FOC braking?

Discussions regarding the Field Oriented Control (FOC) implementation on the VESC.
fest
Posts: 1
Joined: 26 Apr 2018, 07:17

Re: FOC braking?

Postby fest » 26 Apr 2018, 07:42

benjamin wrote:The foc full brake function used 0 modulation, meaning that it alternates between having all low side fets on and having all high side fets on. The bldc full brake will just have all low side fets on. This means that they do the same thing, which is shorting all motor phases. The only difference is that foc has some dead time while switching between the low and high side, while bldc has not.


I've been experimenting with using VESC as absorber/braking motor in ESC testing stand (ESC under test is connected to motor which is mechanically coupled to motor VESC is braking).

When I'm slowly increasing brake current for VESC, there is a threshold after which motor current suddenly becomes positive and braking torque seems to be smaller. Even if the brake current is decreased below this threshold, motor current stays positive.

I quickly skimmed mcpwm_foc.c but I could not find where the "full braking" starts. I would prefer to not activate full braking and instead keep the motor current at the maximum negative value.

Image

pf26
Posts: 298
Joined: 28 Mar 2016, 14:37
Location: FR Valence

Re: FOC braking?

Postby pf26 » 29 Apr 2018, 18:51

I imagine you use "brake mode" and set a brake current using BLDCTools. Did you try to use "current mode", and set a negative current ?
I suspect the issue is related to this in mcpwm_foc.c :
// When the filtered duty cycle in sensorless mode becomes low in brake mode, the
// observer has lost tracking. Use duty cycle control with the lowest duty cycle
// to get as smooth braking as possible.
You could try to comment out the "if ( .. " following the above mentionned comment in the source file.


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