Abstract
A reduced-order model that preserves physical meaning is important for generating insight in large-scale power system studies. The conventional model-order reduction for a multiple-timescale system is based on discarding states with fast (short timescale) dynamics. It has been successfully applied to synchronous machines, but is inaccurate when applied to power converters because the timescales of fast and slow states are not sufficiently separated. In the method proposed here, several fast states are at first discarded but a representation of their interaction with the slow states is added back. Recognizing that the fast states of many converters are linear allows well-developed linear system theories to be used to implement this concept. All the information of the original system relevant to system-wide dynamics, including nonlinearity, is preserved, which facilitates judgments on system stability and insight into control design. The method is tested on a converter-supplied mini power system and the comparison of analytical and experiment results confirms high preciseness in a broad range of conditions.
Highlights
P OWER converters are becoming increasingly common as interfaces for energy resources and loads and appearing at higher power ratings such that they become an important feature of the dynamics of a power system
The conventional peel-off method has higher modeling error for the voltage controlled VSC (VVSC) mode than for the synchronous generator (SG) mode, as shown in the upper part of Fig. 16, which supports our argument that the poor separation of timescale may cause poor accuracy in model reduction, and justifies the necessity of using the proposed “peel-off and add-back” method to account for high converter penetration
The model reduction methodology introduced in this paper proves to be an effective tool for simplifying the study of the stability of power systems rich in power converters
Summary
P OWER converters are becoming increasingly common as interfaces for energy resources and loads and appearing at higher power ratings such that they become an important feature of the dynamics of a power system. This feature enables us to leverage well-developed linear system theories to analyze the structure of the fast submodel, identify the dominant modes with which the slow states may overlap in timescale, and add them back to the reduced model It ensures a reasonable selection of the dynamics to be truncated, so as to preserve the essential information (including nonlinearity of the slow states) of the original system. Single-phase systems present an additional complication, namely an ac operating point of the converter since it has to be modeled in the stationary frame This can be addressed by shifting the center of the preserved region in pole-zero truncation to ±jωs (representing 50 Hz operating point), and by using linear time-periodic not linear timeinvariant theories in subsequent small-signal analysis [25]. A grid-forming VSC can be treated as a special case of a grid-supporting one with droop coefficients of zero
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
