Motor is getting hanged during power ON/OFF continuously

Shruthi,

DRV8313 EVM is not right platform for product level specification testing. Neither the hardware nor software (comes with it)   is tested for such conditions at TI, so it’s obvious that it won’t work during power on/off cycling.

EVM is platform to quickly evaluate the basic functionality of DRV8313/MSP430G25xx combination for sensor and sensor-less BLDC control.

The basic issue with such power-on/off cycling is motor does not comes to halt during such transients and if you try to start the motor from running condition, you run the risk of over-current  because running motor phases have back-emfs. Software does not know the initial condition on phases and tries to align the motor with particular phase-excitation and if that instant particular phase has negative polarity of back-emf, its worst short circuit condition because both applied voltage and back-emfs are additive, causing huge current in motor winding.

Application Software needs to take care such power cycling requirement. There could be many ways, here is one way I feel it can be taken care at system level:

1. Define undevoltage threshold at system level: Let’s say nominal voltage is 24Volt, you can choose under voltage as 18V.
2. As soon as Vm falls below 18V, start decelerating your motor. So lets say , you are at highest speed of 90% duty cycle, you can start reducing it towards 5%-10% duty cycle. Decelerating ramp needs to be decided based on system spec such it does not cause over-voltage at VM.

So basically, as soon as VM is below 18V, in software a command is generates to reduce the speed to level of 5%-10%. During deceleration motor energy will be fed back to VM so VM will sustain for more time than it would have been if motor was running in same speed.

1. Now once you reach to lower speed level 5-10%, apply brake to motor, by turning on all top side or bottom side switches. The idea is that motor back-emfs are at very low level and it won’t cause huge current. Make sure that before hitting under-voltage threshold of DRV8313 i.e. 8V, motor is stopped completely. So next time, when you start the operation when VM reaches to 24Volt, you are starting with completely stopped motor. An hysteresis of 2-3V at under-voltage level  of 18V will help proper starting i.e. while going up on VM, once VM reaches above 20-21 volt, start the operation.

Fine tuning of above scheme is quite complex task and will require software modification and rigorous system level testing to cover all worst case scenarios of power on/off cycle.

Having said all, I would like to suggest that if your application requirement is within Vm-24V/2Amp, I would strongly recommend to go with our new solution DRV10983. I can promise you that it would be very easy to fine tune your application with this and meeting such power cycling requirement would be child’s play because DRV10983 has fly-on catching algorithm which can synchronize to already spinning motor and achieve the smooth start-up

+  plus this solution will be cost-effective

 - will take much smaller board space because DRV10983 has both Motion control engine+ 3-phase H-Bridge in single chip.

 - no software development is require from you end

 - It will apply sinusoidal PWM to motor so motor sppining will be less noisy than Trap algorithm.

Best Regards

Milan-Motor Application Team