Research On Multi-level Photovoltaic Inverter EMC And Leakage Current Suppression

As is well known, the advantage of solar energy is pollution-free, widely distributed and sustainable. In addition, photovoltaic (PV) is the most important way to use solar energy. In PV system, the inverter is the key part. So the quality of the inverter has decisive influence on PV system.(1)Firstly described the basic knowledge of the photovoltaic systems and inverter as well as the development and status of electromagnetic compatibility. Secondly, the principle of electromagnetic compatibility is discussed in details, particularly focus on the coupled channels of electromagnetic interference and EMI (electromagnetic interference) generation mechanism of switching power supply. Then, deeply analysis the EMI caused by the switch on and off in PV system, and the high frequency model of various common electronic devices worked in high-frequency environments and use them in EMI filters.(2)We analyze the topological structure characteristics of several common multi-level inverter and research their output waveform and spectrum, study the influence of the number of different levels on the waveform. Through analyzing with three-level inverter and comparing the existing control strategies, summarizing their respective advantages and disadvantages, we explicitly derive and show the control method of the three-level inverter using space vector pulse width modulation (SVPWM), study and solve the midpoint potential problem produced by SVPWM control method.(3)Analyzing the cause of EMI in multi-level inverter, point that use EMI filter is the major way to control EMI interference. Establish differential mode and common mode, testing the modes correctness and analyzing the influences of impedance adaptation. Through comparatively analyzing the characteristics of inverter with different topological structures and the filter with different structures, making adjustments on the existing filter, we obtain a kind of EMI filter which suppresses both common mode and differential mode. In this EMI filter, we use "I" type, it can reduced the capacitor’s inductive in high frequency and increase filter’s range, increase the filter’s performance. And make simulation test on its performance in Pspice by drawing analog circuit. We also make a parametric analysis for the important components in this EMI filter, and obtain the influence of EMI filter explicitly when parameters vary.(4)We analyze the reason of generating leakage current and the method to suppress it by inverter model established in the former context. Especially consider the effect of symmetry and asymmetry parameter structures on it, and show its correctness by simulation. We also improve the circuit by adding the compensation capacitor, which suppresses the leakage current effectively.