Fuzzy logic systems for electrical machine and drive design

The studies in this area were carried out in the nineties and devoted to acquire the base knowledge about these systems and to identify their potentials in electrical machine and drive design, with experimental verification of the envisaged promising solutions. The fuzzy logic has also been used in the development of drive self-commissioning system as part of an European CRAFT project (Read more). The following topics have been principally investigated.

Fuzzy controllers for drives

The activity started when the knowledge and the diffusion of fuzzy logic were still very limited. A first result is the work

  • S.Bolognani, The application of fuzzy controllers to motor drives, Symposium on Power Electronics, Electric Drives, Advanced electrical Machines (SPEEDAM), Positano, pp.295-300, 1992.

that introduces the fundamentals of fuzzy controllers and examines the issues related to their application to the drives; it has aroused great interest and has been cited several times later.
The work shows a design procedure of a fuzzy controller for the speed loop. Through simulation, its performance is compared with those of a conventional PI. The comparison highlights some significant characteristics of fuzzy controller, including a lower sensitivity to parameter variations.
The next publication illustrates a fuzzy controller for both the speed and the current loops.

  • S.Bolognani, M.Zigliotto, Development of a fuzzy controller for a DC servo-drive, IFAC/IEEE Workshop on Motion Control for Intelligent Automation, Perugia, pp. 235-240, 1992.

It introduces the concept of hierarchical fuzzy controller that consists of a cascade (or a network) of elementary controllers with few inputs. It is therefore easier to be designed and more suitable to the control of the drives. The work also presents the first experimental results to support theoretical derivations and simulations.
The aforementioned hierarchical approach has adopted successful also in developing the control of a mixing /metering liquid valve for the food industry, which was the task assigned to EDLab as subcontractor in an European CRAFT project involving other universities and industries in Europe. The developed fuzzy logic control, manipulates by a hierarchical approach numerous inputs (actual valve position and speed, inlet liquid pressure and temperature etc.) allowing a reduction of the settling time of the temperature of the mixed liquid greater than 50% compared to the time that the previously used classical solutions exhibited. The results were transferred later to an industrial product.

Subsequent studies have explored conceptually the hierarchical approach in the implementation of fuzzy systems, obtaining an original contribution, applied to the control of electrical drives but suitable for a wide spectrum of applications.

  • S.Bolognani, M.Zigliotto, Hardware and software effective configurations for multi-input fuzzy logic controllers, IEEE Trans. on Fuzzy System, vol. 6, n.1, pp.173-179, 1988.

After some investigations in the field of electrified transport where a fuzzy controller with predictive features was proposed for the management of the guide of a railway vehicle, the studies was oriented to the development of a position fuzzy logic control of a DC motor drive

  • S.Bolognani, G.Buja, M.Zigliotto, Fuzzy logic control of a DC servo drive, IEEE Workshop on Neuro-Fuzzy Control, Muroran (Giappone), pp. 370-373, 1993.

The originality of the work lies in the fact that the fuzzy logic is not used to deliver the actual control, but to manage the "gradual" switching between different control strategies (more or less conventional) according to the drive operating conditions. This way to apply the logic that has aroused large interest. In the particular case, the drive controller is mainly based on the sliding mode control which is superimposed also to a classic PID controller; the fuzzy logic management allows the advantages of all the different control techniques to be exploited avoiding at the same time their drawbacks.
Finally, in the paper

  • S.Bolognani, M.Zigliotto, Fuzzy Logic Control of a Switched Reluctance Motor Drive, IEEE Transactions on Industry Applications, IEEE Trans. IA, vol.32, no.5, pp.1063-1068, 1996.

a fuzzy control for a drive with a switched reluctance motor is illustrated. The characteristics inherently non-linear and complex of such a motor can be easily addressed by the fuzzy logic, which is well suited to model involved systems, where a fuzzy system can express its best potential. The structure of the controller is the type of known as “state evaluation fuzzy control” and it combines again a sliding-mode control with a PID controller, resulting in significant benefits in terms of dynamics and, especially, in the mitigation of the torque ripple of the motor.

Application to the design of electrical machines

A different use of the fuzzy logic has been identified in the computer-aided design of electric machines. The principle and the general approach are presented in

  • N.Bianchi, S.Bolognani, M.Zigliotto, Fuzzy logic automatic design of induction machines, Proceedings of the IEEE International Symposium on Electric Power Engineering, Stockholm (Svezia), pp.245-250, 1995.

The work highlights the potential of the fuzzy logic in this field, especially as a means for implementing artificial experience, by which the transfer in automatic procedures of expert designers experience can be readily performed. The publication contains some examples of design of an asynchronous motor assisted by a set of fuzzy rules inferred from the behavior of an experienced staff.
Similar procedure has been further developed and extended in

  • N.Bianchi, S.Bolognani, M.Zigliotto, Fuzzy knowledge based design of PM synchronous motors, Proceedings of International Conference on Electrical Machines (ICEM), Vigo (Spain), pp. 365-369, Sept. 1996.
  • N.Bianchi, S.Bolognani, M.Zigliotto, Optimised design of a double cage induction motor by fuzzy artificial esperience and finite element analysis, Proc. of International Conference on Electrical Machines (ICEM), Istanbul (Turkey), pp. 203-208, 1998.

where it is applied successfully to the design of a trapezoidal brushless motor and, combined with a finite element analysis, to optimize the design of the double cage rotor of an induction motor. The optimization, which is assisted by a fuzzy logic algorithm that contains, albeit in a nuanced way, the knowledge about the behavior of the system to be optimized, becomes practicable even with onerous analysis procedures, (in terms of calculation time) such as the finite element method.

Fuzzy estimators for drives

The objective of this study is to derive an estimate, although not extremely precise, of the air gap flux level in an induction machine, starting from quantities already available in a general-purpose drive (for example based on a V / f control) as the amplitude of the stator current (measured for protection and compensation needs), the frequency, the power factor. The topic is described in

  • S.Bolognani, M.Zigliotto, A novel fuzzy knowledge based flux observer for induction motor drives, Conference Records of IEEE Industry Applications Society (IAS) Meeting, S.Diego (CA), pp.426-431, Oct. 1996.

To cope with the modest accuracy of the measurements and the knowledge of the parameters, it is proposed to extract additional information from the current ripple caused by the PWM, which is affected by the flux level. The use of fuzzy logic allows the many information acquired to be efficiently treated, even if in some cases they may be contradictory, and without a precise implementation of a model of the motor, whose behavior is described only in a "fuzzy mode". The work is supported by an extensive experimental activity and demonstrates the feasibility of the flux estimator.

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