Frequency Stability Support of a DFIG to Improve the Settling Frequency

Jae Ik Yoo,Jung-Wook Park,Eduard Muljadi,Kyu-Ho Kim,Yong Cheol Kang

doi:10.1109/access.2020.2969051

Abstract

To ensure the frequency stability of a power grid, the settling frequency following a frequency event should be stabilized within the maximum steady-state frequency deviation (SSFD) band. If the frequency is stabilized at a value beyond the maximum SSFD band for high penetrations of variable renewable energy, the frequency cannot be restored to the nominal frequency because automatic generation cannot be activated. This paper proposes a primary frequency control support scheme of a doubly-fed induction generator (DFIG) to improve the settling frequency following an event. In the proposed scheme, if the frequency following an event is stabilized at a value beyond the maximum SSFD band, to reduce the output power of synchronous generators, the output power of a DFIG is instantly increased by a constant and maintained until the frequency increases to within the maximum SSFD band. At the same time, the mechanical input power of the synchronous generators is maintained so that the difference between the mechanical input power and electrical output power of the synchronous generators increases the frequency to a value within the maximum SSFD band. The simulation results demonstrate that the proposed scheme can improve the settling frequency while avoiding additional system defense plans when the settling frequency is stabilized at a value beyond the maximum SSFD band.

Highlights

To ensure the stable operation of an electric power grid, the frequency should be maintained within a certain range following an event
When a frequency event occurs, kinetic energy is intrinsically released from the synchronous generators as an inertial response; the frequency keeps decreasing until the power imbalance between generation and load vanishes [1]
PRIMARY AND SECONDARY FREQUENCY CONTROL IN A POWER GRID This section briefly describes the basic principles of primary frequency control (PFC) and secondary frequency control (SFC) in a power grid to provide the theoretical background of the proposed PFC support scheme

Summary

INTRODUCTION

To ensure the stable operation of an electric power grid, the frequency should be maintained within a certain range following an event. For a power grid that has high penetrations of variable renewable energy (VRE) such as wind and solar energy, the frequency stability can be jeopardized if VRE maintains maximum power point tracking (MPPT) operation following an event [3]–[6] This is because fnadir and/or fset are lowered. For high penetrations of VRE, if the frequency is stabilized at a value beyond the maximum steady-state frequency deviation (SSFD) band, the frequency cannot be restored to f0 because AGC cannot be activated [16] In this case, to increase fset to a value that is more than fmssd , which is defined as f0 minus the maximum SSFD in this paper, additional system defense plans should be activated, such as quick-starting generators and interruptible loads [1], but these require additional operating costs. The efficacy of the proposed scheme is verified under various wind speeds and wind penetration levels in the IEEE 14-bus system based on an EMTP-RV simulator

PRIMARY AND SECONDARY FREQUENCY CONTROL IN A POWER GRID

CASE STUDIES

Findings

CONCLUSION