Three-Level Inverter Neutral-Point Balancing With Inductor Charging
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Solution Overview
Problem
Current three-level inverter circuits face challenges in maintaining balanced voltages at the neutral point due to asymmetric working states of switching transistors, leading to unbalanced output voltages or currents, which can damage system components and reduce efficiency.
Innovation Solution
An inverter circuit with a balanced circuit that adjusts the output current of an inductor to charge a target capacitor, reducing the voltage difference between two groups of capacitors and maintaining balanced bus voltages through a collection circuit and a control method that determines when to charge or stop charging based on voltage thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a common-mode component is injected into a switching bridge arm to balance neutral point voltages, then voltage balancing is achieved, but output power is reduced and control capability deteriorates
Solution Approach 1:
The patent introduces a dedicated balanced circuit as an intermediary component that includes an inductor and switching transistors. This balanced circuit is connected in parallel to the switching bridge arm and specifically designed to transfer charge between the two groups of capacitors. By using this intermediary balanced circuit rather than injecting common-mode components into the main switching bridge arm, the patent achieves neutral point voltage balancing while avoiding the loss of output power and control capability that would otherwise occur in the main power conversion path.
2Adaptability or versatility
If switching transistor working states are asymmetric (different models, different loss, asymmetric loads), then adaptability to different operating conditions is improved, but neutral point voltage balance deteriorates
Solution Approach 1:
The patent extracts the voltage balancing function from the main switching bridge arm and places it in a separate, dedicated balanced circuit. This allows the main switching bridge arm to operate with asymmetric transistor configurations adapted to different loading conditions without compromising neutral point voltage balance. The balanced circuit independently manages charge transfer between capacitor groups, decoupling the adaptability requirements from the voltage balancing requirements.
Solution Approach 2:
The balanced circuit acts as an intermediary that compensates for the asymmetric working states of switching transistors. By monitoring the voltage difference between the two groups of capacitors and actively transferring charge through the inductor and switching transistors in the balanced circuit, the system maintains voltage balance even when the main switching bridge arm uses asymmetric transistor configurations for adaptability.
3Quantity of substance
If the difference between end voltage values of two groups of capacitors is large, then energy storage capacity is improved, but system stability and power supply efficiency deteriorate
Solution Approach 1:
The patent implements a feedback control mechanism where the control circuit continuously monitors the voltage difference between the two groups of capacitors (first capacitor and second capacitor). When the voltage difference exceeds a predetermined threshold, the control circuit activates the balanced circuit to transfer charge from the higher voltage capacitor group to the lower voltage capacitor group through the inductor. This feedback-based active balancing maintains voltage equality between capacitor groups, ensuring system stability and power supply efficiency while preserving the energy storage capacity provided by the capacitor voltage difference.
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 improves the stability and power supply efficiency of the inverter by balancing the positive and negative direct current bus voltages, reducing the risk of component damage and enhancing overall system performance.
Implementation Method 1
a balanced circuit and an inductor... adjust an output current of the inductor to charge a target capacitor
Data Source
AI summary
An inverter includes an inverter circuit, a collection circuit, a balanced circuit, and an inductor. The collection circuit is configured to detect a direct current bus voltage, to obtain end voltage values of a first capacitor and a second capacitor. The balanced circuit is configured to: when an end voltage value of a target capacitor is less than or equal to a first voltage threshold, control on or off of a plurality of switching transistors, to adjust a current for charging the target capacitor through the inductor and reduce a difference between the end voltage values of the target capacitor and a non-target capacitor in the two groups of capacitors. When the difference between the end voltage values of the two groups of capacitors in the inverter circuit is large, the balanced circuit may adjust an output current of the inductor to charge the target capacitor.