Research Of Control Strategy And Experiment Based On Multi-modulated Cascade SVG

Reactive power is a great threat to the safety and stability of power system. Static Var Generator(SVG) has many advantages such as compensating reactive power effectively, supporting the system voltage and improving system power factor comparing with the traditional reactive power compensation device. Cascade topology of SVG, which is extendable and capable of providing bigger reactive power capacity, has been brought to use in higher voltage-level power systems. So SVG has been widely researched, representing the direction in the development of dynamic reactive power compensation device. As it’s getting harder to improve the performance of SVG by simply modifying its topology, making changes in the modulation method has come to mind.After comparing the existing modulation methods, this paper introduces the fundamental frequency optimization PAM modulation strategy using on cascade H-bridge topology. And the control pulses rotation method is used on the DC-side as the capacitor voltage on DC-side is unbalanced.Further, the hybrid modulation method of PAM+PWM is put forward in this paper. By combining PWM method and PAM method in SVG, the harmonic of the step voltage wave is effectively reduced and the power losses in the system are greatly cut down. Based on the hybrid modulation, the control pulses rotation method for PAM unit is modified to balance the DC-side voltage. As the parameters of the SVG mathematical model are time-varying and hard to get before operations, the adaptive inverse system PI(Proportional-integral) control method is adopted in this paper, making the control system more flexible and accurate.At last, a great deal of results from PSCAD simulations and experiments on SVG experimental prototype prove the validity of this method.