SEL Microgrid Control and Protection Solutions
Seamless Transitions Between Grid and Islanded Operation
All SEL microgrid systems are based on relays, so it is easy to make an SEL relay perform as a microgrid controller. However, it is impossible to make a microgrid controller act as a protective relay. For small microgrids with below 10 MW generation, sometimes all you need are relays for all microgrid control functions.
The plot shows the last 40 microgrid jobs performed by one of the SEL teams. SEL teams find that when microgrids are larger than 10 MW, centralized powerMAX® Power Management and Control System microgrid controller is a better solution.
All-Relay Microgrid Control System
This is an example of all-relay microgrid control system. SEL supplies an SEL-751 Feeder Protection Relay at the point of common coupling (PCC) and one at every distributed energy resource (DER). These relays intercommunicate with a daisy-chained Ethernet cable via IEC 61850 GOOSE. The PCC relay provides DNP3 summary data to the local SCADA or energy management system (EMS).
The PCC relay receives all the SCADA controls and dispatches them to the DER relays.The PCC relay provides the IEEE 2030.7 mandated transition functions, the IEEE 1547 mandated ride-through compliance, the IEEE 2030.8 data collection requirements, the A25 synchronization functions, and the decoupling/disconnection system that islands the microgrid via protection functions or the remote SCADA request.
The DER relays provide IEEE 2030.7 mandated dispatch functions; the IEEE 1547 mandated ride-through compliance; the IEEE 2030.8 data collection requirements; the load sharing, frequency, and voltage control systems; DER metering; and, of course, they protect the DER from damage as protective relays.
For larger, more complex power systems, the SEL powerMAX controller is employed. The powerMAX controller is a set of proprietary microgrid libraries running on a real-time automation controller (RTAC). To be a powerMAX project, the solution must be purchased from SEL Engineering Services (SEL ES) and follow strict quality control and testing processes.
The powerMAX controller(s) have the functions shown in the bubbles, which vary by customer needs. This central controller uses Ethernet, serial, or time-division multiplexing (TDM) SONET communications to the SEL relays, meters, I/O modules, and SEL-2240 Axion® modules distributed throughout a customer power system.
Lessons Learned From 15 Years of PowerMAX
- Physics are the same, big or small
- HIL testing simplifies commissioning
- Fast control systems prevent outages
- Reliable load balancing maintains stability
- Advanced controllers are superior to PID methods
- Seamless islanding requires protective relays at PCC
- Security-in-depth is mandatory
- Engineering is required