Five-Level Inverter Mode Switching for Junction Temperature Reduction
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Solution Overview
Problem
When the PV input voltage exceeds the bridge line-line voltage command value, five-level inverters automatically switch to a three-level operation mode, leading to increased power loss and junction temperature in switching devices, triggering over-temperature protection and reducing their service life.
Innovation Solution
The method involves switching between two three-level operation modes of a five-level inverter, where the switching devices alternate their operation to share power loss, reducing the maximum junction temperature and heat-dissipation cost, and prolonging the service life by controlling the operation mode based on preset temperature thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the operation mode is switched from five-level to three-level when PV input voltage exceeds the bridge line-line voltage command value, then the inverter can continue to operate, but the power loss of switching devices increases significantly and junction temperature rises
Solution Approach 1:
The patent divides the switching devices into two groups (first switching devices S1Pos, S1Neg and second switching devices S2Pos, S2Neg) and alternates their operation between two three-level operation modes. This segmentation allows the thermal load to be distributed across different device sets, reducing peak power loss and junction temperature in any single group.
Solution Approach 2:
The patent implements periodic switching between the first three-level operation mode and the second three-level operation mode based on junction temperature thresholds. When the first group's temperature exceeds threshold1, switch to the second mode; when the second group's temperature exceeds threshold2, switch back to the first mode. This periodic action prevents sustained high power loss conditions.
2Productivity
If the operation mode is switched from five-level to three-level when PV input voltage exceeds the bridge line-line voltage command value, then the inverter can continue to operate, but the junction temperature of switching devices increases triggering over-temperature protection
Solution Approach 1:
The patent segments switching devices into two groups and alternates their operational burden. By switching between modes where different device groups are active, the thermal accumulation is prevented, keeping junction temperatures below over-temperature protection thresholds.
Solution Approach 2:
The patent employs feedback control by continuously monitoring junction temperatures of switching devices and automatically switching operation modes when temperature thresholds are exceeded. This closed-loop temperature management prevents thermal runaway and over-temperature protection triggering.
3Productivity
If the operation mode is switched from five-level to three-level when PV input voltage exceeds the bridge line-line voltage command value, then the inverter can continue to operate, but the service life of switching devices is reduced greatly
Solution Approach 1:
The patent segments the switching devices into two operational groups and alternates between modes, distributing the cumulative thermal stress and electrical stress across different device sets. This reduces the degradation rate of individual devices, extending their service life while maintaining continuous inverter operation.
Data Source
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AI summary
A method for switching an operation mode of a five-level inverter and a device for switching an operation mode of a five-level inverter are provided. The method includes: determining a first three-level operation mode as a three-level operation mode of the five-level inverter to be switched to from a five-level operation mode in a case that a PV input voltage is higher than a bridge line-line voltage command value of the five-level inverter required when the five-level inverter is connected to a power grid; switching, after the operation mode of the five-level inverter is switched to the first three-level operation mode, the operation mode of the five-level inverter from the first three-level operation mode to a second three-level operation mode, in a case that a junction temperature of a switching device operating in the first three-level operation mode exceeds a first preset value; and switching the operation mode of the five-level inverter from the second three-level operation mode to the first three-level operation mode in a case that the junction temperature of a switching device operating in the second three-level operation mode exceeds a second preset value. According to the provided method, the junction temperature of a switching device still operating after the operation mode of the five-level inverter is switched from the five-level operation mode to the three-level operation mode is reduced.