DC-Link Voltage Control Strategies for Three-Phase Back-to-Back Active Power Conditioners

本論文主旨為提出適用於三相背對背主動式電力調節器之直流鏈電壓控制策略。當微電網發生異常時，主動式電力調節器可藉由實、虛功率補償與雙向功率傳遞，調節微電網之頻率與電壓。此外，為達成功率潮流平衡，直流鏈電容為主動式電力調節器中不可或缺之元件。然而，為提升微電網之穩定度、電力品質以及降低電力調節器所需之直流鏈電容值，本論文提出四種直流鏈電壓調控策略，分別為: (一) 優化電流調變策略，(二) 適應性直流電壓調變策略，(三) 動態優化電流調變策略與 (四) 可變直流鏈電壓斜率控制。 主動式電力調節器於穩態操作下，所提出之優化電流調變策略可減緩輸入電流之擾動，且於一個市電週期內完成直流鏈電壓調控。然而，當輸出功率發生瞬間或連續之改變時，直流鏈電壓將產生劇烈變動，保護機制亦易被觸發。因此，本論文提出適應性直流電壓調變與動態優化電流調變策略，除可避免直流鏈電壓於功率劇烈變動時觸發保護外，亦可降低直流鏈電容值。另一方面，所提出之可變直流鏈電壓斜率控制，可進一步於功率劇烈變動時，減緩直流鏈電壓擾動幅度。本論文完整分析所提出策略之理論推導。最後以5kVA背靠背主動式電力調節器原型機之實驗結果，驗證所提出策略之性能。The objective of this dissertation is to propose a three-phase back-to-back active power conditioner (APC) with dc-link voltage control strategies for micro-grid applications. The demanded active and reactive power of the APC via bi-directional power flow control can help to regulate the frequency and voltage of the micro-grid to achieve high stability. On the other hand, the dc-link capacitor is an essential component of the back-to-back APC for power flow balancing. In order to provide the ability to improve the power quality and stability of the micro-grid as well as to reduce the dc-link capacitance, four dc-link voltage control methods are developed: a) optimal ac line current regulation (OCR) strategy, b) adaptive dc-link voltage regulation (ADVR) strategy, c) dynamic optimal ac line current regulation (DOCR) strategy and d) flexible DC-link voltage slope (FDVS). Under steady state, the proposed OCR strategy is able to minimize the change of the input current variation as well as to achieve the dc-link regulation in one 60Hz cycle. When an abrupt or continuous power change occurs, the dc-link voltage of the APC will be changed dramatically and the voltage protection could easily be triggered. Therefore, the novel ADVR and DOCR strategy are proposed in order to prevent the false alarm as well as to reduce the required dc-link capacitance. On the other hand, the proposed FDVS can further mitigate the DC-link voltage variation during the large power variation transient. Mathematical equations for proposed control strategies are derived thoroughly. Furthermore, procedures to determine the DC-link capacitance with the proposed strategies are developed. Finally, experimental results obtained from a 5 kVA back-to-back APC verify the feasibility and the performance of the proposed line current regulation strategies