Secondary (controllable) loads are often used in islanded (off-grid) diesel hybrid microgrids to dissipate excess power, maximize renewable energy utilization, ensure minimum diesel loading, and maintain system stability. Sustainable Power Systems’ ControlFreqTM Secondary Load Controller (SLC) precisely regulates power flow to an electric boiler, or resistive dump load, by rapidly switching an array of solid-state relays connected to individual boiler heating elements. The SLC incorporates an extremely fast frequency control loop, allowing it to minimize load fluctuations on the diesel generator, improving frequency regulation, increasing diesel efficiency, and prolonging the diesel generator’s life.
The SLC product line has recently been extended to include a Water Pumping Secondary Load Controller that controls a variable speed water pump, providing continuous real-time control of the water pumping electric load. In one application, the Water Pumping SLC may be used to match the load of a large irrigation pump to the fluctuating power output of a wind turbine, reducing the need for diesel backup or energy storage.