靜態同步補償器之分相式主動功率調節策略

Abstract

本論文提出應用於三相四線式電力級架構之靜態同步補償器的分相式主動功率調節策略，其能針對電壓故障及負載需求進行適當之實虛功補償。傳統上，靜態同步補償器的直流端為電容器，當微電網發生故障時，可以透過輸出正負虛功來幫助微電網調節電壓，提高微電網的穩定性及可靠度。而本論文所提出之主動功率調節策略，則是在靜態同步補償器原有之虛功補償功能為優先的情況下，額外增加了實功傳輸功能，以調節微電網之不平衡負載。並且考量到當微電網故障時，靜態同步補償器會面臨同時需要傳輸虛功及實功的情況，所以本論文所提出之分相式主動功率調節策略亦包含一個詳細的功率分配流程。在以補償虛功為優先的條件之下，能經由適當的比例分配實功，而盡量達到等電流操作，以確保各相的元件所承受之電流應力相同，以延長整體電路的壽命。由於本論文之主動功率調節策略會使得靜態同步補償器各相輸出之實、虛功不同，因此需要針對各相進行獨立控制。本論文中，首先利用三相四線式換流器之等效單相電路，推導出功率開關的控制訊號。然後，各相功率便能依照該相的控制訊號進行輸出，進而達到分相控制之目的。接著，由電腦模擬驗證本論文提出的分相式主動功率調節策略之可行性。最後則是實際研製一組6kVA的靜態同步補償器原型機進行實作驗證。

In this thesis, a per-phase active power conditioning (PPAPC) strategy for the three-phase four-wire static synchronous compensators (STATCOM) is proposed. The purpose of the PPAPC is to compensate the active power and the reactive power according to the load requirements and the voltage drop of each phase. Conventionally, the DC side of the conventional STATCOM is a large capacitor bank. The STATCOM can help to regulate the voltage, increase the stability and reliability of the microgrids by injecting or absorbing the reactive power when the faults occur. In addition to the original function of reactive power compensation, the proposed PPAPC strategy has an additional active power transferring function to balance the unbalanced loads of the microgrids. Since the STATCOM needs to transfer the active and reactive power simultaneously when the microgrids fault occurs, power flow distribution criteria is also developed in the proposed PPAPC strategy. For the proposed PPAPC stragegy, each phase of the STATCOM will compensate the reactive power first, then transfer the active power based on a distribution ratio. For the case that two phases absorb the active power and one phase provides the active power, an appropriate distribution ratio of active power will be calculated. It can equalize the each phase’s current stress, so the life time of the power switches will not be affected. According to the equivalent circuit of the three-phase four-wire inverter, the sinusoidal control signal of each phase can be derived. Consequently, the output power of each phase can be independently controlled by the corresponding sinusoidal control signal. Both the computer simulations and the hardware experimental results of a 6kVA prototype circuit are presented to verify the performance of the STATCOM with the proposed PPAPC strategy.