Test: Inverters- 2 - Electrical Engineering (EE) MCQ

• By using adjustable voltage inverter, speed range of motor is limited because of motor cogging at 6 Hz and below.
• In pulse width modulated inverter, input p.f. is good at all frequencies.
• A CSI has the capability of regeneration back to the a.c. line because d.c. link polarity can be reversed.
• In VSI, the misfiring of switching devices may cause short circuit across the source and create serious problems.

Output voltage 
= 254.65 sin314t + 84.88 sin 942t + 50.93 sin 1570t
It is of the general form
V₀ = V₁ sin w₁ t + V₂ sin w₂ t + V₃ sin w₃ t

In case of singte-putse width modulation (PWM), the width of the pulse is adjusted to reduce the harmonic. However, a single phase IGBT bridge inverter produces a square wave. This square wave contains  harmonic, harmonic andharmonic.

The rms value of amplitude of harmonic voltage of a single, pulse modulated wave is given by

(where, p = width of pulse an V_dc = supply dc voltage)
If the 3^rd harmonic Is to be eliminated, then
E_L3 = 0
i.e. 
or, 
or, 
= Required pulse width

The output voltage wave form

at D₁ D₃ Path

In a 1-φ full bridge inverter if RLC load is underdamped, then the two thyristors (namely T₁ and T₂) shown in figure will get commutated naturally and therefore no commutation circuitry will be needed. Thus, load commutation will be possible.

(Here, 2 pulse width = 120°)
∴ 

A voltage source inverter is one in which the d.c. source has small or negligible impedance. Due to low internal impedance, the terminal voltage of a VSI remains substantially constant with variations in load. Reason is also a correct -statement because due to low time constant of internal impedance any short-circuit across the terminals of a VSI causes current to rise very fast. Hence, both assertion and reason are true but reason is not the correct explanation of assertion.

The machine operated at 50 H_z.

Synchronous speed N_s

A slip of S = 0.02
N_r = (1 - S) N_s = 980 rpm.

The average voltage across the inductor for a complete cycle is zero and also the power dissipated across
inductor per cycle is zero So,
The load power only due to resistor 


for 3 phases = 166.62 × 3 ≌ 500 Watt.