Flexible Compensation of Voltage and Current Unbalance and Harmonics in Microgrids

Abstract

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.

Improved secondary control for optimal total harmonic distortion compensation of parallel connected DGs in islanded microgrids

“…4d. T1 has changed from 1 to 0.84 and hence T2 has changed from 1 to 1.16 to satisfy (13). It can be deduced from Fig.…”

“…This equation satisfies (13). By this modification, one can make sure the acceptable THD in other buses while keeping the best THD in SLB.…”

“…The data of the selected microgrid and the parameters of control systems are provided in Tables 1-4. According to the standard, the THD limitation for sensitive buses should not exceed 5% [30] but there may be loads in the system that are much more sensitive to the voltage quality and the 5% limitation does not satisfy their voltage quality requirement such as hospital loads. For example [13] defines different voltage unbalance factors at different buses. In this study, different levels of THD requirement for different buses are considered.…”

Secondary‐control‐based harmonics compensation scheme for voltage‐ and current‐controlled inverters in islanded microgrids

“…The harmonics compensation in MGs by using the VCM units is proposed in [9]- [22]. These methods can be classified to local-data- [9][10][11][12][13][14][15] or communication-based compensation [16][17][18][19][20][21].…”

Power quality enhancement and power management of a multifunctional interfacing inverter for PV and battery energy storage system

“…The concept of using multifunctional inverters has been suggested by some researchers. In this concept, not only the generated power of distributed generator (DG) can be injected to the grid or MG via proper control of inverter but also compensation of nonlinear and unbalanced loads effects can be achieved . In previous studies, the DG units are not modeled and a constant DC source is used as DG units.…”