ControlledRectifier Fed Drive Armature Field ECE 442 Power

Controlled-Rectifier Fed Drive Armature Field ECE 442 Power Electronics 1

Chopper-Fed Drive Armature Field ECE 442 Power Electronics 2

Equivalent Circuit of a Separately-Excited DC Motor ECE 442 Power Electronics 3

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Solve for the motor speed ECE 442 Power Electronics 6

Control of the motor speed • Control armature voltage, Va – Voltage control • Control the field current, If – Current control • Control the armature current, Ia ECE 442 Power Electronics 7

Magnetization Characteristic ECE 442 Power Electronics 8

Characteristics of Separately-Excited Motors Use armature voltage control Use field-current control Rated speed ECE 442 Power Electronics 9

Equivalent circuit of a DC Series Motor ECE 442 Power Electronics 10

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Controlling the Motor Speed • Control the armature voltage, Va • Control the armature current, Ia ECE 442 Power Electronics 12

Characteristics of DC Series motors ECE 442 Power Electronics 13

Operating Modes • In variable-speed applications, a dc motor may be operating in one or more of the following “Modes” • • Motoring Regenerative braking Dynamic braking Plugging ECE 442 Power Electronics 14

Motoring Mode “Back emf”, Eg is < supply voltage Va Both Ia and If are positive Developed torque meets load demand ECE 442 Power Electronics 15

Regenerative Braking Mode Motor acts as a Generator Eg becomes > supply Voltage Va Ia becomes negative Kinetic energy of the motor is returned to the supply ECE 442 Power Electronics 16

Dynamic Braking Replace the supply voltage with a resistor Power dissipated in the resistor rather than given back to the source ECE 442 Power Electronics 17

Plugging Reverse the armature terminals while running Va and Eg act in the same direction Ia is reversed, producing “braking” torque ECE 442 Power Electronics 18

Four-Quadrant Operation ECE 442 Power Electronics 19

Single-Phase DC Drive Change Va by changing firing angle Inductor Lm is a “smoothing” Inductor to prevent discontinuous current ECE 442 Power Electronics 20

Armature Reversal ECE 442 Power Electronics 21

Field Reversal ECE 442 Power Electronics 22

Single-Phase Half-Wave Converter Drive ECE 442 Power Electronics 23

Quadrant of Operation ECE 442 Power Electronics 24

Waveform Summary ECE 442 Power Electronics 25

Single-Phase Semiconverter Drives ECE 442 Power Electronics 26

Quadrant(s) of Operation Semiconverter – one quadrant converter One polarity of output voltage and current ECE 442 Power Electronics 27

Waveform Summary ECE 442 Power Electronics 28

Single-Phase Full-Converter Drives ECE 442 Power Electronics 29

Quadrant(s) of Operation Full converter – two quadrant converter Output voltage polarity can be positive or negative Output current has one polarity ECE 442 Power Electronics 30

Waveform Summary ECE 442 Power Electronics 31

Single-Phase Dual-Converter Drives Dual converter can operate in all four quadrants Output voltage and current can be positive or negative ECE 442 Power Electronics 32