Abstract
In recent years, the harmonics and unbalance problems endanger the voltage and current quality of power systems, due to increasing usage of nonlinear and unbalanced loads. Use of Distributed Generation (DG)-interfacing inverters is proposed for voltage or current compensation. In this paper, a flexible control method is proposed to compensate voltage and current unbalance and harmonics using the distributed generation (DG)-interfacing inverters. This method is applicable to both grid-connected and islanded Microgrids (MGs). In the proposed method, not only the proper control of active and reactive powers can be achieved, but also there is flexibility in compensating the voltage or current quality problems at DG terminals or Points of Common Coupling (PCCs). This control strategy consists of active and reactive power controllers and a voltage/current quality-improvement block. The controller is designed in a stationary (αβ) frame. An extensive simulation study has been performed and the results demonstrate the effectiveness of the proposed control scheme. Depending on the compensation modes, the harmonics and unbalance compensation of DG output current, MG-injected current to the grid, as well as PCC and DG voltages, can be achieved in grid-connected operation of MG while in the islanded operation, and the PCC and DG voltages compensation can be obtained through the proposed control scheme.
Highlights
In recent years, due to the disadvantages of conventional fossil fuels such as air pollution and extinction, the concept of benefitting from renewable energy sources (RESs) has attracted more attention [1,2,3]
Microgrid (MG) and Distributed Generation DG concepts have emerged for better use of the RESs and enhancing efficiency, power quality and reliability of the conventional power systems [4,5]
If a three-phase inverter is connected to a mainly inductive grid, the injected positive sequence active and reactive powers are related to the angle between (PS) active and reactive powers are related to the angle between output voltage of DG and grid (φ) and
Summary
Due to the disadvantages of conventional fossil fuels such as air pollution and extinction, the concept of benefitting from renewable energy sources (RESs) has attracted more attention [1,2,3]. Since the output voltage of many of the RESs are unregulated DC or variable/high frequency AC, the integration of renewable energy to the utility grids or MGs requires power electronic converters, with an inverter as the last conversion stage in case of AC systems [6]. Four harmonic and unbalance compensation modes can be achieved, while the fundamental positive sequence components of DG output voltage can be properly controlled. Simultaneous control of fundamental positive and negative sequences, as well as harmonic components of voltage and current, is achieved for three-phase DG-interfacing inverters. The proposed method is applicable in both grid-connected and islanded modes of three-phase MGs. Four unbalanced and harmonic voltage or current compensation strategies can be achieved using this method.
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