Serial Multiplex Inverter Switching Load Balancing Control
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Solution Overview
Problem
In serial multiplex inverters, existing control methods struggle to evenly distribute switching loads among cells, leading to unbalanced cell voltages, increased power consumption, and reduced component life, particularly in systems using triangular wave comparison PWM methods.
Innovation Solution
A control device that includes a high-level control section and a switching load distribution control section, which stores ON- and OFF-output duration information for each cell, determines pattern shifts, and generates gate signals to optimize switching load distribution by adjusting the output levels of cells based on level commands and output levels, using pattern determination and counter calculation operations to balance the load across cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional triangular wave comparison PWM methods are used in serial multiplex inverters, then the control implementation is simple, but the switching loads among cells become unbalanced
Solution Approach 1:
The control device monitors the output duration of each cell and uses this feedback information to dynamically adjust switching patterns. By tracking which cells have been ON or OFF for the longest periods, the system implements loss equalization control that redistributes switching loads to balance the switching losses among all cells, resolving the unbalance problem while maintaining operational simplicity
Solution Approach 2:
The system changes the switching patterns and gate signal timing based on the monitored output duration parameters of each cell. By dynamically adjusting which cell receives the gate signal next based on their cumulative ON/OFF durations, the system transforms the fixed switching pattern into an adaptive one that equalizes switching losses without complicating the control implementation
2Duration of action of stationary object
If switching patterns are adjusted to balance cell voltages, then component life is extended, but power consumption increases due to additional control operations
Solution Approach 1:
The control device uses the existing output duration information from each cell to automatically determine the next switching pattern. The system serves itself by utilizing the monitored duration data to make balancing decisions without requiring external intervention or complex additional control algorithms, thereby extending component life while minimizing additional power consumption
Solution Approach 2:
The system preliminarily tracks and stores the output duration of each cell before making switching decisions. By having this information ready in advance, the control device can immediately implement loss equalization when needed, extending component life through proactive load balancing without the need for reactive high-power correction operations
3Productivity
If cell voltages are allowed to remain unbalanced, then system efficiency is maintained, but power consumption increases and component life decreases
Solution Approach 1:
The control device continuously monitors output duration feedback from each cell and uses this information to implement loss equalization control. This feedback mechanism allows the system to maintain high efficiency by only making switching adjustments when necessary to balance loads, preventing excessive power consumption while avoiding the energy losses associated with unbalanced cell voltages
Solution Approach 2:
The system dynamically adjusts switching patterns based on real-time output duration conditions of each cell. Rather than maintaining a fixed switching pattern that causes unbalance, the system adapts its behavior to equalize switching losses, thereby maintaining system efficiency while reducing energy losses and preventing the power consumption increase that would result from sustained unbalance
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A higher-level control unit 5 generates a level command L∗ on the basis of a command value cmd. A switching load distribution control unit 6 stores the output period information of each cell and designates a gate signal so that: in case of a pattern by which a cell is changed from ± 1 level to 0 level, the cell having the longest ± 1 level period information is set to 0 level; and in case of a pattern by which a cell is changed from 0 level to ± 1 level, the cell having the longest 0 level output period is set to ± 1 level. This distributes the switching load of each cell in the serial multiplex inverter control device.