Leistungselektronik Grundlagen und Standardanwendungen SS 2012 DC/DC Converter Fundamentals Prof. Hans-Georg Herzog Elektrische Energiewandlungstechnik
Outline 1. Overview on DC/DC Converter 2. One-Quadrant Converter Buck Converter Boost Converter Buck-Boost Converter Cuk Converter 3. Two-Quadrant Converter 4. Multi-Phase DC/DC Converter 2
Overview on DC/DC Converter Fields of Application Switched-Mode Power Supplies ( 300W) Supply of µc PC Power Supply Automotive (some kw) Coupling of Multi-Voltage On-Board Supply Networks Connection of Energy Storage Devices, Thermo-Electric Generators, Solar Panels,... Controlled DC-Drives (several 10 kw) 3
Fields of Application in Vehicles 4
Buck Converter One-Quadrant Converter I U Fields of Application: Unidirectional Coupling of Two On-Board Networks Connecting Components with Lower Voltage Level to a Higher Voltage On-Board Network 5
Buck Converter Principle Circuit Network A (e.g. HV On- Board Network) Buck Converter Network B (e.g. LV On- Board Network) Power 6
Buck Converter Switching States Assumption: V O = const. 7
Buck Converter Switching States Assumption: V O = const. 8
Buck Converter Switching States Assumption: V O = const. Steady-State: Area A = Area B 9
Buck Converter Output Voltage 10
Buck Converter Simulation Results 11
Boost Converter One-Quadrant Converter I U Fields of Application: Unidirectional Coupling of Two On-Board Networks Connecting Components with Higher Voltage Level to a Lower Voltage On-Board Network 12
Boost Converter Principle Circuit Network A (e.g. HV On- Board Network) Boost Converter Network B (e.g. LV On- Board Network) Power 13
Boost Converter Switching States 14
Boost Converter Switching States 15
Boost Converter Switching States Steady-State: 16
Boost Converter Output Voltage 17
Boost Converter Simulation Results 18
Buck-Boost Converter One-Quadrant Converter I U Fields of Application: Voltage Inversion Connecting Components to a Lower/Higher Voltage On-Board Network 19
Buck-Boost Converter Principle Circuit Network A (e.g. HV On- Board Network) Buck-Boost Converter Component B (e.g. Negative Voltage) Power 20
Buck-Boost Converter Switching States 21
Buck-Boost Converter Switching States 22
Buck-Boost Converter Switching States Steady-State: 23
Buck-Boost Converter Output Voltage 24
Buck-Boost Converter Simulation Results Potentialtrennung? 25
Cuk Converter Principle Circuit Network A (e.g. HV On- Board Network) Cuk Converter Component B (e.g. Negative Voltage) Power 26
Cuk Converter Switching States Assumption: v C1 = const C 1 big enough V C1 = V d + V O Diode D conducting i L1 und i L2 flow through D i L1 charges C 1 i L2 delivers Output Current i L1 and i L2 decrease 27
Cuk Converter Switching States Assumption: v C1 = const C 1 big enough V C1 = V d + V O Switch T conducting i L1 and i L2 flow through T C 1 delivers Energy to Output and L 2 Energy in L 1 rises i L1 und i L2 increase 28
Cuk Converter Output Voltage Assumption: v C1 = const C 1 big enough V C1 = V d + V O 29
Two-Quadrant Converters I U Fields of Application: Bidirectional Coupling of Two On-Board Networks Connecting Components with Lower Voltage Level to a Higher Voltage On-Board Network Current Inversion Step Up-Step Down Converter 30
Two-Quadrant Converters Principle Circuit Step Down Mode Source: [2] Network A (e.g. HV Supply) Step Down/ Step Up Converter Power Network B (e.g. LV Supply) 31
Two-Quadrant Converters Principle Circuit Step Up Mode Source: [2] Network A (e.g. HV Supply) Step Down/ Step Up Converter Power Network B (e.g. LV Supply) 32
Step Down/Step Up Converter Simulation Source: [2] 33
Step Down/Step Up Converter Simulation Source: [2] 34
Step Down/Step Up Conv. Requirements Limited at High Power because of Slow Switching of Large Semiconductor Devices Large Smoothing Inductances (due to High Current) High Ripple Current Stress in Smoothing Capacitor Cost-Intensive Passive Components Silicon instead of Passives Multi-phase DC/DC Converter 35
Half-Bridge Multi-Phase Approach U in U out 36
Multi-Phase Approach Ripple-Current Superposition of Individual Phases 37
Multi-Phase Approach Pros & Cons Advantages: + Less Current per Phase + Higher Modulation Frequency + Higher Effective Modulation Frequency by Phase-Shift in PWM Triggering Compact and Cheap Set-Up + Modular Design possible Disadvantages: Risk of Ring Currents Asymmetrical Phase Currents Balancing Alternatives: Series Resistors Central Control Master-Slave Approaches Magnetically Coupled Coils Fuzzy Logic 38
DC/DC Converter Losses Ohmic Losses: Switching Losses: U in On-State Power Losses Transistor: Gate-Triggering: U out On-State Power Losses Diode: Reverse Recovery Diode: Example: 2Q Converter Total: 39
References [1] N. Mohan, T. Undeland, W. Robbins, Power Electronics Converters, Applications, and Design, 3 rd Edition, Wiley, 2003 [2] D. Schröder, Leistungselektronische Schaltungen Funktion, Auslegung und Anwendung, 2. Auflage, Springer, 2008 40