Double-Boost DC/DC Voltage Balancing Without a 4th Converter Leg
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Solution Overview
Problem
Existing double-boost DC/DC converters face limitations in voltage balancing due to the power constraints of the 4th leg converter, particularly during stored-energy operation, leading to DC-link unbalance issues.
Innovation Solution
The proposed solution involves a voltage balancing circuit for a double-boost DC/DC converter that eliminates the need for a dedicated 4th leg converter, utilizing a boost converter to enhance balancing capability and prevent common mode voltage at the DC source terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated 4th leg buck-boost converter is used for voltage balancing, then voltage balancing capability is achieved, but power capability is limited and device complexity increases
Solution Approach 1:
The patent merges the voltage balancing function with the existing dual-boost converter structure by utilizing the midpoint connection between the two boost converters. This eliminates the need for a separate 4th leg buck-boost converter while maintaining voltage balancing capability through coordinated switching of the existing switches.
Solution Approach 2:
The dual-boost converter structure is designed to perform multiple functions: power conversion and voltage balancing. By utilizing the midpoint connection and coordinated switching sequences, the same converter components serve both power transmission and voltage balancing purposes, reducing overall system complexity.
2Reliability
If a dedicated 4th leg converter is used for voltage balancing, then DC-link voltage balancing is achieved, but the power capability is constrained
Solution Approach 1:
The voltage balancing function is merged into the existing dual-boost converter structure, allowing the full power capability of the converter to be utilized for both power transmission and voltage balancing operations, rather than being constrained by a separate smaller 4th leg converter.
3Reliability
If DC offset and even harmonics are introduced in input current, then balanced DC-link voltage is ensured during double-conversion operation, but DC-link unbalance issues occur during stored-energy operation
Solution Approach 1:
The patent implements dynamic switching sequences that adapt to different operation modes. During double-conversion operation, the switching pattern introduces DC offset and even harmonics to balance the DC-link. During stored-energy operation, the switching pattern is dynamically adjusted to maintain balancing without causing unbalance issues, ensuring adaptability across different operational states.
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 approach reduces costs and footprint while improving the balancing capability of the UPS system, enabling compatibility with alternative energy storage systems and allowing for the paralleling of UPS systems at their DC port.
Implementation Method 1
An inductance (L4) is connected between a midpoint (103) of the DC link and a midpoint (121) of the inner switches (112, 113)
Implementation Method 2
outer directional devices (111, 114) and inner switches (112, 113) connected in parallel to the DC-link, wherein the directional devices are connected to capacitors of the split DC-link
Data Source
AI summary
A voltage balancing circuit for a double-boost DC/DC converter includes a split DC-link having a first midpoint, outer directional devices and inner switches parallel-connected to the DC-link, wherein the outer directional devices are connected to capacitors of the split DC-link and to the inner switches. The inner switches are connected to each other at a second midpoint. A DC source terminal, to which a DC source is connectable in parallel over inductances to the inner switches, is included. An inductance is connected to the midpoint of the DC link and to the midpoint of the inner switches.