Strategy Based On MMC Topology DSTAT-COM Control

As an integral part of smart grid, Distribution Static SynchronousCompensator (DSTATCOM) has great research value. It plays an important rolein regulating power quality, reducing electrical power outages and increasing theutilization factor of power. However, the conventional converter topologies usedin DSTATCOM has many deficiencies. Therefore, the New DSTATCOM system,based on novel multilevel converter topology, is the developing trend of thefuture.Modular Multilevel Converter (MMC) has many advantages, such asarbitrary level voltage output, common DC side, high reliability throughredundancy design and applicable to various voltage classes occasion; it is moreappropriate to DSTATCOM than other multilevel converters. This paper appliedMMC to the system of DSTATCOM, built its mathematical model, analyzed itsworking principle and designed its modulation strategy, composite capacitorvoltage control strategy and reactive power compensation strategy.With respect to the modulation strategies design, the main modulationstrategies of MMC, such as the carrier phase shifted sinusoidal PWMmodulation, the carrier phase disposition PWM modulation and the nearest levelmodulation, are modeled and simulated. By comparing these modulations, anovel method combining the methods of the carrier phase shifted sinusoidalPWM and the carrier phase disposition modulation is designed and simulated inPSCAD/EMTDC. Aiming at the capacitor voltage balance control strategy, themechanism of balancing the capacitor voltage by changing the capacitance ofsub-module capacitor is analyzed, it is combined with the strategy of balancingvoltage through control modulate wave, thus a novel strategy is designed andverified by PSCAD/EMTDC. In relation to the reactive compensation controlstrategy, a simplified strategy is designed by controlling the reactive powerapproach to zero, considering the complex process of traditional compensationstrategy, which calculates the real-time reactive power of the system via measurements and then formed the reactive power reference current. As a result,the calculation of the instantaneous reactive power of the distribution network isavoided.Finally, a model of DSTATCOM is built in PSCAD/EMTDC software toverify its performance. As shown by the simulation results, the structure and thecontrol strategy of the system are feasible and advantageous.