Bidirectional buck boost converter design

Abstract

The importance of DC to DC converters increases with developing technology. Many of the electronic devices that we use contain AC/DC or DC to DC converters. One of the areas where DC to DC converters are most used is electric vehicles. DC to DC converters are used to charge the battery and energize the electric motors with the charged battery. There are many different types of DC to DC converters. Some of these have an isolated structure, while some have a non-isolated structure. The isolation status of the converter is determined according to the design needs. Converters operating as standard make a one-way conversion from the input direction to the output direction. However, due to the change and increase in today's needs, one-way DC to DC converters have become ineffective. Where bi-directional operation is required, two DC to DC converters had to be designed. This made the design both larger and less efficient. Therefore, using standard DC to DC converters bidirectionally by making some additions and arrangements is one of the most effective ways. Bi-directional operation is possible in both isolated and non-isolated DC to DC converter structures. Bi-directional buck boost converter can produce a regulated voltage both from input to output and from output to input. In this study, the details of the non-isolated structure that can operate bi-directionally are included. The non-isolated bi-directional converter is in buck boost converter topology. It contains four switching components in this structure. It is possible to operate this structure bidirectionally with the 4 MOSFETs used. While it operates in buck mode, buck boost mode and boost mode in the forward direction, it can operate in buck mode, buck boost mode and boost mode in the reverse direction. The way to achieve these modes is to determine the forward and reverse operating characteristics. The conditions under which the structure operates in forward or reverse direction depend on the input and output voltages. If appropriate source voltage is applied to the input of DC to DC, the structure works in the forward direction and produces output voltage. If the input and output voltage are not within an appropriate range, DC to DC converter goes into protection mode and produces no output. If the appropriate source voltage is applied to the DC to DC converter's output, the output side acts as an input and the input side acts as the output. It is possible to get voltage from the input side with the voltage applied from the output side. The bi-directional buck boost converter structure basically includes the following circuits: bi-directional current measurement circuits, voltage divider circuit MOSFET driver circuits, MOSFETs, switching inductor, microcontroller, auxiliary circuits and temperature measurement circuits. Management of operations within the converter is provided by the microprocessor. The microprocessor performs the operations of measuring input/output voltages, measuring bi-directional input/output currents, measuring temperature from the temperature sensor, and driving MOSFETs according to a certain algorithm. The operating mode of the converter is determined by the voltage and current measurement circuits in the structure. For forward operation, if the input voltage is greater than the output voltage, the converter operates in buck mode, if the input voltage is close to the output voltage, it operates in buck boost mode, and if the input voltage is lower than the output voltage, it operates in boost mode. In reverse operation, if the output voltage is greater than the input voltage, the converter operates in buck mode, if the output voltage is close to the input voltage, it operates in buck boost mode, and if the output voltage is lower than the input voltage, it operates in boost mode. Signals of certain pulse widths are applied to MOSFETs to produce input or output voltages. The width of these signals is determined by the voltage values the microcontroller measure from the input and output. This measurement takes place continuously. To obtain a constant output voltage in a structure where the input voltage varies, the pulse width must be constantly adjusted. The same is necessary for obtaining constant input voltage. As the current measurement circuits included in the converter design, both bi-directional current reading and limiting can be provided. The current can be read from both the input and output sides. If more current is drawn from the input or output of the DC to DC converter than the specified current limit, the current is limited. This limiting process is possible by adjusting the pulse width of the signal applied to the MOSFETs, just like adjusting the voltage.