MMC Modulation Scheme for Zero-Voltage Switching
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Solution Overview
Problem
Existing modular multilevel converters (MMC) fail to achieve zero-voltage switching (ZVS) for all switches during the switching transition, leading to increased switching loss and reduced efficiency.
Innovation Solution
A converter system with a controller that operates in three different modulation schemes to control switches, allowing for zero-voltage switching by manipulating the voltage applied to the arm inductors and capacitors, including a first mode with zero voltage, a second mode with at least one cell voltage, and a third mode with inductor-resonance, reducing switching loss and enhancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional MMC switching operation is used, then the converter can operate with simple topology, but switching loss increases and conversion efficiency decreases
Solution Approach 1:
The patent applies dynamics by making the switching operation adaptive through three distinct modes (insertion, extraction, and resonance modes) that dynamically adjust the switching strategy based on operational requirements. The controller dynamically selects among different switching patterns (e.g., inserting/extracing AC voltage vectors, resonance switching) to achieve zero-voltage switching conditions, thereby reducing switching losses while maintaining conversion efficiency.
Solution Approach 2:
The patent changes operational parameters by introducing three different modes of operation with distinct voltage application strategies. In insertion mode, positive voltage is applied to arm inductors; in extraction mode, negative voltage is applied; and in resonance mode, resonant frequency switching is employed. These parameter changes enable zero-voltage switching transitions, reducing switching losses and improving overall conversion efficiency.
2Productivity
If zero-voltage switching is achieved for all switches, then switching loss is reduced and conversion efficiency is increased, but control complexity increases
Solution Approach 1:
The patent segments the switching control into three distinct modes (insertion, extraction, and resonance modes), each handling specific switching scenarios. This segmentation allows the complex control task of achieving zero-voltage switching for all switches to be divided into manageable segments with specific control strategies, reducing overall control complexity while maintaining high conversion efficiency.
Solution Approach 2:
The patent introduces an intermediary control mechanism that mediates between the power electronic switches and the load. The controller acts as an intermediary by generating appropriate gate signals that coordinate the switching of multiple switches across different cells, ensuring zero-voltage switching conditions are met. This intermediary control layer simplifies the overall control architecture by providing a unified control strategy for achieving ZVS across all switches.
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 proposed modulation scheme achieves zero-voltage switching for all switches, significantly reducing switching loss and increasing conversion efficiency in modular multilevel converters.
Implementation Method 1
at least one of the top arm inductor and the bottom arm inductor resonates with at least one capacitor in the top arm and the bottom arm
Data Source
AI summary
The present disclosure provides a converter system including a branch circuit and a controller. The branch circuit includes a top arm and a bottom arm electrically connected to each other. The top arm includes N cells and a top arm inductor. The bottom arm includes N′ cells and a bottom arm inductor. The controller controls the converter system to operate in first, second and third modes through the plurality of control signal, wherein in the first mode, the voltage applied to the top arm inductor and the bottom arm inductor is substantial zero. In the second mode, the voltage applied to the top arm inductor and the bottom arm inductor is at least one cell voltage. In the third mode, at least one of the top arm inductor and the bottom arm inductor resonates with at least one capacitor in the top arm and the bottom arm.