Research On Topologies And Control Methods Of Lighting Power Sources

Since the concept of “green lighting” has been raised from last century, manycountries have responsed to it, our country also started “the green lighting project”at1993, quality and technology level of lighting has been a significant mark tomeasure the modern development level of one country. Lighting power decides thequality and level of lighting, to develop lighting driving devices with highperformance, high reliabilty and low cost is not only the reqeust of “green lighting”,but also the needs of sustainable development. LED itself has been constantlydeveloped to be more and more mature, it is very possible to replace low powerhigh intensity discharged lamp in the future to become the new generation oflighting source, however, till now there is no mature driving technology for it yet,rearch on the driving device of LED is also imperative.This paper mainly focuses on research of topology and control method of lightingpower used for low power high intensity discharged lamp and high power LEDlighting system, specific research contents are shown as follows.A novel whole range digital control theory for half bridge LCsCp resonant circuitused in high intensity discharged lamp electronic ballast is presented. The LCsCpresonant ignition strategy is adopted, considering the tolerance deviation of thepassive components, an adaptive digital control method for ignition which improvesthe reliability and reduces the cost of the system is proposed. Varying powerreference value close loop control is used in the transition stage during ignition tosteadily increase the lamp power without large current inrush and voltage stress. Asimple close-loop control method based on average active power is presented toassure the reliable constant lamp power without any power over shooting. Low-frequency modulation drive method is adopted to overcome the acoustic resonanceproblem commonly shown in metal halide lamp. A150W metal halide lampelectronic ballast used for projector is built to verify the control method presentedabove, lab experiment tests show that the system can ignite reliably with a smoothtransition stage; steady state constant power can be guaranteed, total efficiency ofthe system above93%is achieved without acoustic resonance.Though high frequency sinusoidal modulation control method has the merits ofsimple control and low cost, but it can not avoid acoustic resonance. Low frequencysquare wave method can fully conduct power frequency spectrum so that it canavoid the normal presented acoustic resonance phenomenon in metal halide lamp.Switches in quasi-resonant half bridge topology can work in zero-voltage switchingand its working frequency can be higher over100khz, comparing with tradition half bridge topology, quasi-resonant half bridge can have higher power intensity. Basedon the application of quasi-resonant half bridge circuit in low power high intensitydischarged lamp electronic ballast, a digital control method is introduced includingthe constant current control in transition period, transient inrush power restrictionmethod in the end of transition period and also the power close-loop control method.A70W sample is built to verify the cotrol method introduced above, the system canachieve nearly constant current control in transient stage, at the same time withsmall inrush and can achieve constant power close loop control reliably.Single stage electronic ballast reduces the cost and raises the reliability with oneless power stage, and it becomes one hot key too. Take single stage electronicballast topology as research object, the application of single stage electronic ballastin metal halide lamp is analyzed, its merits and disadvantages are summarized.Based on the result, a single stage topology based on buck and half bridge ispresented, simulation shows its practicality. Taking low power metal halide lamp ascontrol object, an electronic ballast sample is built based on buck and half bridgesingle stage topology in lab, tests proved PFC is achieved and can provide stableoutput to the downstream converter, and also proves the analysis is practical.LED technology is developing rapidly and shows to trend to take over highintensity discharge lamp as the new generation light power, but traditional threestage LED driver has high cost and low reliability. Based on the research of single-stage electronic ballast, research of single stage AC/DC converter in LED driver isperformed. Boost circuit is widely used in PFC circuit because the advantages likethe inductor is in main power loop and connecting the switch to ground is easy todesign drive circuit. LLC resonant circuit is widely adopted because its softswitching character. AC/DC converter based on interleaving and LLC topology ispresented, bus voltage is only slightly higher than input peak voltage, the softswitching of LLC is not changed, low voltage stress and soft switching of thisstructure raises the efficiency of single stage converter. To raise the load range, asingle stage AC/DC converter based on buck-boost and flyback topology ispresented, due to the adoption of buck-boost structure, bus voltage can be controlledunder450V to reduce the voltage stress of the bulk capacitor, due to the adoption offlyback converter, wider load range can be achieved, but the switch works in thehard-switching state with large switching losses. To solve the large losses issuementioned above, a single stage AC/DC converter is presented based on sepic andflyback, due to the quasi-resonant condition it working in, close to ZVS conditioncan be realized to reduce the switching losses. Three samples are built, tests resultshows the practicality of the topology this paper presented, related design process isgiven.