IET Power Electronics
Volume 9, Issue 15, 14 December 2016
Volumes & issues:
Volume 9, Issue 15
14 December 2016
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- Author(s): Wei-Hsiang Ko and Jyh-Cherng Gu
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2751 –2759
- DOI: 10.1049/iet-pel.2016.0310
- Type: Article
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p.
2751
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(9)
A single-phase electric machine invokes a great reactive power demand in operation, resulting in a large voltage fluctuation in the supply system. Furthermore, the frequent and rapid operating characteristics of an electric welding machine cause a serious voltage flicker problem. The operation of welding equipment also generates significant harmonic current distortion, and distorts the voltage waveform of the supply system. Hence, this study focused on designing and applying a thyristor switched capacitor (TSC) bank for voltage flicker improvement. However, the single-phase TSC should also satisfy the reactive power demand and compensation speed, considering proper ratings of TSC to bear high harmonic distortion. This study shows the calculation results and discusses the impact of different capacities and different step numbers on TSC design. In addition, thyristor switches and a single-phase power factor controller were designed and implemented. The experimental results are also presented.
- Author(s): Xin Chen ; Yuncheng Wang ; Yang Zhang ; Jie Chen ; Chunying Gong
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2760 –2768
- DOI: 10.1049/iet-pel.2015.1016
- Type: Article
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p.
2760
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The distributed generation system (DGS) located far away from load centres leads to the existence of long distance transmission lines and several transformer devices. Consequently, the equivalent impedance is introduced to a grid, which is called a weak grid and shows high impedance characteristic. A weak grid will affect the control loop stability of grid-connected inverters in DGS. To study the effects of a weak grid, the small signal model of single-phase LCL-type grid-connected inverters is first derived in this study. Then, the stability of grid-connected inverters caused by the grid impedance is analysed. Second, two common control schemes of passive and active damping are further studied. Then, the effects of the grid impedance on the damping coefficients under different damping options are analysed in quantity. A novel hybrid-damping control scheme is thereby proposed. Meanwhile, an adaptive control scheme of grid-connected inverters based on the hybrid damping is introduced in combination with the grid impedance online measurement, which ensures the stable performance of grid-connected inverters with different grid impedances. Finally, a prototype is built to verify the effectiveness of the proposed adaptive control scheme.
- Author(s): Clemens Zoeller ; Markus A. Vogelsberger ; Thomas M. Wolbank ; Hans Ertl
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2769 –2775
- DOI: 10.1049/iet-pel.2015.0988
- Type: Article
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2769
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In modern traction propulsion applications, voltage source inverter (VSI) fed traction motors today operate very close to borderline conditions. With new emerging semiconductor technologies, higher inverter switching frequencies will be possible and high inverter dv/dt-rates appear, resulting in transient overvoltages at the machine which increase the stress on the insulation system and lead to insulation degradation. Thus, insulation condition monitoring is getting more and more important to ensure a safe and reliable operation of traction motors in trains and locomotives, trams and so on. This study proposes an online insulation monitoring approach that is able to detect incipient insulation defects by evaluation of the motor transient current response on voltage pulses injected by standard inverter switching. Experimental results of this concept are obtained with tests on a 1.4 MW induction machine for railway application. Additionally, the influence of different dv/dt-rates up to 20 kV/µs on the monitoring performance is verified using a VSI-inverter equipped with SiC semiconductors.
- Author(s): Zhiwen Suo ; Gengyin Li ; Rui Li ; Lie Xu ; Weisheng Wang ; Yongning Chi ; Wei Sun
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2776 –2785
- DOI: 10.1049/iet-pel.2016.0426
- Type: Article
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p.
2776
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This paper studies the submodule configuration of modular multilevel converter (MMC) based non-isolated HVDC-DC autotransformer (HVDC-AT) with DC fault blocking capability, including two-terminal and multi-terminal topologies. The operation principle of the HVDC-AT is described. Considering the arm current differences, the total number of required semiconductors for the HVDC-AT is derived and is compared with the MMC based isolated front-to-front DC transformer. A full operation process for the multi-terminal HVDC-AT considering DC fault is then presented, including normal operation, fault isolation and continuous operation of healthy converters after fault. The submodule configuration and fault recovery of the multi-terminal HVDC-AT are validated by simulations using PSCAD/EMTDC.
- Author(s): Katharina Knaisch and Peter Gratzfeld
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2786 –2794
- DOI: 10.1049/iet-pel.2016.0392
- Type: Article
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p.
2786
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In recent years, there has been an increased interest in inductive charging systems for electric vehicles. Since the efficiency of the charging system is highly dependent on the couplers used, the design of the coil system is a key issue for inductive power transfer (IPT). As the coil system has numerous variables, a full factorial analysis of the system is not possible due to the long computation time of the numerical simulation model. Therefore, a surrogate model is developed, which approximates and interpolates the complex and expensive simulation code. With this ‘model of the model’, a reliable and efficient dimensioning and optimisation of the coil system within seconds is possible. It identifies the main important factors and their influence on the IPT system. Based on this surrogate model, important factor relations can be determined, which allow a significant improvement of the behaviour of the IPT system. All simulations conducted in this study are validated and verified.
- Author(s): Jing Zhou ; Yuqing Gao ; Xiaoyan Huang ; Sideng Hu ; Youtong Fang
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2795 –2802
- DOI: 10.1049/iet-pel.2015.0807
- Type: Article
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The wireless power transfer characteristics of system architectures with single transmitter and multiple receiver coils are investigated. With multiple receivers in a limited space, couplings within receivers occur. Effective resonant frequency is changed due to such couplings, the desired working region should be adjusted accordingly. An equivalent circuit model is developed to describe the system with a single receiver, and extended to describe the system with two receivers. The circuit model yields transfer frequency responses that are in good agreement with experimental measurements over a range of frequencies that span the resonance. In a multi-receiver system, a method for tracking frequency shifts or retuning the lumped capacitance so as to maximise the efficiency is proposed. The simulation and experimental results well agree with the theoretical analysis.
- Author(s): Xintian Zhou ; Yan Wang ; Ruifeng Yue ; Gang Dai ; Juntao Li
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2803 –2807
- DOI: 10.1049/iet-pel.2016.0399
- Type: Article
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p.
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Silicon carbide Schottky barrier diodes (SiC SBDs) are poised to replace silicon PIN diodes as a new choice for the high power and high frequency applications. However, SiC SBDs suffer from ringing which may induce additional power losses when applied in chopper circuit, regarded as the interaction among the depletion capacitance, depletion resistance, parasitic stray inductance and series resistance. The existing SiC SBD models generally treat the resistances as constants and ignore the influence of the MOS, which deviate the switching commutation process significantly on the ringing frequency and amplitude. In this study, a more accurate Spice model of SiC SBD has been developed in which voltage dependent non-linear depletion capacitance and resistances are all considered in the transient analysis based on semiconductor physics, while the Miller capacitance of the MOS performing as a switch in the circuit is also taken into account. The improved model and analysis are validated by the better agreement with the experiments compared with the existing models on the dynamic characteristics.
- Author(s): Natarajan Prabaharan and Kaliannan Palanisamy
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2808 –2823
- DOI: 10.1049/iet-pel.2016.0283
- Type: Article
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Multilevel inverters (MLIs) are gaining familiarity in industries for high-voltage applications. This study is a comparison of symmetric and asymmetric reduced switch MLI topologies which require a lesser number of switches for generating the desired number of voltage levels. In both symmetric and asymmetric conditions, output voltage levels are generated using the same number of switches with different DC source magnitudes. Unipolar pulse width modulation strategy is adapted in these topologies to generate the switching pulses. Three different unipolar references (sine, trapezoidal, 60°) and three different carrier arrangements (phase disposition, alternative phase opposition and disposition and variable frequency) are taken and each reference is compared with three different carrier signals. The performance parameters such as total harmonic distortion (THD), crest factor and distortion factor are evaluated for different modulation indices and compared with both conditions. The proposed topology in symmetric and asymmetric conditions can generate 9-level and 31-level output voltages, respectively, which are simulated using MATLAB/Simulink and verified with the experimental setup. The calculation of %THD using analytical asymptotic formula is also carried out. The theoretical value of %THD is verified to match closely with the simulation and experimental results.
- Author(s): Ruidong Xu ; Yong Zhang ; Long Wang ; Guipeng Chen ; Shiming Liu ; Huiqing Wen
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2824 –2832
- DOI: 10.1049/iet-pel.2016.0386
- Type: Article
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This study reports a new slow-scale bifurcation phenomenon in linear frequency of power factor correction (PFC) cascade converters, which will offer a useful design reference for PFC power application. Compared with the resistive loads analysed before, the stability of PFC cascade converters is studied, which are more complex but practical. This study has introduced the research method that the secondary efficient point-of-load converter can be equivalent to a constant power load. Based on this method, the small-signal model of the whole system is constructed and the characteristic equations are thus derived. Subsequently, the stable boundary is determined when the coefficients of the characteristic equations are positive according to Routh–Hurwitz stability criterion. Furthermore, the time-domain waveforms and phase portraits between the output voltage and the inductor current are given according to numerical simulation and experimental results at different points. Meanwhile, the total harmonic distortion and the fast Fourier transform diagrams are compared to reveal the influence of the bifurcation phenomenon on power quality of the system. The results provide useful information of parameter space for the design and operation of the converter in the desired fundamental stable regime.
- Author(s): Zhenhua Deng and Xiaohong Nian
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2833 –2845
- DOI: 10.1049/iet-pel.2015.0560
- Type: Article
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p.
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Two parallel-connected permanent magnet synchronous motors (PMSMs) fed by a single inverter is investigated in this study. A robust controller is designed for this system via interval matrix, and in terms of bilinear matrix inequalities, sufficient conditions for the existence of the robust controller are derived. The proposed controller not only can deal with the uncertainty of load, but also has robust to the parameter perturbation. The effectiveness of the proposed controller is proved by theory analyses and computer simulation. Besides, the simulation results show that the control performance of the proposed control strategy is better than that of the conventional master–slave strategy.
- Author(s): Chen Xu ; Ke Dai ; Xinwen Chen ; Yong Kang
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2846 –2858
- DOI: 10.1049/iet-pel.2015.1038
- Type: Article
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p.
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Unbalanced voltage fluctuation at the point of common coupling (PCC) is a challenging power quality problem in power distribution system. This study presents an unbalanced PCC voltage regulation scheme with positive- and negative-sequence control for modular multilevel converter (MMC) in medium-voltage distribution static synchronous compensator (DSTATCOM) application. The proposed positive-sequence control is utilised to regulate the positive-sequence component of PCC voltage to rated value, while the negative-sequence control aims to cancel out the negative-sequence component of PCC voltage completely. Compensation commands whether in positive- or negative-sequence control are generated from unbalanced PCC voltage without utilisation of unbalanced load currents. DC circulating currents transferring active power among three phases of MMC are also analysed to illustrate power balance issue resulting from negative-sequence control. Then comparison of negative-sequence compensation capacity between MMC and full-bridge cascaded converter with delta-connection is illustrated. Experiment results acquired from a downscaled 85 V/1.5 kVA apparatus validate the effectiveness of the proposed control scheme.
- Author(s): Shoudao Huang ; Zhongqi Li ; Kaiyuan Lu
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2859 –2864
- DOI: 10.1049/iet-pel.2015.0376
- Type: Article
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p.
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Magnetic resonant wireless power transfer (WPT) is an emerging technology that may create new applications for wireless power charging. However, frequency splitting occurs when the WPT system operates in the over-coupled regime. As a result, the transfer efficiency is very low at the original resonant frequency. In this study, the method of adjusting the load resistor is proposed to suppress the frequency splitting. The efficiency and input impedance can be obtained by solving the system equivalent equations. In addition, the resonant frequencies can be obtained by input impedance equation. The influences of the load resistor on the efficiency and the resonant frequencies are analysed for different transfer distances. Then, the method of adjusting the load resistor is illustrated. Frequency splitting is suppressed and transfer efficiency is improved at the original resonant frequency by the proposed method. The WPT system via magnetic resonance coupling is designed. Simulation and experimental results validating the proposed method are given.
- Author(s): Piotr Musznicki ; Piotr J. Chrzan ; Marcin Rucinski ; Maciej Kolincio
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2865 –2870
- DOI: 10.1049/iet-pel.2016.0053
- Type: Article
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p.
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New low cost and accurate estimation method of transformer stray capacitances for wide band DC–DC converter modelling and design is proposed. The Wiener filter (WF) method is applied to estimate the transformer impedance – referred to the selected transformer winding configurations. Laboratory tests are used to adapt the filter, that is to find optimal impedance which minimises mean square error between measured, noise perturbed current and reconstructed current. Transformer transfer function peaks indicate internal LC resonances. Stray capacitances are extracted based on resonant frequencies determination. The method validation is carried out by simulation and experimental analysis, where estimated stray capacitances by WF are compared with measurements of an impedance analyser.
- Author(s): Roberto Esteban Carballo ; Fernando Botterón ; Germán Gustavo Oggier ; Guillermo Oscar García
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2871 –2879
- DOI: 10.1049/iet-pel.2015.1059
- Type: Article
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A new methodology to design discrete-time multiple resonant controllers for single-phase uninterruptible power supply inverters is proposed in this study. This methodology is based on classical linear tools and consists on the synthesis of the inverter output impedance according to standard specifications. This synthesis is performed using a multi-loop control strategy composed of an inner current control loop using a proportional controller, and an outer voltage control loop using the multiple resonant controller. A prototype was built to demonstrate the practical feasibility of the theoretical proposal. A significant reduction of the output impedance at determined harmonic frequencies resulted in a low-voltage total harmonic distortion of the output voltage of about 1.76%, for IEC 62040-3 reference non-linear load.
- Author(s): Mi Tang ; Alberto Gaeta ; Andrea Formentini ; Kazuhiro Ohyama ; Pericle Zanchetta ; Greg Asher
- Source: IET Power Electronics, Volume 9, Issue 15, p. 2880 –2890
- DOI: 10.1049/iet-pel.2015.0232
- Type: Article
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p.
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High bandwidth and accuracy of the current control loop are fundamental requisites when a fast torque response is required or for facilitating the reduction of torque ripple in high-performance drives, especially at high speed. One of the most suitable control methods to achieve these goals is dead beat current control (DBCC). Many types of DBCCs have been proposed and implemented in the literature. This study proposes a DBCC incorporating two new functionalities. One is a two steps current prediction to improve prediction accuracy when current measurements are taken place before each sampling period; and particularly to reduce the overshoot during transients when mean value is used as current feedback. The second is a novel compensation method for the rotor movement to eliminate offset errors which occur at high speed. Moreover, the dynamic and steady-state performance of the proposed DBCC is assessed in simulations. On the basis of the simulation tests, the control parameters are tuned for experiments and the performance of the proposed functionalities are verified. Finally, the advantage of DBCC, compared with a classical dq proportional–integral current regulator, is verified in experiments.
Design and application of a thyristor switched capacitor bank for a high harmonic distortion and fast changing single-phase electric welding machine
Hybrid damping adaptive control scheme for grid-connected inverters in a weak grid
Impact of SiC semiconductors switching transition speed on insulation health state monitoring of traction machines
Submodule configuration of HVDC-DC autotransformer considering DC fault
Gaussian process surrogate model for the design of circular, planar coils used in inductive power transfer for electric vehicles
Voltage transfer ratio analysis for multi-receiver resonant power transfer systems
Physics-based spice model on the dynamic characteristics of silicon carbide Schottky barrier diode
Comparative analysis of symmetric and asymmetric reduced switch MLI topologies using unipolar pulse width modulation strategies
Research on slow-scale bifurcation phenomenon of PFC cascade converter
Robust control of two parallel-connected permanent magnet synchronous motors fed by a single inverter
Unbalanced PCC voltage regulation with positive- and negative-sequence compensation tactics for MMC-DSTATCOM
Frequency splitting suppression method for four-coil wireless power transfer system
Adaptive estimation of the transformer stray capacitances for DC–DC converter modelling
Design approach of discrete-time resonant controllers for uninterruptible power supply applications through frequency response analysis
Enhanced DBCC for high-speed permanent magnet synchronous motor drives
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