Wind Turbine Converter Pulse Phase De-synchronization
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Solution Overview
Problem
Wind farms face challenges in meeting grid code requirements for low harmonic current levels due to high frequency harmonic emissions from wind turbine converters, which can lead to grid connection prohibition.
Innovation Solution
A method of controlling wind turbine converters by generating pulses with different start phases within a pulse width modulation period, allowing for de-synchronization of converters without fixed phase shifts, and adjusting pulse start phases based on feedback signals and additional parameters like propagation time and communication delays to reduce harmonic content below grid code thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional fixed phase offset de-synchronisation is applied, then harmonic current cancellation is theoretically achieved, but considerable harmonic content remains at the point of common coupling
Solution Approach 1:
The patent applies dynamics by making the pulse start phases adjustable and optimizable rather than fixed. The control system allows dynamic adjustment of pulse start phase differences between converters based on feedback signals and system conditions, enabling the system to adapt to varying operating conditions and achieve better harmonic cancellation than static fixed offset methods
Solution Approach 2:
The patent implements feedback by using measured electrical characteristics (such as harmonic content) from the point of common coupling to continuously optimize the pulse start phases of converters. This closed-loop control allows the system to monitor harmonic emissions and adjust de-synchronisation parameters to minimize harmful effects, directly addressing the insufficient cancellation precision of conventional open-loop fixed offset methods
2Productivity
If high switching frequencies are used in converters, then power conversion efficiency is improved, but harmonic current peaks occur at switching frequency and multiples
Solution Approach 1:
The patent converts the harmful harmonic effects of high switching frequencies into a beneficial outcome by using de-synchronisation of multiple converters. The harmonic currents from individual converters, which would be harmful if synchronized, are deliberately phase-shifted to create destructive interference at the point of common coupling, thereby canceling out the harmful high frequency harmonics while maintaining the efficiency benefits of high switching frequencies
3Reliability
If de-synchronisation is applied to reduce harmonic emissions, then grid code compliance is improved, but control system complexity increases
Solution Approach 1:
The patent manages control complexity by focusing on adjusting a specific parameter (pulse start phase) rather than redesigning the entire control system. The de-synchronisation is achieved by modifying the timing parameters of existing PWM signals, which can be implemented through relatively simple phase shift circuits or software timing adjustments, thereby achieving grid code compliance without excessive complexity increase
Data Source
AI summary
Provided is a method of controlling wind turbine converters of wind turbines parallel connected at a point of common coupling, the method including: generating for each converter within a same length of a pulse width modulation period a pulse, wherein the pulses start for different converters at different pulse start phases, wherein pulse start phase differences of the pulse start phases between at least two of adjacent converters are unequal.