Abstract
In this paper, an enhanced hierarchical control structure with multiple current loop damping schemes for voltage unbalance and harmonics compensation (UHC) in ac islanded microgrid is proposed to address unequal power sharing problems. The distributed generation (DG) is properly controlled to autonomously compensate voltage unbalance and harmonics while sharing the compensation effort for the real power, reactive power, and unbalance and harmonic powers. The proposed control system of the microgrid mainly consists of the positive sequence real and reactive power droop controllers, voltage and current controllers, the selective virtual impedance loop, the unbalance and harmonics compensators, the secondary control for voltage amplitude and frequency restoration, and the auxiliary control to achieve a high-voltage quality at the point of common coupling. By using the proposed unbalance and harmonics compensation, the auxiliary control, and the virtual positive/negative-sequence impedance loops at fundamental frequency, and the virtual variable harmonic impedance loop at harmonic frequencies, an accurate power sharing is achieved. Moreover, the low bandwidth communication (LBC) technique is adopted to send the compensation command of the secondary control and auxiliary control from the microgrid control center to the local controllers of DG unit. Finally, the hardware-in-the-loop results using dSPACE 1006 platform are presented to demonstrate the effectiveness of the proposed approach.
Highlights
Distributed generation (DG) using renewable energy resource (RES) such as wind turbines and solar power plants has been widely used in recent years
The low bandwidth communication (LBC) is applied for sending the data information of the secondary controllers and the point of common coupling (PCC) voltage harmonics from the microgrid control center (MGCC) to the local controller to realize the proposed compensation scheme in DG units in a practical and synchronized manner
To demonstrate the effectiveness of the proposed method in a microgrid with unbalanced resistive load plus nonlinear load connected to the PCC, the output voltages and currents of DG1 and DG2 are shown in Fig. 14 and 15 and the SW1 and SW2 are in the closed state
Summary
Distributed generation (DG) using renewable energy resource (RES) such as wind turbines and solar power plants has been widely used in recent years. The virtual impedance loop is developed to adjust DG equivalent impedance at fundamental positive and negative sequences and harmonic frequencies to alleviate the circulating currents and unbalanced and harmonic power sharing problems [22], [23]. The centralized secondary control scheme for voltage amplitude and frequency restoration purposes of microgrid and the auxiliary controller of selective harmonics compensation of the PCC main voltage harmonics with the low bandwidth communication (LBC) link are presented in this paper. It is a practical and cost-effective approach since only a LBC network is required.
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