Zhengyu Lu

Zhejiang University, Hangzhou, Zhejiang Sheng, China

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Publications (110)66.56 Total impact

  • [Show abstract] [Hide abstract]
    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 01/2014; 29(4):2083-2097. · 4.08 Impact Factor
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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. · 1.56 Impact Factor
  • 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
  • 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
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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 01/2013; 60(10):4243-4252. · 6.50 Impact Factor
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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
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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
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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
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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
  • Source
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    ABSTRACT: This paper presents one non-regenerative front-end three-phase AC/DC power factor correction (PFC) rectifier, which is based on VIENNA topology. At first, the space vector pulse width modulation method (SVPWM) for this converter is theoretical analyzed and the control method based in d-q frame is given. Then the DC-link voltage utilization ratio is studied based on the SVPWM strategy. The unbalance ability by applying SVPWM method is theoretical analyzed. The theoretical analysis is well verified by the experimental results.
    01/2012;
  • K. Lee, Wenxi Yao, Wenbin Lu, Zhengyu Lu
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    ABSTRACT: Although adjustable-speed drives (ASDs) with induction machines (IMs) have already evolved as a mature technology, accurate encoderless operation at very low speed range remains to be problematic for all existing control methods, which include nonlinearity compensation, model-reference-adaptive-system (MRAS), various types of observers, high frequency injection leveraging saliency effects, artificial intelligence (AI) or neural network techniques. These encoderless solutions are integrated into either direct torque control (DTC), or stator current regulated pulse-width-modulated (CRPWM) controllers. The DTC solution can have better dynamic responses, while the CRPWM regulator provides superior steady state performances. In the category of observer formulations without signal injection, one promising dual frame sliding mode observer (DFSMO) can achieve a published performance of below 6 revolutions per minute (rpm) (0.2Hz) at full load under a DTC scheme. DFSMO does not need the rotor position or rotor flux angle, thus it increases the estimation accuracy and is tolerable to IM parameter variations and disturbances. Even though DTC schemes have been researched more in recent years, the rotor flux orientated vector control (RFOVC) architecture still dominates industrial applications. In this paper, instead of DTC, a DFSMO is developed under the RFOVC architecture which cannot be found in published literatures to demonstrate its transient and steady-state low speed performances at both motoring and regenerating mode. Analytical, simulation studies are presented and verified through a 3hp (2.2kW), 380V, 50Hz IM ASD experimental system.
    Energy Conversion Congress and Exposition (ECCE), 2012 IEEE; 01/2012
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    ABSTRACT: This paper presents one front-end three-phase AC/DC power factor correction (PFC) rectifier, which is based on three-level bidirectional-switch VIENNA topology. On one hand, the rectifier, which is designed to operate in continuous-conduction mode (CCM) at full power, operates at reduced load, discontinuous-conduction mode (DCM) occurs in a zone which is close to the crossover of the line voltage. On the other hand, with the reduced input inductance, the DCM mode occurs even when the rectifiers operate at full power. In this paper, the digitized feedfoward compensation method is proposed for the rectifier to reduce the impact of the switch between DCM and CCM. The theoretical analysis of the proposed method is deduced, furthermore, the control design strategy is given. The experimental results are obtained by using a digitally controlled VIENNA rectifier, which validated the proposed compensation method.
    IEEE Transactions on Industrial Electronics 01/2012; 60(4). · 6.50 Impact Factor
  • 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.
    01/2012;
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    ABSTRACT: In this paper, the design of PR regulator which is applied on the grid-connected inverter with LCL-filter, is analyzed in details. By modeling the system under stationary frame, the open and close-loop transfer function is given, which is used in analyzing the impact of each parameter on root locus. Using the root locus theory, the proper parameters are selected so that the resonance of LCL-filter is attenuated, the current ripple is suppressed and the sinusoidal input is well tracked, which means the output grid current is of high quality. A 10kW prototype is built and the result of the experiments verified the effectiveness of the proposed PR regulator design.
    01/2012;
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    ABSTRACT: A magnetic amplifier (Magamp) postregulator using a time-sharing control strategy is proposed when using a multioutput LLC series resonant converter. The operating principles of the proposed converter and the Magamp postregulator are analyzed in detail. Furthermore, the design criterion for the Magamp core is presented, and the dead-time problem of the Magamp postregulator is analyzed. Compared with a flyback converter, the dead-time impact in the LLC structure is much better for two main reasons. The first one is that there is no reverse-recovery resetting effect for the Magamp postregulator in an LLC topology, and the second is that, when the same dead time is applied in both converters, the effect is better by using an LLC topology than a flyback topology. Finally, an experimental prototype of 310-V input and 24-V/3-A and 18-V/2-A outputs was built and tested to verify the zero-voltage-switching (zero-current-switching) operation and the high cross-regulating ratio. The experimental results prove that the dead-time impact over a Magamp in an LLC converter is much better than that when using a flyback converter, since a high cross-regulating ratio was easily achieved without using complicate resetting methods or large dead load.
    IEEE Transactions on Industrial Electronics 10/2011; · 6.50 Impact Factor
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    ABSTRACT: During grid faults, three-phase grid-connected converters neighboring fault points usually operate under unbalanced and distorted operation conditions. This paper proposes a Direct Decoupled Synchronization Method (DDSM) based on direct decoupling of fundamental symmetrical voltages. Specifically, after Clarke transformation of three-phase measured voltage, a decoupling scheme of positive- and negative-sequence components from reference voltage uα, uβ is implemented, in which some advanced single phase PLL modules are used. These modules, which can generate the inphase and quadrature-phase waveforms of the input signals, can be regarded as frequency adaptive filters. DDSM can also be easily expanded to deal with low-order harmonics. In comparison to existing three phase synchronization methods, operation properties and frequency response of the proposed synchronization schemes are analyzed. The conclusions are verified by experimental results.
    01/2011;
  • Wei Chen, Ping Rong, Zhengyu Lu
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    ABSTRACT: A bidirectional DC-DC converter (BDC) with a new CLLC-type resonant tank, which features zero-voltage switching (ZVS) for the input inverting choppers and zero-current switching (ZCS) for the output rectifier switches, regardless of the direction of the power flow, is proposed in this paper. Possessing the very optimal ZVS +ZCS soft-switching feature, this proposed converter will have a minimized switching loss if all of the main switches are implemented with metal-oxide-semiconductor field-effect transistors, and thereby, the proposed converter is fully soft switched and totally snubberless. The detail operation principles, as well as the design considerations, are presented. The methodologies to develop a unidirectional ZVS+ZCS dc-dc converter for the corresponding pulsewidth modulation and frequency modulation converters are proposed. The approach on how to construct a fully soft-switched BDC has also been proposed and analyzed. Finally, a topology extension is made, and another fully soft-switched BDC is derived. A prototype, which interfaces the 400-48-V dc buses for the uninterrupted power supply system with a power rating of 500 VA, was developed to verify the validity and applicability of this proposed converter. The highest applicable conversion efficiencies for the bidirectional operational modes are exceeding 96%.
    IEEE Transactions on Industrial Electronics 10/2010; · 6.50 Impact Factor
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    ABSTRACT: This paper proposes one novel sliding mode controller for the Half-bridge converter to reduce the line and load disturbance. Based on the bilinear model of the Half-bridge DC/DC converter, the small signal model and the design consideration of the sliding mode controller for this converter are deduced and presented. The controller is simply implemented in the analog controller board. The validation of the controller is verified both by theory analysis and experimental results. By applying the novel sliding mode controller, the Half-bridge converter can achieve good transient response.
    Power Electronics Conference (IPEC), 2010 International; 07/2010
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    ABSTRACT: A bidirectional dc-dc converter with a new CLLC type resonant tank, which features in ZVS for the input inverting port switches and ZCS for the output rectifier port switches, regardless of the direction of the power flow, is proposed. If the MOSFETs are implemented as all of the main switches, the proposed converter has a minimized switching loss. The detail operation principles, as well as the design considerations, are presented. A prototype, which interfacing the 400 V/48 V DC buses for the UPS system with a power rating of 500 VA, whose highest conversion efficiencies for the bidirectional mode both exceed 96%, was developed to verify the validity and applicability of this proposed converter.
    Applied Power Electronics Conference and Exposition (APEC), 2010 Twenty-Fifth Annual IEEE; 03/2010
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    ABSTRACT: This paper presents a method to identify the elevator load torque when the brake is released. With the friction model, the identification process is converted to a searching question. The principle of the method is illustrated in detail, and the factors that influence the identification process and sliding distance are also analysed. Finally, the proposed method is implemented and verified by the results on a permanent magnet synchronous motor drived gearless elevator with an absolute encoder ECN413 from Heidenhain.
    01/2010;

Publication Stats

561 Citations
66.56 Total Impact Points

Institutions

  • 2000–2010
    • Zhejiang University
      • • College of Electrical Engineering
      • • Department of Electrical Engineering
      Hangzhou, Zhejiang Sheng, China
  • 2007–2008
    • Nanjing Normal University
      Nan-ching, Jiangsu Sheng, China
    • Nanjing University
      Nan-ching, Jiangsu Sheng, China