Research On The Frequency Control And Voltage Control Based On Time-elasticity Load

In order to avoiding excessive reliance on fossil fuels for power generation using renewable energy is an effective way to provide clean power supply.With the rapid development of power electronics technology,renewable energy integration to the grid is increasing.However,renewable energy is characteristic of inherent intermittency and randomness,and its integration to the grid brings challenges to the safe and stable economic operation.Using demand response to provide frequency/voltage stability control is an effective and feasible measure to ensure the stable operation of the system.Elastic power demand of load is analyzed in this pape.Time elasticity of load is an index of load characteristics,which indicates the selection margin of the load in the power consumption time.In other word,time elasticity of load is the relationship between the user power demand and the power consumption time.And the related factors about time elasticity of load under different time scales are established.Identification model of time elasticity of load is based on long time,short time and ultra-short time.Analytic hierarchy process is used to identify the magnitude of time elasticity of load.Typical industries or users are selected to verify the validity of identification model for time-elasticity load under different time scales.A control strategy for decentralized electric vehicles to participate in frequency regulation asynchronously and fairly is proposed.Electric al vehicle is a typical load with time elasticity,which can flexibly adjust the charging and dischargi ng power according to the operating state of the power system under the condition of satisfying the requirements of the users.Therefore,electrical vehicle is an ideal elastic load to participate in frequency regulation.This paper presents a strategy for decentralized electric vehicles to participate in frequency control fairly.In the absence of communication network or control center,decentralized electric vehicles can participate in frequency regulation in an orderly and coordinated manner.By setting the same participation parameters and frequency detection period,the same probability of participating in frequency regulation service for electric vehicle users with the same willingness can be guaranteed.Not only the fairness of compensation of electrical vehicle users can be ensured but also the overshoot phenomenon caused by the simultaneous response of electric vehicles can be effectively avoided in the control strategy.The effectiveness and feasibility of the control strategy are verified by the simulation results of IEEE 14-bus.An under frequency load shedding method considering power loss of power grid enterprises and user comfort is proposed.In the process of load shedding,power loss for power supply enterprises is rarely considered.In order to minimize the loss of power grid enterprises in the process of load shedding,a new under frequency load shedding control strategy that takes into account time elasticity of load and users' willing to pay is proposed in this paper.The priority of load shedding is determined according to the time elasticity of load and users' willing to pay,and is optimized by NondominatedSorting Genetic Algorithm II(NSGA-II)algorithm.Two different under frequency load shedding control strategies considering only the users' willing to pay or time elasticity of load and considering both coordinatedly are compared,and the decreased power consumption and the users' payment caused by load shedding are calculated.Comparing simulation results of different under frequency load shedding schemes,we can find that the power loss of enterprises and the users' decreased payment for load shedding cannot be optimized at the same time,and only the results of their coordinated optimization can be obtained.An under voltage load shedding strategy considering node voltage sensitivity and time-elasticity of load is proposed.Due to its special geographical location and weak power grid infrastructure,the power supply of island mainly relies on fuel oil transported from the external region to generate electricity,so the power supply is unstable and the price is high.However,there are abundant renewable energy resources in islands,utilizing local renewable energy is an effective way to solve island's energy supply.The development of microgrid provides a platform for the access of various distributed renewable energy sources on island.Establishing microgrid and utilizing the renewable energy in island have become an effective measure to solve the island's electricity supply.However,renewable energy sources are connected to the microgrid using power electronic devices,causing systems ' instantaneous inertia to become smaller,and voltage instability is likely to occur under disturbance.In this paper,an under voltage load shedding strategy with the integration of renewable energy to the grid is proposed.The time elasticity of load and the voltage sensitivity of node are considered to confirm the load shedding priority.The simulation results indicate that the system voltage is stabilized as soon as possible,and the safe and reliable operation of power networks in island are ensured,while improving the utilization of renewable energy.The effectiveness and feasibility of the under voltage load shedding strategy are verified under different scenarios.In this paper,the related researches on the utilization of renewable energy resources and the power quality control induced by the integration of renewable energy resoureces into the grid are carried out.The multi-time scale time elasticity identification model of load and the related strategies for typical time-elasticity load participating in power quality control are discussed.The research of this paper can provide a reference for safe and stable operation of power systems with the access of energy from renewable energy and stable and reliable power supply in island.