DC – DC Boost Converter Boost converter or step – up converter increases input voltage magnitude to a required output voltage magnitude without the use of a transformer at the same time stepping down of current from the input side

DC – DC Boost Converter

Boost converter or step – up converter increases input voltage magnitude to a required output voltage magnitude without the use of a transformer at the same time stepping down of current from the input side. There are various types of dc-dc converters that can be used to transform the level of the voltage as per the supply availability and load requirement. Some of them are:
1. Buck converter 2. Boost converter 3. Buck-Boost converter
Figure 2.6 shows a boost converter consisting of an inductor, a diode and a high frequency switch. The switch can be typically a MOSFET, IGBT or BJT.

The control strategy lies in the manipulation of the duty cycle of the switch which causes the voltage control in the output. In this project boost converter is used for both solar photovoltaic and wind energy system to boost up the output voltage of the two renewables to the same level of DC bus voltage. Ripple in the input and output are reduced by filters made of capacitors or inductors at input and output of converter.

Figure 2.6 Schematic of a boost converter

2.4.1 Design parameters for boost converter

For a boost converter, the values of inductor, capacitor, load and the percentage of duty cycle is determined as follows:

In figure V_s = Supply voltage V_0= Output voltage

Duty cycle (D): It represents the fraction of the commutation period T during which the switch is on. It ranges between 0 (S is never on) and 1 (S is always on).It ca be calculated by knowing input and the required output for a boost converter.
D = 1 – V_s/V_0 * 100 ………………………………………. (2.4)

Inductor : The value inductance is determined as

L ? V_(s * D )/F_(s * ?I_L ) ………………………………………. (2.5)
Where,
? F?_s = Switching frequency in the range of 25 – 10 KHz.
?I_L = Ripple current value of inductor.
According to Thumb rule its value will be in the range of 20 – 40%
V_s = Input supply voltage in Volts
D = Duty cycle

Capacitor : Capacitance value is determined by the following equation

C ? I_(0 * D)/F_(s * ?V_c ) …………………………………… (2.6)
Where,
I_0 = Output current of the converter which is determined by the ratio of desired output power to the desired output voltage.
?V_c = Ripple voltage of capacitance. Generally, its value will be in the range of 1-5% and therefore it is assumed equal to output voltage.

Load resistance: It is determined by the ratio of square of the output voltage to the rated pater of the converter