Could you explain a little bit more
Hi Matt,
I will work the other way round. Rather I would try to post a flow chart (I am not so good at it) so that you and other members can go through it to detect any possible flaws or betterment suggestions. BTW thanks for the block. I was out-of town hence the delay in reply
Regards
Sougata
I have my own transformer manufacturing unit
Hi Matt,
I understand your concern but I am hopeful here since I have got my own transformer manufacturing unit. So from paper to product and fine tuning issues I have got a plus point over here.However I am not sure of the actual losses and bulk of the design for practical use so I might need to design a battery boost circuit.
Regards
Sougata
I will send you my final design
Okay Matt,
That would be great. I need to design a RCD snubber and I don't know the maths may be you can help. I am concerned about the switch off peaks.
I would send you the entire schematic as soon as I finish it up. It will take some time but I will keep in touch.
Regards
Sougata
Is there any better site?
Im trying to download the CHAPTERS from the site.But it is extremely difficult to open.Going to home page most links are not correct and site is under renewal.Can anybody be please send link to mirror site(s)?
Thanks in advance.
Also please let me know if anybody has used transformer after the H-Bridge and whether the operating frquency of transformer supposed to be output sinewave or the switching frequency? In case the fequency is that of output,
then we loose advantage of switching and having small transformers like in smps.
Quote:
Originally Posted by Melanie
As an aside... talking about Transformers... the 50 year Copyright (1953) has expired on the Radiotron Designers Handbook. I use this as my bible for
Transformer Design and it's abosolutely brilliant - the principles in design are as valid today as they were back then. You can download it from the internet from various places (including the link below) - but be warned it's about 70Mb total pdf...
http://elysiansound.com/goo.php
Most Transformer manufacturers have forgotten most of this stuff (and it reflects in the abysmal products they produce). So, if you're into rolling your own (or commercially designing), then you'll love this, if you're not, then it's a sure cure for insomnia.
Power Design circuitery simulations
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... .
I didn't get the issue of the SG3524
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
1 Attachment(s)
Go through the M'CHIP Appnotes
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
I didn't get the issue of the SG3524
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
Quote:
Originally Posted by 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
Have you seen the code at all
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
1 Attachment(s)
Have you seen the code at all
Dear Sougata,
I haven't seen the entire code at all but just one table of delays for
sinewave. Also I have faint recollection of the block diagram.
Truly speaking Im not much PIC er. Im doing everything with ATMEL
micros. I have found this forum while searching for sinewave inverter.
I think it doesn't matter which company U use but design is more importatnt.
So I can understand code very well.
I also have Transformer Unit but it is for HT Instrumentation type.
I think that varying amplitude with delays and error adding will work only
maximum upto 70% of basic amplitude. After that U will have gross THD due
to most of delays at zero crossing very small.(It appears in class D amplifiers
of analog kind). I haven't seen whether such approach works with truly
variable amplitude or from 0 to 120% of the amplitude.
What I m saying is not double conversion but switchng of Buck Boost
mosfets with 2 ports from same PIC outputs and CORRECT amplitude there.(See attached bmp file.) In this s1 and s2 are mosfets whose timings is controlled to vary the voltage.
Im in India but near Mumbai so here not much Inverter brouhaha is there.
Melanie has agreed that this DSP method is not so good although everybody
is claiming otherwise.
I am also looking for design in which there should be no such bulky
transformer of 50Hz. If I have read right then proper driving of mosfets
would result in 20-40Khz output which is double modulated. this can use
high frequency transformer with centre tapped secondary and demodulator cum filter circuit which will give 50Hz output!!
As presently the transformer is costing about 50% of the total invertor
cost and one can imagine savings. Also as many circuits are having SMPS type charger for battery the advantage is obivious.(Compare APLAB 30V 1A
regulated supply with 250W computer smps,)
Hope to have more discussion on this.
regards,
dayama