**A SINGLE-PHASE TRANSFORMERLESS INVERTER WITH CHARGE PUMP CIRCUIT CONCEPT FOR GRID-** **TIED PV APPLICATIONS**

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*Abstract*

This paper proposes a new single phase transformerless Photovoltaic (PV) inverter for grid tied PV systems. The topology is derived from the concept of a charge pump circuit in order to eliminate the leakage current. It is composed of four power switches, two diodes, two capacitors and an *LCL* output filter. The neutral of the grid is directly connected to the negative polarity of the PV panel that creates a constant Common Mode (CM) voltage and zero leakage current. The charge pump circuit generates the negative output voltage of the proposed inverter during the negative cycle. A Proportional Resonant (PR) control strategy is used to control the injected current. The main benefits of the proposed inverter are (1) The neutral of the grid is directly connected to the negative terminal of the PV panel, so the leakage current is eliminated, (2) its compact size, (3) low cost, (4) the used dc voltage of the proposed inverter is the same as the Full Bridge (FB) inverter (unlike Neutral Point Clamped (NPC), Active NPC (ANPC), and Half Bridge (HB) inverters) (5) flexible grounding configuration, (6) capability of reactive power flow, and (7) high efficiency. A complete description of the operating principle and analysis of the proposed inverter are presented. Experimental results are presented to confirm both the theoretical analysis and the concept of the proposed inverter. The obtained results clearly validate the performance of the proposed inverter and its practical application in grid tied PV systems.

**EXISTING SYSTEM: **

In order to eliminate the leakage currents, transformers are commonly used in the PV system to provide galvanic isolation. However, it possesses undesirable properties including large size, high cost and weight with additional losses. Thus, eliminating the transformer is a great benefit to further improve the overall system efficiency, reduce the size, and weight. One of the important issues in the transformerless grid connected PV applications is the galvanic connection of the grid and PV system, which leads to leakage current problems. For transformerless grid connected inverters, Full Bridge (FB) inverter, Neutral Point Clamped (NPC), Active NPC (ANPC) inverter and many other topologies such as H5, H6 and HERIC were proposed to reduce the leakage current with disconnecting of the grid from the PV during the freewheeling modes . However, these topologies are not totally free from Common Mode (CM) current or leakage current. The leakage current still exists due to the parasitic capacitor of the switch and stray capacitance between the PV panel and ground. So, some of these topologies require two or more filter inductors to reduce the leakage current, which leads to a rise in the volume and cost of the system

**PROPOSED SYSTEM: **

Topologies based on H6 are also proposed in to eliminate the leakage current of the grid tied PV application. These inverters consist of six power switches and some diodes for disconnecting the dc side from the grid. These topologies are more costly than the FB inverter, because they use extra switches and diodes. Another disadvantage of these topologies is lower efficiency due to the current that circulates through three power switches at the same time. Several high efficient new H6 transformerless inverters are proposed into achieve light weight and also lower cost. They have the capability of reactive power injection to the grid. The leakage current is not totally eliminated in these topologies, which is the main disadvantage of them. The virtual dc bus generates the negative output voltage. The main drawback of this topology is that there is no path to charge the capacitor *C* during the negative cycle and this will cause a high output THD. The topology presented in, which has a common ground with the grid. The number of semiconductors used in this topology is low. However, the output voltage of this inverter is only two levels including positive and negative voltage without creating the zero voltage, which requires a large output inductor *L* *2* 0278-0046 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. *2* and a filter. The inductor medium type inverter also called “Karschny” is another topology that is derived from the buck-boost topology. This inverter has a high reliability without capability of giving the reactive power to the grid and has four power switches in the current path at the same time, which will reduce the efficiency. ** **

**CONCLUSION **

This paper has proposed a new single phase transformerless inverter for grid tied PV system using a charge pump circuit concept. The concept is proposed to generate the negative output voltage in the proposed inverter. This new topology generates a three level output voltage by employing unipolar SPWM. The negative terminal of the proposed topology is the same as the neutral line in the grid, thus the leakage current is well suppressed and the transformer is eliminated. The proposed topology has also the ability to deliver reactive power into the grid. In addition, the proposed topology can be realized with a minimum number of components, hence a higher power density can be achieved with lower design cost. Compared to other existing transformerless topologies, the performance depicted by the proposed inverter is good. A theoretical analysis performed and it is validated by experimental results for a grid connected inverter prototype. The proposed topology is verified with a 500 W prototype. The maximum efficiency of the proposed inverter is measured to be 97.4%. Experimental results and loss calculations demonstrate the validity of the proposed inverter with lower THD for the grid connected inverter. It can be concluded that the proposed topology is suitable for grid tied transformerless inverter.

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