Operation Risk Control And Restoration Strategies For Power Systems

Modern electric power systems are operated with ever-increasing diversity.Under the social needs to reduce emission and pollution and to improve energy efficiency of the power system,the proportion of power generation from renewable energy sources is rising gradually,the connection between the power system with other energy systems has been increasingly intensive,and the demand difference and market participation of power consumers are enhanced significantly.In the meantime,the reliable and secure operation of the power system is challenged by complicated and varied risks,such as the increasing deployment of intermittent renewable energy sources and gas turbines.If handled improperly,there might be insufficient regulation and spinning reserve problem in the operation strategy which will further induce frequency fluctuations,thus giving rise to possible cascading failures,major outages and even blackouts.Similarly,transactive approaches can reflect the supply cost effectively,provide differentiated services to various energy needs competently,and provide the platform to facilitate the market participation of small size energy entities,whereas the significantly increased risk exposure to the market and other participants cannot be overlooked.Thus,a comprehensive control over the security and market risks as well as the safeguard of important loads could help reduce the occurrence and loss of unexpected outages,and optimized restoration strategies can accelerate the recovery of the power system and energy supply.Given this background,this dissertation investigates the decision-making theories and optimization methods in the pre-and post-fault operation,focusing on the operation risk control,the safeguard of important loads,and restoration strategies of the power system.Specifically,the main contents of this dissertation can be summarized as follows:1)Security risk control methods for power system operation based on well-being analysis(WBA).The various sources of the security risks and their influence on the modern power system are analyzed,taking the new energy subjects and structures in the system,as well as the couplings and connections with other energy systems into account.The state analysis method for a modern power system with complex couplings is studied,which is illustrated by a power system with increasing deployment of renewable energy sources and gas turbines(GT).The fast-responsive characteristics of GTs are first analyzed,and the definition and adaptation of WBA in a power system with increasing deployment of GTs are addressed.Then the equivalent reserve capacity of GTs is estimated,taking demand fluctuations,commitment plans and operation risks of GTs into account.The WBA on the power system with increasing deployment of GTs is conducted considering the generation charaterisctic and capacities of distributed generators and the uncertainties of system operation states.The effective means on power system security risk control in system operation are also explored and examined considering various penetration levels of GTs.2)Market risk analysis,evaluation and control from the uncertainties in price,demand and other energy markets.With the development of power industry restructuring,electricity retail markets are established and thousands of electricity retail companies are gradually built up and involved in electricity retail business.The various sources of market risks and their influence to the power system are analyzed based on the composition of the modern energy markets with different transactive methods and entities.Under the circumstance of the increasing deployment of the intermittent renewable energy sources,the financial risks from the coordinated gas-electricity operation are addressed,and the purchase portfolio of a retail electricity company are optimized considering the price and demand uncertainty.Hourly load demands and electricity prices are first represented with the corresponding vectors and their uncertainties are represented by interval numbers.In the meantime,the impacts of the time-of-use(TOU)retail electricity prices on the load shift and the company's market share are investigated.Then,an enhanced interval linear programming(EILP)model maximizing the company's overall daily profit is presented and solved analytically.The proposed method takes the demand and price uncertainties of a for-profit electricity retailer into account,and manages the market risks in the building of the energy purchase portfolio.3)Optimal siting of power emergency multi-point service provisions.The reasonable siting is very demanding for ensuring timely delivery of power emergency service resources,supply safeguard of important loads,and demand fulfillment of differentiated needs,hence reducing the outage costs of power supply.An optimization model is presented accordingly for the problem,with the minimization of the overall cost of power emergency service provisions as the objective and the permitted outage durations of all loads as constraints.The overall cost is composed of the annual construction and service cost of each service point,as well as power supply interruption costs of all important loads.Then,the well-established Floyd algorithm and the related graph theory are employed to solve the developed optimization model,and the optimal siting plan for the specific service area can be developed based on the security requirements of the electricity consumers.The proposed method can balance the security requirements and the emergency service cost of the power supply and provide a specific and sustainable siting plan for the service area.4)Strategy development and optimization of power system restoration based on portfolio optimization and graph theory.The safeguard of important loads are also included in the restoration process.An entropy weight decision-making theory based dynamic strategy for parallel restoration of generators and a path-oriented strategy for power system restoration are proposed based on the restoration process and system characteristics,respectively.On one hand,the optimal restoration strategy is developed with consideration of the whole process of generators' restoration.First,the system benefits of every restoration scheme are analyzed according to the status of the generators.Then,a mixed integer linear programming(MILP)model of dynamic optimization and decision making of parallel restoration of generators is built by using entropy weight-based theory,and the optimal combination of restoration schemes without power supply conflicts can be obtained.With the proposed model,the status information of every generator can be fully considered,and the power supply conflicts of the generators can be appropriately resolved.On the other hand,graph theory is applied to the network reconfiguration strategy decision and a path-oriented power system restoration strategy is proposed.The concept of a specified minimum spanning tree(SMST)is first introduced to describe the path-oriented restoration problems with power system constraints considered,and the modified Prim's algorithm is then adopted to generate the proposed SMST.The developed model and method can improve the efficieny by avoiding the inevitable iterations of the unit-oriented methods based on evolutionary algorithms,and take care of important loads as well.