Ec1010 Power Electronics Aim Application Of Electronic Knowledge In Industry

EC1010 POWER ELECTRONICS AIM Application of Electronic knowledge in industry for rectification of polyphase supply voltage and for control of motor speed and for thermal heating. OBJECTIVES • To study about power electronic circuits for voltage and current control and protection. • To learn the switching characteristics of transistors and SCRs. Series and parallel functions of SCRs, Programmable triggering methods of SCR. • To learn controlled rectification AC supplies. • To study of converters and inverters. • To learn about motor control, charges, SMPS and UPS. UNIT I POWER ELECTRONICS DEVICES 9 Characteristics of power devices – characteristics of SCR, diac, triac, SCS, GTO, PUJT – power transistors – power FETs – LASCR – two transistor model of SCR – Protection of thyristors against over voltage – over current, dv/dt and di/dt. UNIT II TRIGGERING TECHNIQUES 9 Turn on circuits for SCR – triggering with single pulse and train of pulses – synchronizing with supply – triggering with microprocessor – forced commutation – different techniques – series and parallel operations of SCRs. UNIT III CONTROLLED RECTIFIERS 9 Converters – single phase – three phase – half controlled and fully controlled rectifiers – Waveforms of load voltage and line current under constant load current – effect of transformer leakage inductance – dual converter. UNIT IV INVERTERS 9 Voltage and current source inverters, resonant, Series inverter, PWM inverter. AC and DC choppers – DC to DC converters – Buck, boost and buck – boost. UNIT V INDUSTRIAL APPLICATIONS 9 DC motor drives – Induction and synchronous motor drives – switched reluctance and brushless motor drives – Battery charger – SMPS – UPS – induction and dielectric heating. TOTAL : 45 TEXT BOOKS 1. Muhamed H.Rashid : Power Electronics Circuits, Devices and Applications, 3rd Edn. 2004 PHI. 2. Singh and Kanchandani : Power Electronics, TMH, 1998. REFERENCES 1. Sen : Power Electronics, TMH, 1987. 2. Dubey : Thyristorised power controllers, Wiley Eastern 1986. 3. Vithayathil : Power Electronics – Principles and applications McGraw-Hill, 1995. 4. Lander : Power Electronics, 3rd Edition, McGraw-Hill, 1994.

B.E. ELECTRICAL AND ELECTRONICS ENGINEERING SEMESTER V EE 332 - POWER ELECTRONICS Time : 3 Hrs Max. Marks: 100 PART - A (10 x 2 = 20 Marks) 1. What are the differences between Transistor & SCR? 2. Explain latching current and holding current of thyristor. 3. What is natural or line commutation? 4. Why is power factor of semiconverter better than full converter? 5. What are the differences between free wheeling diode and feedback diode? 6. What are the main differences between voltage source inverter and current source inverter? 7. What are the advantages and disadvantages of AC voltage controllers? 8. Explain time ratio control of choppers. 9. Draw the load voltage waveform for a = 150o. 10. Explain the principle of operation of step up chopper. PART - B (5 x 16 = 80 Marks) 11. A dc battery is charged through a resistor R as shown in fig.1. Derive an expression for the average value of charging current in terms of Vm, E, R on the assumption that SCR is fired continuously. a. For an ac source voltage of 230V, 50Hz find the value of average charging current for R = 8O and E = 150V b. Find the power supplied to battery and dissipated in the resistor. c. Calculate supply PF. Fig. 1 12.a) For three phase thyristor controlled half wave rectifier feeding load R as shown in fig. 2. Show that the average output voltages are given by Vo = (3v3 Vm Cos a) / 2p for 0 = a = p/6 Vo = (3/2p) Vm [1+cos (a + p/6)] for p/6 = a = 5p/6 Where Vm is the maximum value of phase voltage and a is the firing angle delay. Fig. 2 (OR) 12.b) A half controlled 3 phase bridge rectifier is supplied at 220v from a source of reactance 0.24O/phase. Neglecting resistance and device volt drops determine mean load voltage for level load current of 40A at a firing delay angle of 45º and 90º. 13.a) Explain the operation of single phase modified MC Murray half bridge inverter (OR) 13.b)i) Explain the operation of modified series inverter with neat diagram. Derive an expression for the output frequency of the inverter. ii) What is the difference between series and parallel inverter? 14.a) Explain the operation of voltage commutated chopper with neat diagram and waveforms. Derive expressions for commutating capacitor (C) and commutating inductor (L). (OR) 14.b) For a current commutated chopper peak commutating current is twice the maximum possible load current. The source voltage is 230V dc and main SCR turn of time is 30µsec. The circuit turn off time is twice device turn off time. For maximum load current of 200A calculate. (i) Values of the commutating inductor and capacitor (ii) Maximum capacitor voltage (iii) Peak commutating current 15.a) Explain the operation of multistage sequence control of ac voltage controllers with neat diagram. (OR) 15.b) Explain the operation of single phase to single phase step down cyclo converter with voltage and current waveforms for (i) Continuous load current (ii) Discontinuous load current