REACTIVE POWER INJECTION TO GRID USING TRANSFORMER-LESS MOSFET BASED SINGLE PHASE INVERTER USING PV TO ACHIEVE HIGH EFFICIENCY

Abstract

The objective of this paper is to improve the power quality of the system by injecting power in to the grid using transformer-less MOSFET based single phase inverter using PV to achieve high efficiency.

The developed topology for PV inverter is proposed with following objectives:

• Designed switching strategy for inverter to reduce the flow of leakage current.
• Developing a gate pulse switching of Grid-tied Inverter with combination of SPWM and triangular wave.
• Comparing the results of simulation and hardware of proposed topology.
• As transformer is considered heavy weighted and expensive the proposed topology is designed to implement an inverter circuit without transformer to obtain maximum efficiency and reduce Total Harmonic Distortion.
• Injecting reactive power into the system to reduce losses and hence increase the overall efficiency.

Methodology:

The transformer-less inverter has an increasing demand due to its low cost, high efficiency and reliability. The elimination of transformers from grid connected PV enables to create the leakage currents across stray capacitance, which is connected between PV and ground. To overcome this disadvantageous issue, the topology used is a single step conversion process of directly connecting coupled inductor to the grid. The efficiency and the quality of AC output current is improved by implementation of high frequency PWM switching commutation to the converter. The proposed system is focused to inject reactive power to the grid, changing the controlling techniques used for the Gate Pulse input, and reducing the number of switches, passive elements and harmonics.

Findings:

The prototype for 12V/13.2V is utilized to set up a practical prototype for 200V/310V which can be synchronized with grid-tied PV system. The values for the practical set up are summarized in the above table I. this also aims at producing a maximum efficiency of 98.04% with a THD of 0.915%. The prototype for 12V input, 13.2V output was verified using a hardware and a simulation model. The obtained output AC voltages for both the prototypes are said to be same i.e., 13.2V.

Originality/value:

Our contribution in the emergent field of power generation using renewable resource is designing a prototype of highly efficient transformer-less topology for grid connected PV system. The proposed system topology injects reactive power into the grid and reduces the output harmonics and distortions. Higher switching frequency operation reduces current ripples in the output, while the inverter efficiency is still maintains high. This topology does not face reverse recovery issue even when the reactive power is injected into grid. The CM mode voltage is maintained constant during all switching modes of operation and thus, the leakage current is reduced to a great extent. This topology is a single step conversion process from the coupled inductor directly into the grid without a transformer. The switching commutation of high-frequency pulse width modulation (PWM), increases the converter efficiency and improves and boosts the quality of the output AC current. The efficiency obtained in 12V/13.2V and 200V/310V prototype is observed to be 98.04%.