Conventional PV-fed three-level DC-DC converter has greater leakage current due to varying common mode (CM) voltage, and thus requires galvanic isolation if interfaced with on-grid inverters. To reduce the leakage current and eliminate the requirement of galvanic isolation, a low-leakage three-level DC-DC converter is proposed for residential application. Efficacy of the converter is demonstrated by proposing a two-stage single-phase on-grid PV system by interfacing with a three-level transformerless single-phase inverter topology. The DC-DC converter has reduced leakage current, which decreases the overall leakage current in the PV inverter system. In addition, smaller filter magnetics are required for both the three-level converter and three-level inverter. The CM analysis of the proposed system is presented. The proposed system is simulated using PSCAD and a laboratory prototype is developed for experimental evaluation. The experimental results show a part-load efficiency of >96% for the overall system. Furthermore, the measured leakage current in the proposed system is <10 mA, which is below the prescribed RMS limit, as specified in German DIN VDE 0126-1-1 standard.
Stand-alone PV systems are increasingly being used in rural areas to drive basic loads typically less than 300 VA. Such systems are beneficial where grid electricity is unreliable or not present at all. A 250 VA battery integrated stand-alone PV system is proposed here. This PV system is based on simple hardware structure. It is possible to design this system at lower cost with higher reliability. DC link capacitor is selected for longer life time. The overall reliability of the whole system is estimated using the data from Military Handbook. It is shown that the proposed system has higher life time than other conventional PV systems. Open loop control is proposed for inverter output voltage control, thereby making it possible to implement on low cost micro-controller with fewer sensing components. The proposed system can be designed for a 12 V or 24 V PV panels, which are commonly used in rural areas. Efficacy of the whole system is verified in PSCAD and simulation results are provided. A hardware prototype is built for actual implementation of the PV system.
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