444 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 22, NO. 2, MARCH 2007 Dynamical Characterization of Peak-Current- Mode-Controlled Buck Converter With Output-Current Feedforward Matti Karppanen, Mikko Hankaniemi, Student Member, IEEE, Teuvo Suntio, Member, IEEE, and Mika Sippola Abstract—The paper investigates the effect of unity-gain output- current-feedforward in a peak-current-mode-controlled (PCMC) buck converter. A consistent theoretical basis is provided showing that the unity-gain feedforward can improve significantly the load invariance and transient performance of a PCMC buck converter. The nonidealities associated to the scheme would, however, deteri- orate the obtainable level of invariance. The nonidealities can be maintained at acceptable level, and therefore, the scheme would provide a viable method to reduce significantly the load interac- tions as well as improve the load-transient response. The theoret- ical predictions are supported with comprehensive experimental evidence both at frequency and time domain as well as compar- isons between three different buck converters. Index Terms—Buck converter, load–current feedforward, output impedance, peak-current-mode control (PCMC). I. INTRODUCTION I NTERCONNECTED regulated power supply sys- tems—known also as distributed power supply (DPS) systems (Fig. 1)—are extensively used to supply different electronic loads [1], [2]. The nonlinear nature of the associated regulated converters would make the interconnected systems prone to stability and performance problems [3]. Basically it is a question of the interactions caused by the different imped- ances [i.e., the output impedance of the source system ( , Fig. 1) and the input impedance of the load system ( , Fig. 1)] associated to the specified interface within the system [4], [5], [14]. A natural desire would be to get rid of those interactions. It is well known that the load impedance (i.e., , Fig. 1) may affect adversely the voltage-loop gain of the converter (i.e., the supply converter in Fig. 1) [4]–[6], [14]. It is claimed explicitly in [4], and implicitly in [5] and [6] that the load invariance may be achieved by designing the voltage-loop controller in such a way that makes the closed-loop internal output impedance small. According to sound scientific theory, the load interac- tions are reflected into the converter dynamics via the open-loop internal output impedance [14], [15]. Therefore, it may be ob- vious that the perfect load invariance at arbitrary load may be Manuscript received November 3, 2005; revised June 10, 2006. Recom- mended for publication by Associate Editor F. L. Luo. M. Karppanen, M. Hankaniemi, and T. Suntio are with the Department of Electrical Engineering, Institute of Power Electronics, Tampere University of Technology, Tampere FI-33101, Finland (e-mail: teuvo.suntio@tut.fi). M. Sippola is with Efore Oyj, Espoo FIN-02211, Finland. Digital Object Identifier 10.1109/TPEL.2006.889921 Fig. 1. Interconnected regulated system. achieved only, if the open-loop internal output impedance is de- signed to be zero [9], [13]. It was demonstrated in [15] that even the zero open-loop output impedance does not necessarily en- sure load invariance, because the load may interact the converter dynamics via the internal input impedance at the presence of the source impedance. The use of output-current feedforward has been demon- strated to improve the output-voltage transient performance for the load-current changes in a hysteretic current-mode-con- trolled (HCMC) buck converter in [7]. According to the applied theory, the zero output impedance would be achieved by using unity-feedforward gain. The peak-current-mode-con- trolled (PCMC) buck converter is treated in [8]. The effect of output-current feedforward on the output impedance of the converter is comprehensively analyzed. Close to unity-feedfor- ward gain is stated to give the minimum output impedance. The general conditions for achieving zero output impedance have been derived in [9]. It was stated that the zero output impedance can be implemented in any converter regardless of topology but the validations were only carried out by using a buck converter. A voltage-mode-controlled (VMC) buck converter has been treated in [10] but the theoretical basis for the design approach is not explicitly defined and therefore, the validation of the method is difficult. The experimental load transients shown in [12] imply that the zero output impedance may not be achievable in a boost converter by applying output-current feedforward, i.e., a better transient behavior may be achieved by optimizing the voltage-loop-controller design. A theoretically consistent treatment of the effect of output- current feedforward in a regulated converter is presented in [13]. 0885-8993/$25.00 © 2007 IEEE