Abstarct: The inverter and pulse width modulation are used in PMSM motor drives at appropriate operating point included required torque, power, and speed. In usual, the motors are drive with fixed switching frequency. This leads to creation harmonics of switching frequency in voltage and current spectrum. Motor converts this harmonic to whistling noise. To keep up efficiency, the switching frequency is less than 10 kHz in most of power electronic converter for driving motors. In this frequency range the human ear has high sensitivity. So whistling noise emitted from the motors would be troubling for humans. In addition to, concentration of noise power in multiples of switching frequency causes electromagnetic interference (EMI). In last decades, RPWM techniques have been presented for solving this problems. RPWM methods evens the voltage spectrum by randomly changing the switching frequency. In other words, when using RPWM, in voltage spectrum almost all frequencies are excited and components frequency have identical amplitude. RPWM techniques has been solved the EMI and whistling noise, but excite the motor resonant frequency and increase acoustic noise and vibration. In this dissertation, a method for switching period selection has been presented. In that, According to the duty ratio and structure of power electronic converters, the switching period is chosen so that a selective frequency can be eliminated from RPWM wave. This prevent motor resonant excitation and reduces the acoustic noise. The proposed method is applicable to the majority of power electronic converters which using PWM concept. Then, way of applying it to the three-phase inverter baxsed on SPWM, SVPWM and direct torque control for permanent magnet motor drive will be presented.