Abstract

In this paper, an efficient under frequency control and the energy management of a distributed energy resources (DERs)-based microgrid is presented. The microgrid is composed of a photovoltaic (PV), double-fed induction generator (DFIG)-based wind and diesel generator with critical and non-critical loads. The system model and the control strategy are developed in a real time digital simulator (RTDS). The coordination and power management of the DERs in both grid-connected and islanded operation modes are implemented. During power imbalances and frequency fluctuations caused by fault or islanding, an advanced automatic load shedding control is implemented to regulate and maintain the microgrid frequency at its rated value. One distinct feature implemented for the load shedding operation is that highly unbalanced critical loads are connected to the microgrid. The diesel generator provides the required inertia in the islanded mode to maintain the microgrid rated frequency by operating in the isochronous mode. The International Council on Large Electric Systems (CIGRE) medium voltage (MV) test bench system is used to implement the DERs and their controller. The proposed control approach has potential applications for the complete operation of microgrids by properly controlling the power, voltage and frequency in both grid-connected and island modes. The real time digital simulator results verify the effectiveness and superiority of the proposed control scheme in grid connected, island and fault conditions.

Highlights

  • A small-scale power grid with distributed storage, distributed generation (DG) and loads connected to each other with a clear electrical boundary is a microgrid [1,2]

  • Systems control their real and reactive power output using the control schemes described in Section 3, while the diesel generator operates in droop control to exchange real and reactive power with the grid

  • An efficient advanced automatic load shedding and power management control scheme of a microgrid based on PV, double-fed induction generator (DFIG) based wind, diesel generator and local loads is presented in this paper

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Summary

Introduction

A small-scale power grid with distributed storage, distributed generation (DG) and loads connected to each other with a clear electrical boundary is a microgrid [1,2]. A microgrid control must regulate the power, voltage, and frequency when in grid-connected or islanded operation within specified thresholds of power quality and reliability. A significant challenge to microgrid implementation is the stable control of voltage and frequency during grid-connected and islanded operation modes. Load shedding control should operate rapidly to restore the power balance in the microgrid to avoid voltage and frequency collapse [18,19,20,21]. An efficient automatic load shedding control strategy for microgrids supplying critical and non-critical loads is proposed and implemented. In island mode of operation, the DERs supply the loads and a controller is proposed and implemented for the diesel generator to control the frequency in isochronous mode, by maintaining a constant speed regardless of the load.

System Configuration
Proposed Control Scheme
Diesel Generator Model and Control
Load Shedding Scheme
Results and Discussion
Grid-Connected to Islanded Mode Switching
Load Shedding Control during Fault in Islanded Mode
Conclusions
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