Research on a Micro-Grid Frequency Modulation Strategy Based on Optimal Utilization of Air Conditioners
With the proportion of air conditioners increasing gradually, they can provide a certain amount of frequency-controlled reserves for a micro-grid. Optimizing utilization of air conditioners and considering load response characteristics and customer comfort, the frequency adjustment model is a quadratic function model between the trigger temperature of the air conditioner compressor, and frequency variation is provided, which can be used to regulate the trigger temperature of the air conditioner
... the air conditioner when the micro-grid frequency rises and falls. This frequency adjustment model combines a primary frequency modulation method and a secondary frequency modulation method of the energy storage system, in order to optimize the frequency of a micro-grid. The simulation results show that the frequency modulation strategy for air conditioners can effectively improve the frequency modulation ability of air conditioners and frequency modulation effects of a micro-grid in coordination with an energy storage system. Energies 2016, 9, 1085 2 of 12 and its feasibility is verified. In [7-9], considering customer comfort, a variable participation degree control strategy for thermostatically controlled loads is proposed which participates in micro-grid frequency regulation through controlling thermostatically controlled loads. At present, the relevant research mainly focuses on verifying thermostatically controlled loads participate in primary frequency regulation of micro-grid in coordination with energy storage system (ESS), which can improve the system frequency effect. However, the improvement of the frequency regulation capability of thermostatically controlled loads and the further optimization of the frequency modulation effect are ignored. In this paper, taking air conditioners as an example, the frequency regulation method for controllable air conditioners is proposed to regulate the frequency of the micro-grid in coordination with the primary frequency modulation method of the battery. Considering load response characteristics, this air conditioner frequency regulation method is achieved by establishing a quadratic function model between the air conditioning compressor commitment trigger temperature and system frequency variation. Moreover, the air conditioner frequency modulation strategy considers two factors: the optimal utilization for the cluster air conditioner and customer comfort. When micro-grid frequency decreases, the trigger temperature of air conditioning increases based on its set value. When micro-grid frequency increases, the trigger temperature of air conditioning decreases based on its set value. Finally, the air conditioner frequency regulation method can further optimize frequency modulation results in coordination with the energy storage system's secondary frequency modulation method. Isolated Micro-Grid System and Its Control Structure This isolated micro-grid system consists of a photovoltaic system, a wind generator, a battery, uncontrollable loads and air conditioners as a representative of thermostatically controlled loads which can participate in micro-grid frequency regulation. Thermostatically controlled loads can provide limited frequency regulation capacity because they are restricted by temperature limits and start and stop interval times. Therefore, thermostatically controlled loads and the energy storage system are used to optimize the system frequency jointly based on the micro-grid hierarchical control structure in this paper. The hierarchical control configuration of micro-grid is shown in Figure 1 .