Integration and Interconnection of Distributed Energy Resources

Transcription

1 University of Illinois Urbana-Champaign Integration and Interconnection of Distributed Energy Resources Geza Joos, Professor Electric Energy Systems Laboratory Department of Electrical and Computer Engineering 4 November

2 Overview and issues addressed Background Distributed generation and resources definition and classification Benefits and constraints Grid integration issues Grid interconnection and relevant standards Distribution systems standards Steady state and transient operating requirements Protection requirements General requirements types of protection Islanding detection Concluding comments Distributed energy resources microgrids and isolated systems Future scenarios 2

3 Electrical power system renewable generation Generation Transmission HVDC Conventional Storage Custom Power FACTS Distribution Renewables Industry Transportation Commercial Residential 3

4 Future electric distribution systems a scenario (Microgrid) 4

5 Distributed generation definition classification A subset of Distributed Energy Resources (DER), comprising electrical generators and electricity storage systems Size from the kw (1) to the MW (10-20) range Energy resource Renewables biomass, solar (concentrating and photovoltaic), wind, small hydro Fossil fuels microturbines, engine-generator sets Electrical storage batteries (Lead-Acid, Li-Ion) Other fuel cells (hydrogen source required) Connection Grid connected distribution grid, dispersed or embedded generation, may be connected close to the load center, voltage and frequency st by the electric power system Isolated systems voltage and frequency set by a reference generator 5

6 Distributed generation definition features Not centrally planned (CIGRE) is often installed, owned and operated by an independent power producer (IPP) Not centrally dispatched (CIGRE) IPP paid for the energy produced and may be required to provide ancillary services (reactive power, voltage support, frequency support and regulation) Connection at any point in the electric power system (IEEE) Interconnection studies required to determine impact on the grid May modify operation of the distribution grid Types of distributed generation Dispatchable (if desired) engine-generator systems (natural gas, biogas, small hydro) Non dispatchable (unless associated with electricity storage) wind, solar 6

7 Distributed generation installations Typical installations, from large to small Industrial Generating plants on industrial sites, high efficiency, in combined heat and power (CHP) configurations Commercial Residential installations, typically solar panels (PV) Features of smaller power dispersed generation Can typically be deployed in a large number of units Not necessarily integrated in the generation dispatch, not under the control of the power system operator (location, sizing, etc) 7

8 Distributed generation drivers Promoting the use of local energy sources wind, solar, hydro, biomass, biogas, others Creating local revenue streams (electricity sales) Creating employment opportunities (manufacturing, erection, maintenance, operation) Responding to public interest and concerns about the environment public acceptance can be secured Green power Greenhouse Gas (GHG) reduction 8

9 Distributed generation technical benefits Enhanced reliability generation close to the load Peak load shaving reduction of peak demand Infrastructure expansion deferral local generation Distribution (and transmission) system loss reduction generation close to load centers Lower grid integration costs local generation reduces size of connection to the main grid Distribution voltage connection (rather than transmission) ease of installation and lower cost Voltage support of weak distribution grids 9

10 Distributed generation typical installations Typical power plant types Hydraulic, 5-10 MW Biomass, 5-10 MW Biogas, 5-10 MW Wind, MW Total installed power (2011): 61 plants, 350 MW Connection: MV grid (25 kv, nominal 10 MW feeders typical for Canadian utilities) Ref: Presentation Hydro-Quebec Distribution,

11 Hydro-Quebec on-going projects Biomass 4 plants 25 MW on MV grid Commissioning Small hydro 8 plants 54 MW on MV grid Commissioning Wind power plants 5 plants 125 MW on MV grid Commissioning

12 DG connection to the grid options Connection options Distribution network low (LV), typically 600 V, and up to 500 kw Distribution network - medium voltage (MV), up to 69 kv, typically 25 kv, up to MW Transmission network aggregated units, typically 100 MW or more Power system impacts Distribution local, typically radial systems Transmission system wide, typically meshed systems Differing responsibilities and concerns Distribution power quality (voltage), short circuit levels Transmission stability, voltage support, generation dispatch Integration constraints in relation to the electric power grid Power quality should not be deteriorated Power supply reliability and security should not be compromised 12

13 Integration and interconnection issues Integration of the generation into existing grids constraints Operating constraints maximum power (IPP paid for kwh produced), desired operation at minimum reactive power (unity power factor) Dealing with variability and balancing requirements (if integrated into generation dispatch) characteristic of wind and solar installations Integration into the generation dispatch requires monitoring, energy production forecasting Interconnection into the existing grid constraints Connection to legacy systems protection coordination, transformer and line loading, impact on system losses Reverse power flow from end-user/producer to substation Increased short circuit current DG contribution Operational issues grid support requirements and contribution 13

14 Specific DG interconnection issues Generation power output variability Short term fluctuations flicker (wind, solar) Long term fluctuations voltage regulation, voltage rise at connection Reactive power / Voltage regulation coordination Reactive compensation interaction with switched capacitor (pf) Voltage regulation impact on tap-changing transformer operation Impact on Volt/Var compensation interference Harmonics and static power converter filter interaction Voltage distortion produced by power converter current harmonics Resonances with system compensating capacitors Islanding and microgrid operation Operation in grid connected and islanded modes transfer Microgrids possibility of islanded operation aid to system restoration 14

15 DG interconnection and control requirements Reactive power and power factor control required Voltage regulation may be required (using reactive power) Synchronization to the electric power system Response to voltage disturbances steady state and transient Response to frequency disturbances steady state and transient Anti-islanding usually required (to avoid safety hazards) Fault, internal and external overcurrent protection Power quality harmonics, voltage distortion (flicker) Grounding, isolation Operation and fault monitoring Grid support larger units

16 General DG standards Distributed resources (DR) standards IEEE 1547, Standard for Interconnecting Distributed Resources with Electric Power Systems and applies to DR less than 10 MW Generally applicable standards for the connection of electric equipment to the electric grid. IEEE in North America and IEC in Europe, cover harmonic interference and electrical impacts on the grid. Most commonly used are the IEEE 519 and the IEC series. Utility interconnection grid codes and regulations issued by regional grid operators as conditions for connecting DGs to the electric grid 16

17 Operational requirements larger installations Based in part on conventional generation (synchronous) may apply to DGs connected to the distribution grid Voltage regulation may be enabled Frequency regulation may be required Low voltage ride through (LVRT) may be required Power curtailment and external tripping control may be required Control of rate of change of active power ramp rates Other features typically required for large wind farms (> 100 MW, transmission connected), may be required for farms > 5-25 MW control of active power on demand reactive power on demand inertial response for short term frequency support Power System Stabilization functions (PSS) special function 17

18 DG protection issues general considerations Operational requirements Distribution system must be protected from influences caused by DG during faults and abnormal operating conditions DG must be protected from faults within DG and from faults and abnormal operating conditions caused by distribution circuits Specific considerations Impact of different DG technologies on short circuit contribution and voltage support under faults induction generators, synchronous generators, static power converters (inverters) Impact of power flow directionality (reversal) on existing distribution system protection Instantaneous reclosing following temporary faults Utility breaker reclosing before DG has disconnected may lead to outof-phase switching avoided by disconnecting the DG during the autoreclosing dead time (as low as 0.2 s)

19 Protection system role and requirements Role to detect and isolate only the faulty section of a system so that to maintain the security and the stability of the system Abnormal conditions include effect of short circuits, overfrequency, overvoltages, unbalanced currents, over/under frequency, etc. Protection system requirements rated adequately selective will respond only to adverse events within their zones of protection dependable will operate when required secure will not operate when not required Faults seen by the DG Short circuits on the feeder Loss of mains feeder opening and islanding 19

20 Protection functions of a DG interconnection ~ S PCC -HV bus T1 PCC -LV bus cb1 cb2 Line1 cb4 Line2 Line3 cb7 cb TL L1 T2 R7 cb5 L3 T3 R7 cb8 DG1 L2 L4 DG2 - PCC HV side PCC LV side DG LV side Distance Automatic recloser Frequency (over and under frequency) Pilot differential Fuses Voltage (over and under voltage) Phase directional overcurrent Voltage (over and under voltage) Overcurrent (instantaneous and delayed) Ground directional overcurrent Overcurrent (instantaneous) Loss of mains (islanding) Automatic recloser Underfrequency Synchronization Undervoltage Phase directional overcurrent Loss of earth (grounding) Overvoltage Ground directional overcurrent Neutral overcurrent Transformer differential Negative sequence (voltage, current) Directional overcurrent Reverse power flow Zero sequence Generator (loss of excitation, differential) Distance relay 20

21 DG islanding detection requirements Unintentional islanding defined as DG continuing to energize part of distribution system when connection(s) with area-eps are severed (also referred to as loss of mains ) IEEE the DG shall cease to energize the Area EPS circuit to which it is connected prior to reclosure by the Area EPS Repercussions of an island remaining energized include: Personnel safety at risk Poor power quality within the energized island Possibility of damage to connected equipment within the island, including DG (due to voltage and frequency variations) Utility grid codes may allow islanded operation during major outages may help restore service in distribution system 21

22 Islanding detection techniques passive Passive approaches Frequency relays (Under/Over-frequency) - use of the active power mismatch between island load and DG production levels Voltage relays (Under/Over Voltage) - based on voltage variations occurring during islanding, resulting from reactive power mismatch ROCOF relays (Rate Of Change Of Frequency resulting from real power mismatch in the case an island is created Reactive power rate of change resulting from reactive power mismatch in the case an island is created Other approaches Active protection based on difference in area-eps response at DG site when islanded; injection of signature signals at specific intervals Communication-based protection using a communication link between DG and area EPS (usually at the substation level) to convey info on loss of mains (and possibly activate a transfer-trip) 22

23 Alternative approach intelligent relays Alternative (intelligent) proposed approach passive, using only measured signals (current, voltage and derived signals) Use of a multivariate approach to develop a data base of islanding patterns Use of data mining to extract features from the running of a large number of operating conditions (normal) and contingencies (faults) Use of extracted features to develop decision trees that define relay settings 23

24 DG variables monitored multivariable approach 24

25 Feature extraction methodology Data Mining a hierarchical procedure that has the ability to identify the most critical DG variables for islanding pattern detection, or protection handles Decision Trees define decision nodes; every decision node uses different DG variables to proceed with decision making on identifying the islanding events Training data set islanding (contingencies) and non-islanding events Time dependent decision trees generated extracted at different time steps up to the maximum time considered/allowable Choice of decision tree for relay setting (best) based on Dependability (ability to detect an islanding event as such) and Security (ability to identify a non-islanding event as such) indices 25

26 Performance requirements islanding detection Requirements - defining maximum permissible islanding detection time (typically 0.5 to 2 s) Performance indices Dependability and Security indices Speed of response, or detection time Existence of non detection zones Constraints accounting for Interconnection Protection response times (reclosers) detection of islanding and tripping before utility attempts reclosing (out of phase reclosing may be damageable) Nature of relay and impact on performance requirements short circuit detection needs to be faster that islanding detection allows additional to refine the decision tree 26

27 Real Time Simulator set up basic relay testing Distribution system Part 1 Distribution system Part 2 Islanding relay 27

28 Decision trees typical results 28

29 Comparative performance relay settings Protective Device Setting Time delay Intelligent Decision Tree 100 ms Under Frequency 59.7 Hz 100 ms Over Frequency 60.5 Hz 100 ms ROCOF 0.1,0.25,0.5 Hz/s 0ms, 50ms 29

30 Dependability indices comparative evaluation 30

31 Security indices comparative evaluation 31

32 Non detection zones comparative evaluation 32

33 Feasibility and performance of intelligent relays The proposed data mining approach is capable of Identifying the DG variables that capture the signature of islanding events, in any given time interval Recommending variables and thresholds for protection relay setting The islanding intelligent relay Operates within prescribed time requirements (or faster) Can be configured for delayed operation possible Dependability and security indices typical better than existing passive techniques Offers improved performance, including smaller non detection zones Can be configured for different types of DG (rotating and power converters based), multiple DG systems and mixed DG type systems Can also be used for short circuit detection (including high impedance faults) and other types of faults 33

34 Impact of DG technology on protection design DG operation dependent upon the type of generator used Rotating converters: synchronous and induction generators Static power converter interfaces (inverter based): wind turbine (Type 4), solar power converters Mixed: doubly-fed induction generators (wind turbine, Type 3) Impact of the type of generator connected to the grid on protection design Short circuit level typically lower in inverter based systems (1-2 pu) Transients fully controlled in inverter based systems, dependent on controller settings Speed of response of real and reactive power injection typically much faster in inverter based systems Real and reactive power capability and control independent control in inverter based systems 34

35 DER integration opportunities in microgrids DER integration into distribution systems As individual systems, either generation or storage, connected to a feeder or in a substation Integrated into a self managed system, or microgrid Aggregated to form a Virtual Power Plant Microgrid definition a distribution system featuring Sufficient local generation to allow operation in islanded mode A number of distributed generators and storage systems, including generation based on renewable energy resources A local energy management system A single connection to the electric power system, with possibility of islanded operation The controllers required to allow connection and disconnection and interaction with the main 35

36 Microgrid types and uses Microgrid deployment drivers general and current Increasing the resiliency and reliability of critical infrastructure and specific entities, in the context of exceptional events (storms) reducing dependence on central generation and the transmission grid Facilitating the integrating renewable energy resources managing variability locally Taking advantage of available local energy resources renewables and fossil fuels (shale gas) Reducing greenhouse gases and reliance on fossil fuels costs Types, applications and loads Military bases embedded or remote Large self managed entities university campuses, prisons Industrial and commercial installations Communities managing storage and generation locally 36

37 Isolated/autonomous grids applying DER Solar Photovoltaics PCS Isolated Microgrid Wind Wind generator(s) Diesel plant Battery storage Distributed Energy Resources ESS Grid Interface Dump load Community loads Synchronous generator Conventional Generation 37

38 Benefits of storage and demand response In conjunction with renewable DG Reducing power variations in variable and intermittent generation Ability to provide voltage support and voltage regulation Enabling operation of DG at peak power and efficiency Power quality voltage sag and flicker mitigation Possibility of islanded operation microgrid operation Distribution system benefits Ability to dispatch/store energy and manage peak demand Reduced line loading managing line congestion Frequency regulation, black start, reactive power Ability to provide other ancillary services Ability to perform arbitrage on electricity prices market context 38

39 Electrical storage technologies Source: Fraunhofer UMSIGHT 39

40 Demand response characteristics Available loads Electric hot water heaters thermal storage Other curtailable loads on critical Electric vehicle battery storage systems Features of loads Dispersed low power, large numbers are required Availability short duty cycles Controllability usually only in curtailment, possibly as additional laod Duration of service limited curtailment 40

41 Storage vs demand response interchangeable? Demand response Benefits: instantaneous response Drawbacks: unavailability, discrete control, requires a large number of loads (stochastic behavior) Others: no power quality issues, but discrete steps Operational: energy restoration time management Implementation, hardware: minimal Electrical storage Benefits: fully controllable, can inject energy into the system Drawbacks, implementation: complex, requires power electronic converters, life expectancy, maintenance Other: losses (standby), energy efficiency Operational: recharging management 41

42 Distributed energy reources scenarios 2020 Scenario 1 Low DG penetration (<10 %), connection mostly to the MV grid business as usual Reduction of impact on existing grid power quality (flicker, voltage variation) Source of power (MW) limited contribution to voltage and frequency regulation Islanding required in case of loss of mains Scenario 2 Increase in DER penetration (> 20 %?), connection mostly to the MV grid individual or in microgrids Integration into the generation dispatch need for monitoring and forecasting production (wind and solar) Participation in ancillary services voltage and frequency regulation Requirements to remain connected for temporary loss of mains low voltage ride through 42

43 Distributed energy resources scenarios 2020 Scenario 3 Increase in the penetration of DER, with connection to the MV grid and the low voltage grid PV panels, smaller units, controllable loads, including electric vehicles For MV connections, same considerations as for Scenario 2 For low voltage connections (residential, commercial), with a large number of units, a number of outstanding questions Integration in generation dispatch included? Participation in ancillary services frequency/voltage regulation? Role of smart grids in managing a large penetration Financial consideration generation (feed-in tariffs), ancillary services impacts on the grid power quality (voltage rise), distribution system loading 43