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POWER ELECTRONICS ECE 105 Industrial Electronics

POWER ELECTRONICS ECE 105 Industrial Electronics. Engr. Jeffrey T. Dellosa College of Engineering and Information Technology Caraga State University Ampayon, Butuan City. Power Electronics. Introduction

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POWER ELECTRONICS ECE 105 Industrial Electronics

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  1. POWER ELECTRONICSECE 105 Industrial Electronics Engr. Jeffrey T. Dellosa College of Engineering and Information Technology Caraga State University Ampayon, Butuan City

  2. Power Electronics • Introduction Power electronics is the technology of converting electric power from one form to another using power semiconductor devices based circuitry. It incorporates concepts from analog circuits, electronic devices, control systems, power systems, magnetics, and electric machines.

  3. The converter enables either the following: DC-DC: conversion AC-DC: rectification DC-AC: inversion AC-AC: cycloconversion Power Electronics

  4. In the power converter, the power semiconductor devices function as switches, which operate statically, that is, without moving contacts. The time durations, as well as the turn ON and turn OFF operations of these switches are controlled in such a way that an electrical power source at the input terminals of the converter appears in a different form at its output terminals. Power Electronics

  5. Power Electronics Here power converter high conversion efficiency  is essential! High efficiency leads to low power loss within converter. Efficiency is a good measure of converter performance. Hence, a goal of current converter technology is to construct converters of small size and weight, which process substantial power at high efficiency.

  6. Power Electronics Components used in power electronics circuitry are:

  7. Rapid development of power semiconductor devices led to significant improvement in, • Speed • Power capability • Efficiency Hence increase the range of applications • DC Servo control • AC motor control • Sophisticated power supplies (switching-mode, uninterruptible) • High power DC transmission Power Electronics

  8. Power Electronics Often power loss in power semiconductor device (when viewed as an ideal switch) is based on the following: Thus an ideal power semiconductor device is characterized by zero resistance during ON-state, infinite resistance during OFF-state, zero transient time from ON to OFF and vice-versa. Practical power semiconductor device has limited voltage and current handling capability, an ON-resistance greater than zero and finite switching times.

  9. Power Electronics • Power Electronics Devices • Power Bipolar Transistors (BJTs) • Power Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) • Insulated Gate Bipolar Transistors (IGBTs) • Thyristors • Gate Turn-Off Thyristors (GTOs) • Power Diodes

  10. Power Electronics

  11. Power Electronics

  12. Alternatively power semiconductor devices can be classified into 3 groups according to their degree of controllability. • Power Diodes - ON and OFF states controlled by the power cct. • Thyristors - Latched ON by a control signal but must be turned OFF by the power cct. • Controllable Switches - Turned ON and OFF by control signals. • The controllable switches include • i) BJTs • ii) MOSFETs • iii) Gate Turn-OFF Thyristors (GTOs) • iv) Insulated Gate Bipolar Transistors (IGBTs) Power Electronics

  13. Power Electronics • Power Diodes The circuit symbol for the diode and its steady state v-i characteristics are as shown.

  14. Power Electronics • Power Diodes

  15. Power Electronics • Thyristors The circuit symbol for the thyristor and its steady state v-i characteristics are as shown.

  16. Power Electronics • Thyristors In its OFF state, the thyristor can block a forward polarity voltage and not conduct, as is shown by the off-state portion of the i-v characteristic. The thyristor can be triggered into the ON state by applying a pulse of positive gate current for a short duration provided that the device is in its forward-blocking state. The resulting i-v relationship is shown by the ON state portion of the characteristics shown. The forward voltage drop in the ON state is only a few volts (typically 1-3V depending on the device blocking voltage rating).

  17. Power Electronics • Power BJTs The circuit symbol for the BJTs and its steady state v-i characteristics are as shown.

  18. Power Electronics • Power BJTs As shown in the i-v characteristics, a sufficiently large base current results in the device being fully ON. This requires that the control circuit to provide a base current that is sufficiently large so that where hFE is the dc current gain of the device BJTs are current-controlled devices, and base current must be supplied continuously to keep them in the ON state: The dc current gain hFE is usually only 5-10 in high-power transistors. BJTs are available in voltage ratings up to 1400V and current ratings of a few hundred amperes.

  19. Power Electronics • Power BJTs • BJT has been replaced by MOSFET in low-voltage (<500V) applications • BJT is being replaced by IGBT in applications at voltages above 500V

  20. Power Electronics • Power MOSFETs The circuit symbol for the MOSFETs and its steady state v-i characteristics are as shown.

  21. Power Electronics • Power MOSFETs • Power MOSFET is a voltage controlled device. • MOSFET requires the continuous application of a gate-source voltage of appropriate magnitude in order to be in the ON state. The switching times are very short, being in the range of a few tens of nanoseconds to a few hundred nanoseconds depending on the device type.

  22. Power Electronics • Power MOSFETs

  23. Power Electronics • IGBTs The circuit symbol for the IGBTs and its steady state v-i characteristics are as shown.

  24. Power Electronics • IGBTs • The IGBT has some of the advantages of the MOSFET, & the BJT combined. • Similar to the MOSFET, the IGBT has a high impedance Gate, which requires only a small amount of energy to switch the device. • Like the BJT, the IGBT has a small ON-state voltage even in devices with large blocking voltage ratings (for example, VON is 2-3V in a 1000-V device)..

  25. Power Electronics • IGBTs

  26. Power Electronics • Several Applications of Power Electronics A laptop computer power supply system.

  27. Power Electronics • Several Applications of Power Electronics An electric vehicle power and drive system.

  28. Power Electronics • Transient Protection of Power Devices Snubber circuit limits , as well as voltage and peak current in a switching device to safe specified limits! Switching device’s rating is significant during the switching device (e.g. thyristor) turn-OFF process. Voltage can increase very rapidly to high levels. If the rate rise is excessive, it may cause damage to the device.

  29. Power Electronics • Transient Protection of Power Devices

  30. Power Electronics • Transient Protection of Power Devices

  31. Power Electronics • Transient Protection of Power Devices

  32. Power Electronics • Transient Protection of Power Devices

  33. Power Electronics • Transient Protection of Power Devices

  34. Power Electronics • Transient Protection of Power Devices

  35. Power Electronics • Power and Harmonics in Non-sinusoidal Systems Non-sinusoidal waveforms are waveforms that are not sine waves. , Non-sinusoidal waveforms can be described as being made of harmonics (multiple sine waves of different frequencies). Thus for a waveform whose fundamental frequency is , than second harmonic has a frequency 2and so on. Waveforms occurring at frequencies of 2, 4, 6, … are called even harmonics; Those occurring at frequencies of 3, 5, 7, ... are called odd harmonics.

  36. Power Electronics • Power and Harmonics in Non-sinusoidal Systems Thus for the circuit shown (a non-sinusoidal system),expressing the circuit’s voltage and current as Fourier series: ,

  37. Power Electronics • Power and Harmonics in Non-sinusoidal Systems ,

  38. Power Electronics • Power and Harmonics in Non-sinusoidal Systems Expression for average power becomes , So power is transmitted to the load only when the Fourier series of v(t) and i(t) contain terms at the same frequency. Eg. if the voltage & current both contain 3rd harmonic, then they lead to the average power

  39. Power Electronics • Power and Harmonics in Non-sinusoidal Systems With the rms voltage defined as , Inserting Fourier series into the above, an expression of rms voltage for non-sinusoidal voltage waveform Notice harmonics always increase rms value & increased in rms values  increased losses!

  40. Power Electronics • Power and Harmonics in Non-sinusoidal Systems For efficient transmission of energy from a source to a load, it is desired to maximize average power, while minimizing rms current and voltage (and hence minimizing losses). Power factor is a figure of merit that measures how efficiently energy is transmitted. It is defined as , Notice harmonics always increase rms value & increased in rms values  increased losses!

  41. Power Electronics • Basic Magnetics Inductance (measured in Henry) is an effect which results from the magnetic field that forms around a current carrying conductor. Inductance can be increased by looping the conductor into a coil which creates a larger magnetic field. , An inductor is usually constructed as a coil of copper wire, wrapped around a core either of air or of ferrous material. Core materials with a higher permeability than air confine the magnetic field closely to the inductor, thereby increasing the inductance. Inductors come in many shapes. Most are constructed as enamel coated wire wrapped around a ferrite bobbin with wire exposed on the outside, while some enclose the wire completely in ferrite and are called "shielded". Some inductors have an adjustable core, which enables changing of the inductance. Small inductors can be etched directly onto a printed circuit board by laying out the trace in a spiral pattern.

  42. Power Electronics • Basic Magnetics Current flowing through an inductor creates a magnetic field which has an associated electromotive force (emf). This inductor’semf opposes the change in applied voltage. The resulting current in the inductor resists the change but does rise! , • An inductor resists changes in current. • An ideal inductor would offer no resistance to direct current; however, all real-world inductors have non-zero electrical resistance. In general, the relationship between v(t) across an inductor with inductance L and i(t) passing through it is described by the differential equation: The inductor is used as the energy storage device in power electronics circuitries.

  43. Power Electronics • Basic Magnetics Transformers -- widely used in low-power electronic ccts for voltage step-up or step-down, & for isolating DC from two ccts while maintaining ac continuity. -- consists of 2 windings linked by a mutual magnetic field. When one winding, the primary has an ac voltage applied to it, a varying flux is developed; the amplitude of the flux is dependent on the applied voltage and number of turns in the winding. Mutual flux linked to the secondary winding induces a voltage whose amplitude depends on the number of turns in the secondary winding.

  44. Power Electronics • Basic Magnetics Mutual magnetic flux coupling is accomplished simply with an air core but considerably more effective flux linkage is obtained with the use of a core of iron or ferromagnetic material with higher permeability than air. The relationship between voltage, current, & impedance between the primary & secondary windings of the transformer may be calculated using the following relationships.

  45. Power Electronics • Basic Magnetics The basic phase relationship between the signals at the transformer input & output ports may be in-phase, or out-of-phase. Conventionally, the ports that are in-phase 1, and 3, are marked by dot notation as shown.

  46. Power Electronics • Basic Magnetics EXAMPLE

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