Abstract
With reference to the newly released microgrid standards, design and real-time implementation of a centralized microgrid control system is presented in this article. In the grid-connected mode, the utility grid will provide the voltage and frequency reference at the point of connection. The assets within the microgrid will follow power command references provided by the control system. In the islanded mode, the energy storage system (ESS) can provide the voltage and frequency reference to all other generators. Based on the state-of-charge of the ESS, a rule-based dispatch is proposed, with priority given to diesel generator and then the storage in the middle state of charge range. To alleviate power fluctuations, meet smooth planned islanding requirement, and compensate for the feeder losses ignored in dispatch algorithm, a supplementary slack-bus power control based on closed-loop feedback and first-order filter is proposed. The potential of the storage system in firming short-time power fluctuation and providing long-term load shifting capabilities is exploited. An emergency dispatch function for unplanned islanding considering the speed of response limitation of a diesel generator is also proposed. The proposed control strategy is implemented and tested on a controller hardware-in-the-loop test bench. It demonstrates the capability of the control system to reduce load shedding and renewable curtailment, and to implement power management at the point of interconnection.
Highlights
I N THE past decade, microgrids have drawn wide attention by researchers for their capability of providing resilient power supply and effective integration of distributed renewable resources (DERs)
Assuming the considered microgrid is at low voltage level, reactive load is balanced by diesel generator and inverterinterfaced assets, while no SVC and FACTS devices are used
The feeder losses and power fluctuation will be reflected on PPOI, which can be compensated by slack-bus power control
Summary
I N THE past decade, microgrids have drawn wide attention by researchers for their capability of providing resilient power supply and effective integration of distributed renewable resources (DERs). A C-HIL testbench implementing constant power at point of interconnection (POI) in the grid-connected mode and fixed-frequency control in the islanded mode is developed in [5], but transition and dispatch function are not fully tested. In [9], a control scheme with the energy storage system (ESS) used for power smoothing and state of charge (SoC) fixed around 0.5 is proposed for grid-connected and islanded operation modes. A comparative study of load-following control and cycle-charging control applied to an islanded PV-dieselESS microgrid is conducted in [10] where the ESS and diesel generator, respectively, are used as the main source to fulfill power balance. In response to microgrid controller standardization, a centralized MGCS is designed and implemented in this article, based on the authors’ precedent work [11]. The control strategy is implemented with a C-HIL test-bench, with multiple test scenarios presented to demonstrate its effectiveness
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