Active Harmonic Filter for Wind Turbine High Frequency Compensation
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Solution Overview
Problem
Wind turbines with doubly fed induction generators face challenges in mitigating high frequency harmonics due to high impedance at frequencies above twice the rotor frequency, making it difficult for active harmonic filters to effectively compensate, especially since the harmonic current at these frequencies is low, and increasing compensator gain can lead to unstable operation.
Innovation Solution
An active harmonic filter is integrated into the stator power path of the wind turbine system, controlled by a processor to selectively extract high frequency harmonic components, determine whether they are positive or negative sequence harmonics, and compensate accordingly to mitigate these harmonics in the output current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gain of the generic compensator is increased to compensate for high frequency harmonics, then the compensation effect at high frequencies is improved, but the operation stability deteriorates and lower harmonic frequencies exceed prescribed limits
Solution Approach 1:
The patent segments the harmonic compensation task by frequency ranges. A generic compensator handles lower frequency harmonics with moderate gain, while a resonant compensator specifically targets high frequency harmonics (above twice rotor frequency) with frequency-specific high gain. This segmentation allows each compensator to operate within stable gain ranges while achieving effective compensation across the full harmonic spectrum.
Solution Approach 2:
The patent changes the compensator parameters based on frequency. The resonant compensator uses frequency-dependent gain that peaks at high frequency harmonics (twice rotor frequency and above) while maintaining lower gain at other frequencies. This parameter adaptation enables effective high frequency compensation without causing instability or excessive compensation at lower frequencies.
2Measurement precision
If the gain of the generic compensator is increased to compensate for high frequency harmonics, then the compensation effect at high frequencies is improved, but the compensation effect at lower harmonic frequencies deteriorates (exceeds prescribed limits)
Solution Approach 1:
The patent divides the compensation function into two segments: the generic compensator handles lower frequency harmonics with controlled gain to prevent exceeding limits, while the resonant compensator specifically targets high frequency harmonics with frequency-selective high gain. This segmentation ensures each frequency range receives appropriate compensation without interfering with other frequency ranges.
Solution Approach 2:
The resonant compensator acts as an intermediary that specifically bridges the gap at high frequency harmonics. It introduces frequency-selective gain that peaks at problematic high frequencies (twice rotor frequency and above) while having minimal effect on lower frequencies, thereby mediating between the need for high frequency compensation and the constraint of maintaining lower frequency harmonics within limits.
3Ease of manufacture
If passive solutions such as stator distortion filters are used to reduce harmonic level, then implementation is simple, but they do not always meet harmonic reduction requirements
Solution Approach 1:
The patent replaces passive mechanical filter systems with an active control-based compensator system. Instead of relying on fixed passive filter components that have limited effectiveness, the system uses controllable compensators (generic and resonant) that can dynamically adjust compensation based on actual harmonic conditions, achieving superior harmonic reduction while maintaining implementation feasibility through control algorithms.
4Measurement precision
If active harmonic filters are used to compensate high frequency harmonics, then compensation capability is provided, but the high network impedance at high frequencies makes effective compensation difficult
Solution Approach 1:
The patent addresses the high impedance challenge by changing the compensator parameters to include resonant frequency characteristics. The resonant compensator is designed with frequency-dependent gain that peaks at high frequency harmonics, effectively overcoming the high network impedance at these frequencies. This parameter design enables the compensator to provide sufficient compensation gain where network impedance is highest without requiring excessive system complexity.
Data Source
AI summary
A method of mitigating high frequency harmonics in an output current of an electrical power system connected to a power grid includes providing an active harmonic filter in a stator power path connecting a stator of the generator to the power grid. Further, the method includes controlling, via a controller, the active harmonic filter to selectively extract a high frequency harmonic component from the output current. The method also includes determining, via the controller, whether the high frequency harmonic component is a positive sequence harmonic or a negative sequence harmonic. Moreover, the method includes compensating, via the controller, for the high frequency harmonic component based on whether the high frequency harmonic component is the positive sequence harmonic or the negative sequence harmonic to mitigate the high frequency harmonics in the output current.