# Power Electronics

## Questions & Answers

Problem 1: A single-phase half bridge inverter Figure 1, has a resistive load of R=4.00 and the DC input voltage is Vs=48V. a) Derive and compute the RMS output voltage. b) Derive and compute the Instantaneous voltage for the output components (the first 30harmonics) c) Derive and compute the RMS voltage for the output components (the first 30 harmonics) d) Output Power e) Average and peak current for each transistor, assume duty cycle of 50% Total Harmonic Distortion (THD) g) Distortion Factor (DF) h) Harmonic Factor of the lowest order harmonic

Full wave SCR converter circuit is used to regulate power across a 100 resistance. 120V RMS voltage. Trigger angle is 72º. a. Power across the load. b. RMS current of the load.

We know that the PN junctions, diodes, photodiodes (LEDS and photodetectors) have similar physical structure. But +ve and -ve terminals and direction of currents depends on how the device is being operated.Consider following PN junctions with light shining on it, such that hv > Eg. Here E,is the band gap of the semiconductor material of the PN junction. We are considering three cases of using the PN-junction, as shown in the first column of the table. Fill in the table based on your understanding of rectifier diodes, photodetectors and solar-cells.

Half wave rectifier Converting 120VRMS voltage into DC. \text { - Load is } 5 \Omega 1. Average voltage across the load.2. Average voltage of the source.3. RMS voltage of the load 4. RMS current of the load.5. 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]