Three-Phase DC/DC Converter Ripple Current Elimination
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Solution Overview
Problem
Fuel cell power systems with single-phase DC/AC inverters experience reduced efficiency and shortened lifespan due to AC ripple current, which also affects fuel cell controller tripping and fuel efficiency, and existing DC/DC converters face challenges with high power operation, high voltage conversion ratios, and high input currents, leading to inefficiencies and increased costs.
Innovation Solution
A three-phase transformer isolated phase shift DC/DC converter with active current ripple control, utilizing a delta-wye connection to reduce turns ratio and interleaved control to minimize passive components, achieving zero voltage zero current switching over a wide load range without auxiliary circuitry, and incorporating a current loop to suppress output current ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-phase DC/AC inverter is used in fuel cell power systems, then the system structure is simple, but AC ripple current is generated which reduces efficiency and shortens fuel cell lifespan
Solution Approach 1:
The single-phase inverter is segmented into multiple parallel phases (three-phase configuration). Each phase processes a portion of the power, and the phases are staggered in time to cancel out ripple currents. This segmentation allows the system to maintain simplicity while eliminating the harmful ripple current that reduces fuel cell efficiency and lifespan.
2Power
If a DC/DC converter is added to boost fuel cell output voltage, then the required voltage level for inverter operation is achieved, but the system complexity and cost increase
Solution Approach 1:
The voltage boosting function and the inverter function are merged into a single integrated three-phase inverter system. The inverter directly converts DC to AC while simultaneously providing the necessary voltage transformation through its switching topology, eliminating the need for a separate DC/DC converter stage and reducing overall system complexity.
3Reliability
If passive energy storage components are added to reduce ripple current, then fuel cell lifespan is extended, but the system cost and size increase
Solution Approach 1:
The harmful ripple current generated by the inverter is converted into a beneficial cancellation effect through the multi-phase staggered switching strategy. The ripple currents from different phases, being out of phase with each other, naturally cancel out when combined, transforming the potential harm into a benefit without requiring additional passive energy storage components.
4Reliability
If the fuel cell controller trips under instantaneous over current condition, then system protection is provided, but the output capacity and fuel efficiency are reduced
Solution Approach 1:
The system employs dynamic current management through the three-phase staggered switching strategy, which smooths out current fluctuations and prevents instantaneous over-current conditions. The dynamic balancing of phases ensures that the total current drawn from the fuel cell remains within safe operating limits while maximizing continuous output capacity and fuel efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution significantly reduces fuel cell current ripple, enhances efficiency, and lowers costs by eliminating the need for additional energy storage components, achieving high efficiency across a wide power range and reducing the size and weight of the converter.
Implementation Method 1
A three-phase transformer isolated phase shift DC/DC converter
Implementation Method 2
achieving zero voltage zero current switching over a wide load range
Data Source
AI summary
DC/DC converter has a transformer having primary coils connected to an input side and secondary coils connected to an output side. Each primary coil connects a full-bridge circuit comprising two switches on two legs, the primary coil being connected between the switches on each leg, each full-bridge circuit being connected in parallel wherein each leg is disposed parallel to one another, and the secondary coils connected to a rectifying circuit. An outer loop control circuit that reduces ripple in a voltage reference has a first resistor connected in series with a second resistor connected in series with a first capacitor which are connected in parallel with a second capacitor. An inner loop control circuit that reduces ripple in a current reference has a third resistor connected in series with a fourth resistor connected in series with a third capacitor which are connected in parallel with a fourth capacitor.