# 40042 - Electric Drives for industrial and Wind Energy Applications

## Learning outcomes

The aim of the course is to provide a general approach to an understanding of the performance and control of electrical machines and drives. The course emphasizes the physical aspects of the electrical machines, from circuit behavior to electromagnetic torque production, and then develops basic equations from physical phenomena. Mathematical models of electrical machines, which are valid for steady-state and transient analysis, will be derived. At the end of the course the students will be able to model and simulate dc motor drives, permanent magnet brushless motor drives,  induction motor drives, stepper motors and reluctance machines.

## Course contents

The course is hold by two professors, i.e., prof. Domenico Casadei (30 hours) and Prof. Luca Zarri (60 hours)

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. Electromechanical energy conversion principles. Torque production principles. Types of electrical machines.

DC motor drives

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

Dynamic model of the 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 DC motor drives.

Brushless DC motor drives

Magnetic circuit analysis. 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.

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.

W. Leonard: CONTROL OF ELECTRICAL DRIVES. Springer-Verlag, Berlin.

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, 1993.

W. Leonard: CONTROL OF ELECTRICAL DRIVES. Springer-Verlag, Berlin, 2001

## Teaching methods

The theoretical explanations are integrated by numerical simulations of electrical drives in SIMULINK/MATLAB. Assignments of work projects to groups of 3-5 students.

## Assessment methods

The exam consists at least of two parts, ie., a written test and a discussion of a project. 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).

If a student is not satisfied by the mark of the written test, they can ask for an additional oral test, provided that 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.

## Teaching tools

PDF copy of the Power Point slides used for lecturing.

Basic mathematical models of electrical drives for numerical simulations.

## Office hours

See the website of Luca Zarri