Multilevel Converter Cell Selection Using Phase Arm Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Multilevel converters experience high switching losses due to unnecessary switching activities at high current levels, which are not effectively addressed by conventional methods that do not consider current levels during switching.
Innovation Solution
A method and device for selecting switching cells in a multilevel converter that considers the phase arm current to minimize switching by formulating a switching pulse pattern with low losses, using a voltage change matrix and cell selection matrix to determine which cells to switch based on reference voltage and current, thereby reducing high current level switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If cells are switched frequently to maintain reference voltage and balance cell voltages, then voltage control precision is improved, but switching losses increase
Solution Approach 1:
The patent changes the parameter of cell selection criteria from conventional methods to a new approach that considers current direction and magnitude. By selecting cells based on current direction (positive or negative) and using specific selection criteria (highest voltage for positive current, lowest voltage for negative current), the patent reduces unnecessary switching while maintaining voltage control precision within acceptable ranges.
Solution Approach 2:
The patent applies partial action by not switching cells at every opportunity but only when necessary to maintain voltage balance. The method allows cell voltages to fluctuate within a defined range (not always maintaining exact balance) and reduces switching frequency by selecting cells based on current direction, thereby reducing switching losses while still achieving adequate voltage control.
2Loss of energy
If cell switching is reduced to minimize losses, then switching losses are reduced, but voltage balancing capability deteriorates
Solution Approach 1:
The patent changes the approach to voltage balancing by introducing current direction as a key parameter in cell selection. Instead of using conventional balancing methods that require frequent switching, the patent selects cells based on current direction (positive or negative) and applies specific voltage selection criteria, thereby maintaining voltage balancing capability with reduced switching frequency and lower switching losses.
Solution Approach 2:
The patent uses a simplified control strategy that copies the essential function of conventional balancing methods through a different approach. By selecting cells based on current direction and voltage magnitude rather than continuous feedback control, the patent achieves voltage balancing with fewer switching operations, reducing losses while maintaining the core balancing function.
3Device complexity
If conventional cell selection methods are used, then implementation simplicity is maintained, but switching losses increase due to high current level switching
Solution Approach 1:
The patent introduces current direction as an additional parameter in the cell selection process. By determining whether current is positive or negative and applying different selection criteria accordingly (highest voltage cell for positive current, lowest voltage cell for negative current), the patent reduces switching losses at high current levels while keeping the control method relatively simple and easy to implement.
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
The invention concerns a method and computer program product for selecting switching cells (C1u1, C2u1, C3u1, C4u1, C5u1) for voltage contribution in a phase arm of a multilevel converter (10), a cell selecting control device (12) for a multilevel converter and a multilevel converter. The cell selecting control device and multilevel converter comprises a balancing control element(14) that obtains a reference voltage (Vref) for the phase arm, obtains a measurement of the current (I) running through the phase arm and selects cells for contributing to an AC voltage output from the multi level converter based on the reference voltage (Vref) and the magnitude of the phase arm current.