Frequency Response of Motor Drive Loads in Microgrids

Abstract

Islanded microgrids require power reserve with fast primary-frequency response to operate stably. Primary-frequency response from generators or batteries incurs high costs. Alternatively, primary-frequency responsive loads reduce costs by allowing generators and batteries to operate more flexibly. In industrial microgrids, which comprise a significant portion of the microgrid market, electrical motors are a significant portion of the total load. However, existing demand response mechanisms are not suitable for motor loads in microgrids. In this article, a novel grid-supporting motor drive controller is proposed. This controller can be retrofitted to motor drive loads to provide fast primary-frequency response. A reduced-order analytical model of the motor drive load is derived, which can be directly integrated into system-wide frequency stability studies. Additionally, the primary-frequency response time of the motor drive is assessed, analytically and through EMT simulation, and is less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{100 ms}$</tex-math></inline-formula> , which is comparable to large battery energy storage systems. Finally, the behaviour of a microgrid system that includes two large motor drive loads is assessed during various large disturbances through EMT simulation.