Research On Modeling And Control Strategy For Air Conditioning Loads To Participate In Demand Response In Power System

In recent years, China's installed capacity has grown rapidly, and the power supply is surplus. But as the population of the metropolis gathers constantly, power consumption in the city's core area continues to rise. With the access of renewable energy sources, their anti-peaking characteristics make the gap between peak load and valley load in power system further enlarged, and the contradiction between local supply and demand becomes more and more serious. The existence of these factors has brought risks to the stability of the power grid.On the other hand, in a summer peak load period, air conditioning loads accounts for a high proportion of the total loads. They are important demand response resources because of a certain heat storage capacity. A change in the operating status of an air conditioner (AC) in a small range will not noticeably affect the users' comfort level. What's more, the electricity reform document No. 9 clearly put forward to carry out demand side management and demand response.This thesis takes the above as an opportunity to carry out the research on modeling and control strategy for AC loads to participate in demand response in power system. The mechanism and influencing factors of the AC load are analyzed. The optimal dispatching scheme of the regional grid to reduce the AC load is established. Based on this scheme, the AC load is modeled on a second timescale and minute timescale respectively, and a closed-loop control strategy is designed. Besides, the hierarchical control architecture and effective control methods for large-scale AC loads are proposed. The modeling method and closed-loop control strategy can realize precise regulation of large-scale AC resources. So that they can not only participate in the peak shaving to ease the contradiction between power supply and demand, but also participate in the frequency regulation to reduce the frequency deviation and improve the system frequency stability. The specific work of this thesis can be summarized as follows:(1) The mechanism of control and modeling of AC loads to participate in the demand response is analyzed. The appropriate industry is selected to implement AC load control.Then the energy model of AC's components and the equivalent thermal parameter model of AC rooms are established. On this basis, the model of load shedding potential of the AC group is put forward The effects of urban microclimate, including heat island effect,cumulative effect and temperature- humidity effect are considered as important influence factors of AC loads. A comprehensive load reduction potential table for AC loads is established with the influence of urban microclimate from the indoor temperature, control duration, pre-cooling time and other angles.(2) Based on the mechanism of AC resources to participate in demand response and their maximum load shedding potential, the model of dispatching AC loads in the regional power grid is constructed, and the direct load control (DLC) method is adopted to reduce the load of ACs. Through the appropriate reduction of AC load, the distribution network reconfiguration and orderly electricity can be avoided, the equipment investment can be reduced, and the pressure of regional power grid dispatch can be eased. An improved Tabu search technique is proposed to solve the problem of network dispatch in distribution systems in order to reduce the resistive line losses and to eliminate the transmission congestion in lines under normal operating conditions. The optimal node solution is obtained to find the best location and reduction capacity of ACs for load control.(3) On the basis of the optimal load reduction scheme, a closed loop dynamic response model of AC loads on a minute timescale is proposed for peak reduction in power system.The thermodynamic model of ACs is used to study the aggregate power of a number of ACs that respond to the step signal of a temperature set point. The influence of the parameters of each AC in the group to the indoor temperature and the total load is analyzed, and a simplified control model based on the two order linear time invariant transfer function is derived. Then,the stability of the model and designs its Proportional-Integral-Differential controller based on the particle swarm optimization algorithm is also studied. Besides, the influence of urban microclimate on parameters of the transfer function model is considered. The case study simulates both scenarios of constant ambient temperature and changing ambient temperature to verify the proposed transfer function model and control strategy can closely track the reference peak load shifting curves. The study also demonstrates minimal changes in the indoor temperature and the users' comfort level.(4) In order to further tap the potential of air conditioning load to participate in demand response, a closed loop dynamic response model on a second timescale of AC loads to participate in the frequency modulation of power system is proposed. Full frequency sweep of central ACs is carried out by using sine sweep test method. And the obtained data were analyzed in the frequency domain. The least squares fitting algorithm is used to identify the transfer function parameters of the control model, and the continuous dynamic response control structure of closed loop feedback is proposed. This method breaks through the limitations of traditional way to switch the equipment on or off to adjust the frequency, by continuously adjusting the fan speed to make the AC loads to track the grid auxiliary service signal. In addition, the control model and control strategy for the large-scale central ACs to adjust the frequency of the power system directly are proposed. The power recovery rate of ACs and the secondary frequency adjustment factor are optimized by the genetic algorithm.(5) Based on the study of the above small-and-medium-sized AC resources to participate in the demand response, a hierarchical control architecture is proposed to deal with the demand response of large scale AC loads. The function of each layer and the mechanism of information exchange and cooperation among the layers are designed. The topology model of multi-agent and its communication network is established by using graph theory. It is concluded through the analysis that the demand side cost of the grid company is the quadratic function for the user's capacity of load shedding. A leader- follower consistency decentralized collaborative control algorithm based on the incremental cost of load shedding is proposed to realize the effective control of a large number of distributed AC load resources.