Hierarchical Power Systems Control : Its Value in a Changing Industry

Deregulation is causing dramatic change in the power industry but little is known about how power systems will function under competition. What are suitable performance objectives? What control designs are required and what economic techniques should be used? This detailed analysis attempts to answer these questions. The authors provide a modelling, analysis and systems control framework that makes it possible to relate distinctive features of the electric power industry to more conventional supply/demand processes in other industries. Some parts of the system can be distributed while other parts must remain co-ordinated. This authoritative and detailed study is highly topical and will be of interest to those working in the systems control area, especially in electrical power. It is also most relevant for industrial economists as well as academics in electrical power engineering.

1 Introduction: Basic Assumptions and Concepts.- 1.1 Importance of the envisioned control structures in a changing industry.- 1.2 System regulation issues affected by the vertical separation of the transmission grid from generation.- 1.3 Organization of this text.- 2 The Nested Hierarchy as a System Structure in a Changing Industry.- 2.1 Principles of existing horizontally structured electric power systems.- 2.2 Industry changes leading to the nested hierarchy structure.- 2.3 Examples of new industry arrangements as particular cases of the nested hierarchy structure.- 2.4 The need for new control structures.- 2.5 Can generation-based regulation be made price-competitive?.- 2.6 Relevance of dynamic problem formulation over mid- and long-term horizons.- 3 Performance Criteria Relevant to Operating Interconnected Electric Power Systems.- 3.1 Dynamics of system inputs to which the control responds.- 3.2 Time frames for present performance objectives.- 3.3 Modeling for systems control services in a changing industry.- 3.4 Performance criteria at the subsystem level.- 3.4.1 Static optimization objectives.- 3.4.2 Dynamic optimization objectives.- 3.5 Static optimization in an open access system.- 3.5.1 Some assumptions under which present optimal scheduling algorithms are designed at the system level.- 3.5.2 Generation cost minimization: Ideal technical efficiency.- 3.5.3 Basic operating cost of keeping the system together.- 3.5.4 Achievable technical efficiency in the regulated industry.- 3.5.5 Assumptions that do not hold in a deregulated industry.- 3.5.6 Need for relaxing the demand-related assumptions (2 and 4).- 3.5.7 Need to reconsider the performance objectives (assumptions 1–3).- 3.5.8 Hierarchical structures in a distributed industry.- 3.5.9 Achievable efficiency under open access-ISO market level.- 3.5.10 Achievable efficiency of competitive supply and demand.- 3.5.11 Achievable economic efficiency of generation-based systems control.- 3.5.12 Need for coordinated generation-based systems control in support of competitive markets.- 3.5.13 Optimal structure for operating and pricing electric power systems under open access.- 3.6 Static optimization of a horizontally structured system.- 3.7 Present criteria for mid- and long-term dynamic performance.- 3.7.1 Criteria for load frequency control (LFC)/ automatic generation control (AGC).- 3.7.2 Dynamic performance objectives over long-term horizons in a horizontally structured industry.- 3.7.3 Functional requirements for advanced LFC/AGC in a changing industry.- 3.7.4 Conceptual problems with meeting mid-term dynamic performance objectives by means of present AGC in a changing industry.- 3.7.5 Conceptual problems with meeting long-term performance objectives in a changing industry.- 3.8 Static performance criteria for reactive power/voltage support.- 3.8.1 Criteria for mid- and long-term voltage control (AVC) at a subsystem level.- 3.9 Summary.- 4 Structural Modeling and Control Design Using Interaction Variables.- 4.1 Structural modeling.- 4.1.1 Modeling issues.- 4.1.2 Modeling process.- 4.1.3 Local dynamics.- 4.1.4 Network constraints.- 4.1.5 Structural dynamic model.- 4.1.6 Control-induced time scale separation.- 4.2 Hierarchical control design.- 4.2.1 Controllability.- 4.2.2 Conventional secondary-level control.- 4.2.3 Improved secondary-level control.- 4.2.4 Quasi-static interaction variables.- 4.3 Tertiary level coordination.- 4.4 New tertiary-level aggregate model.- 4.5 Comparison of the proposed control structures to those used at present.- 4.6 Summary.- 5 Generation-Based Regulation of Real Power/Frequency.- 5.1 State of the art and potential problems of frequency regulation.- 5.2 New modeling.- 5.2.1 Local dynamics.- 5.2.2 Network coupling.- 5.2.3 Regional dynamics.- 5.3 Analysis.- 5.3.1 Network properties.- 5.3.2 Structural singularity.- 5.3.3 Inter-area dynamics.- 5.3.4 Computation of inter-area variables.- 5.3.5 Interpretation of inter-area variables.- 5.3.6 Comparisons with conventional models.- 5.3.7 An example.- 5.4 Model derivations.- 5.4.1 Quasi-static model.- 5.4.2 Generator power model.- 5.5 Control design.- 5.5.1 Regulating frequency at the secondary level.- 5.5.2 Automated regulation of tie-line flows at the tertiary level.- 5.6 Summary.- 6 Generation-Based Regulation of Reactive Power/Voltage.- 6.1 Modeling.- 6.1.1 Local dynamics.- 6.1.2 Network constraints.- 6.1.3 Structural dynamic model.- 6.2 Quasi-static voltage model.- 6.3 Quasi-static interaction variables.- 6.4 Voltage regulation.- 6.5 Regional voltage control.- 6.5.1 Conventional secondary-level control.- 6.5.2 Improved secondary-level control.- 6.5.3 The 9-bus example.- 6.6 Tertiary coordination.- 6.6.1 Performance criteria.- 6.7 New tertiary level-aggregate models.- 6.7.1 Centralized aggregate models.- 6.7.2 The 9-bus example.- 6.7.3 Fully centralized optimization.- 6.7.4 Fully decentralized optimization.- 6.7.5 Combined centralized/decentralized optimization.- 6.7.6 Simulations study of the French power network.- 6.7.7 IAVC.- 6.7.8 Control at the tertiary level.- 6.8 Summary.- 7 The Value of Generation-Based Regulation: Competition Versus Coordination.- 7.1 Relevant optimality questions for determining the value of control services.- 7.2 Control-dependent values of subsystems in a competitive environment.- 7.3 Systems control structure-related issues.- 7.4 Long-term stability of decentralized systems control services.- 7.5 Achievable optimality as a function of the level of control co-ordination.- 7.6 Limitations of existing systems control in a competitive environment.- 7.7 Proposed approach to real-time systems control and its pricing in a competitive market.- 7.7.1 Basic steps for linking technical and pricing processes.- 7.7.2 Operations planning for the anticipated contract at the tertiary level.- 7.7.3 Estimating at the tertiary level the economic value of systems control services to the contract participants i1 and i2.- 7.7.4 Pricing for systems control at the ISO (tertiary) level to accommodate transaction i1 – i2.- 7.7.5 Contribution of individual components to the economic values at buses i1 and i2.- 7.7.6 Interpretation of our approach in terms of generalized localized marginal costs.- 7.7.7 From cost-based to value-based future pricing: incentives for high-quality systems control services.- 7.7.8 Revisiting the “poolco” structure.- 7.7.9 Revisiting the bilateral structure.- 7.8 Summary.- 8 Network-Based System Regulation.- 8.1 Engineering issues and opportunities in operating power transmission grids of the future.- 8.2 Recent changes affecting the transmission grid and their relation to the basic engineering issues.- 8.3 A brief review of the present principles for regulating a transmission grid and the power system.- 8.4 The basic planning problem on a transmission grid.- 8.5 Operating problems using mechanically switched reactive devices.- 8.6 Opportunities and problems presented by very fast regulation of the transmission grid: FACTS trends.- 8.7 Direct flow control via FACTS devices.- 8.7.1 All tie lines directly controlled.- 8.7.2 Only a subset of tie lines directly controlled.- 8.8 Summary.- 9 Conclusions.- 9.1 Summary of our approach to linking technical and economic processes under competition.- 9.2 Relevance of our proposed modeling and control framework.- 9.3 A Final Word.