Are u agree with this statement?

[powersys]

The classic formula for True Power i.e. (RMS volts X RMS current X Cos Theta) is VALID ONLY WHEN THE VOLTAGE AND CURRENT SIGNALS ARE PURE SINUSOIDS.

Are u agree?

 

[Kral]

powersys,
Yes. Phase shift only has meaning for sinusoids. However, by doing a Fourier analysis of the voltage and current waveforms, you can compute the power contribution for each frequency by using this formula, and then add up the individual power components for each frequency.
Regards,
Kral

 

[powersys]

powersys,
Yes. Phase shift only has meaning for sinusoids. However, by doing a Fourier analysis of the voltage and current waveforms, you can compute the power contribution for each frequency by using this formula, and then add up the individual power components for each frequency.
Regards,
Kral

Were you referring the 'Phase shift' to the 'cosθ' in the formula?

Say I have a buck converter. The output current Iout is constant, but the output voltage Vout has litte ripple. On the other hand, the input voltage Iin is constant, but the input current Iin is pulsating.

I wish to calculate the input power Pin, and output power Pout, of the converter to calculate the efficiency. My idea is as follows:
1) Calculate the rms of input voltage and current.
2) Calculate the rms of output voltage and current.
3) Calculate the Pin = Vin-rms X Iin-rms
4) Calculate the Pout = Vout-rms X Iout-rms
5) Efficiency = Pout/Pin

Do you think my method has any mistake?

 

[diemilio]

I think the way you're trying to solve your problem is correct, but I would calculate Pin and Pout using the average power expresion, not RMS value, since calculating RMS is more tedious.

P=1/T*integral(i(t)*v(t),t,0,T). Since Iout is constant your Pout expresion would reduce to calculate the integral of the output voltage, which will probably be the average value of Vout since ripple signals usually are simetric AC signals with a DC component. The same thing would happen with Pin since Vin is constant. The Pin calculation will reduce to find the area under the pulsating signal and then to multiply it with Vin.

Efficiency=Pout/Pin

I'm not sure if I made myself clear, but I hope that this helps you.

 

[m.mokhtar]

Sure ur statement is absolutely true

 

[huojinsi]

Say I have a buck converter. The output current Iout is constant, but the output voltage Vout has litte ripple. On the other hand, the input voltage Iin is constant, but the input current Iin is pulsating.

I wish to calculate the input power Pin, and output power Pout, of the converter to calculate the efficiency. My idea is as follows:
1) Calculate the rms of input voltage and current.
2) Calculate the rms of output voltage and current.
3) Calculate the Pin = Vin-rms X Iin-rms
4) Calculate the Pout = Vout-rms X Iout-rms
5) Efficiency = Pout/Pin

Do you think my method has any mistake?

I absolutely agree with your idea!

 

[mkjjtamz]

i agree with you!!!!!!!!!!!!!!!!!!!

 

[El-Hadidy]

Hello,

From your question I feel you have some doubt about this relation of Power,isn't it?. Why do you doubt about that if yes?

Thnaks

El-Hadidy

Added after 55 seconds:

Sorry (Thanks)

 

[powersys]

From your question I feel you have some doubt about this relation of Power, isn't it?. Why do you doubt about that if yes?

That's true... but now the doubt is cleared. Thanks for the inputs from you guys. Now I'm thinking of how to measure the efficiency of a dc-dc converter...

 

[El-Hadidy]

Good luck with your job.

Have a nice time...

El-Hadidy

 

[dreamcard]

If your true power means effective power, I agree with that...

 

[scart]

powersys

man if u want to be shore of ur formula u should use Fourier analysis to prove ur equations and u sould analyse the input & output voltages and currents and also u should analyse for harmonic distortion causit effect the input power factor

regards

 

[voldemort_001]

The classic formula for True Power i.e. (RMS volts X RMS current X Cos Theta) is VALID ONLY WHEN THE VOLTAGE AND CURRENT SIGNALS ARE PURE SINUSOIDS.

Are u agree?

Yes. It is indeed true. We have proven that out, when I was in college.

 

[magnetra]

Yes, I agree with ur statement. THe formulas have been derived with pure sinusoid waveforms for V and I.

M

 

[engr_najam]

yes
while for DC it is only the product of voltage and current
P=V.I

 

[easternbean]

the state is right.

 

[brrk007]

even i completely agree with you

 

[the_risk_master]

thats true and logical, I agree...