Balance Circuit Neutral Voltage Control for Circulating Current Suppression
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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 harmonic distortion and potential neutral point shifts, which affect the entire system's operation.
Innovation Solution
A power system with a balance circuit that includes first and second capacitors and an energy storage inductor, where the controller detects circulating currents and operates the switches to charge the capacitors, regulating the neutral voltage to suppress the circulating current by generating an inductor current opposite to the circulating current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple power modules are connected in parallel with unidirectional AC/DC topology, then the system capacity is increased, but circulating current occurs due to voltage differences between DC buses
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 positive and negative DC buses, which act as mediators to equalize voltage differences between modules. By providing this intermediate voltage balancing mechanism, the system can maintain multiple parallel modules without suffering from circulating currents, thus preserving power conversion efficiency while scaling system capacity.
2Volume of moving object
If unidirectional AC/DC topology is adopted to reduce module size, then the module size is reduced, but circulating current causes harmonic distortion in input current
Solution Approach 1:
The balance circuit serves as an intermediary that prevents circulating current generation at its source. By equalizing voltages between parallel modules through the capacitor network, the system eliminates the root cause of harmonic distortion in input currents, allowing compact unidirectional topology to be used without suffering from harmonic pollution.
3Device complexity
If circulating current is allowed to flow, then the circuit architecture remains simple, but neutral point potential shifts occur affecting system operation
Solution Approach 1:
The balance circuit with capacitors on both positive and negative DC buses acts as a voltage stabilization intermediary. This configuration provides a reference potential that prevents neutral point drift, ensuring reliable system operation while maintaining relatively simple circuit architecture.
Solution Approach 2:
The patent implements equipotentiality by using capacitors to maintain equal voltage potentials between corresponding buses of parallel modules. The balance circuit ensures that positive and negative DC buses maintain stable potential differences, preventing neutral point potential shifts that would otherwise occur with circulating currents.
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 power conversion efficiency and preventing harmonic distortion, ensuring normal system operation by regulating the neutral voltage.
Implementation Method 1
operates the first switch and/or the second switch of the balance circuit of the at least one of the plurality of power modules to let the energy storage inductor generate an inductor 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
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AI summary
A circulating current suppression method of a power system (1) having a plurality of power modules (10) is provided. Each power module (10) includes a high-voltage bus (13), a low-voltage bus (14) and a balance circuit (11) having a neutral voltage (Vn). The circulating current suppression method includes: in each balance circuit (11), disposing a first capacitor (C1) electrically coupled between the high-voltage bus (13) and the neutral voltage (Vn), and disposing a second capacitor (C2) electrically coupled between the neutral voltage (Vn) and the low-voltage bus (14); acquiring a current effective value (iz) of an input of each power module (10); if detecting that the current effective value (iz) of at least one power module (10) doesn't remain at a current reference value (iref), determining that a circulating current occurs in the at least one power module (10); and operating the balance circuit (11) of the at least one power module (10) to charge the first capacitor (C1) or the second capacitor (C2) to regulate the neutral voltage (Vn) for suppressing the circulating current.