## 2 Energy Router-Based HEMS  
Figure 1 is the vision of the energy router-based HEMS in the future Energy Internet. The energy routers will serve as the \"energy hub\" between the energy subsystems (could be a house, an office or a charging station) and the distribution network, as well as the energy interfaces (both AC and DC) for all the DGs, energy storage system and loads within the home area energy network. The EMS of the energy router will schedule the energy prosumption within the home area energy network such that energy is distributed adequately among the loads, and redundant energy from the DGs could be stored by ESS or fed back into the distribution grid.  
Figure 2 shows the configuration of the energy router-based HEMS in detail, which features high quality bidirectional power conversion, standardized plug-and-play power interfaces, as well as local operational information collections and effective energy management strategies. The energy router is mainly composed of the following components: (1) the power electronics converters, including the DC/AC converter for bidirectional power flow between the AC and DC buses, and the power converters for energy transfer between the power sources and the DC bus; (2) the plug-and-play interfaces for all the DGs, ESS and loads; (3) the self-energy storage system consists of battery, supercapacitor and their power converters, which serves as the \"energy buffer\" of the HEMS; (4) the Static Transfer Switch (STS) used for grid connection; and (5) the EMS which consists of the communication module, intelligent control module, and HMI module.  
As shown in Figure 3, there are various topologies for the power electronic converters to accommodate different types of DGs and ESSs. A bidirectional DC/AC converter lies between the DC and AC buses. The plug-and-play power interfaces for DGs and loads can be classified into  
Figure 1: Architecture of the energy router-based HEMS.  
Figure 2: Configuration of energy router-based HEMS.  
unidirectional AC or DC interfaces for the DGs and loads, and bidirectional DC interfaces for the EV and ESS. Power metering modules are embedded in the plug-and-play power interfaces to monitor the operation status and power quality of the DGs, and upload these measurements to the intelligent control module. Besides, protection functionalities are also provided by the plug-and-play interface in case faults or failures may occur.  
Random and intermittent characteristics of the RESs will bring voltage fluctuations, frequency fluctuations and other power quality problems to the HEMS [13; 29; 30]. As the \"energy buffer\" within the energy router, the self-energy storage system can be used to maintain power balance for the whole system.  
The communication module provides various information access interfaces and supports multiple communication protocols. Wired communications such as Ethernet, power line carrier (PLC) and RS485, and wireless communications such as Wi-Fi, 4G and ZigBee, can be utilized to collect operational data such as voltage, current and frequency from the DGs, ESS, loads, power lines and the converters in real time, and can also be used for information interaction among the intelligent control module, HMI module and other energy routers.  
The intelligent control module is the \"brain\" of the energy router. It analyses the operational data collected from the DGs, ESS, loads, power lines and the converters, schedules the operation status of the converters such that energy is allocated adequately among the loads, and redundant energy from the DGs could be stored by ESS or fed back into the distribution grid.  
The HMI module enables the user to learn about the operation status of the HEMS, and provides the functionality for the user to run the power management process manually. Preventive maintenance and operation parameter setting for the energy router can also be performed remotely through the HMI.