Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • converters for ac motor drives and uninterruptible power supplies Switch-Mode DC-AC Inverters Chapter 8 8-1 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Block diagram of a motor drive where the power flow is unidirectional Switch-Mode DC-AC Inverter 8-2 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Block diagram of a motor drive where the power flow can be bi-directional Switch-Mode DC-AC Inverter 8-3 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Four quadrants of operation Switch-Mode DC-AC Inverter 8-4 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • The mid-point shown is fictitious 8-5 One Leg of a Switch-Mode DC-AC Inverter Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters Synthesis of a Sinusoidal Output by PWM 8-6 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Control voltage can be assumed constant during a switching time-period Details of a Switching Time Period 8-7 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Harmonics appear around the carrier frequency and its multiples Harmonics in the DC-AC Inverter Output Voltage 8-8 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • These are harmonics of the fundamental frequency Harmonics due to Over-modulation 8-9 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Shows the linear and the over-modulation regions; square-wave operation in the limit 8-10 Output voltage Fundamental as a Function of the Modulation Index Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Harmonics are of the fundamental frequency Square-Wave Mode of Operation 8-11 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Capacitors provide the mid-point Half-Bridge Inverter 8-12 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Consists of two inverter legs 8-13 Single-Phase Full-Bridge DC-AC Inverter Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • The dotted curve is the desired output; also the fundamental frequency PWM to Synthesize Sinusoidal Output 8-14 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Small fictitious filters eliminate the switchingfrequency related ripple Analysis assuming Fictitious Filters 8-15 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Bi-Polar Voltage switching DC-Side Current 8-16 Copyright © 2003 by John Wiley & Sons, Inc. • Harmonic components around the switching frequency are absent Chapter 8 Switch-Mode DCSinusoidal AC Inverters Output Waveforms: Uni-polar Voltage Switching 8-17 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Uni-polar voltage switching 8-18 DC-Side Current in a Single-Phase Inverter Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Phase shift allows voltage cancellation to synthesize a 1-Phase sinusoidal output Sinusoidal Synthesis by Voltage Shift 8-19 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Analysis at the fundamental frequency Single-Phase Inverter 8-20 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • PWM results in much smaller ripple current Square-Wave and PWM Operation 8-21 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Low Voltage to higher output using square-wave operation Push-Pull Inverter 8-22 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Three inverter legs; capacitor mid-point is fictitious Three-Phase Inverter 8-23 Copyright © 2003 by John Wiley & Sons, Inc. ThreePhase PWM Waveforms Chapter 8 Switch-Mode DCSinusoidal AC Inverters 8-24 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters Three-Phase Inverter Harmonics 8-25 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Linear and over-modulation ranges 8-26 Three-Phase Inverter Output Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Harmonics are of the fundamental frequency 8-27 Three-Phase Inverter: Square-Wave Mode Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Analysis at the fundamental frequency can be done using phasors Three-Phase Inverter: Fundamental Frequency 8-28 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • PWM results in much smaller ripple current Square-Wave and PWM Operation 8-29 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • The current consists of a dc component and the switching-frequency related harmonics 8-30 DC-Side Current in a Three-Phase Inverter Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • devices conducting are indicated Square-Wave Operation 8-31 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • devices conducting are indicated PWM Operation 8-32 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • top group or the bottom group results in short circuiting three terminals Short-Circuit States in PWM Operation 8-33 Copyright © 2003 by John Wiley & Sons, Inc. • Results in nonlinearity Effect of Blanking Time Chapter 8 Switch-Mode DCSinusoidal AC Inverters 8-34 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Voltage jump when the current reverses direction Effect of Blanking Time 8-35 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Effect on the output voltage Effect of Blanking Time 8-36 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Angles based on the desired output Programmed Harmonic Elimination 8-37 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Results in a variable frequency operation Tolerance-Band Current Control 8-38 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Better control is possible using dq analysis Fixed-Frequency Operation 8-39 Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Can analyze based on the fundamentalfrequency components 8-40 Transition from Inverter to Rectifier Mode Copyright © 2003 by John Wiley & Sons, Inc. Chapter 8 Switch-Mode DCSinusoidal AC Inverters • Functional representation in a block-diagram form Summary of DC-AC Inverters 8-41
