Power Electronics

TECHNICAL REPORT It is required to prepare and submit a technical report that include, but not limited to, the following information concerning the main Power Electronics Switches: Basic Construction; ✓ Symbols; Classifications in terms of Controllability; ✓Latching or Continuous (Voltage or Current Controlled); ✓ Voltage Withstanding Capability; ✓ Current Withstanding Capability; ✓ Recent Voltage and Current Ratings. ✓ Any other relevant information.

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

(a) The single phase half-bridge inverter in Fig.Q6(a), has a load with resistance of R = 25 £2.The DC input voltage of Vs =100 V. (i)Sketch the load voltage and current waveforms. (ii) Calculate the output power Po. (iii) Determine the peak current of each transistor. (iv) The total harmonic distortion (THD) in the output voltage (b) A single phase 50 Hz bridge rectifier is fed at 240 V (rms). The load is a resistance of 350 ohms. Design an LC filter for the purpose of providing a maximum ripple factor of 5% in the load. The design should specify suitable values for L and C. Explain any assumptions made. The output/input voltage ratio of the filter is given by: \frac{V_{\text {out }}}{V_{\text {in }}}=\left|\frac{1}{1-\omega^{2} L C}\right|

Problem 2: Consider the Buck-Boost regulator in Figure 2. Take Vs=12V & Is= 0.5A. Take L=200µH, C= 250µF. Compute a) The average output voltage Va, b) The average output current la, c) Peak to eak output voltage ripple, AVC, d) Peak-to-peak ripple current of inductor, Al, Peak current of the transistor, Ip. The Consider the following scenarios: 1. K=0.5, The switching frequency is swept from 10KHz to 100KHz with increments of 5Khz 2. K is swept from k=0.1 to 0.9 with 0.05 increments, switching frequency is fixed at 25 KHz.Show the results in tabular form and graph.

100MVA synchronous generator is connected to a 25 kV infinite bus through two parallel transmission lines. X_{s}=2.5 \Omega \text { - } X_{\text {line }}=2 n 100MVA is delivered to the infinite bus at 0.8 lagging power factor. Whether the generator can still deliver the load if one of the transmission lines is knocked out and the mechanical power and excitation to the generator does not change.

●Full wave SCR converter circuit is used to regulate power across a 100 resistance. 120V RMS voltage. ●Trigger angle is 60°. a. Conduction period. b. Average voltage of the load. c. Average voltage of the SCRs. d. RMS voltage of the load. e. Average current. f. Power consumed by the load.

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.

Problem 4: A BJT is as shown in Figure 4 is specified to have BF in the range of 8 to 40. The load resistance is Rc=12.0 ohms, The DC supply voltage Vcc= 200V and the input voltage to the base circuit is VB=10V, the saturation collector emitter voltage VCESAT =1.0V and the saturation base emitter voltage VBESAT=1.5V. Find RB, B forced and Power loss (PT) in the transistor for ODF range=1 to 12 increments of 0.5. Note. Show your computation for each case and summarize all results in a tabular form. Plot ODF versus PT.

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.

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.

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.

I wanted to see whether this class made any difference on your conception of the electric energy systems. This question should be easy, but single word answers will not get you those points nor will full blown essays. You need to be able to concisely convince me that you fully understand opinions based on what we had discussed in class. 1. Which idea or concept that we discussed made the most impression on you? Why? 2. Are you more optimistic or pessimistic about our energy future after having taken this class? Why? 3. After having taken this class, are you more or less curious about our electrical energy future as a consumer? Why? 4. Would you consider going into electric power as a career option after having taken this class? Why? 5. Did this class change your outlook on the complexity of the electric energy system?Name one thing that was a key to changing your outlook. Why?

Given: \text { - } 480 \mathrm{~V}, 60 \mathrm{~Hz} 3 \text { phase induction motor. } \text { - } R_{1}=R_{\mathbf{2}}^{\prime}=0.3 \Omega -X_{e q}=1.0 n \cdot X_{M}=600 \Omega \text { - At full load, } n=1120 R P M \text { - } P_{\text {not }}=400 W \text { - } P_{\text {Core }}=1 k W 1. Slip2. Full load torque 3. Rotor current 4. Copper loss 5. Input power 6. Reactive power at input. Motor power factor.

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]

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

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.

Problem 3: Consider the Chuck regulator in Figure 2. Take Vs=12V & Is= 0.5A. Take L=200µH, C=250µF. The energy transfer Capacitance, C1 is 200µF, and Inductance, L1= 250µH.Compute f) The average output voltage Va, g) The average output current la, h) Peak to peak output voltage ripple of Capacitor C1, AVc1, i) Peak-to-peak ripple current of inductor L1, AI1, j) Peak to peak output voltage ripple of Capacitor C2, AVC2, k) Peak-to-peak ripple current of inductor L2, A12, 1) Peak current of the transistor, Ip. The Consider the following scenarios: 3. K=0.5, The switching frequency is swept from 10KHz to 100KHz with increments of 5Khz 4. K is swept from k=0.1 to 0.9 with 0.05 increments, switching frequency is fixed at 25 KHz .Show the results in tabular form and graph.

(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]

As an engineer you are asked to design LEDS for traffic light signals. Specifically, you are asked to design LEDS for yellow light at wavelength A, = 590 nm and red light at wavelength A, = 625 nm. You are provided gallium arsenide and gallium phosphide material systems to reach these designs. Consider the plot on the left. Here T refers to T valley in the transition of electron in the band structure of GaAs1-x Px. T-branch in the plot refers to direct band gap transition leading to radiative recombination. L branch refers to indirect bandgap radiative recombination. Finally, X refers to indirect band gap transition but in this branch, the momentum recombination which is not a conservation during recombination is sufficient enough for a photon emission (refer notes for details). That is, X branch is indirect recombination but still produces radiative recombination, and therefore can be used for LED material. Find out the formula for the ternary semiconductor material GaAs1-xPx, by finding the value of x for(a) Yellow LED (b) Red LED of t

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.

Problems-a) Consider a Si-solar cell with square cross-section with dimensions 2 cm x 2 cm, with thermal current Ith= 32 nA (here thermal current is same as leakage current) with an optical generation rate of 1018 EHP cm³s within Lp=Ln=2 µm of the junction. If the depletion width is 1 µm, calculate the short-circuit current and the open-circuit voltage for this cell. Also calculate the power expected from the single cell of the fill factor is known to be 0.7. (EHP means electron hole pairs) b) Because Si-bandgap is 1.1 eV, what is the cut-off wavelength for the photo current to be produced due to an incidence of light. c) Can sunlight in the visible region produce a photo current for this solar cell? (compare the calculated wavelength from (b) with the sunlight wavelength).

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?)