In this article, a novel single-stage transformerless buck–boost inverter is introduced. The proposed inverter can share a common ground between the DC input side and the grid; this leads to having a zero-leakage current. The proposed inverter also provides the buck and boost voltage capabilities. Additionally, the power switches are operated at high frequency in the half-cycle of the sinusoidal wave, so the efficiency of the proposed inverter can be improved. Operating analysis, design consideration, comparison, and simulation study are presented. Finally, a 500 W laboratory prototype is also built to confirm the correctness and feasibility of the proposed inverter.

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A Novel Single-Stage Common-Ground Transformerless Buck–Boost Inverter

A novel single-stage doubly grounded transformerless inverter configuration which can buck-boost the output voltage is proposed in this paper. In this transformerless inverter configuration grid neutral is directly connected to PV panel negative rail which suppresses/eliminates the PV leakage currents. In addition, the tracking of maximum power point is possible for wide variation of weather conditions due to buck-boost voltage capability of inverter. Moreover, the proposed inverter topology has symmetrical operation in both half cycles hence injects negligible DC offset current in to the grid. Here the symmetrical operation of inverter is achieved due to one inductor is used for both half cycles of the grid. The proposed topology is realized using five switches, two of which work at 50 Hz and remaining three switches at high frequency which reduces overall semiconductor losses. Further, the proposed inverter topology is controlled through a newly developed modulation technique and possible working modes are analyzed and described thoroughly. For performance validation, the experimental analysis of grid connected proposed inverter is performed on a 1 kVA system and results show that proposed inverter feeds power in to the grid with lesser THD while achieving greater efficiency. 

A Single Stage Doubly Grounded Transformerless Inverter Topology With Buck-Boost Voltage Capability for Grid Connected PV Systems

A novel single-stage doubly grounded transformerless inverter configuration which can buck-boost the output voltage is proposed in this paper. In this transformerless inverter configuration grid neutral is directly connected to PV panel negative rail which suppresses/eliminates the PV leakage currents. In addition, the tracking of maximum power point is possible for wide variation of weather conditions due to buck-boost voltage capability of inverter. Moreover, the proposed inverter topology has symmetrical operation in both half cycles hence injects negligible DC offset current in to the grid. Here the symmetrical operation of inverter is achieved due to one inductor is used for both half cycles of the grid. The proposed topology is realized using five switches, two of which work at 50 Hz and remaining three switches at high frequency which reduces overall semiconductor losses. Further, the proposed inverter topology is controlled through a newly developed modulation technique and possible working modes are analyzed and described thoroughly. For performance validation, the experimental analysis of grid connected proposed inverter is performed on a 1 kVA system and results show that proposed inverter feeds power in to the grid with lesser THD while achieving greater efficiency.

Photovoltaic (PV) transformer-less single-phase inverters are widely used in the solar generation systems because of low cost, high power density, and high efficiency. However, there is a common mode leakage current in the transformer-less inverters, which may endanger personal safety. In order to reduce the common mode leakage current, extra semiconductors should be added into the PV inverters to decouple the dc side from the ac side. However, the common mode leakage current is affected by the environmental condition and parameters of power devices. Since grounds of the PV array and the output terminal of the inverter are shorted, the common mode leakage current in the doubly grounded inverters can be eliminated thoroughly. Topologies of the doubly grounded inverters are reviewed in this paper, which can be divided into two categories, that is, hybrid topologies and topologies using energy storage elements. Derivation of the reviewed topologies is given. Different topologies of doubly grounded transformer-less single-phase inverters are compared. 

Topology review of doubly grounded transformer‐less single‐phase inverters

This paper analyses a new half-bridge current–source inverter for avionic systems. In the circuit, two 28 V batteries are used as inputs. These voltage sources are connected to inductors which create a constant current source. Then only two high-frequency switches are used to waveshape the positive and negative half-cycles. The SCR-based half-bridge allows positive and negative current flow properly. The inverter output uses a CL filter to remove PWM components and to obtain 400 Hz sinewave output. Simulation and HIL experiment results are provided with feedback control to prove the concept of the proposed topology. The study shows that the new current–source topology provides promising results while complying with aviation standards.

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Design of a Half-Bridge Current-Source Inverter Topology for Avionic Systems

Doubly grounded transformerless grid-connected inverters are widely used in the PV application because of no common mode leakage current. A boost converter should be added into the doubly grounded PV inverters under shading condition to have boost function. However, the inverter with boost capability is a two-stage system and all switches are operated at high frequency, which reduce efficiency of the system. In addition, processing power of the boost converter is high. Therefore, a single-stage doubly grounded transformerless PV grid-connected inverter with boost function is proposed. The proposed inverter consists of two boost and one buck converters. A cooperative control method among different periods is proposed to reduce processing power of the boost converter and simplify the two-stage system to a single-stage system in each period. In addition, only one switch is operated at high frequency in each period, so efficiency of the system can be improved. Operating principle of the proposed inverter is illustrated. Control strategy is designed. Filter design guidelines and example are given. Loss calculation of the proposed inverter is given. Simulation and experimental results of the proposed inverter verify the theoretical analysis. Finally, comparison among other inverters and the proposed inverter is provided.

Zhong Wang

Papers

Single-Stage Doubly Grounded Transformerless PV Grid-Connected Inverter With Boost Function