A Simple Switched Capacitor Compensator to Minimize Zero-Crossing Distortion in Single-Phase PFC Converters

Yan Zhang,Jinjun Liu,Chaoyi Zhang 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

This paper explorers techniques for minimizing zero-crossing distortion in single-phase PFC converters from the angle of topologies. Zero-crossing distortions of typical single-phase PFC topologies are compared in theory to reveal that cusp distortion is predominant responsible for zero-crossing distortion. PWM rectifier with the capability of bi-directional current can minimum and eliminate zerocrossing distortion even though there is phase displacement in current loop at the cost of increasing switching loss and larger boost inductor. Then, a simple switched capacitor compensation scheme with low voltage rating switching devices and low switching frequency is presented to minimum zero-crossing distortion. Furthermore, the proposed switched capacitor circuit can be added to existing single-phase PFC converters without modification of original topologies and controllers, hence it is economically feasible. Numerical simulations are given to validate the theoretical analysis and effectiveness of the proposed scheme. With switched capacitor compensator, single-phase PFC converters demonstrate good input performance.

Study on the Influence of Distribution Lines to Parallel Inverter Systems Adopting the Droop Control Method

Zhang, Xuan,Liu, Jinjun,You, Zhiyuan,Liu, Ting The Korean Institute of Power Electronics 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.4

This paper takes into account the influence of the different impedances of distribution lines on power distribution among inverters when the inverters are paralleled with the droop control method. The impact of distribution lines on the power distribution of inverters can be divided into two aspects. Firstly, since the distributed generators are in low voltage grids, there is resistive impedance in the distribution lines, which will cause control coupling and reduce system stability. The virtual negative resistive impedance of inverters is adopted in this paper to neutralize the resistive element of distribution lines and thus make the distribution line impedance purely inductive. Secondly, after solving the resistive impedance problem, the difference in the inductive impedance value of distribution lines due to the low density of distributed generators will cause an unequal share of reactive power. With regards to this problem, modification is put forward for the droop control strategy to share the reactive power equally. The feasibility of the design is validated by simulation and experimental results.

Comparison of Conventional DC-DC Converter and a Family of Diode-Assisted DC-DC Converter in Renewable Energy Applications

Zhang, Yan,Liu, Jinjun,Ma, Xiaolong,Feng, Junjie The Korean Institute of Power Electronics 2014 JOURNAL OF POWER ELECTRONICS Vol.14 No.2

In the conventional dc-dc converter, a pair of additional diode and the adjacent passive component capacitor/inductor can be added to the circuit with an X-shape connection, which generates a family of new topologies. The novel circuits, also called diode-assisted dc-dc converter, enhance the voltage boost/buck capability and have a great potential for high step-up/step-down power conversions. This paper mainly investigates and compares conventional dc-dc converter and diode-assisted dc-dc converter in wide range power conversion from the aspects of silicon devices, passive components requirements, electro-magnetic interference (EMI) and efficiency. Then, a comprehensive comparison example of a high step-up power conversion system was carried out. The two kinds of boost dc-dc converters operate under the same operation conditions. Mathematical analysis and experiment results verify that diode-assisted dc-dc converters are very promising for simultaneous high efficiency and high step-up/step-down power conversion in distributed power supply systems.

Efficacy of a DNA Vaccine Carrying Eimeria maxima Gam56 Antigen Gene against Coccidiosis in Chickens

Jinjun Xu,Yan Zhang,Jianping Tao 대한기생충학열대의학회 2013 The Korean Journal of Parasitology Vol.51 No.2

Signal Detection Based on a Decreasing Exponential Function in Alpha-Stable Distributed Noise

( Jinjun Luo ),( Shilian Wang ),( Eryang Zhang ) 한국인터넷정보학회 2018 KSII Transactions on Internet and Information Syst Vol.12 No.1

Signal detection in symmetric alpha-stable (SaS) distributed noise is a challenging problem. This paper proposes a detector based on a decreasing exponential function (DEF). The DEF detector can effectively suppress the impulsive noise and achieve good performance in the presence of SaS noise. The analytical expressions of the detection and false alarm probabilities of the DEF detector are derived, and the parameter optimization for the detector is discussed. A performance analysis shows that the DEF detector has much lower computational complexity than the Gaussian kernelized energy detector (GKED), and it performs better than the latter in SaS noise with small characteristic exponent values. In addition, the DEF detector outperforms the fractional lower order moment (FLOM)-based detector in SaS noise for most characteristic exponent values with the same order of magnitude of computational complexity.

Drag reduction of a disk with an upstream rod

Zhang, Panfeng,Gao, Lei,Wang, Jinjun Techno-Press 2006 Wind and Structures, An International Journal (WAS Vol.9 No.3

The pressure and drag measurements were carried out in the wind tunnel to investigate the drag reduction of the disk by using an interference rod placed upstream. The results indicate that there is a pair of standing vortices in the front stagnation region of the disk induced by the rod. The standing vortices can decrease the pressure on the disk upwind side; hence it can reduce the drag of the disk. With an increasing rod diameter, the standing vortices are strengthened and more drag reduction can be achieved for the disk. With rod diameter d/D = 0.05 (d, D are the diameters of rod and disk, respectively), the total drag of the disk can be reduced by about 9% compared with that of the bare disk.

Study on the Influence of Distribution Lines to Parallel Inverter Systems Adopting the Droop Control Method

Xuan Zhang,Jinjun Liu,Zhiyuan You,Ting Liu 전력전자학회 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.4

This paper takes into account the influence of the different impedances of distribution lines on power distribution among inverters when the inverters are paralleled with the droop control method. The impact of distribution lines on the power distribution of inverters can be divided into two aspects. Firstly, since the distributed generators are in low voltage grids, there is resistive impedance in the distribution lines, which will cause control coupling and reduce system stability. The virtual negative resistive impedance of inverters is adopted in this paper to neutralize the resistive element of distribution lines and thus make the distribution line impedance purely inductive. Secondly, after solving the resistive impedance problem, the difference in the inductive impedance value of distribution lines due to the low density of distributed generators will cause an unequal share of reactive power. With regards to this problem, modification is put forward for the droop control strategy to share the reactive power equally. The feasibility of the design is validated by simulation and experimental results.

Virtual negatively resistive output impedance for power sharing among paralleled inverters in microgrid

Xuan Zhang,Jinjun Liu,Ting Liu 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

In this paper, a new control method for paralleled inverters in microgrid is presented. The strategy of power sharing among inverters in microgrid can be divided into control with and without communication. When there is no communication among inverters, droop control is used to share power. But droop control is effective only when the transmission line is approximately pure inductive. Microgrid is in the distribution network in power system, so the resistive component in transmission line is very high. Under this condition, there is severe coupling in droop control and power sharing mechanism is invalid. In this paper, by making use of virtual impedance, the equivalent output impedance of inverter becomes negatively resistive, while its amplitude equals to the value of resistive component in transmission line, so the resistive component in transmission line will be neutralized. So the circuit can be viewed as inverter supplying power through pure inductive transmission line. Therefore, the coupling in droop control can be removed and power sharing mechanism is effective. The analysis of the proposed method and design procedure are provided. Simulation results validate the proposed control strategy.

Comparison of Magnetic Force Calculation on Permanent Magnets with Models of Equivalent Magnetic Charge and Magnetizing Current

Yuyang Zhang,Yonggang Leng,Jinjun Liu,Dan Tan 한국자기학회 2019 Journal of Magnetics Vol.24 No.3

Accurate magnetic force calculation is essential to effectively analyzing a system or device containing magnets. Among several approaches used in the interacting magnetic force calculation of permanent magnets, equivalent magnetic charge and equivalent magnetizing current models are widely adopted. In this paper, we choose cubes and cylinders as calculating objects to investigate the detailed calculation procedures. Higher calculation accuracy of the equivalent magnetizing current model is verified by comparison between simulation and experiment results. Furthermore, we analyze the relations between two models and discriminate their equivalence in the magnetic force calculation respectively at both micro and macro scale. Reference basis for choosing a proper model to calculate magnetic force is provided in this work, which is beneficial for the design of electro-mechanical structures with permanent magnets.

Study on Magnetic Force Calculation of Spherical Permanent Magnets

Yuyang Zhang,Yonggang Leng,Dan Tan,Jinjun Liu Korean Magnetics Society 2018 Journal of Magnetics Vol.23 No.4

This paper presents three approaches to calculate the interacting magnetic force about spherical permanent magnet, respectively based on magnetic dipole-dipole model, equivalent magnetic charge model and equivalent magnetizing current model. We use all of three models to fully calculate and study the behaviors of lateral and axial forces with respect to the related positions between a pair of spherical magnets. The accuracies of the calculation results are compared with the experimental data. In conclusion, the magnetic dipole-dipole model has the most advantageous accuracy and efficiency for the magnetic force calculation about spherical permanent magnets on account of the particularity of sphere. Our study provides an important criterion for choosing a proper method to calculate magnetic force about spherical permanent magnet.