ForskEL-6316 project
Operation and Control of Modern
Distribution Systems
Institute of Energy Technology, Aalborg University (AAU)
Himmerlands Elforsyning (HEF)
SEAS-NVE Energy Group
Dansk Energi Forskning og Udvikling (DEFU)
March 2007-May 2010
Part A PhD started in March 2007, Part B PhD started in June 2007
Aims
•Study the effects of load management systems and on-line real
time electricity pricing systems in modern distribution systems
•Develop the models, operation and control strategies for such
distribution systems in normal operation for maximising the
benefit from the renewable DGs in a load management and real
time pricing power market
•Establish the control approach for such distribution systems in
contingency situations, for example, island operation, for
minimising the possible damage to costumers and restoring power
system normal operation quickly
Subprograms of the project
The project has two parts:
Part A: Normal Operation Optimization
Part B: Control Strategies in Abnormal Operation
Situations
Main Contents of Part A
1. Electricity market and on-line real time electricity price.
2. Development of models to represent the relationship between
the electricity price and the load characteristics controlled by a
load management system.
3. Development of models to represent the relationship between
the electricity price and dispersed generation units.
4. Power system operation constraints will be added to electricity
pricing system, to establish an over all system model.
5. Development of operation and control strategies for DG units
and the load management system to minimize the overall
system cost.
Electricity Market Survey
Survey the electricity market situation and development all over the world
The traditional vertical and integrated power system which is a comprehensive
monopoly generation, transmission and distribution system.
Electricity Market Survey
Most countries have finished their wholesale market at transmission level and
now they are on the way to a comprehensive market.
Electricity Market Survey
Patterns
Auction bidding
Wheeling
trading
Decentralized trading
Main element of price
Generation cost
Transmission
tariff
Contract
Usual application
Spot market
Regional market
Bilateral, future and
contract based market
Typical examples
UK/Australia/ New
Zealand power pool
California pool
US interstate
market, National
region market,
international
market
UK NETA,
California new trend
Features
Complex; mostly single
side; high price variation;
market power
Easy; less
benefits to end
users;
transitional
pattern
Not too complex; wide
trade participation; two
side; High organizing
and running costs
Different wholesale market forms and their characteristics
Electricity Market Survey
Specific wholesale market conditions on Nordic area and Denmark
•
The auction of the spot market is a two-side bidding at
wholesale level.
A trader can submit negative capacity versus the increasing
prices, which indicates that he would like to sell the electricity at
higher prices although he is a buyer often.
The main market environment for modern distribution system
•
On distribution level, most countries have opened the retailing
market, which means that the customers have the full right to
select their willing retailers as well as contract forms.
Retail Price and Customer Categories
customer categories and their quantities and consumption in load
Customer (load)
type
Quantity
ratio
Electricity
consumption
ratio
Load
flexibility
Industrial
0.4%
32.5%
high
Commercial
14.2%
31%
low
Residential
88.3%
36.5%
medium
Source: Department of Energy, USA
load flexibility and response of industrial, commercial and residential customers
Retail Price and Customer Categories
usual DG possession and their market participation possibilities
for different customer categories
Customer (load) type
usual DG types
Possibility of self owned DG
participate into market
Industrial
Larger unit
high
Commercial
UPS, diesel engine,
fuel cell
low
Residential
Solar, wind
low
Operation of DG integrated with system
•
DG is operated in coordination with the local load requirements
•
DG is operated in coordinated with the price signals
Data Work
Typical weekly samples for price data
€Euro/MWh
(source: Nordic Pool)
Current Study
• Collect load data
• The pricing scheme
• Study the activities of customers in the
electricity market
Main contents of Part B
1. Effective detection method of operation states .
2. Power system protection system and power
electronic converters in island operation conditions.
3. Control strategies for stable transition between
different operation states.
4. Coordination control of the stand alone system to
minimize the damage and inconvenience to
consumers .
DG and Islanding
• The current practice is that almost all utilities require that
distributed generators should be disconnect from the grid as
soon as possible in case of islanding.
• In future, current practice of disconnecting the DG
following a disturbance will no longer be a practical or
reliable solution. Also, the IEEE Std. 1547-2003 states, the
implementation of intentional islanding of DGs is one of the
tasks for future consideration.
Islanding Issues
•
•
•
•
•
•
Line worker safety.
Maintaining voltage and frequency.
DG interconnection grounding.
Out of phase reclosing.
System’s stability.
Protection system co-ordination.
Scope of the Project
•
•
•
•
•
Effective islanding detection.
Developing operating strategy for DGs.
Designing an additive protection system.
Investigating the stability of system in both mode.
Investigating the commercial impact of DG islanding.
Islanding Detection
• The main philosophy of detecting an islanding situation is to measure
the DG output parameters and from these parameters a decision is
taken to decide whether or not an islanding situation has occurred.
Islanding Detection
Remote Technique
Local Technique
Passive
Active
Islanding detection technique
Operation of DG
DG Operation
Grid connected
mode
When generation
less than demand
•
•
•
Islanding
mode
When generation
equal/more than
demand
DG acts as a constant power source when connected to the grid.
DG supports the voltage when islanded
DSM/load-shedding when power from DG is not enough to support load.
DG Protection and Stability
• Fault current seen by the protective equipment may not be
same when the system is islanded and when it is not.
Furthermore, radial system has protection system designed
for unidirectional flow. So, additive protection system is
needed, which will operate satisfactorily under both
conditions.
• DGs may cause overall stability and dynamics in
distributions system, may affect distribution system's
stability. Ability of the system to maintain stability (voltage
and angle) in case of N-1 contingency has to investigated.
Thank you for your attention