Nested Control Loop for Heterogeneous LED Strings
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Solution Overview
Problem
Modern LED luminaires designed with constant voltage power sources cannot utilize highly integrated, low-cost constant current power supplies, which are advantageous for controlling luminous characteristics like CRI and CCT, due to incompatibility.
Innovation Solution
A controller implements a nested control loop to drive multiple, parallel-connected heterogeneous strings of LEDs using a constant current power supply, with an inner loop controlling the relative drive strength of each string and an outer loop maintaining the power supply output voltage at a constant value by adjusting the total current drawn.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a constant voltage power supply is used to drive LED strings, then the circuit design is simple and compatible with modern LED luminaires, but the control over luminous characteristics (CRI, CCT) and efficiency is limited
Solution Approach 1:
The patent divides the LED lighting system into multiple independent strings, each with its own current regulator, allowing separate control of luminous characteristics for each string while maintaining compatibility with constant voltage power supplies
Solution Approach 2:
The patent implements dynamic control mechanisms where current regulators adjust the current through each LED string based on feedback signals, enabling real-time adjustment of luminous characteristics such as CRI and CCT
2Adaptability or versatility
If a constant current power supply is used to drive multiple heterogeneous LED strings, then advanced control of luminous characteristics is achieved, but the power supply output voltage fluctuates and requires complex voltage regulation
Solution Approach 1:
The patent implements a feedback control mechanism where the controller monitors the output voltage of the constant current power supply and adjusts the total current drawn by the LED strings to maintain stable operating conditions
Solution Approach 2:
The patent anticipates voltage fluctuations by implementing pre-control measures through the controller that adjusts current distribution before significant voltage instability occurs, maintaining power supply stability
3Ease of operation
If current shunting methods are used to control LED brightness, then the implementation is simple, but the control range and efficiency are limited
Solution Approach 1:
The patent replaces static current shunting with dynamic current regulation through controlled switches and current regulators, enabling broader control range and higher efficiency by actively managing current distribution based on lighting requirements
Solution Approach 2:
The patent changes the control parameter from simple current shunting to regulated current distribution, allowing adjustment of multiple parameters including current magnitude, distribution ratio among strings, and timing, thereby expanding control range and efficiency
Data Source
AI summary
A controller in a solid state luminaire implements a nested control loop to drive multiple, parallel-connected, heterogeneous strings of series-connected LEDs using a constant current power supply. The current through each string is independently controlled by a current regulator in series with the LEDs. An inner (current) control loop alters the relative drive strength of each LED string, to achieve desired luminous characteristics, such as CRI, CCT, and the like. An outer (voltage) control loop monitors the output voltage of the power supply, and the total current drawn. The outer control loop adjusts a gain factor applied to the control signals for each current regulator, to control the total current drawn—while maintaining the relative ratios of drive strength between the strings—so as to maintain the power supply output voltage at a substantially constant value.