PWM Inverter Switching Pattern Alternation for Harmonic Emission Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing PWM inverters struggle to meet harmonic current emission requirements of grid codes without complicating control methods.
Innovation Solution
Control PWM inverters by alternating between two different switching patterns during successive periods, with time-shifted start times, to reduce harmonic current emissions without modifying the inverters or grid filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a single switching pattern is used for PWM inverter operation, then the control method is simple, but harmonic current emissions exceed grid code requirements
Solution Approach 1:
The patent applies periodic action by alternating between different switching patterns in successive periods. The controller switches between a first switching pattern during a first period and a second switching pattern during a second period, creating a time-varying switching sequence that spreads harmonic emissions across different frequency spectra, thereby reducing peak harmonic current emissions to meet grid code requirements while maintaining relatively simple control logic.
Solution Approach 2:
The patent implements dynamics by making the switching pattern variable over time rather than static. The controller dynamically selects between multiple switching patterns based on the operating period, adapting the switching behavior to reduce harmonic emissions. This dynamic approach allows the system to meet emission requirements without requiring complex real-time calculation or control algorithms.
2Object-generated harmful factors
If multiple switching patterns are applied successively, then harmonic current emissions are reduced, but the control method becomes more complex
Solution Approach 1:
The controller implements periodic action by systematically alternating between different switching patterns in successive periods. This structured periodic switching spreads the harmonic energy across different frequency ranges, reducing peak emissions. The periodic nature provides a predictable and manageable control approach that avoids the need for complex real-time decision-making while achieving emission reduction goals.
Solution Approach 2:
The patent applies parameter changes by varying the switching pattern parameters over time. Different switching patterns have different characteristic frequencies and harmonic spectra. By changing the switching pattern parameter (which pattern is active) in successive periods, the system redistributes harmonic emissions across the frequency spectrum, reducing peak emissions without requiring complex control algorithms.
3Object-generated harmful factors
If PWM inverters are modified to reduce harmonic emissions, then emission requirements are met, but the inverter design and grid filters require changes
Solution Approach 1:
The patent replaces physical modifications (mechanical/electrical changes to inverter hardware and filter design) with a control-based solution. Instead of modifying the inverter circuitry or redesigning grid filters to handle harmonics, the system uses intelligent switching pattern selection to inherently reduce harmonic emissions. This substitution approach maintains existing hardware designs while achieving emission compliance through control software.
Solution Approach 2:
The PWM inverter system provides self-service by using its own control mechanism to reduce its harmful emissions. The controller monitors and adjusts the switching patterns to minimize harmonic current emissions generated by the inverter itself, without requiring external filtering equipment or hardware modifications. The system essentially cleans up its own emissions through intelligent control.
Data Source
AI summary
The invention relates to a method for controlling one or more PWM inverters. The method comprises determining first and second periods of the first PWM inverter for operating the first PWM inverter with respective first and second switching patterns wherein the first and second switching patterns have different harmonic spectrums, and operating the first PWM inverter with the first and second switching patterns applied successively during the respective first and second periods.