Research Of SVG Based On Cascade H-bridge Topology And Modulation Strategy

Static Var Generator SVG can compensate reactive power effectively,maintain the system voltage stability, improve power quality, improvesystem power factor. Compared with the traditional reactive powercompensation device, SVG has obvious advantages, represents thedevelopment direction of dynamic reactive power compensation device.Cascaded topology of SVG increases the capacity and the output voltagelevel, which makes the application of SVG possible in middle and highvoltage systems.In order to reduce switching losses, the fundamental frequencyoptimization PAM modulation strategy is used on cascade H-bridgetopology in the paper. Each H-bridge are working on the fundamentalswitching frequency, reducing the switching losses. Meanwhile the outputvoltage of each H-bridge is superimposed as step wave to approximatethe sine wave. The initial switching angles are getting by the areaequivalent theory, after the iterative calculation the optimal switchingangles are obtained, making the harmonic distortion least. The pulse cycle transposition is used on the DC side, making them balance in the averagemeaning. The current indirect control method is used by adjusting powerangle to control the output reactive power simply and effectively,inverse system PI control method is added to make the device responsespeed faster. Simulation results show the effectiveness of the methodabove.Based on the fundamental frequency optimization PAM to improvethe quality of the output waveform further, the hybrid modulation methodof PAM+PWM is introduced in this paper. By adding the PWM unit, theunipolar-frequency doubling SPWM modulation is applied to achievecurrent direct control, which improves the control accuracy and responsespeed of the device. The PWM unit can compensate the output harmonicof the step wave effectively, meanwhile the harmonic self-compensatingmethod is introduced, which improves the quality of the output waveformfurther, reduce the output harmonic distortion factor. The model ofcascade SVG is built in Matlab/Simulink, the result proves the validity ofthis method.