1.5 kW伺服器前級電源功率因數修正之系統性能析與改善

Abstract

本文主要探討用於伺服器電源前級AC-DC電源，採平均電流控制模式、具功率因數修正、輸出電壓調節之連續導通模式升壓式功率因數修正轉換器之控制迴路分析與性能改善。文中將針對採用連續導通模式控制之升壓式功率因數修正轉換器說明平均電流控制模式的原理及電路控制架構、電路設計與控制信號回授方式，再針對其電流迴路、電壓迴路及輸出阻抗進行小訊號模型及頻率響應推導與分析，藉以探討在不同工作點下電壓迴路之相對穩定性。最後就前述分析，針對控制系統中的電壓迴路補償器進行設計並加入一個陷波濾波器以提升系統電壓迴路之頻寬以及暫態響應，降低120 Hz之輸出電壓漣波之影響，使系統功率因數得以至少提升5%。本文採用PSIM模擬軟體針對時域上之穩態、暫態之輸出電壓控制、輸入電流之功率因數校正進行模擬，以及頻域上電流迴路、電壓迴路之迴路增益以及系統輸出阻抗進行頻率響應之模擬，並與實驗結果互相比對驗證。

This paper presents the analysis and improvement in power factor correction (PFC) and output voltage regulation of a boost PFC converter by using average current mode control scheme in applications to an 1.5 kW server power supply. Average current control scheme is adopted for the current regulation of the boost PFC converter due to its high efficiency and robust control characteristics for large load variations in high power applications. The selection of PFC controller IC with its auxiliary circuit realization has been described. The small-signal model of the PFC converter has been derived for the control loop design of both inner current loop and outer voltage loop to achieve a compromise between line current distortion and output voltage regulation. In order to achieve fast dynamic response for output voltage regulation, a notch filter is designed to minimize double line frequency distortion within the voltage control loop. The effect of Q factor and phase distortion of the notch filter can be revealed by the simulated loop gain. With a proper design of the notch filter and the voltage loop compensator, significant improvement of the dynamic response under step load change has been verified by using computer simulation oriented design with PSIM, a circuit simulator for power electronic circuits. Extensive computer simulations of static behavior and dynamic responses of the PFC converter have been carried out to illustrate both the design procedure and designed results. Experimental verification has been carried out on a constructed 1.5 kW PFC converter for servo power supply applications. Experimental results are consistent with the simulation results and verify the performance improvement by using the proposed frequency domain design methodology.