3.5 Examples of DER Grid Codes for Advanced Functions

3.5.4 PJM and Other ISOs Use of DER Frequency-Watt Function

PJM is a Regional Transmission Organization (RTO) that is part of the Eastern Interconnection grid operating an electric transmission system serving all or parts of Delaware, Illinois, Indiana, Kentucky, Maryland, Michigan, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia and the District of Columbia.

PJM has integrated many types of generators into their system, and has recently started to include DER systems as well. For instance, PJM is interested in using the fast responding frequency control capabilities of electric vehicle chargers and other DER systems (called the Frequency-Watt function). This autonomous Frequency-Watt function can respond to frequency variations in milliseconds. PJM recently devised a scheme to use two AGC signals to be compliant with FERC 755 (a ruling that requires RTOs and ISOs to compensate frequency regulation resources based on the actual service provided). A traditional AGC (Reg-A) signal is used for the slow responding generators and a dynamic (Reg-D) signal for the fast responders.   NYISO uses only one AGC but differentiates the compensation for fast and slow responders. 

Starting in 2011, Beacon Power operates a 20 MW flywheel farm in Stephentown, NY, which covers up to 30% of the ACE in NYISO with 10% of the capacity, clearly showing the benefit of the fast responder. Beacon was one of the companies that pushed FERC to come out with Order 755.  But the flywheels only last for 15 minutes so NYISO must manage the AGC to bring them to neutral within the 15 minutes.  Beacon has another 20 MW farm  hooked to the PJM Reg-D signal which reached full capacity in July 2014.  PJM is unique in lowering the minimum capacity to participate in regulation to only 100 kW.   This was driven in part because of their interest in the EVs. 

For small grids such as ERCOT, a small isolated utility on a real island or in Alaska, or an islanded microgrid, the use of autonomous Frequency-Watt by DER systems could perform most of the frequency regulation.  For any grids that have large amounts of PV and where there may be insufficient frequency response from droop generators in fossil fuel plants, the autonomous DER Frequency-Watt function may really be needed.

On larger grids such as the Eastern and Western Interconnection with many balancing areas, the choice of using DER systems for frequency control becomes more of a business and operating issue.  The AGC for a balancing area is derived from the Area Control Error (ACE) where NERC defines ACE as the difference between the actual and scheduled net interchange of the balancing area less a factor times the difference in actual versus scheduled frequency. In ERCOT and small grids, there are no interchange errors so the AGC is always proportional to frequency error.  But for the other balancing areas, it becomes more complex to figure out how to integrate the autonomous Frequency-Watt function.  As an example, it could be set to only operate during a high/low frequency ride-through event or other an emergency.  But it could also be used with large aggregations of DER systems to respond to frequency variations very rapidly so that frequency is smoothed out significantly. Then AGC frequency regulation would only be needed to deal with interchange errors.