Development of a Hardware in the loop Platform for Microgrid Energy Management System
In this work we build a Hardware In the Loop (HIL) platform for testing the Energy Management System (EMS) of Micro- grids (MG). The HIL platform includes simulated MG in Real Time Digital Simulator (RTDS), the EMS in PC, and the com- munication interface between EMS and MG.
A Microgrid is a local electricity grid with elements of dis- tributed energy resources (DER), distributed energy storage systems and local loads. The MG can operate both in grid- connected mode and islanding mode. The operation of a MG becomes significantly complex with the high penetra- tion of renewable energy resources, demand side manage- ment, market participation, disconnection and reconnection to the utility grid. Therefore the development of advanced energy management system (EMS) for MG able to support all these features is a real challenge.
From the point of view of operator of the MG, the EMS should be able to gather real-time monitoring information, to analyze the measurement data and thus determine con- trol actions, and to send optimized set point references and control commands to the components. As for the compo- nents, the renewable energy resources should be able to execute the tasks set by the EMS, with fast dynamics and satisfactory accuracy, especially to realize a smooth transi- tion between MG grid-connected and islanding operation. The goal of optimum and stable operation of a MG can be achieved only with the coordination between all active components. In order to achieve this goal, suitable commu- nication interfaces and protocols have to be implemented between all the components in the MG and EMS. The HIL platform that we are building enables the testing of the ma- nagement and operation functions of the EMS.
The set-up of this platform is composed of three parts: RTDS real time simulation, communication interface and a PC-based EMS. The dataflow between these parts is de- picted in the figure. The MG simulated in RTDS can be AC, DC, or hybrid, with different topologies, and different types of distributed generation. In the MG, every component has its own local controller which regulates the output power through the output current, or can form the bus voltage by controlling voltage magnitude and frequency. The con- trol commands of real/reactive power set points, voltage/ frequency set point and the commands to switch mode of operation are generated by the EMS externally to the real time simulation, and sent to RTDS through the communica- tion interface.
The communication interface is based on the Xilinx ML507 evaluation board, which provides wide bandwidth and low latency communication. The interface is responsible for transferring monitoring data and control commands bet- ween RTDS and the PC-based EMS.
The EMS works as central controller of the MG; supervising the control and operation of all the active components in the MG. Besides sending the set points to the local cont- roller, it commands connection/disconnection of DER units, load shedding, and determines the operating modes of the MG. The data received by the EMS are the measurements of the MG components, load profiles, DER generation data, and electricity price. The EMS computes the optimum set points (e.g. active and reactive power, voltage and frequen- cy, status of switches) based on collected data, and sends them to the components in MG. Different self-developed al- gorithms for EMS can be implemented and tested.