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Y. Tang,W. Yao,F. Blaabjerg 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
In single-phase uninterruptible power supply (UPS) applications, it is well known that the AC side instantaneous power is not constant by nature. The resulting input current from the DC source side will inevitably contain low frequency ripple components that may largely deteriorate the system performance in terms of efficiency and reliability. In order to solve this issue, this paper presents a dual-mode operated boost inverter, which can simultaneously work in both Differential Mode (DM) and Common Mode (CM) operations. Its DM operation ensures regulated sinusoidal AC output voltage as well as active power conversion, while its CM operation is controlled in such a way that the low frequency ripple current on the DC side can be maintained in a minimum level. The proposed ripple current reduction method may not only work with linear loads, but also nonlinear loads, where more sophisticated controller design are required. Since the presented inverter essentially consists of two DC/DC boost converters, an interleaved Pulse-Width Modulation (PWM) can be adopted to further reduce the high frequency switching ripple current on the DC side. Both Simulation and experimental results are presented to demonstrate the effectiveness of input ripple current reduction.
Transformerless Photovoltaic Inverters with Leakage Current and Pulsating Power Elimination
Y. Tang,W. Yao,H. Wang,P. C. Loh,F. Blaabjerg 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
This paper presents a transformerless inverter topology, which is capable of simultaneously solving leakage current and pulsating power issues in grid-connected photovoltaic (PV) systems. Without adding any additional components to the system, the leakage current caused by the PV-to-ground parasitic capacitance can be bypassed by introducing a common mode (CM) conducting path to the inverter. The resulting ground leakage current is therefore well controlled to be below the regulation limit. Moreover, the proposed inverter can also eliminate the well-known double line frequency pulsating power that is inherent in single-phase PV systems. By properly injecting CM voltages to the output filter capacitors, the pulsating power can be decoupled from the dc-link. Therefore, it is possible to use long lifetime film capacitors instead of electrolytic capacitors to improve the reliability of the PV system. The mechanism of leakage current suppression and the closedloop control of pulsating power decoupling are discussed in the paper in details. A 500 W prototype was also built and tested in the laboratory, and both simulation and experimental results are finally presented to show the excellent performance of the proposed PV inverter.