Generator Control Arrangement for Harmonic Voltage Regulation
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Solution Overview
Problem
Conventional control systems for wind turbine generators face challenges in efficiently managing stator currents and harmonic voltages due to modulation limits and DC-link voltage constraints, leading to transient over-modulation and converter trips, resulting in reduced efficiency and increased current requirements.
Innovation Solution
A control arrangement that includes a fundamental current controller, a harmonic voltage controller, and an optional negative-sequence current controller, which separately manage stator currents and voltages in the dq-frame, allowing for the regulation of harmonic currents and voltages to reduce harmonic distortions and improve efficiency by controlling the d-component of the harmonic current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a simple PID controller is used to regulate the fundamental generator voltage in the dq-frame, then the average value of the generator voltage can be controlled to a reference voltage, but the peak value of the generator voltage may be higher than the modulation limit due to high frequency harmonics, causing transient over-modulation and converter trips
Solution Approach 1:
The control system is segmented into separate controllers: a fundamental voltage controller for average voltage regulation and a harmonic voltage controller for peak voltage regulation. This segmentation allows each controller to address specific voltage components independently, preventing over-modulation while maintaining operational simplicity.
Solution Approach 2:
A harmonic voltage controller acts as an intermediary between the fundamental voltage controller and the converter. It specifically targets and regulates the 6th order harmonic voltage component, mediating the conflict between average voltage control and peak voltage limitation to prevent converter trips.
2Reliability
If the average generator voltage reference is set to a constant value lower than the modulation limit to avoid converter trips, then converter reliability is improved, but total generator/converter current increases and efficiency decreases due to higher field weakening current
Solution Approach 1:
The harmonic voltage controller uses feedback from the measured generator voltage to detect and regulate the 6th order harmonic component. This feedback mechanism allows the system to maintain the average voltage reference at the modulation limit while actively suppressing harmonic peaks that would cause over-modulation, thereby improving efficiency without sacrificing reliability.
Solution Approach 2:
The control approach changes the parameter being regulated from average voltage to peak voltage through harmonic-specific control. By targeting the 6th order harmonic voltage component specifically, the system can operate at higher efficiency points without causing converter trips, effectively changing the control parameter from general voltage magnitude to specific harmonic content.
Data Source
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AI summary
It is described a control arrangement (260, 360) for controlling plural stator currents (Ia, Ib, Ic) of plural stator windings (113, 115, 117) of an electrical machine (111, 211), comprising: a fundamental current controller (371); at least one harmonic voltage controller (373a, 373b) configured to receive as inputs a winding voltage signal (391) related to voltages at the plural stator windings, a reference winding voltage signal (392) related to reference voltages at the plural stator windings and an electrical angle (Θe) of the electrical machine, wherein the harmonic voltage controller is configured to output an reference harmonic current command (393, Idnref); at least one harmonic voltage calculation module (369a, 369b) configured to receive the reference harmonic current command (393a, 393b) and to output a harmonic voltage command (Vdnh, Vqnh) based on the reference harmonic current command; and a summation system to obtain a summed voltage command (398, Vd, Vq) based on which the converter (119, 219) is controllable.