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In this paper, a novel 12-sided polygonal space vector structure is proposed for an induction motor drive. The space vector pattern presented in this paper consists of two 12-sided concentric polygons with the outer polygon having a radius double the inner one. As compared to previously reported 12-sided polygonal space vector structures, this paper subdivides the space vector plane into smaller sized triangles. This helps in reducing the switching frequency of the inverters without deteriorating the output voltage quality. It also reduces the device ratings and dv/dt stress on the devices to half. At the same time, other benefits obtained from the existing 12-sided space vector structure, such as increased linear modulation range and complete elimination of 5th and 7th order harmonics in the phase voltage, are also retained in this paper. The space vector structure is realized by feeding an open-end induction motor with two conventional three-level neutral point clamped (NPC) inverters with asymmetric isolated dc link voltage sources. The neutral point voltage fluctuations in the three-level NPC inverters are eliminated by utilizing the switching state multiplicities for a space vector point. The pulsewidth modulation timings are calculated using sampled reference waveform amplitudes and are explained in detail in this paper. Experimental verification on a laboratory prototype shows that this configuration may be considered suitable for high power drives. Index Terms--Pulsewidth modulation (PWM) timings, three-level neutral point clamped (NPC) inverter, twelve-sided polygonal space vector structure.

A simple and novel pulsewidth modulation (PWM) technique is presented. It uses a trapezoidal modulator wave and a sinusoidal carrier signal with variable frequency. The instantaneous frequency of the carrier wave is proportional to the slope of the modulator signal, and only two parameters (the slope of the trapezoidal edges and the proportionality constant of the carrier wave frequency) allow one to control the output voltage level and the number of commutation per cycle in real time. The proposed technique generates high-quality voltages with very few commutations per cycle, and it is particularly appropriate for reducing commutation loss. Results are checked experimentally and compared to other PWM techniques, yielding better signal quality with an important reduction in the number of commutations. Index Terms--Commutation losses, harmonic analysis, harmonic distortion, induction motor drive, pulsewidth modulation (PWM), PWM inverters, quality voltages, signal quality, slope PWM (SLPWM), variable frequency.

Multiphase (more than three phases) drives possess interesting advantages over conventional three-phase drives. Over the last years, various topics related to the extension of the classical control schemes to these specifics drives have been covered in depth in literature, such as vector control of a six-phase induction machine with two sets of three-phase stator windings spatially shifted by 30 electrical degrees (also called asymmetrical dual three-phase ac machine). In this paper, a model-based predictive control (MBPC) for the current regulation of asymmetrical dual three-phase ac machines is analyzed. MBPC overcomes the difficulties of multiphase current control, avoiding complex controllers and modulation techniques, but at the expense of an increased computational cost. Simulation results are provided to examine the potential of the control method. The influence of the number of voltage vectors considered to evaluate the predictive model is studied, and different cost functions are analyzed. The computation time needed for the implementation of the control method is discussed to prove its real-time feasibility. Finally, experimental results are given to illustrate the capability of the control method. Index Terms--Analysis, asymmetrical dual three-phase induction machine, modeling, multiphase drives, predictive control.

Multiphase (more than three phases) drives exhibit interesting advantages over conventional three-phase drives. Over the last years, topics related to the extension of control schemes to these specific drives have been covered in depth in the literature. Direct torque control and predictive current control are normally used in conventional ac drives when fast electrical dynamic performance is required. In this paper, a one-step modulation predictive current control technique is proposed for asymmetrical dual three-phase ac drives. Based on the use of a predictive model including the motor and the inverter, the control algorithm determines the switching state which minimizes errors between predicted and reference state variables. The period of application of the selected switching state is then obtained, resulting in a submodulation method. The proposed predictive current control algorithm uses a prediction horizon of one sampling period; however, two switching states are applied during the sampling period. The switching states are the selected optimum active vector and a null voltage combination. Simulation and experimental results are provided to examine the features of the control method. Performances, advantages, and limitations are also discussed. Index Terms--Asymmetrical dual three-phase ac machine, multiphase drives, predictive current control.

In this paper, we present a predictive control algorithm that uses a state-space model. Based on classical control theory, an exact discrete-time model of an induction machine with time-varying components is developed improving the accuracy of state prediction. A torque and stator flux magnitude control algorithm evaluates a cost function for each switching state available in a two-level inverter. The voltage vector with the lowest torque and stator flux magnitude errors is selected to be applied in the next sampling interval. A high degree of flexibility is obtained with the proposed control technique due to the online optimization algorithm, where system nonlinearities and restrictions can be included. Experimental results for a 4-kW induction machine are presented to validate the proposed state-space model and control algorithm. Index Terms--Induction motor drives, predictive control, state-space methods.

This paper develops a seven-level inverter structure for open-end winding induction motor drives. The inverter supply is realized by cascading four two-level and two three-level neutral-point-clamped inverters. The inverter control is designed in such a way that the common-mode voltage (CMV) is eliminated. DC-link capacitor voltage balancing is also achieved by using only the switching-state redundancies. The proposed power circuit structure is modular and therefore suitable for fault-tolerant applications. By appropriately isolating some of the inverters, the drive can be operated during fault conditions in a five-level or a three-level inverter mode, with preserved CMV elimination and dc-link capacitor voltage balancing, within a reduced modulation range. Index Terms--Capacitor voltage balancing, common-mode voltage (CMV) elimination, multilevel inverter, open-end winding induction motor.

An adaptive nonlinear controller for wind energy doubly fed induction machines is introduced in this paper. The proposed controller is based on the feedback linearization technique and includes a disturbance observer for estimation of parameter uncertainties. Estimated uncertainties values are injected in order to construct the control law, improving in this way the system's performance. The controller behavior, when tracking power references, is tested with realistic Electromagnetic Transients for dc /Power Systems Computer-Aided Design simulations. In addition, the controller performance is checked in the presence of parameter uncertainties and nearby faults. Index Terms--Doubly fed induction machine (DFIM), feedback linearization (FL), nonlinear observer, voltage source converter (VSC), wind energy conversion (WEC).

The paper assesses the steady-state performance of a five-phase induction machine fed by a modified open loop constant volt/hertz (V/f) control method, which imposes a trapezoidal induction waveform in the air gap under varying load conditions. The trapezoidal air gap induction is achieved through the imposition of an appropriate combination of the third harmonic and fundamental stator voltages. This harmonic combination is determined from the steady-state model using a mathematical optimization procedure, which allows to obtain the optimal weighting factors for each harmonic component. The optimized reference voltages lead to a trapezoidal air gap induction, which allows a better iron utilization and higher output torque for the same rms stator current when compared to sinusoidal air gap induction. The resulting air gap induction is obtained from the induced voltage of a full pitch search coil placed in the air gap. The proposed control scheme was successfully simulated and implemented on a five-phase prototype machine running under different load conditions. Experimental and simulations results show an increase in the torque/ampere relationship for loads above 50% when compared to the conventional V/f method using only the fundamental current and air gap induction. A comparison between the simulation and experimental curves presents a very good agreement that confirms and validates the parameters and model used. Index Terms--AC motor drives, induction machines, modeling, volt/hertz (V/f) control.

In this paper, a controller for induction motors is proposed. A continuous feedback is first applied to obtain a discrete-time model in closed form. Then, on the basis of these exact sampled dynamics, a discrete-time controller ensuring speed and flux modulus reference tracking is determined, making use of the sliding mode technique. The resulting controller is hence hybrid, in the sense that it contains both continuous and discrete-time terms. It is shown how to implement such a hybrid controller using the so-called exponential holder, which is the only device to be implemented analogically, together with an analog integrator. Moreover, a discrete-time reduced-order observer is designed for rotor fluxes and load torque estimation. The performance of the proposed controller is finally studied by simulation and experimental tests. Index Terms--Exponential holder, induction motors (IMs), sampled closed form, sliding mode control.

The necessity of the compactness of the converters in many applications imposes the reduction of the size of their different components when it is possible. In this paper, a control method allowing the use of a small size dc-link capacitor ([C.sub.o]) for the cascade of voltage controlled-rectifier/inverter-motor drive system is proposed. This is achieved by adding the power balance equation in the system's model and the application of an exact I/O feedback linearization technique in a way that the rectifier controller compensates any sudden change in the inverter load, which is here an induction motor. Since the exact I/O feedback linearization technique is sensitive to the uncertainties over system parameters, a robust control strategy based on sliding mode controller (SMC) is proposed. By this approach, the dc-link voltage ([v.sub.dc]) becomes almost insensitive to the load variations. As a result, the level of [v.sub.dc] could be stabilized with a small [C.sub.o]. Without any considerations of the RMS current stress on the [C.sub.o], a calculation method of a minimum dc-link capacitor [C.sub.o](min) based on its storage energy is proposed. All the investigations are shown by computer simulations and the performance of controlled system is verified by experimentation results. Index Terms--Controlled rectifier, induction motor, I/O linearization technique, sliding mode control, small dc-Link capacitor.

This paper analyzes the effects of unbalanced voltage on doubly fed induction generators. It also presents a novel control strategy based on direct power control (DPC+) applied to this type of generators, predominant in wind energy applications, that enables them to work under perturbed conditions and achieve optimum results. Although the technique can be implemented to control both rotor converters and grid converters, we will hereby exemplify the former which regulates stator active and reactive power. The results obtained with DPC+ are then compared through experimental tests to indicate that the technique is suitable and achieves good dynamic responses while controlling current distortion, power or torque oscillations. The validation of results has been performed through experimental tests on a 20-kW generator. Index Terms--Direct power control (DPC+), doubly fed induction generator (DFIG), unbalanced voltage, voltage dip.

This paper presents a novel control strategy, dynamic programming power control (DPPC), to be applied to doubly fed induction generators most commonly used in wind energy applications. Although the technique can be implemented to control both rotor and grid converters, it will hereby be expounded the former, which regulates stator active and reactive powers. The results obtained are compared with those from other techniques, such as direct torque/power control (DTC/DPC) through the use of experimental tests, and indicate that DPPC achieves gains in dynamic response and considerable improvements in terms of ripple reduction and frequency spectrum as a result of constant switching frequency operation. The validation of results has been performed through experimental tests on a 6-kW generator. Index Terms--Direct power control (DPC), doubly fed induction generator, dynamic programming.

Direct torque control (DTC) is one of the most excellent control strategies of torque control in induction machine. It is considered as an alternative to the field oriented control (FOC) or vector control technique. These two control strategies are different on the operation principle but their objectives are the same. They aim to control effectively the torque and flux. Torque control of an induction machine based on DTC strategy has been developed and a comprehensive study is present in this research. The performance of this control method has been demonstrated by simulations performed using a versatile simulation package, Matlab/Simulink. Several numerical simulations have been carried out in a steady state and transient operation on a speed control mode. Key words: Direct torque control, induction machine, vector control, Matlab/Simulink, INTRODUCTION For many years, induction machine have provided the most common form of electromechanical drive for industrial, commercial and domestic applications that can operate at essentially constant speed. Induction machines [...]

This paper proposes a novel robust adaptive speed/ position tracking control for a linear induction motor (LIM) with both end-effect and secondary resistance unknown. The practical current-fed controlled LIM, with residual current error, is considered, i.e., the traditional ideal current-loop assumption is relaxed. More practical conditions, such as bounded primary voltage and a finite absolute-integral of current tracking error is considered. To overcome the high nonlinearity and nonzero current error, a backstepping method, combining virtual desired variable synthesis, is developed for the speed and position tracking. Then, the controller achieves asymptotic speed and position tracking even with unknown parameters and immeasurable secondary flux. Furthermore, the effect of the residual current error is attenuated in an [L.sub.2]-gain sense. The experiments for several scenarios are carried out to verify the theoretical result. Index Terms--Adaptive control, linear induction motors, position tracking, semi-current-fed model, speed tracking.

The development of the brushless doubly-fed induction generator (BDFIG) system and flexible power flow controller for the wind energy conversion is proposed in this paper. The system employs two cascaded induction machines to eliminate the brushes and copper rings in the traditional DFIG. The dynamic model of BDFIG with two machines' rotor electromechanically interconnected is presented and the control strategy for flexible power flow control is developed. The independent control of the active and reactive power flows is achieved by means of a four quadrant power converter under the closed-loop stator flux oriented control scheme. The experimental results obtained verify the proposed controller scheme, which allows wide operational range and reactive power control. Index Terms--Brushless doubly-fed induction generator (BDFIG), maximum power point tracking (MPPT), power flow, wind energy conversion.

This paper proposes a wind speed estimation based sensorless maximum wind power tracking control for variable-speed wind turbine generators (WTGs). A specific design of the proposed control algorithm for a wind turbine equipped with a doubly fed induction generator (DFIG) is presented. The aerodynamic characteristics of the wind turbine are approximated by a Gaussian radial basis function network based nonlinear input-output mapping. Based on this nonlinear mapping, the wind speed is estimated from the measured generator electrical output power while taking into account the power losses in the WTG and the dynamics of the WTG shaft system. The estimated wind speed is then used to determine the optimal DFIG rotor speed command for maximum wind power extraction. The DFIG speed controller is suitably designed to effectively damp the low-frequency torsional oscillations. The resulting WTG system delivers maximum electrical power to the grid with high efficiency and high reliability without mechanical anemometers. The validity of the proposed control algorithm is verified by simulation studies on a 3.6 MW WTG system. In addition, the effectiveness of the proposed wind speed estimation algorithm is demonstrated by experimental studies on a small emulational WTG system. Index Terms--Doubly fed induction generator (DFIG), Gaussian radial basis function network (GRBFN), sensorless control, variable-speed wind turbine, wind speed estimation.

In this paper, a new predictive direct torque control (DTC) strategy of the doubly fed induction machine (DFIM) is presented. It is especially designed to operate at a considerably low constant switching frequency, reducing the electromagnetic torque and rotor flux ripples, in order to provide good steady-state and fast dynamic performances. This control is convenient for high power drive and generator applications, with restricted switching frequency. The DFIM is connected to the grid by the stator and the rotor is fed by a two level voltage source converter. In addition, this control method allows to implement a technique that reduces the switching power losses of the converter. Finally, experimental results show that the proposed DTC method effectively reduces the torque and flux ripples at low switching frequency, even under variable speed operation conditions. Index Terms--Constant switching frequency, control of doubly fed induction generator, power electronic converter, predictive direct torque control (DTC).

A sensorless direct rotor field-oriented control (SDRFOC) scheme of three-phase induction motors for low-cost applications is presented in this paper. The SDRFOC algorithm is based on a sensorless closed-loop rotor flux observer whose main advantages are simplicity and robustness to motor parameter detuning. The whole algorithm has been developed and implemented on a low-cost fixed-point digital signal processor controller. Experimental results are presented for a 0.5-kW induction motor drive for a primary vacuum pump used in industry applications. Index Terms--Digital control, digital signal processor (DSP), induction motor drive, low-cost applications, sensorless field-oriented control (SFOC).

Temperature- and frequency-dependent variations of the rotor ([R'.sub.r]) and stator ([R.sub.s]) resistances pose a challenge in the accurate estimation of flux and velocity in the sensorless control of induction motors (IMs) over a wide speed range. Solutions have been sought to the problem by signal injection and/or by the use of different algorithms for the different parameters and states of the same motor. In this paper, a novel Extended-Kalman-Filter (EKF)-based estimation technique is developed for the solution of the problem based on the consecutive operation of two EKF algorithms at every time step. The proposed 'braided' EKF technique is experimentally tested under challenging parameter and load variations in a wide speed range, including low speed. The results demonstrate a significantly increased accuracy in the estimation of [R.sub.s] and [R'.sub.r], as well as load torque, flux, and velocity in transient and steady state, when compared with single EKFs or other approaches taken to estimate these parameters and states in the sensorless control of IMs. The improved results also motivate the utilization of the new estimation approach in combination with a variety of control methods which depend on accurate knowledge of a high number of parameters and states. Index Terms--Braided Extended Kalman Filter (EKF), induction motors (IMs), load-torque estimation, rotor- and stator-resistance estimation, speed sensorless control.

This paper presents a new sensorless method for the vector control of Doubly-Fed Induction Machines (DFIMs) without using speed sensors or rotor position measurements. The proposed sensorless method is based on the Model Reference Adaptive System (MRAS) estimating the rotor position and speed from the machine rotor currents. The method is appropriate for both stand-alone and grid-connected operation of variable speed DFIMs. To design the MRAS observer with the appropriate dynamic response, a small signal model is derived. The sensitivity of the method for variation in the machine parameters is also analyzed. Speed catching on the fly and synchronization of the Doubly-Fed Induction Generator with the utility are also addressed. Experimental results obtained from a 3.5-kW prototype are presented and fully analyzed. Index Terms--AC generators, induction motors, sensorless control, wind power generation.

The aim of this paper is to design and analyze reduced-order observers of the rotor flux of induction motors. The design is carried out in two steps. In the first step, a boundary of the stability region of the observation error is obtained corresponding to a chosen Lyapunov function. In the second step, the boundary is translated into a performance index that is minimized with respect to stator and rotor resistance variations and differences of voltages supplying the motor and those supplying the observer in order to obtain the largest stability region. Implementation of the observer on a low-cost fixed-point digital signal processor using look-up tables is described. Experimental results are shown with reference to a prototype consisting of a simple proportional--integral controller, the proposed observer, and a 2.2-kW induction motor; the implementations of both the controller and the observer are carried out on a DS1104 d-Space microcontroller using the fixed-point option. Index Terms--Induction motors, low-cost implementation, rotor flux observers.

This paper analyzes the effects of injecting additional signals in induction machines for the purpose of speed control. A new saturation model able to correctly model the interaction between the added signal and saturation of the motor core due to the main torque-producing flux is presented. The introduction of a variable saturation factor is used to model the variation of the saturation level due to the additional signal. A third harmonic rotor circuit is also introduced to take account of the third harmonic component of the air-gap flux, due to saturation. An additional balanced voltage set is added to the normal supply to analyze the effects of such signals on a saturated induction motor. Simulation results of such a model both at no load and full load are presented together with experimental measurements. Index Terms--Air-gap flux harmonics, flux position estimation, q-d model, saturation modulation, sensorless control.

In this paper, a novel control method for a six-phase induction machine with nearly square air-gap flux density is proposed and evaluated. In this method, the stator phase windings alternately act as either flux- or torque-producing phases. In this way, the flux and the torque of the induction machine are directly controlled with no vector transformation used. Theoretical and finite-element analyses are used to calculate, among other things, the torque and the decouple control constant of the drive. The steady-state measured results of a small six-phase induction machine drive with the proposed control scheme implemented show good agreement with calculated results. The proposed control drive system is also shown to have a fast torque response. Index Terms--Direct control, finite-element (FE) analysis, flux, six-phase induction machine, torque.

A field-programmable gate array (FPGA)-based adaptive backstepping sliding-mode controller is proposed to control the mover position of a linear induction motor (LIM) drive to compensate for the uncertainties including the friction force. First, the dynamic model of an indirect field-oriented LIM drive is derived. Next, a backstepping sliding-mode approach is designed to compensate the uncertainties occurring in the motion control system. Moreover, the uncertainties are lumped and the upper bound of the lumped uncertainty is necessary in the design of the backstepping sliding-mode controller. However, the upper bound of the lumped uncertainty is difficult to obtain in advance of practical applications. Therefore, an adaptive law is derived to adapt the value of the lumped uncertainty in real time, and an adaptive backstepping sliding-mode control law is the result. Then, an FPGA chip is adopted to implement the indirect field-oriented mechanism and the developed control algorithms for possible low-cost and high-performance industrial applications. The effectiveness of the proposed control scheme is verified by some experimental results. With the adaptive backstepping sliding-mode controller, the mover position of the FPGA-based LIM drive possesses the advantages of good transient control performance and robustness to uncertainties in the tracking of periodic reference trajectories. Index Terms--Adaptive backstepping control, field-programmable gate array (FPGA), indirect field-oriented control, linear induction motor (LIM), sliding-mode control.

This study mainly deals with the key problem of chattering phenomena on the conventional sliding-mode control (SMC) and investigates an adaptive fuzzy sliding-mode control (AFSMC) system for an indirect field-oriented induction motor (IM) drive to track periodic commands. First, an indirect field-orientation method for an IM drive is introduced briefly. Moreover, a fuzzy logic inference mechanism is utilized for implementing a fuzzy hitting control law to remove completely the chattering phenomena on the conventional SMC. In addition, to confront the uncertainties existed in practical applications, an adaptive algorithm, which is derived in the sense of Lyapunov stability theorem, is utilized to adjust the fuzzy parameter for further assuring robust and optimal control performance. The indirect field-oriented IM drive with the AFSMC scheme possesses the salient advantages of simple control framework, free from chattering, stable tracking control performance, and robust to uncertainties. Furthermore, numerical simulation and experimental results due to periodic sinusoidal commands are provided to verify the effectiveness of the proposed control strategy, and its advantages are indicated in comparison with the conventional SMC system and the SMC system with a boundary layer. Index Terms--Fuzzy inference mechanism, indirect field-orientation method, induction motor (IM) drive, Lyapunov stability, sliding-mode control (SMC).

The objective of the present work is to improve the output waveform of three level inverters used in high-power applications, where the switching frequency is very low. This is achieved by maintaining the synchronization, half-wave symmetry, quarter-wave symmetry, and three-phase symmetry in the pnisewidth modulation (PWM) waveforms. The principles of achieving synchronization and symmetries in terms of space vectors for three level inverters are presented. A novel synchronized space vector pulsewidth modulation (SVPWM) algorithms is proposed and verified experimentally. The experimental waveforms of the inverter output voltage and motor no load current for different operating conditions of the drive are presented. The performance measure in terms of the weighted total harmonic distortion (THD) of the line voltage is computed for the linear modulation region of the drive for the proposed algorithm and compared with that of synchronized SVPWM and synchronized sine-triangle pulsewidth modulation (SPWM) technique. The comparative results show that consideration of synchronization and symmetry results in improved THD. Another significant feature of the proposed algorithm is that the symmetry and synchronization leads to self-balancing of the direct current (dc) bus capacitor voltages over every one third cycle of the fundamental. Index Terms--Harmonic distortion, induction motor drives, pulsewidth modulated inverters, pulsewidth modulation.

This paper focuses on the development of a Petri-fuzzy-neural-network (PFNN) control for an indirect field-oriented linear-induction-motor (LIM) drive. First, an indirect field-oriented mechanism for a LIM drive is derived to preserve the decoupling control characteristic. Then, the concept of a Petri net (PN) is incorporated into a traditional FNN (TFNN) to form a new type of PFNN framework for alleviating the computation burden. Moreover, the supervised gradient descent method is used to develop the online training algorithm for the PFNN. In order to guarantee the convergence of tracking error, analytical methods based on a discrete-type Lyapunov function are proposed to determine the varied learning rates of the PFNN. With the proposed PFNN control system, the mover position of the controlled LIM drive possesses the advantages of good transient control performance and robustness to uncertainties for the tracking of periodic reference trajectories. In addition, the effectiveness of the proposed control scheme is verified by both numerical simulations and experimental results. Furthermore, the superiority of the proposed PFNN control system is indicated in comparison with the TFNN control system. Index Terms--Fuzzy neural network (FNN), indirect field-oriented mechanism, linear induction motor (LIM), Petri net (PN), varied learning rates.

In this paper, extended-Kalman-filter-based estimation algorithms that could be used in combination with the speed-sensorless field-oriented control and direct-torque control of induction motors (IMs) are developed and implemented experimentally. The algorithms are designed aiming minimum estimation error in both transient and steady state over a wide velocity range, including very low and persistent zero-speed operation. A major challenge at very low and zero speed is the lost coupling effect from the rotor to the stator, which makes the information on rotor variables unobservable on the stator side. As a solution to this problem, in this paper, the load torque and the rotor angular velocity are simultaneously estimated, with the velocity taken into consideration via the equation of motion and not as a constant parameter, which is commonly the case in most past studies. The estimation of load torque, on the other hand, is performed as a constant parameter to account for Coulomb and viscous friction at steady state to improve the estimation performance at very low and zero speed. The estimation algorithms developed based on the rotor and stator fluxes are experimentally tested under challenging variations and reversals of the velocity and load torque (step-type and varying linearly with velocity) over a wide velocity range and at zero speed. In all the scenarios, the current estimation error has remained within a very narrow error band, also yielding acceptable velocity estimation errors, which motivate the use of the developed estimation method in sensorless control of IMs over a wide velocity range and persistent zero-speed operation. Index Terms--Extended Kalman filter (EKF), induction motor (IM), low/zero-speed operation, sensorless control.

This paper presents a sensorless technique for high-performance induction machine drives based on neural networks. It proposes a reduced order speed observer where the speed is estimated with a new generalized least-squares technique based on the minor component analysis (MCA) EXIN + neuron. With this regard, the main original aspects of this work are the development of two original choices of the gain matrix of the observer, one of which guarantees the poles of the observer to be fixed on one point of the negative real semi-axis in spite of rotor speed, and the adoption of a completely new speed estimation law based on the MCA EXIN + neuron. The methodology has been verified experimentally on a rotor flux oriented vector controlled drive and has proven to work at very low operating speed at no-load and rated load (down to 3 rad/s corresponding to 28.6 rpm), to have good estimation accuracy both in speed transient and in steady-state and to work correctly at zero-speed, at no-load, and at medium loads. A comparison with the classic full-order adaptive observer under the same working conditions has proven that the proposed observer exhibits a better performance in terms of lowest working speed and zero-speed operation. Index Terms--Field oriented control, induction machines, least-squares (LS), neural networks, reduced order observer, sensorless control.

This paper proposes two speed observers for high-performance induction machine drives, both adopting an online adaptation law based on a new total least-squares (TLS) technique: the TLS EXIN neuron. The first is a model reference adaptive system (MRAS) observer with a neural adaptive integrator in the reference model and a neural adaptive model trained online by the TLS EXIN neuron. This observer, presented in a previous article of the authors, has been improved here in two aspects: first, the neural adaptive integrator has been modified to make its learning factor vary according to the reference speed of the drive, second, a neural adaptive model based on the modified Euler integration has been proposed to solve the discretization instability problem in field-weakening. The second observer is a new full-order adaptive one based on the state equations of the induction machine, where the speed is estimated by means of a TLS EXIN adaptation technique. Both these observers have been provided with an inverter nonlinearity compensation algorithm and with techniques for the online estimation of the stator resistance of the machine. Moreover, a thorough theoretical stability analysis has been developed for them both, with particular reference to the field-weakening region behavior for the TLS MRAS observer and to the regenerating mode at low speeds for the TLS adaptive observer. Both speed observers have been verified in numerical simulation and experimentally on a test setup, and have also been compared experimentally with the BPN MRAS observer, the classic adaptive observer and with an open-loop estimator. Results show that both proposed observers outperform all other three observers in every working condition, with the TLS adaptive observer resulting in a better performance than the TLS MRAS observer. Index Terms--Field oriented control, induction motor, Luenberger observer, model reference adaptive system (MRAS), neural networks, sensorless control, speed observers, total least-squares (TLS).

This study focuses on the development of a robust Petri-fuzzy-neural-network (PFNN) control strategy applied to a linear induction motor (LIM) drive for periodic motion. Based on the concept of the nonlinear state feedback theory, a feedback linearization control (FLC) system is first adopted in order to decouple the thrust force and the flux amplitude of the LIM. However, particular system information is required in the FLC system so that the corresponding control performance is influenced seriously by system uncertainties. Hence, to increase the robustness of the L1M drive for high-performance applications, a robust PFNN control system is investigated based on the model-free control design to retain the decoupled control characteristic of the FLC system. The adaptive tuning algorithms for network parameters are derived in the sense of the Lyapunov stability theorem, such that the stability of the control system can be guaranteed under the occurrence of system uncertainties. The effectiveness of the proposed control scheme is verified by both numerical simulations and experimental results, and the salient merits are indicated in comparison with the FLC system. Index Terms--Decoupled control, feedback linearization, fuzzy neural network (FNN), linear induction motor (LIM), Lyapunov stability theorem, Petri net (PN).

We present here a globally stable nonlinear dynamic output feedback controller for torque tracking and flux regulation of induction motors. The control law is globally defined (even in startup), requires only measurement of stator variables and rotor speed, and does not rely on cancellation of the systems nonlinearities. Our work extends in several directions the result of the paper by Ortega et al., where the torque tracking problem was solved for a model where the variables are expressed in a frame rotating at an arbitrary angular frequency (dq model). First, we obviate the need to transfer the dq control signals of the paper by Ortega et al., to the physical input variables in the stator frame, hence providing a directly implementable control law. Second, besides the torque tracking objective, we include the practically important rotor flux regulation task. Third, by choosing a more suitable representation of the motor model, we simplify the controller structure and provide a better understanding of its derivation and behavior.

Sensorless speed control of an induction machine can be achieved by synthesizing a slip estimate solely from stator voltages and currents. Stator or rotor flux linkages can likewise be estimated, thereby allowing alignment of such flux linkages with a rotating coordinate axis to produce rapid torque and speed responses. Six published methods of rotor slip estimation have been evaluated with simulated data in this study - only two of these showed signs of being usable. These are both based on the steady-state machine model and produce a fair slip accuracy for a machine running under perfect field alignment conditions. It was not determined whether the other four techniques were unsuccessful because they require a closed-loop speed controller whether they were presented incorrectly in the literature or whether they contain fundamental deficiencies. Based on the experience gained from these evaluations, a new technique has been developed, and both measured and predicted results are presented to show that it works well. Moreover, this new technique has many features that make it theoretically and practically more attractive than most of the other existing techniques.

The boiler on Southern California Edison's 750 MW Ormond Beach Unit 2 was extensively modified to reduce minimum load from 250 MW to 36 MW. With the unit operating at minimum load frequently at night, it became economically attractive to install adjustable-speed drives (ASDs) on each of the 6250 hp Forced Draft Fan Motors. The ASD technology that was used is a fourth generation current-source, GTO-PWM inverter that is used in a configuration fostered by a series of five ASD field tests conducted for EPRI by Bechtel in the period from 1984 to 1989. This ASD concept has features that ensure the high degree of reliability that is needed in these high capacity utility power plant applications. These features are as follows: 12 pulse inverter to minimize harmonics to the utility bus. UPS for ASD control power to eliminate outside influences on the operation of the ASD. Input transformer and ground at the motor side of the inverter to prevent high line-to-neutral voltage on the motor. Selective harmonic elimination inverter control to preclude electrical resonance between output filter and motor. Liquid cooling of thyristors to prevent temperature-related failures. The Ormond Beach ASD system is the world's largest and most sophisticated of its kind. These 7200hp ASDs have operated for 3 years with no backup system, attesting to the reliability that can be achieved with this approach. This paper describes the application concept that has evolved from the EPRI tests, the GTO-PWM ASD technology, field test results of power savings, measured harmonics at utility bus and at the motor, effect of THD reduction by using an input harmonic filter, and operating experience to date. Fan inlet vanes have been removed, and no ASD bypass was provided.

In this paper, we attempt to control induction motors with maximum power efficiency as well as high dynamic performance by means of decoupling of motor speed (or motor torque) and rotor flux. For maximum power efficiency, the squared rotor flux is adjusted according to a minimum power search algorithm until the measured power input reaches the minimum. Since the motor speed is dynamically decoupled from the rotor flux, this can be done successfully without any degradation of motor speed responses. Our controller depends on rotor resistance but not on stator registance. However, the performance of our control scheme is robust with respect to variations in rotor resistance because an identification algorithm for rotor resistance is employed. Our identification algorithm for rotor resistance has some advantages over the previous methods. To demonstrate the practical significance of our results, we present some experimental results.

This paper presents a V/f PWM inverter control algorithm based on controlling the stator flux vector of an induction motor. The algorithm permits an automatic boost of inverter voltage in such a way that the stator flux magnitude is kept constant. The voltage auto-boost method is based on knowledge of the IM equivalent circuit parameters and given load characteristics. An off-line auto measurement of the equivalent circuit parameters using a PWM inverter is described. The technique consists in performing the no-load and single-phase tests when the motor is connected to the inverter. The complete control system has been constructed and tested and the experimental results have been found satisfactory. The proposed method has achieved a considerable improvement of IM torquespeed characteristics under optimal slip frequency operation.

For a high-power induction motor drive, the switching frequency of the inverter cannot become higher than a few kilohertz, and such a switching frequency produces a large current ripple, which then produces torque ripple. To minimize the current ripple, a new method based on deadbeat control theory for current regulation is proposed. The PWM pattern is determined at every sampling instant based on stator currents measurements, motor speed, current references, and rotor flux vector, which is predicted by a state observer with variable poles selection, so that the stator currents are controlled to be exactly equal to the reference currents at every sampling instant. The proposed method consists of two parts: 1) derivation of a deadbeat control and 2) construction of a state observer that predicts the rotor flux and the stator currents in the next sampling instant. This paper describes a theoretical analysis, computer simulations and experimental results.

It is shown that in the paper by Rehman (2005) the proposed method for a stator flux estimation does not have an advantage over a current model. Index Terms--Induction machine, sliding mode, voltage model flux observer.