Engineer/Geek Types, questions about PWM controlled Brushless and Voltage Boosters

[engineermike]

A digital signal is not a sign wave, its a square wave if anything. This wave doesn't make the voltage going to the pump AC. The reason why I would still call it DC voltage out is because the polarity is not flipping. Positive and negative on the pump is always positive and negative.
Anyone saying the pump remains at a constant speed like an AC motor..... Is wrong. It has to change speeds in order to change flow rate.

I was drawing a parallel to an AC motor because the premise of speed control of a DC Brushless motor is more like an AC motor than DC. The frequency of alternation between 0 and X volts is what determines the speed. AC motors aren't constant speed, but they run near sychronous to grid frequency OR some other frequency generated by a VFD/inverter. The DC Brushless controller is more like a VFD/inverter than a typical DC resistor or PWM driver.

What I'd like to know is if the Brushless controller senses the system voltage increase and, in turn, use logic to allow higher frequency/speed to be commanded. If it doesn't, then that just means higher voltage will result in lower current for any given speed and power, which will help prevent over-amping but won't directly increase fuel supply.

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[markmurfie]

No the frequency between 0-x volts does not determine the speed of the DC motor. The resistance, voltage, and current still do that. At some point the frequency and just having the pump just on all the time, will be nearly the same. Higher frequency will not change the loads resistance allowing more current to the motor and for it to spin faster. The curve of frequency to current is logarithmic and tops out at a limit.

With an AC motor the higher frequency reduces what is no long resistance but rather Impedance and with increasing frequency that Impedance reduces which increases current flowing to the load(motor).

 

[engineermike]

mark, I believe you and I are talking about two different things. You seem to be describing exactly how a PWM brushed DC motor works, to a tee. A DC *brushless* works completely differently.

My electrical engineer buddy just explained how a DC brushless works to me in detail and it makes a lot more sense to me how voltage affects it.

Basically, in a DC brushless motor the rotor has permanent magnets and the stator has an array of electromagnets (polls). The controller energizes the stator polls, one by one, to "pull" the rotor around. It also has a reluctor and pickup to measure speed and ensure there is no slip. If it can't maintain zero slip by increasing voltage within limits, then it will intentionally slow it down until torque reduces to a level where slip is eliminated. Higher voltage will allow it to make more torque without slip. Assuming Angrey's pump is currently reducing the speed in order to keep slip under control, then more voltage would help allow more torque and more speed.

If this makes any sense, you can see why I said that the frequency of the voltage determines the speed. It's pulsing each stationary poll as the permanent rotor magnets approach it. Higher frequency = higher speed. You can also see why it's akin to an AC motor, in that the sync speed, a frequency of 60 hz, determines the speed (usually as a function of the number of polls).

 

[markmurfie]

The requirement of a precise energizing sequence to control the speed of the motor, does not change the fact that the DC pulses and their frequency, have no effect on the resistance of each coil. It's speed will have a limit set by the amperage the voltage can force through in the maximum pulse window. At some point the frequency and just being full on would be indistinguishable going higher would not produce a benefit.

It's pointless to even talk about this as what will be logged and should be watching is what the regulator is doing for the control signal. That and the fuel rail pressure.

 

[engineermike]

The requirement of a precise energizing sequence to control the speed of the motor, does not change the fact that the DC pulses and their frequency, have no effect on the resistance of each coil. It's speed will have a limit set by the amperage the voltage can force through in the maximum pulse window.

The maximum pulse window is geometrically determined by the number of polls and permanent magnets. More polls = less window, but in no case would more than 50% duty cycle of any one magnet produce more torque. However, to get more speed requires faster rotation of the field (higher frequency) which means higher frequency pulsing. More torque results in more slip, so the controller increases current to control slip. Run out of current and the controller sends a lower frequency to reduce speed, which reduces torque requirement. More voltage lowers the current required to achieve zero slip, thereby increasing the max torque and, in this case, max speed, pressure, and flow.

It sounds like you agree that an increase in voltage would reduce the amperage and get it off a limit, though, which is the crux of what Angrey is looking for.

At some point the frequency and just being full on would be indistinguishable going higher would not produce a benefit.

I can't imagine a Brushless controller would be designed to go so high in frequency that its indistinguishable from constant voltage. It would totally defeat the purpose.

@Angrey I had recorded some videos a while back showing an oscilloscope readout of the PWM signals from the PCM to the FPDM and from the FPDM to the fuel pump under different loads. You can watch the two different [constant] frequencies increase in unison as load rises as the duty cycles approach 50 and 100%, respectively. But apparently they were taken down from YT.

 

[markmurfie]

OP told me there's nothing to log, after I told him what wires to log. He might understand more now as I described how to wire the regulator into the Ngauge.
No way he knows what he is looking at on an oscilloscope. Keep it 4th grade like he asked.
Pointless to even talk about that side of this.

How he was able to just hook this up and it works, with out logging any sort of pump control, is beyond me being able to explain.

 

[Angrey]

Let's simplify things a bit. The DC voltage system isn't constant (I wish it were, life would be so much simpler with a traditional voltage regulator). How does either PWM modulated or a VFD modulated system manage subscriber output/performance in a framework where the voltage can vary moment to moment from say 12.8 volts up to 13.6 volts?

As I understand it (going a level up from your granular discussion) you can manage it either by sending pulses that vary in length (and corresponding dwell time).

OR you can modulate based off a constant pulse and simply modulate based off frequency. Higher frequency gets you closer and closer to full ground/constant (in this case DC) condition.

I do not think either the Fuelab regulator or the DW controller have the physical components to modulate voltage. Neither of them is physically large enough or with the requisite heat dissipation features to do so. The DW controller simply takes the available voltage and passes it along through a series of ground on-off events. The Fuelab regulator gives the requisite instructions to the DW controller to increase or decrease and the DW controller simply adjusts the amount of ground time (via frequency) that it passes along to the pump. I'm unclear as to whether this is through a negative relationship (i.e. less voltage from 0-5 from the Fuelab signal means higher output, or more voltage from 0-5 yields higher output).

In any case, whether it's managed through pulse width or pulse frequency, the motor will achieve the output that the controller will adjust according to the Fuelab signal, which adjusts based off the desired flow/backpressure on the return line.

After discussing all this, I'm not a bit concerned that if I plug this thing in (the booster) it's going to mess with my tune. I'm hopeful that's not the case and I have a call in to DW to go over some of these questions and concerns.

 

[Angrey]

From this pretty good article/explanation:

" The higher the frequency or the quicker the ESC goes through the 6 intervals, the higher the speed of the motor will be. "

How Brushless DC Motor Works? BLDC and ESC Explained (howtomechatronics.com)

 

[markmurfie]

Voltage drives amperage

Frequency also drives amperage.

Amperage is what determines the motors speed.

This is all true for both AC and DC.
The difference is DC does not actually need a frequency component for delivering current and its all determined by resistance. You get to a point where an increase in frequency of DC pulses does not provide more current, because its resistance is always phase angle 0, essentially no different than being connected full time with 0 frequency in that circuit. You want more speed, you need more amps, the only way to do that is more voltage. Or design a lower resistance motor.

In AC the frequency component is essential. It completely changes the concept of resistance in a circuit. Applying a phase angle to resistance, introduces a new concept that is called impedance that changes with the frequency because frequency in AC changes the phase angle. Impedance is actually what determines the delivered amps and controls those motors speed.

Frequency does not control a motors speed. The amperage made available to the motor by the frequency does. If theres no increase in amperage, an increase in frequency does nothing. If theres no reduction in amperage, a reduction in frequency does nothing.
You could argue and say well it always changes a little bit, but there comes a point where the changes are so small, you would be using quantum field theory to model it. long before that point we would just call the change nothing.

Literally no point in talking about this, its nothing of concern, and you are not going to change anything about it.


Put the voltage booster on it will not change your tune as that is set to the fuel rail pressure controlled by the regulator.
If you want to reduce the work load of the electrical system and of the pump when its not needed, and have total control over its speed, you have to log the regulator you have commanding the pump controller. Then tune it mechanically via altering the return flow. The closer you have it to returnless, the less buffer in engine fuel demand you are going to have. The voltage booster just puts you further away from returnless, giving you more buffer, but only if the regulator is at the end of its control range.

 

[Angrey]

Voltage drives amperage

Frequency also drives amperage.

Amperage is what determines the motors speed.

This is all true for both AC and DC.
The difference is DC does not actually need a frequency component for delivering current and its all determined by resistance. You get to a point where an increase in frequency of DC pulses does not provide more current, because its resistance is always phase angle 0, essentially no different than being connected full time with 0 frequency in that circuit. You want more speed, you need more amps, the only way to do that is more voltage. Or design a lower resistance motor.

In AC the frequency component is essential. It completely changes the concept of resistance in a circuit. Applying a phase angle to resistance, introduces a new concept that is called impedance that changes with the frequency because frequency in AC changes the phase angle. Impedance is actually what determines the delivered amps and controls those motors speed.

Frequency does not control a motors speed. The amperage made available to the motor by the frequency does. If theres no increase in amperage, an increase in frequency does nothing. If theres no reduction in amperage, a reduction in frequency does nothing.
You could argue and say well it always changes a little bit, but there comes a point where the changes are so small, you would be using quantum field theory to model it. long before that point we would just call the change nothing.

Literally no point in talking about this, its nothing of concern, and you are not going to change anything about it.


Put the voltage booster on it will not change your tune as that is set to the fuel rail pressure controlled by the regulator.
If you want to reduce the work load of the electrical system and of the pump when its not needed, and have total control over its speed, you have to log the regulator you have commanding the pump controller. Then tune it mechanically via altering the return flow. The closer you have it to returnless, the less buffer in engine fuel demand you are going to have. The voltage booster just puts you further away from returnless, giving you more buffer, but only if the regulator is at the end of its control range.

You're contradicting yourself. Frequency is tied to the current that's passing through a device to ground. In a pulsed electrical feed, if the pulses are constant durationa and spacing, then a higher frequency results in more total time that the electrical flow is on than off, which results in more current passing through the device/to ground.

And to be more broad, ENERGY drives motors. That can be achieved with higher voltage and lesser current or vice versa (with detrimental affects to electric motors during low voltage/high current conditions).

The underlying physics doesn't change. Total energy is the flow of electrons multiplied by the relative energy density of those electrons (j/c*c/s). If we fix the voltage, then the only way to vary the energy applied is through the current. In a system where it's pulsed, the only way to do that (again with fixed voltage and pulse parameters) is to vary the frequency.

 

[Angrey]

You're contradicting yourself. Frequency is tied to the current that's passing through a device to ground. In a pulsed electrical feed, if the pulses are constant durationa and spacing, then a higher frequency results in more total time that the electrical flow is on than off, which results in more current passing through the device/to ground.

And to be more broad, ENERGY drives motors. That can be achieved with higher voltage and lesser current or vice versa (with detrimental affects to electric motors during low voltage/high current conditions).

The underlying physics doesn't change. Total energy is the flow through the electrons multiplied by the relative energy density of those electrons (j/c*c/s). If we fix the voltage, then the only way to vary the energy applied is through the current. In a system where it's pulsed, the only way to do that (again with fixed voltage and pulse parameters) is to vary the frequency.

 

[engineermike]

Let's simplify things a bit. The DC voltage system isn't constant (I wish it were, life would be so much simpler with a traditional voltage regulator). How does either PWM modulated or a VFD modulated system manage subscriber output/performance in a framework where the voltage can vary moment to moment from say 12.8 volts up to 13.6 volts?

In a PWM at 100% duty cycle, you'll just wind up with lower power delivered at a lower voltage. If your system is <100% duty cycle and it's on a control system, then it will simply increase the duty cycle to counteract the reduction in voltage.

In a Brushless DC, a lower voltage will reduce the amount of torque it can sustain at a given amperage limit. This will result in a lower speed because the controller will sense the slip and reduce speed as a result.

As I understand it (going a level up from your granular discussion) you can manage it either by sending pulses that vary in length (and corresponding dwell time).

OR you can modulate based off a constant pulse and simply modulate based off frequency. Higher frequency gets you closer and closer to full ground/constant (in this case DC) condition.

It's the latter. The brushless controller controls the speed via the frequency of pulses. Your link explains it better than I did earlier.

So, the frequency determines the speed. The voltage is whatever you supply it with, and the amperage rises and falls with torque to maintain speed. If the amperage hits a limit, then the controller slows it down (the frequency) to prevent overload. More voltage lowers the amps for a given load, so it will allow more power and more speed to be produced.

After discussing all this, I'm not a bit concerned that if I plug this thing in (the booster) it's going to mess with my tune. I'm hopeful that's not the case and I have a call in to DW to go over some of these questions and concerns.

If it's set up right, then it will only sustain the desired pressure, not change it. It should extend the operating range of the system.

 

[markmurfie]

You're contradicting yourself. Frequency is tied to the current that's passing through a device to ground. In a pulsed electrical feed, if the pulses are constant durationa and spacing, then a higher frequency results in more total time that the electrical flow is on than off, which results in more current passing through the device/to ground.

You are the only one who is contradicting themselfs. Constant duration= More time?

 

[Angrey]

If it's set up right, then it will only sustain the desired pressure, not change it. It should extend the operating range of the system.

That's what I'm hoping but this whole thread now has me nervous and second guessing it.

 

[Angrey]

You are the only one who is contradicting themselfs. Constant duration= More time?

You indicated amperage is the controlling factor, but then you discuss frequency. In a constant voltage system (either pulsed, alternated) whether it's A/C or DC, increasing the frequency of the pulses or the alternating phases will result in HIGHER CURRENT (which is higher amperage).

So whether it's semantical or not, if all other things remain constant, increasing the frequency in a modulated system will result in a higher transfer of energy, which in our case results in a higher amount of WORK being done to the system and an increase in pump output.

Again, I'm making the assumption that based off the schematics I've seen, neither the DW controller NOR the Fuelab regulator have the physical capability of modulating the voltage. They simply pass along whatever voltage the system has available in packets of current and increasing or decreasing the frequency of that transfer results in higher or lower current.

I think it's more elegant and correct to say that ENERGY is what drives the pump, because I can achieve the SAME pump output on a DC pump by applying a lower current (with higher voltage) or a higher current (with lower voltage) or any combination in between.

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