Burst Modulation

[fangas]

While replying to a question from "Heretic" I got to thinking about burst modulation to control a universal motor. I've never tried it in that type of application. Works great into a resistive load though.

Anybody got any insight or experience in applying it to an inductive load like a DC motor?

 

[jbartos]

Suggestion: Visit

http://www.atmel.com/dyn/resources/prod_documents/u3280m_u9280m_sec.pdf

http://www.atmel.com/dyn/resources/prod_documents/u3280m_u9280m_sec.pdf

http://polimage.polito.it/~lmr/articoli/ieee.cs.ps.pdf

The Pulse Burst Modulation (PBR) is very similar to Pulse Rate Modulation (PRM) or Pulse Frequency Modulation (PFM). Its unique characteristics consists of very short burst that include a number of pulses.
The burst modulation is linked to an integral cycle control of load power. It is different from PWM modulation. However, it is not defined in IEEE Std 100 "Dictionary"

 

[wired1]

This sounds like a technique also known as "bang-bang" (on-off) control; commonly used to control a resistive heater. It is used on electric valve actuators - ac and dc both. The bang-bang controller is a PIC chip that "bumps" the motor while a feedback pot monitors the shaft position.

 

[fangas]

jbartos,

Thanks for the response. 2 of your links went to RFID things. Did I miss something?

wired1

Yours also.

Perhaps my question was not clear. By burst modulation, I was speaking of whole cycle control. in this technique, you would gate a device on for some number of whole cycles in a given time-frame. The effective power would then be taken as a function of duty cycle. I know it works well in a resistive application like heating. Just wanted to know if someone has tried it on a relatively dynamic load like a motor. The lack of RFI kinda looks good. Could I, for instance, drive a set of SCR's into a bridge and develope the necessary effective DC to control a motor?

 

[ScottyUK]

fangas,

Hope your application can stand torque ripple, or you have a nice heavy flywheel in there somewhere.

You should include a freewheel diode across the rectifier for the inductive load current to circulate through when the thyristors are blocking.

 

[Marke]

If you tried this on an induction motor, expect big problems due to the "auto reclose effect"
The problem is that while stator current is flowing, you induce a rotor current to flow and the motor develops torque and hopefully rotates. When the stator current is stopped, the magnetic field of the rotor will cause the motor to become a generator. When you next apply voltage to the stator, the voltage of the stator and supply will be out of synch resulting in a large current and torque transient. - damaged equipment!!
Best regards

Mark Empson

http://www.lmphotonics.com

 

[jbartos]

Clarification to Fangas marked ///\\\: ///I was trying to present some applications that would support the theoretical link that is explaining the burst modulation in mathematical terms.
One of those duplicate links is incorrect. I had there something else (I beg your pardon).

The paper indicates:\\f. Pulse Burst Modulation (PBM): the activity value is a function of the number of pulses contained in a relatively short burst:
Ni = Kn x delta(ALPHAi); (7)
where Kn is a proportionality factor which gives the maximum number of pulses in each burst. Within bursts, fB is the peak bit rate.
Quite often, Kn is a low number, therefore PBM heavily discretizes activity values. The eects of this discretization can often be reduced by using a non-
linear (e.g. logarithmic) PBM [35]. Neither the pulse
rate fB, nor the repetition frequency are relevant.
This modulation (especially in its dierential form, see
Sect. II-B) has recently been used in several \percep-
tive" applications, such as retinas [35], in conjunction
with Event Driven Multiplexing (see Sect. II-C).
In practice, PBM is very similar to PRM and several authors inappropriately call it PRM. The main dierence is that, while the former is more a time-continuous method (in the sense that the average frequency can be latter is clearly an intrinsically time-sampled method.
Bursts of pulses occur only when the input activity is sampled. Yet, the long-term average pulse rate of the two is identical, except for an immaterial multiplicative factor ( fB/fmax). The maximum sampling frequency
of the system is fB/Kn, while Kn is also the maximum
number of pulses in each packet.
///The paper shows one example where the fB is 1MHz. This would be a relatively high frequency packet for the motor control/propulsion.\\\
The Reference [35] is:
Lazzaro, et al., \Silicon Auditory Processors as Computer Peripherals", in IEEE Trans. on Neural Networks", Vol. 4, no. 3, May 1993, pp. 523-528.

 

[jbartos]

Suggestion: Visit

http://www.get.agilent.com/gpinstruments/tutorials/English/BI_FuncGen_f.shtml

for an example of the burst modulation