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QUESTION: 1

A three phase bridge inverter is fed from a 500 V dc source. The inverter is operated in 180° conduction mode and it is supplying a purely resistive, star – connected load. The RMS value of the output (line) voltage is

Solution:

= 0.816 × 500 = 408 V

QUESTION: 2

In a three phase voltage source inverter operating in square wave mode, the output line voltage is free from

Solution:

The rms nth component of the line voltage is

where Vdc is the input source voltage for n = 3, line voltage

Third harmonic component would not appear in the output

*Answer can only contain numeric values

QUESTION: 3

In single pulse modulation of PWM inverter, 3^{rd} harmonic can be eliminated if pulse width is equal to______ (in degrees)

Solution:

Pulse width for eliminating

n^{th} harmonic

*Answer can only contain numeric values

QUESTION: 4

A three – phase bridge inverter delivers power to a resistive load from a 450 V dc source. for a star connected load if 10Ω per phase. What is the load power for 180° conduction mode ______________ (in kW)

Solution:

QUESTION: 5

A 3 ϕ bridge inverter delivers power to a resistive load from a 400 V dc. For a star – connected load of 15 Ω per phase, determine load power and R.M.S value of thyristor current for 120° mode

Solution:

load power = 3I^{2}_{or }R = 3 × (10.87)^{2} × 15 = 5.317kW

*Answer can only contain numeric values

QUESTION: 6

A 3 phase MOSFET inverter is connected between a balanced star connected resistive load with R_{L} = 10 Ω and a 250 V dc supply. The inverter frequency is set at 33 Hz, and the switches have 120° conduction periods. Calculate the load power _______ (in kW)

Solution:

= 3.13 kW

*Answer can only contain numeric values

QUESTION: 7

for a single pulse – width modulation of a single phase inverter, The distortion factor for pulse width of π/2 is ___________

Solution:

given, 2d = π/2

single pulse modulation output for pulse width 2d = π/2 is shown below.

from Fourier series, fundamental output voltage is

from output voltage wave form

QUESTION: 8

For a load of R = 10 Ω and L = 0.03 H, Find the RMS value of the fundamental component of inverter output current in case inverter of part Quasi-square output with 120° pulse width. The source voltage is 230 V and frequency 50 Hz

Solution:

__Concept:__

The output voltage is controlled by varying the pulse-width 2d. This shape of the output voltage is called Quasi-square wave.

Fourier series of this wave from is

Fundamental component of output voltage

__Calculation:__

Load impedance at Fundamental Frequency is

For Quasi-square wave or single-pulse modulated wave where pulse width, 2d = 120° or d = 60°

∴ R.M.S value of fundamental current

*Answer can only contain numeric values

QUESTION: 9

The inverter is operated at 50 Hz. In 180° square wave mode. Find the peak to peak inductor i_{0} in the circuit shown in figure.

Solution:

at, t = 0, i_{0} = -i_{p} and t = t_{1}, i_{0} = i_{p
}

*Answer can only contain numeric values

QUESTION: 10

For the symmetrical two pulse modulation with pulse width 36°. Find the percentage of 3^{rd} harmonic in the output voltage is_______

Solution:

__Concept:__

In multiphase pulse modulation, several equidistant pulses per half cycle are used.

Fourier series of multiple pulse modulation is

N = pulse per half cycle

__Calculation:
__

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