Current Controller for Unbalanced Stator Winding Impedance
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Solution Overview
Problem
Electrical AC machines with unbalanced stator winding impedance experience unbalanced currents, leading to increased losses, vibration, and noise, which hinder full utilization of converter current rating and require additional costs or hardware changes.
Innovation Solution
A current controller system comprising positive-sequence and negative-sequence current controllers that generate voltage commands in a dq-frame, allowing for balanced stator currents by separately controlling positive and negative sequence components, and using adaptive filters and PI-regulators to manage harmonics and unbalance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If unbalanced stator winding impedance is present, then the electrical machine can be operated, but unbalanced currents occur leading to increased losses, vibration, and noise
Solution Approach 1:
The controller segments the current control into positive-sequence and negative-sequence components. The positive-sequence current controller handles the balanced current component, while the negative-sequence current controller handles the unbalanced current component. This segmentation allows independent control of each sequence component, enabling the system to compensate for unbalanced impedance effects and reduce losses without changing the hardware configuration.
2Productivity
If unbalanced stator currents occur, then the machine can run, but converter current rating cannot be fully utilized and additional costs or hardware changes are required
Solution Approach 1:
The controller dynamically adapts to unbalanced impedance conditions by continuously adjusting the negative-sequence voltage command based on real-time detection of current unbalance. This dynamic control allows the system to maintain optimal converter current rating utilization under varying unbalanced conditions without requiring additional hardware or complex mechanical modifications.
3Object-affected harmful factors
If unbalanced currents are present, then the generator operates, but acoustic noise and vibration increase
Solution Approach 1:
The controller converts the harmful effect of unbalanced impedance into a controllable parameter by injecting a specifically designed negative-sequence voltage command. This transformation allows the system to use the unbalance detection itself as the basis for generating the compensating control signal, thereby converting the harmful unbalanced current effect into a beneficial control mechanism that reduces noise and vibration while maintaining operational reliability.
Data Source
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AI summary
It is described a current controller (560) for controlling plural stator currents (Ia, Ib, Ic) of plural stator windings (113, 115, 117) of an electrical machine (111, 211, 212), in particular generator, wherein the plural windings are separately connectable to a converter (119, 219, 220, 519), the current controller comprising: a positive-sequence current controller (601) configured for providing a first voltage command (631), in particular in a rotating dq+ frame, based on the plural stator currents (Ia, Ib, Ic); a negative-sequence current controller (603) configured for providing a second voltage command (639), in particular in the dq+ frame, based on the plural stator currents (Ia, Ib, Ic); a summation system (641) for adding the first voltage command and the second voltage command to obtain a summed voltage command (643, Vd, Vq) based on which the converter (119, 219, 220, 519) is controllable.