A Single Stage Common Ground Three-Level PV Inverter With Integrated Power Decoupling

Abstract

In this paper, a T-type common ground transformerless 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-powerprocessing 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 dclink approach, which allows a large swing of the dc-link to reduce the decoupling capacitor requirement, enabling an allfilm 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.

An improved quasi Z‐source based H5 inverter with low leakage current for photovoltaic applications

“…However, the proposed topology requires only oneinput dc power source, compared to two in the case of the qZS-CMI 20 topology; this advantage out weighs the disadvantage associated with the TBV. The reliability of the power converter proposed in ref 29 is lower to the one proposed in this manuscript owing to the requirement of higher number of diodes and the shoot though problem associated with it Reference 29. The presence of clamping Voltage across each capacitor diodes in qZS-NPC 19 make it susceptible to failure and excessive power losses.…”

“…The Total Blocking Voltage (TBV), which is the sum of the voltages blocked by individual devices of a given power converter, is also lower for the proposed converter compared to all other topologies except the qZS-CMI 20 and the one described in ref 29 . However, the proposed topology requires only oneinput dc power source, compared to two in the case of the qZS-CMI 20 topology; this advantage out weighs the disadvantage associated with the TBV.…”

“…However, in this topology, at any given instance of time, a higher number of semiconductor devices conduct to produce the same voltage level compared to the proposed power converter. Furthermore, the power circuit configurations enumerated in ref 25‐30 need capacitors of higher voltage rating compared to the one proposed in this manuscript.…”

“…A detailed comparison of the proposed converter with existing literature is provided in table 2. Amongst the existing PV based inverters, shown in Reference 25‐30, the proposed inverter has the lowest switch count to provide five‐level output except the one described in Reference 26, which has same switch count. However, it suffers from the shoot‐through problem associated with single stage boosting.…”

Multilevel common‐ground inverter with voltage boosting for PV applications

“…While the magnetic-based topology in [26] require two inductors and capacitors has reduced efficiency. Topology in [27], connects the neutral of the grid with the negative terminal requires six switches, three inductor with two capacitor while generating a three-level waveform.…”