Research On Grid-connected Pv System Based On Series Z-source Inverter

The series Z-Source inverter is a novel power conversion topology. By inserting shoot-through state, it could fulfill the buck/boost function which generally could only be done by two-stage topology such as DC/DC+DC/AC. Thus the series Z-Source inverter has a great furture in the field with a wide input voltage range, such as PV grid-connected system.This paper analyses the operation principle of the series Z-Source inverter first, and then studies on an improved SVPWM, which could increase the equal switching frequency of the Z-Source network. The designed principle of hardware based on this SVPWM is also analyzed.The DC-link voltage control methods are summarized, and after introducing their virtues, this paper proposes an indirect control method for the DC-link peak voltage. The principle of the method is simple, and could be realized conveniently. It could hold the DC-link peak voltage as a constant while the input voltage is varying, which not only make the inverter part work in a steady state, but also reduce the designing difficulty of adjustment of the inverter part.This paper also proposes a series Z-Source grid-connected PV system, then studies on the decoulping control strategy of grid current in dq reference based on the mathematical model, which makes the active and reactive current can be controlled respectively. The control strategy of the system is designed, which could fulfill the functions of boost voltage,grid-connected and MPPT synchronously.The mathematical model of the series Z-Source inverter with LC filter and R load is researched , and verified by simulation. The transfer function of Z-Source capacitor voltage to shoot-through duty cycle is in-depth studied. After reduced-order treatment, a pole-zero compensation regulator is designed, which increases the bandwidth and the stability of the system significantly.A 3kVA prototype is built up, the hardware and software schemes are also introduced. Simulation and experimental results are given to demonstrate the validity of the proposed indirect control method of DC-link peak voltage, the series Z-Source grid-connected PV system and its control strategy are verified with a low grid voltage. All the experimental results verified the correctness of the theory.