This research is one of the researches of the roadmap
“Power Grid Monitoring Based on Microcontroller”. This research has been preceded
by the research with title “Measure RMS Voltages and Currents in Power Grid
Based on Microcontroller”. In that research, the microcontroller ADC samples
the voltage and current grid 64 times per period of the grid voltage with 8 bit
data format, so that we obtain 64 instantaneous values of grid voltage and
current per period. The result can measure RMS voltage from 25 V to 250 V at
frequency from 22 Hz to 80 Hz and current up to 5 A. To expand its ability to
measure power and power factor of load, this research must add an algorithm to
calculate it.
This research was done by adding three special algorithms. First algorithm will multiply each
of instantaneous value of grid voltage and its corresponding current data, so
that we obtain instantaneous electric power value. Second algorithm integrates
all the instantaneous electric power values so that we obtain electric power
value. The last algorithm computes power factor that is a comparison between
the value of electric power and the product of RMS voltage and current. All
calculation have been done quickly without involving floating point numbers and
held on the sidelines of the sampling process.
Product of this research is a digital wattmeter that can measure
frequency, RMS voltage and current, power and power factor up to 1 kVA of
loads. Maximum measurement error of power and power factor is 2 %. All of those
quantities are calculated ten times per second and display is updated once per
second by average value of ten existing data. Next research, this microcontroller-based system should be
added an algorithm for data reporting to computer, so that we can monitor all
values graphically in computer screen.
