Project 1 - Loss calculation for a DC/DC converter-MATLAB

PROJECT 01

AIM:- Design of boost converter, and calculating the loss of different components including

power switching device and deriving efficiency of boost converter. This is applicable in power

supply industry, electric vehicles etc where DC-DC converter is required to boost the voltage

from DC source. All the aspects of this project with loss calculation, device selection, simulation

etc are industry relevant.

For this project i will design a BOOST Converter with the following parameters.

• Input voltage 200V
• Output voltage 400V
• Power 2Kw

Based on these parameters we will calculate the Duty cycle, Inductor (20% Ripple)

and Capacitor (5% ripple).

We know Foe a boost converter Duty cycle an be calculated as.

Vout/Vin = 1/(1-D)

=>D = (Vout-Vin)/Vout

D = (400-200)/400

D = 0.5

We will choose the switching frequency as 50KHz = FS

Load resistance will be calculated as

RL = Vout^2/P

RL = 400^2/2000

RL = 80ohm.

IL = vout/(1-D)*R

IL = 400/(1-0.5)*80

IL = 20A

We will design the Inductor for our converter with 20% ripple

=> delta(IL) = (IL/100)*20

delta(IL) = (20/100)*20

delta(IL) = 4A

=> L = (Vin)/Fs*delta(IL)

L = (200)/50KHz*4

L = 0.5mH

L = 50e^-3 H

Also we will the Converter Capacitor with 5% ripple voltage

delta(Vout) = 5*(Vout/100)

delta(Vout) = 5*(Vout/100)

delta(Vout) = 20V

also delta(Vout)/Vout = 20/400

delta(Vout)/Vout = 0.05V

C = D/(R*Fs*(delta(Vout)/Vout ))

C = 0.5/200

C = 0.0025mF

C = 2.5e^-6F

Now we have all the parameters Calculated , we will consider the followinf resistances for loss calculations

rL = 5*10^-3 ohm #Inductor resistance

rC = 5*10^-3 ohm #Capacitor ECR

rMOSFET = 1*10^-3 ohm # Mosfet internal resistance

rDIODE = 1*10^-3 ohm # Diode R on resistance

By considering these parameters we will build a simulink model as shown below.

Simulink model for Boost converter

Input and Output voltage waveforms

The above simulink model of boost converter has a Effeciency of 96%

Now we will consider the losses which are present in the converter like the Mosfet loss

Diode loss, Inductor loss due to its internal resistance od coil, Capacitor ECR loss.

These losses are in direct relationship with the duty cycle. When the integrated

high-side MOSFET turns on, the load current flows through it. The drain-to-source channel

resistance (R_DSON) causes power dissipation, which can be expressed as.

Pmosfet = (Iout^2)*Rdson*D

Where D = Duty cycle =0.5 Calculated

Losses in Diode are given as

Pdiode = Vf*Iout*(1-D)

Vf = Forword voltage drop in diode here in this case i have considered 0.2V

there are conduction losses in the inductor as well because every inductor has a finite DC

resistance (DCR), which is the resistance of the wire in the coil. Equation 3 expresses the

dissipation in the inductor as:

Pind = (Iout^2)*DCR

Losses in Capacitor ESR is given as

PcapESR = Vesr*Iesr

The conduction losses depend on the load current. With heavier loads, the conduction

loss in the MOSFET increases and is the dominating factor. Conduction losses plus switching,

driver and internal low-dropout regulator (LDO) losses lead to a considerable generation of

heat and increase the junction temperature of the integrated circuit (IC). Equation 4

expresses the increase in junction temperature as:

ICtj = (ICpd*Qja) + Ta

here IC_Tj is the junction temperature of the IC, T_A is the ambient temperature, θ^JA is the

junction-to-air thermal resistance and IC_Pd is the total power dissipation just in the IC

equal to . The R_DSON of the MOSFET typically has a temperature coefficient (R_dsonTco).

With an increase in the junction temperature of the IC, the R_DSON would increase above

the nominal based on the temperature coefficient. While this parameter may not be

available in the data sheet, TI’s WEBENCH® Power Designer software has that

information and uses it for calculating the design efficiency, thus making the results

accurate. Equation 5 can adjust the R_DSON based on the junction temperature:

Rdson = Rdsonnom+(ICtj-Ta)*Rdson

where R_dsonNom is the nominal value of R_DSON

Pconduction loss = Pmos+Pdiode +Pcap+Pinductor

Ptotal = Pconduction + Pdriver LDO + Psw

Effeciency = Pout/(Pout+Ptot)