40042 - Electric Drives for industrial and Wind Energy Applications

Learning outcomes

At the end of the course, the student knows: - the general methodologies to understand the performance and control of electrical machines and drives - the fundamentals of the electrical machines, from circuit behavior to electromagnetic torque production, and the basic equations of the physical phenomena - the mathematical models of electrical machines, which are valid for steady-state and transient analysis - how to model and simulate dc motor drives, permanent magnet brushless motor drives, induction motor drives, and stepper motors. Also, the course focuses on the fundamentals of electric generators and drives for wind energy systems, which are used as examples of applications.

Course contents

Introduction and basic principles of energy conversion

Force on current-carrying conductors. Voltage induced in a moving conductor. Magnetic materials. Magnetic circuits. Coupled coils. Coefficient of coupling. Self and mutual inductances. Voltage equations. Stored energy in the magnetic field. Fundamentals of electromechanical energy conversion and torque production. Types of electrical machines.

DC motor drives

Separately-excited DC machines. Mathematical model. Steady state characteristics, and control of the armature and field currents. Control of DC motors in the constant-torque speed region and in the field-weakening region. Transition from motoring to braking operation. DC drives with force-commutated converters. Single-, double-, and four-quadrant operation. Constant-torque and constant-power operation.

Dynamic model of a DC machine. Dynamic behavior of DC motors with constant flux. Block diagram of a DC motor coupled with a mechanical load. Torque production and control. Closed-loop control of torque and speed. Field weakening. Starting and speed reversal transients. Application to DC motor drives.

Brushless DC motor drives

Analysis of the magnetic circuit. Torque and back-emf equations. Winding inductances and armature reaction. Torque/speed characteristics: performance and efficiency. Three-phase brushless DC motor. Position sensors. Drive characteristics and control principles. Application of brushless DC motor drives.

Variable frequency synchronous motor drives

Magnetic circuit analysis of synchronous machines. Synchronous reactances (d-, q-axis). Torque and machine equations. Steady-state characteristics. Open-loop control of voltage source inverter drives. Starting performance by squirrel gage rotors. Closed-loop control of current controlled PWM inverter drives. Applications.

Brushless AC motor drives

Dynamic model of permanent magnet synchronous machines with surface mounted magnets. The dq machine and flux equations. Principles of field orientation. Torque production and control. Dynamic model of permanent magnet synchronous machines with interior magnets. The dq machine and flux equations. Torque production and control. Control of the synchronous machine supplied by current controlled PWM inverter. Simulation of electromechanical transients. Maximum torque capability of the machine in the flux weakening region.

Induction motor drives

Analysis of induction motors based on steady-state machine model. Torque and machine equations. Steady-state characteristics. Starting of induction motors. Constant terminal volts/hertz operation. Torque characteristics. Low-frequency performance with increased volts/hertz. Constant air-gap flux operation. Torque characteristics. Current-source inverter drive with slip frequency control. Current controlled PWM inverter drive with slip frequency control. Constant-horsepower operation. Dynamic model of induction machines. The dq machine and flux equations. Torque equation. Principles of field orientation. Machine equations and torque in the rotor flux oriented reference frame. Decoupling control of flux and torque in the rotor flux oriented reference frame. Flux models. Direct scheme and indirect scheme of induction motor field oriented control. Control of the induction machine supplied by current controlled PWM inverter. Simulation of electromechanical transients. Maximum torque capability of the machine in the flux weakening region. Applications.

Stepper motors and Switched-Reluctance Motors

Reluctance torque. Fundamentals of stepper motors. Design of a stepper motor. Hybrid stepper motors. Torque characteristics. Stability region and behavior at high speed. Power converters for stepper motors. Structure of a switched reluctance motor. Design of a SRM. Torque expression and control loop. Lead angle. Behavior of SRMs at high speed.

Wind energy systems

Structure of a wind turbine. Betz's limit. Power of the wind. Power coefficient. Drag and lift forces. Maximum power point tracking. Control scheme based on PM machines and doubly-fed machines.

Readings/Bibliography

I. Boldea, S. A. Nasar: ELECTRIC DRIVES, CRC Press, New York.
P. Vas: VECTOR CONTROL of AC MACHINES, Oxford University Press, New York.
T.J.E. Miller: SWITCHED RELUCTANCE MOTORS AND THEIR CONTROL. Clarendon Press, Oxford.
Bimal Bose: MODERN POWER ELECTRONICS AND AC DRIVES, Prentice-Hall.
Takashi Kenjo: STEPPING MOTORS AND THEIR MICROPROCESSOR CONTROLS, Clarendon Press, Oxford, 1985.

Teaching methods

The theoretical explanations are integrated with the solutions to numerical problems.

The teaching language is ITALIAN.

Assessment methods

The exam consists of two parts, ie., a written test (mandatory ) and a discussion of a Simulink project (optional). The mark of the written test is in the range 0-30, whereas the mark of the project is usually in the range 0-3 (depending on the project complexity).

*** Note: The Simulink project is feasible only if the University of Bologna provides the students with the Matlab licenses.

If the students are not satisfied with the mark of the written test, they can ask for an additional oral test. This is possible only if the mark of the written exam is at least greater than 14 points. The oral exam takes about 1 hour and covers all topics of the course. The final score is the average between the score of the written and oral tests.

Teaching tools

Powerpoint slides used for lecturing and basic mathematical models of electrical drives for numerical simulations are available.

The password will be given by the professor at the beginning of the lessons.

Office hours

See the website of Luca Zarri