Coupled-Inductor CMVC Circuit for Inverter Common-Mode Voltage
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Solution Overview
Problem
High-speed switching devices in power converters and inverters generate high-frequency oscillatory common-mode and normal-mode voltages due to parasitic stray capacitance, leading to various electrical system issues.
Innovation Solution
A common-mode voltage cancellation (CMVC) circuit using coupled inductors with specific polarity arrangements to cancel or reduce common-mode voltage components by inducing out-of-phase voltages, followed by additional filtering if needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-speed switching devices are used in power converters and inverters, then switching frequency and operating characteristics are improved, but high-frequency oscillatory common-mode voltage and normal-mode voltage are generated due to parasitic stray capacitance
Solution Approach 1:
The patent uses the parasitic capacitance that causes harmful common-mode voltage to generate a compensating signal. The circuit detects the common-mode voltage generated by switching devices and uses the same parasitic capacitance to generate an opposing voltage signal that cancels the harmful effect, converting the harmful capacitance into a beneficial compensation mechanism
Solution Approach 2:
The patent applies preliminary anti-action by generating a compensating voltage signal before the harmful common-mode voltage affects the system. The CMVC circuit detects the upcoming common-mode voltage transient and applies an opposing voltage in advance to cancel or reduce the harmful effect before it propagates through the system
2Object-generated harmful factors
If common-mode voltage cancellation circuit is implemented, then common-mode voltage is reduced, but device complexity increases due to additional coupled inductors and windings
Solution Approach 1:
The patent makes the coupled inductors serve multiple functions: they perform normal power conversion functions while simultaneously generating common-mode voltage cancellation signals. The same inductors that transfer power also detect common-mode voltage and generate compensating signals, eliminating the need for separate cancellation circuitry
Solution Approach 2:
The patent merges the common-mode voltage cancellation function with the existing power conversion circuitry. The coupled inductors are integrated into the power stage, and their windings serve both power transfer and common-mode detection/cancellation purposes, combining multiple functions into a single unified structure
3Object-generated harmful factors
If traditional LC filters are used to filter common-mode voltage, then filtering performance is achieved, but filter size, weight, and cost increase
Solution Approach 1:
The patent replaces the mechanical LC filter structure with an electronic active cancellation system. Instead of using large inductors and capacitors to physically block common-mode voltage, the system uses electronic signal generation and injection through coupled inductors to actively cancel the common-mode voltage, achieving filtering without heavy passive components
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 cancels or reduces common-mode voltage, allowing for smaller, lighter, and less expensive LC filters, thereby improving electrical system performance.
Implementation Method 1
inducing a respective third voltage at the respective secondary windings of the second set of coupled inductors that is out of phase from the second voltage
Data Source
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AI summary
A common-mode voltage cancellation (CMVC) circuit (117), is disclosed. The circuit includes a first set of coupled inductors (555), each having a primary winding (511) defining a first polarity, and a secondary winding (512, 522, 532). The secondary windings (512, 522, 532) are electrically coupled in series. Each primary winding (511) receives a phase voltage (VA1, VB1, VC1) having a common mode voltage (Vcm) component from a respective input line (110). The circuit (117) includes a second set of coupled inductors (620) comprising at least one primary winding (621) and at least one secondary winding (612, 622, 632). The at least one primary winding (621) receives a second voltage (VA2, VB2, VC2) from the series connected secondary windings (512, 522, 532) of the first set of coupled inductors (555). Each at least one secondary winding (612, 622, 632) is coupled in series with a respective input line (110) such that the common mode voltage component (Vcm) received on the input lines (110) will be reduced at an output of the set of secondary windings (612, 622, 632).