Three-Level Inverter Control Method Reducing Switching Losses
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Solution Overview
Problem
Three-level inverters face challenges in reducing switching operations, leading to increased losses and costs, particularly in low output voltage regions, and require high-performance arithmetic units for efficient control, making them inefficient and costly.
Innovation Solution
A control method and system for three-level inverters that reduce switching operations by dividing the output voltage command period into sections, alternately turning on and off semiconductor switching elements based on output voltage commands, and using a less expensive microcomputer to manage on-time ratios, thereby reducing switching losses and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional control methods are used in low output voltage regions, then the inverter can operate, but the number of switching operations increases leading to increased losses and costs
Solution Approach 1:
The control method segments the output voltage command period into multiple sections and processes each section independently with optimized switching strategies. By dividing the control period and applying different switching patterns to different sections, the patent reduces the total number of switching operations while maintaining output voltage accuracy, thereby reducing switching losses in low output voltage regions.
Solution Approach 2:
The patent implements periodic switching patterns within each section of the output voltage command period. By using predetermined switching patterns that repeat periodically and optimizing the number of switching operations per period, the control method reduces overall switching frequency and losses while maintaining effective inverter operation in low output voltage regions.
2Measurement precision
If high-performance arithmetic units are used for efficient control, then control precision improves, but system cost increases
Solution Approach 1:
The control algorithm is segmented into discrete, manageable steps that can be implemented with simpler arithmetic units. By breaking down the control process into section-based operations with predetermined patterns, the patent achieves adequate control precision without requiring high-performance (and expensive) arithmetic units, thus reducing system cost while maintaining manufacturability.
3Loss of energy
If the number of switching operations is reduced, then switching losses decrease, but the range of output voltage may be limited
Solution Approach 1:
The control method dynamically adjusts the switching patterns and section divisions based on the actual output voltage requirements. By making the switching strategy adaptive rather than fixed, the patent can reduce switching operations in low output voltage regions while maintaining the ability to expand the output voltage range when needed, thus resolving the contradiction between reducing losses and maintaining versatility.
Solution Approach 2:
The patent changes control parameters such as section division points and switching patterns based on the desired output voltage level. By adjusting these parameters dynamically, the system can optimize for reduced switching losses at low output voltages while preserving the capability to operate across a wide voltage range when required, thereby maintaining both efficiency and adaptability.
Data Source
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AI summary
In a control method of a three-phase three-level inverter that makes switching elements in the inverter turned-on and -off according to an output voltage command to output three-phase AC voltage, the inverter having three of three-level inverters connected in parallel to one another each being capable of outputting a DC high voltage, DC middle voltage and DC low voltage, the method carries out operations for providing on-time ratios in one switching period of the switching elements, makes one inverter for one phase turn-on and -off switching elements respectively connected to a high voltage point and a middle voltage point with their respective on-time ratios to alternately output the DC high voltage and the DC middle voltage, makes one inverter for another phase fix the switching element connected to the middle voltage point in a turned-on state to output the DC middle voltage, and makes one inverter for the rest phase turn-on and -off the switching elements respectively connected to the middle voltage point and a low voltage point with their respective on-time ratios to alternately output the DC middle voltage and the DC low voltage.