- 學位論文
最小化分離式電容電壓漣波之主動式功率調節策略
Active Power Conditioning Strategy for Split-Capacitor Voltage Ripple Minimization
摘要
本論文提出應用於三相四線式併網換流器之最小化分離式電容電壓漣波主動式功率調節策略，藉由調節各相實功分配減少流入分離式電容之中性線電流，達成電容電壓漣波最小化之目的。當電網電壓發生驟降時，為了提升電網的穩定度與可靠度，三相換流器可透過輸出虛功來協助調節電網電壓，並且可持續提供實功傳輸。然而，雖然可維持三相換流器之操作，但由於不平衡情況下，容易產生中性線電流，導致分離式電容之電壓漣波，大量的中性線電流漣波會降低電解電容壽命，且產生過大的電容電壓漣波導致三相換流器輸出電流失真。嚴重則使電容電壓最大值超過電容耐壓而損害電容，降低整體電路的可靠度。因此需較大容量之分離式電容以降低電容電壓漣波，但同時也增加電路成本及體積。 為了解決上述之情況，本論文提出最小化分離式電容電壓漣波主動式功率調節策略，亦包含詳細的功率分配流程。當電網電壓驟降時，以虛功補償為首要考量之條件下，藉由適當比例的實功分配，減少中性線電流，降低分離式電容電壓漣波。故可延長電容壽命，且能以較小容量之分離式電容完成電路操作。本論文將詳細說明最小化分離式電容電壓漣波主動式功率調節策略之操作原理與數學公式推導，並藉由電腦模擬驗證此控制策略之可行性。最後以一組三相6kVA原型機之實驗結果來驗證此控制策略的表現。
並列摘要
The active power conditioning strategy for split-capacitor voltage ripple minimization of three-phase four-wire grid-tied inverter is proposed in this thesis. The purpose of the proposed strategy is to solve the problem of split-capacitor voltage ripple caused by neutral line current under unbalanced grid voltage. When a grid voltage sag occurs, the three-phase inverter can help to regulate the grid voltage via injecting the reactive power in order to improve the stability and reliability of the ac grid. At the meantime, the active power transmission is also allowed. However, due to the unbalanced power flow, the neutral line current will be produced resulting in split-capacitor voltage ripple. The large neutral line current ripple flowing through the capacitor reduces the life-time of capacitor. Also, the large capacitor voltage ripple may distort the output current of the inverter, or exceed the maximum operating voltage and damage the capacitor. Eventually, large capacitors are required to reduce the capacitor voltage ripple, but the cost and size of the converter will be increased. In order to minimize the split-capacitor voltage ripple, the active power conditioning strategy for the power flow distribution process is proposed in this thesis. When the grid voltage sag occurs, the reactive power will be compensated first. Then the split-capacitor voltage ripple can be reduced by decreasing the neutral line current with proper distribution ratio of active power. Thus, the capacitance of capacitor can be reduced and the life-time of capacitor can be increased. Details of operation principle and the mathematical derivations are presented in this thesis. Both the computer simulations and experimental results of a 6kVA prototype circuit are presented to validate the performance of the proposed strategy.