Research On Power System Stability Considering Thermostatically Controlled Load

Dynamic load characteristics have great impact on the power system stability.However, in our country the load model which used in the stability calculation aremostly motor load or static load model, does not consider thermostatically controlledload. Thermostatically controlled load is a load which is controlled by thermostatcontroller, such as industrial heating, electric water heater and electric space heater,Many domestic and foreign industrial, commercial and residents living load with thistype of load characteristics. With the proportion of the thermostatically controlledload（Thload） increasing in the composite load, the influence to the power systemstability is more significant.This article dissertates the influence of the thermostatically controlled load’scharacteristic to the power system stability. First of all, the mathematical model, therunning mechanism and the physical property of the thermostatically controlled arediscussed. Base on the PSAT （Power System Analysis Toolbox） in MATLAB, Atypical example of a3-generator9-bus power system contain thermostaticallycontrolled load is given to analysis the influence to the power system stability. Thenthe results on single-machine infinite-bus system with thermostatically controlledload demonstrate the impact of the parameters of this load on the eigenvalues of thesystem. Simulation and analysis results show that compare with static load model,thermostatically controlled load has negative influence on power system smalldisturbance stability. The gain of proportional controller, ambient temperature,reference temperature, time constant of integral controller have much influence on thesmall disturbance stability. The gain of proportional controller, the gain of integralcontroller and time constant of integral controller have little influence on the smalldisturbance stability.Secondly, a typical example of a4-generator2-area interconnected power systemis given. The impact of the parameters of thermostatically controlled load on powersystem’s low-frequency oscillations was discussed and some valuable conclusions aredrawn: thermostatically controlled load mainly affects the range of oscillation mode,and have little impact on local low-frequency oscillation mode. When the receivingend contain thermostatically controlled load, the interval oscillation mode frequencywill be slightly lower, The sending end contain thermostatically controlled load can raise the interval oscillation mode frequency. The impact of the parameters ofthermostatically controlled load: When the receiving end contain thermostaticallycontrolled load, the damping ratio increase with the increasing of K_P、ΔT and candecrease with the increasing of T₁.When the sending end contain thermostaticallycontrolled load, the damping ratio increase with the increasing of T₁and candecrease with the increasing of K_P、ΔT. Other parameters have little influence to thefrequency and the damping ratio.Thirdly, a typical example of distribution network contain thermostaticallycontrolled load was built to make transients simulation. Then the results onsingle-machine infinite-bus system with thermostatically controlled load demonstratethe impact of the parameters of this load on the transient voltage stability of thesystem. The results show that: the thermostatically controlled have an adverse effecton the system transient voltage stability compared with the ZIP load. When thethermostatically controlled access different kinds of network nodes, the further theinfinite system, the smaller the impact on system voltage stability. When theparameters in the credible range. The gain of proportional controller, ambienttemperature, reference temperature, time constant of integral controller have muchinfluence on the transient voltage stability. The gain of proportional controller, thegain of integral controller and time constant of integral controller have little influenceon the transient voltage stability. Because the thermostatically controlled load haveslow dynamic response. So in the range of electromechanical transient time, theinfluence of the thermostatically controlled to the power system transient voltagestability is very limited.