Design And Control Research Of New Quasi-Z-source T-type Three-level Inverter

As a newly proposed topology,three-level quasi-Z-source inverter combines the advantages of quasi-Z-source inverter and multilevel converter,including single-stage buck and boost capability,continuous input current,lower switching voltage stress,better output waveform,etc.However,the existing three-level quasi-Z-source converter topology have to short the whole dc-link in the shoot-through state,which makes it difficult to insert the shootthrough state into the converter output state,or may cause the loss of the converter output volt-second area.To address this problem,this paper proposes a new quasi-Z-source T-type three-level converter topology.In this topology,one more input voltage source is introduced and the midpoint of input voltage source and dc-link are connected,which make it possible to short the upper and lower dc-link separately in the short-through state.The research work is organized as follows:Firstly,the boost operating principle of the quasi-Z-source network and the basic principle of the T-type three-level converter are presented,which proves that,with the proposed topology,the shoot-through state can be inserted without any volt-second area loss.Then,the suitable pulse-width modulation strategies are proposed,including the improved carrier disposition sinusoidal pulse width modulation and the equivalent two-level space vector modulation.Besides,the stand-alone mode operating principles of the system is studied,and the small-signal model of the quasi-Z-source network nearby its steady working point is derived,from which,the dc-side closed-loop controller is designed.The state-space averaging model of the T-type converter is also given,from which the inside current loop and outside voltage loop controllers are designed.Finally,the simulation model in the MATLAB/Simulink and a 3.5kW prototype in the laboratory are built respectively,and the simulation and experimental results prove the correctness of the operating principle and the effectiveness of the PWM and the control strategies.