本論文提出以正弦脈衝寬度調變(SPWM)方式為基礎的分切合整數位控制
(D-Σ control)，來實現三相三線雙向換流器模組並聯。分切合整數位控制係透過抵消系統參數如直流鏈電壓、切換週期及電感變化對受控體的影響，來設計控制器並得到開關責任比率控制法則。藉由使用此控制法則，每部換流器模組可獨自追蹤自己的參考電流命令，又能同時抑制系統環流。此換流器系統考慮電感值變化和市電諧波失真，並經由分切合整控制來達到市電併聯及整流兼功因修正的功能，可降低電感鐵芯體積。本論文詳細推導分切合整數位控制法則並且使用通式表示，使其能容易地在軟體上實現。在設計與實現上，本論文將電感值隨電感電流的變化存在微控制器中，以利微控制器每週期調變迴路增益。此外，本論文利用主僕式控制的方式，主換流器執行直流鏈穩壓，副換流器追蹤根據直流鏈電流及模組數量計算出的電流命令，來達到均流的效果。
本研究的主要貢獻包含以下幾點：第一點為採用分切合整數位控制法，可考慮電感值變化且無需傳統 abc 至 dq 軸轉換處理。第二點為提出環流控制方式，無需如傳統採用空間向量調變的方式下加入零序電流補償。第三點為副換流器直接利用直流鏈電流及模組數量，計算出電流命令來達到均流，因此無需額外的中
控介面來調節穩壓及均流。最後，本研究實作一組三部三相三線雙向換流器模組並聯系統，並經由實測結果驗證本論文所提出的控制法則，可達到均流及降低環流。

This paper presents an SPWM-based division-summation (D-Σ) digital control for paralleled three-phase grid-connected inverters. This study first derives the plant, and then design the controller to cancel the variation effects of dc voltage, switching period and inductance. With the D-Σ digital control, each inverter can track sinusoidal reference current of each phase independently, eliminating circulation currents. The inverter system can achieve the functions of grid connection and rectification with power factor correction by taking into account wide filter-inductance variation and grid-voltage distortion, reducing core size significantly. The control laws for achieving the desired functions are derived in detail and they are expressed in general forms for readily software programming. In the design and implementation, the inductances corresponding to various inductor currents were measured at the start-up and stored in the controller for scheduling loop gain cycle by cycle. Additionally, this study adopts master-slave control, the master inverter is responsible for DC-bus voltage regulation, while the slave ones track the current command calculated by the DC-bus current and the number of modules to achieve equal current distribution.
The major contributions of this research can be summarized as follows. First, the control law derived based on D-Σ digital control principle can take care of inductance and grid voltage variations. Secondly, the proposed control strategies can suppress circulating current without using zero-sequence current injection. Thirdly, slave inverters use the DC-bus current and the number of modules to calculate the current command for achieving voltage regulation and equal current distribution. Finally, these paralleled three-phase bi-directional inverters have been implemented and tested. Simulated and experimental results have shown that equal current distribution and suppression of circulating current can be achieved with the proposed control scheme.

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