Inverter Commutation Pattern Selection for Harmonic Reduction
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Solution Overview
Problem
Converter-based energy transmission units in power grids generate harmonics due to their structure and operation, leading to resonances and excessive harmonic content in the power distribution network, which existing filtering methods struggle to fully mitigate due to varying impedance and resonance frequencies.
Innovation Solution
A method for operating converters in power distribution systems that involves selecting commutation patterns based on system state variables, including resonant frequencies, to minimize harmonic excitation and resonance, using techniques like Selective Harmonic Elimination, and employing in-phase or anti-phase fundamental waves to cancel out harmonics across multiple converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If filters are provided on every converter to reduce harmonics, then harmonic content at connection points is reduced, but device complexity and cost increase significantly
Solution Approach 1:
The harmful harmonic filtering function is extracted from individual converter units and relocated to the transmission network level. The network operator implements centralized filtering measures at specific network nodes rather than requiring filters at every converter, thereby reducing overall system complexity while maintaining harmonic reduction effectiveness.
Solution Approach 2:
A centralized control and filtering system acts as an intermediary between multiple converters and the transmission network. This intermediary coordinates harmonic management across the network, providing filtering services to multiple converters without each converter needing its own filter, thus reducing device complexity while maintaining harmonic control.
2Reliability
If filters are dimensioned to avoid critical states with varying impedance, then resonance and amplification are prevented, but device complexity and cost increase
Solution Approach 1:
The system implements continuous monitoring of network impedance and resonant frequencies, with the centralized filtering system adjusting its operation based on real-time feedback. This allows the system to adapt to varying impedance conditions without requiring overly complex pre-dimensioned filters, maintaining reliability while reducing device complexity.
Solution Approach 2:
The filtering system transitions from static, pre-dimensioned filters to a dynamic system that can adapt its filtering characteristics based on real-time network conditions. This dynamic approach allows the system to handle varying impedance and resonant frequencies more effectively with simpler filter components, as the filtering action is adjusted programmatically rather than requiring complex hardware.
3Ease of operation
If multiple converters operate independently with fixed commutation patterns, then operation is simple, but harmonic content in the AC network remains excessive
Solution Approach 1:
Converters receive feedback signals from the centralized control system regarding network harmonic content and resonant frequencies. Based on this feedback, converters dynamically adjust their commutation patterns to minimize harmonic generation, achieving low harmonic content while maintaining operational simplicity through automated control.
Solution Approach 2:
The system changes operational parameters (commutation patterns, switching angles) of converters based on real-time network conditions. By dynamically adjusting these parameters rather than using fixed patterns, the system reduces harmonic content in the AC network while keeping the control logic centralized and manageable.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces the overall harmonic content in the power grid by dynamically adjusting commutation patterns to align with system conditions, thereby minimizing harmonic introduction and resonance, ensuring a lower harmonic component in AC networks during energy transmission.
Implementation Method 1
the system state variable comprises a resonant frequency of the power distribution system (1), and the commutation pattern is selected such that there is reduced or no excitation at the resonant frequency
Data Source
Figure 1~2
Figure 3~5
Figure 4a
AI summary
The invention relates to a method for operating a converter (2) in a power distribution system (1), wherein the converter (2) supplies electric power provided by a source to an AC system (3) at a coupling point (E) or draws electric power from the AC system (3) at the coupling point (E), wherein the AC system (3) is coupled to further converters for supplying or drawing electric power, wherein the converter (2) has an inverter (23) that is provided with power switches in order to provide an electrical variable, comprising the following steps: – provision of one or more system state variables that indicate a system state of the system (3); – selection of one of a plurality of commutation patterns on the basis of the one or more system state variables; and – actuation of the inverter (23) in accordance with the selected commutation pattern.