Bus Balancer Apparatus for DC Bus Voltage Equalization
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Solution Overview
Problem
Conventional power converter systems, such as three-phase inverters, face DC bus imbalance issues due to unbalanced loads, which can lead to undesirable ripple currents even when the load is balanced, as existing balancer circuits fail to effectively manage voltage imbalances across DC buses.
Innovation Solution
A bus balancer apparatus comprising serially-connected energy storage devices and windings with bidirectional switches and diodes, where the windings are magnetically coupled and operated at a synchronized duty cycle to equalize voltages across capacitors or batteries, using a control circuit to manage the switches and maintain equilibrium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional balancer circuits are used to address DC bus imbalance, then voltage imbalance is addressed, but undesirable ripple currents are generated even when load is balanced
Solution Approach 1:
The balancer circuit operates by periodically switching the bidirectional switches at a duty cycle less than 50%, creating periodic action that balances capacitor voltages while minimizing ripple currents. The switches are turned on for a portion of the switching period and off for the remainder, allowing controlled charge transfer between capacitors without continuous connection that would generate ripple.
Solution Approach 2:
The invention changes the operating parameters by using a duty cycle less than 50% and operating frequency in the range of 20-200 Hz, which are optimized to reduce ripple currents while maintaining effective voltage balancing. This parameter optimization resolves the contradiction between achieving voltage balance and minimizing harmful ripple effects.
2Object-generated harmful factors
If bidirectional switches are used with duty cycle less than 50%, then ripple currents are reduced, but circuit complexity increases
Solution Approach 1:
The bidirectional switches serve multiple functions: they enable charge transfer between capacitors for voltage balancing, allow current to flow in both directions for flexible energy management, and can be controlled with a simple duty cycle approach. This multi-functionality justifies the added complexity by consolidating multiple operations into single components.
3Reliability
If magnetically coupled windings are used for voltage equalization, then balancing effectiveness is improved, but manufacturing complexity increases
Solution Approach 1:
Multiple windings are magnetically coupled and connected in series to form a unified balancer circuit structure. This merging of windings creates efficient magnetic coupling that enables effective voltage equalization across multiple capacitors while using a standardized transformer-like structure that can be manufactured using conventional techniques.
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 effectively balances voltages across multiple energy storage devices, reducing ripple currents and maintaining equilibrium, even under unbalanced loads, thereby enhancing the performance and efficiency of power converter systems.
Implementation Method 1
first and second windings are magnetically coupled to one another and wherein the third and fourth windings are magnetically coupled to one another
Data Source
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AI summary
An apparatus includes a string of serially-connected energy storage devices, a string of serially-connected windings on at least one core and having a first medial node coupled to a first medial node of the string of serially-connected energy storage devices, and first and second switches configured to connect first and second end nodes of the string of serially-connected storage devices to respective first and second end nodes of the string of serially-connected energy storage devices. A control circuit is configured to operate the first and second switches at the same duty cycle.