InstanSpin labs - Lab 4 – Current Loop Control

Dario Detomaso

Other Parts Discussed in Thread: DRV8301

Hi ,

currently, I'm working with hub motor (for electric bike ) 500W power output , nominal voltage 36V.

The hub motor is located within a rim for bicycles, and no load is connected. See this figure:

In the datasheet InstanSPIN FOC I have read:

"Caution: When in Torque mode you are commanding a constant torque.
You should always apply a load to the motor or you risk even a small constant torque command creating
a motor that quickly goes as fast as mechanically possible, which can create a fault and damage the inverter, motor, or user."

Now I want to use lab 4a ( Current Loop Control ) , and I would like to set a value of gMotorVars.IqRef_A

different from 0 Ampere ( e.g. 0.5 A), without damaging the kit.

which precautions must I take to no damaging the kit DRV8301 69M ?

I known that because the motor is unloaded, the shaft will spin to full (voltage limited) speed.

Thanks in advance

Best Regards,

Dario Detomaso

over 11 years ago

0 ChrisClearman over 11 years ago

TI__Guru** 119680 points

you won't damage the kit unless the rotor reaches a Hz where this Hz * the flux (V/Hz) is > 60V.

0 Dario Detomaso over 11 years ago in reply to ChrisClearman

Intellectual 945 points

hi,

I did not understand.

Can I perform this lab 4 with the electric motor without load, without damaging the kit ?

thanks for the reply

0 ChrisClearman over 11 years ago in reply to Dario Detomaso

TI__Guru** 119680 points

what is the ID'd Flux of the machine?
what is the expected maximum frequency of the machine?

multiply those two numbers and make sure it is less than 60V. You should be fine.

0 Dario Detomaso over 11 years ago in reply to ChrisClearman

Intellectual 945 points

After the identification process I got FLUX ( V/hz ) = 0.351.

From datasheet of motor , no load speed is 470 RPM , 125hz @36V

multiply those two numbers , the result is about 43 V.

If i set with power supply 28 V , I should get that the motor is running without load at a speed about 400 RPM.

do you think it is right what I wrote ?

0 ChrisClearman over 11 years ago in reply to Dario Detomaso

TI__Guru** 119680 points

I think your 28V supply will be saturated by the Bemf of the machine at about 80 Hz, so you won't reach 400 RPM. You can use over modulation (lab10) or field weakening (lab09) to get closer.

0 Dario Detomaso over 11 years ago in reply to ChrisClearman

Intellectual 945 points

1016.user.h

Hi Chris,

After the lab 2a, I got these parameters. You can see "MY MOTOR" in file user.h .

With power supply at 28V and the same test bench.

I tried to spin the hub motor at maximum speed (in speed control). The motor does not exceed this speed :150RPM - 40 hz

Is there a way to check this value (150RPM)?

If I use this equation

V = Ke * omega + R*I

Ke = 0.35 V/hz

omega = 40 Hz

the product Ke*omega = 14V but V = 28.

Where am i wrong ?

Best Regards,

Dario Detomaso

0 ChrisClearman over 11 years ago in reply to Dario Detomaso

TI__Guru** 119680 points

Just taking the Vbus / Flux does not give you the maximum frequency that the motor WILL reach. It's always less than this theoretical value. For example the small motor we provide in our kits would give 24 V / 0.034 V/Hz = 700 Hz. But with no load it only does about half of that value. Same for small hobby motors - they never run fast enough to produce a Bemf larger than the bus.

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InstanSpin labs - Lab 4 – Current Loop Control