An emulator apparatus that emulates entities included in a microgrid is described herein. The emulator apparatus emulates a load with time-varying inductance/resistance or an energy storage device or combination of energy storage devices. The emulator apparatus is electrically coupled to a system or device that is desirably tested/maintained/designed. The emulator apparatus emulates a particular device, and response of the system of device to the emulated device is monitored for purposes of design, testing, or maintenance.