# Grid-Friendly Active Demand Strategy on Air Conditioning Class Load
## 6 Results and Discussion  
Figure 10 is the voltage waveform monitored from the DC bus of the energy storage interface and current waveform of the grid side. The left is voltage waveforms that happened at the time of nonlinear group load normal operation, LVRT beginning, LVRT process, and LVRT ends, respectively. The right is the three-phase power supply current waveform connected to the load that goes through this process. The voltage amplitude fluctuates at 540 V, and the maximum value does not exceed 541 V. The current amplitude is 5 A, and the phase of each current is two-thirds \(\pi\) radian apart. With reactive compensation, the system passes LVRT smoothly  
Limited by the speed of serial communication, to solve the problem of complete display on the upper computer of the data collected by the lower computer, some of the data collected by the lower computer are firstly stored in the Excel table, and then the upper computer reads them from Excel table and then displays them; thus, the abscissa in the figure is the change value of the second hand of the actual clock, which is displayed cyclically from 0 to 59 s. The abscissa in the left figure shows the time of the LVRT process, but the figure on the right does not reflect the true sinusoidal frequency. The true sinusoidal frequency is 50 Hz. The current date on the right is from the Excel table, where the real sampling period from the lower computer is 10 us, and the collected complete sine cycle contains 5000 data. However, the read data period of the host computer from the Excel table is 1.75 ms, and the sine waveform is continuously refreshed. The figure also shows that, when the grid is normally supplied local load, due to grid voltage fluctuation, there are continuous small fluctuations in the DC bus line of AC/DC/AC. When an LVRT occurs, the air conditioning loads are directly supplied by the energy storage inverter system, which is connected to the DC bus; obviously, the voltage fluctuation of the DC bus during the LVRT process is  
Figure 10: Waveforms of DC bus interface voltage and current on the grid side. smaller than before. Furthermore, the DC bus voltage drops no more than about 0.35 V. Once the LVRT process ends after 311 s, the original volatility state is reproduced. On the other hand, it can also be seen from the right current waves that, whether before or after LVRT, few harmonic components are produced. The simulation results also show that, during the period, the maximum current amplitude increases to 6 A, which is represented by the black and red lines, and then gradually recovers. Thus, it is verified that the filter design can actively suppress the harmonics caused by the nonlinear load to the grid. With energy storage participating in grid fault control, DC bus voltage can be maintained constant during the grid LVRT. Once the grid is restored, the load resumes normal grid power supply. Waveforms also show that harmonic suppression and LVRT prevention designed can play a good role in the grid fault. An active demand management function can also be implemented. In this manuscript, a new active demand-side management strategy is proposed for the air conditioning group load operation. A collaborative control scheme is given. The research focuses on harmonic active suppression and LVRT technology, reactive compensation, and simulation software is used to design the system. The summary is as follows. 1. By studying the characteristics of the group air conditioning operation, a hybrid model of the electronic circuit is determined with similar nonlinear characteristics as the load model. 2. By studying the influence characteristics of the air conditioning load model operation on the power grid, for the harmonic characteristics, the hybrid application of the double hysteresis APF and the PF are introduced to weaken the influence of harmonics on the grid actively. 3.