Transformerless Power Conversion Grounding Scheme
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Solution Overview
Problem
Transformerless power conversion systems face efficiency issues due to low common mode impedance and lack of ground fault protection, which are not adequately addressed by existing technologies.
Innovation Solution
A power conversion system design that includes a power converter with a grid side filter and a load side filter, where neutral points of both filters are connected to form a node not directly grounded, and a common mode filter coupled between the grid side filter and the power converter, along with an impedance connected to ground to provide high impedance for fault current limitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an isolation transformer is used in power conversion systems, then ground fault protection is provided, but efficiency decreases due to size specifications
Solution Approach 1:
The patent removes the isolation transformer from the power conversion system and replaces it with an alternative grounding scheme using a neutral point connection between grid side and load side filters that is not directly grounded. This extraction eliminates the efficiency losses associated with transformer operation while maintaining ground fault protection through the filtered neutral point connection.
Solution Approach 2:
The patent introduces a neutral point as an intermediary element between the grid side filter and load side filter. This neutral point provides a reference for ground fault detection without requiring a direct ground connection or isolation transformer, thereby maintaining protection functionality while avoiding transformer-related efficiency losses.
2Ease of operation
If the neutral point is directly grounded, then ground reference is provided, but fault current increases causing equipment damage
Solution Approach 1:
The neutral point serves as an intermediary that provides a ground reference for normal operation without creating a direct low-impedance path for fault currents. By connecting the neutral point between the grid side and load side filters rather than directly to ground, the system maintains voltage reference stability while limiting fault current magnitude.
Solution Approach 2:
The patent changes the grounding parameter from direct ground connection (zero impedance) to a filtered neutral point connection (high impedance). This parameter change transforms the neutral point into a high-impedance reference that provides stable voltage grounding during normal operation while automatically limiting fault currents to safe levels without requiring additional current limiting components.
3Loss of energy
If transformerless power conversion system is used, then efficiency is improved, but ground fault protection is lost
Solution Approach 1:
The neutral point connection between grid side and load side filters serves multiple functions simultaneously: it provides voltage reference stabilization, enables ground fault detection, and limits fault currents. This multi-functional design replaces the isolation transformer's protection role while maintaining the transformerless system's efficiency advantages.
Solution Approach 2:
The neutral point connection creates a feedback path that allows the system to detect ground faults by monitoring voltage imbalances between the connected filter neutrals. This feedback mechanism enables ground fault protection in the transformerless system by providing continuous information about system grounding status and fault conditions.
Data Source
AI summary
A power conversion system includes one or more power conversion devices coupled to a grid connection. Each of the power conversion devices includes a power converter for converting a first multiphase current provided by the grid connection into a second current; a grid side filter coupled between the grid connection and an input of the power converter; a load side filter coupled to an output of the power converter; neutral points of the grid side filter and the load side filter connected together to form a first node; wherein the first node is not directly grounded.