## 5 Case Study and Simulation Results
### Simulation Cases
#### 5.2.3 Case 3  
Case 3 investigates the characteristics of the energy router-based HEMS in response to drastic variations of load consumptions and its functionality to collaborate with the power grid in suppressing the impact of load consumption fluctuations. The active load power increases to the peak value during 1.0-2.0 s, which corresponds to the situation around t3 in Figure 9. The active load power decreases drastically at 2.0 s. The simulation results are demonstrated in Figure 15.  
When the HEMS operates without the energy router, the PV power has to be fed into the power grid immediately when it is generated, then all the power for load consumptions will come from the grid. In that case, the power grid will suffer \"double impacts\" of RES power injections during daytime and peak loads in the evening, as shown in the profiles of measured daily PV generation and load consumptions in Figure 9.  
Figure 15b demonstrates the profiles of active power imported from the distribution network to the HEMS at the peak load moment of t3. The two curves show the power injections under the situations with and without energy router, when the load demand varies drastically. When the HEMS operates with the energy router, the self-energy storage system is in charging state during day time  
Figure 15: Simulation results of energy router in case 3: (**a**) Load consumptions; (**b**) The active power imported from the distribution network with or without energy router; (**c**) Total charging or discharging power of the self-energy storage system; (**d**) DC bus voltage; (**e**) AC bus phase voltage; (**f**) AC bus frequency.  
when PV output exceeds the load demand. When load peak comes in the evening, as shown in case 3, most part of the load variation is \"damped\" by the self-energy storage system. Therefore, the profile of power imported from the grid is quite smooth, comparing with the situation without the energy router.  
Figure 15d-f demonstrate the profiles of the DC bus voltage, AC bus voltage and frequency during the process of load variation. As the \"energy pool\" of the HEMS, the DC bus voltage fluctuates a little when the load demands change abruptly, while the AC bus voltage and frequency are smooth and not disturbed by the load variations during the whole process, owe thanks to the power compensation from the self-energy storage system. Although the energy router does not facilitate autonomous load shifting, the self-energy storage system has been successful in \"energy shifting\" by keeping surplus solar power stored during day time and feeding it back in support of the power grid during load peak time in the evening. The AC bus voltage and frequency maintain stable, which means the load variations within the HEMS does not have negative effects on the power grid since the HEMS is in connection with the grid at this moment. Therefore, we can conclude that if all the residential energy prosumers could handle the problem of RES generation and load variation like the presented energy router-based HEMS does, the peak load burden to the power grid would be alleviated considerably.