Power Electronics and Drives


This subject aims at the acquisition by the students of sufficient knowledge and competence in the area of power electronics in actuators, where the students should be capable to select and/or design the most suitable power converter for a certain application. Students must acquire knowledge about the composition, properties and functioning of the power electronic circuits and devices generally used in electromechanical drives. Students should become able to design and build some circuits, following given specifications. Students should also develop soft skills such as: ability to categorize priorities in the analysis of a technical problem, ability to make structured and clear decisions and improve their written and oral communication skills. The final objective is to contribute to a more interdisciplinary profile of the student, and thus to improve his employability.

General characterization





Responsible teacher

Stanimir Stoyanov Valtchev


Weekly - 4

Total - 112

Teaching language



Electronics I + Theorectical Electrotechnics


Ned Mohan, Power Electronics: A First Course,John Wiley & Sons, Inc., 2012.

Ned Mohan, Tore Undeland, William Robbins, Power Electronics: Converters, Applications and Design, John Wiley & Sons, Inc., 2003.

Ned Mohan, Tore Undeland, and William Robbins, Solutions to Supplemental Problems to accompany the Power Electronics: Converters, Applications and Design, 2006

Valtchev, S.,.. Efficient Resonant Power Conversion, IEEE Transactions on Industrial Electronics, IE–37, pp. 490–495, DOI 10.1109/41.103453, 1990.

Valtchev, S.,.. Super–Resonant Converter with Switched Resonant Inductor with PFM–PWM Control, IEEE Tr on PE, pp. 760–765, DOI 10.1109/63.471296, 1995.

S. Valtchev,.. Control for the Contactless Series Resonant Energy Converter, pages 102-140, DOI: 10.4018/978-1-5225-5870-5.ch005, 2019.

(books in pdf, internal use)

Teaching method

Scientific principles are explained by the teacher in the theory class, aided by slides. The student’s capacity for oral communication is stimulated through debate around technical and scientific questions.

In practical classes a collection of technical problems is offered to be solved by students based on theoretical class knowledge by calculation. The dialogue between the students is encouraged, and qualitative evaluation is made.

Evaluation method

1st Way: test No.1 (30%, but with a minimum note of 8, being this test eliminatory, i.e. not permitting continuing this way), test No.2 (45%), 4 reports on laboratory exercises (25 % of the final note, being the reports compulsory, and having average score at least 9.5, for guarranteeing the the permission to be examined = frequency);

2nd Way: 4 reports on laboratory exercises (25 % of the final note, being the reports compulsory and having average score at least 9.5, for guarranteeing the the permission to be examined = frequency), exam of retrying (75%).



Subject matter

  1. Thematic contents, in English


* Importance and functioning of the subject. Relation with other subjects:


* Terminology. Types of conversion and energy converters. Power electronics and linear electronics.

* Revision of the applications, especially in the area of the actuators. Classification of converters. The interdisciplinary nature of power electronics. Latest power electronics circuits, intelligent and microminiaturized circuits. Contactless energy transfer and energy harvesting.

* Basic principles of the DC-DC converter. Chopper and pulse modulation.  BUCK Converter and its operation. BOOST, BUCK-BOOST, FORWARD and FLYBACK converters. Continuous and discontinuous current operation. Control methods, voltage mode and current mode.

* Revision of the electronic devices applied to control the energy flux. Characteristics: idealized and real. Diodes. Thyristors. Application limits and protection circuits. Triac. Fully controllable power electronic devices. Bipolar power transistor. Protection circuits. Unipolar transistor and power MOS. Characteristics and applications. SOAR. Gate control. IGBT as a compromise. Recent solutions. GTO, SITh, MCT etc.  

* Natural (line) commutated converters (excl. resonant). Uncontrolled rectifiers. Basic concepts. Monophasic rectifiers. Calculation of characteristic values. Three-phase rectifiers. N-phase rectifier and voltage multipliers. Uncontrolled rectifiers working with complex load. Phase-controlled rectifiers (SCR). Protections. Rectifier and inverter. Cyclo-converter. AC switch and regulator, dimmer.

* Voltage inverter and current inverter. Differences and preferences. Single phase inverter, half-bridge and full bridge. Resistive and complex load. Harmonics reduction. Control methods. Pulse modulation and "Notching". Sinusoidal modulation. Applications that include transformer.

* Forced commutated converters. Schematic solutions for aided commutation of thyristors. Series and parallel inverters. Resonant load commutation. Induction heating. DC-DC converters with internal resonant loop. Sub-resonant and super-resonant converters. ZVS and ZCS. PWM and phase-shift control. Parallel and series load, parallel and series resonance. Resonant switches and quasi-resonant converters.

* DC motor control. Different versions of the AC motor control. Control of induction motor. Brushless DC PM motors drives. V, f, V/f and vector control of motors. Characteristics. Renewable energy applications. Power factor improvement methods for converters. 

* AC Motor Frequency controllers, PWM and Multilevel.



Programs where the course is taught: