Project 1 - Loss calculation for a DC/DC converter-MATLAB
Aim:
Designing a boost convertor & calculating the various losses in the convertor.
Design inputs:
We are going to consider the following inputs:
`V_(i n) = 100V`
`D = 0.6`(Duty Cycle)
`R = 20Omega`
`f_s = 20kHz`(Switiching frequency)
`DeltaI_L = 10% of I_L`
`DeltaV_0 = 10% of V_o`
`R_(d_(mos f et)) = 42mOmega`
`R_(d_(diode)) = 3.2mOmega`
`t_r = 31ns`(Rise time of MOSFET)
`t_f = 21ns`(Fall time of MOSFET)
Schmeatics:
Calculations:
We know that for a boost convertor:
`V_(out)/V_(i n) = 1/(1-D)`
`=> V_(out) = 100*(1/(1-0.6)) = 250V`
`I_o = V_(out)/R`
= `250/20 = 12.5A`
`I_L = I_(i n) = I_0/(1-D)`
`= 12.5/0.4 = 31.25A`
`DeltaI_L = 10/100*31.25 = 3.125A`
`L = V_(i n)*D/(f_sDeltaI_L)`
= `(100*0.6)/(20*10^3*3.125) = 0.96mH`
`C = D/(Rf_s((DeltaV_(out))/V_(out))`
=`0.6/(20*20*10^3*0.1) = 15muF`
Graphs & results:
Output Voltage
`V_(out) = 245V`
Output Current
`I_o = 12.3A`
Input Voltage
Inductor Current
`I_L = 31A`
The various power convertors topologies have power loss components which are the switches, diodes, Inductors & capacitors.
Following are the Power losses which is going on in the boost convertor as shown in schematic:
1) MOSFET losses
2) Diode losses
3) Inductor losses
As per the current & voltage inputs & calculations, following are the MOSFET & Diode selected from different electronics website, same is attached.
MOSFET: IRFS4229PbF
Diode: DPF80;C200HB
Below are the calculations of the power losses:
MOSFET losses:
`P_(mos fet_(DC)) = R_(d_(mos f et))I_(out)^2D`
= `0.042*12.5^2*0.6 = 3.9375W`
`P_(mos fet_(AC)) = (R_(d_(mos fet))*I_(AC)^2*D^3*(1-D)^3)/12`
where `I_(AC) = (DeltaI_L)/D`= 3.125/0.6 = 5.21A
`P_(mos fet_(AC)) =( 0.042*5.21^2*0.6^3*0.4^3)/12`
= 0.003283W
Total Power loss in MOSFET = 3.9407W
Diode losses:
`P_(diode_(DC)) = R_(d_(diode))I_(out)^2(1-D)`
= `0.0032*12.5^2*0.4 = 0.2W`
`P_(diode_(AC)) = (R_(d_(diode))*I_(AC)^2*D^2*(1-D)^3)/12`
= `(0.0032*5.21^2*0.4^2*0.6^3)/12 = 0.0002502W`
Total Power loss in diode = 0.20025W
Inductor losses:
`P_(L_(DC))= R_LI_(out)^2`
= `0.01*12.5^2 = 1.5625W`
`P_(L_(AC)) = (R_*I_(AC)^2D^2(1-D)^2)/12`
= `(0.01*5.21^2*0.6^2*0.4^2)/12 = 0.013W`
Total Power loss in inductor = 1.564W
Switching losses in MOSFET:
`P_((sw)_(dc)) = (V_(out)I_(out)(t_r+t_f)f_(s))/2`
= `(250*12.5*(31+21)*10^-9*f_s)/2`
= 1.625W
`P_(sw_(AC)) = (V_(out)I_(out)(t_r-t_f)f_(s)D(1-D)^2)/4`
= `(250*12.5*(31-21)*20*10^3*10^-9*0.6*0.4^2)/4 = 0.015W`
Total Power switching losses = 1.64W
Total power loss = `P_(mos) + P_(diode) + Psw+ P_(i nd)`
= 7.34095W
`P_(out) = V_(out) * I_(out)`
= `250*12.5 = 3125W`
Efficiency is given by :
`eta = P_(out)/(P_(out)+P_(losses))`
= `3125/(3125+7.34095)*100 = 99.765%`
P.S: Please refer the paper attached from which referernce has been taken to evaluate the loss values.