Sine wave power inverter

[babalola]

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.

[sougata]

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.

[samrulezzz]

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]

[sougata]

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 !!!!!!!!!!!

[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.

[picgak]

Hi sougatha and Thank you,
I have been a regular visitor to the Thread sine wave power inverter for a long
time. I am happy to get a reply for my first query from one of the experienced hands. My
knowledge of PIC programming is minimal. I got the inspiration to do this project for my
home from here. Can you kindly suggest me a link to learn PICBASIC commands in some detail.

[sougata]

Hi,
With the above diagram. The Bridge Rectifier part from the AC mains turns it into an online UPS and needs to be controlled type for steady DC Bus Voltage. As already mentioned if the DC bus voltage is kept steady the output would also be steady.
Regarding PICbasic Pro, I learnt everything from this forum and owe all the contributors a lot. Best is take up one programming challenge at a time and get a grip on the concepts involved. This forum is a life-saver. I do not do basic much still while searching information this is the first place I take a peek.
Good Luck.

[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.

[samrulezzz]

hi Sougata


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

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

[sougata]

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.


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.

[picgak]

hi
I want to make a sine wave inverter with 310 vdc H bridge as the final stage driven by signal from sine tabled PWM from PIC microcontroler. can anybody suggest me a cheap and best controller from the pic family.

[sougata]

Hi,
A PIC16F616 could be a good choice or even better a PIC16F1824 The later runs at 32MHz has ECCP and supports linear addressing and shadow registers for fast interrupt return.
Since you would be having a High Voltage DC Bus it is easy to keep it regulated / overcurrent protected and simply drive the output bridge using a micro though a sine table. The only complication could be isolation between the battery boost and the output stage if the same micro is used for housekeeping too.

P.S. - Personally I would have selected a PIC18F1330.