Low-Frequency Instability Induced by Hopf Bifurcation in a Single-Phase Converter Connected to Non-Ideal Power Grid

Zhiwei Han,Zhigang Liu,Hong Chen,Wenqian Yu,Ibrahim Adamu Tasiu,Qixiang Yan

doi:10.1109/access.2020.2983479

Abstract

With the high-density operation of China Railways High-speed (CRH) series vehicles in railways, a large number of power electronic converters are connected to the traction network. Due to the nonlinear characteristics of power electronic converter, it is easy to cause the low-frequency oscillation (LFO) in the single-phase vehicle-grid system of high-speed railways when the converter is connected to a non-ideal power grid. In order to solve this problem, the time domain nonlinear dynamic average model is proposed in this paper. Given Jacobian method to probe into the low-frequency stability of single-phase vehicle-grid system based on Hopf bifurcation, the characteristics and applicability of this method is summarized. The effects of electrical and control parameters can be analyzed with this model. In addition, with the emergence of LFO, the stability boundary leading to catastrophic bifurcation is discussed in detail. In the end, theoretical analysis results are verified by simulations and hardware-in-the-loop (HIL) platform.

Highlights

With the wide applications of a large number of power electronic components, the single-phase vehicle-grid system shown in Fig. 1 has brought some unstable phenomena, such as the harmonic oscillation [1], [2], the low-frequency oscillation (LFO), the sideband oscillation and the near-synchronous oscillation
It is reported that when power electronic converters are connected to the non-ideal power grid, the single-phase system will generate LFO overvoltage [4]–[7]
ANALYSIS OF THE SINGLE-PHASE VEHICLE-GRIDE SYSTEM In order to analyze the LFO of single-phase vehicle-grid systems, the time-domain nonlinear dynamic average model should be adopted to describe the dynamic characteristics of the system and the steady-state point need to be solved from state equations in this paper

Summary

INTRODUCTION

With the wide applications of a large number of power electronic components, the single-phase vehicle-grid system shown in Fig. 1 has brought some unstable phenomena, such as the harmonic oscillation [1], [2], the LFO, the sideband oscillation and the near-synchronous oscillation. The impedance modeling method is very complicated and neither method considers the case where the converter is connected to the non-ideal grid, simplifying the modeling process and adopting nonlinear dynamic average model based on time domain are very necessary. Traditional stability criteria such as Nyquist and Bode plot methods are mainly aimed at frequency domain modeling, but they are not applicable to the time domain modeling method proposed in this paper. B) Explains LFO, using the Hopf bifurcation, caused by the impedance from the non-ideal power grid connected to the single-phase converter. ANALYSIS OF THE SINGLE-PHASE VEHICLE-GRIDE SYSTEM In order to analyze the LFO of single-phase vehicle-grid systems, the time-domain nonlinear dynamic average model should be adopted to describe the dynamic characteristics of the system and the steady-state point need to be solved from state equations in this paper

ESTABLISH STATE EQUATIONS

THEORETICAL ANALYSIS

THE INTEGRAL OF VOLTAGE LOOP ON VEHICLE SIDE

THE DC LINK CAPACITOR ON LOAD SIDE

EXPERIMENTAL OBSERVATION

CONCLUSION