| In recent years, a novel Z-source inverter who boosts the DC voltage with a single-level structure by inserting shoot through state was proposed. It's simple to control and has high realiability. However, it has defects such as a high Z-source network capacitor voltage and low voltage gain.Therefore, this paper investigates an extended Z-source inverter which has a high voltage gain and low current ripple. It also can be cascaded to increase its voltage gain, so it is appropriate to the low input application such as the new energy sources.In order to analyse the working principle and circuit parameters relationship of the steady-state and fully understand the system characteristics. The small singal model is got by using signal flow graph methed through which the system control to output transfer function is deduced. Combined with the mathematical models and simulation, the influence of the device parameters to the dynamic characteristics of the system are analysed, and the detection of the right-half-plane zero proves the existence of the non-minimum phase characteristics. It is also found that the increases of the device parameters will weak the dynamic characteristics.In light of the traditional modulation doubles the switching frequency and has a high voltage stress and curret ripple, a maximum constant control method based on SVPWM for the Z-source inverter is proposed in this paper. Under the condition of fully using the zero vector time and not increasing the curret ripple, the maximum constant shoot-through time in SVPWM was derived, and the detailed formulation is given to prepare for its realiation by software. The shoot-through time is devided into six parts and inserted into the switching cycle, which not only reduces the switching frequency but also has a small voltage and current ripple. In order to inhibit the DC voltage and current ripple increased by shoot through state and improve the output power quality. According to the modulation, this paper designs the network device parameter to meet the conditions for ripple rejection and the critical value of the inductor under the current continuous state. The voltage and current stress of the power switches is also stusied. Based on the minimum reactive capacity of filter, the out lowpass filter is designed and a structure which can suppress the oscilation at a low load is also desgined, which ensure the stability and quality of output waveform.In order to ensure the DC bus voltage stability when there is an input voltage disturbance and the AC side output voltage stability when the load changes, the closed-loop control strategy for both DC side and AC side of the extend Z-source inverter is studied. Integrating the mathematical model and modulation strategy, this paper designs the form of double zero-pole PI controller for DC side. Through establishing a mathematical model of the output filter, the mathematical relationship of the closed-loop control parameter and the disturbance is clearly analysed, after which a double-loop decoupling controller is designed for AC side. This strategy makes the inverter meet the requirements on various occasions and has advantages of fast response, and no steady-state error in AC output. The AC side and DC side also cooperate well with each other under this control strategy. |
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