Direct Torque Control for Matrix Converter PMSM
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Solution Overview
Problem
Existing direct torque control methods for matrix converters suffer from torque ripples and inconsistent switching frequencies, compromising system stability and efficiency in motor speed control systems.
Innovation Solution
A novel direct torque control method is introduced, which establishes an MC voltage vector switching table to visually display torque and flux changes, using a spatially rotational coordinate system and defining torque and flux evaluation functions to optimize the mark-to-space ratio, thereby inhibiting torque ripples and achieving constant switching frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional DTC with hysteresis comparator and voltage vector switching table is used, then the control structure remains simple and independent from motor parameters, but torque ripple becomes too large and switching frequency becomes inconstant
Solution Approach 1:
The patent dynamically adjusts the voltage vector selection based on real-time torque and flux hysteresis comparator outputs. Instead of using a fixed switching table, the system adaptively selects from multiple voltage vectors (including fundamental, third harmonic, and fifth harmonic vectors) according to the current operating state, thereby achieving constant switching frequency while maintaining simple control structure
Solution Approach 2:
The patent changes the selection criteria for voltage vectors by introducing multiple hysteresis comparators that monitor both torque and flux simultaneously. The system switches between different voltage vectors based on the combined feedback from these comparators, which changes the switching frequency characteristics from inconstant to constant while reducing torque ripple
2Reliability
If multi-stage hysteresis and multi-vector subdivision are employed to inhibit torque ripples, then torque ripple inhibition improves, but switching frequency becomes inconstant
Solution Approach 1:
The patent segments the voltage vector selection into multiple categories (fundamental vectors, third harmonic vectors, fifth harmonic vectors) with different functions. Each segment is selected by specific hysteresis comparators based on the current torque and flux error signals, allowing independent optimization of torque ripple inhibition and switching frequency consistency for each segment
Solution Approach 2:
The system dynamically switches between different voltage vector segments based on real-time feedback from torque and flux hysteresis comparators. This dynamic selection ensures that the appropriate vector type is applied at the right moment, achieving both torque ripple inhibition and constant switching frequency
3Measurement precision
If voltage vector switching table is replaced by SVM to accurately control torque and flux, then torque and flux control precision improves, but control structure becomes more complicated and requires rotational coordinate transformation
Solution Approach 1:
The patent extracts and eliminates the complex rotational coordinate transformation and PI controller components from the conventional SVM approach. Instead, it uses a simplified switching table method with multiple hysteresis comparators that directly select voltage vectors based on torque and flux error signals, achieving comparable control precision with much simpler structure
Solution Approach 2:
The patent creates a simplified version of SVM by using a voltage vector switching table that copies the essential functionality of SVM (voltage vector selection based on torque and flux) without requiring the complex mathematical transformations. The switching table is designed to provide accurate torque and flux control through direct lookup based on hysteresis comparator outputs
Data Source
AI summary
The present invention relates to a direct torque control method for inhibiting torque ripples, mainly comprising the following steps: establishing an MC voltage vector switching table visually displaying degrees of change in torque and flux, and, proposing, on the basis of the MC voltage vector switching table visually displaying the degrees of change in torque and flux, an MC-DTC mark-to-space ratio computing policy for torque quantification control. The MC-DTC mark-to-space ratio computing policy allows for inhibition of torque ripples of a PMSM speed control system and for a constant switching frequency, uses the MC voltage vector switching table visually displaying the degrees of change in torque and flux, has a simple algorithm, does not reply on motor parameters, and obviates the need for rotational coordinate transformation.