Power Converter Harmonic Current Control for Lower Motor Torque Peaks
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Solution Overview
Problem
Existing power converters that supply power to motors tend to increase the effective value of motor current, leading to decreased efficiency and operating area, with solutions like increasing motor size or switching element capacity resulting in increased size and cost.
Innovation Solution
The power converter incorporates a control unit that generates a power source current command value with multiple extrema in a power source half cycle, synthesized from fundamental, third harmonic, and fifth harmonic waves, to minimize the effective value of motor current and reduce peak torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional power conversion control is used, then the motor can operate at rated power, but the effective value of motor current increases and peak torque increases, decreasing efficiency and operating area
Solution Approach 1:
The invention changes the waveform parameters of the power source current by superimposing harmonic components (third and fifth harmonics) onto the fundamental wave. This parameter modification allows the current waveform to have multiple extrema per half-cycle, which redistributes the torque production throughout the cycle, thereby reducing peak torque while maintaining effective power delivery and improving motor efficiency
Solution Approach 2:
The invention employs periodic harmonic injection into the power source current, where third and fifth harmonic waves are systematically added to the fundamental frequency component. This periodic structure creates a current waveform with multiple peaks and valleys that distributes torque generation more evenly over time, reducing peak torque demands while maintaining overall productivity
2Force
If motor size is increased to reduce peak torque, then peak torque is reduced, but the size and cost of the converter increases
Solution Approach 1:
Instead of physically increasing motor or converter size, the invention changes the electrical parameters of the power source current waveform. By introducing harmonic components and creating multiple extrema in the current waveform per half-cycle, the torque production is distributed more evenly, reducing peak torque demands without requiring larger mechanical components
3Force
If switching element capacity is increased to reduce peak torque, then peak torque is reduced, but the size and cost of the converter increases
Solution Approach 1:
The invention modifies the electrical parameters of the input current waveform by superimposing harmonic components, which redistributes torque production over time. This parameter-based approach reduces peak torque demands on the switching elements, allowing the use of smaller, less expensive switching components while maintaining the same torque output capability
Data Source
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AI summary
A control unit (40) that controls a switching operation is provided for a power converter having a plurality of switching elements (Su, Sv, Sw, Sx, Sy, Sz). The control unit (40) controls the switching elements (Su, Sv, Sw, Sx, Sy, Sz) such that two or more extrema appear in a power source half cycle in a waveform synthesized from second, fourth, and sixth harmonics which have a power source frequency as a fundamental frequency and are extracted from a waveform of an absolute value of a motor current vector.