Subjects: Dynamic and Electric Engineering >> Electrical Engineering submitted time 2023-04-25
Abstract： There are many impedance-based methods to analyze the oscillation of grid-connected converter system (GCS) via dq frame, sequence frame and polar frame, which can be transformed into each other and are equivalent in judging the stability of the system. However, the discrepancy and adaptation of these methods has not been discussed theoretically. Therefore, the impedance models of GCS are established in above three kinds of coordinates respectively, then the mathematical and physical characteristics of them are analyzed. Secondly, the decoupling of impedance models in different frames are analyzed, and the differences of the impedance criteria in stability analysis and mechanism interpretation are given. Furthermore, the sub-synchronous oscillation caused by the phase-locked loop considering converter four quadrant operation scenario are illustrated, and the existence of open-loop transfer function right half plane poles and its sensitivity to uncertain parameters are analyzed from the nominal performance and robustness of the impedance criteria. On this basis, the adaptation of several impedance criteria of GCS are analyzed. Theoretical analysis and simulations confirm the validity of the proposed conclusion.
Subjects: Dynamic and Electric Engineering >> Electrical Engineering submitted time 2022-05-29
Abstract：
Many methods and criteria of stability assessment have been proposed due to the complex dynamics of renewable power system. The physical implications of these methods/criteria and their scopes of adaptation are different. It is difficult to theoretically answer that, for certain stability issue, which stability criterion is suitable and whether the corresponding physical interpretation is reasonable. This paper was divided into two parts. The methods for assessing the adaptation of stability criteria were put forward, and the question whether the corresponding physical interpretations were reasonable were answered in part I. While the adaptation of each stability criterion was analyzed by applying the method and the physical interpretation of each stability problem was derived in part II. In part I, the derivation process of the existing stability criteria and their underlying physical significance were reviewed at first. Secondly, the selection principles of stability criteria were proposed from 3 aspects, namely stability equivalence, nominal performance and robust stability. And the quantitative index named loop gain sensitivity was proposed. Finally, the adaptation of several impedance criteria of grid-connected converters were analyzed.?It was shown that the nominal performance and robustness of these impedance criteria were not equivalent in frequency domain modal analysis. The adaptation of other typical stability criteria and the corresponding physical interpretation were analyzed in part II.
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Peer Review Status:
Awaiting Review
Subjects: Dynamic and Electric Engineering >> Electrical Engineering submitted time 2022-05-29
Abstract：
From the perspective of stability equivalence, nominal performance and robustness, the qualitative principles and quantitative evaluation index of stability criterion adaptation are proposed in Part Ⅰ. In addition, the adaptation of the existing stability criteria and the physical interpretation of instability corresponding to the suitable stability criterion are analyzed for the typical equipment in power system, such as synchronous machines, doubly-fed induction generators (DFIG) and converters in Part II. Thereby the stability classification of the renewable power system is discussed based on dominant output variable. Firstly, aiming at low-frequency and sub-synchronous oscillation/resonance (SSO/SSR) of synchronous machine, the rationality of the existing stability analysis methods and physical interpretation is verified by using the proposed evaluation index. Secondly, the proposed evaluation index is used to analyze the oscillation of converters and DFIG, and the suitable stability criterion, derivation mechanism and dominant output variable are further discussed. Finally, a novel idea of equipment stability classification based on physical mechanism and dominant output variables are proposed, which classifies equipment stability from the vector perspective into three categories: phase-dominated synchronous stability, amplitude-dominated voltage stability, and electrical resonance formed by their special combination. Issues such as the concept of wide-band oscillation, the distinction between equipment stability and system stability, and the extensibility of their classification are further explored.
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Peer Review Status:Awaiting Review
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