Abstract

This paper presents the modelling and dynamic analysis of a Virtual Synchronous Generator (VSG) operating under three representative load models: constant impedance (Z), constant power load (CPL), and composite ZIP (constant impedance, constant current, and constant power) loads. The VSG control strategy enables voltage-source converters to emulate the inertial behavior of synchronous machines. However, load characteristics strongly affect the stability of such systems, and CPLs can be particularly destabilizing because of their negative incremental impedance. This study provides a theoretical and simulation-based analysis of VSG performance under Z-, CPL, and ZIP load conditions. A swing-equation-based control model is linearized to obtain a reduced-order small-signal stability model. The incremental impedance properties of the load types are evaluated analytically, showing that CPL behavior reduces effective damping and can destabilize the system. The resulting analytical stability condition provides a practical basis for selecting virtual inertia and damping parameters. Practical DC-side energy storage and current-limiting constraints associated with inertia emulation are also discussed. The analysis is supported by simulation studies that quantify the influence of load dynamics on frequency stability and transient response. In contrast to current research, this paper offers a single comparative framework in which all load types are analyzed under the same operating conditions and derives analytical stability conditions that inform the selection of virtual inertia and damping parameters.

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