以單晶片DSP為基礎應用返覆控制理論於低諧波失真可程式交流電源供應系統之研製

Abstract

一般交流電源穩壓系統或UPS系統在接上非線性負載時,其輸出波形通常會 產生週期性的諧波失真.本文探討應用返覆控制理論以消除此週期性干擾, 並以數位信號處理器實現所設計的控制器,完成一個具有低諧波失真的可 程式交流電源穩壓系統.文中建立脈寬調變換流系統之數學模型,根據其頻 率響應分析輸出波形失真之原因,並提出一種控制架構以改善系統的暫態 與穩態響應.首先建立一脈寬調變換流器之動態模型並以狀態變數回授法( state feedback method)設計一基本控制器負責系統暫態響應,據此再設 計一返覆控制器以改進整個閉迴路之穩態響應,並根據Nyquist criterion 提出系統穩定之充分條件,同時分析在此系統下,穩態誤差的收斂與否.在 符合所提出穩定之充分條件的情況下,可以估計系統針對週期性及非週期 性干擾之反應.由所提出之系統架構及穩定條件,證明穩態及暫態控制器可 以各別獨立設計,而無需滿足某一前提.為證明此理論之可行性,吾人設計 一以數位信號處理器TMS320C14為基礎之數位控制系統,藉數位信號處理器 優異之計算能力,結合一切換在45 kHz,取樣頻率15 kHz,以MOSFET為切換 元件之脈寬調變換流器,發揮控制系統的優點.由模擬及實驗的結果可知, 當交流電源穩壓系統接電流峰均比(crest factor)為3之整流性負載,總諧 波失真低於1.4%,而在相同的負載下,未加返覆控制器時.其總諧波失真 為5%.此外,在遭遇瞬間300 VA負載變化,系統也能在0.6 ms 時間內將波形 變化衰減至10%.而模擬結果與實驗結果的吻合,更說明理論與分析之正確 性.所研究之返覆控制理論除了可應用在交流電源供應系統之外,尚可運用 在具有返覆特性之工業產品,如磁碟機伺服馬達控制系統,機械手臂控制系 統,以及噪音防治系統.希望此論文的內容,能對此有所貢獻. The purpose of this theis is to analyze and implement an ac power source system based on digital signal processors (DSP) usingthe repetitive control algorithm. (1) To established a mathematic model of a PWM controlled inverter system.Authors have investigated the reason why the output waveform of an ac power sourcemay be distorted due to connected nonlinear loads. Much previous research was explored from the standpoint of instant-command tracking and steady- state regulation. A PWM inverter was model by its dynamic equations and the optimal state feedback method was investigated to govern the transient response of the ac source systems. (2) To propose a control strategy and an algorithm for ac voltage regulation of a PWM inverter. According to the built control system, a repetitive control strategy was proposed to improve the steady-state reponse under the assumption of periodic disturbances. Authos discussed a sufficient condition of the stability of the repetitive control system and the convergence of the error induced by periodic disturbances from the Nyquist criterion in discrete-time domain. Under this sufficient condition, the response to harmonic inputs and to non-harmonic inputs could be predicted. (3) To design a TMS320C14 DSP-basd control board. The TMS320C14 control board included an eight-channel A/D converter and memory devices. In this control board, PWM switching signals and feedback signals can communicate between the digital controller and the power stage. The read-write memory device was needed for the implement of the time-delay function in the repetitive control system. A numverical realization of the repetitive control algorithm applied on the control of a PWM inverter has been presented. According to the characteristics of the well-design servo control system, all of the blocks in the repetitive control system can be determined from the sufficient condition.