Interleaved Neutral Coupling Circuits for Inverter Efficiency
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Solution Overview
Problem
Inverters in power systems face challenges in reducing switching losses and component stress, particularly in managing voltage asymmetry and high-frequency currents, which affect efficiency and reliability, especially in large-scale or modular UPS applications.
Innovation Solution
The implementation of an inverter apparatus with interleaved neutral coupling circuits and a control circuit that generates pulse train signals to selectively couple DC buses to a neutral terminal, allowing for voltage range shifting and reduced current through common mode inductors, thereby enhancing power conversion efficiency and reducing component stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single neutral coupling circuit is used to shift voltage range between DC buses, then switching losses and component stress are reduced, but current ripple and electromagnetic interference increase due to high-frequency switching
Solution Approach 1:
The single neutral coupling circuit is divided into two parallel neutral coupling circuits (first and second circuits). Each circuit handles a portion of the current, and their operations are interleaved to reduce ripple. This segmentation allows the system to maintain the voltage shifting function while distributing the switching current across multiple paths, thereby reducing current ripple and electromagnetic interference.
Solution Approach 2:
The two neutral coupling circuits operate in an interleaved periodic manner, where one circuit switches while the other is in a different state. The control circuit coordinates their switching cycles so that their current ripples are out of phase and cancel each other out. This periodic interleaved operation maintains the voltage range shifting benefit while significantly reducing the harmful current ripple effects.
2Object-generated harmful factors
If high-frequency switching elements are used to reduce ripple current, then current ripple is reduced, but switching losses and device complexity increase
Solution Approach 1:
Instead of using a single high-frequency switching circuit, the system segments the function into two parallel neutral coupling circuits operating at a lower frequency in an interleaved manner. Each circuit uses standard-frequency switching elements, but their combined interleaved operation achieves ripple current reduction without requiring ultra-high-frequency switching components, thus avoiding the associated switching losses and complexity.
Solution Approach 2:
The two parallel neutral coupling circuits are merged in their output function to collectively reduce ripple current. By combining their interleaved switching actions, the system achieves the ripple reduction effect of high-frequency switching while using lower-frequency switching elements, thereby reducing individual switching losses while maintaining overall performance.
3Object-generated harmful factors
If larger inductors and capacitors are used to filter current ripple, then ripple current is reduced, but device size and cost increase
Solution Approach 1:
The interleaved periodic operation of the two neutral coupling circuits naturally reduces current ripple through phase cancellation, eliminating the need for large filtering inductors and capacitors. The coordinated switching creates a smoother combined current waveform, allowing the use of smaller passive components while achieving the same ripple reduction that would otherwise require bulky filters.
Solution Approach 2:
The system replaces the mechanical/fphysical approach of using large inductors and capacitors for ripple filtering with an electronic control approach. By using control circuitry to coordinate interleaved switching of the two parallel circuits, the system achieves ripple reduction through electronic timing and phase management rather than through large passive filtering components, thereby reducing size and cost.
Data Source
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AI summary
A power converter apparatus, such as an uninterruptible power supply (UPS), includes an inverter having an input coupled to a first DC bus and a second DC bus and configured to generate an AC output with respect to a neutral terminal at a phase output terminal thereof. The apparatus further includes first and second neutral coupling circuits, each configured to selectively couple the first DC bus and the second DC bus to the neutral terminal, and a control circuit configured to cause interleaved operation of the neutral coupling circuits.