Distributed Generation Operation for Distribution System Volt/Var Control
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This document discusses DG participation in distribution system volt/var control. It proposes an effective methodology for multi-objective variable power factor operation of DGs for distribution system volt/var control during normal and emergency situations. The document outlines electric distribution systems, distributed generation resources, volt/var control in distribution systems with DGs, and DG participation in volt/var control. It reviews literature on DG operating at constant and variable power factors for volt/var control.
Distributed Generation Operation for Distribution System Volt/Var Control
- 1. DG participation in DS control 1 / 62
- 2. DG participation in DS control DG Operation for Distribution System Volt/Var Control N. Daratha guided by Prof. J.D. Sharma and Prof. B. Das Department of Electrical Engineering IIT Roorkee PhD Seminar Course 2 / 62
- 3. DG participation in DS control Proposition There is a need for an effective methodology of multi-objective variable-power-factor distributed generation operation for distribution system volt/var control during normal and emergency situation. 3 / 62
- 4. DG participation in DS control Outline Electric Distribution System Distributed Generation Volt/Var Control In Distribution System With DGs DG Participation in Volt/Var Control 4 / 62
- 5. DG participation in DS control Electric Distribution System Electric Power System Distribution System 5 / 62
- 6. DG participation in DS control Electric Distribution System Elements of Distribution Systems Excluding DG, .... All DS must have feeders and transformer with On-load Tap Changer. Most of them have shunt capacitors and/or shunt reactor fewer of them have SVC (static Var compensator) even fewer of them have D-STATCOM. 6 / 62
- 7. DG participation in DS control Electric Distribution System We Want Many Objectives A distribution system must have good voltage regulation be energy efficient have wide stability margin support transmission system reactive power need of course, maximize overall profit. However, achieving all of them at the same time is NOT possible. 7 / 62
- 8. DG participation in DS control Electric Distribution System Feeders: Minimum Losses = Minimum Voltage Drop Feeders bring electricity to consumers. A feeder power loss is minimum when when load is pure resistive. A feeder voltage drop is minimum when load capacitive reactive power equals feeders requirement. 8 / 62
- 9. DG participation in DS control Electric Distribution System Control Devices in Distribution Systems For effective, secure, and safe operation of DS, utility control: Switches Voltage regulators (OLTC, SC, SR) Distributed Generators Energy Storages 9 / 62
- 10. DG participation in DS control Distributed Generation Distributed Generation (DG) definition, altenative names a distributed generation (DG) is a small generation connected to distribution network IEEE Standard Dictionary Terms : Electric generation facilities connected to an Area EPS (Electric Power System) through a PCC (Point of Common Copling); a subset of DR (Distributed Resources). alternative names: embedded generation, dispersed generation 10 / 62
- 11. DG participation in DS control Distributed Generation Distributed Generation (DG) International Energy Agency’s Definition 1 Distributed generation is generating plant serving a customer on-site or providing support to a distribution network, connected to the grid at distribution-level voltages. Dispersed generation is distributed generation plus wind power and other generation, either connected to a distribution network or completely independent of the grid. 1 Distributed Generation in Liberalised Electricity Markets, IEA, Paris, 2002 11 / 62
- 12. DG participation in DS control Distributed Generation DG Classifications DGs can be. . . renewable (wind,PV,hydro) or non renewable (diesel) dispatchable (diesel, micro/small hydro) or not-dispatchable (wind, PV) intermittent (PV, wind, ocean wave) or steady (diesel, hydro, fuel cell) grid-connected or isolated 12 / 62
- 13. DG participation in DS control Distributed Generation DG-to-Power Grid Interface DG Type Electric Machine Interface ICE SG directly IG directly Gas Turbines SG directly Micro-turbines PMSG rectifier+inverter or AC/AC converter Squirrel cage IG directly Wind DFIG rectifier+ inverter SG or PMSG rectifier + inverter Photovoltaic inverter Fuel cell inverter 2 2 ICE=Internal Combustion Engine; SG=Synchronous Generator; IG= Induction Generator; PMSG = Permanent Magnet SG; DFIG=Doubly Fed IG 13 / 62
- 14. DG participation in DS control Distributed Generation DG Impacts on Voltage Regulation Before Fault 14 / 62
- 15. DG participation in DS control Distributed Generation DG Impacts on Voltage Regulation After Fault 15 / 62
- 16. DG participation in DS control Distributed Generation DG May Not Participate in Voltage Regulation IEEE Standard 1547-2003: 4.1.1 Voltage regulation The DR shall not actively regulate the voltage at the PCC. The DR shall not cause the Area EPS service voltage at other Local EPSs to go outside the requirements of ANSI C84.1-1995, Range A. 16 / 62
- 17. DG participation in DS control Distributed Generation Some DGs Reactive Power Capability Interface that can control reactive power : synchronous machine 3 (hydro,diesel) voltage source converter (PV, DFIG4 , Ocean Energy) (a) Synchronous Generator (b) Doubly-Fed Induction Generator 3 J. Y. Jackson, “Interpretation and use of generator reactive capability diagrams”, Industry and General Applications, IEEE Transactions on, vol. IGA-7, no. 6, pp. 729 –732, nov. 1971 4 S. Engelhardt, I. Erlich, C. Feltes, J. Kretschmann, and F. Shewarega, “Reactive power capability of wind turbines based on doubly fed induction generators”, Energy Conversion, IEEE Transactions on, vol. 26, no. 1, pp. 364 –372, march 2011 17 / 62
- 18. DG participation in DS control Distributed Generation DGs Have Low Utilization Level PV depends on solar irradiance. Wind generator depends on wind speed. Both solar irradiation and wind speed is highly intermittent There is significant fraction of the time when DG works much below rated power. During those time, DGs can provide reactive power service. 18 / 62
- 19. DG participation in DS control Distributed Generation Distributed Reactive Power Generation Control for Voltage Rise Minimization in Distribution Network5 Prevent significant voltage rise because of DG presence. 2 ∗ X X 2 2RPG QG ≈ − − PG + 2 R2 + X 2 R2 + X 2 R + X2 Compared with constant power factor approach. Effective reactive power control with two consequences: increased stress on tap changers. increased feeder losses. Voltage become almost independent of DG real power generation. Voltage dependence on load is almost unchanged. 5 P.M.S. Carvalho, P.F. Correia, and L.A.F. Ferreira, “Distributed reactive power generation control for voltage rise mitigation in distribution networks”, Power Systems, IEEE Transactions on, vol. 23, no. 2, pp. 766 –772, may 2008 19 / 62
- 20. DG participation in DS control Distributed Generation Voltage Become Almost Independent of DG Real Power Generation 20 / 62
- 21. DG participation in DS control Distributed Generation Voltage Dependence on Load is Almost Unchanged 21 / 62
- 22. DG participation in DS control Distributed Generation Grid Interconnection of Renewable Energy Sources at Distribution Level with Power Improvement Features 6 Some other functions that can be provided by DGs: power transfer at unity power factor local reactive power support harmonic mitigation load balancing Those functions can be achieved simultaneously or individually no additional hardware is needed 6 M. Singh, V. Khadkikar, A. Chandra, and R.K. Varma, “Grid interconnection of renewable energy sources at the distribution level with power-quality improvement features”, Power Delivery, IEEE Transactions on, vol. 26, no. 1, pp. 307 –315, jan. 2011 22 / 62
- 23. DG participation in DS control Distributed Generation Observation I DG can cause voltage rise on the feeder to which it is connected. There is a method to mitigate the voltage rise variable power factor operation increased number of switching and losses. Current grid code do not allowed DG to control its output voltage. DGs is also potential to improve power quality. 23 / 62
- 24. DG participation in DS control Volt/Var Control In Distribution System With DGs Works in which DGs are in constant power factor mode. 24 / 62
- 25. DG participation in DS control Volt/Var Control In Distribution System With DGs Optimal Distribution Voltage Control and coordination with distributed generation 7 Minimize total losses and voltage deviation Control OLTC, Shunt Capacitor (SC), Shun Reactor (SR), Step Voltage Regulator (SVR), Static Voltage Controller (SVC) Optimization methods : Genetic Agorithm DGs = PVs with constant unity power factor. Centralized control 7 T. Senjyu, Y. Miyazato, A. Yona, N. Urasaki, and T. Funabashi, “Optimal distribution voltage control and coordination with distributed generation”, Power Delivery, IEEE Transactions on, vol. 23, no. 2, pp. 1236 –1242, 2008 25 / 62
- 26. DG participation in DS control Volt/Var Control In Distribution System With DGs Optimal Distribution Voltage Control and coordination with distributed generation Objective: min w1 |Vn,ref − Vn | + w2 Loss Contraints: voltage limits tap position limits (OLTC) Optimization methods : Genetic Agorithm 26 / 62
- 27. DG participation in DS control Volt/Var Control In Distribution System With DGs Optimal Distribution Voltage Control and coordination with distributed generation SVC Model 27 / 62
- 28. DG participation in DS control Volt/Var Control In Distribution System With DGs Optimal Distribution Voltage Control and coordination with distributed generation SVR Model 28 / 62
- 29. DG participation in DS control Volt/Var Control In Distribution System With DGs Works in Which DGs are in CONSTANT power factor mode 1 Alessandro Casavola, Giuseppe Franzè, Daniele Menniti, and Nicola Sorrentino, “Voltage regulation in distribution networks in the presence of distributed generation: A voltage set-point reconfiguration approach”, Electric Power Systems Research, vol. 81, no. 1, pp. 25 – 34, 2011 → OLTC only Joon-Ho Choi and Jae-Chul Kim, “Advanced voltage regulation method of power distribution systems interconnected with dispersed storage and generation systems”, Power Delivery, IEEE Transactions on, vol. 16, no. 2, pp. 329 –334, April 2001 → OLTC only 29 / 62
- 30. DG participation in DS control Volt/Var Control In Distribution System With DGs Works in Which DGs are in CONSTANT power factor mode 2 D. Viawan, F.A.; Karlsson, “Combined local and remote voltage and reactive power control in the presence of induction machine distributed generation”, IEEE Transactions on Power Systems, vol. 22, no. 4, pp. 2003–2012, 2007, cited By (since 1996) 10 → OLTC and SC Miyoung Kim, R. Hara, and H. Kita, “Design of the optimal ultc parameters in distribution system with distributed generations”, Power Systems, IEEE Transactions on, vol. 24, no. 1, pp. 297 –305, feb. 2009 → OLTC only all of them do not include SVC and D-STATCOM 30 / 62
- 31. DG participation in DS control Volt/Var Control In Distribution System With DGs Observation II: Constant Power Factor Operation Among paper considering DG constant power factor operation: most include OLTC and DG other also include SC only one include SVR and SVC none include D-STATCOM single objective mathematical programming 31 / 62
- 32. DG participation in DS control DG Participation in Volt/Var Control Works in which DGs are in variable power factor mode 32 / 62
- 33. DG participation in DS control DG Participation in Volt/Var Control Minimizing Reactive Power Support for Distributed Generation8 Choosing power factor of DGs and setting of OLTC Maximising DG reactive power generation Reducing transmission system burden Enhanced passive approach vs active approach Uses DG and OLTC only 8 L. F. Ochoa, A. Keane, and G. P. Harrison, “Minimizing the reactive support for distributed generation: Enhanced passive operation and smart distribution networks”, Power Systems, IEEE Transactions on, vol. PP, no. 99, pp. 1, 2011 33 / 62
- 34. DG participation in DS control DG Participation in Volt/Var Control Multiagent Dispatching Scheme for DGs for Voltage Support on Distribution Feeders9 Each generator control its output based on local measurements. Those measurements used to calculate sensitivity factors. Coordination between DGs through a Control Net Protocol (CNP) Reliable communication network Uses DG and OLTC only 9 M.E. Baran and I.M. El-Markabi, “A multiagent-based dispatching scheme for distributed generators for voltage support on distribution feeders”, Power Systems, IEEE Transactions on, vol. 22, no. 1, pp. 52 –59, feb. 2007 34 / 62
- 35. DG participation in DS control DG Participation in Volt/Var Control Options for Controls of Reactive Power by Distributed PV Generators 10 Local control of PV generators Local measurements were sufficient for voltage regulation Support the idea of Baran and Markabi (2007) Uses DG and OLTC only 10 K. Turitsyn, P. Sulc, S. Backhaus, and M. Chertkov, “Options for control of reactive power by distributed photovoltaic generators”, Proceedings of the IEEE, vol. 99, no. 6, pp. 1063 –1073, june 2011 35 / 62
- 36. DG participation in DS control DG Participation in Volt/Var Control Voltage and Reactive Power Control in Systems with Synchronous Machine-Based Distributed Generation11 Minimize total losses. Include OLTC and SC. DG regulate voltage at point of common connection. If SC is enough, DG participation does not reduce losses significantly. Excess reactive power can support transmission system (Ochoa, et. al. , 2011). 11 F.A. Viawan and D. Karlsson, “Voltage and reactive power control in systems with synchronous machine-based distributed generation”, Power Delivery, IEEE Transactions on, vol. 23, no. 2, pp. 1079 –1087, april 2008 36 / 62
- 37. DG participation in DS control DG Participation in Volt/Var Control Short-Term Schedulling and Control of Active Distribution Systems with High Penetration of Renewable Energy Resources12 a day-ahead scheduler + intra-day (15 minutes) scheduler. includes dispatchable and not-dispatchable DGs. a day-ahead scheduler is a forecaster of generator and energy storage. intraday scheduler minimize generation deviation define by the other scheduler. 12 A. Borghetti, M. Bosetti, S. Grillo, S. Massucco, C.A. Nucci, M. Paolone, and F. Silvestro, “Short-term scheduling and control of active distribution systems with high penetration of renewable resources”, Systems Journal, IEEE, vol. 4, no. 3, pp. 313 –322, sept. 2010 37 / 62
- 38. DG participation in DS control DG Participation in Volt/Var Control 38 / 62
- 39. DG participation in DS control DG Participation in Volt/Var Control The Day-Ahead Scheduler objective is minimal energy cost R N min cj,r ∆tPjr r =1 j=1 constraints: Electrical Load balance Storage units Power and energy limits Thermal load balance inputs: load forecast, generation forecast, energy cost, limits of generating units, initial status of storage units. 39 / 62
- 40. DG participation in DS control DG Participation in Volt/Var Control The Intra-day Scheduler Multiobjective: min αSP + βPloss + γSV ∆x minimal voltage deviation minimal generation deviation minimal network losses Input: 15-minutes ahead forecast, state estimation results output: control signal for OLTC, voltage regulators, DGs and energy storages controlled variable: active and reactive power generation and OLTC tap position 40 / 62
- 41. DG participation in DS control DG Participation in Volt/Var Control 41 / 62
- 42. DG participation in DS control DG Participation in Volt/Var Control What are missing? Further considerations are needed: switching seguence? transition cost? security? Optimum path? Reachability? Initial state Proposed Optimum State 42 / 62
- 43. DG participation in DS control DG Participation in Volt/Var Control Reducing Number of Switching: 1. Constraint Addition 43 / 62
- 44. DG participation in DS control DG Participation in Volt/Var Control Importance of Switching Reduction switching may initiate transients device has limited total number of switchings DG’s variable power factor mode increase OLTC’s switching numbers slow mechanical switch vs fast load change and intermitent renewables 44 / 62
- 45. DG participation in DS control DG Participation in Volt/Var Control Reactive Power and Voltage Control in Distribution System with Limited Switching Operation 13 Objective : min energy losses 23 min E = f (x1 (t), x2 (t), x3 (t)) t=0 x1 discrete variables: OLTCs and Capacitors x2 Q and V x3 P and θ 13 M.B. Liu, C.A. Canizares, and W. Huang, “Reactive power and voltage control in distribution systems with limited switching operations”, Power Systems, IEEE Transactions on, vol. 24, no. 2, pp. 889 –899, may 2009 45 / 62
- 46. DG participation in DS control DG Participation in Volt/Var Control Reactive Power and Voltage Control in Distribution System with Limited Switching Operation Constraints: power flow equations tap positions limits capacity limits additional constraints : Maximum Allowable daily switching operation (MADSON) 23 h(x1 (0), x1 (1), ..., x1 (23)) = |x1(t+1) − x1(t) | ≤ Sx1 Cx1 t=0 46 / 62
- 47. DG participation in DS control DG Participation in Volt/Var Control Reactive Power and Voltage Control in Distribution System with Limited Switching Operation Proposed optimization method: discrete variables are treated as continous variables inequality constraints are converted into equality constraints with help from slack variables x1(t) + su1(t) = x1(t)max x1(t) − su1(t) = x1(t)min x2(t) + su2(t) = x2(t)max x2(t) − su2(t) = x2(t)min h(x1(0) , x1(2) , ..., x1(23) ) = Sx1 Cx2 su1(t) , sl1(t) , su2(t) , sl1(t) ≥ 0 47 / 62
- 48. DG participation in DS control DG Participation in Volt/Var Control Reactive Power and Voltage Control in Distribution System with Limited Switching Operation Proposed optimization method: interior point method was used KKT are derived and solved with Newton-Raphson method. compared with Genetic Algorithm, BARON and DICOPT test cases: Baran and Wu 69-buses system and chinese 14-buses system the proposed method is faster than other methods. 48 / 62
- 49. DG participation in DS control DG Participation in Volt/Var Control 49 / 62
- 50. DG participation in DS control DG Participation in Volt/Var Control Alternative Approach: Rule-based Control 50 / 62
- 51. DG participation in DS control DG Participation in Volt/Var Control Reasons for Alternative Approach Our problem is NP-hard MINLP unless some simplification is assumed. Distribution system is large Slow voltage controller movement and changing load and generation profile minimum switching is favorable some switching action are mutually exclusive 51 / 62
- 52. DG participation in DS control DG Participation in Volt/Var Control Configurable, Hierarchical, Model-Based Control of Electrical Distribution Circuits14 objective : close and better operating state; minimize change of state preference-based multi objectives and constraints: voltage regulation Capacity constraint losses priority is adjustable control devices : SC, OLTC, SVR, DG single step (SS) : SC, DG (on-min-on) multi step (MS) : OLTC, DG (min - max discretized) 14 J. Hambrick and R. P. Broadwater, “Configurable, hierarchical, model-based control of electrical distribution circuits”, Power Systems, IEEE Transactions on, vol. PP, no. 99, pp. 1, 2010 52 / 62
- 53. DG participation in DS control DG Participation in Volt/Var Control CHMC Main Loop 53 / 62
- 54. DG participation in DS control DG Participation in Volt/Var Control CHMC Main Loop 54 / 62
- 55. DG participation in DS control DG Participation in Volt/Var Control Selection of New State If voltage deviation is smaller than before, accept this newer state. 55 / 62
- 56. DG participation in DS control DG Participation in Volt/Var Control Selection of New State 56 / 62
- 57. DG participation in DS control DG Participation in Volt/Var Control Selection of New State 57 / 62
- 58. DG participation in DS control DG Participation in Volt/Var Control Ways to Reduce Number of Switching Using previous methods, variable power factor DGs operation increase number of switching. There are to ways to reduce the number: MADSON constraint rule-based optimization 58 / 62
- 59. DG participation in DS control DG Participation in Volt/Var Control Observation III: Variable Power Factor Operation Among paper considering DG variable power factor operation: most include only OLTC and DG (one include DG) single-objective mathematical programming increased number of switching is expected 59 / 62
- 60. DG participation in DS control DG Participation in Volt/Var Control Observation IV: Possible Gaps for Future Research What is not available in literature is volt/var control strategy/method which: include a rather complete types of (potential) voltage regulator is multi-objective optimization plus higher information processing In addition, optimum switching sequence needed to reach the optimum state has not been well studied. 60 / 62
- 61. DG participation in DS control Summary Summary DGs reactive power capability is not fully utilised. Grid codes require constant-power factor operation. Most published research follow the grid codes. Some works consider the variable-power factor (VPF) operation. VPF operation increase number of switchings of voltage regulators two ways in limiting switching number: MADSON constraint and a rule-based approach 61 / 62
- 62. DG participation in DS control Summary Thank You Very Much DG Operation for Distribution System Volt/Var Control N. Daratha guided by Prof. J.D. Sharma and Prof. B. Das Department of Electrical Engineering IIT Roorkee PhD Seminar Course 62 / 62