| With the increasing interconnection of power grids,the operation of power systems has become more and more complex,and the reliable operation of power systems faces new challenges.During the operation of complex power systems,uncertainties including load fluctuations and random equipment failures will have significant impacts on the secure and reliable operation of power systems.Therefore,in order to enhance system operational reliability,operating reserves are usually adopted to ensure real-time balance between power generation and load requirement.Traditional operational reserves are usually provided by generating units.However,in the process of providing operating reserves,conventional generating units may suffer from stochastic failures,which will affect power outputs and then endanger the reliable operation of power systems.During actual operation of power systems,due to aging or degradation process,generating units may present intermediate states between "perfect functioning" and "complete failure".Therefore,this entails a need to propose a reliability analysis method for power systems which considers multi-state characteristics.In addition,traditional reliability analysis methods usually focus on systems where the mean time to failure follows exponential distributions.This limits the application of traditional reliability analysis techniques.It is necessary to develop an efficiently operational reliability analysis approach for multi-state systems where the mean time to failure follows arbitrary distributions including commonly used exponential distributions.In the meantime,the rapid developments of smart grid technologies and information and communication technologies have enabled demand side resources,for example,air conditioners,electric vehicles,to provide operating reserves to power systems like traditional generating units,and actively participate in the framework of smart grid operation.Therefore,from the perspective of the location of these operating reserves,reserves can be divided into reserve in generation side and reserve in demand side.However,when flexible loads in demand side provides reserve through demand response strategies such as load shifting and load curtailment,it may affect chronological characteristics of flexible loads.Furthermore,multiple uncertainties,such as equipment failures,environmental conditions,operating conditions,etc.,will affect reserve capactiy of flexible loads in participating the operation of smart grids,which in turn affects system reliability.Therefore,it is essential to study the reliability of smart grids with reserve in demand side under multiple uncertainties,which lay a solid foundation for realizing the bilateral interaction between reserves in demand side and power grids.In this paper,for power systems with reserves from different sides,in the generation side,the system reliability analysis method for multi-state generation systems,activation sequence optimization of generating units considering operational reliability,and operational reliability analysis of power generation systems considering reserve sharing are proposed to accurately evaluate operational reliability of multi-state power generation systems;in the demand side,considering chronological characteristics and uncertainties including stochastic failures of information and communication systems,the reliability equivalent model for reserves in demand side is supposed to be analyzed.Finally,comprehensively considering reserves from both generation side and demand side,the operational reliability analysis framework for power systems is proposed.By identifying the risk level of power systems under influences of multiple uncertainties,the proposed framework can provide a scientific basis for the reliable and secure operation of smart grids.The main work is organized as follows.(1)The operational reliability of multi-state power generation systems with reserves is studied in Chapter 2.Considering different reliability characteristics before and after generating units providing reserves,a novel reliability analysis method based on multi-state decision diagram is proposed.The proposed technique can handle arbitrary distributions of state transition processes for multi-state generating units,including commonly used exponential distributions.(2)Activation sequence optimization of generating units considering operational reliability of power generation systems is proposed in Chapter 3.Based on the research in Chapter 2,an automatic calculation algorithm for operational reliability analysis of power generation systems based on multi-state decision diagram method through diagram construction,simplification and decomposition is developed.In addition,system operational reliability is optimized by exploring the optimal activation sequence of generating units.(3)The reliability analysis method of power generation systems considering reseeve sharing mechanism is proposed in Chapter 4.Based on the research in Chapter 2 and Chapter 3,an operational reliability analysis method utilizing multi-valued decision diagram technique for power generation systems is developed.A mathematical model for power generation system with reseeve sharing is first established.In this model,the reserve capacity of different subsystems can be transmitted through transmission lines.Then,based on the proposed model,a reliability analysis method based on multi-valued decision diagram is proposed.The method can realize time-varying reliability of power generation systems by calculating occurrence probabilities of reliable paths in the multi-valued decision diagram,which provides an effective and technical approach for solving the reliability evaluation of power generation systems with reserve sharing.(4)A reliability equivalent model for reserve in demand side under multiple uncertainties is proposed in Chapter 5.The influence of chronological characteristics of flexible loads considering shifting and curtailment is analyzed,where multi-state load model considering demand response strategies is proposed.Then,the multi-state model of uncertainties including consumers',participation level,random failures of information and communication systems,and different load types are established.The reliability equivalent model for reserve in demand side is developed for comprehensively incorporating both chronological characteristics and uncertainties.The proposed reliability equivalent model can lay a foundation for reliability analysis of power systems with reserve in demand side.(5)A reliability analysis method for power systems with both reserves in generation side and demand side is developed in Chapter 6.On the basis of Chapter 5,comprehensively co-ordinating multi-state power generation systems in Chapter 2,3,and 4,an optimal dispatch model for power systems considering reserves from both sides is formulated based on optimal power flow for minimizing system operating cost.After solving the optimization problem,load shedding can be obtained for evaluating system reliability indices based on Monte Carlo simulation techniques. |
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