Transformerless Grid-connected PV Inverter Research Articles

Five-Level Transformerless Common Ground Type Inverter with Reduced Device Count

In recent days, the transformerless grid-connected PV inverter is paid more attention due to its compactness and high efficiency with low cost. This paper presents a new five-level transformerless switched capacitor type inverter with a reduced number of power components. The proposed topology has a lower number of power components with a common ground connection between the negative terminal of the input side and load that eliminates the leakage current. The switched capacitors do not require any sensors for their balancing. The different modes of operation and control of the PWM technique are discussed. The proposed topology is compared with recent transformerless inverters, and the advantages of the proposed topology are highlighted. The simulation and experimental results are presented. The prototype hardware setup is built for 1.2 kW and has the simulated maximum efficiency of 96.4%. The performance of the proposed topology is measured by applying various load and modulation index variations.

Design of A Single-Phase Transformerless Grid-Connected PV Inverter ‎Considering Reduced Leakage Current and LVRT Grid Codes

Design of A Single-Phase Transformerless Grid-Connected PV Inverter ‎Considering Reduced Leakage Current and LVRT Grid Codes

Transformerless Grid-Connected PV Inverter Without Common Mode Leakage Current and Shoot-Through Problems

As there is shoot-through problem and common mode leakage current in conventional transformerless grid-connected PV inverters, a transformerless grid-connected PV inverter without common mode leakage current and shoot-through problems is proposed. The proposed inverter consists of a buck-boost converter and a dual-buck half-bridge inverter, so there is no shoot-through problem in the proposed inverter. As grounds of the input source and the grid are shorted, there is no common mode leakage current. No current flows through the body diodes of switches, so efficiency of the system is improved. Operating principle of the proposed inverter is elaborated in detail. Experimental results of a 350 W proposed inverter validate the theoretical analysis.

Mitigation of DC Current Injection in Transformer-Less Grid-Connected Inverters Using a Voltage Filtering DC Extraction Approach

Transformer-less grid-connected PV inverters are an attractive technology choice due to their high-efficiency performance and relatively small volume. However, in the absence of galvanic isolation, dc current can potentially flow into the grid and adversely affect the grid performance. In addition, as the sinusoidal ac output is significantly larger than the dc injection component, accurate dc current sensing at the inverter output remains a technical challenge. As a result, this paper proposes a two-stage dc voltage detection technique that employs an isolated RC attenuation circuit and a software dc-component filtering algorithm. The principle of the proposed technique can be applied in many switch-mode power converter topologies. The simple and cost-effective combination facilitates dc component extraction within the accuracy of 1 mV; moreover, this can be further used as digital dc feedback for active current control purposes. Experimental results from a laboratory prototype demonstrate the high performance of the proposed dc extraction and suppression approach.

A Reliable Three-Phase Transformerless Grid-Connected PV Inverter With Inductive DC Link

In this paper, a modified buck–boost grid-connected three-phase photovoltaic inverter is presented. In the structure of inverter, an inductive dc link is used between the input and output. The merits of the employed inverter are soft switching and step-up/down conversion without any additional power converter stage. It is a transformerless inverter with no leakage current issue. Moreover, as a result of increased switching frequency, it offers output current total harmonic distortion within standard limits. It uses only one current sensor and there is no electrolytic capacitor in it, which leads to high reliability. The operating principle is thoroughly explained and a simple control strategy with a new maximum power point tracking (MPPT) algorithm is proposed. The simulation and experimental results are provided to verify the behavior of a modified inverter, its control strategy, and the MPPT method.