A Continuous Input Current Quasi-Z Source Inverter With High Gain And Its Control To Grid-Connection

Compared with traditional voltage inverter, traditional Z-source inverter has many advantages. Its special structure can take advantage of the shoot-through vectors to realize DC/DC single stage boost ability. But with the research of Z-source inverter in-depth, the insufficient of traditional Z-source inverter appear, such as the discontinuous of input side current, high Z-source network capacitor voltage and lower boost gain. Therefore, this paper investigates a continuous input current Quasi-Z source inverter with high gain based on the traditional Quasi-Z source inverter. It has high boost gain, lower inductance current ripple and one lower Z-source network capacitor voltage in symmetrical position. The high degree symmetry of its structure makes the circuit analysis and parameter design simplified.Firstly, in order to obtain the transfer function of capacitance voltage and direct duty radio, model of the impedance network of the continuous input current Quasi-Z source inverter with high gain is built to get the small signal model. MATLAB is used for analysing the transfer function. Under the situation that just one factor is changed and the other factors are constant, observing the changes of zero pole distribution system by using MATLAB to analysis the transfer function.and then obtaining the impacts of capacitor, inductor and direct duty ratio on the transfer function which can provide theoretical basis for parameter design.Secondly, the special structure of Z-source inverter needs special modulation method. For the continuous input current Quasi-Z source inverter with high gain, the existing common modulation method are simple booster modulation, the harmonic injected three times, maximum pressure modulation and constant pressure modulation. This paper mainly expounds the pass-through piecewise SVPWM modulation method, makes a compare about all kinds of modulation method, and validates the advantages of direct segmentation SVPWM modulation method. Simulation models of the continuous input current Quasi-Z source inverter with high gain using different modulation method are built to acquire the outcomes which can be used to contrast analysis of the parameter performance.Finally, this paper investigates application of the continuous input current Quasi-Z source inverter with high gain to grid-connection. The dc voltage of the inverter is rectangular wave which cannot be measured directly. In this paper, the dc side voltage stable can be kept by controlling impedance network capacitance voltage. Based on building model of the inverter part, the state space equation of the coordinate system can be obtained by coordinate transformation and the model structure can be therefore achieved. Building the continuous input current Quasi-Z source inverter with high gain grid-connection system simulation model in the MATLAB/SIMULINK, the outcome validates the adjustment ability of input voltage mutation and the grid disturbance.