G. Figalli

An optimal feedback control for a bilinear model of induction motor drives

Abstract The use of optimization techniques for the control of drives using a frequency controlled induction motor as an actuator is considered. The approach proposed is based on the choice of a specific control law in the framework of a prefixed class of stabilizing feedback controls. The optimized performance index is obtained a posteriori by applying the Bellmanns principle to a problem with an index in which the term depending on the state is initially unspecified. Successively, the control law is developed, and it is proved how it minimizes a particular index which takes into account both the influence of the error and the control effort. This index has proved very useful in the control choice since it makes it possible to determine a correspondence between the elements of the weighting matrices and the system transient behaviour.

A Microcomputer-Based Optimal Control System to Reduce the Effects of the Parametric Variations and Speed Measurement Errors in Induction Motor Drives

A control methodology is presented for induction motor drives which makes it possible to reduce effectively the dependence of the stator flux and current both on the motor parametric variations and on the error on the motor angular speed measurement. To this aim, also the determination of the slip has been inserted in the closed-loop control system, and an optimization technique proper to bilinear systems has been applied. Then, a possible structure of the microcomputer-based controller is described, and the obtainable performances are examined by digital simulation.

Realization of a control device for a robotic manipulator based on nonlinear decoupling and sliding mode control

The realization of a control system for a robotic manipulator is described. The control scheme is subdivided into two hierarchical levels: the inner level performs the output decoupling of the joint dynamics: the outer one computes the desired accelerations. The decoupling, obtained by a simplified compensator and a sliding mode technique, is realized by means of analog circuits, while the tracking of the desired trajectories is performed by a digital computer. The description of measurements and tests is included. >

A Discrete Feedback Suboptimal Control for Induction Motor Drives

An approach is presented which simplifies the problem of applying optimal control techniques to frequency controlled induction motor drives. This approach consists of subdividing the optimization problem in two subproblems, the solution of which is less difficult than that of the global problem. The controller is obtained by using a discrete-time model for the motor electromagnetic circuits. This has made it possible to take into account both the discretization introduced by the inverter and the computation delay due to the microcomputer-based controller.

On the Selection of the Commutating Instants in Induction Motor Drives

The main auxiliary phenomena are considered which arise in the drives using a frequency-controlled induction motor supplied by a three-phase bridge inverter as an actuator. Particularly, three quality indexes connected with these phenomena are taken into account and, for different drives, the commutating instants, which separately optimize the quality indexes, are determined. Lastly, a comparison among the optimum values of the quality indexes makes it possible to obtain simple variation laws of the commutating instants, which shows the overall behavior of the drive.

A Microcomputer-Based Control System for an Inverter Supplying State Feedback Controlled Induction Motors

Abstract The applications of state feedback optimal control techniques to the drives using as an actuator a frequency controlled induction motor are exciting a great interest. These applications are based on the employment of a microcomputer-based control system, which is characterized by a finite computation time. In addition, during a sampling period, they give as output either the desired values of the modulus and the phase-displacement of the representative vector of the motor supply voltages or the desired values of the pre-jections of this vector according a pair of orthogonal axes. Owing to this, it is impossible to utilize the usual modulation techniques, which allow imposing the modulus and the angular frequency of the representative vector of the motor supply voltages. The paper describes a modulation technique, which is suitable to be used with three-phase bridge inverters and can be utilized in the aforesaid applications, since it accepts as inputs the projections of the voltage representative vector according to two orthogonal axes fixed with the stator windings of the motor. The description of an algorithm for the implementation on a microcomputer-based control circuit of the proposed modulation technique and some remarks about the obtained results conclude the paper.

COMPARISON AMONG VARIOUS APPROACHES FOR THE OPTIMAL FEEDBACK CONTROL OF INDUCTION MOTOR DRIVES

An approach to this problem consists of its subdivision in two control loops: an outer one giving the required value of the motor torque and an inner one that forces the electromagnetic circuits of the motor to produce the desired torque. This second control loop is the more difficult to be synthetized. The paper takes into consideration several different approaches to the optimal tracking problem for the electromagnetic state variables of the motor. The main peculiarities of the different approaches are described, the obtained control solutions are presented and their performances and computational difficulties are compared by simulation. Also the implementation problems of each solution on a microcomputer-based system are evaluated.

Simplified Analysis and Design of an AC/DC Power Conversion System for Traction Drives

An ac/dc power conversion system suitable for traction drives supplied by an ac feeder line is considered. In order to work out a simple procedure for the preliminary design of the conversion system, some simplifying hypotheses are made. These hypotheses allow a simple analysis of the overall steady-state behavior of the power conversion system. In this way the selection of the circuit components is very easy; it is also possible to determine the most suitable commutating instants of the power converter. Finally, the validity of the simplifying hypotheses is tested and confirmed taking into account the specifications of the converter employed in a traction drive.

Feedback control for the discrete non-linear model of induction motor drives

An investigation is made of the stability for the discrete control of drives using a frequency induction motor as an actuator. The approach proposed is based on the choice of a particular model of the discretized system which is non-linear in the state and linear in the control. Because the model parameters depend only on the value of the slip angular frequency, the stabilizing control law is obtained by considering the non-linear time-invariant system as a linear time-varying one. As a consequence, the feedback control is a linear function of the state variables with coefficients depending on the actual values of the time-varying system parameters. The difficulty for computing these coefficients in line is overcome by proposing a suitable choice of constant feedback coefficients, which, for the case of the induction motor, give very efficient and satisfactory results.

Application of pulse-ratio-modulation to fixed frequency sinusoidal tracking inverters

The paper concerns the application of pulse-ratio-modulation techniques in the field of fixed frequency inverters with sinusoidal output waveform. In particular, the criteria are analyzed to choose the parameters of the output filter and of the compensation network and a comparison is effected between the results obtained by employing either the aforesaid modulation technique or a fixed frequency pulse-width-modulation technique. The comparison, effected by simulation, has taken into account also a non-linear load and it has shown that the employment of the pulse-ratio-modulation technique allows a remarkable reduction of the inverter supply overvoltage necessary to use tracking control techniques with high modulation frequencies. Lastly, the results obtained by simulation have been confirmed by a prototype.