Sine wave power inverter

[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... .

[sougata]

Hi Suded,

If I have understood right then you are suggesting that I build a hf oscillator around the SG3524 then use the PIC18F452 to supply the closed loop control voltage to the SG3524 (the PIC HWPWM acts as a DAC).

Now the issues are,

1. I already have two HWPWMs built into the PIC

2. The SG3524 allows dead-time programming through a simple resistor but while switching phases I again need a few logic chips to get it done.

3. I have designed the software around interrupts. I am doing an AD-Oversampling which bruce, tim and melanie suggested in the MELAB forum.For a pulse by pulse current limiting (so that the MOSFETs don't blow up) I am using a comparator to sense the current and generating an INT to turn off the MOSFET drives.(Heh! Heh! a digital copy of the SG3524 current limit scheme).
So why use the SG3524 as the ad-sample and dac conversion will add up to the loop error.

The only thing that concerns me is the THD introduced while driving inductive loads as my routines are not so fast to correct that in realtime. I tried but the results are erratic (thats because of lack of knowledge from my side). The PIC is running at 40MHz (10MIPS,10MHz@HSPLL). Now I am concentrating on reducing noise on the AD line, using interrupt based AD (PBP tends to waste time while doing AD).

BTW can anybody shed some light on the time consumed by LCDroutines. Because while processing interrupts with PBP I found glitches while the LCD was being updated.

Thanks to psdayama and doctor for the links. As far as PSPICE goes I am not sure whether my knowledge is sufficient to handle them (I don't have an engineering background)

Regards
Sougata

[mat janssen]

That's why I used a serperate pic for the display.

[sougata]

Hi there,

Yes matt. I did it earlier with two PIC18F452 communicating by the USART. What I did was adapt an asm INT UART routine to handle the remote display found from the MELABS page.

Regards

[pramodsinha]

hi saugata
i need three phase sine wave generation circuit i have the full knowledge of how to drive msosfet and igbt in three phase configuration.
pramod

Hi Suded,

If I have understood right then you are suggesting that I build a hf oscillator around the SG3524 then use the PIC18F452 to supply the closed loop control voltage to the SG3524 (the PIC HWPWM acts as a DAC).

Now the issues are,

1. I already have two HWPWMs built into the PIC

2. The SG3524 allows dead-time programming through a simple resistor but while switching phases I again need a few logic chips to get it done.

3. I have designed the software around interrupts. I am doing an AD-Oversampling which bruce, tim and melanie suggested in the MELAB forum.For a pulse by pulse current limiting (so that the MOSFETs don't blow up) I am using a comparator to sense the current and generating an INT to turn off the MOSFET drives.(Heh! Heh! a digital copy of the SG3524 current limit scheme).
So why use the SG3524 as the ad-sample and dac conversion will add up to the loop error.

The only thing that concerns me is the THD introduced while driving inductive loads as my routines are not so fast to correct that in realtime. I tried but the results are erratic (thats because of lack of knowledge from my side). The PIC is running at 40MHz (10MIPS,10MHz@HSPLL). Now I am concentrating on reducing noise on the AD line, using interrupt based AD (PBP tends to waste time while doing AD).

BTW can anybody shed some light on the time consumed by LCDroutines. Because while processing interrupts with PBP I found glitches while the LCD was being updated.

Thanks to psdayama and doctor for the links. As far as PSPICE goes I am not sure whether my knowledge is sufficient to handle them (I don't have an engineering background)

Regards
Sougata

[pramodsinha]

i went through all options to make a sine wave inverter but it was defficult to make it in basic language.

[peterdeco1]

Attached is a sinewave generator from PIC outputs going high 1 at a time. Hope this helps.

[sougata]

Hi Pramod,

Microchip has a very comprehensive appnote AN843 that demonstrates how to use a PIC18Fxxx to generate three phase PWM signals. Since the basic 18F series has onto two hardware PWMs inbuilt you have to rely on software PWM for the third. Definitely not through the Pbasic PWM function. As you are aware that designing a sine wave inverter entirely in PIC Basic is difficult (due to limited interrupt capabilities and latency issues) you have to structure your software around assembly. I am attaching a pbp source code alongwith the sinetable and firing concept. It may help. I have heavily commented the code to facilitate understanding.Let me know if it helps you out.I am sorry due professional restriction I cannot give you the entire code. But we can communicate through this forum so that other users of this forum may also benefit.

Microchip makes some special PICs in the PIC18F2331/4331 series which have an enhanced PWM hardware that supports programmable dead time. It also includes 3 or more PWMs. Coupled to that are ADCs which have a much lower conversion time. This would give you the lowest THD (tighter and faster correction loop) and still have enough room left for some housekeeping such as pulse by pulse overload limiting, overtemperature protection, line monitor, battery monitor, serial com, etc.



By the way you mentioned that you are well familier with MOSFET drive techniques.Could you enlighten me on that. May be this forum is not the right place (off topic). You can drop me a private message so that I can give you my email id.

I have desingned the MOSFET driver on a totem-pole circuitry. However I am not satisfied with the slope.I believe a steeper slope would effectively reduce switching losses. I tried MOSFET drivers from Microchip too but they blew up. Possibly due to latch up or improper grounding of the PCB traces. They are costly too here in Kolkata. Photovoltaic drivers with active discharge is not available here in Kolkata. Also I need to understand why my MOSFETs blew up during initial testing phase while the inverter was unloaded.

regards

Sougata

[wire042]

Please am having problem with my inverter that is posted on this forum on page 5.

[iw2fvo]

No chance to have something working on this forum expecially for the inverters or MPPT .
It should be an homebrewers or do it youself forum... but it is not.
Ambrogio

[psdayama]

Hi Saugata,
I think that for controlling the amplitude a hardware approach is better
as so many delays and errors can creep in. There is a Buck Boost circuit with
two mosfets and an inductor and few diodes. The DC input to H bridge can be
controlled with B/B circuit with reqd. time delays generated by Micro output(which doesn't have to be so fast as changing per cycle of sinewave)
The shape and frequency then can be generated by normal 2 PWM outputs(Actually one is enough just route the output to another branch with a gate and this also have dead time built in).
I still wonder why anybody is not responding about my querry of transformers. The output of Inverter is serries of pulses at high frequencies with polarity reversal at 50-60 Hz. So is the transformer used designed for
50 Hz operation or high frequency like say 20KHz? There is huge difference
in size of transformers.
regards,
purushottam dayama

Hi Suded,

If I have understood right then you are suggesting that I build a hf oscillator around the SG3524 then use the PIC18F452 to supply the closed loop control voltage to the SG3524 (the PIC HWPWM acts as a DAC).

Now the issues are,

1. I already have two HWPWMs built into the PIC

2. The SG3524 allows dead-time programming through a simple resistor but while switching phases I again need a few logic chips to get it done.

3. I have designed the software around interrupts. I am doing an AD-Oversampling which bruce, tim and melanie suggested in the MELAB forum.For a pulse by pulse current limiting (so that the MOSFETs don't blow up) I am using a comparator to sense the current and generating an INT to turn off the MOSFET drives.(Heh! Heh! a digital copy of the SG3524 current limit scheme).
So why use the SG3524 as the ad-sample and dac conversion will add up to the loop error.

The only thing that concerns me is the THD introduced while driving inductive loads as my routines are not so fast to correct that in realtime. I tried but the results are erratic (thats because of lack of knowledge from my side). The PIC is running at 40MHz (10MIPS,10MHz@HSPLL). Now I am concentrating on reducing noise on the AD line, using interrupt based AD (PBP tends to waste time while doing AD).

BTW can anybody shed some light on the time consumed by LCDroutines. Because while processing interrupts with PBP I found glitches while the LCD was being updated.

Thanks to psdayama and doctor for the links. As far as PSPICE goes I am not sure whether my knowledge is sufficient to handle them (I don't have an engineering background)

Regards
Sougata

[sougata]

Hi Dayama,

You are right that only a single PWM can be used and done exactly the same. It is modulated with a sine table (32 samples). The transformer needed is a 50Hz type. The transformer, output choke and capacitors form a low pass filter (actually the sinewave is integrated) and the output waveform is a sinewave.

Your approach of using a B/B converter would rather complicate things up and also be costly. That is basically a dual conversion design if I understood right. With a MCU you can tune , upgrade your design without actually increasing the production cost. If you are in India then you may be aware of the latest buzz of "DSP" sinewave inverter. Here the approach is same.However a DSP gives you much better ADs and fast computation with dedicated hardwares (for e.g a 32 x 32 Multiply) so you can keep your sinewave undistorted with inductive or mixed load.

I could not post the whole code due to professional restriction but here is what it does :

1. On Interrupt it fetches the sinetable vaue (indexed) for PWM

2. Offset it with ERROR from previous and current sample (a PID style error loop)

3. Turn on the MOSFETs with the calculated value.

What I don't do is dynamically correct a voltage error in the same index pointer. My ADC conversion time does not allow me to do that. To mess up things more I actually take 4 samples and do and average to deal with noise. Then I have a nifty LCD routine, a battery monitor, RS232 interface (to shutdown my computer and inverter when not needed)

BTW where is Pramod who kicked this thread into existence again.

Regards

Sougata

[sougata]

Hi Dayama,

It is possible to reduce the size of the transformer. Looks like a class-d amp solution to me. A simple filter would reconstruct the sinewave and remove the HF component.Did you find anything or anyone having done it on the net. I will also search and probably would like to develop one. But some practical start point is needed.

Regards

Sougata

[psdayama]

Here is the link:They make readymade PWM amplifiers but don't ask cost!!!!!
http://eportal.apexmicrotech.com/mai...m_overview.asp

I asked their reps in Mumbai and they said each IC costs Rs.25,000/-
But one can make PWM output like that and then have just High freq. txr or
direct output with filter.
regards,
Dayama

Hi Dayama,

It is possible to reduce the size of the transformer. Looks like a class-d amp solution to me. A simple filter would reconstruct the sinewave and remove the HF component.Did you find anything or anyone having done it on the net. I will also search and probably would like to develop one. But some practical start point is needed.

Regards

Sougata

[psdayama]

Hello everybody (Saugata,Mel xxxx)
I wonder why there is no activity here since last month!
I have just now made a inverter of Delhi type with sinewave output.
The transformer for 500VA output is whopping 10kg in weight.
You all may be discussing sine wave with PIC but practically
there is no use if such big transformers have to be used and adding
to cost about 60% of the project.
I have hit an idea to circumvate this and will discuss if anybody
is interested.
HAPPY DIWALI!!
dayama

[Panzer]

Hi Saugata,
....
I still wonder why anybody is not responding about my querry of transformers. The output of Inverter is serries of pulses at high frequencies with polarity reversal at 50-60 Hz. So is the transformer used designed for
50 Hz operation or high frequency like say 20KHz? There is huge difference
in size of transformers.
regards,
purushottam dayama

Hi psdayama,
As the inverter is working as D class Amp - the end of the MOSFER matrix must be smooth with low-pass filter. Then you will have a nice sine wave only 50 Hz - and the transformer will work nice.
If you are trying to combine the transformer to be puss one over the 20KHz then will become some more complex and for sure the PIC as a 8-bit machine will be not enought.
The usual case is using a schematic of push-pull converter (as 3525) for rising the voltage level to 30% over the output one and then to converted to AC with MOST matrix only.
This way will save you a lot of pain in the ass.
WBR
Panzer

[maviblue47]

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

[iw2fvo]

Hi to all in the forum and to Sougata,

I am still waiting for a complete project for a sine wave inverter ... it will be a replicable one.
I will like to implement it.
Any new since this long time ?
Thanks for any help.
Regards,
Ambrogio