Introduction to Distributed Energy Resources

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Introduction to Distributed Energy Resources

• Masoud H. Nazari
• Doctoral Student of Engineering Public Policy
• mhonarva_at_andrew.cmu.edu
•  

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Talk outline

• Centralized Electric Power systems vs.
  Distributed Energy Resources
• Different Technologies of Distributed Energy
  Resources (DER)
• Advantages of DER
• Governmental Incentives for DER
• Potential Problems and Solutions
• Policy Implications and Conclusions

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The historical Structure of Electric Power Systems
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Drawbacks of Traditional Electric Power Systems

• Low Efficiency in producing power ( 30)
• High Power Loss through transmission and
  distribution network (10-15)
• Low Reliability Availability
• Not environmentally friendly

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The Future Structure of Energy Systems with
multiple Distributed Energy Resources
Distributed Energy Resources or Distributed
Generation (DG) units are small-scale power
generators (typically in the range of 3 kW to 10
MW) used to provide electricity close to
consumers and from many small energy sources.
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Technologies of Distributed Energy Resources

• 1) Wind converting the kinetic energy in wind
  into electrical energy

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• 2) Solar thermal converting solar energy to
  thermal energy and then electrical energy

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• 3) Biomass using living and recently dead
  biological material as fuel for producing
  electricity

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• 4) Photovoltaic cell (PV) converting light into
  electric current using the photoelectric effect

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• 5) Hydro the production of power through use of
  the gravitational force of falling or flowing
  water

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• 6) Fuel cell producing electricity from chemical
  reaction of fuel (Hydrogen) and an oxidant
  (Oxygen)

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• 7) Tidal energy form of hydropower that converts
  the energy of tides into electricity

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• 8) Wave power capturing the energy by ocean
  surface waves to produce electricity

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• 9) Geothermal producing electric power from heat
  stored in the earth

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• 10) Cogeneration (CHP) using a power station to
  simultaneously generate both electricity and
  useful heat

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Benefits of DG

• Increasing Efficiency (Combine Heat and Power
  (CHP) gt 95)
• Reducing CO2 Emission
• Power Loss Reduction
• Voltage Improvement
• Decreasing Lines Congestion
• Increasing Reliability Availability

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Reducing CO2 Emission

• Due to using renewable energy resources (like
  Wind or Solar) or higher efficiency (e.g.
  Combined Heat Power)

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Power Loss Reduction

• Reducing power loss through Distribution and
  Transmission lines due to decreasing current

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Optimum Locating DGs with respect to Loss
Minimization

• Optimum Power Flow (OPF)
• Optimal DG locations with respect to network
  power loss minimization
• Optimal voltage setting for DGs

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• Using IEEE-30-bus distribution network test
  system
• Two combustion turbines (C-T) with the same
  capacity of 750 KW
• providing 10 of total demand (15 MW)
• Power loss reduction by optimum placement and
  utilization is (0.7
• MW) 50

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Voltage Improvement in Distribution Network

• Voltage profile improvement by voltage
  optimization

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Decreasing Lines Congestion

• Decreasing Lines Congestion or Capacity Release
  due to decreasing apparent power through the lines

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Increasing Reliability

• By losing one DG, at most 1 MW generation is lost
  
• By losing one central power plant in average
• 1 GW is lost
• Thus, Increasing Reliability by using DGs

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Increasing Availability

• By Providing electricity for local consumers
  during power outage electricity availability
  increases (Islanding Phenomena)

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Federal Government Goals for DGs

• Deployment of renewable power (often sub-set of
  DG) is being widely encouraged through various
  state policies such as renewable portfolio
  standards (RPS)
• Proposals for a national standard to require up
  to 30 of electricity from renewable sources by
  2025
• High incentives for increasing energy efficiency
  and conservation (7-10 loss reduction)
• Distributed Generators (DG) potentially improve
  efficiency (power loss reduction high
  efficiency)

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Potential Problems

• Economy
• Losing economy of scale
• Technical
• Relay coordination (Short Circuit problem)
• Potential frequency instability

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Losing Economy of Scale

• One can always double up units to lower cost
• Example, one fuel cell X, two fuel cells less
  than 2X

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Increasing Short Circuit Current

• Increase the short circuit levels

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Selectivity problem in loop with DGs
Problem Unnecessary relay tripping
Solution ???
DMS Group DMS Smart Grid, DMS Group, Novi
Sad, Serbia
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Potential Frequency Instability Problems in
Distribution Networks due to DGs

• Frequency instability in the electric network
  means blackout
• If penetration of DGs is low (1-2)
• DGs may get damaged without adequate protection
  (blades breaking)
• Protection of DGs may disconnect them
  automatically
• If penetration of DGs is high (10-15) Donnelly,
  Lopes, Cardell
• Only local (distribution) system may be affected
• If penetration of DGs is very high (gt 20)
  Guttromoson
• Both local and backbone (EHV,HV) transmission
  systems may be affected
• No precise explanation and systematic solution
  for the problem

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Real world exampleform Portugal distribution
network

• Each area has synchronous machines (DGs)
• There is an electromechanical mode of
  oscillatory between two areas
• To resolve the problem Power System stabilizer
  (PSS) is implemented
• Effectiveness of PSS depends on observability
  and controllability of the system

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Research Questions (Motivation)

• Answering the following questions
• What are the basic causes of frequency problems
  in local (distribution) networks with larger DGs
  sending power into the grid?
• What are the possible solutions for avoiding
  frequency problems?
• How to design policies to support deploying DGs
  without causing technical problems?

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Small-Signal-Stability (Dynamic) Analysis

• State space model (first order differential
  equations)
• Statefrequency, fuel control, fuel flow,
  derivative of fuel flow, active power
• Typical DG parameters Inertia, Governor Control
  (G-C), Electrical Distance
• Properties of A determine stability of the system
  (Eigenvalue Analysis)
• Sensitivity analysis of the system dynamics

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Dynamic Analysis of Optimum Locations

• Two C-Ts at optimum locations are small signal
  unstable
• Due to short electrical distance (impedance)
  between DGs, Governor-Controls of DGs are
  strongly coupled and acting against each other

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Exhaustive Small Signal Study of Different
Combinations of Locating C-Ts

• Out of 900 possible combinations of locating two
  C-Ts, 192 cases have unstable frequency
• Instability depends on
• Impedance between DGs
• (Electrical Distance) in other words
• Location of DGs (in contrast with
• Cardell results)
• Inertia of DGs
• Governor-Control system and,
• Dynamic model of DGs

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Case B of instability

• Short electrical distance between DG close to
  sub-station and sub-station causes strong
  coupling and makes the DG unstable

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Case C of instability

• Strongly coupling between two DGs and DGs and
  Sub-station
• Instability is aggregated

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Frequency Stability of Hydro Plants

• H-Ps are potentially
• unstable because of
• the non-minimum
• phase properties
• Out of 900 cases 866
• cases are unstable
• Fig. dynamic response at
• optimum locations

?G is the frequency of the generator, q is the
penstock flow, v is the governor droop and ? is
the gate position
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Many small DGs instead of some large ones

• The system of 15 small C-Ts (with G-C) replaced
  by 2 large ones is also small signal unstable
  (total DG capacity is fix)
• In general, decreasing size of DGs cannot improve
  robustness

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Potential Robustness Enhancement Methods

• Changing the locations of DGs
• Cons
• Not being able to minimize power loss
• Slow dynamic response

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Potential Robustness Enhancement Methods

• Increasing inertia of C-Ts By increasing inertia
  tenfold all unstable cases becomes stable
• Cons Increasing inertia means using storage
  which is usually expensive, also dynamic response
  of storage systems is inherently slow

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The Most Effective Robustness Enhancement Method

• High Communication and Observation or Advanced
  Control Systems (work in progress)
• The whole system is fully controllable, also all
  DGs are locally controllable, thus, the system is
  stabilizable either by centralized control
  systems or decentralized control systems
• Choosing between different kinds of control
  systems depends on regulation and policy design
  of the system
• Cons cost of designing and implementing control
  systems

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Potential Frequency Instability

• Implementing Centralized Control for optimum case

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Policy Implications

• Providing small portion of local power by local
  Distributed Generators can significantly reduce
  power loss and increase efficiency of
  distribution networks
• In order to find optimum operating condition
  (location of DGs and operating points), it is
  necessary to use optimization methods for
  planning of future energy systems

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Policy Implications

• Todays distribution electric systems may not be
  capable of accommodating large number of
  Distributed Energy Resources or Distributed
  Generators sending power into the grid
• Often, there is a trade of between efficiency and
  robustness of future energy systems
• Frequency instability depends on networks
  characteristic and DGs technology, location,
  inertia and control systems

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Policy Implications

• There is no single solution to fit all criteria
• Possible policy approaches to solve the problem
• Encouraging DG owners to locate their units on
  initially stable locations (revising planning of
  distribution networks)
• Introducing new standards for future energy
  systems to ensure robustness (beyond IEEE 1547)
  e.g. minimum electrical distance between DGs or
  minimum inertia of DGs
• Designing centralized control systems or advanced
  local control systems (decentralized control
  system)

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Conclusions

• Distributed Generators can significantly improve
  efficiency by reducing power loss
• Todays electric systems may not accommodate
  large number of larger DGs sending power into the
  grid due to frequency problem
• Possible solutions
• Changing planning design of distribution networks
  
• Introducing new standards (beyond IEEE 1547)
• Designing new control strategies

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Thank You for Your Attention