sine wave inverter

[alejandro]

has anyone built a sinewave inverter, I am trying to build it, double conversion( dc-dc/ dc -ac, the first stage is a dc dc converter 12 to 300 VDC and is Ok, it uses a lm3524 at 25 khz in push pull with a ferrite transformer.
The inverter is a full bridge with a 16f73 and IR2110. The transistors are irf450.
anyone has experience or has build  something like this?
thank you

[Kabron]

USe MC3PHAC from Freescale it's free. U'll save time, money and brains.

[alejandro]

Does this MC3PHAC drives ths mosfet directly?

[sam_des]

Hi, alejandro,

  I don't have experience with MC3PHAC, but I do have a lot of experience in building all types of inverters and ups(modified square and sine, push-pull and bridge). Since all of them have been designed by me as consultancy work,I can't give you much details. Still some things worth taking into consideration are as follows,

1) You can use uC for first stage's dc-dc converter also
2) Consider whether you need input power factor correction or not. If yes, that too can built into using uC
3) Decide the switching frequncies for first and second stages. Higher the freq. smaller are the filters required, but more difficult it will be to debug and design. Type of switchng you wish to use - Bipolar or unipolar.
4) Decide accuray of frequency(final filtered o/p) and voltage and upto what degree
6) What additional duties, uC must be doing.
7) Whether charger will be separate or built using same uC
What protections you wish to have.

I think if you decide to integrate all features in single uC, there is no such available.
With DSPs such DSP5680x and dsPIC this is possible, but that will be an expensive affair.

With 16f7x you can build the sine wave inverter having poor THD(12-15%) and regulation(8-10%). And very few additonal features. But that is a complicated thing, especially software part.

You wil far better off with using ATmeag8s. 1 uC for o/p regulation and protections with very fine control(<5% THD, <4-5% regulation(load). Another m8, if you desire for first stage dc-dc converter and PF correction.
You can even use same  full-bridge(used for inverter) for charger(with synchronous rectification) with very high charging currents(upto 15-17A). ATmega8 has all necessary peripherals on-chip.

1. great PWM unit  - ease of drive generation and low THD, bufferred duty change.
                              - High switching freq.
2. 10-bit ADC - very fine measurement and regulation
3. 2 Extenal interrupts for protection
4. 8 Kbyte ROM and 1kByte RAM, 512 EEPROM : can even use an RTOS
5. 16 MIPS throughput

If you wish to use still higher switching frequencies, you can use ATtiny26 which have 2 set of complementary PWMs which can have freq. upto 500kHz with 7-bit PWM. It also has differential ADCs, easing measurement issues.

Additional(& most important) benefit is that both ATmega8 and ATtiny26 are a lot cheaper than P16s and P18s. You also have 'free gcc c-compiler' for AVRs.

Some Refs:
1) Microchip's Ref Note about on-line UPS using P17, P16
2) Freescale's ref Note about on-line UPS using DSP5680x
3) Atmel's App Note for : 1. Battery charger    2. Input power factor correction

If you have any doubts, I will try my best to answer.

sam_des

[alejandro]

Thank you very much sam_des.
One question, Im trying with a 18f452, why you say that with a pic you get poor regulation? the regulation is not obtained by the dc/dc stage?
I am having many problems with the high side driver (ir2110) do you have any simplest and not expensive way to drive it?
Thank you

[sam_des]

Hi alejandro,

I said that PIC16f7x offer poor regulation because -
1) with 16 series, uC throughput is at max 4 MIPS.
2) PIC's interrupt structure sucks, with only single interrupt vector and lack of stack you simply can't handle many events that fast.
3)16 series have only 8-bit ADC.
4) PWM units are very difficult to adapt for inverter/UPS applications.
    (See Micrichip's UPS app. note)

Yes, if you use double conversion , regulation depends on dc-dc's regulation, but as I said you can also integrate that function into uC.

Now you are using 18f452, I have some things against 18s.
1) Cost - too much costly compared to m8, m88, tiny26 etc.
    (Where I live - m8 : $1.5, tiny26: $1.3 and 18f252 : $7  per piece, for even quantity orders)
2) Still only 2 interrupt vectors
3) As far as I remember, ADC of 18s is still 8-bit

Only improvement I think is their EPWM unit capable of driving half-bridge, full-bridge with programmable dead-time insertion. This can be easily generated by AVRs having 16-bit PWM units.

All depends on how much you want to integrate into uC and how much outside. How much accuracy youwant and how much other functions not directly related you want.

As for your last question - IR2110 is high-low side driver(you will need 2 IR2110s for bridge). & No, IR2110 is the most simplest method for driving bridge. As far as costs are considered, in long run IR2110 is more reliable compared to any discreet circuit(there are few circuits available). Some other companies also have high &/or low side drivers e.g. Microchip. But they more costly than IR2110.

By the way what problems are you facing with IR2110 ??

sam_des

[Rahos]

Sam_des

2) PIC's interrupt structure sucks, with only single interrupt vector and lack of stack you simply can't handle many events that fast.

I using 5 interrupt on PORTB in 16F877 and handling 5 events fast.
I can also use 20 int on pic877

[sam_des]

Hi, Rahos,

You are right that you can use 5 interrupts on PORTB. But please read what I said -
"Only single VECTOR for all Interrupts'. This is true for all PIC16s. All the interrupts will jump to '004h' and you will have to poll which of the interrupt sources caused current one.

This polling will be a major factor for interrupt latencies if interrupts are coming quiet fast.
e.g. Sine modulated PWM with frequencies above 50kHz. Remember that PIC16s donot have inbuilt PWMs which are required for Inverter/PWM application. You will have to generate dead-times & Sine modulation and at the same time you will have to monitor multiple feedbacks, execute more than one control loop like PID and regulate output. All this becomes pretty messy and difficult with Single interrupt vector. Inverter and UPS applications have other demands on CPU also. That's why I think, microchip designed EPWM unit available in some newest PIC16s and PIC18s. But here cost comes into play.

By the way, PORTB pin change interrupts have limitation - If PORTB is being accessed by a unrelated code at the precise moment PORTB pin changes then RBIF will not be set. Though this can happen rarely, we just can't leave anything to luck when we design for commercial purposes, don't we ?

sam_des

[andig]

Hi All,
 
PIC 18F452 uses a low priority and high priority interrupt structure. It gives you shadow registers (stack, w, etc) too so for fast interrupt (say a current limit protection) you can just jump to 0008H and turn of the MOSFETs. It offers two PWM units with upto 10bits of resolution with external AND circuitry they can be combined two give upto 16BIT easily. It does not have EPWM (Enhanced PWM) they are suppoerted in the higher ranges. So deadtime control has to be taken care of in software. It has a 10bit ADC which will suffice for the said application. Clocking at 40MHz gives you a maximum throughput of 10MIPS. Yes I agree in India it is costlier than the ATMEL stable. Flash is of 32K so enough space for lookup table , house keeping other function, EEPROM 256, RAM 1056. Linear addressing is another feature to ease programming. Three hardware external interrupt sources plus others from the peripheral (like port on change).
 
Best Regards
 
andig

[chandra2sekhar2000]

Hi i too looking for the same.i also waiting for both hardware and software for a 2kva ups.
thanks in advance if any guy can supply

[mpavlica]

Hello!
Consider using "PICREF-1" document from www.microchip.com (use google.com)
Of course, there is no need to use SAME PIC, u may use any other that have same or simmilar hardware possibilities.
I think that it is nice startpoint for sine-wave ups.
See ya...