Electrical Machines and Drives

Electric Machines

Windings of rotating machines, force and torque calculation, induction of rest and motion

Force and torque calculation of heteropolar machines in electromagnetic systems. The design of concentrated and distributed (in slots) windings of electric rotating machines, details of the calculation of the voltage induced in the windings. Relationships between the voltage level, the slot shape and the applicable insulation system. Modelling of the air gap field (main field) and leakage field created by the current flowing in the coils. Basics of designing rotating field windings. Determination of electric and magnetic stresses. (1 week)

Synchronous machines

Concentrated parameter equivalent circuit and torque generation of the cylindrical rotor and salient pole synchronous machine. Motor and generator operating states. Static stability, loadability, purpose and process of excitation control. Modelling the additional losses. Reluctance, permanent magnet and hybrid rotor topologies. Synchronous linear motors. (1.5 weeks)

Induction machines

The concentrated parameter equivalent circuit and torque generation of the induction machine. Analogies with the transformer equivalent circuit. Machines with deep slot and two-cage rotors. A comparison between a caged and a wound rotor. Effect of spatial harmonics. Starting and speed change methods. Modelling the additional losses. Machines with single-phase and auxiliary-phase windings. Linear induction motors. (1.5 weeks)

DC machines

DC machine armature windings. Design of excitation coil and permanent magnet poles. Theory of torque and flux generating current components. The role of the auxiliary pole and compensating winding. Mechanical and electronic commutation. Characteristic curves of external, series, parallel and mixed excitation generators and motors in steady state. Starting the motors and changing their speed. (1 week)

Application of modern calculation methods

The theoretical foundations of using the finite element method (FEM) in electromagnetic field calculations (spatial discretization with meshing methods, Poisson's equation, Lagrange interpolation polynomials, Dirichlet and Neumann boundary conditions). Modelling simple 2D electromagnetic problems with FEMM software, examples of steady state testing of rotating machines. (1 week)

Electric drives

Kinetics of electric drives

Conversion of torques and masses to a common shaft. The motion equation of electric drives. A condition for drive stability. Definition of time constants. (1 week)

DC drives fed from a DC chopper

One quadrant circuits. Control modes. Examination of current pulsation.

4/4 circuit. Control modes. (2 weeks)

Frequency converter-fed induction motor drives

Types of frequency converters (AC/DC/AC conversion chain, DC/AC conversion). Possible construction of general, network-fed drives, drives with direct DC supply. (2 weeks)

Construction of a two-level and three-level intermediate dc-link frequency converters. Sensing and realization of signals necessary for control. Control of semiconductors (Gate drivers, control dead time and its effect on the system)

Overview, characterization and implementation of inverter control methods (simple inverter control, PWM methods) (2 weeks)

Vector representation method. Harmonic analysis. U/f characteristic curve. Field weakening. Outlook to field-oriented control. Applications: vehicles, wind generators. (2 weeks)

Exercises:

Modelling and calculation of magnetic circuits (1 week)

Operational calculation of synchronous machines, examination of the physical relationships between the armature winding and the excitation winding (2 weeks)

Operational calculation of induction machines, determination of model parameters, examination of their effects. (2 weeks)

Operational calculation of direct current machines (1 week)

DC machine fed from a four-quadrant chopper: Modelling. Calculation of current and torque pulsation (2 weeks)

Diode rectifier sizing, sizing of the intermediate DC-link of three-phase, two-level voltage-source inverters, semiconductor sizing and loss calculation, matching of current and voltage sensors to control circuits (2 weeks)

Park-vector representation method calculation. Calculation of induction machine operating points using space vector representation (1 week)

Examination and calculation of U/f control: Modelling. Setting parameters and examining their effect. Practical implementation questions (2 weeks)