Author Topic: Variable Frequency Drive?  (Read 1000 times)

Offline nabzim

  • High Voltage Enthusiast
  • *
  • Posts: 24
  • Karma: +0/-0
  • My full name is Adam Baltazar Mizban. Hello there!
    • View Profile
    • My YouTube Channel
Variable Frequency Drive?
« on: July 15, 2017, 09:11:09 PM »
Hi all,
After building a half-bridge sstc (and after reading a little bit about VFDs), I feel like I could potentially build the same circuit (half bridge) with a few modifications, to use as a VFD to power AC induction-motors with full speed control.

Any feedback/suggestions of what modifications the circuit would need? ( I'm fairly certain that I don't need to run off of a feedback-loop like the sstc)

Offline Hydron

  • Administrator
  • High Voltage Engineer
  • *****
  • Posts: 226
  • Karma: +6/-0
    • View Profile
Re: Variable Frequency Drive?
« Reply #1 on: July 16, 2017, 12:36:42 AM »
Gate drive would not be possible via transformers without more complex circuitry - VFD will not be 50% duty cycle like a SSTC.

Other than that the concept is reasonably similar - both are hard switching half bridges (3 of them in the case of a VFD).

Offline Mads Barnkob

  • Administrator
  • High Voltage Senior
  • *****
  • Posts: 985
  • Karma: +15/-0
  • Denmark
    • View Profile
    • Kaizer Power Electronics
Re: Variable Frequency Drive?
« Reply #2 on: July 16, 2017, 09:32:26 AM »
You are spot on in your discovery that power electronics / inverters / power conversion bridges are often identical in many applications as Tesla coil, induction stove, audio amplifier, variable frequency drives, power supplies, etc etc.

As Hydron says the biggest difference is how you drive the bridge, which controller, timing, phasing of outputs etc that you have. For a 3 phase induction motor you would need to time the phases 120 degrees from each other and have a variable frequency and PWM control table to stay within a certain V/Hz ratio.

As illustrated here and with their description for a single phase output:


source: http://www.vfds.com/blog/what-is-a-vfd

Quote
The blue sine-wave is shown for comparison purposes only. The drive does not generate this sine wave.

Notice that the output from the VFD is a “rectangular” wave form. VFD’s do not produce a sinusoidal output. This rectangular waveform would not be a good choice for a general purpose distribution system, but is perfectly adequate for a motor.

If we want to reduce the motor frequency to 30 Hz, then we simply switch the inverter output transistors more slowly. But, if we reduce the frequency to 30Hz, then we must also reduce the voltage to 240V in order to maintain the V/Hz ratio (see the VFD Motor Theory presentation for more on this). How are we going to reduce the voltage if the only voltage we have is 650VDC?

This is called Pulse Width Modulation or PWM. Imagine that we could control the pressure in a water line by turning the valve on and off at a high rate of speed. While this would not be practical for plumbing systems, it works very well for VFD’s. Notice that during the first half cycle, the voltage is ON half the time and OFF half the time. Thus, the average voltage is half of 480V or 240V. By pulsing the output, we can achieve any average voltage on the output of the VFD.
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline nabzim

  • High Voltage Enthusiast
  • *
  • Posts: 24
  • Karma: +0/-0
  • My full name is Adam Baltazar Mizban. Hello there!
    • View Profile
    • My YouTube Channel
Re: Variable Frequency Drive?
« Reply #3 on: July 19, 2017, 07:39:35 PM »
Gate drive would not be possible via transformers without more complex circuitry - VFD will not be 50% duty cycle like a SSTC.

Other than that the concept is reasonably similar - both are hard switching half bridges (3 of them in the case of a VFD).
Any idea what kind of more-complex circuitry? I would have guessed maybe just a different ic chip for an interrupter, but in this case it would be attached to the enable-pin of UCCs, so technically I guess you could call it an "enabler" instead, haha.
Also I'm only really interested in driving a single phase motor.

As for Mads' comment, the thing that I don't know how to do is create a waveform like those second two, where there's multiple positive pulses then multiple negative pulses. Is there a special IC chip that performs this function? That is where I am lost
« Last Edit: July 19, 2017, 07:42:37 PM by nabzim »

High Voltage Forum

Re: Variable Frequency Drive?
« Reply #3 on: July 19, 2017, 07:39:35 PM »

 


* Recent Topics and Posts

post Re: Offgrid 48V solar to 24V battery setup
[Electronic circuits]
Mads Barnkob
Today at 11:24:46 AM
post Re: ZVS Mazzilli circ with active gate driver - what causes ringing?
[Electronic circuits]
flyrod
Today at 03:22:54 AM
post Re: Are bleeder resistors necessary if I can easily discharge my capacitor?
[Spark gap Tesla coils]
profdc9
Today at 03:18:52 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
petespaco
May 18, 2019, 10:48:59 PM
post Re: Is one of these good?
[Dual Resonant Solid State Tesla coils]
Golddustpeak
May 18, 2019, 04:19:11 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
petespaco
May 17, 2019, 10:57:17 PM
post Are bleeder resistors necessary if I can easily discharge my capacitor?
[Spark gap Tesla coils]
jpb133
May 17, 2019, 09:41:56 PM
post Re: Is one of these good?
[Dual Resonant Solid State Tesla coils]
Uspring
May 17, 2019, 12:41:17 PM
post ZVS Mazzilli circ with active gate driver - what causes ringing?
[Electronic circuits]
82026
May 16, 2019, 04:15:58 PM
post Re: Identification of unknown embedded computer, help needed.
[Computers, Microcontrollers, Programmable Logic, Interfaces and Displays]
Fumeaux
May 16, 2019, 02:19:39 PM
post Re: Is one of these good?
[Dual Resonant Solid State Tesla coils]
Golddustpeak
May 16, 2019, 01:50:44 PM
post Re: Is one of these good?
[Dual Resonant Solid State Tesla coils]
Uspring
May 16, 2019, 12:17:01 PM
post Re: Identification of unknown embedded computer, help needed.
[Computers, Microcontrollers, Programmable Logic, Interfaces and Displays]
Fumeaux
May 16, 2019, 08:45:15 AM
post Re: Identification of unknown embedded computer, help needed.
[Computers, Microcontrollers, Programmable Logic, Interfaces and Displays]
Mads Barnkob
May 15, 2019, 11:49:59 PM
post Re: Identification of unknown embedded computer, help needed.
[Computers, Microcontrollers, Programmable Logic, Interfaces and Displays]
Hydron
May 15, 2019, 10:51:33 PM
post Identification of unknown embedded computer, help needed.
[Computers, Microcontrollers, Programmable Logic, Interfaces and Displays]
Mads Barnkob
May 15, 2019, 09:35:41 PM
post Re: Is one of these good?
[Dual Resonant Solid State Tesla coils]
Golddustpeak
May 15, 2019, 05:07:20 PM
post Re: Mounting LCD CFL's around DRSSTC?
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
May 15, 2019, 12:46:33 PM
post Re: General Oscilloscope Probing Techniques for (DR)SSTC h-bridge
[Beginners]
Mads Barnkob
May 15, 2019, 10:08:11 AM
post Re: Is one of these good?
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
May 15, 2019, 10:04:59 AM
post General Oscilloscope Probing Techniques for (DR)SSTC h-bridge
[Beginners]
L_Mangold
May 15, 2019, 12:42:46 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
hightemp1
May 14, 2019, 11:28:43 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
badpeter
May 14, 2019, 09:58:28 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
hightemp1
May 14, 2019, 08:35:28 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
badpeter
May 14, 2019, 07:41:48 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
hightemp1
May 14, 2019, 06:05:25 PM
post Is one of these good?
[Dual Resonant Solid State Tesla coils]
Golddustpeak
May 14, 2019, 04:21:07 PM
post Re: X ray Transformer Offer
[X-ray]
Mads Barnkob
May 14, 2019, 02:20:27 PM
post Re: One model of L2 can run at several different frequencies. But which is the best?
[Dual Resonant Solid State Tesla coils]
Uspring
May 14, 2019, 12:58:30 PM
post Re: Gate Resistor Calculation
[Dual Resonant Solid State Tesla coils]
coil1002
May 14, 2019, 06:35:32 AM
post Re: One model of L2 can run at several different frequencies. But which is the best?
[Dual Resonant Solid State Tesla coils]
VNTC
May 14, 2019, 01:20:37 AM
post Mounting LCD CFL's around DRSSTC?
[Dual Resonant Solid State Tesla coils]
fafler
May 13, 2019, 07:58:25 PM
post Re: One model of L2 can run at several different frequencies. But which is the best?
[Dual Resonant Solid State Tesla coils]
Uspring
May 13, 2019, 03:24:34 PM
post Re: Just how large?
[Dual Resonant Solid State Tesla coils]
Fumeaux
May 13, 2019, 03:17:50 PM
post Just how large?
[Dual Resonant Solid State Tesla coils]
Golddustpeak
May 13, 2019, 03:04:50 PM
post Re: Gate Resistor Calculation
[Dual Resonant Solid State Tesla coils]
Hydron
May 13, 2019, 11:17:38 AM
post Re: One model of L2 can run at several different frequencies. But which is the best?
[Dual Resonant Solid State Tesla coils]
VNTC
May 13, 2019, 04:45:13 AM
post X ray Transformer Offer
[X-ray]
Joshua Guertler
May 13, 2019, 04:08:13 AM
post Re: Gate Resistor Calculation
[Dual Resonant Solid State Tesla coils]
profdc9
May 13, 2019, 03:05:03 AM
post Re: Gate Resistor Calculation
[Dual Resonant Solid State Tesla coils]
coil1002
May 13, 2019, 01:49:00 AM
post Re: Gate Resistor Calculation
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
May 12, 2019, 10:17:22 PM
post Re: My first DRSSTC on bricks
[Dual Resonant Solid State Tesla coils]
Laci
May 12, 2019, 09:49:02 PM
post Re: Gate Resistor Calculation
[Dual Resonant Solid State Tesla coils]
Uspring
May 12, 2019, 06:42:53 PM
post Re: Gate Resistor Calculation
[Dual Resonant Solid State Tesla coils]
profdc9
May 12, 2019, 05:41:02 PM
post Re: One model of L2 can run at several different frequencies. But which is the best?
[Dual Resonant Solid State Tesla coils]
Uspring
May 12, 2019, 03:38:12 PM
post Re: One model of L2 can run at several different frequencies. But which is the best?
[Dual Resonant Solid State Tesla coils]
VNTC
May 12, 2019, 03:17:01 AM
post Gate Resistor Calculation
[Dual Resonant Solid State Tesla coils]
coil1002
May 12, 2019, 02:50:11 AM
post Re: adventures in homemade flyback bobbins.
[Transformer (ferrite core)]
dexter
May 12, 2019, 12:40:56 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
petespaco
May 12, 2019, 12:18:58 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
Mads Barnkob
May 11, 2019, 08:34:31 PM

Sitemap 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30