Your controller will be attempting to generate a near-sinusoidal waveform to create a field to match that generated by the rotor as it rotated inside the stator. The motor has inductance, which will define how quickly the current can change when voltage is applied.
How you simulate the sinusoidal waveform in your controller depends on many issues: your commutation rate as compared to your maximum motor speed being of primary importance. The relationship between any three-phase peak and rms values hold for your motor. However, you are using PWM to generate your sinusoid, so your instantaneous peak current must have the duty cycle applied to it to give you your answer.
In the first sample below, one of my motor designs is providing an RMS phase current of 5 amperes while not running full speed. The supply current is less than the RMS phase current of a single phase, but the PWM means that the RMS phase voltage is only 13.9 volts.
The good news: the math is straightforward for brushless permanent magnet motors: torque is directly proportional to current and speed is directly proportional to voltage.
So design your controller to handle peak currents 25-50% higher than the motor rating, and provide a voltage higher than the motor voltage rating to give you some headroom and keep you from stalling. You need this because when you command a speed increase under a full torque load, your motor must handle the additional torque from inertia, and if you are running at full speed and put on a load, the controller will want to increase voltage temporarily to get back up to speed. This headroom will keep your PID loop working.
You can figure out the current from the motor's torque constant, usually expressed in torque/current (Nm/A). There is also a back emf constant, expressed in a number of different ways: Voltage/Speed (sometimes V/kRPM). If you play with radians, volts and amperes you can prove that these two constants are actually the same variable, with units swapped around, but often both are presented.
Any permanent magnet brushless motor can be run either six-step or sinusoidal. The second example shows the same motor running six-step. Motors are wound differently for different applications. Motors labelled "PMSM motors" are generally designed to be run sinusoidal; the brushless motor shown below was wound for either operation. The price for running a sinusoidal motor in six-step mode is torque and current ripple.
Good luck!
