Running 24V BLDC motor with 7s battery

[fedimakni]

ello,

I am building an ESC for a BLDC motor to use it in a robot.
My BLDC motor is a 24V one
My battery is a 7s so its max voltage will be 29.4V.

Is it ok to connect the battery voltage directly to the 3 phase half bridges or i need to use a buck-boost converter to generate a stable 24V?

Thanks

[Martinn]

The nameplate voltage of BLDC motors is somewhat arbitrary. Primarily it means that the motor will achieve a certain speed at the given voltage.
For example, for 24 V 6000 rpm might be given. The motor will run roughly at 3000 rpm with 12 V or 12000 rpm at 48 V (something might break though mechanically at massive overspeed). This is governed by the motor back EMF constant. A 24 V run at 30 V will be a bit faster (do the math), which is irrelevant as you'll run closed loop position control in a robot anyway.
You don't do buck or boost converters with motors, the motor already consists of inductors, no need to add another supply loop.

[Doctorandus_P]

As Martinn already mentioned, there is no need to add extra hardware, there is no hard limit on motor voltage. Your motor can also run from an 50V power supply, provided that the motor controller itself can work with this voltage. There are some additional constraints, when you are overvolting the motor it can also take more power from the power supply, and when you do this for a long time, (minutes) the motor will overheat. But it's not the extra volts that kill it, it's the excessive heat.

The difference between 24V and 30V is pretty small and this probably ndoe not need any extra sort of protection. If the difference gets bigger, then a method to prevent the motor driver from applying the full input voltage may be an additional precaution. And also keeping an eye on the motor temperature. In industrial applications it's very common to protect motors with extra safety devices such as a PKZ.