Connecting the Home Grid to the Public Grid: Field Demonstration of Virtual Synchronous Machines

Abstract

Power systems are going through a paradigm shift. More and more distributed energy resources (DERs) and loads are being connected to power systems, mostly through power electronic converters. These power electronic converters can be controlled as virtual synchronous machines (VSMs), leading to a unified interface for grid integration. As a result, all active players in a power system can take part in the regulation of system frequency and voltage in a synchronized and democratized (SYNDEM) manner, significantly simplifying system operation and improving grid stability, reliability, resiliency, security, and sustainability. This article presents a pilot smart home grid at the Llano River Field Station, Texas Tech University Center at Junction, that is built according to the SYNDEM grid architecture. The home grid consists of five DER units, including four 3-kW solar units and one 3-kW wind unit with built-in battery storage in each unit, and one energy bridge for grid connection. The energy bridge has two VSMs connected back-to-back with a common dc bus. All the units are equipped with a self-synchronized universal droop controller (SUDC) with many advanced functions, i.e., black-start, grid-forming, self-synchronization without a phase-locked-loop (PLL), voltage and frequency regulation, power sharing, and power quality control. The home grid can work with or without the public grid, with seamless mode change between grid-tied operation and islanded operation. All the functions are achieved without using a communication network; hence, potential cyberattacks can be avoided. Field operation results of the home grid are presented to demonstrate the autonomous operation of the system.