Analysis and Design of Single-Phase Transformerless Inverter for Photovoltaic Applications
2021
This thesis provides a comprehensive analysis of different transformerless inverter topologies (TLIs) and their control and modulation techniques. Considering the challenges and merits of the transformerless inverter, four different types of transformerless inverter topologies for PV applications have been investigated, analysed and designed in this thesis.
The first topology is H-bridge Zero Voltage Switch Controlled Rectifier (HB-ZVSCR) transformerless mid-point-clamped inverter. The operating principle and CM effect of the proposed topology are analysed and compared with the conventional topologies. This is followed by the thermal analysis and loss calculation which shows better efficiency over the conventional topologies. Validation is carried out using MATLAB-Simulink using the PLECS toolbox followed by a scale-down prototype of 1.5 kW.
The second topology is a single-phase switched-capacitor (SC) based (2n+1)-level inverter with reduced number of components and input DC voltage supply magnitude. The total number of output voltage levels can reach up to (2n+ 1) levels, where n ≥ 2 is the number of switching cells consisting of three power switches and two switched-capacitors. The operating principle is presented in detail followed by comparative analysis, thermal modelling and design guidelines. Finally, measurement results are carried out for a 5-level inverter with two SC cells as an example to verify the performance of the proposed (2n+1)-level inverter over different operating conditions.
The third topology is a novel dual-mode five-level common grounded type (5L-DM-CGT) transformerless inverter topology for a medium-power application with a wide input voltage range (200 V – 400 V). The theoretical analysis shows the advantages of the dual-mode inverter for various industrial applications. Finally, the laboratory test results are presented to verify the theoretical analysis.
The final topology is a novel configuration of switched capacitor multilevel inverters (SCMLIs) with a lower number of power components with inherent voltage boost. The proposed topology is compared with other existing five-level inverter topologies to show its superior capabilities/advantages. The performance of the proposed topology is validated by OPAL-RT.
Overall, this thesis provides a comprehensive analysis of all transformerless inverter topologies and their control and modulation techniques and come up with the concept of new single-phase transformerless inverter topologies. The new topologies utilizes minimal components with low voltage stress and offers high power quality output with low total harmonic distortion (THD), high efficiency and power density, low cost and size, and simple modulation techniques.
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