PWM frequency for high power DC motor

[sabri]

I want control a high power DC motor.
Refer to discussions in this useful forum ,I understand that PWM method is the best way.I construct PWM pulses ,but i have two problem with it:
1) With microcontrollers(PIC) I construct PWM pulses with 5Volt amplitude ,But i need 250Volt amplitude to setup the DC motor.How i can convert/switch 5Volt PWM to 250Volt??
2) Which PWM pulses Frequency is better to setup the DC motores?

Thanks.[/b]

 

[mostafa0020]

choosing a pwm frequency

dear sabri
u have generated the "driving" pulses of the power circuit,the power circuit id the circuit that deals with high voltage,high current and high power ratings,the coupling is acheived through electronic switches trigged by this driving"firing"circuit,for DC motor control while u ask about frequency of PWM pulses,this means that u use a DC-Chopper=DC-DC Converter,MOSFETS,IGBT's are the best electronic switches for medium high power,as it they r voltage controlled switches,means no need for a slaved current source to trigger it,like BJT's.
The frequency of operation is determined i think by the required duty cycle,mode of operation"continuity or discontinuity of current" which is a function of DC motor inductance and resistance,and the freewheeling diode too.

 

[nicleo]

motor pwm frequency

Something to add. Pls refer the figure in attachment.

The driving circuit block includes the circuit that generates PWM pulses. These pulses will be connected to driver to amplify the power (not voltage) so that it can supply sufficient peak current to drive high-power switches. The out of the driving circuit block will be 5V or 15V PWM pulses that is capable of driving high-power switches.

H1, H2, L1, and L2 are high-power voltage-controlled switches/transistors (e.g. as mentioned by mostafa0020, MOSFETS, IGBT, etc). These switches, for example, can switch 600V/200A.

Besides the factors mentioned by mostafa0020, some designer prefers to use PWM frequency higher than 20kHz (FYI, 20Hz ~ 20kHz is the audible range of human ear).

 

[btbass]

choice frequency pwm motor

Also look at IR (International Rectifier) website, they have high side drivers, low side drivers and full bridge drivers to interface between the micro and the IGBT. (IgBots!). There are also a lot of application notes to look at.
A common frequency to use is 16KHz. This can only be heard by bats, dogs and young children. The higher the frequency, more problems with drive and switching losses.

 

[nicleo]

igbt micro pulses

A little bit offtopic ...

Where does the audible sound from? From the wound devices (e.g. motor, inductor, etc) or the power switch?

 

[btbass]

common pwm frequency

The coils sing when you pass power through them switched at high frequency, also, any metal with a resonance close to the switching frequency will ring if it is magnetic. In fact, the whole thing is pulsing with powerful magnetic fields!

 

[flatulent]

best pwm frequency for the motor

The official term for this generation of sound is magnetostriction. It is the magnetic equivalent of piezoelectricity. The dimensions of the metal parts change with magnetic field.

 

[mostafa0020]

drive pwm frequency

by the way,i want to know differences between high side drivers & low side drivers.
I saw them while i searched for MOSFET drivers,but,i have no idea about its configuration nor operation

 

[nicleo]

choice of pwm frequency for motor control

by the way,i want to know differences between high side drivers & low side drivers.
I saw them while i searched for MOSFET drivers,but,i have no idea about its configuration nor operation

MOSFET is voltage-controlled switch. To turn on the switch, VGS (VG - VS) must be higher than a threshold value (e.g. 5V). If the driving circuit (and hence driving signal) shares the same negative (common or ground) rail of the +/- power supply, the lower switch can be turned on as usual because VS (S = source) is also the V- of the power supply. However, for higher switch (HS1 and HS2), the story is different. VF1 is not V-, but equal to V+ minus VDS when HS1 is turned on. In this case, VGS is no longer correct to drive the switch. Also, there will be a short circuit or high current flow from F1 to V-. To solve this problem, we can use optocoupler or signal transformer to isolate the VF1 from V-. Another way is using bootstrap method.

 

[btbass]

pwm frequency high side driver

The low side driver is as it says, to drive the low side of the output stage, the high side driver has a few more problems. IGBT's are normally N type devices, if the motor is being run from 250V, the high side driver provides a floating supply on the output stage and a logic supply on the input stage to form an interface between the micro and the output. To get the required drive voltage to the gate of the output device, a bootstrap circuit is used to boost the driving voltage above the supply rail. For more information and application notes, check out IR website.

 

[sabri]

dc-dc converter pwm frequency

OK, understand that the control driver contain herein parts:
1) Microcontroler that makes PWM pulses
2) Current amplifier of Micro pulses that triggers the DC motor driver(MOSFET)
3) Driver that controls the DC motor RPM with switching method.

My question is about use of power transistores for switching the Hot line of DC motor instead of MOSFETs?
Please introduce me part number of power transistors (e.g. BC108).
Finally, I want send my suggested schematic circut for PWM in the image(JPEG) format ,but i do not know how i can do that? Please help me.

Thanks.[/b]

 

[nicleo]

pwm frequency problem

Also look at IR (International Rectifier) website, they have high side drivers, low side drivers and full bridge drivers to interface between the micro and the IGBT. (IgBots!). There are also a lot of application notes to look at.
A common frequency to use is 16KHz. This can only be heard by bats, dogs and young children. The higher the frequency, more problems with drive and switching losses.

Something (a bit off-topic) to add:

**broken link removed**[/I] ]What switching frequency (for SMPS design) to choose?

* It is assumed that the design will use some kind of "Soft Switching", and/or "Low Losses/Non Dissipative Snubbers". Today, for a new, competitive design, just using "Hard Switching" is no longer an option.

* We believe that choosing the switching frequency must be done at the beginning of a new design, taking in consideration: power level, cooling method, application specifics.

1. Power levels 0-50W: any switching frequency between 100kHz and 1MHz may be a good choice, depending of application.

2. Power levels 50W-500W: best choice would be between 200kHz and 500kHz. Use 200kHz for a higher efficiency and 500kHz for a higher density and easier filtering.

3. Power levels 500W-5kW: best choice would be between 100kHz and 200kHz. Use 100kHz for a higher efficiency; otherwise 200kHz is the best choice.

Choosing a much different switching frequency than those suggested above, may work for a while, but soon you will discover that your competitor has a product with a higher power density, or better efficiency. Do not find out too late.

 

[aslm]

dc motor pwm frequency

Tried to understand this myself some time ago, more in detail.

The hard part is the hi-side driver for the h bridge and the problem of making shoure that the high and low mosfet on one of the sides is not on at the same time, would make a short of the suply voltage.

som place to study further that I found...
https://www.learn-c.com/experiment7.htm

re Me

 

[cetc1525]

driving circuits for power switches

I think you can use a full-bridge driver

 

[tocal09]

choosing pwm frequency for h-bridge

And a IR2105 driver half bridge .It can work at high voltage out put.Try it
(IRF.com)