Power Converter Neutral Circuit Decoupling
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Solution Overview
Problem
Existing AC-UPS systems face challenges in decoupling AC-input from AC-output without introducing distortion, high common mode noise, and preventing the use of surge protection diodes due to high frequency switching of the neutral leg, which results in inefficiencies and reliability issues.
Innovation Solution
A power converter with a line frequency commutated neutral circuit and an auxiliary converter circuit that decouples AC-input from AC-output during zero crossings, using pulse width modulation signals to control auxiliary switching devices, reducing high frequency switching losses and common mode noise, and enabling the use of surge protection diodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high frequency PWM switching is used for the neutral leg to decouple AC-input from AC-output, then decoupling performance is improved, but high frequency switching losses increase and common mode noise is generated
Solution Approach 1:
The patent applies periodic action by switching the neutral leg at line frequency (50/60 Hz) rather than high frequency PWM, creating a periodic switching pattern synchronized with the AC waveform. This eliminates high frequency switching losses while maintaining decoupling performance through the periodic commutation of the neutral point potential.
Solution Approach 2:
The patent changes the switching frequency parameter from high frequency PWM to line frequency, and modifies the switching pattern to a specific periodic sequence that commutes the neutral leg potential between positive and negative DC bus potentials. This parameter change resolves the contradiction by eliminating high frequency losses while maintaining decoupling.
2Reliability
If high frequency PWM switching is used for the neutral leg, then decoupling is achieved, but common mode noise is generated requiring larger filter components
Solution Approach 1:
By using line frequency periodic switching synchronized with the AC waveform, the patent eliminates high frequency common mode noise generation. The periodic commutation pattern creates minimal electromagnetic interference compared to high frequency PWM, reducing the need for large common mode filter components.
3Reliability
If high frequency switching of the neutral leg is implemented, then decoupling performance improves, but surge protection diodes cannot be used
Solution Approach 1:
The line frequency periodic switching pattern creates voltage conditions that allow surge protection diodes to function properly. The slower switching rate and specific commutation sequence prevent the voltage stress conditions that would otherwise prevent diode operation, enabling both decoupling and surge protection functionality.
Data Source
AI summary
The present disclosure provides to a power converter including an AC input terminal (ACin), a neutral terminal (N), an AC output terminal (ACout), an AC/DC converter circuit (210) connected between the AC input terminal, a positive DC terminal (DCP), and a negative DC terminal (DCN), a DC capacitor (C15) connected between the positive DC terminal (DCP) and the negative DC terminal (DCN), a line frequency commutated neutral circuit (220) connected between the positive DC terminal (DCP), the negative DC terminal (DCN), and the neutral terminal (N), and a DC/AC converter circuit (230) connected between the positive DC terminal (DCP), the negative DC terminal (DCN), the AC output terminal (ACout), and the neutral terminal (N). The power converter further includes an auxiliary converter circuit (240) connected between the positive DC terminal (DCP), the negative DC terminal (DCN), and the neutral terminal (N).