LCL Active Power Filter for Harmonic and Reactive Current Compensation
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Solution Overview
Problem
Existing electrical networks face issues with harmonic distortion, phase shift, and imbalance due to non-linear loads, particularly from renewable energy sources, which degrade signal quality and efficiency, and require complex and costly filtering solutions that can cause resonance and active power consumption.
Innovation Solution
A 4-wire compensation system with an LCL filter and control unit that cancels harmonic and reactive content, compensates for imbalances, and maximizes active power output by using a control algorithm to generate signals in opposite phases to counteract non-linear load disturbances, employing sliding mode and higher-order controllers for robust control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a first-order filter with high inductance is used to block switching components, then filtering efficiency is improved, but the phase shift between desired current and injected current increases and dynamics slow down
Solution Approach 1:
The patent uses an LCL filter with variable parameters that can dynamically adjust the filtering characteristics. The control system modifies the effective inductance and capacitance values based on operating conditions, allowing the filter to maintain both high filtering efficiency and fast dynamic response across different scenarios.
Solution Approach 2:
The invention changes the parameters of the filtering system by using an LCL configuration with specifically optimized inductance and capacitance values. The control unit adjusts the operating parameters of the power electronic switches to optimize the filter's frequency response, achieving both blocking efficiency and dynamic performance.
2Speed
If a first-order filter with low inductance is used, then dynamics and current change rate are improved, but filtering efficiency decreases and switching components are injected into the network
Solution Approach 1:
The LCL filter with active control provides dynamic adjustment capabilities, allowing the system to maintain low effective inductance for fast response while using control actions to block switching components. The control unit actively compensates for the reduced passive filtering capability.
Solution Approach 2:
The patent replaces the reliance on purely passive mechanical filtering (large inductors) with an active control system that uses power electronic switches and control algorithms to achieve filtering. This substitution allows fast dynamics while maintaining filtering efficiency through intelligent control rather than bulky passive components.
3Object-affected harmful factors
If an auxiliary passive filter is added to improve filtering, then high-frequency component blocking is improved, but resonance with other passive elements occurs and active power is consumed
Solution Approach 1:
The patent extracts the harmful high-frequency switching components from the injected current using the LCL filter's frequency-selective properties. The control system identifies and removes these components through synchronized switching, preventing their injection into the network without requiring additional passive filtering elements that would consume power.
Solution Approach 2:
The invention replaces passive auxiliary filters (which consume active power through damping resistors) with an active control mechanism. The control unit uses power electronic switches to actively cancel high-frequency components, eliminating the need for power-consuming passive damping elements while maintaining filtering performance.
4Object-affected harmful factors
If an auxiliary passive filter is added to improve filtering, then high-frequency component blocking is improved, but resonance with other passive elements occurs
Solution Approach 1:
The LCL filter configuration, combined with active control, extracts high-frequency switching components before they can interact with other passive elements in the network. This prevents the formation of resonant circuits by removing the excitation source (switching harmonics) that would otherwise cause resonance with existing passive elements.
Solution Approach 2:
The patent replaces passive filtering elements that could create resonance issues with an active control system. The control unit actively manages the filtering function without introducing additional passive L-C networks that could resonate with existing system elements, thereby improving reliability by eliminating resonance risks.
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
The system effectively filters harmonics and reactive power, optimizes active power output, and stabilizes voltage quality, reducing resonance risks and active power consumption while maintaining efficient energy management.
Implementation Method 1
a filter 5 configured to block the high-frequency switching components contained in the signal to be injected into the electrical network 1
Implementation Method 2
A first-order filter, the most commonly used; composed of a simple inductor
Implementation Method 3
an LCL filter 11, combining two inductors and a capacitor
Implementation Method 4
Inverters, most often consisting of bidirectional, open- and closed-controlled power electronic switches, such as IGBTs and GTOs
Implementation Method 5
By a set of appropriately controlled switches (usually pulse-width modulation), the source is modulated to obtain an alternating signal
Implementation Method 6
a control unit 12 configured to identify and control the current injected into the network 1 and to control the inverter 9 to generate this current... generates a signal of intensity I inj configured in opposite phase to cancel, at the connection point C, the non-active disturbances
Implementation Method 7
employing sliding mode and higher-order controllers for robust control
Data Source
Figure 1a~1b
Figure 2
Figure 3
AI summary
The invention relates to a current compensation device (7) able to be connected, in parallel, between an electrical network (1) and non-linear and linear electrical loads (2), and downstream of at least one renewable energy generation power unit (100) coupled to an energy storage element (3), the compensation device (7) comprising: - a power conversion unit (8) comprising at least one voltage inverter (9) able to generate an alternating current; - an output filtering unit (10) comprising a filter (11) designed to block the harmonic components due to the switching of the inverter (9); - a control-command unit (12) comprising a unit (25) for computing reference currents and a switching control device (21) that controls the switching of the inverter (9) as a function of the identification of the currents by the unit (25) for computing reference currents.