Overview of Microgrid Operation Under 

Different Conditions

In normal conditions, the microgrid system operates in any mode inside

the inner loop. The outer loop is the emergency operation mode, which is

caused by various reasons, such as internal/external faults, unscheduled

outages, or voltage/frequency transients.

IEEE PES General Meeting 2018

Portland, Oregon

August 5–9, 2018

NREL/PO-5D00-72148

Design of a Microgrid Transition Controller II: 

System Recovery Under Abnormal Conditions

Jing Wang, Annabelle Pratt, and Murali Baggu

Power Systems Engineering Center, National Renewable Energy Laboratory Golden, CO 80401, USA

This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding 

provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. 

Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or 

reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

Conclusions

The developed microgrid transition controller focuses on operation

functionalities for emergency operation, which is validated by

numerical simulation in MATLAB/Simulink. The results show that

the developed microgrid transition controller can handle

emergency operation and transition the system to normal

operation.

Additional Reading Jing Wang, Changhong Zhao, Annabelle Pratt, and Murali Baggu. 2018. “Design of an Advanced Energy

Management System for Microgrid Control Using a State Machine.” Applied Energy 228: 2407–2421.

Abstract

This paper presents a microgrid transition controller for managing

emergency operation when the microgrid experiences a system blackout

caused by an internal or external fault. The developed transition controller

consists of various application function blocks (AFBs), including normal

operation, emergency operation, and coordination between them. The

developed microgrid transition controller is validated by a sample

microgrid, and two test cases are investigated: islanded black start and

grid-connected black start. The simulation results demonstrate the

feasibility and effectiveness of the proposed controller for handling

emergency operation and transitioning to normal operation.

Design of the Microgrid Transition 

Controller

• Layered structure: DNO control room, supervisory level, device

control level, field level

• AFBs and coordination among them.

Schematic diagram of the transition controller

Results

Scenario 1: Islanded Black Start

The microgrid system starts from operating in grid-connected mode. Then

an external fault is triggered and removed after a certain amount of time.

The microgrid controller detects the situation, opens the PCC circuit

breaker, and black starts the system in islanded mode.

Scenario 2: Grid-Connected Black Start

The microgrid system starts from operating in islanded mode. Then an

internal fault is triggered and removed after a certain amount of time. The

microgrid controller detects the situation, turns off all generation, closes the

PCC circuit breaker, and black starts the system in grid-connected mode.

AFB#1: Operation Mode Management

Distribution network operator (DNO) signal processing, point of common

coupling (PCC) disconnection enable signal, and PCC reconnection enable

signal and operation mode decision

AFB#8: Emergency Operation

• Detection of blackout

• Decision of black-start option

• Sequences of black start: grid-connected or islanded

• Check completion of black start.

Coordination signals inside the 

microgrid transition controller

Measurements at PCC: circuit 

breaker status, voltage, etc.

Measurements at PCC: circuit breaker status, voltage, etc.