Abstract
The concept of virtual synchronous machine (VSM) was proposed to deal with the shortcomings of low inertia and damping of traditional control strategies for power electronic converters. But what if all distributed energy resources and controllable loads in a microgrid adopt the VSM control strategy, and will it present better performance than conventional droop control-based microgrid (DMG)? In this paper, the VSM-based microgrid (VSMG) is analyzed. The small-signal modeling of the VSMG is studied at first. Then static stability and dynamic characteristics of the VSMG are analyzed and compared with the DMG in both frequency-domain and time-domain. With the growing scale of microgrids, their modeling and simulation are becoming significant computational burdens. Inspired by the participation factor analysis of the VSMG and the concept of coherency in power systems, the VSMG small-signal model is equivalent to a modified third-order synchronous generator (SG) model in this paper. The equivalencing involves gray-box system identification and is realized by estimating equivalent electrical parameters alternately and iteratively. The equivalent SG (EqSG) model is compared with three representative model order reduction methods to verify its effectiveness. Simulation results confirm the accuracy of the EqSG model substituting detailed VSMG model in time-domain simulations.
Highlights
With high penetration of distributed energy resources (DERs) and mass access of controllable loads, power systems are experiencing a paradigm shift from centralized and rotational generator-dominated systems to distributed and inverter-dominated systems [1]
EQUIVALENT synchronous generator (SG) MODEL OF THE VSM-based microgrid (VSMG) The participation factor analysis confirms that modes in group 1, which are low frequency oscillation modes with relatively large time constants and highly influencing the system stability, are mainly derived from states related to the SG and virtual synchronous machine (VSM) control loop
Since the equivalent model is effective under small disturbances, the linearized equivalent SG (EqSG) model is used in the equivalencing procedure, which can speed up the gray-box system identification
Summary
With high penetration of distributed energy resources (DERs) and mass access of controllable loads, power systems are experiencing a paradigm shift from centralized and rotational generator-dominated systems to distributed and inverter-dominated systems [1]. In [17], the SP method was used to obtain the reduced-order small-signal model of a microgrid in both grid-connected and islanded conditions. In [21], [22], black-box models for microgrids using the Prony method were proposed based on measurements of voltage, current and output power at the point of common coupling (PCC). Inspired by the conclusion of participation factor analysis and the thought of coherency in power systems, a new MOR method for VSMG is proposed by equivalencing the detailed small-signal model to a modified third-order SG model. SMALL-SIGNAL MODELING OF THE VSMG modeling of the VSMG is analyzed and expressed in terms of DAEs at first These equations are nonlinear and need to be linearized around a set of equilibrium points, i.e., small-signal modeling, to study the system static stability and dynamic responses.
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