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Power Analyzer Design Problem

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Ishaan Karnik

Member level 3
Jun 16, 2012
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I need to design a low cost power analyzer for my thesis work (solar inverter system) as one is not available and their is no plan to buy a new one.
Power Analyzer will only be used as an instrument for measuring electrical signal of characteristics 230VAC; 0.5-10 Amps. current; Single Phase and frequency 50Hz.
I have access to Infineon Relax Kit (in my possession) and/or ATSAM4CMS Demo Board (planned) and plan to use on chip ADC. Available ADC : 12 bits-4M Samples in Infineon XMC4500 and 20-bit Sigma Delta Converter 16kS/s.
I need some advice/guidance regarding :
  1. How to find out Total Harmonic Distortion (low order; up to 20th order)
  2. How to find Power Factor Corruption
  3. How to find fundamental frequency of a signal

List of all measurement that will be take :
  1. IRMS
  2. IPEAK
  3. VRMS
  4. VPEAK
  5. PAVG
  6. Power
  7. Energy
  8. Frequency
  9. THD
  10. PFC

Any other economical development board recommendation may be considered if the above mentioned board are not adequate for mentioned operation.

Finally the power analyzer will be connected to Laptop/PC to display all relevant reading on screen. Complex mathematical operations could be dome on PC is required.
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Audacity (free) has a FFT Spectrum Analyzer so if you use a resistor divider to 1V for AUX input you can record and analyze.> plot Spectrum


With Stereo, you can monitor a Current Shunt or CT with 1V full scale for example and export the data into Excel and do some interesting calculations with RMS , PF etc.

As far as I understand, SunnySkyguy suggests to use L+R sound card channels for simultaneous voltage and current measurement. All you have to supplement is a suitable probe connection and software.

In my view, an isolated interface (current transformer, voltage measurement transformer or differential probe amplifier with large common mode range) would be preferred.


with the soundcard solution: You may expect phase deviation between the two channels, caused by voltage measurement circuitry and current measurement circuitry.
You should calibrate for phase angle with a known pure ohmic load resistance.


fundamental frequency can be found by counting the samples between zero crossings

Total Harmonic Distortion can be found by taking FFT of voltage output and finding the RMS addition of higher frequency components more than the fundamental signal

power factor can be found by calculating the phase displacement between voltage and current signals with their zero crossings.
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