Performance Comparison And Optimization Of Multi-Segmented LED Drivers

LEDs have many favorable features,such as high luminous efficacy,long lifespan,environmental friendliness,etc.Amongst AC input applications in particular,AC-DC LED drivers are required for lighting DC LEDs.Advantages of multi-segmented LED drivers using piecewise linear topologies include high efficiency,high power factor?PF?and low total harmonic distortion?THD?of the input current.While LED drivers developed using the traditional switching-mode topologies contain either energy-storing inductors or electrolytic capacitors,the multi-segmented LED drivers consist mainly of a series of controllable current sources,which give it additional advantages such as reducing electromagnetic interference?EMI?,smaller size and lower cost of production.In this dissertation,the working principles of multi-segmented LED drivers based on three different input-current strategies were introduced in detail.The derivation of idea waveforms based on theoretical formulas was then presented.In order to verify the actual effect and compare performance,three average 6-W input power prototype LED drivers were implemented.The test results found that without input filter,all three prototypes of multi-segmented LED drivers show the efficiency in the range of 81%to 86%,and the PF value in the range of 0.91 to0.97 in wide input voltage range.The prototype LED drivers based on sinusoidal input-current shaping strategy and constant current strategy had the THDi40 value from 16.83%to 24.84%,and with the harmonic quality of input current mostly satisfied the Class-D standard.However,the prototype LED driver based on negative sine input-current shaping strategy had the THDi₄₀value ranging from 29.70%to 41.25%,with 5⁶th harmonics exceeding the Class-D standard at every input voltage level.In addition,loss analysis was also carried out for each prototype LED driver.The experimental data on efficiency,PF and THDi₄₀ were then used to study the performance optimization of multi-segmented LED drivers.Based on the three established input-current control strategies,the sinusoidal input-current shaping strategy and the negative sine input-current shaping strategy were combined and applied to develop an enhanced design of multi-segmented LED drivers.A prototype of LED driver with an average 6-W input power was created for the experiment.The test results show that the prototype LED driver had the efficiency from 81%to 86%,the PF value ranging from 0.97 to 0.98 and the THDi40 value ranging from18.16%to 22.72%,the harmonic quality of the input current mostly satisfied the Class-D standard,with smaller power fluctuation as well.Considering load combination is the main decision variable,the most optimal design algorithm of multi-segmented LED drivers was derived.The algorithm ensures optimal performance of multi-segmented LED drivers for the selected LED load within its corresponding wide range input voltage.The processing speed for choosing the best load was also increased using the proposed algorithm.Furthermore,a MATLAB GUI interface was developed to enhance the user-friendliness of the LED driver optimization process.