Research On The Technology Of Low Power Transformerless Grid-connected Photovoltaic Inverter

The increasingly serious energy crisis and environmental pollution stimulate the development of clean renewable energy, which that, Photovoltaic power generation has got more and more promotion and application because of the large storage, pollution-free and other advantages. However, the performance of the grid connected inverter indicators if photovoltaic energy can be efficient and reliable use or not. It is clear that transformerless topology has become the mainstream direction of the small and medium-sized power grid-connected inverter because of the advantage of high efficiency, light weight.This paper first analyzed the working principle of the two-stage grid-connected inverter with dual-loop controller based on dead-beat control theory. So that the grid current fast track the grid voltage. Second, with the summary of commonly used sinusoidal pulse width modulations, the paper present the simple unipolar modulation method on the basis of the request to ensure power factor1. The modulation is demonstrated its feasibility by simulation. The common mode leakage current is the key issues of non-isolated grid system. The paper analysed the frequency-domain characteristics of the resonant circuit and proposed that, using the filter capacitor to control the resonance point frequency within common-mode voltage harmonic weak points in order to suppress the leakage current. The thesis was verified by simulation and experimental. The design of the inverter in this paper based on IGBT and the CoolMOS hybrid H-bridge topology, combined with simple unipolar modulation mode to further enhance the efficiency of the inverter performance.A4kW transformerless inverter was designed based the DSP TMS320F28335. The experimental study and test verified the high efficiency of the topology and the modulation with maximum efficiency of97.51%. It is also verified that the deadbeat control can ensure the high power factor and good harmonic characteristics with THD of2.12%. Meanwhile, the inverter with the Perturb&Observe algorithm can well tracking the maximum of the power curve of the solar panels that, steady-state tracking efficiency was maintained at above99%, to maximize the use of solar panels.