Switch Capacitor Buck-Boost Converter for Electric Vehicle Power Density
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Solution Overview
Problem
Conventional DC-DC boost converters for electric vehicles are inefficient due to high power rating requirements, leading to large and costly inductors, and poor partial-power efficiency, especially at high voltage ratios, which also increase cooling system size and weight.
Innovation Solution
A bidirectional switch capacitor buck-boost voltage converter that eliminates the need for a large inductor and filtering capacitor by using a switch capacitor circuit with a three-level inverter configuration, allowing for higher energy density and reduced costs, and is designed to handle high-power applications by limiting charging current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional DC-DC boost converter is used to achieve voltage conversion, then the required DC-link voltage can be obtained, but the converter requires a large and costly inductor with high power rating
Solution Approach 1:
The patent removes the large inductor from the conventional boost converter topology and replaces it with a capacitor-based voltage multiplication circuit. This extraction of the inductor eliminates the associated weight, cost, and copper/core losses while achieving the same voltage boosting function through capacitive energy storage and switching.
Solution Approach 2:
The patent substitutes the magnetic field-based inductor with an electric field-based capacitor switching network. This replacement transitions from magnetic energy storage to electric energy storage, eliminating the need for heavy magnetic cores and windings while achieving identical voltage conversion functionality.
2Power
If the inductor size is increased to match battery pack power, then the power rating is sufficient, but the copper and core losses increase proportionally
Solution Approach 1:
The patent replaces the magnetic field-based inductor with an electric field-based capacitor switching network. This substitution eliminates copper losses in the inductor windings and core losses in the magnetic material, while maintaining the same power handling capability through capacitive energy transfer.
3Power
If the boost converter operates with high duty cycle to achieve high voltage ratio, then the desired voltage can be obtained, but the efficiency is relatively low
Solution Approach 1:
The patent employs periodic switching of capacitor charge and discharge cycles to achieve voltage multiplication. By rapidly switching capacitors between charging and discharging states, the circuit achieves high voltage ratios with low duty cycles, improving efficiency by avoiding the high-duty-cycle operation that plagues conventional boost converters.
4Power
If a high duty cycle is used for boosting, then the voltage ratio is achieved, but the RMS current applied to the bus capacitor increases impacting its size and cost
Solution Approach 1:
The patent uses periodic switching of multiple capacitors in a voltage multiplication configuration, where capacitors are charged and discharged in alternating phases. This distributes the RMS current across multiple capacitors and switching events, reducing the current burden on any single bus capacitor and allowing for smaller, less expensive capacitor components.
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
The solution achieves higher power density, reduced weight, and improved efficiency by eliminating the inductor and using a switch capacitor technique, enabling higher voltage levels and efficient voltage conversion without the need for expensive batteries or complex battery management systems.
Implementation Method 1
a capacitor in the switch capacitor circuit configured to store charge during the charging state and drain charge during the discharging state
Data Source
AI summary
A voltage conversion system including a source configured to supply a voltage and a switch capacitor circuit electrically coupled to the source. The switch capacitor circuit is configured to switch between a discharging state and a charging state. The switching between the discharging state and the charging state produces a boost to the supplied voltage. The voltage conversion system includes a capacitor in the switch capacitor circuit configured to store charge during the charging state and drain charge during the discharging state. The voltage conversion system includes a switching arrangement having a plurality of switch pairs configured to supply a converted voltage to a load. The switch capacitor circuit and the switching arrangement are interfaced to produce a unified circuit.