Current-Mode Pulse-Train Control Techniques for Buck Converter: Inductor-Current PT and Capacitor-Current PT Gasore Ignace 1 School of Electrical Engineering, Southwest Jiaotong University, Chengdu 6117 56, PR.China Email: gasoreignace@gmail.com Professor Jin Sha 2* School of Electrical Engineering, Southwest Jiaotong University, Chengdu 6117 56, PR.China Email:j.sha@swjtu.edu.cn Abstract—Pulse train (PT) control technique is a discrete control technique for switching DC-DC converters, which benefits from fast transient response. However, as output voltage ripple based control technique, when PT controlled switching DC-DC converter operates in continuous conduction mode (CCM), low frequency oscillation exists which seriously affects its steady state and transient performances. Capacitor-current pulse-train (CC-PT) control technique can eliminate the low frequency oscillation. In this paper, the CC-PT control is studied by comparing with conventional inductor-current pulse-train (IC-PT) control. And the control parameter design of the CC-PT controller is given. Experimental results are presented to verify the analysis results. Keywords—Capacitor current control, pulse train control, switching DC-DC converter I. INTRODUCTION To improve transient response of switching DC-DC converters, pulse train (PT) control technique has been proposed and studied recently [1-5]. Different from conventional PWM based control techniques, which realize the control of switching DC-DC converters by adjusting the duty ratio of control pulse cycle by cycle, PT control technique utilizes two preset control pulses, high power control pulse PH and low power control pulse PL, to realize the regulation of switching DC-DC converters. Without error amplifier and its corresponding compensation network, PT controller is simple to design and benefits from ultra-fast transient response. For PT controlled switching DC-DC converters, when output voltage is lower than desired output voltage, a high power control pulse PH is applied as active control pulse to increase output voltage. Similarly, when output voltage is higher than desired output voltage, a low power control pulse PL is applied as active control pulse to decrease output voltage. There are two conventional ways to generate control pulses PH and PL [4]: voltage-mode PT (VM-PT) control and inductor-current PT (IC-PT) control. In VM-PT control, the duty ratios of PH and PL are preset, while in IC-PT control, inductor peak currents are preset to generate PH and PL. PT control technique is a power based control technique in nature, which makes it suitable for the control of switching DC-DC converter operating in discontinuous conduction mode (DCM) [6-8]. While for PT controlled switching DC-DC converter operating in continuous conduction mode (CCM), a unique low-frequency oscillation phenomenon exists as inductor current at the beginning and at the end of each switching cycle is not the same, i.e. inductor may store or release energy in one switching cycle[7, 9, 10]. When PH is applied as active control pulse, if average inductor current in one switching cycle is less than load current, output voltage will decrease rather than increase. Similarly, when PL is applied as active control pulse, if average inductor current in one switching cycle is more than load current, output voltage will increase rather than decrease. Thus, different from PT controlled switching DC-DC converter operating in DCM, the increase or decrease of output voltage of PT controlled CCM switching DC-DC converter in one switching cycle not only depends on control pulse, but also on inductor current. Thus, the unique low-frequency oscillation phenomenon which appears in PT controlled CCM switching converter, seriously affects its steady state and transient performances. Previous studies show that unique low frequency oscillation of output voltage exists when equivalent series resistance (ESR) of output capacitor is small [7]. To eliminate this unique low frequency oscillation, large ESR is required. However, large ESR will increase output voltage ripple. Capacitor-current PT (CC-PT) control technique is proposed in [9], and experimental results verify that low frequency oscillation which exists in conventional PT controlled CCM buck converter no longer exists in CC-PT controlled CCM buck converter, and CC-PT controlled CCM buck converter benefits from a much faster transient respond than conventional PT controlled CCM buck converter. The principles of low frequency oscillation elimination and the steady-state performance were not studied in [9]. In this paper, comparison study of conventional IC-PT control technique and CC-PT control technique is performed. A brief overview of IC-PT and CC-PT control techniques are presented in Section II. The steady-state performances of IC- PT and CC-PT controlled buck converters operating in DCM and CCM are given in Section III and Section IV, respectively. Upon which, the control parameters design of CC-PT controlled buck converter is deduced in Section V. A n d t h e