Uninterruptible Power Supply Common Mode Current Suppression
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Solution Overview
Problem
Conventional uninterruptible power supply apparatuses experience noise issues due to ripple voltage and common mode current flowing through the bidirectional chopper circuit and battery stray capacitance, causing interference with AC power supply and load systems.
Innovation Solution
Incorporating a common mode reactor and capacitors between the bidirectional chopper circuit and battery electrodes, which suppresses common mode current and reduces noise by redirecting it to a virtual neutral line, thereby minimizing ripple voltage impact on the power supply and load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bidirectional chopper circuit is used to supply DC power between capacitor and battery, then power supply function is achieved, but common mode current flows through battery stray capacitance causing noise
Solution Approach 1:
A common mode reactor is introduced as an intermediary component between the bidirectional chopper circuit and the battery. This reactor blocks the common mode current path while allowing the bidirectional chopper circuit to continue performing its power supply function between the capacitor and battery, thereby eliminating noise without sacrificing reliability
Solution Approach 2:
The harmful common mode current is extracted or removed from the circuit by blocking it at its source path. The common mode reactor specifically targets and removes the common mode current component while leaving the useful power transmission function intact, thus eliminating noise generation
2Object-generated harmful factors
If capacitors are connected between battery electrodes and virtual neutral line, then common mode current is redirected to virtual neutral line, but circuit complexity increases
Solution Approach 1:
Capacitors are introduced as intermediary elements that provide a low-impedance path for common mode current to flow to the virtual neutral line. These capacitors act as mediators that redirect the harmful common mode current away from the battery stray capacitance, thereby reducing noise while maintaining a relatively simple circuit structure
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
The solution effectively reduces noise and ripple voltage levels, improving the reliability of the power supply by limiting common mode current and minimizing interference with commercial AC power and load circuits.
Implementation Method 1
a common mode reactor having first and second coils with one terminals thereof being connected to a positive electrode and a negative electrode of a battery
Implementation Method 2
a second capacitor connected between a positive electrode of the battery and a virtual neutral line, and a third capacitor connected between a negative electrode of the battery and the virtual neutral line
Data Source
AI summary
In an uninterruptible power supply apparatus, a common mode current flowing from nodes (N1 to N3) to a line of a ground voltage (GND) through a stray capacitance (41) of a battery (40) is limited by a common mode reactor (34), and the low-level common mode current passing through the common mode reactor (34) is caused to flow to a virtual neutral line (NL) through a common mode capacitor (37). Therefore, the level of noise caused by the common mode current can be reduced.