Abstract
In this paper, a T-type common ground transformer-less single phase inverter with dynamic swing of the dc-link voltage is presented for photovoltaic (PV) application. The topology is a combination of a bi-directional, partial-power-processing boost stage and an asymmetric half-bridge inverter stage along with a T-branch. It takes advantage of the three-level switching states with reduced voltage stress on the main switches to achieve lower switching loss and almost one-half the inductor current ripple w.r.t. two level implementation. The double line frequency power decoupling is addressed by a dynamic dc-link approach, which allows a large swing of the dc-link to reduce the decoupling capacitor requirement, enabling an all-film capacitor implementation. This topology also significantly reduces the high-frequency capacitive coupled ground current by directly connecting the PV negative terminal to the grid neutral. Moreover, an adaptive dc-link voltage control scheme that optimally changes the average value of the dc-link voltage as the operating conditions (load and power factor) vary, has been proposed and thoroughly investigated from the perspective of better utilization of passive components and further reduction of switching losses. A SiC MOSFETs-based 1 kVA laboratory prototype has been built to validate the converter's operation at 200 V dc nominal input and 120 V/60 Hz ac nominal output with a wide range of power factor and load operations. Extensive experimental results validate the superior performance of the topology with the adaptive dc-link voltage control implementation showing a peak efficiency of 98.22% and a CEC efficiency of 98.03% at 50 kHz switching frequency.
Highlights
Power electronic converters are the key components in a grid connected photovoltaic (PV) system for interfacing the solar panels to the grid and extracting the maximum power from the PV source
This paper presents an in-depth analysis of the T-type common ground voltage swing inverter topology as applicable to the single-phase PV inverters with significant performance gains, analytical design complexity, and wider range of specifications, especially in terms of power factor operation in comparison to [19]
ADAPTIVE DC-LINK VOLTAGE CONTROL The instantaneous values of each of the HB voltage levels needs to satisfy the constraint in (3) at any operating pf, where vg = Vg sin(ωt ). These two constraints place a limit on the minimum value of the PV voltage and the maximum voltage swing allowed at the dc-link. This ensures that the HB inverter stage does not operate at modulation index more than 1, which would otherwise distort the output waveforms and impact the total harmonic distortion (THD)
Summary
Power electronic converters are the key components in a grid connected photovoltaic (PV) system for interfacing the solar panels to the grid and extracting the maximum power from the PV source. This paper presents an in-depth analysis of the T-type common ground voltage swing inverter topology as applicable to the single-phase PV inverters with significant performance gains, analytical design complexity, and wider range of specifications, especially in terms of power factor (pf) operation in comparison to [19]. An adaptive dc-link voltage control scheme is studied from the perspective of the dynamic dc-link active power decoupling and maximizing the utilization of the passive components (effectively designed for the worst case operating condition) over the entire operating range to improve on the overall converter efficiency performance, which was not previously considered in [19]. R one advantage that the topology of Fig. 5 has over the T-type voltage swing inverter is wider range allowable in the input voltage due to the front end boost stage
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