The Effects And Control Of Electric Vehicles And Air Conditioning Loads On Voltage Stability

The large-scale integration of Electric vehicles(EVs)and air conditioning loads(ACLs)is bound to affect the normal operation of power grid.It is of great significance to investigate the effects of EVs and ACLs on voltage stability of power system and control strategies.Based on the effects of EVs and ACLs on grid voltage stability,this paper has studied control strategies under poor grid voltage situation.Large-scale penetration of EVs and ACLs is bound to worsen the grid voltage situation.Based on the statistical model and electrical model of EVs and ACLs,different scenarios are set up in Nordic32 system to simulate and quantitatively analyze the effects of EVs and ACLs on static voltage stability,transient voltage stability and mid-long term voltage stability.On this basis,appropriate control strategies of the two type loads are analyzed.The optimal scheduling of EVs can effectively improve the voltage distribution of the system and avoid possible voltage emergency situations.This paper proposes an day ahead voltage optimization control model of EVs with considering EV charging demands,EV charging constraints,power output limits of generators,power flow equations,voltage limits of buses,line flow limits and N-1 security constraints.The bus voltage fluctuations and network power losses are considere d as multi-objective functions.To reduce the computational burden,lagrangian relaxation is introduced to handle time coupled constraints and benders decomposition is introduced to handle contingencies.Case studies are conducted on Nordic32 system to analyze the proposed model and solution methods.The results verify the proposed approaches.Under grid voltage poor situation,combined considering the traditional voltage stability coordination control strategy and the application background of the smart grid,this paper proposes a bi-layer cooperative generation-load voltage control strategy on basis of reactive voltage control based on hierarchical layered voltage control structure.The upper layer is the control center layer.The control variables are set as the generator active output and the flexible load adjustment of each node,and a cooperative generation-load voltage control model is established to ensure the system voltage stable while ensuring users' comfort.The lower layer is the load agent layer,and the main task is to control the flexible loads to implement the upper scheduling plan.The load agents and multi-agent structure is applied to control different types of flexible load and different types of ACLs,corresponding.The air conditioning agent economic dispatch model is used to assign load regulation of each agent.An optimal temperature control of fixed-frequency air conditionings(ACs)agent is proposed to track the control commands.The control strategies are simulated in Nordic32 system and the results verify the effectiveness of the proposed approaches.Under grid slight tight situation,load shedding is usually considered as one of the most effective methods to recover the voltage.This paper proposes an on-line distributed load shedding strategies for voltage collapse prevention based on precision load shedding system to make full use of the interruptible characteristics of electric vehicles and air conditioning loads.Firstly,improved voltage stability indicator and voltage aptitude are set as two types voltage stability evaluation indicators,which can early warn the system instability and determine the optimal load shedding time.Then,the grid is partitioned into several areas based on voltage control sensitivity to determine the control regions.Then,voltage recovery sensitivity of the load bus to the voltage stability alarm buses is analyzed in load shedding control master station,which can determine the optimal load shedding position and the regional load shedding optimal problem is formed.A piecewise linearization method is used to solve the problem.Finally,load shedding control center station collects optimal load shedding schemes of load shedding control master stations and performs load shedding amounts coordination.Case studies have been conducted on Nordic 32 system to verify the effectiveness of the proposed method.