INDUCTION MOTOR DRIVE STABILIZATION WITH STATOR CURRENT FEEDBACK

ABSTRACT

The use of state feedback to control Induction motor drive systems is examined. Using the machine currents and speed as the system states, a general linearized formulation of the problem is derived. This formulation has the advantages of previous forms based on complex variable analysis, but is not subject to the limitations of that method.

The proposed model Is used to study machine control with stator current feedback. The results show that stator current feedback can be used to improve the dynamic characteristics of the drive system. Comparisons of stator current control with the uncontrolled machine and with the slip controlled machine are presented over the range of operating speed, load, and inertia. In all cases, advantages of current controlled operation can be seen.     

Interface potential barrier height and leakage current behavior of Pt/(Ba,Sr)TiO3/Pt capacitors fabricated by sputtering process

Abstract

Variations of the leakage current behaviors and interface potential barrier height (φ _B ) of rf-sputter deposited (Ba, Sr)TiO₃ (BST) thin films, with thickness ranging from 20nm to 150 nm are investigated as a function of the thickness and bias voltages. The top and bottom electrodes are dc-sputter-deposited Pt films. φ _B critically depends on the BST film deposition temperature, postannealing atmosphere and time after the annealing. The postannealing under N₂ atmosphere results in a high interface potential barrier height and low leakage current. Maintaining the BST capacitor in air for a long time reduces the φ _B from about 2.4 eV to 1.6eV due to the oxidation. φ _B is not so dependent on the film thickness in this experimental range. The leakage conduction mechanism is very dependent on the BST film thickness; the 20nm thick film shows tunneling current, 30 and 40 nm thick films show Schottky emission current and the thicker films show a mixed characteristics and bulk and interface limited currents although the mechanism is not clearly understood at this moment.     

Variations of interface potential barrier height and leakage current of (Ba,Sr)TiO3 thin films deposited by sputtering process

Abstract

Variations of the leakage current behaviors and interface potential barrier height (Φ_B) of rf-sputter deposited (Ba, Sr)TiO₃ (BST) thin films with thicknesses ranging from 20 nm to 150 nm are investigated as a function of the thickness and bias voltages. The top and bottom electrodes are dc-sputter-deposited Pt films. Φ_B critically depends on the BST film deposition temperature, postannealing atmosphere and time after the annealing. The postannealing under N₂ atmosphere results in a high interface potential barrier height and low leakage current. Maintaining the BST capacitor in air for a long time reduces the Φ_B from about 2.4 eV to 1.6 eV due to the oxidation. Φ_B is not so dependent on the film thickness in this experimental range. The leakage conduction mechanism is very dependent on the BST film thickness; the 20 nm thick film shows tunneling current, 30 and 40 nm thick films show Schottky emission current.     

ROLE OF TORQUE ANGLE IN INVERTER-FED INDUCTION MOTOR DRIVES

ABSTRACT

It is shown from the induction motor differential equations that changes in load torque, speed reference and torque angle are accompanied by a transient change in the speed of the air-gap mmf. The time constant associated with the torque angle change is different for a voltage source and a current source inverter-fed induction motor. This aspect throws light on the instability of current source inverter-fed induction motor on open loop operation. Evidently, the solution to overcome this instability is to use the torque angle for feedback control. It is proved that torque angle feedback alone is not sufficient for stabilization of the current source inverter-fed induction motor.     

THE COMPENSATION OF NON-ACTIVE CURRENTS FOR THREE-PHASE POWER SYSTEMS IN SINUSOIDAL STEADY STATE

ABSTRACT

The present paper deals with the compensation of non-active currents for three-phase power systems In sinusoidal steady state; the voltages are not required to constitute a symmetrical three-phase set. It is shown that all non-active current components can be compensated by reactive lossless parallel elements. The explicit expression of the compensating reactances is derived and the multiplicity of the solution is discussed. An example illustrates the application of the result.     

TIME DOMAIN ESTIMATION TECHNIQUES FOR HARMONIC LOAD MODELS

ABSTRACT

In this paper we present two novel time domain techniques for load modelling in the presence of harmonics. In the first technique, the harmonic contents of the load voltage and current waveforms are assumed to be known in advance. The second technique uses samples of the load voltage and current waveforms directly. The least errors square parameter estimation algorithm is used to estimate the load resistance, inductance and capacitance. The residual current associated with incomplete extraction of the parameters for all significant signal frequencies is also estimated. We also identify harmonics that are not common between the load voltage and current waveforms. The proposed techniques are applied to synthetic and actual recorded data. The paper's conclusions are based on comparing the results obtained using both techniques.     

CALCULATION OF MACHINE-SLOT PARAMETERS BY COMPLEMENTARY VARIATIONAL TECHNIQUE

ABSTRACT

Complementary formulations of a machine-slot problem are derived by the systematic partitioning of a standard error form that pertains to mismatch in constitutive relationships. The theory indicates that complementary solutions of the harmonic eddy current problem do not provide upper and lower bounds. Finite element computational results, for a number of coarse meshes at different frequencies, support the theory, but suggest that complementary estimates do tend to envelope the exact values of slot resistance and inductance.     

ON-LINE FAULT LEVEL MEASUREMENT

ABSTRACT

The fault level represents the maximum short circuit current that a power system causes to flow to the point of short circuit. Due to change of network configuration, the fault level at any point of the power system network changes accordingly

It is not practical to apply full short circuit on the system in order to determine the fault level. This paper describes scheme for continuous measuring of the fault level at any point of the power system network. This scheme is composed of an antiparallel thyristor pair. The thyristor current, which is controlled by the firing angle, can be used to perform the on-line fault level measurement

However, problems are associated with such measurement. These are mainly the complexity of the current waveform and its dependence on the system impedance. The effect of the system X/R ratio on the measurement is also analyzed.     

CURRENT AND TORQUE STRESSES IN SYNCHRONOUS MACHINES DUE TO SEQUENTIAL OUT-OF-PHASE SYNCHRONIZING

ABSTRACT

The effects of non-simultaneous closing of breaker poles during out-of-phase synchronizing on the stator current, electrical and shaft mechanical torques of a turboset are investigated and compared with the current and torque peaks following simultaneous three-phase and single-phase out-of-phase synchronizing. It has turned out that in comparison with the three-phase out-of-phase synchronizing considerable increase in the current and torque peak values can occur following an unfavourable sequential closing.     

An induction motor model with deep-bar effect and leakage inductance saturation

Contents A two-phase dynamic induction motor model is derived which includes the effects of rotor bar eddy currents and leakage inductance saturation. The model is based on approximate analysis of the air-gap and slot electromagnetic fields which leads directly to lumped circuit equations. New expressions are given for the variation of the zig-zag and slot leakage inductance with saturation. — The model is applied to the calculation of both steady state and dynamic characteristics for a large induction motor.

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Ein Modell des Asynchronmotors mit Hochstabläufer-Effekt und Sättigung der Streuinduktivität

Übersicht Es wird ein zweisträngiges Modell eines Asynchronmotors abgeleitet, das Wirbelströme in den Läuferstäben und die Sättigung der Streuinduktivität berücksichtigt. Grundlage des Modells ist eine angenäherte Analyse der Felder im Luftspalt und in den Nuten, die direkt auf Gleichungen mit konzentrierten Elementen führt. Es werden neue Ausdrücke für die Abhängigkeit der doppeltverketteten und der Nutstreuung von der Sättigung angegeben. Das Modell wird für die Berechnung stationärer und dynamischer Vorgänge bei einem großen Asynchronmotor angewendet.

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List of Symbols A magnetic vector potential - B flux density - G describing function - g air-gap length - H magnetic field intensity - I _Om rotor saturation current - I _r rotor current matrix - l _r ^j current in thejth rotor slot - l _rm amplitude of the fundamental ofI _bir ^j distribution - I _rr rotor harmonic conceptual current matrix - I _s stator current matrix - I _ss stator harmonic conceptual current matrix - i _mne m, nth modal eddy current in thejth rotor slot - i _nb nth harmonic conceptual current at the interface betweenjth rotor slot and slot neck regions - i _n ^rj nth harmonic conceptual current at the opening of thejth rotor slot - i _n ^sj nth harmonic conceptual current at the opening of thejth stator slot - i _Ob rotor zero order conceptual current matrix - i _Oi ^j conceptual current at thejth rotor slot due to daturation of the tooth tips - K _nw nth harmonic winding distribution factor effective length of the motor - L _nc self inductance of the eddy current modei _One ^j - L _r rotor inductance matrix - L _s stator inductance matrix - P _p pole pitch - M _ne mutual inductance betweeni _One ^j andI _r ^j and rotor modal eddy currents - M _ri mutual inductance matrix between rotor winding and rotor conceptual winding due to saturation of the tooth tips - M _rr mutual inductance matrix between rotor winding and rotor conceptual winding - M _rss mutual inductance matrix between rotor winding and stator conceptual winding - M _si mutual inductance matrix between stator winding and rotor conceptual winding due to saturation of the rotor tooth tips - M _sr mutual inductance matrix between stator and rotor windings - M _srr mutual inductance matrix between stator winding and rotor conceptual winding - M _ss mutual inductance matrix between stator winding and stator conceptual winding - N ₁,N ₂ number of stator and rotor slots - R _ne resistance of eddy current modei _One ^j - R _r rotor resistance matrix - R _s stator resistance matrix - s ₁,d ₁ dimensions of a stator slot - s ₂,d ₂ rotor slot opening and rotor slot neck height - s _b ,d _b dimensions of a rotor bar - s _p slot pitch - N _c number of turns per slot - U _s applied voltage matrix - q number of slots per pole phase group - rotor flux linkage matrix - y_s stator flux linkage matrix - , inductance coefficients - O angular position - conductivity of rotor bars - eigenvalues - resistivity of rotor bars     

LEAKAGE CURRENT MECHANISM OF POLYCRYSTALLINE BiFeO3 FILMS WITH PT ELECTRODE

ABSTRACT

Leakage current mechanism of the polycrystalline BiFeO₃ film annealing at 923 K with Pt electrodes was discussed based on Schottky-emission conduction, Poole-Frenkel trap limited conduction, Fowler-Nordheim tunneling conduction and space charge limited current (SCLC). The leakage current mechanism at room temperature is as follows; Schottky-emission or Poole-Frenkel was the candidate leakage current mechanism at low electric field and then leakage current mechanism was changed to the SCLC at high electric field. When decreasing the measuring temperature, the leakage current mechanism at low electric field was Poole-Frenkel trap limited conduction, though the electric field region of the PF trap limited conduction was much broader than that of the room temperature.     

Modeling of metal-ferroelectric-semiconductor field effect transistor subthreshold current

Abstract

A subthreshold current model for metal-ferroelectric-semiconductor field effect transistor (MFSFET) is derived from a new analytical ferroelectric hysteresis model,^1.2 the semiconductor surface model,³ the classical diffusion current model,⁴ as well as the Maxwell equations. The model predicates the shift of MFSFET subthreshold current between forward sweep and backward sweep of gate bias. The simulation results show the effects of coercive voltage, the remanent polarization, the saturation polarization, and the free interface charge between ferroelectric and semiconductor. The external field effect on the saturation polarization (better known as ferroelectric space charge effect) is also modeled. The conventional method to evaluate the interface trapped charge for metal-oxide-semiconductor system is also proposed for MFS system based on the ideal subthreshold current model and its experimental data.     

COMPARATIVE STUDY OF TWO QUADRANT CHOPPERS

ABSTRACT

The paper presents a comparative study of chopper circuits capable of providing two quadrant operation of do separately excited motor consisting of forward motoring and braking. The comparative study deals with the motor performance characteristics, motor armature current ripple, supply current harmonics, regenerated power, efficiency of regeneration and steady-state transfer characteristics.     

Simulation Study on On-Line MTPA/MTPV Trajectory Tracking in PMSMs with Power Management

Abstract

This paper proposes an on-line maximum torque per ampere (MTPA)/maximum torque per voltage (MTPV) trajectory tracking method in permanent magnet synchronous machines (PMSMs) with power management. The on-line MTPA/MTPV machine current trajectory tracking algorithm is developed from PMSM model. Maximum source current and machine current are regulated to enhance hardware protection during machine current trajectory tracking. The maximum source current management is achieved by iterating within the current trajectory tracking algorithm over continuous torque command modifications based on power flow analysis, and the maximum machine current management is achieved by torque command limiting based on current angle modulation. Different from the existing techniques in literature, the proposed method has an unique feature of providing on-line regulation of source current, while maintaining on-line MTPA/MTPV trajectory tracking in PMSMs. It also provides machine and inverter overcurrent regulation to enhance their protection. In addition, the proposed method is flexible to tune and does not require off-line calibration. The effectiveness of the proposed method is confirmed by simulation results in MATLAB.     

Memories,CCD microprocessors,and pyroelectric detectors based upon sol-gel ceramic ferroelectric films

Abstract

The integration of PZT ceramic thin films into the current technology of silicon-based integrated circuits is discussed. The most widespread and obvious applications are considered: memory ICs, parallel analog processors, and pyroelectric detectors.     

Specific absorption rate (SAR) simulations for low-field (< 0.1 T) MRI systems

Objective

To simulate the magnetic and electric fields produced by RF coil geometries commonly used at low field. Based on these simulations, the specific absorption rate (SAR) efficiency can be derived to ensure safe operation even when using short RF pulses and high duty cycles.

Methods

Electromagnetic simulations were performed at four different field strengths between 0.05 and 0.1 T, corresponding to the lower and upper limits of current point-of-care (POC) neuroimaging systems. Transmit magnetic and electric fields, as well as transmit efficiency and SAR efficiency were simulated. The effects of a close-fitting shield on the EM fields were also assessed. SAR calculations were performed as a function of RF pulse length in turbo-spin echo (TSE) sequences.

Results

Simulations of RF coil characteristics and B₁⁺ transmit efficiencies agreed well with corresponding experimentally determined parameters. Overall, the SAR efficiency was, as expected, higher at the lower frequencies studied, and many orders of magnitude greater than at conventional clinical field strengths. The tight-fitting transmit coil results in the highest SAR in the nose and skull, which are not thermally sensitive tissues. The calculated SAR efficiencies showed that only when 180° refocusing pulses of duration ~ 10 ms are used for TSE sequences does SAR need to be carefully considered.

Conclusion

This work presents a comprehensive overview of the transmit and SAR efficiencies for RF coils used for POC MRI neuroimaging. While SAR is not a problem for conventional sequences, the values derived here should be useful for RF intensive sequences such as T_1ρ, and also demonstrate that if very short RF pulses are required then SAR calculations should be performed.

     

FERROELECTRIC GATE FET MEMORY BASED ON CONDUCTION OF FERROELECTRIC-INSULATOR INTERFACE

ABSTRACT

A new type of ferroelectric gate field effect transistor (FET) using ferroelectric-insulator interface conduction has been proposed. Drain current flows along the interface between ferroelectric and insulator layers and needs no semiconductor. This FET consists of source and drain electrodes on ferroelectric film (Pb(Zr_0.52Ti_0.48)O₃(PZT)) prepared on Pt/TiO₂/SiO₂/Si substrate, and gate electrode on HfO₂ insulator film on the PZT film between the source and the drain electrodes. Drain current flows through the interface of the ferroelectric and the insulator. Drain current versus gate voltage characteristics shows clockwise hysteresis loop similarly to the conventional p-channel FET with ferroelectric gate. The FET shows that the On/Off ratio of the conduction current is about 10⁵ and the Off state current is about 10^{? 10}A.     

TERTIARY TUNING FOR IMPROVED PERFORMANCE IN A SYNCHRONOUS DRIVE

Abstract

Tertiary capacitor tuning in the armature of a 3-phase synchronous motor is used to increase pull-out torque, efficiency and power factor. It also reduces the required field current and increases the leading component of the input current.

In addition to its tuning and control function, the tertiary current contributes to the output torque. A system analysis based on an equivalent circuit is given with experimental verification     

Analysis of work of liquid metal induction pump

Contents In the paper the finite element method is presented so as to determine electromagnetic field distribution in a cylindrical liquid metal induction pump. The effect of exciting current frequency, the channel width and the channel material conductivity on dynamic parameters of the pump has been analysed. — The obtained calculation results have been shown in the graphs.

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Analyse der Pumpe für ein flüssiges Metall

Übersicht Im Beitrag wurde die Methode der finiten Elemente zur Bestimmung der Verteilung des elektromagnetischen Feldes in einer zylindrischen Pumpe für ein flüssiges Metall verwendet. Man hat den Einfluß des Erregerstroms, der Kanalbreite und der Leitfähigkeit des zum Aufbau des Kanals benutzten Stoffes — auf die dynamischen Parameter dieser Pumpe untersucht. Die erhaltenen Ergebnisse hat man in Form von Diagrammen dargestellt.

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List of symbols A vector potential - A vector potential (complex r.m.s. value) - A z-component of vector potential (complex r.m.s. value) - A _i ,A _j ,A _k vector potential values in nodal pointsi, j, k (complex r.m.s. values) - B magnetic induction - B magnetic induction (complex r.m.s. value) - B _x ,B _y components of magnetic induction (complex r.m.s. values) - F _t electrodynamic force - F mean force - F _a alternating force - F _x ,F _y components of the mean force - conductivity of the liquid metal - J current density (complex r.m.s. value) - J _a current density - J _w exciting current linear density (complex r.m.s. value) - l length of the channel - magnetic permeability of the liquid metal - M torque acting upon the liquid metal - current pulsation - p pressure of transported metal - Q pump efficiency - v _x ,v _y components of the liquid metal's velocity in the 0X and 0Y direction - z ^* conjugate complex number ofz     

Voltage Sensorless Control of Single-phase Active Power Filter Based on the Second-order Generalized Integrator Algorithm

Abstract—A single-phase active power filter is presented for small-scale, single-phase loads based on the second-order generalized integrator control method is presented in this article. The proposed system does not require voltage sensors on the AC and/or DC side. Only two current sensors are used to measure load and converter currents. Consequently, a proportional-integral regulator is not used, and there is no need for additional calculations for the determination of the grid-current amplitude. To obtain the correct reference grid current, the distorted load current is first processed by using the second-order generalized integrator algorithm, which does not require voltage information. A step-by-step performance study, in a real-time environment, shows that the proposed control technique is able to generate the proper compensating reference current for small-scale non-linear loads. As a result, the total harmonic distortion of the grid current is reduced from 25.33 to 3.80%, which meets the recommended IEEE 519-1992 Standard.