Overview of Microgrid Control Principles and Strategies Rev0

8/22/2019 Overview of Microgrid Control Principles and Strategies Rev0

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OVERVIEW OF MICROGRID CONTROL

PRINCIPLES AND STRATEGIES

Bucharest, 05th

September 2013

drd.ing. Andrei HORHOIANU Prof.dr.ing. Eremia MIRCEA

University Politehnica of BucharestRomania


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CMDM Conference, 2-5 September, Bucharest

1.What is a Smart Grid and a Microgrid?

Smart Grid - an electricity network based on digital technology that is used to

supply electricity to consumers via two-way digital communication. This system

allows monitoring, analysis, control and communication within the supply chain

to help improve efficiency, reduce the energy consumption and cost, and

maximize the transparency and reliability of the energy supply chain.

Microgrid - a group of interconnected loads and distributed energy resources

within clearly defined electrical boundaries that acts as a single controllable

entity to the grid. A microgrid can operate in both grid-connected or island

mode


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2. Microgrid Arhitecture


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3. Microgrid Benefits and Resulting Challenges

Benefits

Short-and long-term energy storage units can

play a major role in control and operation Ability to provide prespecified power quality

levels or preferential services to some loads

Monitoring and diagnostics of the entire systemby collecting data from microsources and

consumers

Active and reactive power control ofmicrosources present in the microgrid,to

maintain voltage and frequency within the limitsset

Assurance of power supply to consumers withinthe microgrid during outages in the main grid.

Resulting

Challenges

Microgird is inherently subject to a significant

degree of imbalance due to the presence ofsingle-phase loads and/or DER

A noticeable portion of supply within amicrogrid can from noncontrollable

sources;

Economics often dictate that a microgrid

must readily accommodate connection

and disconnection of DER units and loads

while maintaining its operation

Safety operation issues during island

mode

TWO-WAY COMMUNICATION, MONITORING AND CONTROL ACTIONS


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4. Control Principles and Strategies - Microgrid Supervisory Control

A microgrid, through its control system, must ensure all or a subset of the required functions. The objectives are

achieved through either a centralized or a decentralized supervisory control that includes three hierarchical

levels

Distribution Network Operator (DNO) and Market Operator (MO)

Microgrid Central Controller (MCC)

Local Controllers (LCs) associated with each DER unit and/or load.

Decentralized Control SystemCentralized Control System


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4. Control Principles and Strategies DER Controls

Common architectures for electronically interfaced DER units:

Nondispatchable photovoltaic (PV)-based DG unit for which the

PV array, through a converter system, is interfaced to the host

microgrid. The converter is a dc-dc-ac system composed of one

dc-dc converter and one dc-ac converter.

Hybrid electronically coupled DER unit for which the converter

system is composed of two parallel dc-dc converters and onedc-ac converter. Although the PV array provides

nondispatchable power, the converter system can be controlled

to provide a dispatchable power at the output of the unit.

Electronically coupled genset DG unit that is augmented with a

capacitive energy storage unit. The genset is a slow-acting

dispatchable DG unit that is coupled to the host microgrid

through an ac-dc-ac converter system. The capacitive storage

unit is interfaced to the dc link of the ac-dc-ac converter system

through a dc-dc converter and provides short-time power flow

requirements during start up and/or acceleration/deceleration

intervals of the slow genset


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Grid Following: Power Export Grid Following: Power Dispatch


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Grid Forming : Voltage and Frequency Control Grid Forming : Load Sharing

Remark: Control strategies for DER units within a microgrid are selected based on the required functions and

possible operational scenarios. Controls of DER units are also determined by the nature of its interactions with

the system and other DER units.


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4. Microgrid Energy Management System

Functions of Real-Time EMS for a MicrogridThe PMS/EMS assigns real and reactivepower references for the DER units to:

appropriately share real/reactive power

among the DER units

appropriately respond to the microgriddisturbances and transients

determine the power set points of the

DER units to balance the microgrid power

and restore the frequency

enable resynchronization of the microgrid

with the main grid, if required.


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5. Microgrid Energy Management System

Centralized Energy Management System Decentralized Energy Management System


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6. Conclusions

Market acceptability of DER technologies and the gradual and consistent increase in their

depth of penetration have generated significant interest in integration, controls, and

optimal operation of DER units in the context of microgrids

With increasing penetration of communication and control technologies that enable smart

grid functionalities, an infrastructure is rapidly evolving that will support the formation of

networks of sources and loads microgirds that are amorphous and dynamic,

completely unlike any power system network that is extant today.

The problem of optimal management of the resources in a microgrid is being widelyinvestigated and recent studies have proposed the application of both centralized and

distributed control schemes by using multi-agent systems, heuristic methods and

optimization algorithms.

A decentralized control approach intends to provide the maximum autonomy for the DER

units and loads within a microgrid.

A microgrid, through its control system, must ensure all or a subset of functions such as:

supply of electrical and/or thermal energy, participation in the energy market, prespecifiedservice level for critical loads, black start subsequent to a failure, provision for ancillary

services, etc


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7. Perspectives

Development of an industrial microgird with hierarchical control based on artificial intelligence techniques


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THANK YOU !

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Overview of Microgrid Control Principles and Strategies Rev0