Multi-level Reinjection Voltage Source Conversion Based On DSP

As the essential equipment, the ac/dc converter is used in FACTS and HVDC.The new concept of multi-level reinjection VSC(MLVR-VSC)is a combination of the multi-level, soft switching and reinjection conversion concepts. The MLVR-VSC is to provide a solution of dynamic voltage balancing for direct series connected switching devices to form high voltage valves, to reduce the harmonic content to produce high quality waveforms, to improve the conversion efficiency and reliability by using low switching frequency and soft switching conditions for main bridge switches.The Ideal Reinjection waveforms to achieve perfect harmonic cancellation are firstderived for 12-pulse configurations; to simplify the requirements applying to the dc source, two approximations are made to the ideal reinjection waveforms, i.e. the fully symmetrical ESEDS (minimization of Error Square and Error derivation Square) and Linear Reinjection. Finally multi-level fully symmetrical reinjection approximations are are made to the Linear Reinjection waveforms for practical implementation, meanwhile the multi-level Multi-Level Voltage reinjection converter topology structure was built and the voltage waveforms were simulated by the matlab softwave.A control strategy is proposed for achieving the system capacitor voltage balancing; the switching sequence which maintains capacitor voltage balancing, is presented. For STATCOM application the phase angle difference between the converter output and the source voltagesφis used to control dc voltage; consequently control the converter ac output; and thus controls the converter reactive power.The digital signal processor TMS320F2812 is used as core of control circuit, the firing logic for the switches and the reactive power PID controller are programmed. The test was carried out to verify the firing logic at last.