The Filière Energie et Techniques environnementales (FET) has the digital systems course and labs in the 3rd (autumn) semester. The semester counts 15 weeks and ends with a little project. The aim of the generator synchronzation project is to align an AC motor used as a generator to a reference 50 HZ signal.
The reference signal and the generator output are digitized to 1 bit with the help of two comparators. The digital circuit receives these signals and controls a DC motor coupled to the generator.
The circuit can be controlled by 4 buttons. It can display information on a row of 8 LEDs.
The circuit works as follows:
- the difference between the mains period and the generator period is calculated
- if the generator is too slow, the DC motor voltage is raised; if the generator is too fast, the DC motor voltage is diminished
The system consists of
- an assembly of a DC motor and an AC generator
- an FPGA prototyping board
- an I/O board with 2 sinewave inputs and a PWM output
- an user board with 4 buttons and 8 LEDs
The DC motor is controlled via a 12 V PWM signal. It is mechanically coupled to the DC generator. With a mean voltage of 6 V, the assembly turns at a frequency close to 50 Hz.
Synchro I/O board
The HEB-synchro I/O board receives 2 sinewaves: one from a 50 Hz function generator and one from the AC generator. These signals are converted to 3.3 V logic levels by CMOS Schmitt triggers for the FPGA. The 50 Hz analog input should have the proper amplitude and offset to fit within the 0 V to 3.3 V power supply range.
The FPGA delivers a PWM output which controls a power switch. The switch then drives the DC motor. The PWM frequency should be smaller than 100 kHz.
In order to start the projects you should do the following:
- Read carefully the specifications above
- Draw the architecture of the circuit in the form of a block diagram
- Consult the guides for the first steps into the design software