Abstract

The displacement of rotational generation and the consequent reduction in system inertia is expected to have major stability and reliability impacts on modern power systems. Fast-frequency support strategies using energy storage systems (ESSs) can be deployed to maintain the inertial response of the system, but information regarding the inertial response of the system is critical for the effective implementation of such control strategies. In this paper, a moving horizon estimation (MHE)-based approach for online estimation of inertia constant of low inertia microgrids is presented. Based on the frequency measurements obtained in response to a non-intrusive excitation signal from an ESS, the inertia constant was estimated using local measurements from the ESS’s phase-locked loop. The proposed MHE formulation was first tested in a linearized power system model, followed by tests in a modified microgrid benchmark from Cordova, Alaska. Even under moderate measurement noise, the technique was able to estimate the inertia constant of the system well within ±20% of the true value. Estimates provided by the proposed method could be utilized for applications such as fast-frequency support, adaptive protection schemes, and planning and procurement of spinning reserves.

Highlights

  • The inertia of modern power systems is in continuous decline due to the increased utilization of renewable energy sources (RESs) displacing traditional rotational synchronous generation

  • We propose a real-time inertia estimation technique based on moving horizon estimation (MHE) for low-inertia microgrids that utilizes local frequency measurements from a phase locked loop (PLL) of an energy storage systems (ESSs)

  • The inertia constant of the system is set to 4 s and the damping constant to 1.5%

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Summary

INTRODUCTION

The inertia of modern power systems is in continuous decline due to the increased utilization of renewable energy sources (RESs) displacing traditional rotational synchronous generation. U. Tamrakar et al.: Real-Time Estimation of Microgrid Inertia and Damping Constant much like during the inertial response stage of a synchronous generator. Tamrakar et al.: Real-Time Estimation of Microgrid Inertia and Damping Constant much like during the inertial response stage of a synchronous generator When deploying such strategies, an energy reserve is required to emulate the inertial behavior [5], which could come in the form of energy storage systems (ESSs) and/or even curtailed operation of RESs [6]. Beneficial in traditional synchronous generation based power systems, offline estimation approaches are not suitable for real-time adaptive control systems/protection schemes as the information may arrive late. We propose a real-time inertia estimation technique based on moving horizon estimation (MHE) for low-inertia microgrids that utilizes local frequency measurements from a PLL of an ESS.

MODELING OF MICROGRID FREQUENCY DYNAMICS
MODELING OF THE FREQUENCY CONTROL LOOPS
CONCEPTS OF MOVING HORIZON ESTIMATION
FORMULATION OF MOVING HORIZON ESTIMATION
IMPLEMENTATION OF MOVING HORIZON INERTIA ESTIMATION
RESULTS AND ANALYSIS
ESTIMATION WITH GAUSSIAN NOISY MEASUREMENTS
EFFECT OF ESTIMATION TIME HORIZON ON PARAMETER ESTIMATES
ESTIMATION WITH NON-GAUSSIAN NOISY MEASUREMENTS

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