Small white in a recent study FOC brushless motor drive, there is a doubt: three phase current for Ia, Ib, Ic for sinusoidal current, clark transformation after Ix, Iy for sinusoidal current, park transformation after Id, Iq should also sinusoidal current; But see online say Id, Iq is constant current, this can be achieved by PID tuning into the fixed value of electric current? Wish everyone a great god, pointed to the spot where I misunderstand, thank you!