Wind Turbine Inverter DC Offset Reduction via Dynamic Band Limits
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Solution Overview
Problem
Wind turbines using multi-phase inverters often experience DC offsets in their output current due to component tolerances and parasitic effects, which degrade the output vibration spectrum and require expensive component precision to mitigate.
Innovation Solution
A procedure that adjusts the tolerance band limits in a multi-phase inverter's tolerance band process to minimize the difference in switching frequencies between upper and lower switches, thereby reducing DC offsets and improving the vibration spectrum without requiring low-cost components, by changing one band limit to align the switching frequencies of the upper and lower switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the tolerance band width is narrowed to reduce current variation from the sinusoidal waveform, then the quality of the generated alternating current is improved, but the switching frequency increases
Solution Approach 1:
The patent applies dynamics by making the tolerance band width variable rather than fixed. The control device dynamically adjusts the tolerance band width based on the operating point of the wind turbine generator, allowing the system to optimize between current waveform quality and switching frequency under different operating conditions. This resolves the contradiction by adapting the tolerance band width to match the specific operational requirements at each moment.
Solution Approach 2:
The patent changes the parameter of tolerance band width from a static value to a dynamically adjustable parameter. By modifying this parameter based on the generator's operating point (such as power output, speed, or load conditions), the system can achieve high current waveform quality when needed while avoiding excessive switching frequencies during other operating conditions, thus resolving the technical contradiction.
2Manufacturing precision
If high precision components are used to eliminate DC offset in the output current, then the harmonic spectrum is improved, but the inverter design becomes expensive
Solution Approach 1:
The patent implements feedback by using a control device that continuously monitors the output current of the inverter and detects DC offsets. Based on this feedback information, the control device dynamically adjusts the reference values or control parameters to compensate for and eliminate the DC offset. This feedback mechanism allows the system to achieve high output current precision using standard components rather than requiring expensive high-precision components.
Solution Approach 2:
The inverter system performs self-correction by automatically detecting and compensating for its own DC offsets through the control device. The system uses its own output current information to adjust its operation, eliminating the need for external high-precision components. This self-service approach maintains high manufacturing precision while keeping the design cost-effective.
3Manufacturing precision
If the switching frequency of upper and lower switches is made equal to eliminate DC component, then the DC offset is minimized, but the control complexity increases
Solution Approach 1:
The patent applies partial action by focusing the control effort on achieving equal switching frequencies only for the upper and lower switches of the same phase, rather than attempting to control all switches in the multiphase inverter. This selective approach eliminates DC offsets in each phase independently while avoiding the excessive complexity of coordinating all switches across multiple phases, thus resolving the contradiction between DC offset elimination and control complexity.
Data Source
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AI summary
The invention relates to a method for generating a multi-phase alternating electric current having a sinusoidal fundamental wave in each phase by means of a multi-phase inverter of a wind turbine. The multi-phase inverter is activated using a tolerance band method which has an upper band limit and a lower band limit for each of the phases of the inverter. For each phase, the inverter has at least one top switch for generating a positive half sine wave of the alternating current of the phase and at least one bottom switch for generating a negative half sine wave of the alternating current of the phase. The method comprises the following steps: generating the positive half sine wave by means of the top switch and generating the negative half sine wave by means of the bottom switch depending on the band limits for the alternating electric current of the phase; changing at least one of the band limits such that a signal component superimposed on the respective sinusoidal fundamental wave is reduced.