What happens if the controller is turned off during flux weakening?
Turning off the controller during flux weakening should be avoided at all costs, as it can lead to permanent damages.
Situation 1: Controller is switched off but the battery is connected
The motor will rapidly (uncontrollably) decelerate to the nominal speed. Inrush current will flow into the battery. This inrush current can not be controlled, because the controller is off. This inrush current may damage the controller or BMS.
If due to the inrush current BMS turns off the ports, you get the same situation as in Situation 2.
Nominal speed is the top speed of the motor without flux weakening (e.g. /driver/dac/fwc set to 0) at a given DC voltage.
Solution
Do not use a kill-switch that turns off the controller. Instead, set the drive mode to freewheel and allow a controlled deceleration first.
For such a purpose, the LYNX implements seat switch feature. This disables the ride, but keeps the controller alive.
Situation 2: The battery is disconnected
It can happen by a BMS cut, by a fuse/pyro-fuse trigger, or by physically disconnecting the battery. In such situation, the damage from the overvoltage is imminent. Such a damage usually leads to a phase short circuit and makes the motor to stop violently.
Solution
- Never disconnect the battery during the active motor control.
- Use a dual-port BMS. Dual-port BMSes allow current to flow from the motor into the battery.
- For a single port BMS, ensure that the controller is informed about the imminent BMS cut. The BMS must send a warning about reaching some level of protection so that the controller can take precautions. Consult this issue with the BMS vendor and ask for the communication protocol, so we can assess the feasibility.
- For such a purpose, the LYNX implements the BMS communication feature.
- siliXcon BMS1 is designed to handle all such hazardous situations, yet allows getting the maximum out of drivetrain under every condition.