POWER ELECTRONICS

The course provides an introduction to the most used power electronic circuits and power electronic devices in the conversion of electricity

Knowledge and understanding

Knowledge of the operation and application field of rectifiers, dc-dc converters with and without insulation, and inverters. Knowledge of the characteristics, operation, advantages and limitations of various power electronic devices (diode, BJT, MOSFET, IGBT). Knowledge of new technologies (SiC and GaN).

Basic knowledge of problems related to passive components, heat dissipation and control.

Applying knowledge and understanding

The student will be able to analyze the behavior of power electronic converters when parameters, components and control change. The student will be able to analyze the behavior of the devices also taking into account the parasitic components of the converters and of the devices themselves. The student will be able to use circuit simulators and understand the circuit models of the devices.

Making judgements

The student will be able to choose either the topologies and control techniques of the converters either the devices that are most suitable for the main applications in the industrial, commercial and domestic sectors; in the field of electric traction and electrical networks.

Communication skills

The student will learn the technical language of power electronics. The course includes seminars that allow interaction between students and experts from the industrial and academic fields.

Learning skills

The student will acquire the fundamentals necessary to understand the operation of converters and power devices not covered in the course. This ability will be refined through participation at seminars whose understanding requires the knowledge and understanding of the topics covered by the course.

Introduction

Introduction to the field of Power Electronics. Advantages and applications. Overview of power semiconductor devices.
Sinusoidal and non-sinusoidal steady-state. Fourier series. Line current distortion.
Hopkinson’s lax. Inductor. Circuit model of the non-ideal transformer.

ac-dc converters

Single-phase rectifier: ideal circuit, effects of the input inductance, voltage distortion at the PCC. Voltage-doubler rectifiers. Effect of single-phase rectifiers on neutral currents in three-phase with four-wire. Three-phase rectifier: ideal circuit, effects of the input inductance. Basic notes on the controlled rectifiers.

dc-dc converters without isolation

Introduction to the dc-dc converters. Buck, Boost e Buck-Boost converters. Full-bridge dc-dc converter: PWM with bipolar and unipolar voltage switching. Basic notes on synchronous and bidirectional dc-dc converters.

dc-ac converters

Introduction to the inverter and to bidirectional converters. Half-bridge inverter. Full-bridge inverter: PWM with bipolar and unipolar voltage switching; square-wave control. Single-phase inverters with voltage cancellation. Push-Pull inverter. Three-phase inverter: PWM and square-wave control. Inverter ripple. Effect of the blanking (dead) time. Programmed harmonic elimination switching. Basic notes on current-regulated (current-mode) modulation.

dc-dc converters with isolation

Introduction to the dc-dc converters with isolation. Flyback and Forward converters. Push-pull. Half-bridge and full-bridge dc-dc converters with isolation.

Semiconductor physics

Recap of the basics on semiconductor physics. The p-n junction. Main trade-offs in power devices.

Power diode

Structure and characteristic. Conductivity modulation. Power losses. Breakdown voltage. Diode switching characteristics: inductively-loaded clamped switching circuit. Schottky diode.

Power BJT 

Structure and characteristic. Current gain and Darlington configuration. Conductivity modulation: quasi-saturation and hard-saturation. Power losses. Breakdown: avalanche and thermal runaway. BJT switching characteristics: inductively-loaded clamped switching circuit. SOA.

Power MOSFET 

Basic notes on JFET. Structure and characteristic. Threshold voltage. Breakdown voltage. Power losses. MOSFET switching characteristics: inductively-loaded clamped switching circuit. Effect of parasitics on the switching waveforms: overvoltage, positive and negative glitch, oscillations. Parasitic BJT. SOA.

IGBT 

Structure and characteristic. Power losses. Breakdown voltage. IGBT switching characteristics: inductively-loaded clamped switching circuit. Latchup. SOA.

Positioning and trend of switching power devices

Main structures and characteristics of discrete devices and modules. Switching power devices: application fields and market trend. Silicon Carbide and Gallium Nitride power devices.

Seminars

The contents of the seminars are not considered during the exam. The following list reports the content of seminars held during previous courses. This list is as an example of potential topics that could be treated, the actual list will be provided to the students during the lessons once the seminars are planned with the speakers. 

- Power factor correction (PFC)
- Design of a Boost PFC TM pre-regulator
- Multilevel converters
- Resonant converters
- Design of a Flyback converter
- Power converter control loop design
- Electromagnetic compatibility
- SiC power devices for automotive and sustainable energies
- GaN power devices: current applications and future trend
- SuperJunction MOSFET
- Power devices reliability

1) Ned Mohan, Tore M. Undeland, William P. Robbins, "Power Electronics: Converters, Applications, and Design". 3rd Edition, John Wiley & Sons, Inc., New York, November 2002.

2) B. Jayant Baliga, “Fundamentals of Power Semiconductor Devices”, Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA, 2008.

Oral exam concerning a topic related to converters and one related to the devices. An additional question may be asked to pass with honors. The average duration of the oral exam is one hour.

Learning assessment may also be carried out on line, should the conditions require it.

Single-phase rectifiers: effect of input inductance in the case where the load is approximated with a current generator

Buck converter: operation in continuous, discontinuous and "transition" mode

PWM with unipolar voltage switching in an inverter

Dead time effect

Flyback converter

Switching of the clamp diode in an inductive load circuit

Breakdown mechanisms in BJT

Losses in conduction of VD-MOSFET and U-MOSFET structures

Static and dynamic latchup in the IGBT