Neutral-Point-Clamped Converter With Coupled Inductors for Common-Mode Noise
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Solution Overview
Problem
Existing electrical infrastructure for grid-connected devices, particularly in reduced or zero-emission electric vehicles, faces challenges with voltage stress on switches and common-mode voltage issues that lead to system noise and high-frequency currents, necessitating improvements in converter technology.
Innovation Solution
The use of coupled inductor topologies in neutral-point-clamped inverter circuits, such as NPC-CII circuits, which include cross-coupled inductors and filter inductors, reduces inductor size and flux, allowing for smaller components and improved power flow management, including bi-directional power transfer, and reduces common-mode voltage and high-frequency currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If prior converter approaches are used, then device simplicity and low cost are achieved, but voltage stress on switches increases and common-mode voltage issues occur
Solution Approach 1:
The converter is segmented into multiple levels (three-level topology) with neutral point clamping, dividing the voltage stress across multiple switches rather than requiring a single switch to handle the full bus voltage. This segmentation allows simpler individual switch requirements while maintaining overall system functionality.
Solution Approach 2:
The neutral point and clamping diodes act as intermediaries that redistribute voltage stress across multiple paths. The coupled inductor serves as an intermediary element that manages common-mode voltage by providing alternative current paths and reducing the direct coupling between differential and common-mode signals.
2Device complexity
If prior converter approaches are used, then device simplicity is maintained, but common-mode voltage produces system noise and high-frequency currents
Solution Approach 1:
The coupled inductor acts as an intermediary that decouples common-mode and differential-mode signals. By using two magnetically coupled inductors with appropriate winding configurations, the circuit provides separate paths for common-mode currents, effectively filtering them while maintaining the simplicity of the overall converter structure.
Solution Approach 2:
The circuit parameters (inductance values, coupling coefficient, switching frequency) are optimized to shift common-mode noise to frequencies that can be more easily filtered, while maintaining the fundamental conversion function. The neutral-point clamping configuration changes the voltage stress distribution parameters to reduce common-mode generation.
3Volume of moving object
If coupled inductor topologies are used, then inductor size is reduced, but circuit complexity increases
Solution Approach 1:
The filter function and power conversion function are merged into a single coupled inductor structure. The inductors serve dual purposes: performing the DC-AC conversion while simultaneously providing harmonic filtering and common-mode suppression, eliminating the need for separate filter components and reducing overall inductor volume.
Solution Approach 2:
The coupled inductor topology provides multiple functions within a single circuit structure: voltage conversion, current filtering, common-mode suppression, and power factor correction. This multi-functionality reduces the total component count and overall inductor size compared to traditional approaches that require separate dedicated components for each function.
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
This approach results in smaller inductor sizes, reduced voltage stress, lower harmonic content, and improved power quality, enabling efficient charging infrastructure for electric vehicles and reducing common-mode noise and current issues.
Implementation Method 1
The use of coupled inductor topologies in neutral-point-clamped inverter circuits, such as NPC-CII circuits, which include cross-coupled inductors and filter inductors
Data Source
AI summary
A grid-connected converter device for interfacing a grid network and coupling the grid network to a direct current (DC) source or DC Bus/Network is provided. According to this embodiment, the device includes a neutral-point-clamped inverter circuit having a voltage vdc across the DC source or DC Bus/Network, the neutral-point-clamped inverter circuit including one or more switch legs, each switch leg comprising a corresponding pair of switches having an electrical midpoint between the switches of the pair of switches. Said device further including an inductor network coupled to the neutral-point-clamped inverter circuit, the inductor network comprising a set of parallel inductor legs, each parallel inductor leg coupled to a corresponding electrical midpoint of a corresponding switch leg and also coupled to an output electrical node coupled to the grid network. In a variation, the inductor network can include cross coupled inductors, limbed inductors, or filter inductors.