Does Inverters in VFDs for ( 3 phase Induction motor) use PWM or Modified Sine Wave ?

[atifsheikh_91]

Hello All!

I am making a project on 3 phase induction motor drives , for this I require an inverter to convert DC\[\to\] AC . I am a bit confused that should the inverter be PWM based or it should be modified sine wave inverter ?

My aim is to save energy in AC motors ., so which inverter will suite my design?

Regards.

 

[kak111]

The usual method used to achieve variable motor voltage is pulse-width modulation (PWM). With PWM voltage control, the inverter switches are used to construct a quasi-sinusoidal output waveform by a series of narrow voltage pulses with pseudosinusoidal varying pulse durations.

AC motor characteristics require the applied voltage to be proportionally adjusted whenever the frequency is changed in order to deliver the rated torque. For example, if a motor is designed to operate at 460 volts at 60 Hz, the applied voltage must be reduced to 230 volts when the frequency is reduced to 30 Hz. Thus the ratio of volts per hertz must be regulated to a constant value (460/60 = 7.67 V/Hz in this case). For optimum performance, some further voltage adjustment may be necessary especially at low speeds, but constant volts per hertz is the general rule. This ratio can be changed in order to change the torque delivered by the motor.

In addition to this simple volts per hertz control more advanced control methods such as vector control and direct torque control (DTC) exist. These methods adjust the motor voltage in such a way that the magnetic flux and mechanical torque of the motor can be precisely controlled.
(Wikipedia)

Variable-frequency drive - Wikipedia, the free encyclopedia

**broken link removed**

 

[atifsheikh_91]

In addition to this simple volts per hertz control more advanced control methods such as vector control and direct torque control (DTC) exist. These methods adjust the motor voltage in such a way that the magnetic flux and mechanical torque of the motor can be precisely controlled.
(Wikipedia)

thanks Kak111 ; please can you much more elaborate me about vector control and DTC, .. can u help me in my project of VFD , in this project i am also doing Active Power Factor correction...

If I go for PWM rather than modified sine wave inverter than would it be also a feasible solution ?...

Can you give me reference of few practical approach to books or papers.

Regards.

 

[Tahmid]

Hi,
The most common method is to use sinusoidal pulse width modulation (SPWM), ie PWM (square wave signals where you continuously vary duty cycle according) is used to generate a sinusoidal wave shape.

For control of speed, a simple and common method is constant V/F drive.
You can read these documents:
ww1.microchip.com/downloads/en/AppNotes/00843a.pdf
ww1.microchip.com/downloads/en/AppNotes/00887a.pdf
ww1.microchip.com/downloads/en/AppNotes/00967A.pdf
www.atmel.com/dyn/resources/prod_documents/doc7545.pdf

Check out this thread: https://www.edaboard.com/threads/142271/

Which microcontroller do you plan to use? I've made a simple inverter with a dsPIC33MC although it never went on to completion, but the motor control was nice. Using a dsPIC33MC for motor control is pretty easy once you get the hang of things, since it is specialized for such application.

Hope this helps.
Tahmid.

 

[kak111]

I'm not very deeply specialized to the finest details in circuit implementations of VDF´s
I think other guys can teach and help you better than me.

But here is something to read....

3-Phase AC Induction Motor : Look these...
--Application Notes
--Reference Designs
--AC Induction Motor Basics

Motor Control 3-Phase AC Induction Motor Solutions By Freescale

3-Phase AC Motor Control with V/Hz Speed Closed Loop Using the 56F800/E
http://cache.freescale.com/files/dsp/doc/app_note/AN1958.pdf

Vector Control of a 3-Phase AC Induction Motor Using the Z8FMC16100 MCU
http://www.zilog.com/docs/z8encoremc/appnotes/AN0247.pdf

TMPM370 product series - 3-phase BLDC Vector Motor Control
**broken link removed**

Implementing Embedded Speed Control for AC Induction Motors
http://am.renesas.com/media/products/mpumcu/child/Renesas_Jani_Seminar.pdf

Block Diagram (SBD) - Motor Control: AC Induction - TI.com

and google finds more eg. "3-phase ac motor drive application" or "3-phase induction motor controller mcu"

KAK

 

[atifsheikh_91]

I have 3 phase motor or .25kW 220v/1Amps ; for such moderate rating sould i used MOSFETs BJTs or IGBTs.. which offers more bright career ? and least consumptions of wattage?

And one more question to ask.. IRFz44n has pwr rating of 60W , what it means ? Does it means that this MOS will always consume 60W ?

 

[Tahmid]

At this power rating, I think MOSFET is best.

---------- Post added at 00:31 ---------- Previous post was at 00:29 ----------

This means that it can dissipate maximum 60W energy. If you can fully turn on the MOSFET (applying >8(to 10)V at the gate), the conduction loss in the MOSFET = I²R - I being the current through the MOSFET and R being the on-state drain-to-source resistance [Rds(ON) specified in the datasheet]. The total loss would be slightly higher than the conduction loss (total loss includes other losses such as switching loss).

---------- Post added at 00:33 ---------- Previous post was at 00:31 ----------

You can not use IRFZ44N as the maximum drain-to-source voltage it can withstand is 55V. So, if you convert 220V to DC, it becomes 220√2 = 311VDC. This will almost instantly destroy the IRFZ44N.

Hope this helps.
Tahmid.

---------- Post added at 00:37 ---------- Previous post was at 00:33 ----------

MOSFETs are better than BJTs (especially at higher voltages) because they usually require lower current than BJTs for turning on, but more importantly have lower loss as the power dissipation across a BJT is likely to be higher as it has a pretty large VCE saturation voltage which results in a higher loss (usually) than that in a MOSFET. IGBTs are better than BJTs in this respect, but I don't think you will benefit much from using IGBTs at such low powers.

By the way, IRFZ44N has a maximum power dissipation value of 94W @ 25°C (from the IR datasheet).

Hope this helps.
Tahmid.

 

[atifsheikh_91]

You can not use IRFZ44N as the maximum drain-to-source voltage it can withstand is 55V. So, if you convert 220V to DC, it becomes 220√2 = 311VDC. This will almost instantly destroy the IRFZ44N.

So what will u use if u were in my place :? IGBTs or MOSFETS

Another question to ask; If i use MOSFETS than the IR2111 is better or IR2110 as a gate driver IC, I know that IR2111 has all it has to drive the MOSFETs but its turn on and turn off time is very large as compare to IR2110.

Regards
Atif

 

[Tahmid]

At this low power, I would choose MOSFET. Did you select any MOSFET to use here?

I would choose IR2110 as it has better switching times and gives you individual control of the high and low side MOSFETs.

Hope this helps.
Tahmid.

 

[atifsheikh_91]

At this low power, I would choose MOSFET. Did you select any MOSFET to use here?

i am thinking to work on irf840. is it fi9 to work with?

My freinds are working on the motor of 1.5kW should they use IGBTs or MOS?

 

[Tahmid]

At 1.5kW, you can use MOSFETs. No problem. IGBTs are fine as well. If you plan to use a higher frequency, MOSFET is better.

You previously stated that current is 1A. IRF840 is okay for this, since it's rated for 8A. If nominal current is 1A, max current should be within limits of the IRF840. Make sure you drive it properly.

Which microcontroller are you using? How to you plan to drive the MOSFETs?

 

[Rose Wesley]

I am using a Toshiba micro controller for my Toshiba drives and seems just working fine with my VFDs