IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE) e-ISSN: 2278-1676, p-ISSN: 2320-3331, Volume 16, Issue 4 Ser. II (Jul. – Aug. 2021), PP 20-28 www.iosrjournals.org DOI: 10.9790/1676-1604022028 www.iosrjournals.org 20 | Page Voltage Unbalance compensation using virtual impedance loop M.V. Subramanyam, 1 A. Pavan Kumar 2 1(EEE Department, Assistant Professor, Matrusri Engineering College, Hyderabad. India) 2(EEE Department, Student, Matrusri Engineering College, Hyderabad. India) Abstract: In microgrids Voltage Source Inverters are most widely used for integration of distributed energy generation resources to supply the load demand. Microgrids have the capacity to meet the power demand of local loads in case of the main grid failure. .Under this condition voltage and frequency support from the main grid is not possible , so it is the responsibility of Voltage Source Inverter’s(VSI) is to keep voltage and frequency of the microgrid within limits .Loads such as Unbalanced three phase loads, single phase high impedance faults, or nonlinear loads (rectifier, Asynchronous Drives, Variable Frequency Drives etc) may cause severe voltage unbalance and harmonic distortion. Voltage unbalance in an islanded microgrid is removed by implementing a novel virtual impedance loop. The proposed control strategy is based on Synchronous Reference Frame (SRF) theory. The proposed microgrid is simulated in MATLAB/Simulink SimPower System toolbox. Key Words: Nonlinear loads, harmonics, power factor, grid, voltage source converter, impedance loop, --------------------------------------------------------------------------------------------------------------------------------------- Date of Submission: 01-08-2021 Date of Acceptance: 15-08-2021 --------------------------------------------------------------------------------------------------------------------------------------- I. Introduction The widespread use of non-linear loads is leading to a variety of undesirable phenomena in the operation of power systems. The harmonic components in current and voltage waveforms are the most important among these. Conventionally, passive filters have been used to eliminate line current harmonics. However, they introduce resonance in the power system and tend to be bulky. So, active power line conditioners have become more popular than passive filters , as it compensates the harmonics and reactive power simultaneously. The active power filter can be connected in series or shunt and combinations of both. Shunt active filter is more popular than series active filter because most of the industrial applications require current harmonic compensation. Different types of active filters have been proposed to increase the electric system quality. The classification is based on following criteria. i)Power rating and speed of response required in compensated system. ii)System parameters to be compensated (e.g. current harmonics, power factor and voltage harmonics) iii) Technique used for estimating the reference current/voltage. Current controlled voltage source inverters can be utilized with an appropriate control strategy to perform active filter functionality. The electrical grid contains a very large number of small producers those who use renewable energy sources, like solar power or wind power. II. Power Quality and its Problems Electric systems and grids are complex dynamic systems. These systems suffer usually from unexpected or sudden changes of the currents and voltages. These changes are due to the different types of linear and non-linear loads to which they are connected. In addition, to different types of accidents which can intervene into the grid. With the increasing use of power semiconductors in the most of industrial and domestic procedures, the electric grids are polluted with different harmonic currents and voltages. These harmonics affect the normal function of the most of the grid connected devices; in addition to considerable economic losses. Many classic and modern solutions have been proposed in the literary for the harmonic problems. Power quality is a term that means different things to different people. Institute of Electrical and Electronic Engineers (IEEE) Standard IEEE1100 defines power quality as “The concept of powering and grounding sensitive electronic equipment in a manner suitable for the equipment.” As appropriate as this description might seem, the limitation of power quality to “sensitive electronic equipment” might be subject to disagreement. Electrical equipment susceptible to power quality or more appropriately to lack of power quality would fall within a seemingly boundless domain. All electrical devices are prone to failure or malfunction when exposed to one or more power quality problems. The electrical device might be an electric motor, a transformer, a generator, a computer, a printer, communication equipment or a household appliance. All of these devices and others react adversely to power quality issues, depending on the severity of problems.