Sine wave power inverter

[sougata]

Hi PICers,

I want to design a 24V DC to 50Hz/240AC power inverter. My choice of PIC is the 18F452 (HWPWM). But I am not sure whether the ADC conversion time would be short enough for dynamic correction.

Any thoughts

Regards

Sougata
The Andig Technologies

[NavMicroSystems]

Sougata,

I don't think a PIC is the right choice.

I would use one of the SMPS-Controllers that are designed for this this kind of application.

[sougata]

Dear Ralph,

Thanks for the reply. I don't know which SMPS controller your are talking about. But if you are talking about PWM controllers like SG3524/25 or even TC140 from the microchip family then I am afraid the only possibility of generating a sine wave is a resonant tank at the secondary side. I am talking about weighted sine through PWM lookup table. The Hardware PWM coupled with high speed would be choice. The trend is using DSP (from TI or AD) which have onboard peripherals specially useful for this type of applications. There are a family of PICs which has EPWM (enhanced) circuitry onboard but recent ones are not supported by pbp and I am not so conversant with either asm or C. In fact microchip had an appnote using the 17C familiy for an online UPS. You can go through AC induction motor appnotes to understand what I mean

Regards

[mat janssen]

I made once a ac generator which was capable for automatic syncronising with an external signal for 45 till 65 Hz (zero crossing) and it had an output from 0 to 230V sinewave (input 0-10V). I used a pic16F873 on 20Mhz. So it is possible. I cannot give you the source because I made some promissis about the it for not given the design away. I say it is possible, just try !

[sougata]

Hi there,

What I have planned is having a sinelook up table calling periodically through timer overflow interrupt and a closed loop voltage monitoring to adjust the value of the lookup table on the fly to minimize voltage drifts and sinewave distortion. Now the problem is that the PIC takes altleast 21us for the ad conversion then comes the calculation part. Also I am unsure which PWM freq. to use (over audible range) and how to design the parallel mosfet power output stage. For overload protection I am going to use a different comparator and do a pulse by pulse limitimg through high priority interrupts. What is the best way to protect the mosfets. I don't know how to design a RCD snubber but my scope shows ringing and peaks during switch off in a normal square wave design. I beleive they are the reason for MOSFET heat up. I have searched and read quite a lot appnotes from SOA limiting to optimizing gate drive but still experience counts. So if anybody out there please help. By the way mat I don' t want a word from your source can you at least guide on the flow.

Regards

Sougata

[mat janssen]

I will draw a block diagram and I will post it here.

[psdayama]

I have found other site which is better than one I was telling about:
http://www.oldradioz.com/manuals/rdh4/

After going thru the Table of contents only Chapter 5 & 6 are
concerned with Transformers. Other are for Valve radios & components.
It is excellent material for those who may not have seen valves intheir
lifetime.
I suppose that there are few more sites which have design guides
for transformers and inductors using ferrite cores which will be found
in most recents equipments.

[suded]

Dear Sougota,
You are possibly trying to use the Micro (PIC XXXXX) as part of the control loop to regulate the amplitude of your sine wave.
The alternbative approach is to build the control loop around SG 3524 PWM control IC & use you PIC XXXX micro to supply the set point to SG 3524.
SG 3524 will provide you with a very fast control action with minimum No. of components.
The point of using PIC micro in your application is to generate variable amplitude variable frequency sine wave using the PWM command in PIC Basic Pro.
You can also use a normal iron core transformer to check the results then convert to ferrite the ferrite core will icrease the effiiciency of your design.
A center tapped transformer is a good choice!!!
Reagrds.
Suded.

[Doctor]

For Simulation of power circuit and also recognized
in most universities is the PSPICE software;you
could find the software and the environmental package
in the following two sites:

http://www.ousetech.co.uk/winspice2/index.html
http://www.5spice.com/

all you need in power designing in addition to snubbers
simulations, etc... .

[maviblue47]

thanks all. but i need sine wave schema for pic16f84 and inverter

[MKA341]

your design is very good, can you give me some idea about making a inverter by using pic basic?

Hi PICers,

I want to design a 24V DC to 50Hz/240AC power inverter. My choice of PIC is the 18F452 (HWPWM). But I am not sure whether the ADC conversion time would be short enough for dynamic correction.

Any thoughts

Regards

Sougata
The Andig Technologies

[sougata]

Hi,

Manish originally the inverter was built ono the PIC18F452 and had loads of features like true synchronized changeover using MOSFET based static switches to perform like a pseudo online UPS. Actually it was an adaptation of my motor control system using 18F4331. However the BOM cost was high so it was scaled dowm to mimic other designs already based on 16F72. Uses a pseudo software PWM. (Utilizes the inbuilt unit in compare mode to generate int and fire mosfets). Half-Bridge driving and a half cycle boost PFC for charging control. Vertical-Horizontal current based lookup table to get precalculated points (16F series do not support harware multiply). Most of the credit goes to Mr. Pramod Sinha of Jetmark Systems Delhi cause my 16F skill sucks. We could not share the code as it is a commercial project and we are legally binded. For clarifications and solving issues this forum is a great place and people (far far better than myself, Perhaps) would surely help you out. Best of luck. Where are you located in Delhi, I drop in there almost every month and stay in A6 Paschim Vihar.

[pramodsinha]

I have written a sine wave generating routine in pbp. It is tested.but i am too busy because summer is my business season give me few days to edit and post it to forum.
thanks everybody.

[Pranav Verma]

[QUOTE=sougata;35864]Hi,

I am devloping a proogramm for inverter,but i need some helps, More over i have devloped the programm on theory.but in practical i have some problem

i have genrate 50 Hz frequency by a loop and delay.Out Put is Ok but when put load about 100 wats on it
the output voltage go down more tahn 40 volts.

Please help me to do it in write way, I am the lerner and new in the are of pic programming.

Please helps me

[sougata]

Hi,

You need to modulate your sinewave according to a modulation index (that increases decreases the output voltage) derived from the error. Inititally a proportional error scheme is okay to experiment with later can add up to PID. In addition you can do a point by point correction to lower distortion. In 16Fs multiply is not supported in Hardware thus a different approach may be taken. Use a sliding lookup table. Here you have more number of points in the lookup table than regular 32/64 points. However it should be a single quadrant lookup table. Now if the resolution of the lookup table is increased you can have a sliding index (according to error) to have voltage correction without much software overhead.

[babalola]

since no one would review my c-code on this subject, ih have decided to modified suogata bacis code on sine wave inverter thread. i am using PIC16F72 for the evaluation because that is the processor that is readily available with me now.

The picbasic iam using is the pro demo version and so i appriciate that i can't run a code more than 31 command line.however upon trying to compile the code ,the following erros are reported:

1: Error line 116 :redefinition of label T0CON

2: Error line 119: bad expression

3: Demo limit of 31 command line exceeded (this is understood)

pls, can any one fix these problem for me?.

(a): With the way the modified code stands,can it generate two complimentary sine pwm signals DRIVE1& DRIVE2?.if yes how do i include a delay routine of about 470ns for dead-time control between the two signals?

(b): If the code cannot generate the two complimentary sinepwm signals what do i do to fix the stuff?.

regards,
babalola.

[mincing]

dear Sougata,

i am working on similar pic based inverter too.Could you please tell me which topology are you using for inveter bridge.

I am working on H-bridge.Have difficulty in Identifiying the brdge drivers.

It would be great if you could help me on transformer desin.

[Rishi]

Hello friends I am power electronics enggineer having experience of 7 years plus.
presently i am working on double conversion inverters.

[mat janssen]

Hallo Rishi. Can you post the schema and the code for this? All of us will learn about this subject!

[Navneet Vinaik]

Dear Mincing,

Thanks for your reply, and sorry for the delay.

I want to understand the technicalities involved in designing systems on ferrites. To be precise, what would be the kind of drive systems, snubbers, clamps and most important transformer design in case of ferrite based systems.
I would be grateful if you could provide me some details etc.

Regards

Navneet Vinaik

[mincing]

Dear Mincing,

Thanks for your reply, and sorry for the delay.

I want to understand the technicalities involved in designing systems on ferrites. To be precise, what would be the kind of drive systems, snubbers, clamps and most important transformer design in case of ferrite based systems.
I would be grateful if you could provide me some details etc.

Regards

Navneet Vinaik

could you Pl. give me your mail ID ,I will forward some documents!

[Navneet Vinaik]

Dear Mincing,

Thanks a lot for your helping hand...
My email ID is [email protected]; [email protected]

I am pretty confident that I can build a good quality HF inverter, presently busy in getting all the tools ready...I have an old oscilloscope which has served us for the past 45 years but for this technology I am arranging resources to get a DSO among others tools.
Please send me whatever help that you can, I would be grateful to you as it will help be do my homework before I get into the battlefield!!!

[Rishi]

Hallo Rishi. Can you post the schema and the code for this? All of us will learn about this subject!

hello mat

Yes i will send u details but it will take some time.

i have design 12v/24v dc to 350v dc converter with analog ic sg3525 and already
achieve effeciency more then 90%.

[sougata]

Hi everybody,

I have been greatly helped by this site http://schmidt-walter.fbe.fh-darmsta..._e/smps_e.html . It is the english version of the original german site by the author. Great work, great javascript based smps calculator.

I hope things become easier right now.

Regular bread and butter (hard to earn in my city ) jobs leave me almost no time to work on this project. But seeing this thread still kicking does give me some inspiration.

Thanks to everybody who contributed to this thread.

[BrianT]

Take a look at Don Lancaster's site at www.tinaja.com. Search for MAGIC SINEWAVES and you will find information on how to build very low harmonic sinewaves.

HTH

Brian

[sanjay_9991]

if any one willing to share pic based sinewave upscum inverter design can plz contact me

[walkura]

I was reading the posts in this topic and maybe i'm a bit late with my reply ,but i just found this forum .
The flux imbalance problem i saw mentioned before is something i know from smps designing .
Especialy in transistor push pull it can be a nasty subtle failure (with mosfets you have this problem already a lot less but i get back to that) .
The essence of flux imbalance is this you start at the 0 Gauss point ,gate 1 opens mosfet1 for x time transporting an amount of charge of x (m)Joule inducing a magnetic fieldstrength of x Gauss in you're core (depending on the frequency usualy between 1200 to 2000 +-) .
When for some reason there is a difference in
A : timing (Volt-second imbalance) better said (pulse 1 is shorter/longer then pulse 2 (technicaly impossible with 3525 etc. but homebrew program's might have different idea's)
B : while making you're ferrite you wound more on 1 of the windings .
In either of these cases pulse 1 will create a certain amount of Gauss and pulse 2 is not making exactly the same amount magnetic fieldstrength (youre core doenst get as much Gauss down as it went up).
The result is that you're core slowly accumulates that little remainder of fieldstrength after a x amount of pulses it runs into the flat part of the curve the core is so called saturated and according to Faradays law it can't support the magnetic field you're induction (ac resistance) drops to almost 0 Ohm destroying you're transistors .
From what i saw everyone here used mosfets ,in this aspect it suprises me a little you mention fluximbalance .
A normal transistor has a negative temperature coeeficient (this will increase the destruction speed in imbalanced transformers)
Mosfets however are the opposit when you have a imbalance one mosfet gets warmer its resistance increases and amount of joules delivered to the coil(core) go's down .
I hope this explained in normal human words the concept of flux imbalance .
For the people that want the more in depth story i would advice read the book from pressman called switch mode powersupply design .
This book offers in relative understandable language the concept and theory on +-15 topology's (not to mention good chapters on magnetics ,feedback & gatedriving etc. etc.)


Last summer i tryed a pwm sine inverter but lack of time froze the project for now .
Although i did have it working low power it never came out of experimental fase.
You may call me nuts but i did it with a st7lite25 + pushpull stage ,second order chebchev filter.
Next round will be sg3525 (for generation of 500 watt +- 310 volt) sync. rectification ,half bridge pwm stage + lc filter like you would expect in a class D amplifier .
(my last setup worked very well in low powers but what with 500 or 1000 watt ,how to filter?)

Good luck with youre inverters everyone

[sougata]

Hi,

That was a great explanation walkura and thanks for the "human" explanation. Now I would try to dig into the software aspects a little. I am a complete self taught and know my lackings, so please correct me if I am conceptually wrong.

• While changing cycles within the software the loop latency may be variable if you are not using your own asm interrupts to deal with that. Since this is all about PBP my recommendations are for time critical routines use asm. As already proved asm+PBP=muscle. Considering a round-robin multitasking with no blocking codes would ensure specific time slots alloted to different routine on priority basis.
• Your load is imbalanced. I have seen a few cheap soldering irons which has a single diode inside them. Causing to draw current in only cylce.
• For ease of manufacturing I have seen MOSFETs on a common heatsink. This reduces a per channel MOSFET Rds-On difference and thus should be avoided for a stable design and utilize the MOSFETs property of negative temperature co-efficient for balancing.
• Per cycle flux reset may be applied during the dead-time with its own pros-cons (may not be applicable for ZVT implementation)
• Since the current drawn per cycle is also a function of the impedance it may be accomodated in software as well as almost all hardware designs support current sensing.
• Sometimes ADC based current sensing can take longer to come into action and kill your MOSFETs. So my advice is use a comparator based sensing to quickly turn-off your MOSFETs under fault conditions and use the current sense for your other tasks or PID.
• If you are into serious intelligent smps design then consider the dsPIC (No PBP support however). Your tasks become real easy for only smps implementation.

[mincing]

Hi all,
NOw I have completed quite a bit.yet there are two issues that are still dogging me.
1.Output stabitity,
2.Heat at no load( the power dissipation)

The output sine wave is quite stable as long as the system does not enter the closed loop.
Once it enters there is a continuous up/down swing of out put voltage and sine wave.

We could control it to quite a bit by putting a PI controller before the feed back.
still there is a fluctuation of about5 to 6 volts.


2.heat is toomuch.the no load currnent of the unit is 2A at 24V and when added with more during loading,i am afraid I can run unit like this.
any suggestions are welcome!

[sougata]

Hi Mincing,

Sorry for the late reply. I really do not get time (or get into weired problems) to log into this forum. Without specific details about your circuit like schematic, code it is impossible to suggest anything.

[Pranav Verma]

Hi PICers,

I want to design a 24V DC to 50Hz/240AC power inverter. My choice of PIC is the 18F452 (HWPWM). But I am not sure whether the ADC conversion time would be short enough for dynamic correction.

Any thoughts

Regards

Sougata
The Andig Technologies

Hi sougata,

i wants to devolope a programm for inverter which will suitable for microtek square wave inverter, i have done the invertring section,overload section and battery low section,but there was problem with the charging section.

in the circuit mains Freuency sample is avilavle at portc.
in our programm having the vivration at the time of charging.

Hence it is request to u that pl help me and give the write logic for charging section.


Thanking u.
Pranav.

[Pawanbahl]

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.

[babalola]

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

[mincing]

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,

[babalola]

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.

[babalola]

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