# Research Needs for Realization of Zero-Carbon Power Grids with Selected Case Studies
## 3 Selected Case Studies and Numerical Results
### Balancing Service Provision by Energy Storage  
Real-Time Control and Analysis of Electrical Storage  
Apart from HVAC units, behind-the-meter electrical energy storage is a promising DR resource. For example, many residential and commercial buildings are equipped with wall-mounted batteries and EV charging stations. Using such batteries, buildings can provide ancillary services aiding supply-and-demand balancing in real time, thus mitigating the balancing reserve requirements imposed on dispatchable generator units. Electric batteries exhibit high energy densities and rapid dynamic responses, rendering them suitable for high-power cyclic operations. Battery life reduction is caused by deep discharge during driving, not by small swings in the SOC caused by direct load control (DLC) [66].  
The distribution of the DLC signal to individual EV batteries requires careful consideration; grid operators will encounter difficulties when simultaneously controlling a large number of EV batteries. A new type of building electrical system, and building- and EV-level controllers, are needed to achieve efficient distribution of DLC signals and hence reliable provision of ancillary services. In [48], an electrical system for a commercial building (Figure 13) coordinated the building-level controllers and the EV charging controllers. Thus, the building served as an intermediate aggregator between the grid operator and multiple EV owners and, consequently, operated as a large-scale stationary battery. This facilitated centralized and decentralized control of the EV batteries. Figure 14 shows a new FR strategy using a building's electrical system, wherein the EV batteries compensate for rapid load variations via DLC, reducing the frequency deviation and the required reserve capacity of synchronous generators [67]. In practice, SFC signals contain long-term variations in DC offset, motivating the design of high-order filters to remove that offset. The proposed FR strategy was implemented using a laboratory-scale micro  
Figure 12: (**a**) A flowchart for implementation of the proposed FVCs and (**b**) comparisons of \(V_{DC}\), \(V_{Lauf}\), \(Q_{DG}\), and \(P_{DC}\) (from top to bottom) between the new proposed VR strategy (Cases 1 and 2) and conventional VR strategies (Cases 3 and 4) for NR-aided load restoration.  
grid with a real DLC-enabled battery pack, as shown in Figure 13b. The laboratory-scale microgrid corresponds to the IEEE 34-node test feeder with the total capacity of 25 MVA; the detailed specifications of the test feeder were provided in [67]. Figure 15 shows the results of experimental case studies; the FR strategy using EV batteries maintained the real-time supply-and-demand balance more effectively than did a conventional strategy (with no battery) as the feedback controllers, battery capacities, and the maximum PV power generation varied.  
Figure 14: A block diagram of the ancillary service provision by buildings including EV batteries.  
Figure 13: (**a**) A schematic of a new electrical system inside a commercial building and (**b**) the experimental setup of an MG including a generator emulator, a battery pack, and a load emulator.