Power Electronics

A practical switch is operating at a switching frequency of 100 kHz and a 0.5 duty cycle. The switch has the following parameters: Von = 0.1 V Voff = 80 V Ion = 100 A loff = 0.1 A ton = toff = 100 ns (switching on and off times) delay = 0 Determine: 1) The total average power loss in on switching cycle. 2) The maximum instantaneous power. Hint: Draw the switching waveforms for the current and the voltage assuming linearized waveforms

Given: 150kVA 2400V/240V 60 Hz transformer. Open circuit test on the 240V winding of the transformer gives: o VocO= 240V loc = 16.75A Poc=580 Watts Short circuit test was done with the low voltage winding short circuited. Vsc= 63V Isc= 62.5A Psc = 1600 Watts Exciting admittance, conductance, and susceptance. Equivalent primary impedance, reactance, and resistance. For efficiency of the transformer at the rated load at 0.8 lagging power factor.

DC/DC buck converter Input voltage of 100V ●Duty ratio of 0.2 a. Load voltage. b. On-time is 0.1ms. Switching frequency of the converter.

a) Choose the BEST answer only for each of the following questions: (ii) In a three phase uncontrolled full wave rectifier, each diode conducts for: (iii) The switching control action in Fig. Q4(a-iii) is known as: (iv) The ratio between the height of the reference wave and the carrier wave in inverter-control is called: (v) For the three phase inverter circuit shown in Fig. Q4(a-v1), the state given in Fig.Q4(a-v2) results in which combination of line voltages? (vi) The AC voltage of a square wave inverter is likely to have which of the following harmonic contents? (vii) The extent of harmonic pollution in a current or voltage waveform can be determined by: A three-phase fully controlled bridge rectifier is delivering a constant DC current of 50A to load from a 415V, 50Hz three phase source with a source inductance of 4.8mH per phase(and negligible source resistance). Neglecting the Thyristor forward voltage drop, for a firing angle of 45° determine: (i)The mean output voltage of the circuit The overlap angle The generalised mean output voltage of a p-pulse converter is given by the expression: V_{\text {mean }}=\left(\frac{p V_{\max }}{\pi} \sin \frac{\pi}{p}\right) \cos \alpha-\frac{p X}{2 \pi} I_{L} The generalized expression of mean voltage with overlap angle y is expressed as follows: V_{\text {mean }}=\left[\frac{p V_{\max }}{\pi} \sin \left(\frac{\pi}{p}\right)\right]\{\cos \alpha+\cos (\alpha+\gamma)\} (c) With the aid of appropriate sketches, discuss how a pulse width modulated control signal with variable duty cycle can be generated to control a dc/dc converter.[6]

Half wave rectifier converts a 120V RMS voltage into DC. Load resistance is 59. a. Average voltage across the load. b. Average voltage of the source. c. RMS voltage of the load. d. RMS current of the load. e. Power consumed by the load.

(a) The DC chopper in Fig. Q5(a) has a resistive load, R=30 £2, and input voltage V₁=230 V.The on-state voltage drop of the switch is 1.5V and the switching frequency is 15kHz. Ifthe converter duty cycle is 65%, calculate: (i)The mean load voltage. (ii)The RMS load voltage. (iii) The ripple factor of the output voltage (iv) The converter efficiency (b) In power electronic equipment, most of the waveforms are non-sinusoidal. Discuss: (i) The significance of the presence of voltage/current harmonics caused by AC/DC converters. (ii) How the impact of those harmonics can be mitigated in power electronic circuits. (c) With the aid of a well labelled diagram, explain the application of power electronics in solar photovoltaic energy systems.[4]

Write the general equation governing the photo generation phenomenon in a PN junction diode. In the equation you should have the current-term due to the voltage biasing and the photo generated current term due to an incident light. Mark the terms in your provided equation. (1) Draw the I-V current relation (I versus V plot) for changing gop (rate of optical generation). (2) Which quadrant of this I-V relation is utilized for solar-cell applications. (mark in your I-Vcurve)? (3) Which quadrant of the I-V relation is utilized for photo-detector application (mark in your I-Vcurve)? Now consider the photogeneration current term. What will be the effect on photo generated current, if the P and N sides are highly doped in comparison to light doped. (hint: how depletion region width changes? How does depletion width change the current?)