具磁滯電流控制之三相換流器研製

Abstract

本論文旨在研製一組具磁滯電流控制之三相四線式換流器以應用於太陽能發電系統。三相四線式換流器輸入端具有兩顆串聯的直流鏈電容，當兩顆電容電壓出現不平衡時，將導致電路操作不穩定。因此本論文根據直流鏈電容電壓與中性線電流之關係，提出控制方法，藉由偵測直流鏈電容電壓之變化產生中性線電流訊號，以調節磁滯電流區間的偏移量，避免電容電壓偏移，達成電容電壓平衡之目的。此外，由於三相四線式換流器具有較多開關，功率開關切換時造成的功率損失，將造成轉換效率降低。因此為了降低功率開關的切換損失，本論文將控制電感電流使其在每個切換週期皆能雙向流動，達成開關零電壓切換，以提升轉換效率。最後，以電腦模擬及硬體電路實驗結果驗證本論文所研製具磁滯電流控制之三相四線式換流器可行性與電路性能。

A three-phase four-wire inverter with hysteresis current control for the photovoltaic (PV) system application is proposed in this thesis. There are usually two series-connected dc-link capacitors in the input side of a three-phase four-wire inverter. Unstable operation may result if the two capacitor voltages are different. In this thesis, a control method is developed according to the relationship between the dc-link capacitor voltage and the neutral wire current. By detecting the dc-link capacitor voltage, the neutral wire reference current signal can be generated to adjust the offset of hysteresis current band, so the capacitor voltage shifting and unstable operation can be avoided. On the other hand, there are many switches in the three-phase four-wire inverter and their switching losses dominate the inverter’s efficiency. In this thesis, the zero voltage switching operation is achieved by producing the bi-directional inductor current so that the switching loss can be reduced. Finally, simulation and hardware implementation results verify the feasibility and performance of the proposed three-phase four-wire inverter with hysteresis current control.