Single-stage Non-isolated Double Zeta Inverter

Photovoltaic Inverter is a must as power processing interface between the PV energy source and power grid. Along with the developing of grid connected photovoltaic systems, the design of photovoltaic inverters is required higher and higher. Because the photovoltaic sources are intermittent and fluctuant, the photovoltaic Inverters are required to boost or buck the input voltage. It is significant to design a photovoltaic Inverter which has a higher efficiency, higher reliability, longer life time, smaller size & weight and a lower price.Compared with structure and performance of the existing inverters, the single stage non-isolated inverters which can buck and boost the input voltage are more suitable for the photovoltaic inverters. So a novel single stage non-isolated dual Zeta inverter has been proposed in this paper. This inverter is composed of two Zeta converters with input in series connection and output in parallel. The structure of the dual Zeta inverter is very simple. It has only four power switches. It can buck and boost the input voltage with the same characteristics of Zeta converter. According to the design feature of the dual Zeta inverter, semi-cycle control and full cycle control are used to control the inverter. The detail of working principle and modulation has been analyzed for the dual Zeta inverter of two control methods. A function transform linearization method is proposed against the nonlinear characteristics of the dual Zeta inverter. One cycle control and proportional-resonant control are used in this circuit to make the output voltage in sinusoidal. The two methods of close loop control are studied by simulation. The research results show that two power switches of the dual Zeta inverter can be soft-switching automatically, so the power loss is smaller and the efficiency is higher. The inductor current has no discontinuous conduction mode, so the output voltage does not exist the zero crossing distortion. Because the dual Zeta inverter has no electrolytic capacitor, it has a longer life time and works more reliable. Linearization method makes the design of closed-loop control and output filter easier.On the basis of theory research and simulation results, the main circuit and control circuit are designed. A 500 W prototype of the dual Zeta inverter is designed and the experimental results have proved that theoretical analysis and control strategy is correct and feasible.