Research On Control Method For Cascade Statcom With Harmonic Suppression Capacity

In recent years, due to the increasing complexity of the power grid, nonlinear, impulsive load is put into the grid, power quality problems such as reactive power sources and harmonic sources in power distribution network are more and more serious. In the aspect of improving power quality, cascade static synchronous compensator (STATCOM) can not only compensate the reactive current in real time, but also combine the active power filter technology to suppress the harmonic. It has been widely used in engineering application because of its fast dynamic response, modular design, high reliability and many other advantages. With the continuous deepening, the cascade STATCOM control method has become a research hotspot.The main circuit topology and basic principle of cascade STATCOM are analyzed in detail,in this paper, the mathematical model is deduced. In order to make the cascade STATCOM with harmonic suppression ability, the method of command current detection combined with synchronous rotation coordinate transformation and sliding window iterative discrete Fourier transform is used, simulation and experimental results show that the method is correct and feasible, can accurately detect the harmonic and reactive current in the load. For the current tracking control method, the compensation ability of the traditional PI controller for specific harmonic is difficult to achieve the control target, in this paper, the current tracking control combined with PI control and vector proportion integral (VPI) control is used, the triangular wave control and the PI-VPI control are simulated and the results are analyzed. After comparison, it is proved that the control effect of PI-VPI is better. The DC side capacitor voltage of the main circuit H bridge structure can directly affect the stable operation of the system. In this paper, the control method of active vector superposition is adopted to achieve the voltage balance control. When the reactive power compensation and harmonic suppression capacity exceeds the design capacity of the device, it is necessary to take effective current limiting control method to meet the power quality requirements of the grid. In this paper, a priority current limit control method combined with the target power factor method is proposed,which improves the harmonic suppression ability while satisfying the system power factor in view of the situation that the command current exceeds the rated current of the device. The simulation model is established in MATLAB/Simulink, and the results are analyzed to prove the feasibility and effectiveness of the above control method.On the experimental platform of cascade STATCOM, the software control of DSP and FPGA is accomplished. The adopted control methods are experimented on the platform, the experimental results verify the correctness and effectiveness of the above control method.