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This letter describes a high-resolution technique called thermally stimulated depolarization current (TSDC) that can be used for the measurement of space charge accumulation in the medium voltage magnet wires operating on pulsewidth modulated (PWM) inverters. Index Terms--Fast rise time pulses, induction motors, inverterfed drive motors, magnet wires, space charge injection.

This paper presents the results of an investigation regarding the thermal behavior of a three-phase induction motor when supplied by a reconfigured three-phase voltage source inverter with fault-tolerant capabilities. For this purpose, a fault-tolerant operating strategy based on the connection of the faulty inverter leg to the dc link middle point was considered. The experimentally obtained results show that, as far as the motor thermal characteristics are concerned, it is not necessary to reinforce the motor insulation properties since it is already prepared for such an operation. Index Terms--Alternating current (AC) motor drives, fault tolerance, thermal performance.

Most sensorless algorithms for a motor drive are based on a mathematical model including electrical variables such as motor current and voltage. Therefore, the accuracy of such variables largely influences the performance of the sensorless motor drive. However, the output voltage of the space vector pulsewidth modulation of the voltage-source inverter supplying a motor is error-prone in the motor's low-speed range because it has a poor resolution in a low-output voltage command. This letter proposes a variation of the dc-link voltage as a high-performance strategy for overcoming the above problem in a sensorless induction motor drive. The proposed strategy is verified through simulation and experimentation. Index Terms--Sensorless induction motor drive, space vector pulsewidth modulation (SVPWM), variable link voltage, voltage source inverter (VSI).

In this paper, the application of an additional excitation in induction motor (IM) drives for static, dynamic, and mixed eccentricity diagnosis is proposed. The additional excitation consists in a predefined inverter-switching pattern that is applied on the motor for a short time, while the fundamental excitation is canceled. This excitation was used previously to implement a position estimation strategy. The strategy obtains information about the rotor position from the motor saliencies effects over the zero-sequence voltage. The air-gap eccentricity is a kind of saliency that affects the zero-sequence voltage and allows the use of the additional excitation for eccentricity diagnosis. For the evaluation of the feasibility of this proposal, a multiple-coupled circuit model of the IM is used. The effects of series and series-parallel stator winding connections on the diagnosis signals are shown. Experimental results to validate the proposal are also given. These results show that it is possible to use the diagnosis strategy in a self-commissioning scheme. Index Terms--Air-gap eccentricity, fault diagnosis, induction motor drives, position estimation.

This paper (also presented at [27]) presents an integrated design approach to small drives for emerging 42-V automotive systems. The emphasis is on motors for ancillary loads. The final result offers a simple and low cost solution with high efficiency and high power density. Motor and inverter designs are combined to gain advantages in power factor and operating range. A near-minimum-distortion method is introduced for the overmodulation regime to improve power factor without sacrificing harmonic performance. The design is addressed in several steps: integration of the induction motor into a 42-V environment, selection of the inverter modulation scheme, and final system integration. The proposed system consists of an induction motor wound for the proper voltage range and driven by an inverter. The inverter is used partly in the overmodulation regime when bus voltage is low. A signal is formed based on triangle injection to minimize distortion. Some alternative modulation approaches are also analyzed and compared with the proposed solution. Experimental results confirm that a low-distortion overmodulation approach can be implemented successfully. Index Terms--Automobile auxiliary loads, dc bus utilization, 42-V automotive power, induction motor, overmodulation, pulse-width modulation (PWM), three-phase inverter.

Split-phase (six-phase) induction motor stator windings consist of two sets of three phase windings, which are spatially phase separated by 30 electrical degrees. Due to mutual cancellation of the air gap flux for all the 6n [+ or -] 1 (n : 1, 3, 5....) order harmonic voltages, called zero sequence components, large harmonic currents are generated in the stator phases. Only the 12n [+ or -] 1 (n = 0, 1, 2, 3....)-order harmonic voltage components contribute toward the air gap flux and electromagnetic torque production in the machine. In this paper, a novel scheme is proposed where two six-phase induction motors are connected in series with proper phase sequence so that the zero sequence component voltages of one machine act as torque and flux producing components for the other. Thus, the two six-phase motors can be independently controlled from a single six-phase inverter. A vector control scheme for the dual motor drive is developed and experimentally verified in this paper. Index Terms--multiphase winding, series-connected multimotor control, vector control.

The switching characteristics of an inverter feeding an induction motor controlled with the direct torque control (DTC) technique are assessed in steady state. At first, the application share of the inverter voltage vectors for the stator flux covering half a sextant is defined and predicted. The prediction indicates that, under operation at fixed inverter dc link voltage and stator flux magnitude, the application share depends only on the supply frequency of the motor and, to a small extent, on the load. Afterwards, the inverter transitions and the corresponding phase commutations within a stator flux sextant are analyzed. The outcome of the analysis permits to compute the commutations of the inverter phases in one turn of the stator flux and, from them, the inverter switching frequency is obtained. Its value is influenced by the sampling interval and the control delay arising from the microprocessor implementation of DTC. For given sampling interval and control delay, it is shown that the inverter switching frequency depends on the same quantities as the application share of the inverter voltage vectors. A comparison with the switching characteristics of an inverter controlled with the space vector modulation technique is carried out. At last, the paper discusses the sensitivity of the switching frequency of an inverter for DTC to the following quantities: inverter dc link voltage, sampling interval and control delay. Throughout the paper simulation and experimental results are given to confirm the theoretical findings. Index Terms--Direct torque control (DTC), induction motor drive, inverter switching frequency.

Pole-phase modulation adjusts the pole-phase ratio of an induction machine and requires a multileg, multiphase inverter. This paper analyzes an n-leg, n-phase inverter, and presents techniques for n-phase space vector pulse width modulation (SVPWM). In particular, nine-phase SVPWM is developed and implemented on a nine winding induction machine. The nine-phase SVPWM is compared to nine phase sine-triangle PWM in terms of dc bus utilization. Index Terms--Inverter, pole phase modulation, space vector pulse width modulation.

This paper suggests a fault-detection technique to monitor defects such as cracked rotor bars in induction machines. It has been introduced as the Vienna monitoring method [1], [2]. Rotor bar faults cause an asymmetric magnetic flux pattern in the air gap. Thus, the current phasor (or voltage phasor at current-controlled machines), flux phasor, and air-gap torque differ from those of an ideal symmetric machine. The Vienna monitoring method compares the outputs of a reference model, which represents an ideal machine, to a measurement model. Observing the deviations of these two models makes it possible to detect and even locate rotor faults. It can be applied to inverter fed machines as no frequency analysis is used. The method is verified by on-line experimental results from a digital signal processor (DSP)-controlled insulated gate bipolar transistor (IGBT) inverter drive. The findings match the outcomes of a detailed machine simulation. Air-gap flux density evaluation by a measurement coil system proves both the excellent sensitivity and fault location ability of the proposed scheme. Index Terms- Induction motor, inverter, on-line monitoring, rotor fault detection.

In this paper, a direct torque control (DTC) method of an induction machine is proposed which enables the minimum torque ripple control, while maintaining constant switching frequency. Some drawbacks of the conventional DTC are the relatively large torque ripple in a low speed range and the variation of switching frequency according to the amplitude of hysteresis bands and the motor operating speed. In the proposed strategy, an rms torque-ripple equation is derived using instantaneous torque equations and, at each switching cycle, an optimal switching instant which satisfied the minimum torque-ripple condition is determined based on the ripple equation. The proposed strategy improves the performance of the DTC by combining a low-torque-ripple characteristic in steady state with the fast torque dynamics. Experimental results prove the feasibility of the proposed strategy as compared with the conventional method. Index Terms: Direct torque control, induction motor control, inverter, minimum torque ripple

In this paper, the time-stepping coupled finite-element state-space (TSCFF-SS) model developed in an earlier companion paper is applied here for assessments of effects of machine geometry and magnetic circuit design modifications, and effects of pulsewidth modulation (PWM) carrier frequency on performance characteristics of induction motor drives. Namely, this has been accomplished through analysis of developed torque profile ripples and harmonic spectra of mid-air-gap radial flux density waveforms of the case-study motor. Furthermore, consequent effects of design modifications pertaining to geometry and/or magnetic circuit modifications and PWM carrier frequency on ohmic and iron core losses are investigated. The investigation has been performed on a case-study motor, which is a Y-connected single-layer three-phase two-pole 1.2-hp 208-V squirrel-cage induction motor with 24 slator slots and a cage with 34 rotor bars. Index Terms: Adjustable-speed drives, finite element, induction motors, inverters, phase ABC flux linkage frame of reference, pulsewidth modulation, state-space model, time stepping

This paper presents a dual-bridge inverter approach to eliminate the motor common-mode voltage and resulting bearing and leakage currents. The novel dual-bridge inverter is controlled to generate balanced excitation of the induction motor under pulsewidth modulation (PWM) inverter operation. Theoretical analysis, simulation results, and experimental results are presented to verify this concept. Index Terms - Adjustable-speed drive, bearing current, common-mode voltage, drives, leakage current, shaft voltage.

In Part I of this paper, the possibility of using an ac (alternating current) electrical system instead of the present dc system in the automobile was discussed. The various possible architectures were described in Part I. Part II continues with the issues of various tradeoffs related to cost, size, and overall system reliability/robustness and simplicity when compared to the existing dc system in the automobile. The components primarily discussed in this paper are the inverter and induction motors. Comparison between single- and three-phase systems is also done. The benefits of the ac system are not based on only the cost, but reliability and robustness too, and it seems that a replacement of the present automotive electrical system with a three-phase ac system is a reasonable step toward alternative electrical system selections. Index Terms - Aerospace electrical system, automotive/automobile electrical system, automotive electrical system architecture, automotive lighting system, induction motor, power electronic converters, PWM inverter.

In the aerospace industry, the 400-Hz ac system replaced the dc system, and the latest trend in aerospace industry involves a combination of mixed ac and dc electrical system applications. With more and more equipment in the newer automobiles and a corresponding increase in power requirement, it is anticipated that in the not too distant future higher voltage and/or some different architecture will be necessary in order to have an efficient electrical system. The question addressed in this paper is whether an alternative single- or three-phase ac electrical distribution and load system could replace the present dc system and, if so, what kind of architecture should be used. In this paper, first the electrical system architecture is described. Other issues discussed include the comparison of relative cost and size issues arising due to: 1) additional dc-ac power electronic converter hardware; 2) changes in the wiring system; and 3) the use of induction motors which can adequately handle the motor loads without any added power and/or control electronics at certain chosen frequency(ies). It is shown that for a three-phase system there will be a net total saving. The benefits of the ac system are not just based on cost, but on reliability and robustness as well. It seems that a replacement of the present electrical system with a three-phase ac system could be a reasonable step toward alternative electrical system selections. Index Terms - Aerospace electrical system, automotive/automobile electrical system, automotive electrical system architecture, automotive lighting system, induction motor, power electronic converters, PWM inverter.

Predicting conducted emissions in pulsewidth modulation (PWM) inverter induction motor drive systems requires various frequency-dependent effects to be considered. A frequency domain method has advantages in such cases compared to a time domain approach. based on the modal analysis presented in Part I, this paper develops frequency domain models to evaluate the spectra of the conducted emissions directly. The common and differential mode excitation sources are modeled in the frequency domain and related to the switching functions of the PWM inverter. Network models are established where the induction motor is represented using its frequency-dependent impedance characteristics, which can be obtained from measurements. The influences of system unbalances and of transmission-line effects due to long cables are investigated. Predicted emission spectra are compared with laboratory measurements and those derived from the time domain simulation. It is found that the agreement is good. The proposed method allows emission spectra to be predicted without recourse to specialist circuit simulators. Index Terms - Conducted emissions, drives, electromagnetic compatibility, power converters.

Neural networks are receiving attention as controllers for many industrial applications. Although these networks eliminate the need for mathematical models, they require a lot of training to understand the model of a plant or a process. Issues such as learning speed, stability, and weight convergence remain as areas of research and comparison of many training algorithms. This paper discusses the application of neural networks to control induction machines using direct torque control (DTC). A neural network is used to emulate the state selector of the DTC. The training algorithms used in this paper are the backpropagation, adaptive neuron model, extended Kalman filter, and the parallel recursive prediction error. Computer simulations of the motor and neural-network system using the four approaches are presented and compared. Discussions about the parallel recursive prediction error and the extended Kalman filter algorithms as the most promising training techniques is presented, giving their advantages and disadvantages. Index Terms - Adaptive neuron algorithm, backpropagation algorithm, direct torque control, extended Kalman filter algorithm, gradient descent algorithms, induction machines, neural- networks structure and training, Newton algorithms, parallel recursive prediction error algorithm.

The harmonic loss-minimized optimal PWM strategy for three-level inverters is investigated. The different PWM methods for low-, middle-, and high-speed regions are presented. It is shown that for three-level inverters the optimized strategy in all speed regions differs from the optimal PWM strategy of two-level inverters. The developed optimal control ensures a minimum of motor harmonic losses for a predetermined number of commutations of three-level PWM inverters and for a given value of the fundamental harmonic voltage. Index Terms - Harmonic loss-minimized control, induction motor, PWM, three-level inverter.

Acoustic noise emission from PWM-VSI inverter driven induction motors is a well-known problem. The generated noise depends mainly on two factors: the harmonic content of the supply voltage waveform and the mechanical resonance frequencies of the induction motor. It is necessary to know the mechanical resonances to optimize the switching scheme of the inverter to reduce the noise emission. Measuring the resonance frequencies is normally a laborious process. This paper introduces a new method for estimating the mechanical resonances from acoustic noise measurements. Employing random modulation of the output voltage of the inverter, the voltage spectrum can be spread over a wide frequency range. Using the spectrum analysis of the measured acoustic noise, the resonances can easily be estimated as the dominant frequencies of the acoustic noise spectrum. The method was tested on a 2.2-kW induction motor at no load and full load. Some of the mechanical resonances of the motor at no load were calculated by the Holzer method. The calculations showed good agreement with the sound measurements. The influence of the fan cowl was investigated and it is concluded that this is an important factor in the acoustic noise emission. Finally, it was observed that new mechanical resonances appeared when the induction motor was loaded by a pump drive system, and they were estimated by the measurement technique.

The concept of the vector approximation method for CSI-fed induction motors consists of vector control and the shaping of a stator current wave. Vector approximation means that a desirable space current vector is approximated by two realizable current vectors which have only six directions, and by dc link current control. The main purpose of the vector approximation method is not only to decrease torque ripple but also to control instantaneous torque, which is different from the purpose of the general PWM method. Moreover, a parameter adaptation system containing a magnetic saturation table and a model reference adaptive system (MRAS) has been added to the system, and this system works at any constant flux level and the steady state. The simulation and experimental results show the proposed method bring more precise vector approximation and torque control to induction motor drive systems.

This paper presents a simple converter topology for driving a three-phase induction motor with a single-phase ac supply. Using only two active switches and a Triac, the converter can start the motor with high starting torque and low input current, and can bring the motor up to full speed using a very cost-effective, single-phase field-oriented control strategy. The converter supplies balanced output voltages at rated frequency with virtually no output distortion and with very high input power factor. In this paper, the capability contours for different speed ranges and various operating modes are addressed; the trade-offs between output torque, torque ripple, input current distortion, and inverter rating are also explained, and the proposed control approaches are supported by simulation and test results.

In this paper, a new DC-link converter is proposed for induction motor drives. It consists of a three-phase adjustable AC/DC converter as a pre-stage, a three-active-switch converter to simplify the conventional six-active-switch inverter and eliminate the lock-out time circuit, and an adaptive DC-link voltage controller to achieve the optimal DC voltage and minimize the switching frequency of the three-active-switch converter. The simple rotor-flux-oriented control can also be implemented easily using the proposed converter to achieve high performance. Finally, a prototype circuit is constructed and some experimental results are presented for demonstration. Keywords: DC-link, converter, inverter, induction motor drives

In this paper, a novel strategy of current regulation of a field-orientation induction motor drive using the GTO inverter is proposed, which is based on a multivariable state feedback control with an integrator. The controller is designed by pole placement technique of multivariable system regulation theory. In addition, feedforward control is included in the control laws to improve transient responses. For the linear state feedback control, the rotor flux is separated as a disturbance and is estimated with a reduced-order state observer. A good steady-state performance is obtained by means of an integral compensation and symmetrical space voltage vector PWM, and fast transient response is also feasible since the required voltage is directly calculated from the feedforward control. Also, it is demonstrated that an instantaneous current control without the calculation time delay can be implemented. The excellence of the proposed current regulation scheme is verified by experiments for the GTO inverter-fed induction motor drive system controlled by a DSP-TMS320C30.

The reliability of power electronics systems is of paramount importance in industrial, commercial, aerospace, and military applications. The knowledge about the fault mode behavior of a converter system is extremely important from the standpoint of improved system design, protection, and fault tolerant control. This paper describes a systematic investigation into the various fault modes of a voltage-fed PWM inverter system for induction motor drives. After identifying all the fault modes, a preliminary mathematical analysis has been made for the key fault types, namely, input supply single line to ground fault, rectifier diode short circuit, inverter transistor base drive open, and inverter transistor short-circuit conditions. The predicted fault performances are then substantiated by simulation study. The study has been used to determine stresses in power circuit components and to evaluate satisfactory post-fault steady-state operating regions. The results are equally useful for better protection system design and easy fault diagnosis. They will be used to improve system reliability by using fault tolerant control in the next phase of our work.

A phase-difference angle (PDA) controlled pulsewidth-modulated (PWM) inverter is proposed for adjustable speed drive for the two-phase induction motors. Output waveforms are fixed over the whole operating range of the motor. The motor torque is controlled not by the modulation of the phase voltage, but by the PDA. Based on the selected harmonic elimination (SHE) PWM technique, the commutation angles of the output voltage are calculated. Several characteristics of the two-phase induction motor driven by the PDA inverter are analyzed. Second, a hybrid PWM inverter is proposed also to compensate for the degradation of the efficiency at small PDA. Not only the PDA but also the voltage amplitude and frequency are used as the parameters for controlling the torque of the motor in the hybrid inverter. The speed characteristics of the two-phase induction motor driven by the hybrid PWM inverter are more flexible than when the motor in driven by the conventional PWM inverter, which requires adjustable communication angles.

A load-commutated current source inverter (LCCSI) induction motor drive system employing a novel dc-side forced commutation circuit for machine start-up is proposed. To avoid the adverse effects of harmonic resonance between the output capacitor and the inductance of the induction motor, a solution is proposed using a special type of one-notch current PWM, fully utilizing the proposed commutation circuit. A direct vector controller, which refers to the fixed reference frame of the rotor flux without using a speed sensor, is applied. In addition to compensating for the capacitive current, this controller is applied to decouple the torque and flux generating currents and to overcome the instability caused by the output capacitor. The feasibility of the proposed circuit for the high power drive system is verified by computer simulation for a 600 Hp induction motor. Experimental results for a laboratory LCCSI-induction motor (10 Hp) are also included.

The performance of PWM-controlled thyristor rectifier operating at unity fundamental input power factor in PWM current source GTO inverter system for high speed high horse power induction motor drive is analyzed and found out in this paper. With the application of an energy rebound circuit in the dc link of the inverter for PWM control of the thyristor rectifier, a PWM control current source GTO inverter has been proposed. The principles and fundamental behavior of this inverter also have been investigated. A prototype unit of the PWM-controlled current source GTO inverter system is used to drive an 8 pole, 400 Hz, 5.5 kW three-phase induction motor. With the analytical and experimental results, the performance of the dc voltage control of the PWM-controlled thyristor rectifier for various values of the number of pulses for a half period of the supply frequency is also given in detail in this paper.

PWM inverter-fed induction motor drives are being used in greater numbers throughout a wide variety of industrial and commercial applications. PWM inverters provide many benefits to their users including improved control of processes, reduced energy consumption, and expanded diagnostics. Despite these benefits, PWM inverters should be applied with special consideration for low-voltage induction motor operation. The power supplied to the motor by a PWM inverter has some adverse effects which this paper will describe. These effects include increased heating, high peak voltages, and increased audible noise. Many manufacturers of PWM inverters promote to the marketplace that their PWM inverters can successfully operate any low-voltage induction motor. This is often not true. There are many PWM inverter-motor applications which require long periods of low speed operation, wide constant torque speed range, and high starting torque, all of which could cause the motor additional stress resulting in a possible unsuccessful application. The intent of this paper is to highlight some of the known possible adverse effects PWM inverters cause low voltage induction motors and the impact these effects have on the given application. This paper is written for those that are applying PWM inverter-fed low voltage induction motors, not those designing them.

A new PWM strategy suitable for an inverter-fed induction motor is described. The output waveforms in the proposed PWM inverter are investigated both theoretically and experimentally. Although the output waveform is a non-sinusoidal waveform, the induction motor driven by the proposed modulating signal produces approximately constant torque. A modulating signal for the three-phase PWM inverter is obtained by superposing a rectangular wave on the specific trapezoidal wave whose flat portion is 120 degrees. By using the proposed modulating signal, the amplitude of the fundamental component is increased by about 17 percent more than that of a conventional sine wave inverter. The new system reduces the torque ripple as well as achieving the effective utilization of the DC supply voltage for the inverter.

This paper deals with a current source inverter-induction motor drive system without a speed sensor, and the speed estimation with only sense of the motor voltage is investigated. The input dc link current which is kept constant by a pulsewidth modulated (PWM) converter with sinusoidal input current is supplied to the PWM inverter. The inverter output current with sinusoidal wave is directly regulated by employing the modulation index control of the PWM strategy. The motor is driven by a slip frequency/current regulation control. The motor speed is estimated by using the measured voltage and current, or using the measured voltage and the estimated current. The filter capacitor which is installed in the inverter circuit is taken into consideration for the current estimation. A digital signal processor is employed for calculation. As the PWM pulse of the inverter is calculated by a on-line real-time system, the quick regulation of the sinusoidal output current is achieved. The experiments show that the high performance steady state behavior and the acceleration/deceleration characteristics with smooth drives and low noises of a motor is obtained.

The operation of split-phase induction motors from pulse width modulated (PWM) voltage source inverters is examined in this paper. Splitting the phase windings leads to reduced voltage ratings for the inverter switches. As compared with seven positions for the space phasor of voltage in three-phase machines, 48 different locations bounded by a 12-sided polygon are possible in the split-phase machine. Based on space phasor modulation, a three-phase inverter can give a maximum peak fundamental of 0.577 V(sub DC). In comparison, the split-phase configuration can provide an equivalent three-phase maximum peak fundamental of 0.643 V(sub DC) with a dc bus voltage of 0.5 V(sub DC)/cos15.

In order to understand the magnetic behavior of electrical iron sheets assembled into an actual motor core driven by a PWM inverter, we have observed induced voltages and magnetic inductions in the stator core, the stator teeth, and the rotor core of a 3-phase squirrel-cage induction motor driven by both a sinusoidal power supply and a V/f = const PWM inverter power supply, and estimated the magnetic losses in the motor. Though the waveforms of the magnetic flux at the stator core in both driving conditions were approximately sinusoidal, the induced voltage waveforms in each driving condition were similar to the source voltage waveforms. The induced voltage waveform of the stator teeth contains higher harmonics, due to the rotor slots and the power supply waveform, and differs depending on the positions of the teeth only in the case of the inverter supply. The magnetic flux in the rotor core showed a sinusoidal waveform with the slip frequency multiplied by pole pair number, which contained higher harmonics due to the stator slots, the power supply waveform, the primary voltage imbalance, and the non-uniform air-gap between the stator teeth and the rotor core. In spite of the complex distribution of the magnetic induction in the motor core for PWM inverter drive, the magnetic losses of the motor are estimated to be proportional to the running frequency of the inverter and increase from those at the sine drive by a certain rate corresponding to the eddy current losses.

In this paper a new approach to direct torque control (DTC) of induction motor drive is presented. In comparison with the conventional DTC methods [1], [22] the inverter switching frequency is constant and is dramatically increased, requiring neither any increase of the sampling frequency, nor any high frequency dither signal. The well-developed space vector modulation technique is applied to inverter control in the proposed DTC-based induction motor drive system, thereby dramatically reducing the torque ripple and speed ripple. As compared to the existing DTC approach [2], [23] with constant inverter switching frequency, the presented new approach does not invoke any concept of deadbeat control, thereby dramatically reducing the computations. Experimental results are illustrated in this paper confirming that the proposed DTC method has the above-mentioned features even at the low speed range down to [+ or -] 1 r/min. Index Terms--Direct torque control, induction motor drives, inverter.

By putting an LC filter between a PWM voltage source inverter and induction motor, standard industrial motors can be utilized also for adjustable speed drive applications. In this paper the application of an LC filter to medium voltage motors fed by inverters with switching frequencies below 1000 Hz is described. For different filter topologies rules for the electrical design are discussed as well as solutions for the stability problem. Also discussed are solutions against common mode voltage stress on the motor terminals. An example shows the implication of the filter on the minimum inverter power which has to be installed to feed a given motor. Keywords: LC filter, medium voltage, induction motor, voltage source inverter, motor losses, motorfriendly, two-level inverter, three-level inverter, NPC inverter, GTO, resonance damping

In this paper, a detailed description of the simulation of inverter-fed induction motors in adjustable speed drives by a Time-Stepping flux linkage-based Coupled Finite Element/State-Space model for the computation of the drive performance is presented and verified experimentally. The flux linkage-based State-Space model is iteratively coupled to a 2D Time-Stepping Finite Element model. The iterative nature of the coupling between these two models facilitates rigorous modeling of the comprehensive impact of inherent space harmonics due to geometries and motor magnetics and time harmonics resulting from the electronic switching of inverters, as well as effects of the synergistic interaction between these time and space harmonics. The State-Space model includes no frame of reference transformation in so far as the flux linkages, currents or voltages. This implies that the State-Space model directly couples the motor to its power electronic controller in one formulation and the natural variables (voltages and currents) are directly involved in the formulation and computation. Finally, results of motor drive performance simulations and corresponding test results for a six-switch inverter with 180 [degrees] e duty cycle for each switch and a six-switch inverter with Pulse-Width Modulation are given with excellent test result correlations, respectively. Keywords: Time-Stepping, Finite Element, State-Space Model, ABC Frame of Reference, Adjustable Speed Drives, Induction Motors, Inverters, Flux Linkage Frame, Power Electronics.

The distorted power waveform from an inverter includes many time harmonic components which become a factor in increasing losses and generating noise. To evaluate the effect of these harmonic components quantitatively, this paper proposes a new harmonic field analysis method that considers the rotor movement dynamically and the harmonic components of the secondary current as induced current by a 2-dimensional finite element method (2D-FEM) using a time stepping technique. The proposed method is applied to the analysis of a cage induction motor supplied by a PWM inverter. As a result, the harmonic components . of the secondary current and the electromagnetic force are shown quantitatively. These calculated results are confirmed by experiments measuring the secondary current and the sound level. From the comparison of calculated and experimental results, the proposed method is shown to be appropriate and useful for quantitative estimation of harmonic fields for inverter-fed induction motors. Keywords: Induction motor, Inverter, Harmonic field, Secondary current, Electromagnetic force, Finite element method.