Question Details

Consider an ideal full-bridge single-phase DC-AC inverter with a DC bus voltage magnitude of 1000 V. The inverter output voltage v(t) shown below, is obtained when diagonal switches of the inverter are switched with 50% duty cycle. The inverter feeds a load with a sinusoidal current given by, i(t)=10sin(ωt-π/3),  where ω=2π/t. The active power, in watts, delivered to the load is _____. (round off to nearest integer)

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Correct Answer :

3183

Solution :

The correct answer is 3183.

1. Analysis of the Output Voltage Waveform:
From the given waveform of the output voltage v(t), we observe that it is a symmetric square wave with a period of T and a peak magnitude equal to the DC bus voltage Vdc=1000 V.

The voltage waveform can be mathematically represented over one cycle as:
v(t)=1000 V for 0<t<0.5T
v(t)=-1000 V for 0.5T<t<T

2. Fourier Series Expansion of the Voltage:
For a square wave with odd symmetry, the Fourier series expansion consists only of odd harmonic sine terms:
v(t)=n=1,3,5,...4Vdcnπsin(nωt)

The fundamental frequency component (n=1) of the output voltage is:
v1(t)=V1msin(ωt)=4Vdcπsin(ωt)

Substituting Vdc=1000 V:
v1(t)=4000πsin(ωt) V

3. Load Current and Active Power Calculation:
The current delivered to the load is purely sinusoidal at the fundamental frequency:
i(t)=10sin(ωt-π3) A

Since the load current has no higher-order harmonics, active power is only delivered by the fundamental component of the voltage. The active power P is given by:
P=V1,rmIrmscos(ϕ)

where:
- The RMS value of the fundamental voltage is V1,rms=V1m2=4000π2 V
- The RMS value of the load current is Irms=Im2=102 A
- The phase angle difference is ϕ=π3

Substitute these values into the power equation:
P=(4000π2)×(102)×cos(π3)

Since cos(π3)=0.5:
P=400002π×0.5=10000π W

Evaluating this numerically:
P3183.09886 W

Rounding to the nearest integer, we get:
P=3183 W

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