Design and implementation of step down DC to DC converter without an auxiliary power supply

Cascaded buck converters (multistage) are commonly used in many applications where isolation is not an issue and a high conversion ratio is required. In particular, cascaded buck converter has been widely reported in the power electronics literature.  For high conversion ratio (high step

Project Title

Project Area of Specialization

Electrical/Electronic Engineering

Project Summary

For high conversion ratio (high step-down ratio) using conventional buck degradation of output voltage and inductor current occurs. To resolve this issue and to get high conversion ratio, cascaded buck a better way.

In this project, two stage cascaded buck (buck square converter) with high conversion ratio having high input voltages 600V (variable input) to low output voltages 18V (fixed) is designed. It includes of two parts, the power circuit (cascaded buck) and a control circuit (having controller and driver circuit) without and auxiliary power supply.

Mathematical equations were derived and formulas were derived for the components used in converter like inductor, capacitor, duty ratio, etc. The values were obtained for components for the proposed converter. duty ratio is obtained for the desired output using derived formulas.

Power MOSFET's are used for switching purpose. High speed and high frequency PWM are given to MOSFET's for switching through control circuit. Power supply for control circuit is designed using 600V and 18V using topology. Output of first stage is an input of second stage of buck.

Simulations of the proposed converter were performed and desired results were obtained. Code was written for pic controller for the PWM using Mplab software. Hardware design was implemented and results were obtained and the losses in hardware implementation were observed.

Project Objectives

Cascaded buck converter has been widely reported in the power electronics literature. The main features are a high voltage step-down ratio and large regulation range. Applications where high conversion step down ratio is required, cascaded buck converter can be used to perform the task. Conventional buck converter (one stage) has problems related to size of parameters and in addition, it has been reported that once a duty cycle is close to 0 or 1, a degradation of the output voltage and inductor current take place. Cascade Buck converter provides a higher step-down conversion ratio and a large range of load regulation. The proposed design bucks a high voltage DC (600V) to a low voltage DC (18V constant) without using an auxiliary power supply (external power source). This proposed project illustrates the idea of cascaded buck and provide information related to its practical design.

Project Implementation Method

Hardware design of two stage buck converter is implemented. Initially low voltages were applied and then input voltages were raised step by step and output voltages were observed. Switching of MOSFET’s were performed by control circuit. Control circuit includes microcontroller and driver circuit. Switching frequency was adjusted. Output of the first buck is an input of second buck.

The project is done without an auxiliary power supply and the supply to the control circuit and gate driver circuit is given through a circuit that uses input voltages (600V) or output voltages (18V) to give the supply.

Different loads were applied and the results were observed for each. Heat sinks were used for the cooling purpose of MOSFET's.

Benefits of the Project

Buck square (two stage cascaded buck) converter provide us higher step down conversion ratio with large load regulation. So,

This can be used in those application where we need higher step-down conversion ratio.
The proposed project may be used in different project as a part (subproject) or may also be utilized in power supply.
This converter can be used in DC-DC high and low voltage distribution system because of its high step-down conversion ratio.
High voltages DC can be buck (converted) to low voltages DC using this converter without isolation process.

Technical Details of Final Deliverable

Hardware implementaed circuit will be deliver in final form.

Final Deliverable of the Project

Hardware System

Core Industry

Energy

Other Industries

Others

Core Technology

Clean Tech

Other Technologies

Robotics, Others

Sustainable Development Goals

Affordable and Clean Energy, Industry, Innovation and Infrastructure

Required Resources

Item Name	Type	No. of Units	Per Unit Cost (in Rs)	Total (in Rs)
MOSFET's	Equipment	20	200	4000
Gate diver IC	Equipment	5	200	1000
optocoupler	Equipment	4	130	520
Microcontroller and Burner	Equipment	1	11000	11000
Diode	Equipment	25	60	1500
PCB board	Equipment	3	350	1050
Photo paper A4	Equipment	6	35	210
Jumper wires (male to male))	Equipment	1	150	150
Jumper wires (male to female)	Equipment	1	150	150
Glue gun mini	Equipment	1	450	450
Glue stick	Equipment	5	20	100
Connector 2 pin	Equipment	12	20	240
Connector 4 pin	Equipment	8	30	240
Dual wire 23/76	Equipment	1	60	60
Wire 2.5mm	Equipment	2	40	80
12V relay	Equipment	2	50	100
zener diode	Equipment	4	7	28
Led	Equipment	5	3	15
Capacitor 120uF, 450V	Equipment	25	60	1500
Capacitor 3.3uF, 50V	Equipment	15	15	225
Capacitor 10uF, 100V	Equipment	15	15	225
Ferochloride	Equipment	1	200	200
Biasing Circuit (Capacitor, resistor)	Equipment	1	200	200
Inductor core	Equipment	2	350	700
Inductor coil wire	Equipment	1	200	200
Connectors 220V	Equipment	1	160	160
Heat sink	Equipment	6	50	300
Wooden box+ painter	Equipment	1	1500	1500
Loads	Equipment	1	5000	5000
Wire	Equipment	1	500	500
Battery	Equipment	1	80	80
Led lamp	Equipment	1	100	100
Nose cutter	Equipment	1	500	500
DMM	Equipment	1	2500	2500
Voltmetter	Equipment	2	500	1000
Ammeter	Equipment	2	500	1000
			Total in (Rs)	36783