ELECTRICAL DRIVES FOR AUTOMATION
Learning outcomes of the course unit
The course aims at providing basic knowledge pertaining the operation and use of the different types of electric motor drives:
* direct current machines;
* DC and AC brushless;
* asynchronous machines;
* step motor drives.
At the end of the course the students should know, for each type of motor drives:
* construction details;
* operating principles;
* the applicable sensors for current, position and speed sensing;
* the main control schemes and algorithms;
* the possible applications (industrial, powertrain, appliances, etc.).
The latter part of the course aims at providing the basic knowledge and best practices for the digital control of electric drives, in particular using fixed point microcontrollers and DSPs. In this context the students should be able to design control algorithms based on fixed-point processors using the whole available numeric range and implementing good practices of embedded programming.
The laboratory activity aims at providing the instruments and knowledge for writing control firmware for the digital control of electric drives based on fixed-point microcontrollers and DSPs. The acquired knowledge will be applied through a hands-on approach for the implementation of a digital drive control using a development kit that will be provided to students.
Students will have to acquire the best practices for embedded and event driven programming for the real-time control of systems, and apply them to the digital control of an electric motor drive.
The activities will be carried on by teams of 3-4 students, with the additional goal of improving their teamwork soft skills.
Electric circuits; automatic control; general physics, fundamentals of programming, fundamentals of electronic computers.
Course contents summary
Electromechanical energy conversion; DC, AC (brushless, induction) and stepping motor drives; digital control. Laboratory design and implementation of a DSP- or microcontroller-based electric motor drive.
1. Introduction to electric drives, electromechanical energy conversion, common features, operating zones, energy, coenergy, torque calculation. Introduction to polyphase electrical machines, distinction between anisotropy torque and permanent magnet torque. (8 hours).
2. Direct current machine, construction and operating principle. Quadrants of operation, flux weakening. Dynamic model, feedback control of current and speed. Switching power supply through PWM-controlled H-bridge, current ripple, current circulation, freewheeling diodes, braking resistor. (10 hours).
3. DC brushless machine, pole pairs, cogging torque and skewing. Two-phase-on and three-phase-on operation, DC brushless torque calculation. Power supply through three-phase bridge. Control through on/off Hall effect sensors. (6 hours).
4. Current sensors: shunt resistor, uncompensated and compensated Hall effect sensor. Position and speed sensors: tachometric dynamo, absolute and incremental encoder, resolver. (2 hours).
5. AC brushless machine, generation of rotating magnetic field, torque angle, Clarke's and Park's transformations, model of the machine on rotating axes. AC brushless torque calculation, anysotropic machines, flux weakening, vector control and MTPA/MTPV trajectories. (7 hours).
6. Induction machine, slip, circuit model. Induction machine Induction machine torque calculation, torque/speed curve, off-grid operation and starting techniques. Constant V/f control and slip control through inverter. Introduction to vector control. Induction machine tests. (7 hours).
7. Incremental motion drives, variable reluctance, permanent magnet and hybrid types. Open-loop control, microstepping. (2 hours).
8. Comparison of rotating electrical machine types: properties and typical operating fields, automation (axis and spindle drives), powertrain. (1 hour).
9. Introduction to embedded control on fixed-point microcontrollers and DSP. Number formats, fractional representation, arithmetic operators, normalization, differences between DSPs e microcontrollers, numerical saturation techniques, event-oriented programming. (4 hours).
10. Architecture and use of microcontrollers and DSPs for power converter control (2 hours).
11. Programming best practices for embedded event-oriented firmware aimet at real-time control (1 hour).
12. Tutorial on integrated development environments for commercial microcontrollers and DSPs (2 hours).
13. Design and implementation of a DSP- or microcontroller-based electric motor drive in the laboratory (20 hours).
Lecture notes available on the Elly online platform.
The first 2/3 of the course will mainly consist of traditional lectures, with a limited amount of computer simulation.
The last third consists of laboratory activity focused on the design and implementation of a digital control for electric motor drives.
The students, split in groups, will have access to development kits including control boards and electric motors and will have to write the control firmware using integrated development environments on PCs.
Assessment methods and criteria
Report on the laboratory activity and oral examination.
At the end of the laboratory activities each team of students must deliver a written report. After receiving an evaluation of their report, the students can individually take the oral examination.
The result of the oral examination accounts for 2/3 of the final mark, while the laboratory activity evaluation accounts for 1/3.