A motor system may include three switching circuits, each of which includes two upper switching elements and two lower switching elements. A controller includes a signal output module, a signal distribution module, and a signal adjusting module. The signal output module outputs upper and lower PWM signals. The signal distribution module distributes each of the upper (lower) PWM signals alternately to the first upper (lower) switching element and the second upper (lower) switching element of corresponding one of the switching circuits. The signal adjusting module inverts all the PWM signals output by the signal output module when (1) each of currents flowing through two of the three coils has a negative value and all the three upper PWM signals are at HIGH level, or (2) each of currents flowing through two of the three coils has a positive value and all the three lower PWM signals are at LOW level.