Current-Controlled Variable Inductor for LED Driver Harmonic Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing inductor designs with constant inductance fail to meet stringent line-current harmonic limits for LED drivers across universal-line-voltage applications, particularly at low line voltages, due to increased total harmonic distortion and power losses associated with variable bulk-capacitor voltage levels.
Innovation Solution
A current-controlled variable inductor design featuring magnetic cores with separate inductor and control windings, where the control magnetic flux does not intersect the inductor magnetic flux paths, allowing inductance adjustment through varying control current based on line voltage or load current, minimizing power losses and maintaining efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a higher boost inductance is used to limit bulk-capacitor voltage at high line, then bulk-capacitor voltage is reduced to acceptable levels, but at low line the boost inductor enters CCM operation resulting in increased total harmonic distortion
Solution Approach 1:
The patent implements a variable inductance boost converter where the boost inductance dynamically changes based on input voltage conditions. At high line voltage, a higher inductance limits bulk-capacitor voltage to acceptable levels. At low line voltage, the inductance decreases to maintain DCM operation and prevent current waveform bulging, thereby avoiding increased THD. This dynamic adjustment resolves the contradiction between voltage control and harmonic distortion.
Solution Approach 2:
The patent changes the inductance parameter of the boost converter based on operating conditions. By varying the inductance value according to input voltage level, the system maintains optimal performance across different line conditions, preventing CCM operation at low line while controlling bulk voltage at high line.
2Device complexity
If a constant inductance is used to meet IEC 61000-3-2 Class D limits, then the design is simple, but it cannot meet the more stringent IEC 61000-3-2 Class C line-current harmonic limits for lighting applications
Solution Approach 1:
The patent transitions from a constant inductance design to a variable inductance design where the inductance value changes with input voltage. This dynamic adjustment enables the system to meet stringent Class C harmonic limits by maintaining DCM operation across the full input voltage range, while the control mechanism remains relatively simple.
3Use of energy by moving object
If the boost inductance increases during steady-state operation, then bulk-capacitor voltage is limited to acceptable levels, but the input power initially decreases causing a drop in bulk-capacitor voltage and requiring increased duty cycle
Solution Approach 1:
The patent applies preliminary action by pre-adjusting the boost inductance value based on expected operating conditions before steady-state operation begins. This prevents the transient power drop and bulk-capacitor voltage instability that would otherwise occur when inductance changes during operation, ensuring smooth transitions and stable performance.
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 solution effectively adjusts inductance to meet stringent harmonic standards by reducing inductance at low line voltages, limiting bulk-capacitor voltage, and maintaining low total harmonic distortion, thereby enhancing power factor correction and reducing power losses in LED drivers.
Implementation Method 1
A control coil is wound around one or more control sections of the one or more magnetic cores. A control magnetic flux flows through one or more closed flux paths along the control sections of the magnetic core.
Implementation Method 2
The inductance of the variable inductor is varied by varying the control magnetic flux
Data Source
AI summary
A variable inductor comprises one or more magnetic cores providing magnetic flux paths. An inductor coil is wound around one or more inductor sections of the one or more magnetic cores. An inductor magnetic flux flows through one or more closed flux paths along the inductor sections of the magnetic core. A control coil is wound around one or more control sections of the one or more magnetic cores. A control magnetic flux flows through one or more closed flux paths along the control sections of the magnetic core. Under this arrangement, the inductor magnetic flux substantially does not flow through the control sections of the magnetic core and the control magnetic flux substantially does not flow through the inductor sections of the magnetic core. The closed flux paths associated with the inductor magnetic flux and the closed flux paths associated with the control magnetic flux share one or more common sections of the magnetic core not including the control sections and inductor sections. The inductance of said variable inductor is varied by varying said control magnetic flux.