Virtual Earth Regulator for EMC Filter Leakage Current
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Solution Overview
Problem
Existing EMC filters with high Y capacitors in power systems face issues with high earth leakage current, which can be dangerous and interfere with system operation, particularly in star grounded and delta power supplies, leading to tripping of RCD devices and increased filter size and cost due to compensatory inductance increases.
Innovation Solution
The implementation of a virtual earth regulator that stabilizes the potential of the Y capacitor to a reduced level, minimizing earth leakage current by creating a virtual ground node that reduces the potential seen by the Y capacitor, allowing large capacitors to be used without increasing inductance, thus maintaining low earth leakage current during normal and fault conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If large Y capacitors are used in EMC filters to achieve strong common-mode attenuation, then noise suppression effectiveness is improved, but earth leakage current increases causing RCD device tripping and safety hazards
Solution Approach 1:
The patent introduces a virtual earth regulator as an intermediary device between the Y capacitor and the actual earth connection. This regulator creates a virtual ground potential that mediates the connection, allowing the Y capacitor to function for noise suppression while the regulator actively controls and limits the earth leakage current to safe levels, preventing RCD tripping.
Solution Approach 2:
The virtual earth regulator dynamically changes the potential parameter of the virtual ground node, adjusting it to maintain near-zero voltage difference relative to actual earth. This parameter control allows large Y capacitor values to be used while keeping earth leakage current minimal, as the regulator modifies the electrical potential to prevent excessive current flow.
2Object-affected harmful factors
If Y capacitor capacity is reduced to limit earth leakage current, then safety and RCD compatibility are improved, but common-mode attenuation capability deteriorates
Solution Approach 1:
The virtual earth regulator acts as an intermediary that decouples the relationship between Y capacitor size and earth leakage current. By introducing this intermediate control device, the system can use large Y capacitors for strong common-mode attenuation while the regulator ensures earth leakage remains low, thus resolving the trade-off between attenuation capability and safety.
3Reliability
If inductance is increased to compensate for reduced capacitance, then common-mode attenuation is maintained, but filter size, cost, and power loss increase
Solution Approach 1:
The patent changes the electrical parameter approach by controlling the potential of the virtual ground node rather than relying on increased inductance. This parameter change allows the system to maintain common-mode attenuation with smaller inductor values, thereby reducing power losses, filter size, and cost while achieving the same attenuation performance.
Data Source
AI summary
EMC filter, connectable between a supply network and an electric operated appliance to reduce conduction noise between said supply network and said appliance, comprising one voltage regulator having an output terminal whose potential is kept close to the earth potential, in order to reduce the voltage drop, at mains frequency, across a “Y” capacitor or an active shunt module. In this way the leakage current to earth is sensibly reduced. The device of the invention is especially useful in corner-earthed three-phase lines or in conjunction with RCD devices.