arXiv subjects

Deqiang Gan

Publications and source records attributed to Deqiang Gan.

8 recordsLinked to original sources

arXiv2025

Power System Voltage Stability Boundary: Computational Results and Applications

The objective of this paper is to report some computational results for the theory of DAE stability boundary, with the aim of advancing applications in power system voltage stability studies. Firstly, a new regularization transformation for standard differential-algebraic equations (DAEs) is proposed. Then the existence of anchor points on voltage stability boundary is examined, and an optimization method for computing the controlling pseudo-saddle is suggested. Subsequently, a local representation of the stable manifold of the pseudo-saddle on the stability boundary is presented, and a voltage stability margin expression is obtained. Finally, the proposed results are verified using several examples, demonstrating the accuracy and effectiveness of the suggested methods.

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arXiv2025

On the Input-Output Monotonicity of Voltage Dynamics of Power System with Grid-Forming Converters

Integration of renewable resources is profoundly reshaping the dynamics of modern power systems. This study shows that the voltage dynamics of power systems with multiple grid-forming (GFM) converters often enjoys a desirable property called input-output monotonicity. A systematic approach for computing the derivatives of the voltage subsystem is presented first, which provides insight into the structural characteristics of these models. Next, the sign pattern of the trajectory Jacobian matrix associated with the voltage subsystem is analyzed and revealed. The analysis indicates that the voltage dynamics of power systems often exhibits the so-called input-output monotonicity property. The theoretical results are then validated through several simulation examples, underscoring their practical implications.

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arXiv2023

A Gronwall Inequality Based Approach to Transient Stability Assessment for Power Grids

This paper proposes a novel Gronwall inequality-based method for transient stability assessment for power systems. The challenges of applying such methods to power systems are how to construct the differential inequality and how to treat its nonlinearity. By leveraging partial derivatives, a rotor angle difference inequality model is established, and the difficulty of nonlinearity of this model is solved by piecewise linearization. Based on our method, the upper bound of the rotor angle difference is given analytically, which can be used to estimate the stability boundary, i.e. the critical clearing time (CCT) of power systems. A case study on the IEEE 9-bus system shows the accuracy of the approach in early warning of transient instability for power grids.

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arXiv2022

A New Decomposition Strategy for Analyzing Large-Scale Systems Such as Power Systems

In this work, it is demonstrated that the usual power system dynamic model exhibits a feedforward-feedback control structure. The distinct properties of the feedforward and feedback subsystems are identified and studied using respective nonlinear system tools. The stability of the closed-loop system is investigated using a small gain argument from input-to-state stability theory. Test results are provided to further complement the theoretical findings. The introduced methodology also shed light on the dynamics study on other interconnected nonlinear systems.

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arXiv2020

High Voltage Ride Through Strategy For DFIG Considering HVDC System Converter Blocking

This paper presents a P-Q coordination based high voltage ride through (HVRT) control strategy for double fed induction generators (DFIGs) based on a combined Q-V control and P-V de-loading control. The active/reactive power injection effect of DFIG on transient overvoltage is firstly analyzed and the reactive power capacity evaluation of DFIG considering its de-loading operation is then conducted. In the proposed strategy, the reactive power limit of DFIG can be flexibly extended during the transient process in coordination with its active power adjustment, as a result the transient overvoltage caused by DC bipolar block can be effectively suppressed. Moreover, key outer loop parameters such as Q-V control coefficient and de-loading coefficient can be determined based on the point of common coupling (PCC) voltage level and the available DFIG power capacity. Finally, case studies based on MATLAB/Simulink simulation are used to verify the effectiveness of the proposed control strategy

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arXiv2019

Closed Loop Load Model Identification Using Small Disturbance Data

Load model identification using small disturbance data is studied. It is proved that the individual load to be identified and the rest of the system forms a closed-loop system. Then, the impacts of disturbances entering the feedforward channel (internal disturbance) and feedback channel (external disturbance) on relationship between load inputs and outputs are examined analytically. It is found out that relationship between load inputs and outputs is not determined by load itself (feedforward transfer function) only, but also related with equivalent network matrix (feedback transfer function). Thus, load identification is closed loop identification essentially and the impact of closed loop identification cannot be neglected when using small disturbance data to identify load parameters. Closed loop load model identification can be solved by prediction error method (PEM). Implementation of PEM based on a Kalman filtering formulation is detailed. Identification results using simulated data demonstrates the correctness and significance of theoretical analysis.

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arXiv2018

Generalized Short Circuit Ratio for Multi Power Electronic based Devices Infeed Systems: Defi-nition and Theoretical Analysis

Short circuit ratio (SCR) is widely applied to analyze the strength of AC system and the small signal stability for single power elec-tronic based devices infeed systems (SPEISs). However, there still lacking the theory of short circuit ratio applicable for multi power electronic based devices infeed systems (MPEIS), as the complex coupling among multi power electronic devices (PEDs) leads to difficulties in stability analysis. In this regard, this paper firstly proposes a concept named generalized short circuit ratio (gSCR) to measure the strength of connected AC grid in a multi-infeed system from the small signal stability point of view. Generally, the gSCR is physically and mathematically extended from conven-tional SCR by decomposing the multi-infeed system into n inde-pendent single infeed systems. Then the operation gSCR (OgSCR) is proposed based on gSCR in order to take the variation of op-eration point into consideration. The participation factors and sensitivity are analyzed as well. Finally, simulations are conducted to demonstrate the rationality and effectiveness of the defined gSCR and OgSCR.

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arXiv2017

A Generalized Short Circuit Ratio for Multi-Infeed LCC-HVDC System

The relationship between the short circuit ratio (SCR) and static voltage stability is analyzed in this paper. According to eigenvalue decomposition method, a novel concept named generalized short circuit ratio (gSCR) has been proposed for multi-infeed LCC-HVDC (MIDC) systems to mathematically measure the connect-ed AC strength from the point view of voltage stability, which can overcome the rule-of-thumb basis of existing multi-infeed short circuit ratio (MISCR) concept. In gSCR, two indices, the critical gSCR (CgSCR) and the boundary gSCR (BgSCR) are developed to quantitatively evaluate if the connected AC system is strong or weak, in which CgSCR=2 and BgSCR=3 are two critical values for strength evaluation. Finally, numerical simulations are conducted to validate the effectiveness of the proposed gSCR concept.

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