Bus Balancer Apparatus for DC Bus Voltage Ripple Reduction
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Solution Overview
Problem
Conventional balancer circuits in power converter systems generate undesirable ripple currents even when loads are balanced, due to unbalanced loads causing DC bus imbalances in three-phase inverter systems.
Innovation Solution
A bus balancer apparatus with serially connected windings and switches, where the windings are magnetically coupled and operated at a common duty cycle to equalize voltages across energy storage devices, using a control circuit to manage the switches and diodes to minimize ripple currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional balancer circuit is used to address DC bus imbalance, then the voltage imbalance between positive and negative DC buses is corrected, but undesirable ripple currents are generated even when the load is balanced
Solution Approach 1:
The balancer circuit dynamically adjusts the duty cycle of the switches based on the detected voltage imbalance between DC buses. When imbalance is detected, the duty cycle is modified to transfer energy and restore balance. When buses are balanced, the duty cycle returns to normal operation, eliminating unnecessary ripple currents. This dynamic adaptation resolves the contradiction by making the balancer active only when needed.
Solution Approach 2:
The invention changes the operating parameters (duty cycle) of the balancer circuit based on the system state. By monitoring DC bus voltages and adjusting the duty cycle accordingly, the system transitions between balancing mode and normal operation mode, thereby eliminating ripple currents during balanced conditions while maintaining voltage balance when imbalanced.
2Reliability
If the balancer circuit operates continuously to maintain DC bus balance, then voltage equilibrium is maintained, but energy loss increases due to continuous switching
Solution Approach 1:
The balancer circuit operates periodically rather than continuously, activating only when voltage imbalance is detected. The control circuit monitors DC bus voltages and triggers balancing operations intermittently based on the actual need, thereby maintaining voltage equilibrium while minimizing energy loss from continuous switching.
Solution Approach 2:
The system self-regulates by detecting its own state (voltage imbalance) and activating the balancer only when necessary. This self-service mechanism eliminates the need for continuous operation, reducing energy losses while maintaining reliability through on-demand balancing.
3Adaptability or versatility
If unbalanced loads are allowed to operate, then system flexibility is maintained, but DC bus voltage imbalance occurs
Solution Approach 1:
The control circuit continuously monitors the voltages on the positive and negative DC buses and uses this feedback to detect imbalance conditions caused by unbalanced loads. When imbalance is detected, the feedback signal triggers the balancer circuit to adjust the duty cycle and restore voltage balance, thereby maintaining reliability while allowing load flexibility.
Solution Approach 2:
The balancer circuit acts as an intermediary between the unbalanced loads and the DC buses. It mediates the voltage imbalance by transferring energy between buses through controlled switching, allowing the system to maintain both load flexibility and voltage balance simultaneously.
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 apparatus effectively balances voltages across energy storage devices, reducing ripple currents and maintaining equilibrium, even under unbalanced loads, thereby improving the performance of power converter systems.
Implementation Method 1
The first and second windings may be magnetically coupled to one another and the third and fourth windings may be magnetically coupled to one another
Data Source
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.