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Enabling DERs and More: ComEd’s Practice on DERMS Implementation

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Junhui Zhao's picture
Principal Quantitative Engineer , ComEd
  • Member since 2022
  • 1 items added with 2,480 views
  • Jun 29, 2022

This item is part of the DER and Management Systems - June 2022 SPECIAL ISSUE, click here for more

Written by: Junhui Zhao, Belen Hernandez, Lee Luis, and Christopher Gubala

Along with the proliferation of distributed energy resources (DER), distribution networks are challenged to improve their hosting capacity. One example is the Mendota-Dixon Network lies within ComEd’s west portion of the service territory. It is a unique area of the distribution grid with operational characteristics not common in the system. This 34kV sub-transmission network consists of two substations with 138kV sources, three distinct wind farms dispatchable by PJM, and a normally open 34kV tie with Ameren. Due to this network lying within a large, vastly open area of northern Illinois, there is great interest in installing DERs in this area. However, the yield of the high penetration of DER on this network could cause reverse power flow or even overloading on the substation transformer. Traditionally, for DER to connect to this network, an enormous scope of update work is required, which may include miles of high voltage distribution line extension and station work, which could add up to millions of dollars.

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Figure 1. One line diagram of the distribution system

To accommodate the request of DER integration and manage the reverse power flow, ComEd deployed its first Distributed Energy Resource Management System (DERMS). DERMS is a management system that combines software and field hardware to better optimize the grid due to increased presence of DERs, such as solar, wind generation, and battery storage. DERMS provides forecasting, monitoring, and coordinated control of DERs on the system. It monitors transformer loading, DER output, system conditions, and will send signals to control DERs if the triggering criteria is met. With DERMS, DERs would be able to connect onto the network without having to perform the traditional scope of work.

We have been actively deploying the DERMS from aspects of software, hardware, and communication. As the brain of DERMS, the software part defines how to interface with important stakeholders, including SCADA system, the front-end communications/data acquisition with DER customers, user interface, historical information storage and reporting, maintenance (display/database management), and future expansions. To implement coordination beyond a few devices, we utilized a reliable low-latency, high-bandwidth fiber communication system to allow each device to follow a particular control signal. Furthermore, we need to securely extend our SCADA network to the DER’s smart inverter. The team determined to have an enhanced interconnection and add a remote terminal unit (RTU). With the RTU at the PV site, it is able to either curtail PV generation by DERMS or turn on/off the DER by operation control center (OCC) in emergencies.

Figure 2. DERMS overview

DERMS utilizes a rule-based pre-defined logic to sequentially curtail DERs participating in the program. The control strategy is shown as in the following diagram.

Figure 3. DERMS control strategy

Once a reverse power flow in exceedance of 40MVA is detected at the Mendota station transformer, the DERMS software triggers a curtailment strategy to analyze the three interconnections’ sites output. Once triggered, the software records the respective contribution of individual DERs using real-time power flow analysis.

An active power set point is then calculated based on the curtailment needed and is rounded up to 250kW blocks before sent to each of the DER sites in a pre-defined tiered approach. The curtailment priority order is based on last-in-first-out (LIFO) structure, where the latest site to complete the interconnection application is the first site to be curtailed. However, if communication is lost between a DER site and the DERMS platform, this site is skipped in the curtailment logic and the site point of interconnection is opened per contractual agreement with ComEd. Once the event that triggered the curtailment is over, DERMS releases all the sites from curtailment after a dead band of 15 minutes based on pre-defined release strategy, and the 15-minute average is reset to continue monitoring for future events.

To quantify and assess the performance of DERMS, a metrics and validation (M&V) framework was developed. The framework consists of key performance indicators (KPIs), the evaluation process, and a tool developed for the implementation of the strategy. The M&V framework helps users understand control events that take place during the time when DERMS actively managed the output of DERs, providing both an individual perspective of each event and an aggregated view of events over the whole analysis period. For any event, the DERMS monitors and calculates the reverse power flow of the substation, curtailment/release of DER generation, and management success rate to study and evaluate the system’s performance. Especially we track and quantify the following items as part of the M&V plan:

  1. Loading level of substation transformer. The transformer loading is an analog value and can trigger DERMS to manage the output of PVs if the backfeed of the transformer exceeds predefined threshold. When these events occur, it is important to analyze whether DERMS performed appropriately to avoid the transformer overloading.
  2. Control analysis, by DER location. Exceedance events of the transformer triggers the generation curtailment of one or more solar farms. The control analysis could indicate if the curtailment events and quantities follow the control algorithm.
  3. DERMS performance. The DERMS success rate is defined to evaluate whether DERMS worked as designed during the backfeed exceedance events or control events. Operations are considered successful either the control occurs and the reverse power flow is reduced/relieved or the reverse power flow limit is exceeded while PVs are fully curtailed.

DERMS has been running in ComEd’s system for more than fourteen months since it went live on April 01, 2021, with first PV customer. Now we have three integrated solar farms totally 6MW are managed by the DERMS. The statistics shows that, to avoid the overfeeding of the substation, the DERMS has only curtailed around 0.18% of the total PV generation, which demonstrates the implementation DERMS increases DER hosting capacity with little impact on renewable generation.

Managing the DERs is only the beginning. Additionally, the DERMS shows great potentials as a platform to consolidate cutting-edge technologies to benefit the grid, and ComEd has developed a DERMS roadmap plan to integrate weather stations for DER and load forecasting, facilitate voltage management, manage energy storage, etc. ComEd is leveraging new technologies, skills, and information to increase clean energy penetration and enhance the resilience of the grid and communities it services.

Matt Chester's picture
Matt Chester on Jun 29, 2022

DERMS has been running in ComEd’s system for more than fourteen months since it went live on April 01, 2021, with first PV customer. Now we have three integrated solar farms totally 6MW are managed by the DERMS. The statistics shows that, to avoid the overfeeding of the substation, the DERMS has only curtailed around 0.18% of the total PV generation, which demonstrates the implementation DERMS increases DER hosting capacity with little impact on renewable generation.

Has this been deemed a success enough that we can expect further projects coming from ComEd like this in the future? 

Alan Ross's picture
Alan Ross on Jul 7, 2022

The advent of DERs brings with it a problem that many professionals seem to be unaware of, or aware but not concerned about, the fact that this new inverter based grid we are building on top of the old staid grid brings with it an increase in transients. This increase in transients, while may mean nothing for the residential customers, it will mean more power quality issues for industry. The impact of smaller but more frequent  transients will have a potentially significant impact on assets like transformers and cables particularly. Why? Because of their impact on solid insulation. 

 We must begin anticipating what that means for asset life cycle management, in a current environment where lead times are extending dramatically and increased aging of our current infrastructure will only exacerbate that situation. Keeping older assets viable and operating will require testing diligence and increased maintenance, but will also require operators to anticipate these issues and operate their systems accordingly. 

 What are your thoughts? I’d love to hear them. Alan

Junhui Zhao's picture
Thank Junhui for the Post!
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