# Basics of Electromagnetical Power Conversion

(3rd term), V2, U2

Lecture: Prof. Dr.-Ing. B. Ponick

#### Contents

Types of electromagnetic power converters, overview of different types and power spectrum of electrical machines and their economic significance.

Steady-state performance of DC machines: design, induction via rotation, flux distribution in the air gap derived from winding diagram, distribution of ampere-turns and m.m.f curve; voltage equation; torque equation; types of windings, methods of connection, torque-speed characteristics, speed control, commutation, segment-to-segment voltage.

Generalized theory of polyphase machines: development and superimposition of alternating fields of the single phases, determination of the corresponding reactances, law concerning air-gap power splitting, torque equation.

Analytical theory of synchronous machines with cylindrical rotor: design, equivalent circuit diagram, voltage equation, no-load and short-circuit characteristic, synchronization process, over- or underexcited phase shift operation, influence of armature reaction, phasor diagram, current diagram, torque equation, limits of stable operation, special considerations for motor operation.

Analytical theory of induction machines: design, equivalent circuit diagram, voltage equations, current locus diagram, torque-speed characteristic, slip-ring and cage rotors, deep-bar cage motors, prospects of pole-changing motors, starting methods, temperature rise in the windings during start-up and single-phase motors.

Introduction to speed control of induction and synchronous machines via frequency converters.

# Electric Drives

(4th term), V2, U1, L1

Lecture: Prof. Dr.-Ing. A. Mertens

#### Contents

The lecture offers an introduction into electric drives which, as a mechatronic system, consist of actuators, sensors, control electronics and power electronic control elements. Based on the electromagnetical actuators introduced in the lecture "Basics of Electromagnetical Power Conversion", knowledge of the design and different types of electric drives is provided for various fields of application. Different drive solutions are presented and their features are compared using specific examples, as they appear in practice. At the same time, a brief overview of the control of electric drives is given.

# Introduction into German and European Energy Law

(5th term), V2

Lecture: Dr. jur. K. Gent, M.L.E.

The energy market is a very specific market. In accordance with the European regulations implemented by the EnWG 2005 into German law, this market is regulated to a large extent. Students will be taught about European and national "Energy Law". Possible deficiencies in the implementation of European into national law are shown, and requirements and obligations related to energy supply are explained. The lecture basically focuses on developing solutions for case scenarios currently found in practice.

Goal of this lecture is to provide students with the knowledge necessary to become familiar with this specific market.

# Energy Technology

(1st term), V2

#### Contents

Aim of this lecture is to provide power engineering students right at the beginning of their studies with a global overview of the different disciplines in power engineering. For this reason, the lecture is planned as an interdisciplinary series of lectures organized by IAL who also conducts the final exam.

Within the scope of this lecture series, each professor working in the field of power engineering presents his specific discipline. The course thus covers the whole range of power engineering reaching from power plant technologies over turbomachinery and electrical machines to power supplies. The introductory lecture is held by an external lecturer coming from industry.

The lecture series comprises the following individual presentations:

- Overview / primary energy distribution (Dr. Kranz)
- Power plant technologies (Prof. Scharf)
- Technical combustion (Prof. Dinkelacker)
- Thermodynamics (Prof. Kabelac)
- Turbomachinery (Prof. Seume)
- Electrical machines (Prof. Ponick)
- Power electronics (Prof. Mertens)
- Energy storage systems (Prof. Hanke-Rauschenbach)
- High-voltage engineering (Prof. Werle)
- Power supply (Prof. Hofmann)
- Thermal processes (Prof. Nacke)
- Resource-efficient energy use (Prof. Baake)

# Theory of Electrical Machines

(5th term), V2, U1, L1

Lecture: Prof. Dr.-Ing. B. Ponick

#### Contents

Synchronous machines: Design and cooling methods of synchronous machines; performance of salient-pole machines in steady-state operation: phasor diagram, equivalent circuit diagram, locus diagram, voltage equations, Potier diagram, permanent magnet synchronous motors, synchronous reluctance motors; operation of synchronous generators with unsymmetrical load.

Introduction into the rotating field theory, harmonic leakage, skewing.

Electromagnetic design of polyphase machines.

Theory of windings: design laws and calculation of winding factors for integer-slot and fractional-slot windings, imbricated windings and change-pole windings; Goerges polygon for determination of the m.m.f. curve and the harmonic leakage coefficient.

Parametric fields based on fluctuations of the magnetic harmonic conductivity of the air gap (e.g. saturation, eccentricity and slotting fields).

Current displacement in rotor cages; field damping by cage and slip-ring rotors; field damping by parallel paths of the stator winding.

Tangential mechanical forces (generation, asynchronous and synchronous harmonic torques); radial mechanical forces (generation of magnetically excited noise and mechanical vibrations, unbalanced magnetic pull and its effect on the lateral critical speed of the shaft).

Types of losses; additional losses caused by spatial harmonics.

# Modelling of Electromechanical Micro Systems

(6th or 8th term), V2, U1

Lecture: Prof. Dr.-Ing. W. Mathis, Dr.-Ing. J. Steinbrink

#### Contents

Basics of microelectromechanical and nanoelectromechanical systems (MEMS and NEMS), realised by methods based on micro or nano technology.

Introduction by using typical MEMS and NEMS based sensor and actuator systems, basics of mathematical modelling of coupled electromechanical systems, especially with respect to micro and nano technology, origin for numerical simulation methods, multilevel approaches to handle the high complexity of such systems, description of electromechanical models with finite degrees of freedom by means of the Lagrange formalism and models with infinite degrees of freedom using field-theoretical models, consideration of thermal, fluidic, optical and quantum-mechanical aspects, demonstration of the methods by using the examples mentioned above.

Presentation of the functional principles, the rough design, the particularities compared to “macro designs” based on conventional micro actuators, transfer to micro systems, basics of field-theoretical calculation methods (especially electromechanical) including appropriate material description of typical functional materials, determination of the operating behaviour and the control of micro systems by simulation of single examples, discussion of some semiconductor-based MEMS and NEMS sensors and their properties, simulation of the behaviour.

Recommended previous knowledge: micro system technology, control systems, electromagnetic fields, electric grids.

# Electrical Drive Systems

(4th, 6th or 8th term), V2, U1, L1

Lecture: Prof. Dr.-Ing. B. Ponick

#### Contents

Performance of induction machines considering the stator winding resistance.

Special considerations for start-up and acceleration of induction and synchronous motors: inrush characteristics, current and torque peaks, temperature rise during start-up and torque-speed characteristics.

Electric braking methods for induction machines: reverse field braking, DC braking, regenerative braking.

Speed control in induction and synchronous machines: description and comparison of different types of drive systems with regard to additional losses, generation of pulsation torques and cost.

Temperature rise and cooling: cooling methods, operating modes, demands on energy efficiency, determination of steady-state and transient temperature rise in the windings.

Introduction into the calculation scheme of symmetrical components for instantaneous values and the Park transformation (voltage equations, instantaneous value of electromagnetic torque) for simulation of transient phenomena.Simulation of mechanical shafting, influence of mechanical damping, modeling of transient current displacement in the rotor cage; discussion of the most important transient phenomena in induction and synchronous machines (starting, symmetrical and unsymmetrical short circuits, voltage recovery, transfer of bus-bar or incorrect synchronization); reactances and time constants of synchronous machines.

Details of mechanical design: types of construction and cooling methods, explosion-proof machines, mutual effects of different coupling and bearing assemblies; generation and avoidance of shaft voltages and bearing currents.

Investigation and evaluation of acoustic noise emissions.

# Electrical Traction and Vehicle Drives

(6th or 8th term), V2, U1

Lecture: Dr.-Ing. G. Möller

#### Contents

The lecture deals with the basics of electrical traction and aspects concerning electrical vehicle drives.

It is given a survey of the state-of-the-art focusing on electric traction equipment systems. Further on, the basics of electrical traction design are discussed from their requirements to their complete dimensioning. The scope to be dealt with reaches from tramways to high-speed trains. Further topics are the electrical infrastructure in the field of electrical traction and technical solutions for hybrid vehicle drives (e.g. serial hybrid or parallel hybrid).

Basic knowledge in the field of power electronics and electric drive technology is required.

# Small Electrical Motors, Servo and Vehicle Drives

(5th or 7th term), V2, U1, L1

Lecture: Prof. Dr.-Ing. B. Ponick

#### Contents

Low-priced and high-quality designs, overview of externally commutated and self-commutated motors, basic design concepts, permanent magnet materials.

Permanent magnet DC motors: designs (drum-type, disc-type and bell-shaped rotors), applications, magnet materials, performance, speed control.

Universal motors; design, applications, performance, electric and electronic speed control, commutation.

Single-phase induction motors: design, applications, winding types, designs (capacitor motor, resistance and auxiliary winding motor, split-pole motor), performance (generalized symmetrical components, permeance locus diagram), speed control.

Single-phase synchronous machines: design (stator with slots, distinct poles or claw poles), motors with permanent magnet, hysteresis and reluctance rotor.

Basics of servo drives (DC, induction and synchronous servo motors).

Vehicle drives: claw-pole generators (bicycles, motor vehicles), traction motors (types, specific features, energy efficiency), auxiliary motors.

# Small Electrical Motors and Servo Drives (held in English)

(3rd term in master course), V2, U1, L1

Lecture: Jun.-Prof. Dr.-Ing. A. Ebrahimi

#### Contents

Fundamentals of electromagnetism, Maxwell’s equations, Biot-Savart law, Faraday’s law of induction, Lorentz force, fundamentals of electromechanical energy conversion.

Magnetic equivalent circuit for flux calculation in magnetic structures, Ampère’s circuital law, permanent magnet materials, ferromagnetic materials, non-linear BH curves, hysteresis and eddy current losses.

Permanent magnet DC motor, separately excited DC motor, series wound DC motors, universal motors, equivalent circuits and load calculation, lap and wave windings, armature reaction.

Fundamentals of the rotating field theory, three-phase synchronous motor, permanent magnet synchronous motor, BLDC motors.

Basics of control of electrical machines, basics of power electronic devices, pulse width modulation, basics of gearing and mechanical components in mechatronic systems, basics of sensory systems.

Design of a mechatronic device, biomechanical calculation, electromechanical drive calculation, selection of motor, gearing, battery, power electronics and sensory systems.

*) held in English language

# Small Electronically Controlled Motors

(6th or 8th term), V2, U1, L1

Lecture: Prof. Dr.-Ing. B. Ponick

#### Contents

Basic features and comparison of stepping and B.L.D.C. motors.

Application of numerical calculation schemes and tools for dimensioning and simulation of small electronically controlled motors.

Stepping motors: designs (PM, reluctance or hybrid rotor), operating modes, characteristics, control, damping methods, dynamic performance.

B.L.D.C. motors: magnet materials; designs for different number of phases, drum-type and disk-type rotors, motors with slotted stator or air-gap windings, hybrid motors, switched reluctance motors; performance.

Rotor position sensors: incremental and absolute value sensor, magnetic or optic principles of functioning, resolver.

Electronic supply circuits for small machines and actuators: line-commutated converters (uncontrolled rectifiers, half-controlled bridges) and self-commutated converters (DC and AC power controller, phase control)

Types of protection and standards

Procedure and tools for the analysis of small machines (FEM analysis, dynamic simulations)

# Power Electronics I

(5th term), V2, U1, L1

Lecture: Prof. Dr.-Ing. A. Mertens

#### Contents

Tasks and principles of power electronics, fields of application, components, power losses and cooling.

Line-commutated power converters: controlled and uncontrolled rectifiers and converters for single and three-phase AC systems, commutation, mains interactions.

Self-commutated power converters: buck and boost DC to DC converters, three-phase voltage-source inverters, pulse with modulation and control.

Power converter systems: cyclo converters, line-commutated converters with higher number of pulses, PWM voltage-source AC to AC converters.

Recommended previous knowledge: Basics of Electrical Engineering

# Power Electronics II

(6th or 8th term), V2, U1, L1

Lecture: Prof. Dr.-Ing. A. Mertens

#### Contents

Three-phase voltage-source inverters: space vector representation, space vector modulation, optimized pulse patterns, non-ideal characteristics of voltage-source inverters and corrective measures.

Self-commutated converters for high power: multi-level inverters, current-source inverters.

Oscillating circuits in power electronics: basics, commutation circuits, snubber networks, resonant and quasi resonant converters.

Isolated DC to DC converters: transformers, forward converter, flyback converter, bridge converter.

Recommended previous knowledge: Basics of Electrical Engineering, Power Electronics I

# Power Semiconductors and Gate Drives

(5th or 7th term), V2, U1, L1

Lecture: Prof. Dr.-Ing. A. Mertens

#### Learning target:

Comprehension of the relation between the structural design of power semiconductor components and their performance characteristics. Based on this, the influence of the load to be switched, of the gate drive and of the circuit environment on the performance of power semiconductors shall be pointed out by means of examples.

#### Contents:

Repetition of the basics of semiconductors

p-s-n-junction

Space charge region and blocking behaviour; junction capacitance

Conduction behaviour; stored charge in case of bipolar components

Relation between the geometric parameters and the electrical limits

Dynamic behaviour when switching on and off

Bipolar transistor

Thyristor

Structure of modern MOSFETs and IGBTs

Gate drive and switching performance of MOSFETs, IGBTs and IGCTs

Integrated gate drive circuits

The exercise is partly accompanied by practical experiments.

# Control of Electrical Three-phase Machines

6th or 8th term, V2, U1, L1

Lecture: Prof. Dr.-Ing. A. Mertens

#### Learning target

Students shall get to know the dynamic behaviour of controlled drives, understand the principles of field-oriented control for electrical three-phase drives as well as learn about the properties of the different methods. First of all, the complete control loop of a DC drive is investigated. The lecture focuses on drives with asynchronous machines. Drives with synchronous machines will also be considered.

Contents:

- Dynamic behaviour of uncontrolled DC machines
- Torque and speed control of DC machines
- Positioning control
- Dynamic model of three-phase machines
- Principle of field orientation
- Field-oriented control of asynchronous machines
- Reduced models of asynchronous machines
- Control methods without speed sensor
- Field-oriented control of synchronous machines

In the exercise which is partly computer-assisted, students are first of all introduced ino the application of the tools Matlab and Simulink. Exercise examples are treated by simulations carried out on the computer by the students themselves, thus increasing their knowledge achieved in the lecture by own exeriences.

**Necessary previous knowlege:** Basics of Electromagnetical Power Conversion (electrical engineers) or Electric Drives (mechatronic engineers)

**Recommended previous knowledge:** Power Electronics I and Electrical Drive Systems

# Hydrogenerators

(3rd term in master course) V2, U1, L1

Lecture: Jun.-Prof. Dr.-Ing. A. Ebrahimi

**Contents**

Classification of hydropower plants by type, global capacity and trends of hydropower plants, hydropower technologies, pumped storage hydropower plants, hydroelectric power generation and hydraulic calculations, reaction and impulse turbines, velocity triangle and torque calculation.

Hydrogenerators, rotor structure, damper windings, air ducts, stator core, clamping plate, pressing fingers, windings, Roebel bars.

Physical model of a hydrogenerator, dq-transformation, transient and sub-transient inductances, phasor diagram, current locus curve, no-load and short-circuit characteristics.

Analytical modelling of hydrogenerators, magnetic flux density distributed in the air gap and slotting, Carter’s factor, equivalent core length, magnetic voltage of tooth and yoke, leakage fluxes not crossing the air gap, slot leakage inductances, tooth tip leakage inductances, leakage flux in the pole gap, end winding leakage inductances.

Additional losses in hydrogenerators, clamping plate losses, pole shoe surface losses, third-order harmonic losses, additional losses in the damper windings, eddy current losses in the stator winding, skin and proximity effect, double sided skin effect, design of the Roebel bar.

Magnetic noise and vibrations in hydrogenerators, radial air gap forces with centric rotor, stator core oscillations, deformation of the stator core, static and dynamic eccentricity, forces on the slot conductors.

Design of hydrogenerators, machine constant formulation, stress tensor equation, mechanical, electrical, magnetic and thermal loadability.

Inspection and maintenance of hydrogenerators, stator bore contamination, magnetic termites, etc.

# Passive Components in Power Electronics

(1st/3rd term in master course) V2, U1, L1

Lecture: Jun.-Prof. Dr.-Ing. J. Friebe

**Learning target**

The students gain knowledge about passive components of power electronic converter stages and fundamental calculation methods and design strategies. After successful completion, they are able to compare, design and evaluate passive components for various applications on their own. They include inductive components such as inductors and transformers, various types of capacitors, basic power electronics packaging, parasitic component properties, fundamental filter design for power electronic converter stages.

**Contents:**

· Calculation methods, design strategies, examples of magnetic components

· Capacitors, applications, types, pros and cons, typical fields of application

· Basic filter design for frequencies below 30MHz (conducted)

· Power electronics packaging

· Thermal management of power electronic converters

Every student choses an application and develops its components during the exercise in parallel to the lecture. In the laboratory exercise, the corresponding components are selected and built up. The simulation software used is LT-Spice.

Necessary previous knowledge: Power Electronics I

It is recommended to attend the lecture in parallel with Power Electronics II.