Abstract
Inverter voltage control is an important task in the operation of a DC/AC microgrid system. To improve the inverter voltage control dynamics, traditional approaches attempt to measure and feedforward the load current, which, however, needs remote measurement with communications in a microgrid system with distributed loads. In this paper, a load current observer (LCO) based control strategy, which does not need remote measurement, is proposed for sinusoidal signals tracking control of a three-phase inverter of the microgrid. With LCO, the load current is estimated precisely, acting as the feedforward of the dual-loop control, which can effectively enlarge the stability margin of the control system and improve the dynamic response to load disturbance. Furthermore, multiple PR regulators are applied in this strategy conducted in a stationary frame to suppress the transient fluctuations and the total harmonic distortion (THD) of the output voltage and achieve faster transient performance compared with traditional dual-loop control in a rotating dq0 frame under instantaneous change of various types of load (i.e., balanced load, unbalanced load, and nonlinear load). The parameters of multiple PR regulators are analyzed and selected through the root locus method and the stability of the whole control system is evaluated and analyzed. Finally, the validity of the proposed approach is verified through simulations and a three-phase prototype test system with a TMS320F28335 DSP.
Highlights
Microgrid is commonly defined as an integrated power system consisting of distributed generators (DGs), distributed energy storages (DSs), and interconnected load, which can operate in grid-connected mode or in intentional islanded mode [1]
The experimental results are consistent with the simulation results above, which indicates the control strategy proposed in this paper shows an excellent performance on the dynamic response to the load disturbance
This paper has proposed an optimal proportional resonant (PR) control strategy with load current observer (LCO) for a three-phase inverter of islanded microgrid
Summary
Microgrid is commonly defined as an integrated power system consisting of distributed generators (DGs), distributed energy storages (DSs), and interconnected load, which can operate in grid-connected mode or in intentional islanded mode [1]. The proposed control strategy chosen in this paper introduces a load current observer and adopts multiple R regulators under α-β coordinates to track the sinusoidal voltage values. It introduces the load current as the feedforward of the internal current loop, which accelerates the regulating rate of the internal current loop, improves the dynamic response of the system effectively, and restrains the influence on the system caused by the load fluctuation.
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