Drive Control Device Subharmonic Compensation via Coordinate Rotation
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Solution Overview
Problem
Existing drive control devices face issues with unwanted subharmonics in motor voltage and current due to uncompensated intermediate circuit voltage ripples, leading to reduced converter utilization and torque quality, especially at critical output frequencies.
Innovation Solution
A method involving continuous measurement of phase currents, transformation into a second coordinate system to rotate current and voltage vectors, and subsequent correction using a controller, effectively addressing subharmonic frequencies by converting them into constant variables that can be easily corrected.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the modulation factor is lowered at critical output frequencies to compensate for intermediate circuit voltage ripple, then subharmonic components are reduced, but converter utilization is reduced and maximum output voltage is not available
Solution Approach 1:
The patent applies parameter changes by transforming the coordinate system in which current and voltage vectors are represented. By rotating the coordinate system at a specific transformation angle corresponding to the subharmonic frequency, the time-varying subharmonic components become constant DC components in the transformed coordinate system. This allows the controller to easily compensate for subharmonics without reducing the modulation factor, thereby maintaining high converter utilization while eliminating harmful subharmonic effects.
2Object-affected harmful factors
If the modulation factor is lowered at critical output frequencies to compensate for intermediate circuit voltage ripple, then subharmonic components are reduced, but the maximum possible output voltage is no longer available
Solution Approach 1:
The patent changes the parameter of coordinate system orientation by rotating it at an angle corresponding to the subharmonic frequency. This transformation converts time-varying subharmonic AC components into constant DC components in the transformed coordinate system. The controller can then compensate for these subharmonics using simple DC offset correction, allowing the full modulation range to be utilized and maximum output voltage to be available without subharmonic distortion.
3Reliability
If non-ideal compensation of intermediate circuit voltage occurs, then subharmonic components remain in the linear range of the modulator, but torque quality and regulation are degraded
Solution Approach 1:
The patent transforms the coordinate system parameter to rotate at an angle matching the subharmonic frequency. This transformation converts residual subharmonic AC components into DC components in the transformed coordinate system, even when compensation is not ideal. The controller can then effectively eliminate these converted DC components, preventing them from appearing as harmful AC subharmonics in the torque and regulation, thereby improving torque quality regardless of compensation perfection.
Data Source
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AI summary
The invention is a method for operating a drive control device (68) comprising a converter (10) with a voltage intermediate circuit, and a device operating according to the method, wherein phase currents generated by the converter (10) are measured during operation, wherein a current vector (iαβ) is formed from the measured phase currents in a first coordinate system (αβ coordinate system), wherein the current vector (iαβ) is rotated by a transformation angle (ϕfSH) into a second coordinate system (xy coordinate system), wherein a resulting current vector (ixy) in the second coordinate system is supplied to a controller (36), wherein a voltage vector (duxy) resulting at the output of the controller (36) is rotated back into the first coordinate system by the same transformation angle (ϕfSH), and wherein the resulting voltage vector (duαβ) in the first coordinate system is used as an additional control variable for controlling the converter (10).