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Control strategy of three-phase four-leg inverter using an auxiliary triangle waveform
Author(s): 
Pages: 14-21
Year: Issue:  1
Journal: Electric Machines and Control

Keyword:  three-phase four-leg invertertriangle waveformdouble closed loop controlsymmetrical component methodzero sequence harmonic;
Abstract: The common control methods of Three-phase four-leg inverter are open loop control or need a lot of tedious calculation. These methods are not fit for medium-high frequency inverters, which require higher dynamic and static performance. In order to overcome these shortcomings, a control strategy of Three-Phase Four-Leg inverter using an auxiliary triangle waveform was proposed. This control strategy was based on voltage-current double closed loop control principle. Through establishing the voltage and current equations of Three-phase four-leg inverter and deriving the conditions of ensuring the symmetry of three-phase output voltages, the important roles of triangle waveform were found to control all the legs. In this strategy, the first three legs adopted voltage-current double closed loop control method with a triangle wave injection. The modulation ratio could be greater than one, so it can improve the utility ratio of DC voltage. The fourth leg adopted Pulse Width Modulation control method using a composed triangle wave as the modulation signal. The control of this leg ensured that three-phase output voltages were symmetrical when the inverter supply unbalanced loads. A 6kVA prototype was designed. The results of simulation and experiment proved the feasibility of this control strategy.
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