Research On Control Method Of Aggregate Thermostatically Controlled Loads For Serving Power Grid Operation

The stability of power angle and frequency is the guarantee for the safe and reliable operation of the power system,which is closely related to the balance of power generation and consumption in the system.Traditionally,the system adopts the method of tracking load on the generation side to meet the power balance and stability,while the loads side is regarded as a passive physical terminal and is not fully integrated into the regulation system.When it is still difficult to maintain the stability of the system or it needs to pay an expensive price when the output of the generator set is deployed in the traditional manner,the current load shedding/electric abandonment will generate large socioeconomic costs.As load continues to rise,numbers of intermittent power sources are centrally connected to the system,and the proportion of large-capacity supercritical units in the system is increasing,the ability of generation side to flexibly dispatch is gradually weakening.With the development of social economy and the improvement of residents’ living standards,the proportion of flexible loads,such as central air-conditioning,water heaters,and some large industrial users,which is enable to respond quickly to dispatching instructions,has been increasing.Demand response is proposed as a means for loads to participate in the regulation of power system.The development of power-grid-load interactive operation makes it widely concerned that using the existing resources on the demand side to supplement the traditional generation scheduling to participate in the regulation of power system.In this paper,thermostatically controlled loads(TCL)represented by air conditioners,refrigerators,electric water heaters and etc.are taken as the main research object,and study the subject of thermostatically controlled loads participating in multi-objective regulation of power systems from two aspects of aggregate model construction and dispatch utilization strategies.Firstly,an improved heterogeneous TCL bilinear aggregation model is established.By analyzing the energy interaction process and load characteristics of the TCL,the shortcomings of the existing model are found,then based on the second-order equivalent thermodynamic parameter model of the indoor air and the indoor material,the existing bilinear aggregation model is extended to derive a heterogeneous TCL bilinear aggregate model;and optimize the cumulative error caused by the reduction of load transfer rate in the bilinear aggregate model,an improved heterogeneous TCL bilinear aggregate model is finally constructed,which improved the description accuracy of the aggregate model.Secondly,a multi-objective coordinated control strategy for TCL and generator excitation is proposed for the emergency demand response project.The mathematical model of the combined system of generator and TCL is established first,and then based on backstepping control,the coordinate control strategy is designed with multiple control targets such as system power angle,frequency,load node voltage and generator excitation.The research shows that,compared with the traditional PSS excitation control,participation of TCL can effectively improve the dynamic and static adjustment characteristics of the system in disturbances such as short circuit and power adjustment,and with the increase of the adjustable capacity of the TCL,the stability of the system can be further improved.The proposed multi-objective control strategy can be applied to emergency demand response projects in d emand side response.Finally,a distributed hierarchical multi-objective coordinated control strategy based on the virtual AGC model of the regional power grid with multiple machines and multiple load clusters is designed for the demand response auxiliary service project.The multiple units in the regional grid are first equivalent to a generator under the inertia center system,then multiple TCL aggregators are integrated into a virtual AGC unit,and a joint model of the equivalent generator and TCL is established.Then a distributed hierarchical multi-objective coordinated control strategy based on consistency control and backstepping control is constructed.The consistency control is applied at the virtual AGC unit level to balance the output of various load clusters,while the backstepping control is applied at load clusters level to control the loads to track their respective power quotas,which provide active power compensation assistance services to the power system,helping to maintain the stability of power angle and frequency when a large power mismatch occurs.The simulation of the above algorithm on an IEEE 3 machine 9-bus system shows that,the proposed control strategy is superior to traditional centralized and decentralized control in terms of robustness and computability.Based on the research work above,the optimization of the TCL aggregate model in this paper improves its accuracy,and the dispatch control strategies proposed for emergency demand response and auxiliary service broaden the application dimension of flexible loads as a control means to support the reliable and economic operation of the power system,which help fully develop and utilize controllable resources on demand side,and support the implementation of China’s strong smart grid and other energy strategies.