Kinetis Motor SuiteのトピックRe: Problem Controlling E-BIke

Problem Controlling E-BIke

PedroCastro — Mon, 05 Mar 2018 13:54:14 GMT

Hi,

I have a e-bike project that I am using kv31f and kms as the motor controller. Since I need a torque control, I have to use the current control mode of kms. As far as I understood, the torque control must first go through a speed control and after a threshold the torque control takes place. The problem is that in e-bikes the pedal is mechanically coupled with the motor, so when the user pedals the motors also spins. In this situation it seems to me that if the motor is already spinning or even above the rpm threshold, the controller is unable to enter the current control. The faults the system gives is kind of random to me, for example: peak current on phase (A/B/C) which is strange cause I am trying to use current control. Motor overspeed in low rpm and even under voltage using a DC power supply.

So, my question is: How can I use a current control for an e-bike with a motor mechanically coupled with the pedal?

Thanks in advance

Re: Problem Controlling E-BIke

philip_drake — Mon, 05 Mar 2018 20:37:36 GMT

We have had other customers solve this startup issue with a Hall-startup. After startup the Torque control can be used.

Once a motor start is requested with the throttle then the hall-start will read the current motor angle and engage the motor. Once startup mode is exited, sensorless FOC is commanded.

During commissioning you might want to try setting the FOC crossover speed to be higher than the pedal assisted motor speed.

Other than hall startup, we have not developed alternative on-the-fly startup algorithms.

The other way to accomplish this is through a mechanical clutch which would leave the motor not-engaged until the motor RPM exceeded the pedal.

For your e-bike operation you may want to work on the re-generative braking possibilities as well.

Best Regards,

Philip

Re: Problem Controlling E-BIke

linestream-adam — Wed, 07 Mar 2018 16:58:43 GMT

Pedro / Philip,

I wanted to see how hard it would be to modify the startup when using hall start into torque control so that you are always in torque control. It was far simpler than I expected. On my bench it works great. Lets you go into and out of hall mode based on the hall derived speed. I've attached the updated drv.c file that enables this feature. Give it a shot. Hopefully this will help with some of the issues you are seeing.

Re: Problem Controlling E-BIke

PedroCastro — Wed, 07 Mar 2018 17:56:00 GMT

Hi Adam, many thanks for the code! I will test as fast as possible!

Do I have to change the FOCLowSpeed, accel, jerk or anty paramters regarding startup to use this drv.c?

Re: Problem Controlling E-BIke

linestream-adam — Wed, 07 Mar 2018 19:32:03 GMT

The FOCLowSpeed will still be used but now it looks at the speed reported by the halls to determine if it should make the transition to FOC. So if running above that speed it will run FOC, below that speed it will run TRAP.

You can ignore accel & jerk with the startup.

Let me know if this helps resolve the issue in the other thread as well.

Re: Problem Controlling E-BIke

PedroCastro — Wed, 07 Mar 2018 19:55:28 GMT

Adam,

it really worked! It now fits our needs. I appreciate your help

Just one more advice I would like to have from you... In order to do regenerative braking, you suggest to use brake and regen as braking type or use current mode but with negative current demand?

Re: Problem Controlling E-BIke

PedroCastro — Fri, 09 Mar 2018 17:17:22 GMT

Adam,

there is still a bug with the FOCLowSpeed transition. If the motor is above the threshold when the controller comes in, it cannot start the RUN_CURRENT mode. Besides when the transition happens, it seems it gets lost sometimes also. Do you have a solution for this?

Re: Problem Controlling E-BIke

linestream-adam — Mon, 12 Mar 2018 13:27:23 GMT

Pedro,

That is where the need for a "flying start" algorithm comes from. When it attempts to start above the FOCLowSpeed, it will try to start controlling the motor using FOC. But since the estimator hasn't synchronized with the rotor prior to starting to control it can get "lost".

The solution to this problem is to add a flying start algorithm that will allow the estimator to lock onto the rotor before trying to control it. It is possible to modify the drv.c file in order to do this, but I don't have an example I am able to provide.

Re: Problem Controlling E-BIke

PedroCastro — Mon, 12 Mar 2018 13:34:40 GMT

Would it be possible for you to send an updated file today or maybe tomorrow? We have an important event for customers to test the products.

One thing I have tried is to set a really low FOCLowSpeed and the controller always starts above, which gives some torque but it does not reach rated speed. Would it be possible to solve this instead?

Re: Problem Controlling E-BIke

linestream-adam — Mon, 12 Mar 2018 15:21:27 GMT

Pedro,

I won't be able to provide an update that resolves this issue. It requires adding an algorithm and capabilities that are not currently present in KMS.

If anything, I would recommend setting a higher FOCLowSpeed, this way your odds of starting in the FOC region are lower.

Re: Problem Controlling E-BIke

PedroCastro — Mon, 12 Mar 2018 17:44:26 GMT

I am always running above FOCLowSpeed and it mantains a torque with no problem but with limited speed. So am I always in TRAP mode, right? What if I could run until rated speed in this mode?

Re: Problem Controlling E-BIke

PedroCastro — Wed, 21 Mar 2018 14:07:27 GMT

linestream-adamreynolds‌

will be an update to add the flying start algorithm? We are depending on NXP to have a good product we are about to sell hundreds and even thousands

Re: Problem Controlling E-BIke

linestream-adam — Fri, 23 Mar 2018 14:02:20 GMT

Pedro,

There are no plans to add a flying start algorithm into KMS. This is something that you as the product engineering team can add in to differentiate your product from the typical usage of KMS.

Re: Problem Controlling E-BIke

linestream-adam — Thu, 29 Mar 2018 14:26:24 GMT

Pedro,

In order to support a speed-regulated torque mode there are a couple of things you need to do.

On "Protection & Hardware", set the "Stall Speed Error" to be twice the rated speed of the motor.
Click the "Update Motor Drive Configuration" button
Open the watch window, and add the variable: "user.command.IqRefMax",. this will be the torque reference
Go to the "Speed Control" page and enter a target speed of the maximum speed you want the motor to run
Click Start

Now the motor will follow the trajectory and will not exceed that set maximum speed, and it will use up to the amount of torque specified in "user.command.IqRefMax" in order to reach that speed. The goal here is to operate the speed controller in saturation so you adjust how much torque you would like the system to be applying by modifying the user.command.IqRefMax, and you can set an upper boundry on the speed by adjusting the target speed.

Re: Problem Controlling E-BIke

linestream-adam — Thu, 29 Mar 2018 15:44:50 GMT

Also, it could be useful to modify the transition point between TRAP and FOC. You can do this in the GUI by changing the "Speed Threshold" on the Speed Control page. The associated MCU variable is est.config.FOCLowSpeed. If you get the bike started in TRAP mode with the crossover speed high you can lower the crossover speed once the motor is spinning to try and transition into FOC.

Re: Problem Controlling E-BIke

PedroCastro — Thu, 29 Mar 2018 17:15:12 GMT

Adam,

so even in speed control mode, if the motor is already spinning when I command a target speed, the FOCLowSpeed should always be above the current speed, right?

Re: Problem Controlling E-BIke

linestream-adam — Fri, 30 Mar 2018 14:28:43 GMT

Pedro,

Yes, you will want to run for a little bit in the startup region so that the estimator has a chance to stabilize. One thing you will need to be cautious of when running in speed mode is that for startup it will always start from 0. You may need to adjust the trajectory start point to be the current speed of the motor.

Re: Problem Controlling E-BIke

PedroCastro — Tue, 03 Apr 2018 14:23:34 GMT

Hi Adam,

I am not been able to set a FOCLowSpeed during run time, I am using the function above:

void setFOCLowSpeed(float speed)
{
flashSysParams.estCfg.FOCLowSpeed = _LQ24(speed / FULL_SCALE_SPEED_RPM);
}

Should I call DRV_Init(&flashSysParams) after setting the new valeu for it?

Re: Problem Controlling E-BIke

linestream-adam — Tue, 03 Apr 2018 14:27:37 GMT

Pedro,

Instead of setting flashSysParams.estCfg.FOCLowSpeed, set your new value to est.config.FOCLowSpeed

That will update the live value.

Re: Problem Controlling E-BIke

PedroCastro — Tue, 03 Apr 2018 15:56:30 GMT

Thanks Adam,

one more thing, what is the variable to set th trajectory start point? Should I ran in SPEED_RUN or SPEED_RUN_PLAN?