Question

Q5 A three-phase inverter is used to achieve variable-speed control of an induction motor having the following parameters: Rated Voltage: 415V (line-to-line, rms) Rated Frequency: 50Hz Number of Poles: 2 $X_s = 0.70\Omega$ $R_s = 0.09\Omega$ $X_r = 0.90\Omega$ $R_r = 0.15\Omega$ $L_m$ is assumed to be large (a) Sketch the output voltage waveforms produced by fundamental frequency (square wave) modulation of the three-phase inverter. Discuss the problems that would be encountered if this voltage was used to drive a three-phase induction motor. 20% (b) Explain how the inverter can be used to achieve variable speed control of an induction motor and show how the inverter generates a balanced three-phase ac output voltage with controllable amplitude and frequency. 30% (c) If the motor is under constant $V/f$ control operating at a slip of 0.08 and the inverter output frequency is 30Hz, calculate the motor torque and rotor current. 30% (d) The motor operates at steady-state under the conditions specified in (c). If the inverter output frequency is suddenly increased to 40Hz while still under constant $V/f$ control, what is the torque produced at the instant of the sudden frequency increase? 20%

          Q5 A three-phase inverter is used to achieve variable-speed control of an induction motor having the
following parameters:
Rated Voltage: 415V (line-to-line, rms)
Rated Frequency: 50Hz
Number of Poles: 2
$X_s = 0.70\Omega$
$R_s = 0.09\Omega$
$X_r = 0.90\Omega$
$R_r = 0.15\Omega$
$L_m$ is assumed to be large
(a) Sketch the output voltage waveforms produced by fundamental frequency (square wave)
modulation of the three-phase inverter. Discuss the problems that would be encountered if this
voltage was used to drive a three-phase induction motor.
20%
(b) Explain how the inverter can be used to achieve variable speed control of an induction motor and
show how the inverter generates a balanced three-phase ac output voltage with controllable
amplitude and frequency.
30%
(c) If the motor is under constant $V/f$ control operating at a slip of 0.08 and the inverter output
frequency is 30Hz, calculate the motor torque and rotor current.
30%
(d) The motor operates at steady-state under the conditions specified in (c). If the inverter output
frequency is suddenly increased to 40Hz while still under constant $V/f$ control, what is the torque
produced at the instant of the sudden frequency increase?
20%

Q5 A three-phase inverter is used to achieve variable-speed control of an induction motor having the
following parameters:
Rated Voltage: 415V (line-to-line, rms)
Rated Frequency: 50Hz
Number of Poles: 2
Xs = 0.70Ω
Rs = 0.09Ω
Xr = 0.90Ω
Rr = 0.15Ω
Lm is assumed to be large
(a) Sketch the output voltage waveforms produced by fundamental frequency (square wave)
modulation of the three-phase inverter. Discuss the problems that would be encountered if this
voltage was used to drive a three-phase induction motor.
20%
(b) Explain how the inverter can be used to achieve variable speed control of an induction motor and
show how the inverter generates a balanced three-phase ac output voltage with controllable
amplitude and frequency.
30%
(c) If the motor is under constant V/f control operating at a slip of 0.08 and the inverter output
frequency is 30Hz, calculate the motor torque and rotor current.
30%
(d) The motor operates at steady-state under the conditions specified in (c). If the inverter output
frequency is suddenly increased to 40Hz while still under constant V/f control, what is the torque
produced at the instant of the sudden frequency increase?
20%

Added by Curtis M.

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