PE424UCR/HWM Dr. Guru Feb. 06, 2006 Half-wave rectifier feeding a DC Motor This section, let us determine the operation of a dc motor fed by a half-wave rectifier. The motor has been operating for a long time so that it has obtained its stead-state. Let us assume that in its steady-state operation, the motor's speed is nearly constant. When the flux created by the field winding is held constant or it is a permanent-magnet motor, the induced emf (or back emf) in the motor is constant. The equivalent circuit of the motor operating from a 120-V (rms), 60 Hz supply is given below. The diode is assumed as ideal. Motor's parameters: R 4 Ω . L 10 mH . Ea 50 V . AC Source: v s t ( ) Vm sin ωt ( ) . V . where Vm 170 V . and ω 377 rad/s Motor's impedance: z R j ω . L . Z z Z 5.497 Ω = φ arg z ( ) φ 0.75 6 rad = or φ 43.3 04 deg = The diode begins conduction only when the the input voltage goes above the back emf of the motor. The conduction begins when α asin Ea Vm α 0.29 9 rad = or α 17.1 05 deg = When D is on, the differential equation is L di t ( ) dt . R i t ( ) . Ea Vm si n ωt ( ) . 1
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This section, let us determine the operation of a dc motor fed by a half-wave rectifier. The
motor has been operating for a long time so that it has obtained its stead-state. Let us assumethat in its steady-state operation, the motor's speed is nearly constant. When the flux createdby the field winding is held constant or it is a permanent-magnet motor, the induced emf (orback emf) in the motor is constant. The equivalent circuit of the motor operating from a 120-V(rms), 60 Hz supply is given below. The diode is assumed as ideal.
Motor's parameters: R 4 Ω. L 10 mH. Ea 50 V.
AC Source: v s t( ) Vm sin ωt( ). V.
where Vm 170 V. and ω 377 rad/s
Motor's impedance: z R j ω. L.
Z z Z 5.497 Ω=
φ arg z( ) φ 0.756 rad= or φ 43.304 deg=
The diode begins conduction only when the the input voltage goes above the back emf ofthe motor. The conduction begins when