Abstract
This paper proposes a multi-variable robust control scheme for voltage regulation in a diesel-photovoltaic-supercapacitor hybrid power generation system operating in stand-alone mode. First, we study the influence of system parameters on the dynamic behavior of open-loop system measured outputs by means of a stability analysis method based on Monte Carlo simulation. Next, by applying $\mathcal {H}_{\infty }$ control theory, an $\mathcal {H}_{\infty }$ -based voltage controller is proposed to robustly force the voltage magnitude of a point of common coupling such as to satisfy design specifications. A cascaded two-level control architecture, where this controller acts as an upper control level and provides references to classical PI-based current tracking controllers placed on a lower level, is developed. A comprehensive methodology that casts the specific engineering demands of microgrid operation into an $\mathcal {H}_{\infty }$ control formalism is detailed. Effectiveness of the proposed voltage robust control strategy is validated via MATLAB®/Simulink® closed-loop time-domain simulations. Finally, we perform a sensitivity analysis of robust performance of the designed $\mathcal {H}_{\infty }$ controller in the presence of various load disturbances and model uncertainties through a series of closed-loop time-domain simulations carried out in MATLAB®/Simulink®.
Highlights
Given admissible variation ranges of MICROGRID CONTROLM ICROGRIDS (MGs) parameter values, we propose a stability analysis method with the aim of finding out a combination of these MG parameter values that allows to minimize the oscillation amplitude in ∆UP CC
We have studied the influence of system parameters on the dynamic behavior of open-loop system measured outputs by means of a stability analysis method based on Monte Carlo simulation
A voltage robust control design approach based on a cascaded two-level control structure – where classical PI-based current tracking controllers are placed on the low control level and receive references from an H∞-control-based upper level – has been developed in order to satisfy the required dynamic specifications
Summary
M ICROGRIDS (MGs) concept is gaining high momentum as a major, cost-effective solution to integrate distributed energy resources (DERs) into power networks [1]. The distinctive autonomous operational capability of MGs has brought in higher reliability measures in supplying power demands when the utility grid is not available. The stability and control issues of autonomous MGs are among the main challenges due to low inertia, uncertainties, and intermittent nature of DERs [2]. One critical control task in autonomous operation mode is the regulation of the network frequency and voltage magnitude. High-speed storage systems – e.g., lithium-ion batteries, flywheels or supercapacitors – have become necessary, leading to new grid configurations, for which more complex robust control structures are needed for dealing with multiple constraints such as unexpected disturbances and model uncertainties
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