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Author

Yang Zhang

Bio: Yang Zhang is an academic researcher from Zhejiang University. The author has contributed to research in topics: Gyrator & Power (physics). The author has an hindex of 2, co-authored 3 publications receiving 172 citations.

Papers
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Journal ArticleDOI
TL;DR: Based on the Lyapunov linearization method and the mixed potential theory, stability of equilibrium point and an estimation of the region of attraction are investigated for cascaded system in the dc distribution power system as mentioned in this paper.
Abstract: With the development of renewable energy, dc distribution power system (DPS) becomes more and more attractive. The stability of whole system is still a big concern though every single converter is well designed based on the stand-alone operation with sufficient stability. Since the cascaded connection of power converters is one of the most dominant connection forms in the dc DPS, the stability analysis of the cascaded system is very important to ensure stability of the whole system. Based on the Lyapunov linearization method and Brayton–Moser's mixed potential theory, stability of equilibrium point and an estimation of the region of attraction are investigated for cascaded system in the dc DPS. Based on the analysis, stability prediction criteria for cascaded system under small-signal and large-signal disturbances are obtained. The two criteria are simple and straightforward, which can be unified to get a general stability criterion to predict system's stability under both small-signal and large-signal transient disturbances. The relationship between system parameters and the stability is presented and discussed in the paper. Therefore, instead of trial and error, the proposed criterion can predict and guarantee the stability operation of cascaded system during the design process, and it is also helpful to select matched power converters in system level design. The simulation and experimental results verify the effectiveness of the proposed criterion.

198 citations

Proceedings ArticleDOI
Weijing Du1, Junming Zhang1, Yang Zhang1, Zhaoming Qian1, Fangzheng Peng1 
24 Jul 2011
TL;DR: In this article, a reduced order large signal model for the step-down cascaded system was proposed and the stability of converters with CPL based on Lyapunov stability theory was analyzed.
Abstract: Power electronic converters are widely used in advanced automobiles, especially in electrical vehicles (EVs). However, the stability analysis of the advanced automotive electrical systems which composed by multi-voltage level hybrid ac and dc systems is much complex than a single converter. In the system level, the downstream converter behaves as a constant power load (CPL) which shows negative incremental resistance and may cause negative impedance instability in the system. In addition, there is no general model for large signal stability analysis of nonlinear dynamical systems. In view of the above, this paper set up a reduced order large signal model for the step-down cascaded system first, and analyzes the stability of converters with CPL based on Lyapunov stability theory. Phase plane analysis and attraction region are presented to demonstrate the system stability. Key parameters are also analyzed in detail. The simulation results using Saber software confirm the theoretical analysis.

7 citations

Proceedings ArticleDOI
01 Nov 2011
TL;DR: A novel modeling method based on gyrator is proposed that can reduce the system order and is suitable for describing both single and cascaded system with current programmed converters.
Abstract: The stability for complex power electronics system under large disturbance is a key aspect for reliable operation, such as startup and load transient. The large signal model for each module is generally required for system level analysis. Eleven existing methods to establish large-signal models for power electronic converter are reviewed in this paper, which can be classified into three groups. Based on the review, a novel modeling method based on gyrator is proposed. Compared to the existing methods, the proposed model can reduce the system order and is suitable for describing both single and cascaded system with current programmed converters. Simulation and experimental results are presented to verify the feasibility of the gyrator model. Comparisons between these methods are also presented in this paper.

1 citations

Proceedings ArticleDOI
12 May 2023
TL;DR: In this paper , a two-stage equivalent method for wind farms considering the action state of a Crowbar circuit is proposed, where the transient characteristics of different units during the fault period are analyzed, and their action states are used as the preliminary clustering basis.
Abstract: With the popularity of wind power generation, the accuracy and speed of equivalent modeling for wind farms are challenged. In this paper, a two-stage equivalent method for wind farm considering the action state of Crowbar circuit is proposed. Firstly, the transient characteristics of Crowbar circuits of different units during the fault period are analyzed, and their action states are used as the preliminary clustering basis. An ISODATA clustering method for wind farms with small data sets is proposed. Secondly, it aims at the interval range of incomplete action of Crowbar circuit, and the adaptive clustering method based on Gaussian mixture model clustering algorithm optimized by Bayesian information is proposed. Finally, the equivalent model of wind farm under different voltage dip is obtained. Simulation examples show that the proposed method has high precision and effective clustering.
Proceedings ArticleDOI
28 Jul 2022
TL;DR: In this article , a variable switching frequency pulse width modulation (VSFPWM) strategy was proposed for grid-side three-level neutral-point clamped (NPC) converter for doubly-fed induction generator (DFIG) wind turbine.
Abstract: In order to improve the power quality of DFIG power generation, this paper proposes a variable switching frequency pulse width modulation (VSFPWM) strategy for grid-side three-level neutral-point clamped (NPC) converter for doubly-fed induction generator (DFIG) wind turbine. For different voltage vectors, different Thevenin equivalent circuits are used to derive the analytical expressions of the grid-side converter current ripple, and the current ripple slope and effective time of each cycle can be obtained. The VSFPWM strategy takes the peak-to-peak value of the three-phase output current ripple as a constraint, updates the switching frequency in each interruption cycle, and limits the current ripple as the constraint to limit the current ripple to a certain range. The switching frequency is updated in each interrupt cycle to reduce the equivalent switching frequency and electromagnetic interference (EMI) noise. Finally, the simulation results validate the effectiveness of the proposed control strategy.

Cited by
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Journal ArticleDOI
TL;DR: This paper presents an overview of power management strategies for a hybrid ac/dc microgrid system, which includes different system structures, different operation modes, a thorough study of various power management and control schemes in both steady state and transient conditions, and examples of powermanagement and control strategies.
Abstract: Today, conventional power systems are evolving to modern smart grids, where interconnected microgrids may dominate the distribution system with high penetration of renewable energy and energy storage systems. The hybrid ac/dc systems with dc and ac sources/loads are considered to be the most possible future distribution or even transmission structures. For such hybrid ac/dc microgrids, power management strategies are one of the most critical operation aspects. This paper presents an overview of power management strategies for a hybrid ac/dc microgrid system, which includes different system structures (ac-coupled, dc-coupled, and ac–dc-coupled hybrid microgrids), different operation modes, a thorough study of various power management and control schemes in both steady state and transient conditions, and examples of power management and control strategies. Finally, discussion and recommendations of power management strategies for the further research are presented.

707 citations

Journal ArticleDOI
TL;DR: In this paper, an extensive review on control schemes and architectures applied to dc microgrids (MGs) is presented, covering multilayer hierarchical control schemes, coordinated control strategies, plug-and-play operations, stability and active damping aspects, as well as nonlinear control algorithms.
Abstract: This paper performs an extensive review on control schemes and architectures applied to dc microgrids (MGs). It covers multilayer hierarchical control schemes, coordinated control strategies, plug-and-play operations, stability and active damping aspects, as well as nonlinear control algorithms. Islanding detection, protection, and MG clusters control are also briefly summarized. All the mentioned issues are discussed with the goal of providing control design guidelines for dc MGs. The future research challenges, from the authors’ point of view, are also provided in the final concluding part.

452 citations

Journal ArticleDOI
TL;DR: In this paper, the consequences of droop implementation on the voltage stability of dc power systems, whose loads are active and nonlinear, e.g., constant power loads, are shown.
Abstract: The stability of dc microgrids (MG s ) depends on the control strategy adopted for each mode of operation. In an islanded operation mode, droop control is the basic method for bus voltage stabilization when there is no communication among the sources. In this paper, it is shown the consequences of droop implementation on the voltage stability of dc power systems, whose loads are active and nonlinear, e.g., constant power loads. The set of parallel sources and their corresponding transmission lines are modeled by an ideal voltage source in series with an equivalent resistance and inductance. This approximate model allows performing a nonlinear stability analysis to predict the system qualitative behavior due to the reduced number of differential equations. Additionally, nonlinear analysis provides analytical stability conditions as a function of the model parameters and it leads to a design guideline to build reliable (MG s ) based on safe operating regions.

260 citations

Journal ArticleDOI
TL;DR: Based on the Lyapunov linearization method and the mixed potential theory, stability of equilibrium point and an estimation of the region of attraction are investigated for cascaded system in the dc distribution power system as mentioned in this paper.
Abstract: With the development of renewable energy, dc distribution power system (DPS) becomes more and more attractive. The stability of whole system is still a big concern though every single converter is well designed based on the stand-alone operation with sufficient stability. Since the cascaded connection of power converters is one of the most dominant connection forms in the dc DPS, the stability analysis of the cascaded system is very important to ensure stability of the whole system. Based on the Lyapunov linearization method and Brayton–Moser's mixed potential theory, stability of equilibrium point and an estimation of the region of attraction are investigated for cascaded system in the dc DPS. Based on the analysis, stability prediction criteria for cascaded system under small-signal and large-signal disturbances are obtained. The two criteria are simple and straightforward, which can be unified to get a general stability criterion to predict system's stability under both small-signal and large-signal transient disturbances. The relationship between system parameters and the stability is presented and discussed in the paper. Therefore, instead of trial and error, the proposed criterion can predict and guarantee the stability operation of cascaded system during the design process, and it is also helpful to select matched power converters in system level design. The simulation and experimental results verify the effectiveness of the proposed criterion.

198 citations

Journal ArticleDOI
TL;DR: This paper proposes a method that stabilizes the system from source-side converters, instead of from CPL themselves, and proves, both analytically and experimentally, that, in dc microgrids, resonant frequencies of LC filters of paralleled CPLs have to be different to maintain system stability.
Abstract: In dc microgrids, it is common that constant power loads (CPLs) exhibit negative incremental resistance They degrade the stability margin of operation with their LC input filters and, thus, the whole system In traditional active-damping methods, the extra stabilizing current is injected into CPLs to modify its input impedance to fulfill stability criteria However, this injected current may cause undesirable performance of the loads, eg, fluctuation in rotating speed of tightly regulated motors There is always a compromise between stability margin and load performances In order to overcome this drawback, this paper proposes a method that stabilizes the system from source-side converters, instead of from CPL themselves In the proposed method, a virtual resistance is built in the source-side converter This virtual resistor is effective around the resonant frequency of the LC input filter and thus can indirectly reduce its output impedance to fulfill Middlebrook's stability criterion This paper also proves, both analytically and experimentally, that, in dc microgrids, resonant frequencies of LC filters of paralleled CPLs have to be different to maintain system stability Simulation and experimental results are reported to verify the effectiveness of the proposed idea

189 citations