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This study presents the analysis, design and implementation of a simple and cost-effective residential inductive contactless energy transfer system with multiple mobile clamps. The topology is based on the cascaded connection of a buck converter and a high-frequency resonant inverter loaded by several output passive rectifiers. The proposed system includes a sliding transformer to supply the mobile loads, leading to a safe and flexible location of loads. The theoretical analysis and design of the proposed system is based on a mathematical model derived using the first harmonic approximation. Selected experimental results are included to verify the system features. In comparison with conventional topology, the proposed system significantly improves efficiency, complexity and cost. [ABSTRACT FROM AUTHOR]

This study deals with the problem of voltage security in microgrids. In general, voltage security is an issue for power systems, where the lack of reactive power is a concern. For microgrids a complexity is imposed, since frequency and voltage level deviations may take place by the operation of droop-controlled inverters. This study incorporates the load margin calculation into a microgrid structure. For this purpose, a special power flow program is developed in order to consider the effects of the droop-controlled inverters. Simulation results are obtained with the help of an islanded distribution system with only generators coupled by droop-controlled inverters, so the proposed methodology may be tested and discussed. [ABSTRACT FROM AUTHOR]

The injection of sinusoidal current to an electrical grid is nowadays possible with the use of active power filters (APFs). With quasi-steady-state (QSS) nonlinear controllers, these power filters provide low grid-current-harmonic content with simple-control analog implementation. This paper focuses on the design of a QSS nonlinear controller for a single-phase APE A complete analysis based on the sliding-mode-control theory is given. From the analysis, a set of control-design guidelines is presented to select the gains and parameters of the control scheme. Selected experimental results are reported to validate the theoretical design procedure. [ABSTRACT FROM AUTHOR]

This paper presents a sliding-mode control for a single-phase ac/ac quantum resonant converter. The closed-loop system improves regulation, sensitivity to disturbances, and transient response. The design of the closed-loop system is based on the sliding-mode control theory, and it is carried out with the help of an averaged large-signal model of the resonant converter. Simulation and experimental results are reported to validate the theoretical predictions. Essentially, the contribution of this paper is as follows: 1) the averaged large-signal model for the resonant converter; 2) the sliding-mode control scheme; and 3) the design guidelines for the control gains and parameters. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study of sliding-mode control schemes for quantum series resonant inverters. The single-input and two-input resonant systems considered in this study are designed with identical specifications. The control performance is evaluated in aspects such as load transient response, sensitivity to disturbances, and efficiency. Other aspects such as control complexity and cost are also considered. Simulation and experimental results are reported in order to validate the theoretical predictions. Essentially, the study demonstrates the following: 1) The load transient response of the proposed two-input system is insensitive to load variations; 2) the single-input system exhibits higher efficiency, particularly at light load conditions, and 3) both control schemes have similar complexity and cost. [ABSTRACT FROM AUTHOR]

In this paper, the control strategy for a flexible micro- grid is presented. The microgrid presented here consists of several line-interactive uninterruptible power supply (UPS) systems connected in parallel. The control technique is based on the droop method to avoid critical communications among UPS units. Thus, a flexible microgrid is obtained to operate in either grid-connected or islanded mode. A small-signal analysis is presented in order to analyze the system stability, which gives rules to design the main control parameters. Simulation and experimental results are presented, showing the feasibility of the proposed controller. [ABSTRACT FROM AUTHOR]

A dynamic study of the dc/dc series-parallel resonant converter operating with a discrete self-sustained phase-shift modulation technique is presented. The study includes the synthesis of a suitable averaged large-signal dynamic model and the design of a nonlinear feedback controller based in the input-output linearization approach. The proposed controller and modulation type provide some outstanding features: zero-voltage switching operation for the whole load range, narrowed frequency variation range, fast transient response, and robustness in relation to external parameter variations. Experimental and simulation results are reported to validate the theoretical predictions and confirm the superior performance of the nonlinear controller when it is compared with a conventional linear controller. [ABSTRACT FROM AUTHOR]

The aim of this work is the application of the feedback linearization theory to a single-phase shunt active power filter, since this technique has been successfully applied to other areas of power electronic. The active filter is linearized by means of a nonlinear transformation of the system model, deduced from the application of Tellegen's theorem to the system. After that, a sliding mode controller is proposed to impose a desired dynamic behavior on the system, giving robustness and insensitivity to parameter variations. Moreover, the proposed controller ensures proper tracking of the reference signals and simplifies the overall control design. The controller was implemented into a low cost DSP. Experimental and simulation results are provided. [ABSTRACT FROM AUTHOR]

In this paper, a method for the parallel operation of inverters in an ac-distributed system is proposed. This paper explores the control of active and reactive power flow through the analysis of the output impedance of the inverters and its impact on the power sharing. As a result, adaptive virtual output impedance is proposed in order to achieve a proper reactive power sharing, regardless of the line-impedance unbalances. A soft-start operation is also included, avoiding the initial current peak, which results in a seamless hot-swap operation. Active power sharing is achieved by adjusting the frequency in load transient situations only, owing to which the proposed method obtains a constant steady-state frequency and amplitude. As opposed to the conventional droop method, the transient response can be modified by acting on the main control parameters. Linear and nonlinear loads can be properly shared due to the addition of a current harmonic loop in the control strategy. Experimental results are presented from a two-6-kVA parallel-connected inverter system, showing the feasibility of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper deals with the design of the output impedance of uninterruptible power system (UPS) inverters with parallel-connection capability. In order to avoid the need for any communication among modules, the power-sharing control loops are based on the P/Q droop method. Since in these systems the power-sharing accuracy is highly sensitive to the inverters output impedance, novel control loops to achieve both stable output impedance and proper power balance are proposed. In this sense, a novel wireless controller is designed by using three nested loops: 1) the inner loop is performed by using feedback linearization control techniques, providing a good quality output voltage waveform; 2) the intermediate loop enforces the output impedance of the inverter, achieving good harmonic power sharing while maintaining low output voltage total harmonic distortion; and 3) the outer loop calculates the output active and reactive powers and adjusts the output impedance value and the output voltage frequency during the load transients, obtaining excellent power sharing without deviations in either the frequency or the amplitude of the output voltage. Simulation and experimental results are reported from a parallel-connected UPS system sharing linear and nonlinear loads. [ABSTRACT FROM AUTHOR]

This paper presents a novel control strategy for parallel inverters of distributed generation units in an ac distribution system. The proposed control technique, based on the droop con trot method, uses only locally measurable feedback signals. This method is Usually applied to achieve good active and reactive power sharing when communication between the inverters is difficult due to its physical location. However, the conventional voltage and frequency droop methods of achieving load sharing have a slow and oscillating transient response. Moreover, there is no possibility to modify the transient response without the loss of power sharing precision or output-voltage and frequency accuracy. In this work, a great improvement in transient response is achieved by introducing power derivative-integral terms into a conventional droop scheme. Hence, better controllability of the system is obtained and, consequently, proper transient performance can be achieved. In addition, an instantaneous current control loop is also included in the novel controller to ensure proper sharing of harmonic components when supplying nonlinear loads. Simulation and experimental results are presented to prove the validity of this approach, which shows excellent performance as opposed to the conventional one. [ABSTRACT FROM AUTHOR]