TABLE OF CONTENTS CHAPTER NO. TITLE PAGE NO. LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS AND ABBREVIATIONS

Transcription

1 vi TABLE OF CONTENTS CHAPTER NO. TITLE PAGE NO. ABSTRACT LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS AND ABBREVIATIONS iii x xi xvii 1 INTRODUCTION INTRODUCTION BACKGROUND Types of DC-DC Buck Converters Linear and switching converters Isolated and non isolated switching buck converters Feedback Control of Converter Comparison between PWM and PSM Nonlinear Phenomena in Buck Converters Applications of Buck Converters REVIEW OF RELEVANT LITERATURE AIMS AND OBJECTIVES ORGANISATION OF THE THESIS 16

2 vii CHAPTER NO. TITLE PAGE NO. 2 PWM AND PSM DC/DC BUCK CONVERTERS PWM DC DC BUCK CONVERTER Circuit Operation Operating Modes of Converter Voltage Mode Controlled Buck Converter Simulation of Voltage Mode Controlled Converter under CCM Results Observations with Variation in Input Voltage/Load Bifurcation and Chaos in PWM DC DC Converter A Method to generate stepped input voltage variation PSM DC DC BUCK CONVERTER Circuit Operation Operating Modes Continuous conduction mode I Continuous conduction mode II Discontinuous conduction mode Critical mode Modeling of Converter under Continuous Conduction Mode Simulation of PSM Buck Converter under CCM Observations with Variation in Input Voltage/Load 65

3 viii CHAPTER NO. TITLE PAGE NO Bifurcation and Chaos in PSM DC DC Converter CONCLUSION 70 3 PSM BUCK DC-DC CONVERTER UNDER DISCONTINUOUS CONDUCTION MODE DISCONTINUOUS CONDUCTION MODE IN BUCK CONVERTER MODELLING AND SIMULATION OF PSM CONVERTER UNDER DCM Modelling Simulation MODELLING AND SIMULATION OF PSM CONVERTER UNDER FORCED DCM Modelling converter under Forced DCM OBSERVATIONS WITH VARIATION IN INPUT VOLTAGE BIFURCATION AND CHAOS IN PSM CONVERTER UNDER DCM BIFURCATION AND CHAOS IN PSM DC-DC VMC FDCM CONCLUSION 96 4 IMPROVED PSM DC-DC BUCK CONVERTER RIPPLE IN DC-DC BUCK CONVERTERS FACTORS AFFECTING RIPPLE IN BUCK CONVERTERS IMPROVED PSM DC-DC BUCK CONVERTER 110

4 ix CHAPTER NO. TITLE PAGE NO Skip Logic Inductor Current Limit APPLICATIONS OF PSM DC-DC BUCK CONVERTER Regulated Power Supply Simulation Experimental evaluation Chaos Free Operation with Mode Hopping CONCLUSION CONCLUSION AND FUTURE WORK CONTRIBUTION OF THE THESIS FUTURE SCOPE OF THE WORK 133 APPENDIX 136 REFERENCES 145 LIST OF PUBLICATIONS 151 CURRICULUM VITAE 153

5 x LIST OF TABLES TABLE NO. TITLE PAGE NO. 1.1 Comparison between linear and switching converters Specifications of power stage Parameter values considered for simulation Parameter values considered for simulation Pulses applied and skipped over the range of input voltage from 12V to 20V Parameters considered for PSM DC/DC converter under DCM Parameters considered for simulation of Forced Discontinuous Conduction Mode Parameter values considered for the improved PSM buck converter 115

6 xi LIST OF FIGURES FIGURE NO. TITLE PAGE NO. 1.1 Power converter in an electric power system Buck converter Rapid decrease of both conduction and switching losses in skipping mode The schematic of PWM/PSM dual-mode controller The output voltage V O with modulation factor M PWM Buck converter Input voltage presented to LC filter due to switch action Typical waveforms of inductor current i L and Capacitor voltage v C Continuous conduction mode (a) Buck converter circuit (b) Switch open and voltage across inductor is (v in -v 0 ) (c) Switch closed and voltage across inductor is (-v 0 ) Inductor voltage and current-continuous conduction mode Inductor current -Discontinuous conduction mode Third circuit configuration - Discontinuous conduction mode Buck converter circuit Equivalent circuit with (a) switch closed (b) switch open-for developing the state equations Simulink actual model of the buck converter State space averaged model of buck converter SIMULINK PSB model of converter Voltage mode controlled PWM buck converter Closed loop with compensator 32

7 xii FIGURE NO. TITLE PAGE NO PWM generation Step response of uncompensated system Bode plot of uncompensated system Step response of compensated system Bode plot of compensated system SIMULINK Model of PWM buck converter with PID Control Inductor current and output voltage of converter Output voltage ripple for VM controlled buck converter Phase plot between vc and il showing period I operation Response to a step change in input voltage PWM control Response to a step change in input voltage PWM control Response to a step change in load PWM control Response to a step change in load PWM control simulated with PSIM Schematic to generate a stepped input voltage variation Stepped input voltage variation and sampling pulses Phase portrait Switching map PWM converter State trajectory PWM converter period I operation State trajectory in state space PWM converter period II operation Control voltage and ramp during period II operation Bifurcation diagram for PWM converter input voltage in V is parameter Stroboscopic map for PWM converter, at 22.6V 52

8 xiii FIGURE NO. TITLE PAGE NO Strange attractor at V in = 24V PWM converter PSM DC/DC buck converter Waveforms of output voltage, inductor current and gate pulses for a PSM converter PSM control logic Inductor current waveform in CCM I Inductor current waveform in CCM II Inductor current waveform in DCM Inductor current waveform in critical mode PSM buck converter SIMULINK PSB Inductor current for continuous conduction and output voltage. Ripple is observed to be slightly greater than 10% Simulation output showing the ripple in v 0, inductor current and pulses applied and skipped. Ripple is slightly above 10% Average model simulated with input voltage = 12V and D= Output voltage response to step change in (a) input and (b) load current State trajectory in state space - plot between i L and v C Phase portrait - Stroboscopic map PSM converter for V in =12V Bifurcation diagram for PSM converter Bifurcation diagram for PSM converter enlarged over 10V to 20V range Stroboscopic map for PSM converter at V in = 17.6 V 68

9 xiv FIGURE NO. TITLE PAGE NO Inductor current in A with change in input voltage in 2V steps from 12V to 20V K Vs D plot showing DCM/CCM regions separated by the borderline Average inductor current or the load DC current equals half the inductor ripple Modulation factor Vs V in (Increased skipping with V in ) Modulation factor Vs R L. (Increased skipping with R L ) PSM Buck converter waveforms for a load of 500mA Step increase in load and response of output voltage. Load increased from 250mA to 500mA. (a) Load current and output voltage (b) Output voltage and inductor current Step increase in load and response of output voltage Inductor current and applied pulses Typical current waveform in FDCM PSM converter Forced Discontinuous conduction in PSM buck converter Waveforms of Vin, v0 and il in PSM forced DCM showing discontinuous conduction with Ripple 6% Bifurcation diagram for PSM DC/DC buck converter under DCM Bifurcation diagram for PSM DC/DC buck converter under DCM-enlarged view Inductor current and output voltage with V in = 12V for PSM buck converter under forced DCM Ripple 6% 94

10 xv FIGURE NO. TITLE PAGE NO Inductor current and output voltage with V in = 35V for PSM buck converter under forced DCM Ripple 6% Phase plane trajectory i L Vs v C discontinuous current and no Chaos at V in = 12V for PSM converter under forced DCM Phase plane trajectory i L Vs v C discontinuous current and no Chaos at V in = 35V Inductor current in buck converter Equivalent circuit of capacitor with ESR Output voltage ripple Vs Frequency with C as parameter Output voltage ripple Vs Frequency with L as parameter Output voltage ripple Vs Frequency with D as parameter Inductor current in DCM Inductor current and output voltage in PSM converter under CCM Inductor current in PSM converter under CCM Improved PSM DC-DC buck converter-schematic Skip logic sub circuit Inductor current limit sub circuit Typical output voltage and inductor current waveforms - Improved converter CLK and pulses applied to switch Output voltage and load current waveforms at nominal input voltage of 12V Starting output and capacitor voltages and inductor current at 12V input voltage Output Voltage and applied input voltage Response to a step increase in input voltage from 12V to 20V 116

11 xvi FIGURE NO. TITLE PAGE NO Output Voltage and load current response to a step decrease in load current from 1A to 0.5 A Output Voltage Inductor current portrait. Average inductor current or Load current is 1A. Pulses skipped result in periodical inductor current discontinuity Cascaded PSM and linear arrangement for power supply Block schematic SIMPLIS schematic of PSM Buck regulator and linear regulator cascade SIMPLIS simulation output showing reference and output voltage of PSM stage Output voltage of linear regulator. The ripple reduced from 4% to less than 1% Schematic of PSM converter with MOSFET IRF530 cascaded with linear regulator Simulation output showing voltage output of PSM converter, linear regulator and Inductor current along with clock and applied pulses Circuit schematic in express PCB Component side of the board Bottom copper layer PWM/PSM hybrid mode with mode select for chaos free operation Output voltage near transition to PSM from PWM Bifurcation diagram - chaotic to non-chaotic transition at V in = 30V Input current harmonic components PSM converter Interleaved buck converter PWM Control and output current signals PWM 135

12 xvii LIST OF SYMBOLS AND ABBREVIATIONS f a - Actual or effective frequency of the switch CLK - Clock CF-ZVS - Constant Frequency Zero Voltage Switching Quasi -QRC Resonant Converter v con - Control voltage V d - diode drop DCM - Discontinuous Conduction Mode d, D - Duty cycle EMI - Electro Magnetic Interference ESR - Equivalent Series Resistances I L - Inductor current ripple LIR - Inductor current ripple v in - Input voltage LDO - Low Drop Out V L - Lower voltage of ramp M - Modulation Factor M - Modulation factor p (or n) - Number of cycles during charging period q (or m) - Number of cycles during skipping period r - Number of cycles during which inductor current is zero T OFF - OFF state duration T ON - ON state duration v 0 - Output voltage PFM - Pulse Frequency Modulation PSM - Pulse Skipping Modulation PWM - Pulse Width Modulation v ramp - Ramp voltage

13 xviii Vref - Reference voltage x n - State vector n th sample f sw - Switching frequency T - Total duration V U - Upper voltages of ramp r - Voltage Ripple ZVS - Zero Voltage Switching