Inverter Drive Device Torque Fluctuation Control
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Solution Overview
Problem
In drive devices, torque fluctuation occurs when switching from a switching pattern that suppresses LC resonance to a square wave pulse pattern during square wave control, due to the inability to reduce the number of slits or short pulse width below a certain threshold, leading to voltage steps and resonance issues.
Innovation Solution
A drive device with a controller that switches between pulse-width modulation and square wave control modes based on a threshold voltage, using a booster converter to adjust the voltage on the inverter, and employs specific switching patterns to suppress LC resonance, including forming slits and short pulses in the first switching pattern, and increasing the number of slits and pulses in the second pattern, to avoid torque fluctuation by adjusting the duty cycle and cut-off frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the number of slits or short pulse width is gradually reduced when switching from the first switching pattern to the square wave pulse, then the transition between control modes is smoother, but the number of slits or short pulse width cannot be equal to or less than a dead time, causing a voltage step and torque fluctuation
Solution Approach 1:
The patent changes the control parameter from gradually reducing the number of slits/short pulse width to maintaining a fixed number of slits/short pulses while adjusting their width to zero. This parameter change allows the switching pattern to transition to square wave pulse without being constrained by the dead time limitation, thereby eliminating voltage steps and torque fluctuations during mode switching.
2Object-affected harmful factors
If the first switching pattern is used to suppress LC resonance in the first resonance region, then resonance is suppressed, but torque fluctuation occurs when switching to square wave pulse pattern
Solution Approach 1:
The patent introduces a dynamic switching mechanism that selects between the first switching pattern and square wave pulse pattern based on the modulation percentage. When the modulation percentage exceeds a predetermined threshold, the system dynamically switches to square wave pulse pattern, eliminating torque fluctuation while maintaining LC resonance suppression through appropriate pattern selection.
3Object-affected harmful factors
If the second switching pattern with more slits and short pulses is used, then LC resonance in the second resonance region is suppressed, but the complexity of switching control increases
Solution Approach 1:
The patent simplifies the switching control by changing the decision parameter from rotation speed to modulation percentage. This parameter change allows for a simpler control logic that selects between switching patterns based on a single threshold comparison, reducing control complexity while maintaining effective LC resonance suppression across different resonance regions.
Data Source
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AI summary
The first square wave control mode using the square wave pulse pattern is used when the voltage acting on the inverter is equal to or higher than the threshold voltage. On the other hand, when the voltage acting on the inverter is lower than the threshold voltage, a square wave pulse pattern is used when the rotation speed of the motor is equal to or higher than the first predetermined rotation speed that is higher than the first resonance region, and the second square wave control mode using the first switching pattern for suppressing the LC resonance in the first resonance region is used when the rotation speed of the motor is lower than the first predetermined rotation speed.