- 學位論文
獨立型太陽能LED照明技術研究
The research of stand-alone solar-powered LED lighting system
摘要
本研究旨在設計一獨立型太陽能LED照明控制系統，於充電時，利用一金氧半場效電晶體，代替傳統之最大功率點追蹤控制器，配合近最大功率點操作與迴授控制方式，保護電池不過充電，增加電池蓄電力；於放電時，利用一金氧半場效電晶體，代替傳統之直流變壓器，配合迴授控制技術，利用PWM電流，直接由電池出來驅動LED燈具，增加系統續航能力。 本研究於充電方面，測試利用PWM迴授控制技術，除可在電池到達飽充電壓點時，降低充電之平均電流，保護電池不過充電，尚能持續充電，能相較於傳統之開/關式充電方法，增加約18%之蓄電量，大大增加系統續航能力。於放電方面，利用PWM電流，直接由電池輸出電壓驅動LED燈具，並利用迴授控制方式，穩定控制LED燈具之輸入平均電流或平均功率，並證實當利用直驅式PWM定電流驅動技術時，其在最壞情況下之電流偏差量為相對於額定電流之3%，而直驅式PWM定功率驅動技術，其在最壞情況下之功率偏差量為相對於額定功率之2.8%，可有效保護LED燈具不因蓄電池之端電壓浮動而輸入過大之驅動電流或功率，造成LED燈具燒燬。 雖PWM電流可直接驅動LED燈具，但當利用PWM電流驅動LED燈具時，會造成瞬間之大電流產生，可能造成LED驅動時其照明效率之降低；產生PWM電流之切換損失；瞬間大電流是否會造成LED燈具之可靠度下降等問題。 在照明效率損失方面，本研究發現利用PWM電流來直接利用電池輸出電壓驅動LED燈具時，其有平均13.9%之照明效率損失，然而獨立型太陽能LED照明系統之主要考量為系統續航力而非照度大小，若考慮驅動時間，利用PWM電流來直接由電池輸出驅動LED燈具時，其驅動時間超過35.7 Hr，能較利用直流變壓器之驅動時間(30.4 Hr)高出許多，顯示LED燈具利用PWM電流驅動時，其應用於獨立型太陽能系統之優勢；PWM電流之切換損失部分，利用125Hz之PWM驅動頻率下，證實其PWM切換之能量損失低於1%；利用PWM直驅式之LED燈具可靠度於15,000 Hr之可靠度試驗中證實，LED利用125Hz之PWM頻率與輸入瞬間為3倍額定電流之PWM電流驅動下，其PWM驅動方式並不會造成LED壽命之影響。 本研究除去傳統獨立型太陽能充、放電控制系統中的最大功率點追蹤器，亦除去傳統太陽能LED照明系統中，驅動LED燈具所需的直流變壓器，而皆僅簡化利用一金氧半場效電晶體替代，使得本研究所發展之獨立型太陽能LED照明控制器，可大大節省系統成本與增加系統可靠度，更能增加系統之續航能力。
並列摘要
A stand-alone solar LED lighting system usually consists of a DC/DC converter to convert the floating battery voltage into a constant current to drive the LED. A 15% energy loss of the DC/DC converter will then be introduced. The DC/DC converter may also increase system costs and reduce system reliability due to the additional components. The present study first develops an intelligent feedback solar battery charge controller, which can store 18% more energy in the battery. In addition, a direct feedback PWM driving controller (to drive the LED luminaire directly from the battery output using the PWM constant average current, or the PWM constant average power) were developed. The test results show the performance of the controller, which has a 3% deviation for the direct PWM constant current driven technique. The direct PWM constant power driven technique has a 2.8% deviation when the battery voltage is changed from 25.8V to 23V. Therefore, the direct PWM constant current/power driven techniques that avoid overdrive the LED luminaire when battery voltage is changed. However, the instantaneous current stress may cause several problems when using the direct PWM driven techniques. The first of these is the decrease in overall light efficiency of an LED luminaire when it is driven by a PWM current. The results show that the overall lighting efficiency loss is about 13.9% for the junction temperature at 70oC when using a 24V battery system. Although the lighting efficiency will be reduced by the PWM current, the direct PWM driven technique can extend the lighting period to 35.7 hours for the direct PWM constant current driven technique, and 36.44 hours for the direct PWM constant power driven technique. These time values are much longer than the constant current driven technique (30.4 hours), which usually uses a DC/DC converter to drive the LED luminaire. The second concern is the switching loss when driven the LED luminaire. The test shows the switching loss is less than 1% when the PWM frequency is equal to 125Hz. The third problem considers that the instantaneous current stress may decrease the reliability of the LED luminaire. A reliability test has undergone more than 15,000 hours of examination, and indicates that the PWM driving technique will not damage the LED when the PWM frequency is equal to 125Hz and the peak current is equal to three times the rated current. This study shows that the feedback PWM charge system can remove the MPPT controller by a MOSFET and realize the same performance by adopting the nMPPO. The direct PWM driving technique is feasible and capable of driving an LED directly from the battery output in the stand-alone solar system by a MOSFET instead of a DC/DC converter. These features further increase the system’s reliability and reduce the cost when removing the MPPT controller and the DC/DC converter in the system.