• AVR Freaks

AnsweredPIC16F887: Three Phase Voltage Measurement

Page: 12345.. > >> Showing page 1 of 7
Author
TS9
Super Member
  • Total Posts : 841
  • Reward points : 0
  • Joined: 2010/05/07 10:52:22
  • Status: offline
2016/11/18 22:13:31 (permalink)
0

PIC16F887: Three Phase Voltage Measurement

Hello All,
 
Is it possible to do Three Phase Voltage Measurement Without Dedicated IC 
and with PIC 10-bit ADC as per attached Block diagram.
 
Has any body tried this ? What are the main merits and demerits of this topology ?
 
*TS9* 
 
post edited by TS9 - 2016/11/18 22:25:21

Attached Image(s)

#1
Bob White
Super Member
  • Total Posts : 277
  • Reward points : 0
  • Joined: 2010/11/06 19:52:38
  • Location: Denver, Colorado
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/18 22:39:50 (permalink)
0
No.
#2
TS9
Super Member
  • Total Posts : 841
  • Reward points : 0
  • Joined: 2010/05/07 10:52:22
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/18 22:46:26 (permalink)
0
Thanks robertvwhite,
 
Can you specify me the reason and any alternative ? 
 
Or What I need to change in the attached block Diagram .
 
I have taken reference from  Link as below:
 
http://engineerexperiences.com/3-phase-voltage.html
 
 
Thanks again
 
*TS9* 
 
post edited by TS9 - 2016/11/18 22:50:10
#3
DougRice
Super Member
  • Total Posts : 533
  • Reward points : 0
  • Joined: 2008/10/08 23:44:59
  • Location: 0
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/19 00:45:54 (permalink)
+1 (1)
Make sure that all the voltages at the pic pins remain between gnd and Vcc.
There is a good application note about A/D measurements and leakage currents caused by using the input clamping diodes.
 
If there is an input slightly over Vcc, the clamp current can make another AtoD input take more current than normal and the measurement will be wrong.
 
 
#4
TS9
Super Member
  • Total Posts : 841
  • Reward points : 0
  • Joined: 2010/05/07 10:52:22
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/19 00:53:56 (permalink)
0
 
Hi DougRice,
 
Thanks for your Update 

Make sure that all the voltages at the pic pins remain between gnd and Vcc.

That means it is possible at in Block Diagram in Msg #1. ?
Actually I have fed direct AC Stepped Down 0 to 3.3V and then Reading Peak value.
 

There is a good application note about A/D measurements and leakage currents caused by using the input clamping diodes.

Please write me link of that also.
 

If there is an input slightly over Vcc, the clamp current can make another AtoD input take more current than normal and the measurement will be wrong.

 
I will take care of that .
 
Can you let me know .
What are the main merits and demerits of this topology ? over dedicated IC
 
*TS9*
 
 
 
post edited by TS9 - 2016/11/19 03:37:42
#5
TS9
Super Member
  • Total Posts : 841
  • Reward points : 0
  • Joined: 2010/05/07 10:52:22
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/19 04:13:49 (permalink)
0
Please Update me.
#6
qhb
Superb Member
  • Total Posts : 9999
  • Reward points : 0
  • Joined: 2016/06/05 14:55:32
  • Location: One step ahead...
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/19 05:06:06 (permalink)
+2 (2)
Please wait 24 hours before bumping a topic.
 
#7
Bob White
Super Member
  • Total Posts : 277
  • Reward points : 0
  • Joined: 2010/11/06 19:52:38
  • Location: Denver, Colorado
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/19 22:42:20 (permalink)
+3 (3)
One problem is that your diagram is too simplistic.  Are you trying to sense line-to-line or line-to-neutral?  This is not clear.
 
Your diagram shows the symbol for ground which I take as a chassis ground.  Is your "ground" symbol really only to indicate a common signal return?  Or are you meaning a connection to the protective earth connection?  If you have a four-wire wye connected system, does the "ground" symbol mean the "neutral"?
 
The resistive divider circuit is ambiguous as you only show two connections but there must be at least three.  Where is the third connection?
 
Safety is paramount when working with mains voltages.  Since you use the letters R, Y, and B I take it that you are outside the US and probably working with a 416 Vac/230 Vac/50 Hz system.  Do you know what the required creepage and clearance distances are for your circuit?  Does the LCD provide adequate insulation, creepage, and clearance to protect a user that might touch the face of the LCD?
 
Your auxiliary supply is shown as connected line-to-line but referenced to your "ground".  I don't see how this works.
 
Perhaps you provide a complete schematic of the circuit you envision and better feedback to you could be provided.
 
One more thing, in the link you provided, note that in Figure 2 the ac voltages being sensed are apparently low voltages from the output of a 3-phase step-down transformer.  Do you have such a transformer in your circuit?  Also note that what is being sensed is the peak voltage of the line and that the circuit is not measuring the ac voltage directly.
#8
TS9
Super Member
  • Total Posts : 841
  • Reward points : 0
  • Joined: 2010/05/07 10:52:22
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/20 00:34:58 (permalink)
0
Hi,
 
Thanks for update
 
 

One problem is that your diagram is too simplistic.  Are you trying to sense line-to-line or line-to-neutral?  This is not clear.

I have added detailed diagram .
 

Your diagram shows the symbol for ground which I take as a chassis ground.  Is your "ground" symbol really only to indicate a common signal return?  Or are you meaning a connection to the protective earth connection?  If you have a four-wire wye connected system, does the "ground" symbol mean the "neutral"?

No It's Power Supply Ground . It's Three Phase (R = L1, Y = L2, B= L3) Diagram Without  Neutral. Please Check detailed diagram.

The resistive divider circuit is ambiguous as you only show two connections but there must be at least three.  Where is the third connection?

Please Check Circuit diagram.
 

Safety is paramount when working with mains voltages.  Since you use the letters R, Y, and B I take it that you are outside the US and probably working with a 416 Vac/230 Vac/50 Hz system.  Do you know what the required creepage and clearance distances are for your circuit.

 
R = L1, Y = L2, B= L3  440V/ 50Hz 
 

Your auxiliary supply is shown as connected line-to-line but referenced to your "ground".  I don't see how this works.
 
Perhaps you provide a complete schematic of the circuit you envision and better feedback to you could be provided.

 
Please check Circuit .
 

One more thing, in the link you provided, note that in Figure 2 the ac voltages being sensed are apparently low voltages from the output of a 3-phase step-down transformer.  Do you have such a transformer in your circuit?  Also note that what is being sensed is the peak voltage of the line and that the circuit is not measuring the ac voltage directly.

I am not using any transformer in my Circuit.
 
Basically it's a existing circuit. I have to done coding part only. In Coding part I have to measure three voltages from two ADC Channels .  
 
But I was stuck to do this so I have tried to Connect another channel (Third channel)  with Resistance  R4 , R5 to Pin 10 of MCU. But this also fails. [I don't recognise the reason] .
 
So,Not Succeeded Yet .
 
Is there anyway to measure Three Phase from other two phases ?
 
Or any other advice.
 
*TS9*
 
 
 

Attached Image(s)

#9
Mysil
Super Member
  • Total Posts : 3567
  • Reward points : 0
  • Joined: 2012/07/01 04:19:50
  • Location: Norway
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/20 03:10:19 (permalink)
+3 (3)
Hi,
Diagram in message #9 look ugly and dangerous.
Have you really built and connected this circuit to anything live?
 
Hopefully, connections marked with the ground symbol is not connected to anything outside the box.
If you replace all these symbols with the text Vss, it would look less provokative.
 
In the power supply section of the diagram, there is a direct connection from the R phase to D1 and D4 diodes and from there to LM78 regulator,
This will make measurement circuit potential anchored with R phase as reference. 
The two other signals will then either vary from +325 to -325 V in a 230 V Delta system, 0.23mA
or from +560 to -560 V in a 400 V Y system, giving a measurement current of 0.42 mA.
With 1 kOhm resistors R6 and R7, this will only give a voltage of + 0.42 V and -0.42 V,
far too low for any kind of precision.
To avoid problems caused by current in ESD diodes in the PIC16, you may take care to clip the signals using shottky diodes before reaching the ADC.
Also, the signal will go negative half the time, and the ADC in a PIC16F cannot measure that.
 
One possibility could be to replace R6 and R7 with 2 resistors each:
10 kOhm to Vcc and 10 kOhm to Vss, for a bias network giving a midpoint value of Vcc/2 
ADC input voltage would then vary between 2.5 + 2.1 V, and 2.5 - 2.1 V in each Sine period.
Sampling the voltage in microcontroller,
you may calculate average midpoint value and RMS value of  (Vadc - Vmid); 
    Sum +=  (Vadc -Vmid) **2;   for all samples in a period.
    RMS = Sqrt( Sum / n);
 
Program development and debugging for a circuit like #9 have its own challenges.
Connecting a Programmer / Debugger tool to the circuit at the wrong time, could well destroy the tool and your computer, as well as beeing harmful to your health.
 
Microchip do deliver components to companies doing things similar to what you are thinking about.
There are specialized chips, and preprogrammed devices made specifically for Power metering,
both single phase and three phase measurements, voltage, current, active and reactive power.
You could study datasheets and application notes available on Microchip website,
to see how they may be used. Navigate into Applications > Power Monitoring ...
 
Regards,
   Mysil
 
#10
DarioG
Allmächtig.
  • Total Posts : 54081
  • Reward points : 0
  • Joined: 2006/02/25 08:58:22
  • Location: Oesterreich
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/20 03:16:03 (permalink)
0
Yeah,
I used 470K/1K dividers too, but on ADE7754 or alike chips that have a 24bit ADC yelding a much higher precision.
All the rest applies, of course.

GENOVA :D :D ! GODO
#11
TS9
Super Member
  • Total Posts : 841
  • Reward points : 0
  • Joined: 2010/05/07 10:52:22
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/20 09:12:54 (permalink)
0
Hi Mysil, Thanks for your Update... Please See my replies . I am sure you have experience on Three Phase System and I can solve my problems.  
Diagram in message #9 look ugly and dangerous.
Have you really built and connected this circuit to anything live?
Hopefully, connections marked with the ground symbol is not connected to anything outside the box.
Yes, I have made the Circuit in Actual Hardware.No, ground symbol is not connected to  anything outside the box.
If you replace all these symbols with the text Vss, it would look less provokative.
Yes, Replaced Please Check attachment.
In the power supply section of the diagram, there is a direct connection from the R phase to D1 and D4 diodes and from there to LM78 regulator, This will make measurement circuit potential anchored with R phase as reference.
My R Phase Reading is too low.Reading is not correct at this phase .I don't know why this ?. So I have deleted this from Schematic and It Actual Hardware.
The two other signals will then either vary from +325 to -325 V in a 230 V Delta system, 0.23mA or from +560 to -560 V in a 400 V Y system, giving a measurement current of 0.42 mA. With 1 kOhm resistors R6 and R7, this will only give a voltage of + 0.42 V and -0.42 V, far too low for any kind of precision.
I am using 3-Phase 3- Wire system without Neutral.But to Change the Voltages I am using 3 individual Dimmer (For Up Down Voltage ) between  individual Phase(s) w.r.t Neutral (R-N,B-N,Y-N).Check Image for my setup and then Middle of the Dimmer Fed to My Hardware. Is there anyway to measure Three Phase Voltages from other two phases ?or to measure R Correctly with Same Topolgy Hardware. Because  my previous hardware is working fine the previous code[Developed by  some other person].or It's Just as Permutation or Combination of Readings Getting from two ADC Channels with any 10-bit ADC MCU?  Thanks  Mysil for bearing me Once again.  *TS9*
post edited by TS9 - 2016/11/20 09:50:57
#12
Mysil
Super Member
  • Total Posts : 3567
  • Reward points : 0
  • Joined: 2012/07/01 04:19:50
  • Location: Norway
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/20 18:50:46 (permalink)
+1 (1)
Hi,
In a three phase system without a midpoint (neutral) connection,
you may do what you are already doing, measure B and Y phases with reference to R.
An alternative is to  establish a virtual midpoind by use of a resistive network, or if the load have a midpoint connection.
 
"R phase reading is too low" 
Because of how the power supply is arranged, measurement of the R-phase will, at best, measure the voltage feeding the power supply,  approx( V(ZD1) + V(D1)),  or V(D4), changing for each half period of AC.
This is causing some distortion in measurement values of phase Blue and phase Yellow.
You might use measurement of R-phase to adjust readings of B and Y.
 
Another possibillty will be to rearrange the power supply: Reference the power Vss directly to R phase,
feed the diode bridge from Y phase, as now, and from B phase. This will need high voltage capacitors in both wires feeding the bridge rectifier.
 
With measurements like you do, it is possible to calculate the voltage between Y and B, by subtracting ADC values measured by AN0 and AN1.
 
Circuit diagram in attachments, still do not show a resistor network to provide positive bias to ADC voltages AN0 and AN1.
 
Regards,
   Mysil
#13
TS9
Super Member
  • Total Posts : 841
  • Reward points : 0
  • Joined: 2010/05/07 10:52:22
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/22 03:14:07 (permalink)
0
Hello Mysil,
 
Thanks Again
From All your methods, I select below Because In this I need to do less changes Hardware.

"R phase reading is too low" 
Because of how the power supply is arranged, measurement of the R-phase will, at best, measure the voltage feeding the power supply,  approx( V(ZD1) + V(D1)),  or V(D4), changing for each half period of AC.
This is causing some distortion in measurement values of phase Blue and phase Yellow.
You might use measurement of R-phase to adjust readings of B and Y.

 
But which point I have to used for measurement of R Phase voltage  
1) V(ZD1) + V(D1) or
2) V(D4) according to attached Circuit then fed to ADC Channel.
 
I am not getting this. Please check the Attachment and guide me.
I have mentioned point 'A' and point 'B' in Schematic.
 
Again Thanks for your Precious time...
 
 
--
TS9
 
post edited by TS9 - 2016/11/22 03:38:03

Attached Image(s)

#14
microcontrollerslab
New Member
  • Total Posts : 14
  • Reward points : 0
  • Joined: 2015/07/14 14:45:44
  • Location: 0
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/22 04:13:01 (permalink)
0
You can use three ADC's of any pic microcontroller and use step down transformer to step down voltage
#15
microcontrollerslab
New Member
  • Total Posts : 14
  • Reward points : 0
  • Joined: 2015/07/14 14:45:44
  • Location: 0
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/22 04:22:26 (permalink)
+1 (1)

This is a circuit diagram to step down voltage

I love to read technical articles from microcontrollers tutorials and projects hub.
#16
Nikolay_Po
Super Member
  • Total Posts : 1935
  • Reward points : 0
  • Joined: 2012/04/01 13:49:27
  • Location: Russia, Novorossiysk
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/22 04:41:36 (permalink)
+5 (5)
Why not?

 
#17
qhb
Superb Member
  • Total Posts : 9999
  • Reward points : 0
  • Joined: 2016/06/05 14:55:32
  • Location: One step ahead...
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/22 05:04:26 (permalink)
0
No-one else can see that image Nokolay. Try imgur.com
 
#18
Nikolay_Po
Super Member
  • Total Posts : 1935
  • Reward points : 0
  • Joined: 2012/04/01 13:49:27
  • Location: Russia, Novorossiysk
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/22 05:39:47 (permalink)
#19
Nikolay_Po
Super Member
  • Total Posts : 1935
  • Reward points : 0
  • Joined: 2012/04/01 13:49:27
  • Location: Russia, Novorossiysk
  • Status: offline
Re: PIC16F887: Three Phase Voltage Measurement 2016/11/22 05:42:15 (permalink)
+1 (1)
You will see none AC amplitude on Vss phase. But the metering of phase voltages between the phases will be correct.
#20
Page: 12345.. > >> Showing page 1 of 7
Jump to:
© 2020 APG vNext Commercial Version 4.5