Research On Micro-Grid Frequency Modulation Strategy Based On Optimal Utilization Of Controlled Loads

Frequency is an important index to measure the power quality of power system,and it is also the key factor to maintain the stable operation of power system.Because of the fluctuation of the output power of renewable power generation,the power generation and power consumption of the micro-grid system is unbalanced.The frequency of the power grid will have different degrees of fluctuation and deviation relative to its rated value,which will cause great losses to the power users.In order to reduce the system frequency deviation,the traditional ways of regulating the frequency of power system mainly adjust the generator capacity and cut off the user loads to balance the capacity difference of power side and load side and realize the stability and control of system frequency.Compared with the traditional frequency modulation methods,the partial loads are the main research objects of the power system with frequency regulation because of their fast response characteristics,energy storage characteristics,high controllability and zero pollution.In this paper,a case study of using the air conditioning to participate in frequency modulation method is carried out.First of all,the structure and the operation control method of the micro-grid system and the control strategy of micro power inverters should be analyzed.In the micro-grid operation process,the controllable loads participate in the system operation,which will have a certain impact on the stable operation of micro-grid.Thus,to ensure the stability of the micro-grid system,it needs to use the suitable operation control structure of micro-grid.In addition,the battery has the function of the secondary frequency regulation by using the principle of frequency modulation of power system.Through numerical simulation,when micro-grid system is under various fault conditions,the secondary frequency modulation of battery has the influence on micro-grid which is analyzed.And the frequency modulation of battery can be applied to the frequency adjustment process of micro-grid with controllable loads.Secondly,when thermostatically controlled loads(the air conditioners)effectively participate in the process of the system frequency stability and control,the following works are needed to complete in order to make the micro-grid system frequency measurement be close to the system frequency rating:1、The working principle and the working characteristics of air conditioner should be analyzed,describe the mathematical model of air conditioning and design a control strategy of the air conditioning load to participate in the micro-grid frequency regulation process.2、In order to make the frequency deviation of the micro-grid system smaller,it is also necessary to set up a suitable frequency modulation model of the energy storage device.And thermostatically controlled loads and energy storage system will work together to complete the frequency modulation process of the micro-grid system.Finally,in order to verify that the thermostatically controlled loads:combining with energy storage device is effective on the system frequency stability and control,the process that thermostatically controlled loads and energy storage device participate in the system frequency regulation is simulated.Building the model of isolated micro-grid system,through the above simulation,the thermostatically controlled loads combining with the control strategy of energy storage device can reduce the system frequency deviation,which is verified.And the thermostatically controlled loads can replace a part of frequency modulation standby of the power system,and can play a buffer role in the process of system frequency fluctuation.