Analysis and Design of Current Balancing Control in Voltage-Mode Multiphase Interleaved Voltage Regulators

近幾年來，提供中央處理器(CPUs)電源的穩壓器(voltage regulators)廣泛利用多相交錯式電壓控制模式(voltage-mode multi-phase interleaved)的架構。中央處理器的運作就像是一個高頻的動態負載，這個動態負載由幾千赫茲到幾百萬赫茲的步階變化所組成。因為交錯式操作以及高頻動態負載的交互作用，使的穩壓器會產生嚴重的差頻(切換頻率及負載頻率之差)相電流震盪(beat-frequency phase current oscillation)。不管是否有差頻相電流震盪的現象，傳統在多相架構的設計上通常都會使用均流控制迴路來抑制超過的相電流不均量。本篇論文的焦點是在研究均流控制迴路在二相交錯式電壓控制模式穩壓器對差頻震盪的影響。 本論文從相電流平衡跟差頻震盪兩個觀點來對均流控制迴路模型化。從相電流平衡的觀點得到的模型，是利用傳統的狀態變數平均模型法。再利用特別的方式，來定義且提出均流控制迴路增益Tcb。Tcb的資訊對均流控制迴路的設計很有幫助。而從差頻震盪的觀點得到的模型，則是結合狀態變數平均模型法和多頻模型法。由此模型，可以得到一個迴路增益Tbeat ，來描述均流控制對差頻震盪的壓抑量。從中可以發現雖然Tcb 和 Tbeat物理意義不同，但是擁有相同的數學表示式。換句話說，一旦均流控制補償設計完成，就同時決定了相電流平衡特性及壓抑差頻震盪的特性。所以當我們在設計均流控制補償時，必須同時考量此兩個觀點。模擬以及實驗結果也驗證了模型的準確性。 本論文展示出的模型對均流迴路補償設計有很大的幫助。本論文也指出未來研究的方向。In recent years, the voltage-mode multi-phase interleaved buck converter configuration has been used extensively in the voltage regulators for powering computer central processors (CPUs). The CPUs are often operated like a dynamic load with step load frequencies ranging from kilohertz to megahertz. The combination of converter interleaving operation and the dynamic load may cause serious problems with beat-frequency (the difference of switching frequency and load frequency) phase current oscillation. In a multi-phase configuration, a current-balancing control loop is usually employed to reduce excessive phase current imbalance regardless of a beat-frequency oscillations problem. The focus of the thesis is to investigate the effects of the current-balancing control on the beat-frequency oscillation in a voltage-mode two-phase interleaved buck converter. In the thesis, the current-balancing control is modeled from the points of view of phase-current balancing and beat-frequency oscillations. The model for the current balancing aspect was obtained by the conventional average modeling method. From the model, a definition of the control loop gain Tcb was proposed and derived using a rather unconventional approach. Tcb information is useful for designing the current-balancing loop. The model for the beat-frequency oscillations aspect was obtained by using the combination of average model and multi-frequency model. A loop gain expression Tbeat was obtained, which is useful to predict the performance of beat-frequency oscillation. It turns out that the two loop gains, although different in physical meaning, share the same expression form. In other words, once the current-balancing loop compensation is designed, the suppression characteristic on the beat frequency oscillation is also fixed. Therefore, the compensation design of the current-balancing loop must take both aspects into considerations. Simulations and experimental results were given to verify the models. The model presented in this thesis is useful for the designers to compensate the current-balancing loop. Future research directions were also pointed out in the thesis