Model for Frequency Dynamics in an Islanded Microgrid and Primary Frequency Control Based on Disturbance Compensation

Amir Hussain,Wajiha Shireen

doi:10.1109/access.2021.3069769

Amir Hussain, Wajiha Shireen

Open Access

https://doi.org/10.1109/access.2021.3069769

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Abstract

Islanded microgrids have low inertia due to a large penetration of non-inertial inverter based power sources. In such systems, the primary frequency controller (PFC) faces the issue of a higher rate of change of frequency (RoCoF) and large peak frequency deviation in case of a sudden change in load or generation loss. The frequency control becomes more challenging as the variation in the frequency of different sources is not synchronized. This paper proposes a model for frequency dynamics in an islanded microgrid comprised of both inverter based distributed generators (DGs) and synchronous generators (SGs). The model is developed considering the asynchronous variation of frequency among the SGs. Based on the developed model, a novel disturbance compensation-based PFC is proposed. The PFC controls the reference power of a battery energy storage system (BESS) which is operated in grid-following mode and compensates for the power imbalance in the microgrid. The performance of the proposed model and the PFC is verified using Typhoon real-time hardware-in-the-loop simulation.

Highlights

During recent years, electric utilities and large power consumers have been showing increasing interest in microgrids for a variety of reasons such as control flexibility, energy security, cost, enhanced reliability, etc. [1]
The performance of the grid-following mode of operation for frequency control can be improved if the output power of distributed generators (DGs)/battery energy storage system (BESS) is controlled based on the power imbalance/disturbance during the transient
At the instant of disturbance, the rate of change of frequency (RoCoF) can be approximated, in terms of change in active power from BESS, as d ω −1 dt = J ωnom P. It can be observed from (5) that the initial RoCoF is inversely proportional to the virtual inertia which prevents the sudden change in frequency of the grid side converter

Summary

INTRODUCTION

Electric utilities and large power consumers have been showing increasing interest in microgrids for a variety of reasons such as control flexibility, energy security, cost, enhanced reliability, etc. [1]. The performance of the grid-following mode of operation for frequency control can be improved if the output power of DG/BESS is controlled based on the power imbalance/disturbance during the transient. This method requires a model of the microgrid that can estimate the disturbance immediately after its occurrence by observing the deviation in frequency. At the instant of disturbance, the RoCoF can be approximated, in terms of change in active power from BESS, as d ω −1 dt = J ωnom P (5) It can be observed from (5) that the initial RoCoF is inversely proportional to the virtual inertia which prevents the sudden change in frequency of the grid side converter. The frequency dynamics model derived is based on the asynchronous variation of rotor frequency among the SGs which has not been taken into consideration in models presented in literature so far

PROPOSED SYSTEM MODELING

PRIMARY FREQUENCY CONTROL

SIMULATION MODEL DESCRIPTION

VIII. CONCLUSION