The goal of the course is to enable students to master the fundamental elements of the energy conversion produced by renewable sources and their connection to the electric grid. The course covers the analysis, modelling and sizing methods of electronic power converters and the electric machines suitable to photovoltaic and wind applications.

The student knows:

• the principles of the static conversion of electrical energy and understood the logical and mathematical links regarding the main physical quantities that characterize power converters;
• the principles of the electrical machines and understood the logical and mathematical links regarding the main physical quantities that characterize the electromechanical conversion;
• the working principle and the model of the main components of power plants for the electricity generation from renewable sources;
• the layouts of power plants for the electricity generation from renewable sources.

The student will be able to:

• improve autonomously and continuously the detailed knowledge in power converter for renewable energies;
• read and understand generic layout of power plants;
• define the layouts of power plants for the electricity generation from renewable sources and to size the main components.

Part I - Power Electronics and Static Converters

Introduction to power electronics for the electricity static conversion. General overview of switching power converters, power balance. Line commutated and self-commutated switches. Ideal switches and practical switches, conduction and commutation losses.

Overview of power semiconductor switches. Diode, thyrisitor (SCR), gate-turn-off thyristor (GTO), bipolar junction transistor (BJT), insulated gate bipolar transistor (IGBT) metal-oxide-semiconductor field effect transistor (MOSFET), new power switches technologies. Steady state and dynamic thermal models for power semiconductor switches; cooling and heat-sinks. Selection criteria for power switches and verification of the thermal design.

Switching converters. The basic switching cell (chopper). Pulse Width Modulation (PWM). Analog and digital PWM generators.

DC/DC converters. step-down converter (buck), step-up converter (boost), buck-boost converter. Single-quadrant, two-quadrant and four quadrant chopper. Calculation of losses and efficiency. Current control in voltage-source converters: open-loop, feedback and hysteresis regulators.

DC/AC converters. Single-phase inverter and three-phase inverter. Two-level voltage source inverter: power stage. DC bus sizing criteria. Inverter-Control Techniques. Auxiliary circuits. Calculation of losses and efficiency.

Grid interface. Control, Operating limits and constraints.

Part II - Electrical Machines

Introduction. Definition of the main physical parameters for the study of electrical machines.

Transformer. Isolation transformer and high frequency transformer. Example of application in PV fields.

Introduction to electrical rotating machines. The elementary electrical machine. Reversibility. Electromagnetic force and electromagnetic torque.

The rotating magnetic field. The Galileo Ferraris theorem.

Asynchronous machines. Working principle of induction machine. Squirrel cage and wound rotor. Speed-torque characteristics calculation: no-load and load condition. Asynchronous motor and asynchronous generator. Fields of application. Example: the doubly-fed induction generator as a solution for variable speed wind turbines.

Synchronous machine. Working principle of synchronous machine. No load and load condition. Operating characteristics of synchronous machine: power-angle characteristic. Fields of application.

Brushless and Permanent Magnets Synchronous Machine. Equivalent circuits of permanent magnets synchronous machines and speed-torque curve calculation. Example: permanent magnet synchronous generator as a wind power generator.

Students are required to knows the principles and methods of electrical engineering, in particular circuit theory, steady state and transient DC and AC analysis, and magnetic circuits. Students are also required to knows the fundamentals of heat transfer.

The course will offer lectures and exercises. Course attendance is warmly suggested. Students’ knowledge and skills will be evaluated by a written and an oral exam, the latter is at the option of the teacher.

The written test will verify the students’ knowledge and understanding, and applying knowledge and understanding abilities. In the written test the students must answer questions related to the theory and solve numerical problems. The students are required to:

• explain the operation of power converters and electrical machines from an analytical point of view;
• solve numerical problems concerning power converters and electrical machines, and analyze the results critically;
• make correlations between different subjects.