Offset Voltage Generator for Three-Phase Inverter Modulation
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Solution Overview
Problem
Existing three-phase inverters face challenges in switching from continuous to discontinuous modulation modes, requiring additional offset voltage calculations and resulting in increased total harmonic distortion (THD) and switching loss.
Innovation Solution
An offset voltage generator that adjusts the weight to switch between modulation modes without recalculating offset voltages, using limiters and a summer to generate an offset voltage based on phase-voltage signals and DC link voltage, allowing seamless transition from continuous to discontinuous modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If continuous modulation mode is used, then voltage modulation is maintained, but switching loss increases
Solution Approach 1:
The patent implements dynamic switching between continuous and discontinuous modulation modes based on the modulation index. When the modulation index exceeds a predetermined threshold, the system transitions from continuous modulation to discontinuous modulation, thereby dynamically adjusting the switching behavior to reduce losses while maintaining voltage modulation capability when needed.
2Loss of energy
If discontinuous modulation mode is used, then switching loss is reduced, but total harmonic distortion increases
Solution Approach 1:
The patent changes the modulation mode parameter based on the modulation index threshold. By switching between continuous and discontinuous modes according to operating conditions, the system optimizes the trade-off between switching loss reduction and harmonic distortion control, achieving reduced losses without excessive THD increase.
3Measurement precision
If offset voltage is recalculated for mode switching, then accurate modulation is achieved, but calculation complexity increases
Solution Approach 1:
The patent extracts and utilizes the modulation index as a key parameter to determine modulation mode. By base the switching decision on this single extracted parameter rather than recalculating offset voltages, the system maintains modulation accuracy while significantly reducing calculation complexity and control overhead.
Data Source
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AI summary
An offset voltage generator including: a first limiter (502a) configured to compare a first phase-voltage signal with a maximum limit value and a minimum limit value to output a first limit-voltage signal; a second limiter (502b) configured to compare a second phase-voltage signal with the maximum limit value and the minimum limit value to output a second limit-voltage signal; a third limiter (502c) configured to compare a third phase-voltage signal with the maximum limit value and the minimum limit value to output a third limit-voltage signal; and a summer (504) configured to add a difference between the first phase-voltage signal and the first limit-voltage signal, a difference between the second phase-voltage signal and the second limit-voltage signal, and a difference between the third phase-voltage signal and the third limit-voltage signal, to output an offset voltage.