Space Vector Synchronous Modulation for AC Drive Systems
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Solution Overview
Problem
Existing synchronous modulation methods in AC drive systems require complex calculations to maintain accurate timing, leading to performance degradation due to varying input frequencies and increased harmonic waves at low or high frequencies.
Innovation Solution
A space vector based synchronous modulation method that directly calculates and compares output angles of fundamental voltage vectors with a reference angle, eliminating the need for converting angles to periods of time, thereby reducing calculation steps and maintaining accurate modulation angles despite dynamic frequency changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional synchronous modulation methods (triangular carrier wave comparison or polygonal trace tracking) are used, then the switching frequency maintains a proportional relationship with the fundamental wave frequency, but the calculation process becomes complex and modulation angle accuracy degrades under dynamic frequency changes
Solution Approach 1:
The patent extracts and eliminates the angle-to-time conversion step from the conventional modulation process. By directly comparing output angles of fundamental voltage vectors with a reference angle, the method removes the intermediate conversion环节 that causes cumulative errors and computational complexity, achieving both simpler calculation and higher angle accuracy
Solution Approach 2:
Instead of converting angles to time periods as in conventional methods, the patent inverts the approach by directly using angle comparisons. The modulation decision is made based on angle relationships rather than time intervals, fundamentally changing the calculation paradigm to reduce both complexity and error accumulation
2Reliability
If the switching frequency is kept low at low fundamental frequencies, then device stress is reduced, but the number of harmonic waves increases
Solution Approach 1:
The patent implements dynamic segmentation of the frequency range into multiple bands, with each band having an optimized carrier wave ratio. This dynamic adaptation allows the system to use lower switching frequencies at low fundamental frequencies (reducing device stress) while using higher ratios at higher frequencies (reducing harmonics), resolving the contradiction between device tolerance and harmonic content
Solution Approach 2:
The patent changes the carrier wave ratio parameter across different frequency bands rather than keeping it constant. By adjusting this key parameter according to the operating frequency, the system optimizes the balance between switching frequency and harmonic content, allowing low switching frequencies at low fundamentals and high switching frequencies at high fundamentals
3Object-generated harmful factors
If the switching frequency is kept high at high fundamental frequencies, then the number of harmonic waves is reduced, but device stress increases
Solution Approach 1:
The patent uses dynamic frequency band segmentation to adapt the carrier wave ratio to the operating conditions. At high fundamental frequencies, the system automatically selects appropriate segmentation and ratios that reduce harmonics while avoiding excessively high switching frequencies that would stress devices, achieving an optimized balance
Solution Approach 2:
The patent adjusts the carrier wave ratio parameter based on the fundamental frequency band. This parameter change strategy ensures that at high frequencies, the system uses optimized ratios that suppress harmonics without requiring disproportionately high switching frequencies, thereby protecting device tolerance
Data Source
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AI summary
A space vector based synchronous modulating method includes sampling a frequency f of a reference voltage vector; checking a relational table of frequencies and carrier wave ratios by the frequency f so as to obtain a carrier wave ratio N; obtaining a passing angle Δθ of the reference voltage vector by Δθ=2π/N; obtaining a modulating angle θm of the reference voltage vector by θm=(Nth-1)×Δθ, in which Nth indicates which time of sampling; obtaining a modulating ratio m according to a modulating ratio-frequency curve; accounting and synthesizing an output angle of three basic voltage vectors of the reference voltage vector according to the modulating angle θm and the passing angle Δθ of the reference voltage vector and the modulating ratio m; comparing a variable quantity θf of the reference voltage vector angle θ and the output angle of three basic voltage vectors, and outputting corresponding basic voltage vectors according to the comparing result; synthesizing an output voltage in accordance with the reference voltage vector by the basic voltage vectors.