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This paper concentrates on the design, control, and implementation of an LCL-filter-based shunt active power filter (SAPF), which can effectively compensate for harmonic currents produced by nonlinear loads in a three-phase three-wire power system. With an LCL filter added at its output, the proposed SAPF offers superior switching harmonic suppression using much reduced passive filtering elements. Its output currents thus have high slew rate for tracking the targeted reference closely. Smaller inductance of the LCL filter also means smaller harmonic voltage drop across the passive output filter, which in turn minimizes the possibility of overmodulation, particularly for cases where high modulation index is desired. These advantages, together with overall system stability, are guaranteed only through proper consideration of critical design and control issues, like the selection of LCL parameters, interactions between resonance damping and harmonic compensation, bandwidth design of the closed-loop system, and active damping implementation with fewer current sensors. These described design concerns, together with their generalized design procedure, are applied to an analytical example, and eventually verified by both simulation and experimental results. [ABSTRACT FROM PUBLISHER]

The hybrid fuel cell/supercapacitor (FC/SC) system is a promising onboard power supply system for more electric aircraft (MEA), where system stability is a critical issue due to the high penetration of constant power loads (CPLs) in MEA. This article proposes a composite finite-time controller for decentralized power sharing and stabilization of the hybrid FC/SC system with CPLs. It consists of an integral droop (ID) + finite-time controller for the SC converter and a proportional droop (PD) + finite-time controller for the FC converter. First, the coordination of PD and ID achieves decentralized power sharing between FC and SC such that SC only compensates fast fluctuations and FC provides smooth power at the steady state. Then, a finite-time observer is designed to provide feedforward compensation for the disturbances and enables accurate tracking with fast dynamics. Finally, a composite finite-time controller is constructed following a nonrecursive synthesis procedure with a rigorous large signal stability analysis. The proposed controller guarantees finite-time convergence even under large signal variations and can be easily implemented with a practical gain tuning procedure. Simulations and experiments are conducted to verify the proposed technique. [ABSTRACT FROM AUTHOR]

Different from single-bus dc microgrids (MGs), a multibus MG normally bridge multiple dc buses via a complex line impedance network. This intricate configuration together with tickling constant power loads may cause severe stability issues. For system stability improvement, conventional ways include designing small-signal stabilizers in a decentralized way and constructing large-signal stabilizers by solving Lyapunov equation in a central controller. Note that centralized methods may be vulnerable to single point of failures, while decentralized patterns are commended to reinforce MG reliability and scalability. To implement large-signal stabilization in decentralized mechanisms, which has rarely been investigated in the existing literature, a novel uniform nonsmooth control scheme (UNCS) is proposed, in this article. UNCS has the following fourfold advantages. First, UNCS helps to express commonly used dc/dc converters, boost, buck, and buck–boost, into a uniform model. The model substantially facilitates a uniform stabilizer design that accommodates the preceding three converters despite their differences in topology. Second, UNCS assigns each converter based distributed generator (DG) with a composite large-signal stabilizer comprising a nonsmooth observer and a nonsmooth controller. The controller neutralizes the disturbances estimated by the observer, and it also rigorously stabilizes the internal states in DG uniform model. Third, the stabilizer also provides an additional control degree of freedom, a finetuning factor, to refine DG dynamic responses to meet high requirements for voltage and power qualities. Fourth, when numerous DGs with the proposed stabilizer congregate to build a multibus MG, the overall system large-signal stabilization is autonomously attained without communication links, which is mathematically justified by Lyapunov stability analyses. As such, DGs are allowed to randomly plug in/out without worrying about impairing system level stability. Simulations help to properly select relevant key parameters. Experiments show that UNCS outperforms the standardly designed PI controls, and it will stabilize the multibus MG in a large operation range. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) generators have continuously increased in recent years, whose power is usually controlled through the perturbation and observation (P&O) method. In essence, the P&O method is nonlinear and discontinuous. Hence, the conventional small-signal stability analysis is not suitable anymore when the influence of the P&O-based power control is considered. Focusing on this problem, this paper adopts the nonlinear describing function (DF) method to conduct the accurate stability analysis of PV generators with consideration of P&O-based power control. The detailed procedures about the DF method are introduced, and then the related influence factors like perturbation size, filters, and so on are analyzed quantitatively. Furthermore, the comparison with the conventional stability analysis methods is made, which suggests that the DF method can effectively enhance the accuracy of the stability analysis. All the conclusions are verified by the real-time hardware-in-loop tests. [ABSTRACT FROM AUTHOR]