Abstract
This paper proposes detailed and practical guidance on applying model-based design (MBD) for voltage and frequency stability assessments, control tuning and verification of off-grid hybrid power plants (HPPs) comprising both grid-forming and grid-feeding inverter units and synchronous generation. First, the requirement specifications are defined by means of system, functional and model requirements. Secondly, a modular approach for state-space modelling of the distributed energy resources (DERs) is presented. Flexible merging of subsystems by properly defining input and output vectors is highlighted to describe the dynamics of the HPP during various operating states. Eigenvalue (EV) and participation factor (PF) analyses demonstrate the necessity of assessing small-signal stability over a wide range of operational scenarios. A sensitivity analysis shows the impact of relevant system parameters on critical EVs and enables one to finally design and tune the central HPP controller (HPPC). The rapid control prototyping and control verification stages are accomplished by means of discrete-time domain models being used in both off-line simulation studies and real-time hardware-in-the-loop (RT-HIL) testing. The outcome of this paper is targeted at off-grid HPP operators seeking to achieve a proof-of-concept on stable voltage and frequency regulation. Nonetheless, the overall methodology is applicable to on-grid HPPs, too.
Highlights
Off-grid electricity systems have attracted significant attention in emerging and frontier markets in order to conduct rural and island electrification and to supply remote industrial sites [1,2,3]
The novelty of this paper is to propose a model-based design (MBD) approach that includes all necessary building blocks to achieve stable voltage and frequency regulation in off-grid hybrid power plants (HPPs); i.e., the required set of models; a systematic and complete stability assessment; a design and tuning method of a hierarchical control system consisting of central HPP controller (HPPC) and distributed energy resources (DERs) controllers; and final verification and validation of the control system
DERs will leave steady-state errors in voltage and frequency which need to be compensated by secondary control actions of the central HPPC
Summary
Off-grid electricity systems have attracted significant attention in emerging and frontier markets in order to conduct rural and island electrification and to supply remote industrial sites (e.g., mining areas) [1,2,3]. The novelty of this paper is to propose a model-based design (MBD) approach that includes all necessary building blocks to achieve stable voltage and frequency regulation in off-grid HPPs; i.e., the required set of models; a systematic and complete stability assessment; a design and tuning method of a hierarchical control system consisting of central HPP controller (HPPC) and DER controllers; and final verification and validation of the control system. In off-grid on kW-scale either kW-scale or MW-scale and with modular expansion of the production subsystem
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