應用DSP實現為基礎之全數位單相半橋式換流器研製

Abstract

本論文研製一個以數位訊號處理器(DSP)為基礎之全數位控制單相半橋式換流器，發展出具有符合換流器多項控制特色的全數位式電壓輸出控制方法，以解決在一般交流電源輸出供應級操作於非線性負載下之電壓總諧波失真、電壓穩壓率及動態響應不佳等問題。本文選擇普遍應用於中、高功率在線式不斷電系統(UPS)，符合配線法規之共水式半橋式換流器架構，針對換流器控制原理，建立其數學等效模型，並探討電路特性、脈寬調變控制方式、與動態響應特性。控制架構採用多迴路控制方式，包含電流內迴路預測型電流控制器設計、電壓外迴路比例積分控制器及相位領先控制器，以增加電壓回路頻寬，降低輸出電壓諧波失真大小，達到高頻寬快速響應之系統要求。並且加入直流鏈電壓順向前授補償及輸出電壓平衡控制迴路加以改善及有效降低輸出電壓直流量。本文提出之控制方法，具有簡單易於實現的優點，在穩態響應、非線性非平衡負載控制及暫態響應上，皆有顯著的改善。本文採用PSIM軟體進行半橋式換流器之數位式多迴路控制模擬，採用單晶片DSP(TMS320LF2407A)實現所提出之控制法則，並以一個2kVA的功率級完成系統整合之測試驗證。實驗結果顯示所提出控制方法之效果及優越性，在全載輸出時，輸出電壓總諧波失真可降低至2.4%；由無載切換至滿載時，輸出電壓直流量可降低至0.4V，暫態時間為1.2ms。

This thesis presents the research of a DSP-based fully digital-controlled single-phase half-bridge inverter operating in nonlinear loads. The common-neutral half-bridge inverter has an advantage of sharing a common neutral with input utility and is generally adopted in middle-high power range uninterruptible power supply (UPS). The operational principle and control schemes of the half-bridge inverters are described, designed and reviewed. This thesis proposes a multi-loop control scheme for the fast response control of the half-bridge inverter. The proposed controller consists of an inner predictive current-loop controller, an outer PI voltage-loop controller, and output phase-lead compensation control. By using the voltage phase-lead compensation, the output voltage gets larger frequency bandwidth due to the proposed control method has been realized. The output voltage distortion and harmonic components are also significantly reduced. The proposed control algorithm, which is simple and fast, provides a significant improvement in system dynamic responses of imbalance or nonlinear load compared to conventional analog control techniques. The proposed control scheme has been verified by using computer simulation with PSIM and implemented using a single-chip DSP (TMS320LF2407A) controller. Experimental verification has been carried out on a 2 kVA half-bridge inverter. Experimental results show a voltage THD of 2.4% at rated output nonlinear load condition. The dc component of output voltage is lower than 0.4V. Both of simulation and experimental results show the feasibility and superiority of the proposed digital inverter control scheme.