AFE Rectifier Resonance Detection and Damping Control
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Solution Overview
Problem
Power conversion systems face challenges in mitigating input filter resonance, particularly in LCL filters, due to unknown inductance and transient oscillations, which can lead to capacitor degradation and costly maintenance.
Innovation Solution
A controller operates an active front-end rectifier in a standby mode to measure filter voltage or current signals, determines the resonant frequency, and adjusts rectifier control parameters to mitigate filter resonance, using active damping circuitry and feedback signals to selectively adjust PI controller gains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LCL filter is used to remove high-frequency switching currents, then power quality is improved, but filter resonance occurs causing capacitor degradation
Solution Approach 1:
The patent implements feedback control by measuring the actual capacitor voltage or current and comparing it with the reference value. The controller adjusts the active damping current based on the error signal to suppress resonance oscillations in real-time, resolving the contradiction between maintaining power quality and preventing filter resonance.
Solution Approach 2:
The patent introduces an intermediary active damping current that acts as a mediator between the LCL filter and the PWM converter. This intermediate control current counteracts the resonance oscillations without requiring modification of the filter structure itself, thus maintaining power quality while eliminating harmful resonance effects.
2Device complexity
If sensorless active damper is used to estimate capacitor voltage, then system complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent applies self-service principle by using the existing measurable quantities (input current, output current, or capacitor voltage) from the PWM converter system itself to estimate the capacitor voltage or current. The controller leverages the system's own operational data and known parameters to compute the unmeasured quantity, eliminating the need for additional sensors while maintaining sufficient precision for resonance suppression.
3Reliability
If feedback control of capacitor current is used to suppress resonance, then resonance suppression is improved, but device complexity increases
Solution Approach 1:
The patent implements multi-functionality by designing the controller to perform both the primary PWM switching control and the secondary active damping control within a single control unit. The same controller that generates the switching signals also computes the active damping current based on measured quantities, eliminating the need for separate dedicated resonance suppression hardware and reducing overall device complexity.
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 filter resonance, minimizing capacitor degradation and maintenance costs by adaptively controlling the rectifier to match changing grid impedance and load conditions, ensuring stable operation.
Implementation Method 1
determines a resonant frequency based on a transient response of the measured voltage or current signal
Implementation Method 2
selectively adjusts a rectifier control parameter to mitigate filter resonance based on the resonant frequency
Data Source
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AI summary
Disclosed examples include power conversion systems, computer readable mediums and methods for mitigating input filter resonance, in which a controller operates an active front end (AFE) rectifier in a first mode to turn a single rectifier switching device on and off and measures a filter voltage or current signal while all of the rectifier switches are off. The controller determines a resonant frequency based on a transient response of the measured voltage or current signal, and selectively adjusts a rectifier control parameter to mitigate filter resonance based on the resonant frequency.