The subject of the degree thesis is to design an accumulator charger. The accumulators must be chargable from 5V, 12V and 230V line power. Additionally, the output voltage of the battery package must be adjustable, it can be 5V or 12V. The user can set and change this output voltage with switches.
The charging voltage from the line power is created by a Flyback converter. This voltage is connected to the input of a DC/DC converter. We can charge the battery pack (4 cells) with this converter, according to the charge characteristics. There is another DC/DC converter to provide the 12V and 5V outputs. These outputs can be used as inputs, therefore we can charge the battery pack from 5V and 12V. So, this DC/DC converter can function as a Buck or Boost type, it can be bidirectional. The first DC/DC converter - which belongs to the Flyback converter – can only be Buck-type. In this project the Buck converters are synchronous ones.
The cell, output and input voltages and the currents are measured. A Digital Signal Processor (DSP) processes these informations and calculates the duty cycles for the converters. There are NTC resisitors for temperature sensing, so we can detect the overheating and protect the cells.
We use integrated DC/DC converter to provide the needed 5 and 3.3V supply voltages. These are needed by the DSP and other circuits (FET driver, operational amplifier etc.). The converter is connected to the accumulator bus. The DSP has USB connection, and we can program and observe the variables through this USB port.
The embedded software can regulate the charge of the accumulators and control the output voltage. We implemented several controllers for this purpose. The program realizes protections. For example it can detect the low battery voltage or high cell temperature. Every operational mode has multiple state machine statuses, and there are error states as well.
At the end of the degree thesis we can see the electric measurements and tests for the circuits. (Chapter 6)