直流-直流降壓電源轉換器之控制迴路補償技術頻率響應分析

Abstract

本文內容包含控制理論、數學模型以及可實現的電路來實現高效能的直流-直流降壓電源轉換器的補償控制電路。目前直流-直流降壓電源轉換器的控制模式可分為電壓模式以及電流模式控制，主要的差異在於受到主電路裡的電感效應影響的程度大小不同導致補償電路的設計也有所不同。然而如何設計補償電路以期望得到最佳的暫態響應以及系統的穩定度是本文主要研究的項目。 以電壓模式控制的直流-直流降壓電源轉換器而言，主電路裡外接的大電感電容會產生雙極點效應導致整體電路的相位容忍度不足而發生震盪同時也造成了窄頻寬；另外其電容也會產生一個ESR 零點，因此需要形式三或稱為比例積分微分控制器來做為補償。 以電流模式控制的直流-直流降壓電源轉換器而言，由於電感產生的極點被移至高頻段因此在其切換頻率之內不受雙極點影響。其主要由輸出端的電容產生一個極點以及一個ESR 零點所影響，因此需要形式二或稱為比例積分控制器來做為補償。相對於電壓模式控制而言電流模式控制的補償電路複雜度相對簡單，所以也發展出整合型式的補償技術如電壓模式的米勒補償及電流模式的米勒補償，在本文裡也有進一步電容放大技巧的分析。

This thesis contains control theory, mathematical models and the circuit of implementation to achieve high efficiency control loop compensation for DC-DC buck converter. Currently, there are two models for application of DC-DC buck converter that one is voltage control mode and the other one is current control mode. The affection of the inductive effect from the power stage of DC-DC buck converter is different for voltage mode and current mode. Therefore, the design of compensation circuit of control loop got change for them. However, how to design compensation circuit to get desired optimal transient response and stability of the system is a major research project of the thesis. In voltage mode control of DC-DC buck converter, the inductance and capacitance of power stage are supplied from external and they produce double pole to induce inadequate phase margin and then got ring. In the mean time, it also makes narrow bandwidth. In addition, the output capacitance also produces an ESR zero. Consequently, requiring Type III or called PID controller to perform compensation. In current mode control of DC-DC buck converter, as the LC double pole got moved to high frequency so the system could not get influence in the switching frequency. The system only got affection by an output pole which from output capacitance and an ESR zero. Consequently, requiring Type II or called PI controller to perform compensation. The complexity of compensation circuit for current mode control is much simple than voltage mode control. Therefore, On-Chip compensation has been developed, such as current mode Miller (CMM) and time Miller (TMM). The analysis of capacitor magnification techniques also involved.