Sine wave power inverter

Hi Babalola,

I am just recovering from a terrible financial set back. I work in a part of the country where embedded is not done much and low in returns. A joint venture and lack of paper works almost made be broke.

I am learning that coding itself does not help, terms and conditions in black and white ensure that you get paid for the job. (The entire production aside)

I have mentioned in another post by kvrajashekhar (if I remember the name correct) that I could not keep up to my promise so no more commitments. Also being a design house I cannot make the code public due to commercial restriction.

Lacking an engineering background I do not clearly understand the equations and maths involved in a theoretically backed design. However I try to figure out by studying more and more.

In my design I sample the output voltage (a dc average) pass it through a PI routine to derive error. The error is basically and inverse of my sinewave modulating quotient. Which gets multiplied with the look up table. To save instruction cycles during table interrupts the entire lookup table is recalculated during zero cross for a cycle and kept in an array. This does not result in a highly pure sine but THD measured was between 2.5% and 4%. Thus waves are corrected only every 10mS. In fact 20mS was the original design to avoid flux imbalance. Now the routine uses flux reset by just switching on the Lower MOSFETs every zero cross. This gives me enough time for housekeeping etc. Like battery capacity measurement, display, communication, discharge profile log and possible econo-mode change during long power outage hours based on previous history.
All done on a 18F4520 @ 40MHz.

This forum was the starting place and I require less assistance now but I am grateful to people especially....everyone.

Hi Sougata

Hi Sougata

needed a bit of help on inverters using pic16f72
read ur posts on thE thread
this thread is a year or more old so i believe u have advanced ur inverter quite a lot

can u help on pic 16f72 code as i'm very bad on coding weras i ve pretty gud hardware knowledge.......

sam
[email protected]

Hi,

I do not produce inverters commercially. I only developed the firmware. With the newer PICs having better peripherals design is even easier.

Hi Sougata,

Its a long time to hear from you.
To do voltage feedback on the output of inverter with PI routine, is it better done within the main interrupt scheme where the duty cycle is updated or within the background loop and why?.
Iwanted to try the followings for my digital PI control of the inverter output: If my error is negative
U(k+1) = -U(k)+ A*e(k) - B* e(k+1)
If error is positive,
U(k+1) = U(k)- A*e(k) + B*e(k+1), Does the above make meaning?

Can any one advice,

Babalola.

Hi,

With a quick look, I couldn't make anything out of the formula. Explain in details about U seems to be the desired voltage, K constant, e error, what about A and B. Are they the P and I .

How are you tuning k ?

Post Code.

hi Sougata

Actly its like i'm a final engineering student.....n inverter is ma project for final sem.....i ve a hardware design fot inverter....n also interfacing circuits....which actly i got frm my guide...

but now problem is no1 around knows PIC properly to write a accurate program.....


so I was hoping if u could help me on some coding of PIC16f72 to be done.....Particularly PIC16f72 cuz the i ve the design ready for it.....


can u help me to write a code....or if u cuold give some old code (i.e of PIC16f72 inverter code) u have so that it wud help.....

sam
[email protected]

Hi,

To help you with the software flow the schematic is needed. Wondering how you rigged up a schematic without having fully understood the programming philosophy and the 16F72 !!!!!!!!!!!

Hi Das,

The e(k+1) is the present error
e(k) > past error
u(k+1)> present output of the pi controller
u(k) > past output of the controller
the above are digital parameters of the pi controller and in the course of getting these parameter there is alway need for sampling time (T), the propotional gain of the controller Kp and the zero placement of the controller which is WI
INTERGRAL GAIN KI=Kp*WI
therefore A=Kp(WI*T -1)
while B=Kp

Example if kp=0.04 and WI =3140rad/sec SAMPLING TIME OF 10us

KI=188.4
A=0.04(3140*10US-1)
B=0.04

Remember in PI controller proportional looks at present error while intergral looks at past errors

Regards,
babalola.

Hi Das,

The e(k+1) is the present error
e(k) > past error
u(k+1)> present output of the pi controller
u(k) > past output of the controller
the above are digital parameters of the pi controller and in the course of getting these parameter there is alway need for sampling time (T), the propotional gain of the controller Kp and the zero placement of the controller which is WI
INTERGRAL GAIN KI=Kp*WI
therefore A=Kp(WI*T -1)
while B=Kp

Example if kp=0.04 and WI =3140rad/sec SAMPLING TIME OF 10us

KI=188.4
A=0.04(3140*10US-1)
B=0.04

Remember in PI controller proportional looks at present error while intergral looks at past errors

Regards,
babalola.

hi Sougata


Actly my guide provided me with the circuits....

Ive attached few interfacing circuits....
hope this is wot u requested....

Dear Sam,

These are the interfacing circuit to do the following in order of your doc.

1. Mains Sense Circuit: Comes from a small step down transformer. The rectified DC voltage is an average representation of the Mains Input Voltage. AN0 is used to sample this pin and decide the status of the mains input. That is within range or outside range. If out of range switches to inverter mode. While in inverter mode used to sense mains restore condition. So this is part of a periodic ADC routine.

2. Battery Sensing Circuit: Used to sense the battery voltage for deep discharge cut-off and charging state change (Boost/Trickle/Equalize). So this is also used in both the inverter/mains-standby mode. Used AN1

3. Charger Circuit: An inverting amplifier. Note that the same shunt (generally in the low side negative battery terminal) is used to measure battery charge and discharge current. The ADC onbaord 16F72 is 8 bit. If a signed AD was performed by offsetting the signal then you loose one more bit and have 7 bit AD for the current sense. So to channels are used with two amplifiers. This is negative battery dischargei.e., current is being put into the battery, thus the inverting amplifier. Phew......

This goes to AN4 and is used only when charging the battery.

4. Load Sensing Circuit : Same as above but for discharge. So a non-inverting amplifier. connected to AN2. Used for overload protection.

5. Output Voltage Sensing: This either comes from a sense winding on the inverter transformer or a small step down transformer (better) connected to the filtered output of the inverter output. This is the voltage feedback for correcting voltage under different load/battery condition. Average DC represents the average output voltage. No in cycle distortion correction possible. (Not within the scope of 16F @ 20MHz, Needs a 18F @ 40MHz)

6. Power Supply Circuit : Your PIC runs on 5 Volts.

7. Sync Pulse Circuit: PORTB.0 INT based zero cross over sensing. Can measure line frequency. Can detect abrupt mains failure (UPS mode). Can do phase angle control on charge circuit. Can detect mains restore. Important for grid connected inverter, where you need to sync your timebase to the mains.


Assuming the above circuits have been ripped from common inverter design prevalent in India. I don't know why people are still stuck with the 16F72 when there are newer introduction like PIC18F1330. I could upgrade my design. Who would buy it ?? :(

This design is far from complete. You need to design the driver stages. Then decide on the software. In India most designs run on software PWM using the compare module. I don't know why ? But they are commercially successful. .... Well I am not. :o


P.S. - Sorry Sam, I cannot make the code public. (People will come to know about my bad programming skill). I only dream of making an open source sinewave inverter, in PBP. Can't find time. Cause I need to come up with a fresh new design to avoid any legal obligations on my old design.

HI Sougata

Thanking u for takin time of your busy shchedule to explain each of the circuits........

i ve also got the mosfet drive circuits designs......but could not attach as i dont have a soft copy of the designs.....

the design is all but complete for the software code....which i was wanting help on....:)
actly was hopin u wud help me out on the code.....;)


but I fully understand ur situation regarding leagal issues......so if u cud help me in some other way like

if u knw any1 among ur frenz who can help me write the code.....

or u have any bits n pieces of codes u found on net or something dat mite help me


plz let me knw if u can direct me to some other person who can help me with the code.....i don mind paying him his fees for the help in the code....

hopin u can help me out in some way

sam
[email protected]

Quote:

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Originally Posted by samrulezzz

plz let me knw if u can direct me to some other person who can help me with the code.....i don mind paying him his fees for the help in the code....

hopin u can help me out in some way

sam
[email protected]

---

If you surf on the net or follow EFY magazine you will find that there are people who are distributing .HEX files for as less as Rs.20,000.00 (USD$ 400) but you will get zero support as far as an academic project report is concerned. I have no idea whether anybody will give you source code. Most of them don't have it. So asking for paid support may be well exceed the scope of your project.

I personally feel that you should start writing your own code and the forum would help. A student project need not be perfect, but should be a proof of concept. So better start with the sine generation. Open loop-no feedback and then achieve other milestones as per time frame of the project.

Where are you located by the way.

hi sougata

ya wot u tell is true....no1 gives the source code normally....

i ve got bits n pieces of codes wen i surfed....
now trying to write a code on my own....
hoping it turns out gud



me located in mangalore karnataka state

Hi,

One suggestion. Do not rely on PBP while doing multiplication inside your sine lookup code. It takes many MCU cycles. Google for fixed latency multiply on PIC16. It takes more code space but timing is within control.

Good Luck

Dear Sougata,
I am beginning to work on Sine wave inverter generation, I am still a beginner in PIC I would like your guidance whether hardware pwm is better or software pwm, in terms of good working and reliablity also i am considering of using a 50hz type of transformer.
Thanks and Regards.

Hi,

Software PWM may result in a less BOM cost as all the steering is done in software. Also charging PWM controls become easier as you can steer your outputs. Software PWMs used in Sine generation still use the CCP unit in compare mode. @ 20MHz , you may be able to generate 4-6 KHz.

However I prefer hardware PWM as it relieves the MCU. Also much higher PWM frequency results in noiseless designs.

Where are you located anyway ? (Didn't get any info from your public profile)

Since you would be using single conversion, 50Hz transformer, I suggest you use a split bobbin design. I found they work better. However cannot say why as my magnetics knowledge is lower than nil. Somebody else may be able to shed some light on that.

Sougata, Thanks for such a clear guidance.
I am in located in a village called "Sanjan" in GUJARAT, the registration didn't ask questions so may be the profile is not updated i will update it anyway.
Also how can we use the same transformer for charging, since the transformer is in full bridge the MOSFET's body diodes will pass the uncontrolled charging once mains supply is given to transformer.Mains voltage is not same every where then how is charging control achieved unless transformer voltage is quite samll ?
One of my friend told me that SMPS based design is not suitable for all types of load that's why i am doing with 50Hz type transformer
Also my magnetics knowledge is quite poor, I do some designing based on formulas but you can not get good results without practical knowledge, i agree. That's why i am requesting from forum If any body can help me in transformer I would be really thankful.

Hi,

The 2 lower side MOSFETs can boost up the voltage. And yes the body diodes are used for charging.

HI,
I am reading for the first time this argument.
I am asking if there is a sample PICBASIC program and schematics to take as a reference for me to experiment a switch mode power supply using pic PWM.
Could you please give me some help on the matter ?
I do not need more than two amps of current and it will be a buck converter .
I hope to read from you.
Thanks in advance
Ambrogio
IW2FVO
North Italy

Hi,

It would be better if you start a different thread cause a PIC based buck converter is different than a sine wave inverter.

provide the following though

What is the input voltage range (Min - - Max)
What is the output voltage required
Intended Frequency of the switcher (PWM)

MCU being used

BTW it is 2:15 AM in local time and I should get some sleep now. :D

Thanks,
vin=10 to 22 vdc
Vout=7 Vdc max
I out =3 A max

Ambrogio

Hi mincing,
What is your progress regarding inverter? Do you go through the postings here or you left out? I can help you regarding sinewave inverter. Hope to hear from you again. Thanks.

Dear Tahmid,
Thanks for the msg.

I have developed the sine wave inverter but open loop.I am controlling the amplitude based on the rectified DC from output sample.I gotstuck here as I could not find the right formula for closed loop control with sine as iput to ADC.

It would be great if you could throw some light on this,

If you have any guide lines or app notes pls.share.


Thanks again,
mincing

i think you need to provide the plant(inverter) specification most importantly the output filter to be able to develop a model for which ever compensation model to be addopted could be designed.you equally need to specify your power level.

babalola

HI,
I am asking if there is a sample PICBASIC program and schematics to take as a reference for me to experiment a switch mode power supply using pic PWM.
Could you please give me some help on the matter ?
I do not need more than two amps of current and it will be a buck converter .
The PIC I will like to use is the 18f252.
I hope to read from you.
Thanks in advance
Ambrogio
IW2FVO
North Italy

i have being into for a while but is square wave but want tsw

Hi,

I didn't get you quite.....

im reallyin the act of making an inverter for a while but is square-wave using pwm ic but i want to start pure sine wave inverter,if i an get help from the forum how to proceed with it but not with double conversion cos i live in this part of the world where we import nearly everything and cost of importing is high so iwill use the bulky xfomers that is available or if u cant give me hint on how to mke a ferrite xfomers on my own thanks

Hi,

While we have been discussing sine wave inverter in this thread about the internals but not much as code example. Which PIC would you be using ? I wish I could provide some.

Hi,
I want to build up a sine wave inverter too using the PIC18F452. Any help ?
Is there a schematic diagram and some code to take as a referene ?
Thanks
Ambrogio

HI sougata

can you please send me the sourcecode for pic 16f72 based inverter. please find the attachment for 16f72 based inverter circuit.
i'm waiting for your valuable reply.

Thanks and regards,
Karthick
[email protected]

HI sougata

can you please send me the sourcecode for pic 16f72 based inverter. please find the attachment for 16f72 based inverter circuit.
i'm waiting for your valuable reply.

Thanks and regards,
Karthick
[email protected]

Dear Sougata
I have been looking up your posts. I am presently working on a similar product for which i am only searching right now. its a small 110Va inverter that converts 110v Dc+/-25% to 110v AC sine wave. Thermal mnagement and low harmonics are key requirements for me to. i was wondering if you could share with me your learnings from you 2005 inerter poject! Any guidance will be helpful. I am presently struggling with the boost circuitry- WHY DO I NEED TO USE a seperate IC? as well as the output section1 9Very much basically - the entire desgn).
Can you guide?
regards
pawan.

I realy need help for inverter output regulation, i have C- code for open loop control that is working but i realise this thread is confine solely for pibasic compiler, and because the demo version is just for 50 line code. i found out that with this line of code ,no meaningful inverter code can be written.i believe this is one of the reason why issue of software is not common on this thread .is anyone ready to help from this forum?. If there is commitment from someone ,then i will post the schematics and the code.

babalola

I did some work on 18f pics with h/w pwm and closed loop control.I build pid in hardware but thas little slower.

I built a quasi sqare wave inverter with out put regulation using 16fs.

Hope I can throw some light.

Is your a natural freqency or HF.

regards,

thanks mincing for your response, my technology is a direct conversion from 24v to 220vac via a step-up transformer.
i will post the schematics/code later since i have gotten a responce from someone.

hi friends,

attached is my schematic/code .please i need help to achieve:

1: total hamonic distortion THD<3%
2:OUTPUT REGULATION OF 220VAC<+/-3%

if any one is willing to help on pibasic compiler platform, then such person can convert the code to picbasic compiler and give me the source plus hex file for onward download to the pc18f452.

regards,
babalola

Hi to all in the forum,

I will like to build up a sine wave inverter using a PIC microcontroller.
The schematic attached by Babalolo is not readable for me : can it be posted in a different format and with better resolution ?
I see a very long set of messages in the forum, Is some one capable of illustrating me briefly the status of the various projects ?
Is there a valid working project at the moment ?
Thanks a lot for the assistance.
Ambro
Iw2fvo