Peak Power and Nominal power of motor

[electronicsLearner77]

I have a controller which can control the motor (BLDC). There are generally two ratings of the motor Nominal power rating and the Rated power rating (Peak power) for certain duration, for example 1KW (nominal) and 2KW (Peak). Now my question is if i want to attain the rated power rating 2KW, how do i trigger? I mean without demand or load can i still trigger the rated power (based on some input switch)?

 

[crutschow]

I mean without demand or load can i still trigger the rated power (based on some input switch)?

No.
The motor power rating is determined by the load.
Operating at a power rating of 1kW requires a load on the motor that draws 1kW from the mains.
(The load would be slightly under 1kW, depending upon the efficiency of the motor).

 

[Minder]

I have a controller which can control the motor (BLDC). There are generally two ratings of the motor Nominal power rating and the Rated power rating (Peak power) for certain duration,

This also generally applies to motor controllers, they also have a continuous torque rating, as well as a momentary peak rating where this peak can only occur for a very brief period without causing damage to the drive.
And this same torque (current) criteria also applies to the motor.

 

[electronicsLearner77]

as well as a momentary peak rating where this peak can only occur for a very brief period without causing damage to the drive.
And this same torque (current) criteria also applies to the motor.

Is it possible for me to trigger this peak with some switch etc to know if my peak performance is achieved or not? I think it is not possible. Why i am asking is, basically we can achieve higher speeds in vehicles based on throttle position without applying additional load.

 

[Minder]

Why i am asking is, basically we can achieve higher speeds in vehicles based on throttle position without applying additional load.

Of course that is possible, inertia has effect as RPM increases.
What particular applications are these questions applied to specifically?
Or is it just in general?

 

[crutschow]

Why i am asking is, basically we can achieve higher speeds in vehicles based on throttle position without applying additional load.

That makes little sense.
How can you achieve higher speeds without that increasing the load?

 

[electronicsLearner77]

For electric vehicles how to apply peak power to achieve higher speeds.

 

[electronicsLearner77]

That makes little sense.
How can you achieve higher speeds without that increasing the load?

Yes probably we can control the voltage at lower speeds we give low voltage and at higher speeds apply full voltage.

 

[Harald Kapp]

For electric vehicles how to apply peak power to achieve higher speeds.

You increase the power output by increasing the input of power to the motor.
But you can't increase input power to the motor without "removing" this power again. The 1st law of thermodynamics states that energy must be preserved. Therefore the more power you input to the motor, the more power you'll have to remove. This can happen in multiple ways:
- The car can accelerate. The higher power input is used to increase the kinetic energy of the car. The "increase in load" as mentioned by @crutschow here is the energy required to accelerate plus the increase in aerodynamic force.
- The car can move up an incline. The higher power input is used to increase the potential energy of the car. The "increase in load" as mentioned by @crutschow here is the energy required to overcome gravity.
- In both cases part of the power input is converted into thermal energy as the motor gets warm. The "increase in load" as mentioned by @crutschow here is the energy required to heat up the motor.

To prevent overheating (and possibly mechanical damage to the drive train), you cannot apply peak power for a long time. A useful datasheet will show the max. time allowed for peak power or will even have a graph showing peak power as a function of duration.

 

[electronicsLearner77]

So can I assume that I can apply peak power for a limited period of time and the vehicle can accelerate faster. Is my conclusion correct?

 

[crutschow]

So can I assume that I can apply peak power for a limited period of time and the vehicle can accelerate faster. Is my conclusion correct?

Yes.
But you will need to include a time-limit in the software so the peak power time is not exceeded for the motor you have.

 

[electronicsLearner77]

But for the input power to be high voltage remaining constant the current should be increased in peak power conditions. But how do I increase the current if the conditions are the same as the continuous power? It is all ending up in confusion.

 

[Alec_t]

But how do I increase the current if the conditions are the same as the continuous power?

The conditions, and the current, for peak power won't be the same as for continuous power.

 

[Minder]

Basically the voltage controls rpm, the torque is a result of current, In the continuous torque range, This operating current will not damage the motor, once this constant current range is exceeded, damage to the motor and/or drive can occur, if the duration is more than the rated spec.

 

[electronicsLearner77]

So, basically I need to create situation for peak power like over loading etc? Simple case what I am trying to understand is with continuous power I go for example 80Kmph suddenly can I apply peak power and goto 100Kmph for certain time?

 

[electronicsLearner77]

Basically the voltage controls rpm, the torque is a result of current, In the continuous torque range, This operating current will not damage the motor, once this constant current range is exceeded, damage to the motor and/or drive can occur

I only apply for few seconds as per the rating that should be possible.

 

[bertus]

Hello,

Perhaps the following article might interest you:
https://x-engineer.org/automotive-e...ry-electric-vehicles-bev-automotive-industry/

Bertus

 

[Minder]

In a general sense, yes.
As an example, a servo drive, which is usually programmable, the continuous current rating is set by either a pot or a parameter and this allows the drive to operate in a continuous manner within this setting, the other setting is peak current where if the continuous current is exceeded for more than a couple of seconds the drive will fold back or reduce the output power accordingly, therefore preventing damage to both drive and motor.

 

[Harald Kapp]

But how do I increase the current if the conditions are the same as the continuous power?

You can't increase current if the other conditions remain the same.
The current drawn by the motor depends on the power it has to deliver to the load. If the load stays the same and the voltage stays also the same, so will the current. You cannot force power into the motor.
Here's a simple experiment you can do without using fancy BLCD motors and controller, using only a small DC motor, a battery and a multimeter:
Connect the DC motor to a suitable battery, e.g. a 3 V DC motor to a 3 V battery (the exact values are not relevant). Measure the voltage across the motor and also measure the current into the motor.
- Without any load attached, the voltage should be near the battery's open circuit voltage, current should be comparatively small (depending on the motor) and the motor should be running smoothly.
- Now apply a load to the motor, e.g. by applying braking force to the axle (your fingers my suffice). Note how the current rises the more pressure you apply. The voltage should stay nearly the same, depending on the condition of the battery.
Calculate the power for different cases. Notice how the power changes with increasing braking force? That is because the motor tries to counter this force by drawing more power from the battery.

Using the same setup try the following without applying any load (braking) to the motor:
- Change the voltage by using other battery voltages, e.g. 1.5 V, 3 V and 4.5 V (a 3 V motor will usually sustain 4.5 V overvoltage for a short period of time).
Again calculate the power for the different cases. Notice how power increases with voltage even without load attached? That is because the motor runs faster on higher voltage and therefore has to overcome more resistance in the bearings, hence more power is required.

The same applies to more complex motor setups like e.g. a BLDC motor wit controller.

It is a common misunderstanding to think you can control voltage and current and consequently power into a load (motor) independently. You can't.
What you usually do is to apply a supply voltage. The load will then draw current as required. Compare this to the mains installation in your home: depending on where you live you'll have a 115/120 V or 230/240 V mains. You can plug in any load from a small 5 W night light to a 2 kW fridge. The power is determined by the load, not the supply!

In the case of the motor this means:
You may permanently load the motor such that it draws up to 1 kW (nominal rating).
You may overload the motor for a short time such that it draws up to 2 kW (peak rating).
If you overload the motor even more, such that it would require e.g. 4 kW to sustain the rotation, this will destroy the motor very quickly if not immediately.
In any case, the power drawn by the motor is determined by the load it has to drive, regardless whether the load comes from accelerating, climbing a hill, or simply overcoming the losses in the gear train, bearings and wind resistance to the car.

 

[bertus]

Hello,

Perhaps this book might interest you:
https://archive.org/details/hughesa...rives.fundamentalstypesandapplications5ed2019

Bertus