Zhengyu Lu

Zhejiang University, Hang-hsien, Zhejiang Sheng, China

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Publications (132)125.45 Total impact

  • Kai Wang · Wenxi Yao · Bin Chen · Guangtong Shen · Kevin Lee · Zhengyu Lu
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    ABSTRACT: It is necessary to obtain accurate knowledge about the magnetizing curve of an induction machine so that the magnetizing inductance can be updated according to different flux references for either efficiency optimization or field weakening control. This paper proposes a computational saving method to obtain a one-to-one correspondence magnetizing curve without the need for conventional curve-fitting strategies, which require the assumption of explicit analytical curve functions. A detailed comparison between the proposed method and the conventional curve-fitting method has been done. It shows great accuracy improvements of this proposed method. The identification is easy to implement with high precision while maintaining the motor at standstill. No additional sensor devices are needed except the sensors carried by the drive itself. This proposed method is verified by simulation. Further experimental results of this method are utilized in a real control strategy with a 2.2-kW 50-Hz 4-pole induction motor to confirm its validity and feasibility.
    IEEE Transactions on Industrial Electronics 04/2015; 62(4):2144-2155. DOI:10.1109/TIE.2014.2354012 · 6.50 Impact Factor
  • Kahyun Lee · Wenxi Yao · Bin Chen · Zhengyu Lu · Anbo Yu · Di-Jie Li
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    ABSTRACT: Open-loop constant voltage/frequency (v/f) adjustable speed drives (ASDs) can often experience undesirablesustained oscillations. Factors affecting these oscillation states include induction machine (IM) parameters, dead time,dc-link capacitor size, IM saturation, output voltage, carrier frequency, and IM speed. Many literatures have discussedthe instabilities in light-load or low-frequency operating conditions. Quite a few methods have been proposed forstabilizing such a system. However, the instability problems, at different power levels, have not been completelydescribed. This paper analyzes the causes of this instability for constant v/f drives as power levels change. The 2.2-and 15-kW low-voltage IMs and the 746-kW medium-voltage IM are evaluated to illustrate how the motor parameters affectthe system stability. Additionally, a new oscillation mitigation method is introduced to demonstrate its effectivenessin solving the instability problems. It is based on the synchronous reference frame dynamic current feedback through itsmagnetic flux current component bandpass filtering and proportional control. In a theoretical stability analysis beforeand after the current feedback compensation, simulation studies are presented and verified through a 15-kW 380-V 50-HzIM ASD experimental system.
    IEEE Transactions on Industry Applications 11/2014; 50(6):3767-3776. DOI:10.1109/TIA.2014.2320603 · 2.05 Impact Factor
  • Guangtong Shen · Wenxi Yao · Bin Chen · Kai Wang · Kevin Lee · Zhengyu Lu
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    ABSTRACT: In order to improve the performance of sensorless field-oriented controlled motor drives at low speed, the inverter nonlinearity should be compensated for by an accurate voltage error model. This paper proposes a novel method to automatically obtain the total output voltage delay curve, which is a significant part of the inverter voltage error model. Unlike manual measurements of the output delays in earlier literatures, the proposed automatic measurement method achieves low cost in time and labor. Meanwhile the compensation accuracy based on the auto-measured output voltage delay curve is approaching to the performance of compensation by manual measurement method, far better than the accuracy of compensation by the standard square wave model at low speed. Moreover, in contrast to other inverter nonlinearity auto-measurement methods, the measured results of the proposed method can be applied to compensate for inverter nonlinearities at different switching frequencies. The effectiveness of this method is validated in a voltage source inverter fed induction motor drive system experimentally.
    IEEE Transactions on Power Electronics 10/2014; 29(10):1-1. DOI:10.1109/TPEL.2013.2293134 · 5.73 Impact Factor
  • Kai Wang · Bin Chen · Guangtong Shen · Wenxi Yao · Kevin Lee · Zhengyu Lu
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    ABSTRACT: The simultaneous online estimation algorithm of rotor time constant and rotor speed for a speed-sensorless induction machine is proposed. With a small signal injected to the flux command, the method can accurately complete the online tuning of $T_{r}$ over a wide range of speed estimation, including the rated speed and the very low speed of 1 Hz or even lower speeds under both no-load and loaded operations. Sensitivity of stator resistance error is studied, and the impact of stator resistance error on this method is severely reduced by the closed-loop structure of combined voltage and current (UI) mode flux observer. The identification process only needs the ac component amplitude without considering ac component phase drifts; thus, the division by zero at the zero-crossing point is avoided, which greatly increases the accuracy. Furthermore, any differential integral operations or even a filter is not needed; hence, the computation is rather simple and time saving. Moreover, unlike other signal injection methods, there are no special requirements on the injected signal frequency. The accuracy and validity of the method has been verified by Matrix Laboratory simulation model. Further experimental results on a 2.2-kW 50-Hz 4-pole induction motor also show effectiveness of this proposed method.
    IEEE Transactions on Industrial Electronics 09/2014; 61(9):4583-4593. DOI:10.1109/TIE.2013.2288227 · 6.50 Impact Factor
  • Kai Wang · Wenxi Yao · Kevin Lee · Zhengyu Lu
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    ABSTRACT: In speed sensorless induction machine control, the reduced-order observer, i.e., the combined voltage and current (UI) mode flux observer, obtains good flux estimation results in the full-speed range but has some drawbacks in the stability characteristics. This paper constructs the small-signal model of the UI mode flux observer and derives the characteristic matrix to realize the stability analysis, based on which the stable range with corresponding conditions has been calculated explicitly. Furthermore, a cross-coupling feedback mechanism is proposed to solve the instability problem when the machine runs in the low-speed regenerating or plugging-in mode. The cross-coupling feedback coefficient is adjusted by the estimated speed or the speed command (conditional) for further simplification and is easy to be implemented. The improvement strategy is well verified by both the simulation in MATLAB and corresponding experimental results.
    IEEE Transactions on Industry Applications 07/2014; 50(4):2564-2573. DOI:10.1109/TIA.2014.2301869 · 2.05 Impact Factor
  • Ming Zhang · Long Huang · Wenxi Yao · Zhengyu Lu
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    ABSTRACT: An improved circulating current control method by applying a digital plug-in repetitive controller is discussed for harmonic elimination of a carrier-phase-shift pulse-width-modulation (CPS-PWM)-based modular multilevel converter (MMC) in this paper. The performance of the controller is analyzed in detail based on an improved circulating current control model with the consideration of the submodule voltage disturbance. It is shown that the proposed control method has the merits of simplicity, versatility, and better performance of circulating harmonic current elimination than the traditional proportional integral controller. The stability analysis of the proposed method are also discussed in the paper as well as the design principles. Finally, the experimental results including the steady-state performance and the transient response are given, which validates the feasibility and excellent performance of the proposed control scheme.
    IEEE Transactions on Power Electronics 04/2014; 29(4):2083-2097. DOI:10.1109/TPEL.2013.2269140 · 5.73 Impact Factor
  • Bin Chen · Ting Wang · Wenxi Yao · Kevin Lee · Zhengyu Lu
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    ABSTRACT: The convergence rate of speed estimation is an important criterion to evaluate the performance of the adaptive full-order observer (AFO) in speed-sensorless induction motor drives. Based on the analysis of the speed convergence rate, the AFO with different feedback gains has corresponding shortcomings in specific operating regions. Thus, a new proposed design strategy that adopts a different set of feedback gains in different operating regions is more appropriate. In this study, the AFO below rated speed uses two optional sets of feedback gains. In the low-speed regenerative mode, a novel set of feedback gains is proposed to enhance the stability and provide a faster convergence rate of the speed estimation. In the other operating region, the traditional set of feedback gains with zero parameters is selected. The validity of the proposed method is confirmed by simulation study and experimental results. Good sensorless experimental operation, containing zero speed, is implemented.
    IET Electric Power Applications 01/2014; 8(1):13-22. DOI:10.1049/iet-epa.2013.0210 · 1.31 Impact Factor
  • Ming Zhang · Lijun Hang · Wenxi Yao · Zhengyu Lu · L.M. Tolbert
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    ABSTRACT: Unbalanced grids introduce performance deterioration for Vienna rectifier topology by producing twice fundamental frequency ripples in dc-link voltage and input active/reactive power. A common current reference generation for the purpose of eliminating the input power ripple, such as dual-frame hybrid vector control, can maintain constant input power and eliminate ripples in dc-link voltage under light voltage unbalanced grids. Under severe unbalanced grids, this type of a control method will fail to work. This paper first analyzes the theoretical operation area of a constant power control method under unbalanced grids, and then a novel control method is proposed. The proposed control method can work under severe unbalanced grids by injecting a small amount of input power ripple and balance the performance of working area and output dc voltage ripples. Finally, the experiment results using the constant power control method are given and validate the performance of the proposed control method.
    IEEE Transactions on Industrial Electronics 10/2013; 60(10):4243-4252. DOI:10.1109/TIE.2012.2217721 · 6.50 Impact Factor
  • Huiqing Wen · Weidong Xiao · Zhengyu Lu
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    ABSTRACT: A current-fed high-frequency alternating-current (HFAC) distributed power system is presented in this paper for medium- or high-voltage gate driving applications. The distributed gate driving modules (GDMs) at the high-voltage side are isolated from the low-voltage-side current-source power supply through magnetic coupling of current transformers (CTs), which are assembled by a high-voltage cable carrying HFAC and passing through the center of toroid magnetic cores. The centralized high-frequency current-source power supply is designed and composed of a two-stage resonant inverter and a double Γ-CL resonant network. The resonant network is parameterized by considering the tradeoff between the quality factor and component stress. Different magnetic core samples are tested and compared to construct the CTs for improving transmission efficiency. A 400-W prototype was built and experimentally evaluated with two load conditions, including resistive loads and practical GDMs. It showed significant improvements with regard to sinusoidal current output, system stability, and efficiency. Finally, the proposed current-fed HFAC power supply system was successfully applied to a practical solid-state fault current limiter, demonstrating the advantages of multiple outputs (n > 10), high-voltage isolation, low harmonic distortion, high efficiency, easy installation, and flexible extensibility.
    IEEE Transactions on Industrial Electronics 09/2013; 60(9):3736-3751. DOI:10.1109/TIE.2012.2207659 · 6.50 Impact Factor
  • Kevin Lee · Wenxi Yao · Chen Bin · Zhengyu Lu · Anbo Yu · David Li
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    ABSTRACT: Open-loop Volts/Hz controlled industrial adjustable speed drives (ASD) can often experience undesirable sustained oscillations. Factors affecting these oscillation states include induction machine (IM) parameters, dead time, dc link capacitor size, IM saturation, output voltage, carrier frequency, and IM speed. Many literatures have discussed the instabilities in light load or low frequency operating conditions. Quite a few methods have been proposed for stabilizing such a system. However, the instability problems at different power levels, have not been completely described. This paper analyzes the causes of this instability for Volts/Hz based industrial ASDs as power levels change. A 2.2kW and 15kW IMs are evaluated to illustrate how the motor parameters affect the system stability. Additionally, a new oscillation mitigation method is introduced to demonstrate its effectiveness in solving the instability problems. It is based on the dynamic current feedback through its magnetic flux current component band pass filtering and proportional control. Theoretical stability analysis before and after the current feedback compensation, simulation studies are presented and verified through a 20hp (15kW), 380V, 50Hz IM ASD experimental system.
    2013 IEEE Energy Conversion Congress and Exposition (ECCE); 09/2013
  • Bin Su · Huiqing Wen · Junming Zhang · Zhengyu Lu
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    ABSTRACT: An improved soft-switching post-regulator topology for multi-outputs dual forward DC/DC converter is presented. A delay-trailing modulation method is proposed. ZVSZCS on/zero-current-switching off conditions can be realised on both the primary MOSFETs and the secondary rectifying diodes. Excellent decoupling among different outputs and tight output voltage regulation are achieved. The efficiency is improved due to single power-conversion stage and share in the primary components. The operating principle and main feature of this improved topology are analysed. Key design issue including zero-voltage-switching operation, maximum duty ratio of the primary side MOSFETs and parameter determination for the primary magnetising inductor and the secondary additional redistribution capacitor are discussed. Finally, an experimental prototype with two outputs (300–400 V input, 48 V, 6.5 A and 24 V, 11 A outputs) is built to verify the theoretical analysis. The measured efficiency at normal operation input voltage (400 V) is improved by about 0.5–2%, and the measured efficiency under light loads is improved by more than 2%.
    IET Power Electronics 07/2013; 6(6):1069-1077. DOI:10.1049/iet-pel.2012.0516 · 1.32 Impact Factor
  • Bin Su · Junming Zhang · Huiqing Wen · Zhengyu Lu
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    ABSTRACT: A low conduction loss and low device stress three-level rectifier is proposed and the corresponding neutral-point voltage balance control scheme is presented in this study. Compared with the conventional rectifier, the MOSFET voltage rating can be reduced by half. The inductance and the volume of input inductor are reduced. The conduction losses can also be lowered because of the elimination of the front–end bridge rectifier and the adoption of synchronous rectification. The neutral-point voltage balance algorithm based on the average current-mode modulation is illustrated with constant frequency operation. To verify the theoretical analysis, a universal line input 100 kHz, 900 W prototype is built. The experimental results show that the input inductor volume is greatly reduced and the neutral-point voltage balance of the prototype is fulfilled considering various load conditions and dynamic processes. The proposed rectifier improves the efficiency by 2% under 90 V line input voltage compared with the conventional one.
    IET Power Electronics 03/2013; 6(3):478-487. DOI:10.1049/iet-pel.2012.0515 · 1.32 Impact Factor
  • Wenxi Yao · Zhengyu Lu · Huang Long · Bin Li
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    ABSTRACT: Grid-connected inverter is one of the key techniques of renewable energy generation. High-order filter like LCL filter is normally used as a standard interface to the grid to provide the proper attenuation of switching frequency harmonics. However the resonant of LCL filter limits the improvement of both steady state and dynamic performance of grid-connected inverter. In this paper, a new solution of grid-connected inverter with multi-interleaved techniques is investigated, where a simple L filter is employed in each interleaved unit instead of LCL filter. Analytical study and parameters' design of this solution is presented. It can be founded that the total size of passive filter of this type of interleaved grid-connected inverter is almost the half of that of traditional LCL filter based grid-connected inverter. Additionally, the mathematic model of this L-filter based interleaved (LFI) grid-connected inverter is deduced. Although the control structure of the proposed topology is very complex, the control algorithm is comparative simple thanks to the simple equivalent mathematic model. Simulations and experiments are finally conducted to verify the presented method has improved steady state and dynamic performance.
    Future Energy Electronics Conference (IFEEC), 2013 1st International; 01/2013
  • Kai Wang · Wenxi Yao · K. Lee · Zhengyu Lu
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    ABSTRACT: Accurate flux estimation is essential in rotor flux oriented speed sensorless induction machine control. The closed-loop of combined voltage and current (UI) mode flux observer obtains good flux estimation results in the full-speed range but has some drawbacks in the stability characteristics. This paper constructs the small signal model of the UI mode flux observer, derives the characteristic matrix to realize the stability analysis, and then calculates its stable range with the corresponding conditions. In addition, a cross-coupling feedback mechanism is proposed to expand the stable range, especially when the machine runs in the low-speed regeneration or plugging-in mode. Furthermore, the cross-coupling feedback coefficient is adjusted by the working torque to realize the stability in the full-speed range. The improvement strategy is well verified by both the simulation in MATLAB and corresponding experimental results.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • Bin Chen · Wenxi Yao · Kai Wang · K. Lee · Zhengyu Lu
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    ABSTRACT: The adaptive full-order observers have been widely and successfully applied in sensorless induction motor drives. In the design of the observer, selecting proper feedback gains is the key, and many kinds of feedback gains have been proposed in the past years, but there are very few comparative studies. This paper presents a comparative study of three classical sets of feedback gains: Proportional Poles (PP), Left Poles (LP), Complete Stability (CS). The comparative analysis is based on two aspects: the convergence rate of the flux estimation, and the stability of the speed estimation. The advantages and disadvantages of each set of feedback gains are summarized. Not only computer simulations, but also experimental results are presented to confirm the validity of the proposed analysis. For the comparison tests in the paper, the dynamic parameters of both speed estimation and controlling are set at the same value for different feedback gains.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • Sensen Liu · Lijun Hang · L.M. Tolbert · Zhengyu Lu
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    ABSTRACT: A natural abc frame based current control loop, which considerably reduces total algorithm complexity, and also helps to reduce the reactive components size and total loss in comparison to the traditional dual current control schemes, is proposed for a Vienna rectifier under unbalanced input conditions. Experimental results are presented to verify the validity of the proposed controller.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • Zhuang Lin · Wenxi Yao · Zhihong Bai · Zhengyu Lu
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    ABSTRACT: LCL filter presents a significant attenuation of switching harmonics, however its resonance peak influences the system stability. Passive damping reduces the switching current harmonics attenuation and increases the extra losses. Nevertheless, traditional active damping method often needs additional sensors or increases the complexity of algorithm. According the Nyquist stability criterion, a novel active damping method is proposed in this paper based on the grid current feedback compensation which adds no more sensors and easy to control. Two kinds of current compensation transfer function are presented. Moreover, the design principles and the range of stable system with active damping are derived step by step. Finally, it compares the damping effect of the different compensation methods through experiment and verifies the theoretical analysis at the same time.
    Industrial Electronics (ISIE), 2013 IEEE International Symposium on; 01/2013
  • Guangtong Shen · Kai Wang · Wenxi Yao · Kevin Lee · Zhengyu Lu
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    ABSTRACT: A general stimulation method is proposed to identify induction motor (IM) parameters based on inverter at standstill without the need of inverter nonlinearity compensation. Inverter non-linear characteristics are one of the major sources of parameters identification inaccuracies because the voltage error caused by inverter nonlinearity is difficult to compensate for accurately. To overcome the influence of inverter nonlinearity, a dc current bias is added to single phase ac stimulation, which is a common stimulation style of many identification techniques. To prove the effectiveness and universality of the method, it is applied to two kinds of practical offline parameter identification techniques in literatures. One is the recursive least-squares (RLS) technique and the other is impedance equations set technique. Identification results in both simulations and experiments are given to validate the method.
    Energy Conversion Congress and Exposition (ECCE), 2013 IEEE; 01/2013
  • Bin Li · Lijun Hang · Wenxi Yao · Zhengyu Lu
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    ABSTRACT: In this paper, the analysis of Space Vector Modulation (SVM) of three phase/wire/level VIENNA rectifier is conducted, according to which the implementation of the equivalent carrier-based PWM is deduced theoretically within each separated sector in the diagram of vectors. The voltage balancing ability of DC-link neutral point, which depends on the uneven distribution of short vectors, is analyzed as well. An adaptive and robust controller to balance the output voltage under the unbalanced load limit for different modulation index is proposed. Furthermore, the maximum of unbalanced load is deduced versus the modulation index m. An experimental prototype of 2.5kW was built to verify the effectiveness of the theoretical analysis. Finally, the tested unbalanced limit of outputs for the experimental platform was given under different modulation index.
    09/2012; DOI:10.1109/ISIE.2012.6237106
  • Lujun Wang · Damin Zhang · Chong Zhang · Zhengyu Lu
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    ABSTRACT: A high performance Phase-Locked Loop (PLL) based on cascade adaptive notch filters (ANF) is proposed for polluted utility grid in this paper. The proposed cascade structure can regenerate a new signal similar to the fundamental component of the original grid voltage sample signal with the same amplitude and no phase shift. Compared to traditional PLL, The proposed PLL is more accurate especially when the grid voltage contains harmonics. The static behavior of noise rejection and harmonics rejection is verified by simulations and experiments. The dynamic performance of step frequency tracking is also evaluated. Simulations and experiments show that the proposed PLL not only has small static errors but also has a quick dynamic response.
    2012 7th International Power Electronics and Motion Control Conference (IPEMC 2012); 06/2012

Publication Stats

995 Citations
125.45 Total Impact Points

Institutions

  • 2000–2014
    • Zhejiang University
      • • College of Electrical Engineering
      • • Department of Electrical Engineering
      Hang-hsien, Zhejiang Sheng, China
    • Hangzhou University
      Hang-hsien, Zhejiang Sheng, China
  • 2007–2008
    • Nanjing Normal University
      Nan-ching, Jiangsu Sheng, China