Hybrid Multilevel Converter Cell Count Reduction
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Solution Overview
Problem
Cascaded multilevel converters require a large number of cells to achieve desired output voltage levels, leading to increased system costs, and traditional hybrid topologies suffer from unequal losses among high voltage cells and energy imbalance between high and low voltage cells.
Innovation Solution
A cascaded hybrid multilevel converter design with power cells of the same topology but different voltage ratings, where high voltage cells are switched at low frequency and low voltage cells at higher frequency, using a phase-shifted pulse width modulation (PSPWM) scheme to optimize cell operation and reduce the number of cells required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large number of identical power cells are used to achieve desired output voltage levels, then the output voltage control is improved, but the system cost and device complexity increase
Solution Approach 1:
The patent applies local quality by using power cells with different voltage ratings in different positions within the converter. Specifically, it uses a combination of high-voltage power cells and low-voltage power cells, where each type is strategically placed to optimize the overall voltage synthesis capability. This allows the system to achieve the desired output voltage levels with fewer total cells compared to using only identical cells, thereby reducing system complexity while maintaining precise voltage control.
2Device complexity
If higher voltage power cells are used to reduce the number of cells, then the device complexity is reduced, but the system is not optimized for different output voltage levels
Solution Approach 1:
The patent implements universality by designing a hybrid converter topology that can operate efficiently across multiple output voltage levels. The system uses both high-voltage and low-voltage power cells that can be selectively activated based on the desired output voltage level. This multi-functional approach allows the same converter structure to be optimized for different voltage levels without requiring separate dedicated designs, thereby maintaining versatility while reducing overall device complexity.
3Device complexity
If traditional hybrid topologies with different cell topologies and voltage ratings are used, then the number of cells is reduced, but unequal losses among high voltage cells and energy imbalance occur
Solution Approach 1:
The patent applies equipotentiality by ensuring that all power cells, regardless of their voltage rating, operate under balanced conditions. The control strategy is designed to distribute the power processing tasks equitably among high-voltage and low-voltage cells, preventing any single cell or group of cells from bearing excessive stress or energy imbalance. This balanced operation mode ensures that losses are distributed more uniformly across all cells, improving overall system efficiency while maintaining the reduced cell count advantage of hybrid topologies.
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 design reduces the overall cost of the electric drive system by optimizing cell count and minimizing energy imbalances, achieving efficient voltage control with reduced harmonic distortion and optimized voltage levels.
Implementation Method 1
switching a plurality of switching devices of a power cell assembly by generating pulse width modulation signals based upon a plurality of carrier signals compared to a reference signal, wherein the plurality of switching devices are switched at a same switching frequency
Data Source
AI summary
A multilevel converter includes a power supply assembly with a plurality of phases, and a power cell assembly with first power cells and second power cells. The first power cells and second power cells have a same topology and a same current rating, and supply power to the plurality of phases of the power supply assembly. Each phase of the plurality of phases includes a first power cell and a second power cell of the power cell assembly, voltage ratings of the first power cells and the second power cells being different. Furthermore, a method for controlling a multilevel converter and an electric drive system comprising a multilevel converter are disclosed.