Balance Circuit Neutral Voltage Control for Circulating Current
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Solution Overview
Problem
In power systems with multiple modules connected in parallel, voltage differences between DC buses lead to circulating currents, reducing efficiency, causing harmonics and affecting the neutral point, which compromises system operation.
Innovation Solution
A power system with balance circuits that include capacitors and switches to regulate neutral voltage by charging capacitors in response to detected circulating currents, using an energy storage inductor to generate a current opposite to the circulating current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If multiple power modules are connected in parallel to reduce system size, then the system compactness is improved, but circulating current occurs due to voltage differences between DC buses which reduces power conversion efficiency
Solution Approach 1:
The patent introduces a balance circuit as an intermediary component between parallel power modules. This balance circuit includes capacitors connected to the DC bus and switches controlled by a controller. The balance circuit actively regulates voltage differences between DC buses of parallel modules by transferring energy through the balance circuit, thereby eliminating circulating current while maintaining the compact parallel architecture.
2Device complexity
If a unidirectional multi-level converter is adopted in the front-stage AC/DC topology, then the system complexity is reduced, but circulating current causes harmonics in the input current which increases total harmonic distortion
Solution Approach 1:
The balance circuit acts as an intermediary that decouples the harmful effects of circulating current from the input current. By providing an alternative path for voltage balancing through the balance circuit capacitors and switches, the unidirectional converter can maintain its simple topology while the balance circuit absorbs the circulating current, preventing it from distorting the input current harmonics.
3Device complexity
If the negative terminal of the DC/DC output is directly connected to the negative terminal of the DC bus, then the circuit architecture is simplified, but excessive circulating current causes neutral point potential shift which affects normal system operation
Solution Approach 1:
The balance circuit introduces intermediary capacitive elements between the DC bus and the balanced output terminal. These capacitors serve as voltage reference points that stabilize the neutral point potential. The balance circuit actively regulates these capacitor voltages to maintain equal potential references, preventing neutral point shifts while preserving the simplified direct connection architecture.
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
Effectively suppresses circulating currents, maintaining voltage balance and improving power conversion efficiency while reducing harmonics and neutral point shifts.
Implementation Method 1
operating the balance circuit of the at least one power module to charge the first capacitor or the second capacitor to regulate the neutral voltage for suppressing the circulating current
Implementation Method 2
disposing a first capacitor electrically coupled between the high-voltage bus and the neutral voltage, and disposing a second capacitor electrically coupled between the neutral voltage and the low-voltage bus
Data Source
AI summary
A circulating current suppression method of a power system having a plurality of power modules is provided. Each power module includes a high-voltage bus, a low-voltage bus and a balance circuit having a neutral voltage. The circulating current suppression method includes: in each balance circuit, disposing a first capacitor electrically coupled between the high-voltage bus and the neutral voltage, and disposing a second capacitor electrically coupled between the neutral voltage and the low-voltage bus; acquiring a current effective value of an input of each power module; if detecting that the current effective value of at least one power module doesn't remain at a current reference value, determining that a circulating current occurs in the at least one power module; and operating the balance circuit of the at least one power module to charge the first capacitor or the second capacitor to regulate the neutral voltage for suppressing the circulating current.