1788 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 27, NO. 4, APRIL 2012 General Active Global Stabilization of Multiloads DC-Power Networks Pierre Magne, Student Member, IEEE, Babak Nahid-Mobarakeh, Member, IEEE, and Serge Pierfederici Abstract—Implantation of complex dc-power network is one of the main research topics in more electric aircraft (MEA). In such applications, small and light systems are required and so optimiza- tion of passive elements, such as dc-bus capacitance and filtering inductance, is an important issue. It is known that the reduction of dc-bus capacitance may lead to instability of an MVdc network. So, if no stabilizer is used, the risk of instability must be considered, while designing the system passive elements. In this paper, we will first study the small signal stability of an MVdc network composed of three loads: an inverter supplying a permanent magnet syn- chronous motor, a dc/dc converter feeding a resistive load, and a supercapacitor controlled by a bidirectional dc/dc converter. Then, we will propose a large-signal-stabilizing system to ensure global stability by generating proper stabilizing power references for the whole system. The contribution of the loads to network stability is adjustable. The validity of the proposed method will be confirmed by experimentations. Index Terms—AC drives, active stabilization, constant power load (CPL), dc-power network, energy storage device (ESD), fault- tolerant control, Lyapunov methods, more electric aircraft (MEA), MVdc networks, nonlinear systems, power electronics systems, power system stability, stability, supercapacitor (SC). I. INTRODUCTION A S The aircraft industry works on its next generation of engines, an important research and development topic is plane electrification. Significant progress in electrical system reliability, fault detection, and control in degraded mode have helped make “more electric aircraft” (MEA) more of a real- ity [1]–[4]. To optimize on-board energy management, the use of local dc-power networks with reversible loads and energy storage devices (ESDs) is a potential solution. The voltage range of these dc-power networks is situated between 200 and 600 V and such electric structures are often defined as MVdc in the literature. In this context, MVdc networks, including several ac- tuators and ESDs, such as supercapacitors (SC) or batteries, are proposed and studied in the literature [5], [6]. In the aerospace industry, mass optimization is very important and designers are looking for smaller and lighter systems. As passive elements, dc-link capacitors and filter inductances, are Manuscript received December 21, 2010; revised July 19, 2011 and September 2, 2011; accepted September 3, 2011. Date of current version Febru- ary 20, 2012. Recommended for publication by Associate Editor F. Blaabjerg. The authors are with the Groupe de Recherche en Electronique et en Elec- trotechnique de Nancy (GREEN), INPL, University of Lorraine, Nancy 54516, France (e-mail: pierre.magne@ensem.inpl-nancy.fr; babak.nahidmobarakeh@ ensem.inpl-nancy.fr; serge.pierfederici@ensem.inpl-nancy.fr). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPEL.2011.2168426 generally big and heavy, and so their optimization is a main re- search topic related to maximization of weight savings. Unfortu- nately, in the case of two cascaded systems, reducing the bus ca- pacitor value decreases the system damping ratio and enhances instability risk due to the interaction between devices [7]–[11]. To study the instability phenomenon in dc-power networks, loads are often considered as “constant power load” (CPL), i.e., the impact of the dc-link voltage variations on the load power is negligible. This is almost true for tightly controlled converters while the load controllability conditions are satisfied. This approximation permits to consider a load in a restrictive case for stability problem and is applicable for all converters tightly regulated with a high bandwidth and good robustness properties as regard to possible disturbances. This is the case with inverter motor drive systems [8], [10], [12]–[14]. It is also partially true in a faulty mode, where the absorbed power has a significant dc component at high speeds [15]. Stability problems in the case of interaction between a power supply in cascade and a CPL is well known and numerous studies have been published to explain this phenomenon for the inverter motor drive systems [7]–[9]. In the case where the system is lo- cally stable around an operating point, external disturbances like a change in the main voltage or an abrupt load power variation can make it unstable. To analyze this phenomenon, some authors have proposed mathematical methods to obtain an approxima- tion of the domain of attraction of the operating point [16]–[20]. To prevent this instability risk, an appropriate design of passive elements could be done to obtain satisfactory stability margins. In [21], several passive methods were proposed and studied to damp the system and enhance its stability. Unfortunately, this also increases the global mass of the system. To reduce the dc-link capacitor size and ensure a well- stabilized system, several stabilization methods have been pro- posed [10], [13], [14], [22]–[24]. They propose use of a feed- back implementation on the load control improving the stability margins. This permits reduction of the dc-link capacitance. Ex- perimental results prove the efficacy of these solutions but often the stability is studied and proved only for small signal varia- tions around an operating point. In other works [25]–[28], the large signal stability of the system was considered and nonlinear stabilization techniques proposed. In all these cases, stabilizing signals are superposed to the load power references to improve the system stability. This may be considered as a drawback in applications, where we can- not modify the loads dynamics. In [29], it was shown that it is theoretically possible to implement a proper feedback on a controllable voltage source to ensure the small signal stability of a power system composed by two cascaded converters. 0885-8993/$26.00 © 2011 IEEE