EPE Association: EPE 1991 - 16 - Session 2.5: FIELD ORIENTED CONTROL

EPE 1991 - 16 - Session 2.5: FIELD ORIENTED CONTROL
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 1991 - Conference > EPE 1991 - 16 - Session 2.5: FIELD ORIENTED CONTROL

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   SIGNAL PROCESSOR BASED FIELD ORIENTED VECTOR CONTROL FOR AN INDUCTION MOTOR DRIVE
By J. Moerschell [View]
[Download]

Abstract: A voltage source inverter fed induction motor drive is presented for which a completely digital current, speed and position control has been developped and irnplemented on a floating point signal processor based controller. Good torque and flux control decoupling is achieved through field oriented vector control. By choosing the controller sampling rate equal to the inverter commutation frequency, good dynamic performance of the drive is realized and discretization of continuous designed state feedback controllers is simplified. Special attention is paid to inner variable limitation (speed, torque and inverter command voltages) and to compensation of the nonlinear inverter load characteristic.

   A NEW ADAPTATION METHOD FOR INDUCTION MACHINES WITH FIELD-ORIENTED CONTROL
By J. Weidauer; A. Dittrich [View]
[Download]

Abstract: In induction machines with field-oriented control the knowledge of the rotor time constant is of great importance. Because it is not constant, the continuous identification of the rotor time constant is necessary. In this paper a method is presented that provides the possibility to estimate the stator resistance besides the identification of the rotor time constant. The stator voltage, the stator current and the speed are assumed to be known. The identification of the rotor time constant and the stator resistance is realized using parameter estimation techniques and an additional model. Because test signals are not applied the identification does not cause a deterioration of the behavior of the speed controlling system. The identlfication can be done under steady-state or transient load conditions.

   A CONTINUOUS PWM-SQUARE WAVE TRANSITION METHOD FOR VOLTAGE VECTOR CONTROL OF INDUCTION MOTORS
By E. Ch. Andresen; S. Gediga; H.-J. Schwartz [View]
[Download]

Abstract: A control method for switching over from voltage vector modulation to square wave operation without transients is presented. A special voltage vector control range is interposed between the two control ranges. The switching angles are on-line calculated as a function of the lowest pulse fundamental frequency ratio and of the required fundamental voltage. The effectiveness of the method is demonstrated by some digital simulation results.

   VARIABLE STRUCTURE FIELD ORIENTED CONTROL OF AN INDUCTION MOTOR DRIVE
By K. Jezernik; B. Curk; J. Harnik [View]
[Download]

Abstract: The sliding mode control concept is applied in the outer loop of a servo drive system utilizing a squirrel-cage induction machine. A design procedure is outlined for the the sliding mode speed and position controller. The methods of decoupling and torque linearization for the IM are derived using the field orientation as well as the torque angle control concepts. Sliding mode control with cascaded integral operation is used to reduce steady state error. Acceleration sliding lines are introduced to enable better utilization of the torque capability of the drive system. The parameter insensitive response provided by this method of control is demonstrated. The effects on the dynamic and static performance with varying drive inertia and load disturbance are studied.

   INDUCTION-MOTOR SYNCHRONOUS FRAME FLUX CONTROL WITH MECHANICAL STATE-FEEDBACK COMPENSATION
By J. C. Reis e Costa; E. S. Saraiva [View]
[Download]

Abstract: Controlling the stator flux module of a three-phase induction motor leads to bad behaviour, eg. near speed-reversal and in position control due to the possibility of variable components. This paper shows that by making the component q of the stator flux equal to zero and controlling the component d (in a synchronous-reference frame), improved results are obtained with excellent torque controllability, which makes the position-control and tracking-control very easy, using state-feedback techniques. In this new strategy of flux control, the transfer function is independent of speed and machine rotor parameters, which makes its implementation very easy and it is not the case in conventional straregies, namely the vector control method. Finally, to overcome the drawback of the degradation of the system operation in the presence of a load torque, a state feedback structure for position control is developed, with an integral action at the input, in order to cancel out a possible steady state error.

   Discrete-Time Flux Observer for PWM Inverter Fed lnduction Motors
By Joachim Böcker; Jörg Janning [View]
[Download]

Abstract: For the purpose of flux oriented control a standard observer structure is applied to get the unmeasurable rotor flux of an induction motor. Main emphasis is put on discrete-time considerations with respect to microprocessor realizations. This aspect concerns the internal observer structure as well as the data acquisition and sampling strategy, which is synchronized with the pulse width modulation. Measurement results show that the proposed observer provides good results for both motor and generator operation modes and even at standstill. Moreover, the inherent parameter robustness of the used structure is demonstrated.

   VECTOR CONTROL OF A P.W.M. CURRENT SOURCE INVERTER-FED INDUCTION MOTOR
By J. P. Cambronne; B. Semail; C. Rombaut [View]
[Download]

Abstract: A new current source inverter-fed induction machine drive is presented, using three capacitors connected to the motor. In order to minimize current and voltage harmonics in the machine, a P.W.M. strategy has been developed; the inverter firing angles have been calculated as a function of speed and motor parameters, to avoid harmonics amplification in the resonant frequency range. However, self excitation may happen because of the interaction between capacitors and the magnetizing inductances of the motor. A field oriented control scheme, with either torque and flux loops or current compensation terms has been tested in simulation, giving interesting dynamic behaviour.

   FIELD-ORIENTED CONTROL OF HIGH-POWER INDUCTION MOTOR DRIVES BY KALMAN FILTER FLUX OBSERVATION
By F. Ben Ammar; M. Pietrzak-David; B. de Fornel; A. Mirzaian [View]
[Download]

Abstract: In this paper, the authors present a vector control strategy for a high-power induction motor drive, fed by a PWM inverter using gate turn-off thyristors (GTOs). The Kalman filter algorithm is used for tbe stochastic flux estimation. The feed-back regulators working in a coordinate system which rotates synchronously with the rotor flux, allow a complete decoupling between the two stator currents to be obtained. Using this control strategy the simulation results verify that the induction motor has a dynamic behaviour comparable with that of a DC motor drive in all fourth quadrants of the torque-speed plan.

   THE INFLUENCE OF THE DYNAMIC CONTROL ERROR OF THE STATOR CURRENT ON THE VALUE OF THE ROTOR FLUX IN THE INDIRECT FIELD ORIENTED AC DRIVES
By M. Dubowski; T. Citko [View]
[Download]

Abstract: It is well known that the main disadvantage of the indirect method of vector control of the induction motor is its sensitivity to the changes of the rotor resistance. Accurate investigations shown that there also exist another disadvantage of the same importance, i.e. drive sensitivity to the dynamic errors of the stator current control loop. The main danger caused by this phenomenon (like as the changes of rotor resistance) is the increase of the value of the rotor flux . This effect may be significant particulary when the over-current occurs. The drive systems of the machine-tools are especially exposed to this negative phenomenon. In this paper, a method of the estimation of the flux increase and proposition of apropriate countermeasurements are presented.

   TRANSPUTER BASED INDUCTION MOTOR FLUX-CONTROL METHOD
By M. J. Case; W. F. van Wyk [View]
[Download]

Abstract: This paper presents a transputer-based induction motor flux control method which does not depend on stator resistance neither does it require flux transducers. The system is based on a paper published by A. Abbondanti in 1977. The computation algorithm as well as experimental results are presented.

   DECOUPLING THE VOLTAGE / FREQUENCY CONTROL OF A SYNCHRONOUS GENERATOR / BATTERY-FED INVERTER COMBINATION BY TRANSFORMATION TO TWO-AXES STATOR-FLUX CONTROL
By W. Kleinkauf; J. Sachau [View]
[Download]

Abstract: The combination of a synchronous generator and a battery-fed inverter is a suitable solution for the voltage / frequency control of isolated grids which don't have a mechanical drive, e.g. in hybrid power supply systems with photovoltaic generators and wind energy converters. Here, the frequency control has to intervene via the electrical torque, the control of which is coupled with the voltage control. A decoupling transformation to direct and quadrature axis stator flux control is proposed and the results of separate state control are both presented with the controlled circuit model and with a 10 kVA laboratory plant.

   AN INTERNAL MODEL CONTROL STRUCTURE IN FIELD ORIENTED CONTROLLED V.S.I. INDUCTION MOTORS
By J. L. Thomas; M. Boidin [View]
[Download]

Abstract: An Internal Model Control (IMC) structure, used in an indirect vector control scheme, is presented in this paper. It describes a digital robust control approach which allows the obtention of a complete decoupllng between the two stator current components with respect to rotating axes (d,q), and the verification of a dynamic behaviour independent of the working point. The IMC controller design, based on desired closed-loop transfer matrix and combined with the gain scheduling method is explained. Furthermore, a model smoothing concept is introduced in order to minimize disturbances resulting from transition between adjacent models during continuous variation of rotor speed. Finally, simulation and experimental results obtained on a industrial drive system are presented demonstrating performances of the proposed IMC control.

   A SIMPLE ADAPTIVE SCHEME FOR INDIRECT FIELD ORIENTATION OF AN INDUCTION MOTOR
By P. J. da Costa Branco; A. M. Stephan [View]
[Download]

Abstract: The use of AC-motors as controlled electrical drives, in spite or their nonlinear-multivariable characteristic, may be attractive using field orientation and microprocessors. To obtain a high performance with this scheme, it is important to know the instanteneous position of the rotor flux, which depends on the rotor time constant. In this paper, a self-adaptive scheme is described for automatically tracking the temperature and saturation-dependent rotor time constant. This scheme is based on a monitoring signal (PRBS) injected in the process. A cross-correlation function between this signal and the speed error indicates the Tr-changes in direction (increase or decrease) and magnitude. This very simple adaptive scheme presents unique characteristics: it doesn't use current or voltage sensors; it is not motor parameter dependent; the amplitude of the additional PRBS can be reduced with an increase on the speed sensor sensibility and so the interference in the drive performance can be controlled; it works either on steady- and dynamic transient-state. The proposed method needs some load to operate, but this condition is satisfied in all practical cases. Tests were conducted with a 1,2kW fourquadrant AC-drive, the control was implemented with a microcomputer and the motor was supplied by a voltage-source inverter with current control using IGBTs. Experimental and simulated results using this adaptive digital schemz for different loads and values of model Tr (representing a detuned operation) are presented showing very good response. Furthermore, the Tr influence in the induction motor dynamics is also presented.

   FIELD-ORIENTED INDUCTlON MOTOR DRIVE WlTH INDIRECT ROTOR FLUX SENSING
By P. Fedor; V. Fedak; P. Bober; J. Timko [View]
[Download]

Abstract: The paper deals with one of the possible manners of the vector control of an asynchronous motor. The method presented is based on the determination of the magnetic rotor flux and on the adaptation to the changes of rotor resistance. For the magnetic flux determination a structure with parallel reference model is used designed according to the second Lyapunow method.

   lMPROVED SCHEME FOR SPEED CONTROL OF AN ASYNCHRONOUS MACHINE BY FIELD ORIENTED METHOD
By Ioan Felician Soran; Dragos Ovidiu Kisch [View]
[Download]

Abstract: All the field oriented methods of speed control presume as known the position of chosen field. The estimated performances, sometimes obtained by a careful simulation have no value, and cannot be found in practice if the position of the field is wrong synthetised. The paper analyses the errors due to wrong orientation and gives a method to compensate the orientation errors, even dynamically i.e. even at parameters variations due to saturation. This is the main contribution of the paper. Besides there are some details about separation of the leakage reactances for wound rotor machines and the protection against the short circuits in P.W.M. inverter.

   A VARIABLE STRUCTURE APPROACH FOR SPEED CONTROL OF FIELD-ORIENTED INDUCTION MOTOR
By G. Cordeschi; F. Parasiliti [View]
[Download]

Abstract: This paper is concerned with the application of the sliding mode control for the vector controlled induction motor speed drive systems. The model of the induction motor and the variable structure approach are briefly presented. The control strategy and the system are described in detail. Finally, the simulation results are given and discussed. The effects on the dynamic and static performances with varying drive inertia and load disturbance are studied. The parameter insensitive response, provided by this control method, is proved. The sampling effects on the sliding mode control performance are also illustrated and discussed.

   DIGITAL VECTOR CONTROL OF INDUCTION MACHINE USING A PWM INVERTER
By K. Dakhouche; D. Roye [View]
[Download]

Abstract: This paper presents the Vector Control of an induction machine with estimation of the rotor flux which is developed by making use of Two 16-bit microprocessors (8086) and PWM inverter. Usually the Vector Control suffers from the inaccurary of the decoupling terms. In the first part we present the Vector Control system with all the functions and if these functions are executed very quickly the decoupling terms can be eliminated. Experimental results are presented for control of torque and speed.

   COMPARISON OF DYNAMICS OF DOUBLY-FED INDUCTION MACHINE CONTROLLED IN FIELD- AND ROTOR-ORIENTED AXES
By A. M. Walczyna [View]
[Download]

Abstract: Current control of a doubly-fed induction machine allows directly access amplitude and phase of rotor and stator vectors both in static and in dynamic conditions. The best properties are obtained when control in rotating synchronously set of axes is applied as then the MDZ is described by a set of stationary differential equations. A drive system with current control in x-y axes oriented by stator voltage vector has been described in the previous works of the author. The main disadvantage of such a system is its complexity. Considerably simpler structure of DFM control is obtained after application of an induction machine description in rotor d-q axes. In the paper a structure and dynamic properties of such control system are presented and compared with properties of the previous one. In order to obtain good steady-state and dynamic control of rotor currents in d-q axes efficient decoupling of influence of strong disturbances acting at rotor terminals (rotor EMF) should be applied. In the paper efficiency of decoupling of these signals is discussed. It is shown that application of decoupling can cause instability of the drive. It is also shown that application of feed-forward compensation significantly improves control of rotor currents in d-q axes.

EPE 1991 - 16 - Session 2.5: FIELD ORIENTED CONTROL
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 1991 - Conference > EPE 1991 - 16 - Session 2.5: FIELD ORIENTED CONTROL
	[return to parent folder]

	SIGNAL PROCESSOR BASED FIELD ORIENTED VECTOR CONTROL FOR AN INDUCTION MOTOR DRIVE By J. Moerschell	[View] [Download]
Abstract: A voltage source inverter fed induction motor drive is presented for which a completely digital current, speed and position control has been developped and irnplemented on a floating point signal processor based controller. Good torque and flux control decoupling is achieved through field oriented vector control. By choosing the controller sampling rate equal to the inverter commutation frequency, good dynamic performance of the drive is realized and discretization of continuous designed state feedback controllers is simplified. Special attention is paid to inner variable limitation (speed, torque and inverter command voltages) and to compensation of the nonlinear inverter load characteristic.

	A NEW ADAPTATION METHOD FOR INDUCTION MACHINES WITH FIELD-ORIENTED CONTROL By J. Weidauer; A. Dittrich	[View] [Download]
Abstract: In induction machines with field-oriented control the knowledge of the rotor time constant is of great importance. Because it is not constant, the continuous identification of the rotor time constant is necessary. In this paper a method is presented that provides the possibility to estimate the stator resistance besides the identification of the rotor time constant. The stator voltage, the stator current and the speed are assumed to be known. The identification of the rotor time constant and the stator resistance is realized using parameter estimation techniques and an additional model. Because test signals are not applied the identification does not cause a deterioration of the behavior of the speed controlling system. The identlfication can be done under steady-state or transient load conditions.

	A CONTINUOUS PWM-SQUARE WAVE TRANSITION METHOD FOR VOLTAGE VECTOR CONTROL OF INDUCTION MOTORS By E. Ch. Andresen; S. Gediga; H.-J. Schwartz	[View] [Download]
Abstract: A control method for switching over from voltage vector modulation to square wave operation without transients is presented. A special voltage vector control range is interposed between the two control ranges. The switching angles are on-line calculated as a function of the lowest pulse fundamental frequency ratio and of the required fundamental voltage. The effectiveness of the method is demonstrated by some digital simulation results.

	VARIABLE STRUCTURE FIELD ORIENTED CONTROL OF AN INDUCTION MOTOR DRIVE By K. Jezernik; B. Curk; J. Harnik	[View] [Download]
Abstract: The sliding mode control concept is applied in the outer loop of a servo drive system utilizing a squirrel-cage induction machine. A design procedure is outlined for the the sliding mode speed and position controller. The methods of decoupling and torque linearization for the IM are derived using the field orientation as well as the torque angle control concepts. Sliding mode control with cascaded integral operation is used to reduce steady state error. Acceleration sliding lines are introduced to enable better utilization of the torque capability of the drive system. The parameter insensitive response provided by this method of control is demonstrated. The effects on the dynamic and static performance with varying drive inertia and load disturbance are studied.

	INDUCTION-MOTOR SYNCHRONOUS FRAME FLUX CONTROL WITH MECHANICAL STATE-FEEDBACK COMPENSATION By J. C. Reis e Costa; E. S. Saraiva	[View] [Download]
Abstract: Controlling the stator flux module of a three-phase induction motor leads to bad behaviour, eg. near speed-reversal and in position control due to the possibility of variable components. This paper shows that by making the component q of the stator flux equal to zero and controlling the component d (in a synchronous-reference frame), improved results are obtained with excellent torque controllability, which makes the position-control and tracking-control very easy, using state-feedback techniques. In this new strategy of flux control, the transfer function is independent of speed and machine rotor parameters, which makes its implementation very easy and it is not the case in conventional straregies, namely the vector control method. Finally, to overcome the drawback of the degradation of the system operation in the presence of a load torque, a state feedback structure for position control is developed, with an integral action at the input, in order to cancel out a possible steady state error.

	Discrete-Time Flux Observer for PWM Inverter Fed lnduction Motors By Joachim Böcker; Jörg Janning	[View] [Download]
Abstract: For the purpose of flux oriented control a standard observer structure is applied to get the unmeasurable rotor flux of an induction motor. Main emphasis is put on discrete-time considerations with respect to microprocessor realizations. This aspect concerns the internal observer structure as well as the data acquisition and sampling strategy, which is synchronized with the pulse width modulation. Measurement results show that the proposed observer provides good results for both motor and generator operation modes and even at standstill. Moreover, the inherent parameter robustness of the used structure is demonstrated.

	VECTOR CONTROL OF A P.W.M. CURRENT SOURCE INVERTER-FED INDUCTION MOTOR By J. P. Cambronne; B. Semail; C. Rombaut	[View] [Download]
Abstract: A new current source inverter-fed induction machine drive is presented, using three capacitors connected to the motor. In order to minimize current and voltage harmonics in the machine, a P.W.M. strategy has been developed; the inverter firing angles have been calculated as a function of speed and motor parameters, to avoid harmonics amplification in the resonant frequency range. However, self excitation may happen because of the interaction between capacitors and the magnetizing inductances of the motor. A field oriented control scheme, with either torque and flux loops or current compensation terms has been tested in simulation, giving interesting dynamic behaviour.

	FIELD-ORIENTED CONTROL OF HIGH-POWER INDUCTION MOTOR DRIVES BY KALMAN FILTER FLUX OBSERVATION By F. Ben Ammar; M. Pietrzak-David; B. de Fornel; A. Mirzaian	[View] [Download]
Abstract: In this paper, the authors present a vector control strategy for a high-power induction motor drive, fed by a PWM inverter using gate turn-off thyristors (GTOs). The Kalman filter algorithm is used for tbe stochastic flux estimation. The feed-back regulators working in a coordinate system which rotates synchronously with the rotor flux, allow a complete decoupling between the two stator currents to be obtained. Using this control strategy the simulation results verify that the induction motor has a dynamic behaviour comparable with that of a DC motor drive in all fourth quadrants of the torque-speed plan.

	THE INFLUENCE OF THE DYNAMIC CONTROL ERROR OF THE STATOR CURRENT ON THE VALUE OF THE ROTOR FLUX IN THE INDIRECT FIELD ORIENTED AC DRIVES By M. Dubowski; T. Citko	[View] [Download]
Abstract: It is well known that the main disadvantage of the indirect method of vector control of the induction motor is its sensitivity to the changes of the rotor resistance. Accurate investigations shown that there also exist another disadvantage of the same importance, i.e. drive sensitivity to the dynamic errors of the stator current control loop. The main danger caused by this phenomenon (like as the changes of rotor resistance) is the increase of the value of the rotor flux . This effect may be significant particulary when the over-current occurs. The drive systems of the machine-tools are especially exposed to this negative phenomenon. In this paper, a method of the estimation of the flux increase and proposition of apropriate countermeasurements are presented.

	TRANSPUTER BASED INDUCTION MOTOR FLUX-CONTROL METHOD By M. J. Case; W. F. van Wyk	[View] [Download]
Abstract: This paper presents a transputer-based induction motor flux control method which does not depend on stator resistance neither does it require flux transducers. The system is based on a paper published by A. Abbondanti in 1977. The computation algorithm as well as experimental results are presented.

	DECOUPLING THE VOLTAGE / FREQUENCY CONTROL OF A SYNCHRONOUS GENERATOR / BATTERY-FED INVERTER COMBINATION BY TRANSFORMATION TO TWO-AXES STATOR-FLUX CONTROL By W. Kleinkauf; J. Sachau	[View] [Download]
Abstract: The combination of a synchronous generator and a battery-fed inverter is a suitable solution for the voltage / frequency control of isolated grids which don't have a mechanical drive, e.g. in hybrid power supply systems with photovoltaic generators and wind energy converters. Here, the frequency control has to intervene via the electrical torque, the control of which is coupled with the voltage control. A decoupling transformation to direct and quadrature axis stator flux control is proposed and the results of separate state control are both presented with the controlled circuit model and with a 10 kVA laboratory plant.

	AN INTERNAL MODEL CONTROL STRUCTURE IN FIELD ORIENTED CONTROLLED V.S.I. INDUCTION MOTORS By J. L. Thomas; M. Boidin	[View] [Download]
Abstract: An Internal Model Control (IMC) structure, used in an indirect vector control scheme, is presented in this paper. It describes a digital robust control approach which allows the obtention of a complete decoupllng between the two stator current components with respect to rotating axes (d,q), and the verification of a dynamic behaviour independent of the working point. The IMC controller design, based on desired closed-loop transfer matrix and combined with the gain scheduling method is explained. Furthermore, a model smoothing concept is introduced in order to minimize disturbances resulting from transition between adjacent models during continuous variation of rotor speed. Finally, simulation and experimental results obtained on a industrial drive system are presented demonstrating performances of the proposed IMC control.

	A SIMPLE ADAPTIVE SCHEME FOR INDIRECT FIELD ORIENTATION OF AN INDUCTION MOTOR By P. J. da Costa Branco; A. M. Stephan	[View] [Download]
Abstract: The use of AC-motors as controlled electrical drives, in spite or their nonlinear-multivariable characteristic, may be attractive using field orientation and microprocessors. To obtain a high performance with this scheme, it is important to know the instanteneous position of the rotor flux, which depends on the rotor time constant. In this paper, a self-adaptive scheme is described for automatically tracking the temperature and saturation-dependent rotor time constant. This scheme is based on a monitoring signal (PRBS) injected in the process. A cross-correlation function between this signal and the speed error indicates the Tr-changes in direction (increase or decrease) and magnitude. This very simple adaptive scheme presents unique characteristics: it doesn't use current or voltage sensors; it is not motor parameter dependent; the amplitude of the additional PRBS can be reduced with an increase on the speed sensor sensibility and so the interference in the drive performance can be controlled; it works either on steady- and dynamic transient-state. The proposed method needs some load to operate, but this condition is satisfied in all practical cases. Tests were conducted with a 1,2kW fourquadrant AC-drive, the control was implemented with a microcomputer and the motor was supplied by a voltage-source inverter with current control using IGBTs. Experimental and simulated results using this adaptive digital schemz for different loads and values of model Tr (representing a detuned operation) are presented showing very good response. Furthermore, the Tr influence in the induction motor dynamics is also presented.

	FIELD-ORIENTED INDUCTlON MOTOR DRIVE WlTH INDIRECT ROTOR FLUX SENSING By P. Fedor; V. Fedak; P. Bober; J. Timko	[View] [Download]
Abstract: The paper deals with one of the possible manners of the vector control of an asynchronous motor. The method presented is based on the determination of the magnetic rotor flux and on the adaptation to the changes of rotor resistance. For the magnetic flux determination a structure with parallel reference model is used designed according to the second Lyapunow method.

	lMPROVED SCHEME FOR SPEED CONTROL OF AN ASYNCHRONOUS MACHINE BY FIELD ORIENTED METHOD By Ioan Felician Soran; Dragos Ovidiu Kisch	[View] [Download]
Abstract: All the field oriented methods of speed control presume as known the position of chosen field. The estimated performances, sometimes obtained by a careful simulation have no value, and cannot be found in practice if the position of the field is wrong synthetised. The paper analyses the errors due to wrong orientation and gives a method to compensate the orientation errors, even dynamically i.e. even at parameters variations due to saturation. This is the main contribution of the paper. Besides there are some details about separation of the leakage reactances for wound rotor machines and the protection against the short circuits in P.W.M. inverter.

	A VARIABLE STRUCTURE APPROACH FOR SPEED CONTROL OF FIELD-ORIENTED INDUCTION MOTOR By G. Cordeschi; F. Parasiliti	[View] [Download]
Abstract: This paper is concerned with the application of the sliding mode control for the vector controlled induction motor speed drive systems. The model of the induction motor and the variable structure approach are briefly presented. The control strategy and the system are described in detail. Finally, the simulation results are given and discussed. The effects on the dynamic and static performances with varying drive inertia and load disturbance are studied. The parameter insensitive response, provided by this control method, is proved. The sampling effects on the sliding mode control performance are also illustrated and discussed.

	DIGITAL VECTOR CONTROL OF INDUCTION MACHINE USING A PWM INVERTER By K. Dakhouche; D. Roye	[View] [Download]
Abstract: This paper presents the Vector Control of an induction machine with estimation of the rotor flux which is developed by making use of Two 16-bit microprocessors (8086) and PWM inverter. Usually the Vector Control suffers from the inaccurary of the decoupling terms. In the first part we present the Vector Control system with all the functions and if these functions are executed very quickly the decoupling terms can be eliminated. Experimental results are presented for control of torque and speed.

	COMPARISON OF DYNAMICS OF DOUBLY-FED INDUCTION MACHINE CONTROLLED IN FIELD- AND ROTOR-ORIENTED AXES By A. M. Walczyna	[View] [Download]
Abstract: Current control of a doubly-fed induction machine allows directly access amplitude and phase of rotor and stator vectors both in static and in dynamic conditions. The best properties are obtained when control in rotating synchronously set of axes is applied as then the MDZ is described by a set of stationary differential equations. A drive system with current control in x-y axes oriented by stator voltage vector has been described in the previous works of the author. The main disadvantage of such a system is its complexity. Considerably simpler structure of DFM control is obtained after application of an induction machine description in rotor d-q axes. In the paper a structure and dynamic properties of such control system are presented and compared with properties of the previous one. In order to obtain good steady-state and dynamic control of rotor currents in d-q axes efficient decoupling of influence of strong disturbances acting at rotor terminals (rotor EMF) should be applied. In the paper efficiency of decoupling of these signals is discussed. It is shown that application of decoupling can cause instability of the drive. It is also shown that application of feed-forward compensation significantly improves control of rotor currents in d-q axes.