LCL Filter Resonance Mitigation in Voltage Source Converters
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Solution Overview
Problem
LCL filter resonance issues in power conversion systems are not effectively mitigated by existing technologies, leading to instability and harmonic distortion due to varying source impedance, which is not adequately considered in control loop tuning.
Innovation Solution
Estimating source impedance to tune rectifier control loops and employing variable active rectifier carrier frequency, along with passive damping, to detect and mitigate resonance conditions by adjusting control loop parameters and introducing damping resistors as needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If LCL filter is used in power conversion systems, then harmonic distortion and electromagnetic interference are reduced, but resonance issues occur leading to system instability
Solution Approach 1:
The system performs preliminary identification of the resonance frequency of the LCL filter during installation or commissioning. This resonance frequency information is stored and used later to configure the control loops (current, voltage, or power loops) with appropriate bandwidth limits before normal operation begins, preventing resonance issues from developing during operation.
Solution Approach 2:
The invention changes the parameters of the control loops by limiting their bandwidth based on the identified LCL filter resonance frequency. Specifically, the control loops are configured to operate at frequencies significantly below the resonance frequency (e.g., 1/3 to 1/10 of the resonance frequency), thereby avoiding the harmful resonant conditions while maintaining effective control performance.
2Speed
If control loop bandwidth is increased to improve dynamic response, then system responsiveness improves, but resonance amplification increases
Solution Approach 1:
The invention optimizes the control loop bandwidth parameter by setting it to a specific range (1/3 to 1/10 of the LCL filter resonance frequency) based on the identified resonance characteristics. This parameter optimization achieves the best compromise between dynamic response performance and resonance mitigation, allowing fast response without exciting the resonant frequency.
3Device complexity
If source impedance variation is not considered in control tuning, then control loop configuration is simplified, but resonance frequency shifts cause instability
Solution Approach 1:
The system performs preliminary identification of the actual LCL filter resonance frequency taking into account the specific source impedance conditions during installation. This measured resonance frequency is then used to configure the control loops appropriately, ensuring stability for that specific installation without requiring complex adaptive control during operation.
Solution Approach 2:
The invention creates a simplified model or representation of the resonance characteristics based on initial measurements, and uses this copied information to configure control parameters. This approach captures the essential resonance behavior without requiring continuous complex measurements, balancing accuracy with simplicity.
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 mitigates LCL filter resonance, reducing harmonic distortion and system instability by accurately accounting for source impedance, ensuring stable operation of voltage source converters.
Implementation Method 1
LCL filter resonance issues in power conversion systems are not effectively mitigated by existing technologies, leading to instability and harmonic distortion
Data Source
AI summary
Control apparatus, techniques and computer readable mediums are presented to mitigate LCL filter resonance issue for voltage source converters. Two level voltage source converter with and without passive damping of LCL filter are selected for the comparative study. Control algorithms are presented to estimate the source impedance based on variable carrier PWM. Estimated source impedance is used to tune the control of the VSC to avoid the resonance of LCL filter has been presented. In situations in which LCL resonance cannot be avoided by tuning the control parameters, energy efficient techniques are disclosed to provide selective passive damping to facilitate continued power conversion system operation without significant adverse impact on system performance.