LED Driver Current Diversion for Harmonic Distortion Reduction
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Solution Overview
Problem
LED lighting systems with poor power factor due to harmonic distortion in current waveforms, which increases harmonic energy content and reduces energy at the fundamental frequency, are inefficient and may incur higher utility costs.
Innovation Solution
The implementation of a selective current diversion circuitry that diverts excitation current away from LEDs in a series circuit until the current or associated voltage reaches a predetermined threshold, reducing harmonic distortion by extending the input current conduction angle and improving power factor using simple, low-cost, and low-power circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LEDs are used as rectifier loads in AC lighting systems, then the system can provide illumination and rectification functions, but the current waveform becomes distorted with high harmonic content and poor power factor
Solution Approach 1:
The patent introduces an auxiliary switch (transistor Q1) as an intermediary component connected in parallel with the LED rectifier string. This switch acts as a mediator that diverts portion of the AC input current during specific phases, thereby shaping the overall current waveform to reduce harmonic distortion while allowing the LED string to maintain its rectification and illumination functions
Solution Approach 2:
The patent employs dynamic control of the auxiliary switch through a control circuit that responds to the AC input voltage waveform. The switch transitions between on and off states based on the instantaneous voltage level, creating a time-varying current path that optimizes power factor and reduces harmonics throughout the AC cycle
2Object-generated harmful factors
If complex power factor correction circuits are added to LED lighting systems, then power factor improves, but device complexity and manufacturing cost increase
Solution Approach 1:
The control circuit utilizes the existing AC input voltage waveform itself as the control signal for the auxiliary switch. The circuit automatically detects voltage zero-crossings and peak levels to timing the switch operations, eliminating the need for external microcontrollers, sensors, or complex control logic that would increase device complexity
Solution Approach 2:
The patent changes the electrical parameters of the system by introducing a controllable impedance path through the auxiliary switch. By dynamically adjusting the resistance/impedance of this parallel path based on the AC waveform phase, the system modifies the overall input impedance characteristics to achieve better power factor without complex correction circuits
3Object-generated harmful factors
If the conduction angle of AC input current is extended to reduce harmonic distortion, then power factor improves, but the effective illumination time may be reduced
Solution Approach 1:
The patent segments the LED rectifier system into two independent current paths: the main LED string for illumination and the auxiliary switch path for power factor correction. This segmentation allows the auxiliary path to operate during specific waveform phases (extending conduction angle) while the LED string maintains continuous or near-continuous operation for illumination
Solution Approach 2:
The auxiliary switch provides partial current conduction during phases when the LED string is not fully conducting. By diverting current through the auxiliary path during voltage peaks and transition phases, the system achieves extended effective conduction angle for power factor improvement without significantly reducing the illumination-providing current through the LED string
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 significantly reduces harmonic distortion and improves power factor for AC LED lighting systems, achieving high power quality with minimal additional components and manufacturing costs, while maintaining efficient light output.
Implementation Method 1
a first transistor operable to divert a portion of the excitation current away from the string of LEDs
Implementation Method 2
a current sense element having a voltage developed across the current sense element in response to a current flowing through the current sense element
Data Source
AI summary
Apparatus and associated methods reduce harmonic distortion of a excitation current by diverting the excitation current substantially away from a number of LEDs arranged in a series circuit until the current or its associated periodic excitation voltage reaches a predetermined threshold level, and ceasing the current diversion while the excitation current or voltage is substantially above the predetermined threshold level. In an illustrative embodiment, a rectifier may receive an AC (e.g., sinusoidal) voltage and deliver unidirectional current to a string of series-connected LEDs. An effective turn-on threshold voltage of the diode string may be reduced by diverting current around at least one of the diodes in the string while the AC voltage is below a predetermined level. In various examples, selective current diversion within the LED string may extend the input current conduction angle and thereby substantially reduce harmonic distortion for AC LED lighting systems.