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Mathematics and Computers in Simulation. 01/2013;
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ABSTRACT: Model based predictive control is an interesting control method for power electronics as it offers many advantages. A known disadvantage compared to optimal pulse-width modulation control is the deteriorated voltage quality, which results in extra losses in the load. In this paper two ways of analyzing the output voltage quality are presented and applied on the model based predictive control of a three-level flying capacitor inverter. The influence of the weight factor and the system model are analyzed. The voltage quality is shown to be good in the same weight factor range as those resulting in good current and capacitor voltage control. No compromises have to be made in this area. A more accurate system model results in improved voltage (and overall control) quality.
Power Electronics and ECCE Asia (ICPE & ECCE), 2011 IEEE 8th International Conference on; 07/2011
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ABSTRACT: The stator and rotor yoke in a switched reluctance motor form magnetic circuit parts that are typically shared by different phases. If these parts saturate due to the excitation of one phase, this will lead to a change of the magnetic characteristics of all other phases sharing these parts. In several position-sensorless methods, cross-saturation leads to a load-dependent position estimation error. In this paper, the influence of cross-saturation on a resonance-based position estimation method is studied. The method extracts position information from electrical resonances triggered in an idle motor phase. A cross-saturation mitigation scheme is presented in order to reduce the commutation position error. The scheme uses only one additional parameter per phase which can be measured automatically during commissioning of the drive. Experimental results at low and medium speed show that the position estimation error remains smaller dan 2 mechanical degrees over the rated load range.
Electrical Machines (ICEM), 2010 XIX International Conference on; 10/2010
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ABSTRACT: Flying Capacitor (FC) multilevel Pulse Width Modulated (PWM) converters are an attractive choice due to the natural balancing property of the capacitor voltages. A single-leg flying capacitor converter voltage balance dynamics analytical solution may be obtained using switched systems time domain approach based on stitching of switching intervals piece-wise analytical solutions in combination, for inductance dominated load, with a small parameter technique. In this paper, a symmetric five-level H-bridge flying capacitor converter common mode voltage balance dynamics solution is obtained from its single-leg prototype using “mirror hypothesis” formalism. Simple analytical expressions clearly reveal the dependences on load parameters, carrier frequency, and DC PWM normalized voltage command. For AC modulation, the solution obtained by averaging on a fundamental AC period does not depend on a fundamental frequency. The results of the theoretical analysis are confirmed by extensive switched simulations.
Industrial Electronics (ISIE), 2010 IEEE International Symposium on; 08/2010
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ABSTRACT: Flying Capacitor (FC) multilevel pulse width modulated (PWM) converters are an attractive choice due to the natural voltage balancing property. It was previously shown the natural balancing method is falling short for self-precharge of odd-level FC converters. In this paper, a new switching scheme is proposed implementing zero average output voltage during start-up and using a controlled DC-bus voltage rise. The DC-bus rate must depend on the capacitor voltage balancing dynamics.
Power Electronics, Machines and Drives (PEMD 2010), 5th IET International Conference on; 05/2010
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ABSTRACT: The demand for drives with high quality torque control has grown tremendously in a wide variety of applications. Direct torque control (DTC) for permanent magnet synchronous motors can provide this accurate and fast torque control. When applying DTC the change of the stator flux linkage vector is controlled. As such the estimation of the stator flux linkage is essential. In this paper the performance of the Extended Kalman Filter (EKF) for stator flux linkage estimation is studied. Starting from a formulation of the EKF for isotropic motors, the influence of rotor anisotropy and saturation is evaluated. Subsequently it is expanded to highly isotropic motors as well. In both cases the possibilities to add parameter estimations are evaluated.
Power Electronics, Machines and Drives (PEMD 2010), 5th IET International Conference on; 05/2010
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ABSTRACT: By observation of electrical resonances, switched reluctance drives can be controlled without position sensor. The range of resonance frequencies is defined by the position-dependent phase inductance and a parasitic capacitance, mainly associated with the converter switches. In this paper, an analytical model is used to predict the aligned resonance frequency, taking into account material and geometry factors, as well as dynamic effects such as eddy current losses. The range of resonance frequencies can be influenced by mounting external capacitors over the power semiconductor devices. It is shown that an optimal aligned frequency is associated with a trade-off between a high position resolution and a high pulse-width modulation frequency. Good correspondence is obtained between the model-predicted results and measurements on a switched reluctance drive.
Power Electronics, Machines and Drives (PEMD 2010), 5th IET International Conference on; 05/2010
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ABSTRACT: The demand for highly dynamic electrical drives, characterized by high quality torque control, in a wide variety of applications has grown tremendously during the past decades. Direct torque control (DTC) for permanent magnet synchronous motors (PMSM) can provide this accurate and fast torque control. When applying DTC the change of the stator flux linkage vector is controlled, based on torque and flux errors. As such the estimation of the stator flux linkage is essential. In the literature several possible solutions for the estimation of the stator flux linkage are proposed. In order to overcome problems associated with the integration of the back-emf, the use of state observers has been advocated in the literature. Several types of state observers have been conceived and implemented for PMSMs, especially the Extended Kalman Filter (EKF) has received much attention. In most reported applications however the EKF is only used to estimate the speed and rotor position of the PMSM in order to realize field oriented current control in a rotor reference frame. Far fewer publications mention the use of an EKF to estimate the stator flux linkage vector in order to apply DTC. Still the performance of the EKF in the estimation of the stator flux linkage vector has not yet been thoroughly investigated. In this paper the performance of the EKF for stator flux linkage is studied and simulated. The possibilities to improve the estimation by augmenting the state vector and the consequences of these alterations are explored. Important practical aspects for FPGA implementation are discussed.
Applied Power Electronics Conference and Exposition (APEC), 2010 Twenty-Fifth Annual IEEE; 03/2010
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ABSTRACT: In switched reluctance motor drives, the combination of power-electronic converter and a motor phase defines a resonant circuit, comprised by the motor phase inductance and the parasitic capacitance of converter switches, power cables and motor phase winding. If a motor phase is excited by applying very short voltage pulses, the resonance frequency of the circuit can be observed through the subsequent damped oscillation of the induced voltage in the phase. As the phase inductance and associated resonance frequency depend on the rotor position, the method provides a means for estimating the rotor position. This paper discusses the influence of the magnetic inductive coupling between motor phases on the observed damped voltage resonance. It is shown that the motor-converter combination can be modelled as a system comprising different resonant circuits, each associated with one phase of the machine, which are mutually coupled due to the inductive coupling between the motor phases. An eigenvalue analysis reveals the different eigenfrequencies and modes of oscillation for this system. It follows from the analysis that damped voltage resonances occur in all phases of the machine due to the mutual coupling. The model is used to determine the influence of voltage pulses, applied to a single phase or simultaneously applied to different phases, on the observed damped voltage oscillations, and thus on the rotor position estimation.
Industrial Electronics, 2009. IECON '09. 35th Annual Conference of IEEE; 12/2009
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ABSTRACT: In one class of position-sensorless control strategies for switched reluctance motors, the position estimation relies on the measured inductance of an active or idle motor phase. The inductance is calculated from the response of the current to a voltage excitation, e.g. pulse-width modulation in an active phase or injection of high-frequency voltage pulses in an idle phase. With the calculated inductance or flux linkage, the rotor position is retrieved by means of a look-up table or an analytical formula. It is shown in this paper that the measured inductance can significantly deviate from the static inductance when flux penetration in the magnetic core becomes important. This is especially the case when the switched reluctance motor is in a position near alignment and when high-frequency voltage pulses are applied. An analytical wide-frequency model for the motor phase impedance in the aligned position is proposed and calculated results are compared to measured data. The influence of excitation frequency and duty ratio, magnetic core properties and motor geometry on the accuracy of phase inductance and rotor position estimation is discussed.
Industrial Electronics, 2008. IECON 2008. 34th Annual Conference of IEEE; 12/2008
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ABSTRACT: A known way to estimate the position of a switched reluctance motor without the use of a shaft position sensor is by excitation of a resonant circuit comprised by an idle motor phase winding and an external capacitor. This paper discusses the influence of the frequency of the sinusoidal excitation signal on the phase inductance. It is shown that the inductance decreases with increasing excitation frequency. This effect is most pronounced when the rotor is in the aligned position. It is furthermore shown that the frequency for the injected signal should be chosen based on a trade-off between position estimation resolution and bandwidth. The frequency-dependence of the inductance and losses of the magnetic core can be predicted by means of a wide frequency complex permeability model, which takes into account the effect of eddy current losses in the machine core laminations. Results obtained by finite element simulations show a good correspondence between calculated and measured values of the phase inductance and power loss.
Electrical Machines and Systems, 2008. ICEMS 2008. International Conference on; 11/2008
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ABSTRACT: Despite the effectiveness of the standstill frequency-response test or SSFR test in identifying accurate electrical machine models, it has the disadvantage of being a time consuming method. Therefore the use of a broadband signal is proposed instead of the excitation of only one frequency in the test signal and this sequentially for different signal frequencies. Furthermore, the test signals are often generated by using a waveform generator externally applied to the machine, which is not commonly available in the field. In this paper the generation of broadband test signals by using a voltage-source inverter (VSI) resulting in a multisine SSFR test is discussed. Using this multisine SSFR test the influence of saturation and cross-saturation on the q- and d-axis parameters can be swiftly evaluated.
Electrical Machines, 2008. ICEM 2008. 18th International Conference on; 10/2008
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ABSTRACT: Modelling and identification of synchronous machines has attracted much attention during the past decades. Although the standstill frequency response (SSFR) method has become standardized (IEEE Std. 115) it has some disadvantages (e.g. it is a time consuming method). To overcome these, the use of broadband excitation has been proposed in the literature. In this paper the use of broadband excitation for the frequency domain identification of permanent magnet synchronous machines is investigated. The measurement set-up and method are discussed, with special attention to the selection of the applied excitation signals. Three broadband signals suitable for frequency domain parameter identification are discussed and compared in measurements. The obtained frequency domain data can be used in different applications. Examples are given in this paper. Furthermore the extraction of a parametric model from the nonparametric frequency domain data is briefly discussed. The identified parameters can be used to study the influence of saturation or can be applied in the simulation and control of permanent magnet synchronous machines. Measurement results demonstrate that broadband frequency domain identification can be applied to extract the parameters (inductances) of permanent magnet synchronous machines. Moreover, the reproducibility of the method is shown to be good as the variation in the parameters obtained in different measurement sessions is low. Future work on the subject will include a closer investigation of the variations in the obtained parameters, the use of higher order models and the application of more complex estimation algorithms.
Power Electronics, Electrical Drives, Automation and Motion, 2008. SPEEDAM 2008. International Symposium on; 07/2008
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ABSTRACT: The motion states of a salient-pole permanent- magnet synchronous machine (PMSM) at standstill or rotating at low speed are often estimated by measuring the responses on high-frequency test signals. In some drives, the rotor position is computed by measuring the current ripples which are generated by supplying the PMSM periodically with high-frequency voltage test pulses. Besides these ripples, undesired distortions in the steady-state current have been measured. Simulation results have revealed that these distortions are caused by deviations of the steady-state voltage during the test periods. In this paper, a sensorless strategy is discussed where a strong reduction of the aforementioned steady-state distortions is obtained by adapting the test pulses to the steady-state voltage vector. As voltage measurements are often avoided, an estimation of the steady- state voltage is used which is given by the current controller output. The computation of the adaptive test pulses is done taking into account the voltage restriction of the dc-bus voltage. Simulation results as well as experimental measurements indicate the effectiveness of the enhanced test pulses in a sensorless controlled interior PMSM.
Applied Power Electronics Conference and Exposition, 2008. APEC 2008. Twenty-Third Annual IEEE; 03/2008
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ABSTRACT: A new space vector torque control strategy is developed for switched reluctance machines. The method is based on an existing space vector control strategy, which yields an explicit expression for the phase currents realizing a desired torque at a given rotor position. With the improved strategy, a higher torque-current ratio is achieved. A new approach based on space vector trajectories is given to determine the commutation between phases. For a constant reference torque, the improved method guarantees continuous reference currents. Therefore, smooth torque control is possible for a wide speed range and servo-grade performance can be achieved.
Electric Machines & Drives Conference, 2007. IEMDC '07. IEEE International; 06/2007
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ABSTRACT: The use of embedded Runge-Kutta methods for the time-domain simulation of a dynamic finite element model of a switched reluctance motor is discussed, along with the features of embedded Runge-Kutta methods for the numerical solution of this model. It is shown that step size control and interpolator polynomials can be used to take accurately into account the discrete effects of current control and a pulse width modulated supply on the drive dynamics
IET Science Measurement ? Technology 02/2007; · 0.60 Impact Factor
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ABSTRACT: A method is proposed to calculate the vibrations of magnetised electrical steel due to magnetic forces and magnetostriction. As an example, calculations have been carried out on two-pole and four-pole induction machines (IMs) with no load. If only the main components of the vibrations are considered, analysis of the results reveals that, in the case of the two-pole IM, the contributions of the magnetic forces and the magnetostriction add up, whereas, in the case of the four-pole IM, the respective contributions are subtracted. It is concluded that it is not justified to assume that magnetostriction in all cases will increase the vibrations of electromechanical devices
IET Science Measurement ? Technology 02/2007; · 0.60 Impact Factor
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ABSTRACT: In this paper a nonlinear model for AC machines is proposed that takes into account the magnetic saturation and magnetic interaction between both orthogonal magnetic axes. Furthermore, the model includes the presence of air-gap flux harmonic components caused by magnetic saturation and multiple-pole spatial saliencies. Such a model is used to describe in a uniform way motion-state estimators for AC drives that are recently discussed in the literature. Emphasis is given to salient-pole synchronous machines with a rotor field winding or a permanent-magnet excitation (PMSM)
Power Electronics, Electrical Drives, Automation and Motion, 2006. SPEEDAM 2006. International Symposium on; 06/2006
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ABSTRACT: Nowadays numerous techniques to model the behaviour of electrical drives are discussed in the literature. In many cases a linear magnetic network is proposed. This paper proposes a large-signal simulation model of an induction machine that takes into account the magnetizing-flux saturation. The model is given as a state-space model with nonlinear feedback and is implemented in Matlab/Simulinkreg. The advantages of the proposed model include versatility and ease of use. Simulation results from both this model and a linear flux model show the differences between the models. Advantages and disadvantages of the proposed simulation model are discussed and the area of application is defined. The usefulness of the model to study large transients and the dynamic behaviour of induction machines in control loops is discussed. For this purpose the proposed model is used to simulate induction machines in drives, such as direct torque control and indirect field orientation
Power Electronics, Electrical Drives, Automation and Motion, 2006. SPEEDAM 2006. International Symposium on; 06/2006
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ABSTRACT: This paper discusses fundamental equations which can be used in high-frequency signal based position estimators for synchronous machines. For this purpose, a small signal dynamic flux model is presented that takes into account the nonlinear magnetic condition and the magnetic interaction between the two orthogonal magnetic axes. The derivation of this model is based on the relationship between flux and coenergy. The model is given in a complex notation and is used to discuss most high-frequency signal based position estimators that have appeared in the literature. By using the finite element method, the coenergy of a given salient-pole synchronous machine is calculated and from it an estimation is made of the parameters in the proposed model. Through experiments it is shown that, by using the relationship between magnetizing current and flux as modelled in this paper, the nonlinear behaviour of the synchronous machine is quite accurately estimated. Furthermore, the new model is compared with a classical model that neglects mutual saturation effects between quadrature and direct axis windings
Electric Machines and Drives, 2005 IEEE International Conference on; 06/2005
