GATE 2016 EE (EE2) – Question 55

Power Electronics · Voltage and Current commutated Thyristor based converters · 2 marks · Numerical answer

A lossless full bridge supplies the shown RLE load with firing angle 120°. Supply is $v_m(t)=200\pi\sin(100\pi t)$ V, R=20 Ω and E=800 V with the indicated polarity. L makes current IL smooth DC. Power returned to the source in kW is ________.

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Correct answer: 5.9 to 6.1

Explanation

Average bridge voltage is $(2V_m/\pi)\cos\alpha=400\cos120^\circ=-200$ V. The load source has the polarity shown, so the load equation is Vdc=RI−E.

Thus −200=20I−800 and I=30 A. Bridge DC power is Vdc I=−6000 W, signifying transfer from the DC source back to the AC mains.

The returned power magnitude is **6 kW**.

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