Thomas Kirk, senior applications engineer at OPAL-RT TECHNOLOGIES, explores Hardware-in-the-Loop (HIL), a new test technique for microgrids involving digital real-time simulation.
With the promise of improved efficiency and resiliency, and a reduced carbon footprint, the total capacity and spending on microgrids is projected to quintuple by 2028. From universities, hospitals, military bases, airports, and even single properties, microgrid projects range from complex retrofits of existing electrical infrastructure to modern greenfield designs. There is belief that we are in the midst of a reverse Copernican Revolution, where generation will be distributed away from the center to the grid’s edge. Microgrids will even import/export power from each other and help support the main grid. Electric utilities’ existing business models are under threat, and they have been forced to pay attention with some even seeing business opportunities.
By definition, a microgrid must be able to island itself and rely on its distributed energy resources (DERs). As the excellent feature article in June’s IEEE Power Electronics Magazine on AC microgrid control and management strategies notes, this “is not an easy task”, involving up to three levels of hierarchal control. At the “local” DER level, Primary Control is typically bundled per DER to maintain voltage and frequency stability, and reliability. Secondary Control, often associated with the term “microgrid controller”, acts on the entire microgrid to manage deviations in voltage frequency and amplitude to ensure power quality and reliability.
HIL will be used to create cleaner vehicles and supply chains, and increase their levels of connectivity to renewable resources and infrastructure.
Tertiary Control covers power import/export to the main grid and to other microgrids. Both Secondary and Tertiary Control Levels can also be implemented using central or distributed approaches with the latter offering potential redundancy and cost benefit. While the Tertiary level is mainly used currently to optimize import/export economics based on electricity and energy markets, it can also serve to improve power quality in the higher-level system. All three control levels serve critical operational or economical functions within the microgrid and are connected relying upon digital communication. Furthermore, while AC microgrids are currently most common, full or partial DC configurations offer certain advantages and are gaining interest.
Figure 1: Hardware-in-the-Loop (HIL), a test technique where real equipment and software is connected to a digital Real-Time Simulation of a microgrid so they function as if connected to the real thing. (Image: OPAL-RT TECHNOLOGIES)
With so much to consider, vendors, integrators and asset owners face challenges in the development, selection and investment of microgrid control and management systems. How can they assure functionality during key events like unintentional islanding without access to the final system? Digital simulation can be employed for this but lacks fidelity, as it does not include actual devices whose computer models, if supplied, are typically locked by vendors. Enter Hardware-in-the-Loop (HIL), a test technique where real equipment and software is connected to a digital real-time simulation of a microgrid, so they function as if connected to the real thing. As observed in the IEEE Standard for the Testing of Microgrid Controllers, HIL’s flexibility allows for “a level of data collection [that] can far exceed that which is required in the field.” Popular with vendors, utilities, and researchers, HIL setups are safe, reusable and relatively low-cost, allowing for improved quality of work and shorter project timelines. Figure 1 (above) depicts how a real-time simulation can be configured to do such testing on all three control levels. The workflow is straightforward; a user creates the model on their computer, compiles it to run in real-time and then loads it onto the simulator platform equipped with the digital, analog, serial and network inputs/outputs. The simulator can also emulate a number of digital communication protocol connections (e.g. Modbus TCP ), allowing for the incorporation of virtual devices and controllers for further flexibility and cost reduction.
Importantly, HIL drives innovation within the young sector. Take for example NREL’s Energy Systems Integration Facility (ESIF), whom offer state-of-the-art megawatt-scale HIL test capability to manufacturers and integrators, and used their facility for their own competitive procurement of a microgrid controller. The grueling 21-week process is meant to push participating vendors to cover their unique boundary cases while delivering an open and flexible controller for research. The lessons learned of such a project already prove invaluable to all participants and stakeholders in the field.
Around the same time, UC Irvine’s Advanced Power and Energy Program (APEP) was busy with the islanding of their 20MW-class campus using their own Generic Microgrid Controller (GMC). Through collaboration with Southern California Edison and partners ETAP and MelRok, APEP used their OPAL-RT platform for HIL testing of the GMC, culminating in February 2018 with the successful islanding of the campus. But APEP’s work in this area is not done. In their soon-to-be-built Horiba Institute for Mobility and Connectivity, HIL will be used to create cleaner vehicles and supply chains, and increase their levels of connectivity to renewable resources and infrastructure. And you can bet, that as they undergo this new challenge, microgrids are sure to play an important role.
Thomas Kirk is a senior applications engineer at, at OPAL-RT TECHNOLOGIES.
