Inertial Response and Inertia Emulation in DFIG and PMSG Wind Turbines: Emulating Inertia from a Supercapacitor-based Energy Storage System

Abstract

The increasing wind power penetration in electrical power systems results in a reduction of operative conventional power plants. These plants include synchronous generators directly connected to the grid. Facing a change in grid frequency, these generators inherently respond by varying their stored kinetic energy and their output power, which contributes to grid stability. Such a response is known as inertial response. Wind turbines (WTs) are mostly based on Doubly-Fed Induction Generator (DFIG) or Permanent Magnet Synchronous Generator (PMSG) machines. Their power electronics interface decouples the electromechanical behaviour of the generator from the power grid, making their inertial response null or insignificant. Therefore, in order not to weaken the frequency response of the power system, WTs must be able to react to frequency variations by changing their output power, i.e., emulating an inertial response. Common techniques for inertia emulation in WTs rely on pitch control and stored kinetic energy variation. This contribution proposes a strategy (applicable for both DFIG and PMSG) which uses the energy stored in a supercapacitor connected to the back-to-back converter DC link to emulate the inertial response. Its performance is compared by simulation with aforementioned common techniques, showing ability to remove certain limitations.

Inclusion of a Supercapacitor Energy Storage System in DFIG and Full-Converter PMSG Wind Turbines for Inertia Emulation

“…The main drawback of this IE technique is the modification of the turbine speed. The WT is forced away from the MPP, thereby reducing the captured the maximum available power [9]. Due to this reduction in the captured power during the recovery process, a secondary frequency drop (SFD) is likely to occur in a power grid with high wind penetration.…”