Chen Zhang

Chen Zhang
Shanghai Jiao Tong University | SJTU · Department of Electrical Engineering

PhD

About

68
Publications
18,441
Reads
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890
Citations
Additional affiliations
October 2020 - August 2021
Technical University of Denmark
Position
  • Postdoc
March 2018 - March 2020
Norwegian University of Science and Technology
Position
  • PostDoc Position

Publications

Publications (68)
Article
Full-text available
This paper presents a generalized method for converting MIMO dq impedance model of a grid-tied voltage source converter system into its sequence domain SISO equivalents. As a result, two types of SISO impedance models were derived, one of which was derived from relatively strong and dq symmetric grid assumption (reduced SISO model) and the other wa...
Article
Impedance modeling and stability analysis of a grid-voltage source converters (VSC) system under symmetric ac grids have been extensively discussed in the literature, where the dq domain impedances are usually adopted. As for asymmetric ac grids, impedance modeling is no longer straightforward in the dq domain due to the presence of negative se...
Article
Impedance is an intuitive and effective way for dynamical representation of power electronics devices (e.g. VSCs). One of its strengths towards others is the natural association with circuits. However, impedances of VSCs are locally evaluated via linearization, a process dependent on the angle of the reference frame, thus the reference frame transf...
Article
To cope with the weak grid stability issue of grid-tied Voltage Source Converters (VSCs), this letter proposes an Artificial Neural Network (ANN)-based approach for online stabilization control of the grid-tied VSC with the pole-tracking feature. First, an ANN is adopted to establish the mapping between the control parameters and the closed-loop po...
Preprint
Full-text available
Linear Time Periodic (LTP) framework-based analysis of Voltage Source Converters (VSCs) is becoming popular, a driven factor is that many of the existing VSC applications inevitably exhibit the periodic steady-state (PSS), e.g., VSCs with unbalanced grid connections and the operation of a modular multilevel converter (MMC). In these studies, acquis...
Conference Paper
Full-text available
With the increasing penetration of voltage-source-converter (VSC) -interfaced distributed generations(DGs) in power systems, oscillation issues have been widelyconcerned whereas the root cause and nature of the oscilla-tion is sometimes not clear in real cases. This paper focuseson the instability mode recognition (IMR) based on a com-plete data-dr...
Preprint
Full-text available
The high penetration of renewables has imposed great oscillation risks on power grids, especially for the power electronics-dominated hybrid AC/DC grid. Measurement data-driven diagnosis of oscillations regarding where, why and how they happened is crucial to the emergency control. However, before implementing any data-driven diagnosis, a comprehen...
Preprint
Full-text available
Modern power system is undergoing a paradigm shift from the synchronous generators-based system to the power electronics converters-dominated system. With the high penetration of converters, serious stability problems are provoked, especially the wideband oscillations (e.g., sub-synchronous oscillations, harmonic oscillations, etc). Various studies...
Article
Full-text available
The high penetration of renewables has sparked new oscillatory concerns in hybrid AC/DC grids. Knowledge of the oscillation regarding its source and propagation mechanism, is crucial to system operation. In this respect, the frequency-domain modal analysis (FMA) provides a way (e.g., participation factor) to extract these oscillation properties, an...
Conference Paper
Full-text available
This paper presented a distinct control strategy for a grid-connected PV system. The proposed control strategy includes a Beta algorithm for maximizing power extraction, an optimum PI controller for controlling the boost converter, and direct power control (DPC) based on modified sliding mode control (SMC) for controlling a three-phase grid-connect...
Article
This paper investigates and discusses the interaction stability issues of a wind farm with weak grid connections, where the wind turbines (WTs) are controlled by a new type of converter control strategy referred to as the voltage source (VS) control. The primary intention of the VS control method is to achieve the high-quality inertial response cap...
Conference Paper
This paper presented a distinct control strategy for a grid-connected PV system. The proposed control strategy includes a Beta algorithm for maximizing power extraction, an optimum PI controller for controlling the boost converter, and direct power control (DPC) based on modified sliding mode control (SMC) for controlling a three-phase grid-connect...
Preprint
Full-text available
The MMC-HVDC connected offshore wind farms (OWFs) could suffer short circuit fault (SCF), whereas their transient stability is not well analysed. In this paper, the mechanism of the loss of synchronization (LOS) of this system is analysed considering the whole system state from the fault-on to the post-fault, and the discussion on fault type and fa...
Article
Full-text available
Grid-synchronization stability (GSS) is an emerging stability issue of grid-tied voltage source converters (VSCs), which can be provoked by severe grid voltage sags. Although a qualitative understanding of the mechanism behind the loss of synchronization has been acquired in recent studies, an analytical method for quantitative assessment of GSS of...
Preprint
Full-text available
Grid-synchronization stability (GSS) is an emerging stability issue of grid-tied voltage source converters (VSCs), which can be provoked by severe grid voltage sags. Although a qualitative understanding of the mechanism behind the loss of synchronization has been acquired in recent studies, an analytical method for quantitative assessment of GSS of...
Article
A type of peak-value dc voltage control (denoted as PK control) was proposed in the literature for supporting the use of a smaller dc-side capacitance when the single-phase Voltage Source Converter (VSC) is operated as a Static Synchronous Compensator (STATCOM). Although it was demonstrated to operate stably under several conditions, it will be rev...
Article
Full-text available
Frequency-domain model reduction is a crucial concern in applying the prevailing impedance method for the stability analysis of complex systems, e.g., the modular multilevel converter (MMC). Recently, it has been shown that under symmetric conditions, a 2×2 matrix-based impedance model characterizing the two coupled frequencies of MMC are sufficien...
Article
The power electronic converter-based wind farms have imposed great risks on the small-signal stability of the modern power system, mainly characterized by wideband oscillations ranging from one Hertz to several thousand Hertz. To analyze such wideband oscillations problems, a consensus has been reached that the aggregation of the wind farm is indis...
Article
Second-order Generalized Integrator (SOGI)-based quadrature-signal-generator (QSG), in conjunction with either a phase-locked-loop (PLL) or a frequency-locked-loop (FLL), is widely used as the synchronization unit of grid-tied converters. This paper will reveal and discuss the stability impacts of the frequency-feedback-path (FFP) used in connectin...
Conference Paper
Full-text available
A Hilbert filter design is proposed with the intent of assembling a simple, yet frequency adaptive single-phase grid synchronisation unit. The simplicity lies not with the filter itself, but with the linearity of the orthogonal system generator (OSG) and its absence of frequency feedbacks. This is a trait shared with many standard, frequency fixed...
Article
Full-text available
Grid-synchronizing Stability (GSS) is an emerging issue related to grid-feeding voltage-source converters (VSCs). Its occurrence is primarily related to the non-linear dynamics of a type of vastly applied synchronization unit – Phase-locked Loops (PLL). Dynamic characterization and modeling for the GSS analysis can be achieved using a simplified sy...
Article
Full-text available
Recently, small-signal stability of the modular multilevel converter (MMC) based high-voltage direct current (HVDC) transmission for wind farm integration has attracted great attentions. The impedancebased frequency-domain method is an effective tool for such studies, in which the accuracy of the impedance model is of significant importance. Curren...
Article
Full-text available
This paper presents a harmonic domain single-input single-output (SISO) equivalent modeling technique for the impedance modeling and stability analysis of a single-phase grid-connected voltage-source-converter (VSC). The basis is a conversion technique that transforms a harmonic-transfer-function (HTF)-based model into a SISO equivalent model while...
Article
This paper proposes an integrated method for generating the voltage-source-converters’ (VSCs’) periodical steady-state (PSS) conditions and the harmonic-state-space (HSS)-based impedance model. Since these two objectives can be realized in one unified frequency-domain iteration process, it is briefly referred to as the automatic model generation (A...
Data
This is the conference presentation of the paper with the same title. The paper was presented at IEEE - IECON, In Lisbon, Portugal, October 2019.
Article
Recent analyses have shown that the grid-integration of offshore wind farms through MTDC systems has brought low inertia and small-signal stability issues, in which the dynamics of phase-locked-loop (PLL) play a crucial role. To address this issue, this paper proposes a control strategy for the multi-terminal VSCs aiming at PLL-less synchronization...
Conference Paper
Full-text available
Two different single-phase synchronisation schemes based on orthogonal system generation (OSG) are modelled in the linear, time-periodic framework. The frequency adaptive Hilbert phase locked loop (PLL) and the frequency-fixed second-order-generalised-integrator (SOGI) PLL fit smoothly into existing models for the synchronous reference frame PLL, d...
Article
Full-text available
Transient behavior and response of wind turbines have been extensively studied in the context of the low-voltage ride through (LVRT) for many years, in which the identified transients are mostly associated with circuit responses, whereas underlying stability issues relevant to converter control yet remain concealed. Recently, small-signal analyses...
Preprint
Full-text available
A Hilbert filter design is proposed with the intent of assembling a simple, yet frequency adaptive single-phase grid synchronisation unit. The simplicity lies not with the filter itself, but with the linearity of the orthogonal system generator (OSG) and its absence of frequency feedbacks. This is a trait shared with many standard, frequency fixed...
Conference Paper
Full-text available
The modular multilevel converter (MMC) based high-voltage direct current (HVDC) transmission is widely applied for the large-scale wind farm integration making its interaction stability analysis especially significant. However, only a few related researches have so far been done and most of them depict ac-side characteristics of the connected MMC s...
Conference Paper
Full-text available
The accurate sequence impedance model of the modular multilevel converter (MMC) is essential for the precise stability analysis of various MMC-based interconnected systems. This paper presents a modified sequence impedance model for MMC considering off-diagonal coupling effects. Instead of simplifying the MMC as the single-phase model, the three-ph...
Conference Paper
Full-text available
Transients of a typical grid synchronizing VSC are closely associated with the over-current and over-voltage in circuits. Previous analysis in evaluating such transient phenomenon usually ignore the nonlinear control effects of the VSCs (e.g. phase-locked-loop, PLL). Although this assumption allows a simpler analysis of the transient process, it ma...
Conference Paper
Full-text available
As the large-scale wind farms develop rapidly, the dynamic interactions between wind farms and grid are becoming prominent. To study this issue, an accurate aggregation model of the wind farm is required for system-level analysis. However, the original single-machine aggregation model (SAM), which always ignores the wind power converter's nonlinear...
Article
Low‐frequency oscillations of a power system can be greatly affected by the fast growth of wind power due to the converter controls. It will result in a hidden danger to the small signal stability of the overall system if the mechanisms behind are not well understood. Therefore, this article aims to reveal the influence of the nonlinear control eff...
Chapter
Full-text available
The Nyquist stability criterion is a graphical technique for determining the stability of a dynamical system. It relates the stability of a closed‐loop system to the open‐loop frequency response and open‐loop pole location. The Nyquist technique is limited to linear, time‐invariant (LTI) systems and has been widely used for designing and analyzing...
Article
Full-text available
With the increasing penetration of wind power, the effective inertia of the power system reduces. Besides, a series of interactive instability issues including sub-synchronous oscillations and harmonic oscillations were reported due to the weak grid effects. Broadly speaking, those issues are closely related to the PLL and its tuning. Therefore, re...
Article
Full-text available
Impedance-based frequency-domain method is an effective tool for the stability assessment of a doubly fed induction generator (DFIG) system. Several impedance models have been proposed recently; however, these models are usually associated with model reductions since the complexity in achieving a detailed DFIG model. This may lead to unreliable sta...
Conference Paper
Full-text available
In this paper, the stability analysis of the compensated modulation based MMC-HVDC connected wind farms is carried out, where the impedance-based analytical approach is applied. The ac-side impedance models of the MMC with compensated and direct modulation are derived, respectively, and their impedance characteristics are compared. The impact of th...
Preprint
Full-text available
Impedance-based frequency domain method is an effective tool for the stability assessment of a doubly-fed induction generator (DFIG) system. Several impedance models have been proposed recently, however, these models are usually associated with model reductions since the complexity in achieving a detailed DFIG model. This may lead to unreliable sta...
Presentation
Full-text available
This presentation was about how to use the individual impedances of power electronic units to establish an impedance network. The idea is to use basic circuit laws to analyse the system and to use the Nyquist stability criterion to assess the stability. To do that I introduce the impedance operator (IO) with its associated properties and its impact...
Preprint
Full-text available
Impedance is an intuitive and efficient way for dynamic representation of power electronics devices. One of the evident strengths, when compared to other small-signal methods, is the natural association with circuit theory. This makes them possible to be connected through basic circuit laws. However, careful attention should be paid when making thi...
Conference Paper
Full-text available
Conventional small-signal approaches present obvious advantages applied in analyzing closed-loop stability in power electronics systems. However, linearized models fall short of predicting any nonlinear behavior which means not able to acquire the accurate stability margin. This paper mainly analyzes bifurcation behaviors of the Modular Multilevel...
Article
Full-text available
Impedance modeling of a Type-IV wind turbine is usually associated with model reductions, e.g. the grid-side converter (GSC) is modeled in detail, whereas the machine-side converter (MSC) is simplified as a constant power load (CPL). Meanwhile, the Nyquist-based stability analyses are normally conducted on the ac side, where the evaluation of the s...
Preprint
Full-text available
Transients of a grid-synchronized voltage source converter (VSC) are closely related to over- currents and voltages occurred under large disturbances (e.g. a grid fault). Previous analysis in evaluating these transients usually neglect the nonlinear control effects of a VSC (e.g. phase-locked-loop, PLL). Therefore, potential stability issues relate...
Article
Full-scale wind turbines (FSWT) are susceptible to lose synchronization due to the continuous control interaction between FSWT and faulty grid. To reveal the mechanisms, a nonlinear reduced order model of FSWT was deducted based on its multi-time scale properties. Because the derived model has similar structural characteristics to the transient sta...
Article
This study provides a novel control method for voltage source converter high-voltage direct current (VSC-HVDC) systems with two salient features: autonomous grid-synchronisation without phase-locked loop and real-time grid frequency mirroring capability. The first feature is realised using a newly proposed control method for receiving end converter...
Article
Small-signal analysis of power electronic converters and systems is often carried out by impedance-based methods. At the core of these methods lies the impedance modelling, which can either be obtained through analytical calculations, simulations or measurements. The impedance models can be obtained into two main domains - the dq-domain and the seq...
Article
Full-text available
Stability of wind power is the long concerned issue especially in the context of high grid-integration level. According to the size of disturbance, stability for the wind turbine with full scale power converter (FSWT) can be divided into small signal stability and transient stability. This paper was devoted to study the transient stability of FSWT....
Article
Full-text available
Impedance-based stability analysis in the dq-domain is a widely applied method for power electronic dominated systems. An inconvenient property with this method is that impedance models are normally referred to their own local reference frame, and need to be recalculated when referring to a global reference frame in a given network. This letter pre...
Preprint
Full-text available
Impedance models are widely used in assessing small signal stability of grid-tied voltage source converter (VSC) systems. Recent research has proven that impedance models of grid-tied VSC in both dq and sequence domains are generally Multi-Input Multi-Output (MIMO) systems, and the generalized Nyquist criterion has to be applied for stability analy...
Article
Full-text available
Impedance-based stability analysis is appealing in the case of Single-Input Single-Output (SISO) systems. However, in the case of grid-tied voltage source converter (VSC) systems, dq impedances of source and load (VSC) subsystems are typically Multi-Input Multi-Output (MIMO) systems in which case the Generalized Nyquist Criterion (GNC) is required...
Article
Full-text available
Voltage source converters (VSCs) play an important role in the power conversion of renewable power generation (RPG) systems. Conventional power systems are considerably affected by power electronic devices in systems with a high percentage of RPG. Various abnormal interactions in the form of oscillations between VSCs and grid have been reported, wh...
Article
Voltage source converter based HVDC (VSC-HVDC) is a future trend for the large-scale offshore wind farms integrate to the grid. Due to fast current vector control of VSC-HVDC receiving-end, offshore wind farms may present no inertial response and become unstable when grid is weak. This paper proposed a novel control strategy for VSC-HVDC system. Wi...
Article
With the high penetration level of wind power, in particular with large dispersed wind turbines integrated to distribution network, the grid seen by the wind turbines is weak and can no longer be viewed as ideal voltage source. In this context, stability issues due to interactions between wind power and weak grid have been observed, e.g. harmonic o...
Article
The controllable area of DFWT system under abnormal grid voltage was analyzed and it was concluded that limitation of current and modulation are the key factors affectingits operation area. Installation of super-capacitor interfaced with a DC-DC converter is beneficial to suppress DC bus transients and with combined control with grid-side converter...
Article
Full-text available
This paper provides a comparative analysis of impedance models for power electronic converters and systems for the purpose of stability investigations. Such models can be divided into either decoupled models or matrix models. A decoupled impedance model is highly appealing since the Single-Input-Single-Output (SISO) structure makes the analysis and...
Article
Full-text available
Representations of AC power systems by frequency dependent impedance equivalents is an emerging technique in the dynamic analysis of power systems including power electronic converters. The technique has been applied for decades in DC-power systems, and it was recently adopted to map the impedances in AC systems. Most of the work on AC systems can...
Conference Paper
Representations of power systems by frequency dependent impedance equivalents is an emerging technique in dynamic analyses of power systems including power electronic converters. The technique has been applied for decades in DC-power systems, and it has been recently adopted to map the impedances in AC systems. In the impedance-based stability anal...
Article
The soft connection of drive-chain system is usually ignored so that one mass model is used to express the wind turbine and drive chain when dynamic interaction between doubly-fed induction generator (DFIG) and the grid is discussed. This was due to the knowledge of converter could provide enough damping for torsional oscillation caused by soft dri...

Projects

Projects (3)
Project
This aim of this project was design a distinct control strategy for a grid-connected PV system. The proposed control strategy includes a Beta algorithm for maximizing power extraction, an optimum PI controller for controlling the boost converter, and direct power control (DPC) based on modified sliding mode control (SMC) for controlling a three-phase grid-connected inverter. The proposed controller not only solves the issues of conventional DPC and SMC controllers (chattering of control input and variable frequency response), it also establishes a practical path for designing a robust controller in PV systems. On system parameter uncertainty and mismatch uncertainties, the proposed controller performs well. The proposed controller eliminates the necessity of any additional current control loops, resulting in a more straightforward system design and control process and a faster transient response.
Project
The project focuses on modelling of impedances in complex power electronics systems in different domains and discusses the impact (accuracy, rigor) of these models in the assessment of stability based on the Impedance-based stability analysis. The Impedance-based stability analysis is compared and related to other small-signal techniques such as state-space modelling.
Project
Non-stationary signal analysis in Modern Electric Power Systems (Smart Grid, Microgrids) by introducing the concept of Instantaneous Frequency (IF) as a descriptor or the measured physical phenomena.