the dynamic capacitor could output capacitive reactive power compensation current when the duty ratio is constant or specific odd harmonic current when the duty ratio contains specific even harmonic components. Based on this idea, and based on the multiple synchronous rotating coordinate transformation, this paper presents a control strategy for reactive power compensation and harmonic suppression, of which the reactive current and harmonic current control loop are designed respectively.Under the Matlab/Simulink software environment, the circuit model is designed and simulated. And based on the 33 kVA Buck type three-phase dynamic capacitor prototype, several experiments are implemented. The simulation and experimental results show that the dynamic capacitor has good dynamic reactive power compensation and harmonic suppression function.