Single Phase Full Bridge Neutral-Point-Clamped Inverter With Z-source Impedance Network

The single-phase full bridge neutral-point-clamped(NPC) inverter has the multi-level inverter’s advantages of low stress of switching devices, low switching loss and low harmonic distortion.Therefore it is applied to many occasions. But in the photovoltaic system, affected by natural conditions, the voltage of photovoltaic varies in a wide range. But the traditional single-phase full bridge NPC inverter is a buck inverter, which to a certain extent limits its application in photovoltaic system. In this paper, the Z-source impedance network is introduced into the traditional single-phase full bridge NPC inverter for boosting its output voltage in addtion to its voltage-buck behavior.This paper is referred to a large number of domestic and foreign papers. A Z-source impedance network is added between the DC power supply and the inverter bridge of traditional single-phase full bridge NPC inverter. And the shoot-through state becomes a normal working state. The Z-source single-phase full bridge NPC inverter not only has the advantages of multi-level inverter, but also has the advantages of Z-source inverter. The single-phase space vector modulation method is used in this paper, which can insert the shoot-through state conveniently. Combined with the detailed analysis of the working principle of Z-source single-phase full bridge NPC inverter, this modulation method can balance the neutral-point potential without other control method. This paper establishes the independent control strategy of the Z-source capacitor voltage loop and grid current loop. The state-space average method is used to model the topology for controller design, and according to the established model, the controllers of two loops are designed, which make the system meet the requirements of the grid.The simulation based on MATLAB/Simulink and the experiment on the prototype of the Z-source single-phase full bridge NPC inverter are conducted, both of them have proved the correctness of the theoretical analysis and practicability of the modulation and control strategy.