Power Electronics. Contents

Size: px

Start display at page:

Download "Power Electronics. Contents"

Shawn Gibbs
5 years ago
Views:

1 Power Electronics Overview Contents Electronic Devices Power, Electric, Magnetic circuits Rectifiers (1-ph, 3-ph) Converters, controlled rectifiers Inverters (1-ph, 3-ph) Power system harmonics Choppers and Drives

2 What is Power Electronics Power electronics links the two major traditional divisions of electrical engineering, namely electrical power and electronics. Involves the study of electronic circuits which control the flow of energy

3 Definition Power electronics involves the study of electronic circuits intended to control the flow of electrical energy. These circuits handle energy flow at levels much higher than individual device ratings.

4 Power Electronics Overview Conversion Technology Circuit theory Conversion efficiency Switching matrices Signal processing Filters Magnetic components Machines Power electronics Power semiconductor Technology Power devices Power ICs Drive circuits Protection circuits Heat sinks Power control Technology IC control package Microelectronic circuits Microprocessor circuits Digital and analog electronic circuits Control theory: transient and stability issues Digital and information signal processing Simulation Power electronics encompasses three technologies: power semiconductor, power conversion, and power control.

5 Energy source Components of a power electronic system Temporary energy storage or filtering, inductance,capacitance Switch(es) Control hardware and software Load Switch gate-drive circuitry

6 Power electronic system Most power electronic systems consist of two major modules: - The power stage (forward circuit) - The control stage (feedback circuit) η = Efficiency: p p out in X100 x 1, x 2,.., x n are input signals (voltage, current, angular frequency) y 1, y 2,.., y n are input signals (voltage, current, angular frequency) f 1, f 2,.., f n are feedback signals (voltage, current in electric system. or angular speed or position in mechanical system) P in instantaneous input power, P out instantaneous output power

7 Main Objectives of Power Conversion: Efficiency & Reliability Converter sits between source and load. Power input Switching Converter Power output Any energy consumed in conversion is lost to the system. Any failure in the converter results in failure of the system. Control input Efficiency (Target = 100%) η = P P out in 1 P loss = P in P out = P out ( - 1) η

8 Classification of Power Converter Circuits

9 Classification of Power Converter Circuits The function of the power converter stage is to perform the actual power conversion and processing of the energy from the input to the output by incorporating power switching devices * Power conversion refers to the power electronic circuit that changes one of the following: voltage form (ac or dc) voltage level (magnitude) voltage frequency (line or otherwise) - voltage wave-shape (sinusoidal or non-sinusoidal, such as square, triangle, or saw-tooth), voltage phase (single-or three-phase)

10 Classification of Power Converter Circuits There are four conversion circuits that are used in the majority of today s power electronic circuits: ac-to-ac ac-to-dc dc-to-ac dc-to-dc In terms of the functional description, modern power electronic systems perform one or more of the following conversion functions: Rectification (ac-todc) Inversion (dc-to-ac) Cycloconversion (ac-to-ac, different frequencies) or ac controllers (ac-to-ac, same frequency) Conversion (dc-to-dc)

11 Rectification (ac-to-dc) The term Rectification refers to the power circuit whose function is to alter the ac characteristic of the line electric power to produce a rectified ac power at the load site that contains the dc value. ac-dc rectification (a) Simplified block diagram representation (b) Example of ac-dc conversion

12 Inversion (dc-to-ac) The term Inversion is used to power electronic circuits for the function that alters the dc source (e.g. a battery) with no ac components into an inverted ac power at the load that has no dc components. Dc-to-ac inversion (a) Simplified block diagram representation (b) Example of dc-ac inversion (c) Block diagram representation with high frequency inversion

13 Cycloconversion or Voltage Controllers (ac-to-ac) The term Cycloconversion is used for power electronic circuits that convert the ac input power at one frequency to an ac output power at a different frequency using onestage conversion Cycloconversion (a) One-stage ac-to-ac cycloconversion (b) Example of ac-toacc onversion waveforms (c) Two-stage ac-to-ac cycloconversion

14 Conversion (dc-to-dc) dc-to-dc converters are used in power electronic circuits to convert an unregulated input dc voltage to a regulated or variable dc output voltage. Dc-to-dc conversion (a) One-stage dc-to-dc conversion (b) Example of waveforms (c) Two-stage dc-to-dc conversion

15 10 A dc-dc 100 v 50 v 5 Ω converter DC-DC Converter Line-frequency Transformer Utility Supply Rectifier Capacitor filter v d (t) v d range V d min V d Linear Power Supply Series transistor as an adjustable resistor Low Efficiency Heavy and bulky

16 The Switch When on: v = 0 When off: i = 0 Zero power Zero power Switch mode Power supply

17 Switch mode Power supply

18 Switch-Mode Power Supply with Isolation Transistor as a switch ac High Efficiency High-Frequency Transformer dc Rectifier-inverter

19 Basic Principle of Switch-Mode Synthesis 1-Constant switching frequency 2-Pulse width controls the average 3-L-C filters the ripple v oi V oi v ripple v oi (t) = V oi (t) +v ripple i T V o = 1 s t on v dt vd fston T T v oi = = s 0 s d t on T s = 1 f s t off

20 Power electronic conversion system representing four possible conversion functions Simplified Block Diagram representation of the power electronic conversion function

21 Load current i o, and voltage v o, shown in figure below can be either positive or negative, there exist four modes of operation as show in (b) i o Mode II Mode I v o dc rectifier ac Mode III Mode IV converter cycloconverter dc inverter ac (a) Simple power electronic circuit with single voltage source and single load. (b) Possible converter modes of operation

22 Power Electronics Today The fraction of energy that is processed electronically is growing rapidly. Power electronics: every computer, almost every appliance or new electrical product In every motor, alternative energy system, and automobile. Modern devices can manage energy flows from 1 W to more than 1000 MW.

23 Applications of Power Electronics Electrical applications ac and dc regulated power supplies for various electronic equipment, including consumer electronics, instrumentation devices, computers, aerospace, and uninterruptible power supply (UPS) applications. Electromechanical applications used in industrial, residential, and commercial applications Electrochemical applications includes chemical processing, electroplating, welding, metal refining, production of chemical gases, and fluorescent lamp ballasts

25 Power Processor as a Combination of Converters Most practical topologies require an energy storage element, which also decouples the input and the output side converters

26 Power Flow through Converters Converter is a general term An ac/dc converter is shown here Rectifier Mode of operation when power from ac to dc Inverter Mode of operation when power from dc to ac We also have dc to dc and ac to ac

27 AC Motor Drive Converter 1 rectifies line-frequency ac into dc Capacitor acts as a filter; stores energy; decouples Converter 2 synthesizes low-frequency ac to motor Polarity of dc-bus voltage remains unchanged ideally suited for transistors of converter 2

28 Application in Adjustable Speed Drives Conventional drive Adjustable speed drive Conventional drive wastes energy across the throttling valve to adjust flow rate Using power electronics, motor-pump speed is adjusted efficiently to deliver the required flow rate

29 Interdisciplinary Nature of Power Electronics

30 Components in Power Electronics Resistance Capacitor Coil High-frequency transformer Power Devices: Diode, DAIAC Thyristor = SCR = Silicon Controlled Rectifier, TRIAC BJT = Bipolar Junction Transistor MOSFET = Metal Oxide Semiconductor Field Effect Transistor GTO = Gate-Turn-Off Thyristor IGBT = Insulated Gate Bipolar Transistor MCT = Mos-Controlled Thyristors

31 IGCT = Integrated Gate Commutated Thyristor

Chapter 1: Introduction

Chapter 1: Introduction 1.1. Introduction to power processing 1.2. Some applications of power electronics 1.3. Elements of power electronics Summary of the course 2 1.1 Introduction to Power Processing Power input Switching converter