Research On Switching Modulation Technology Of Motilevel Converter

With the development of the power electronic technique, high power electronic converters are needed in more and more occasions. To exalt the power the most familiar method is to put some power devices together in series/parallel as one device, each of which is controlled in the same way, which will bring out dynamic voltage (current) unbalance, destroying the device or losing control of it. In addition, putting some converters in series/parallel which are so-called multiplex structure can also exalt the power. In multiplex structure transformers or reactors are necessary to link multiplex converters in series/parallel on ac side. The bulk, price and efficiency of the transformer and reactor become an obstacle to further exalt upgrade of the multiplex converter power. To solve the two problems above-mentioned the multilevel converters appears.For the multilevel converter the choice of the switching strategies is very important. There are several switching modulation strategies at the present time: staircase pulse width modulation,carriers-based pulse width modulation,multilevel voltage space vector modulation,carrier phase-shifted pulse width modulation and so on. Carriers-based pulse width modulation and carrier phase-shifted pulse width modulation are popular and excellent modulated technique at present. Based on the technique of the general PWM, the output harmonic feature of the multi-modular converters with these two modulation strategies is researched and analyzed through simulation and experiment and draws a conclusion, which proves excellent performance on harmonic feature of multilevel converter output waveform under Carriers-based pulse width modulation and carrier phase-shifted pulse width modulation, so these two modulation strategies are more adapt to engineer application.A speed-loop-open, constant ratio of voltage and controlled empty-load experiment of an AC motor is fulfilled based on three phase 3-level converter.A loop-open modulation is accomplished too based on single phase 7-level diode-clamp converter. All the experiments are controlled by DSP IC of TMS320LF2407A as control core. The experimental result proves the correctness of theoretical analysis and simulation.This work was supported by a grant from the Key Programs National Natural Science Foundation of China (No.50237020)...