LCL Filter Resonance Suppression via Voltage Command Compensation
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Solution Overview
Problem
Conventional power regenerative converters experience resonance phenomena due to LCL filters, leading to oscillations in current and voltage, which are not effectively suppressed by existing damping methods, especially with long-distance wiring and varying power supply impedance.
Innovation Solution
Incorporating a voltage command compensation unit that calculates a compensation value based on the capacitor voltage at the series connection point of the reactors and adds it to the AC voltage command, thereby controlling the power conversion unit to suppress oscillations and resonance in the LCL filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an LCL filter is used to smooth input/output currents, then the influence of high-frequency components is reduced, but resonance phenomenon occurs causing oscillations in current and voltage
Solution Approach 1:
The patent implements feedback control by detecting the actual capacitor voltage in the LCL filter and comparing it with the reference voltage command. The deviation is fed back to the voltage command compensation unit, which adjusts the voltage command to suppress resonance oscillations. This closed-loop feedback mechanism dynamically compensates for resonance effects while maintaining current smoothing performance.
Solution Approach 2:
The patent changes the voltage command parameter dynamically based on the detected capacitor voltage state. By adjusting the voltage command compensation amount according to the resonance condition, the system modifies operating parameters to suppress oscillations without altering the physical structure of the LCL filter, thereby maintaining current smoothing while eliminating resonance.
2Object-affected harmful factors
If a damping resistor is added to the LCL filter to suppress resonance, then resonance phenomenon is reduced, but system complexity and power loss increase
Solution Approach 1:
The patent replaces the mechanical/passive damping resistor approach with an active control system. Instead of adding physical damping elements that increase complexity and power loss, the system uses electronic voltage command compensation based on capacitor voltage detection to suppress resonance, thereby reducing device complexity while achieving resonance suppression.
Solution Approach 2:
The control system performs self-regulation by detecting its own capacitor voltage state and automatically adjusting the voltage command to suppress resonance. This self-service mechanism eliminates the need for external damping resistors or additional complexity, as the system uses its existing control infrastructure to achieve resonance suppression.
3Productivity
If switching elements are used to convert power, then power conversion efficiency is improved, but high-frequency components are generated causing voltage fluctuations
Solution Approach 1:
The patent introduces the LCL filter as an intermediary between the switching elements and the power grid. This filter mediates the high-frequency components generated by switching operations, smoothing them before output while maintaining the efficiency benefits of switching conversion. The voltage command compensation further refines this by actively suppressing resonance in the filter.
Solution Approach 2:
The system uses feedback control to detect voltage fluctuations caused by switching operations and capacitor resonance. The detected capacitor voltage is fed back to adjust the voltage command, creating a compensatory signal that counteracts high-frequency fluctuations and stabilizes output voltage while preserving power conversion efficiency.
Data Source
AI summary
A power regenerative converter includes: a power conversion unit configured to convert AC power supplied from an AC power supply into DC power and convert DC power into AC power to be supplied as regenerative electric power to the AC power supply; an LCL filter including a reactor unit having a plurality of reactors connected in series between the power conversion unit and the AC power supply, and capacitors each having one end connected to a series connection point of the reactors in the reactor unit; a drive control unit for controlling the power conversion unit based on an AC voltage command; and a voltage command compensation unit for calculating a compensation value in accordance with a capacitor voltage being a voltage at the series connection point of the reactors and adding the compensation value to the AC voltage command input to the drive control unit.