Editorial: Protecting Electricity Grid Frequency with Increasing Distributed Energy Resources | New

NREL Network Analysts Wenbo Wang and Xin Fang Discuss Open Communication Networks with Rising Distributed Energy Resources

Xin Fang and Wenbo Wang are part of the Grid Planning and Analysis Center at the National Renewable Energy Laboratory (NREL). In this episode of NREL “Tell Me Something Grid” series, they share their thoughts on cyberphysical dynamics with increasing distributed energy resources.

Distributed Energy Resources (DER) with advanced controls can provide grid services such as frequency response. However, to do this, unlike conventional generators, DERs usually have to regularly exchange signals with distant control centers.

These open communication networks expose the network to communication delays, cyber threats, and other risks. As DERs are increasingly added to the network, it becomes more critical to understand how long it takes devices to communicate with control centers and the impacts on maintaining a stable frequency on the network.

At NREL, we help bridge the gap between electrical systems engineering and communication networks. This will be especially important with the anticipated proliferation of DERs as the United States aims for 100% clean electricity by 2035 and a net-zero carbon economy by 2050.

Over the past two years, we have studied the ability of DERs to provide frequency regulation services and, more importantly, what happens if their control algorithms do not account for communication variations. We test this question through advanced grid modeling and test cases to validate our methodology. This work is supported by the U.S. Department of Energy’s Advanced Power Grids Research and Development Program.

We find that, generally, the longer the communication delay between the device and the control center, the greater the risk of network instability, which underlines why it is extremely important to understand the transmission dynamics and to distribution with increasing DER.

Develop the right co-simulation model

To start studying this topic, we first had to develop the right model to simulate distribution and transmission dynamics with high DER deployment, which has not really been explored in depth.

The power output of DERs can potentially impact local voltage profiles, so it is important to consider local voltage in DER frequency regulation analysis to avoid problems in distribution networks. However, existing frequency dynamics simulation tools have been developed mainly for transmission system and cannot simulate distribution network dynamics with high DER penetrations.

Thus, at NREL, we have developed a new framework for DER frequency response analysis based on the open-source Hierarchical engine for large-scale infrastructure co-simulation (HELICS) Platform. HELICS simulates the behaviors of regional and interconnection-scale electrical systems by integrating the domains of transmission, distribution and communication.

The advantage of our new transmission and distribution dynamic (T&D) co-simulation platform is that DERs are modeled explicitly and accurately in the transmission and distribution simulators for frequency and voltage dynamics, respectively . This modeling gives us the insights we need to investigate how DERs can provide frequency response. More details on this T&D dynamic co-simulation model can be found in our article in IEEE Transactions on the Smart Grid.

Investigate the impact of communication delays

An important aspect of studying the DER frequency response is to understand the impact of DER communication delaysor what if something goes wrong.

Using our new co-simulation tool in the first phase of our research, we modeled dozens of very detailed large-scale scenarios with varying degrees of DER communication failures.

We used a synthetic distribution network as a test case, including 40 DERs at each load bus for a total of 19 load buses in the 39-bus IEEE system with 760 DERs. DER generation accounted for 20% of the loads at each load bus, and the DERs were evenly distributed.

Our results show that a delay of only four seconds causes system instability when using DER to provide secondary frequency control after the system loses a conventional generator. In open communication networks, if multiple interruptions occur, such as communication/routing delay, congestion, or high device response rate, the total delay is at least a few seconds. The longer the delay, the greater the risk of instability. If the design of the forward controls of the DER does not account for communication variations, the risk of instability is even greater, which again indicates why it is important to study the frequency response of the DER.

Electric Vehicle Case Study

In another phase of our research, we delved deeper into DER frequency response with a case study of the impacts of electric vehicles (EV) on power grid frequency regulation.

Battery-powered EVs have the capacity and flexibility to (1) provide fast frequency response, (2) help smooth out system frequency fluctuations, and (3) improve system frequency stability. However, vehicle-to-grid frequency regulation could also impact both the frequency response of the bulk power system and the voltage profiles of the local distribution network. We wanted to know how electric vehicles could support the network in the event of a communication failure.

To carry out this case study, we added a new dynamic model to our co-simulation tool to explicitly simulate the dynamics of EVs. We then modeled scenarios with different degrees of communication failures. We have found that grid-connected electric vehicles have great potential to restore system frequency, and they can restore it most quickly when activated to change from fully charged to fully discharged.

What is the next

These are just a few highlights from our recent analysis of power system operations with prevalent DERs, but we have much more research ahead of us. Communication networks and the electrical system are now fundamentally linked, but they have always been compartmentalised.

The future energy system is based on the communication network, and the communication network is also based on the energy system. We must work together across disciplines to co-plan operations and ensure the lights stay on in a low-carbon energy future.

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