This article proposes an analytical model that provides accurate self-inductance and mutual inductance calculations for two mutually coupled rectangular, planar, and spiral coils with an air core, which are equal and parallel, including the possibility of a lateral misalignment. Both single- and double-layered coil geometries were modeled by considering an arbitrary number of turns with a circular cross section per layer. The model equations, which can be readily implemented in software, are the results of a systematic approach that starts from the equations for the self-inductance of a wire and the mutual inductance of two parallel and misaligned wires that lie on the same plane. Accuracy is guaranteed by considering all the magnetic interactions among the individual turns in the two coils, while the simplifications involve only the calculations made at the corners of the coils. The model was validated by taking as reference experimental measurements carried out on a rectangular and a square magnetic coupler. A second analytical model, based on equivalent single-turn coils, was also tested for comparison purposes. The validation was extended with finite-element analysis tools by considering a wide range of coil side lengths, air gaps, number of turns, and lateral misalignments. The proposed model can, therefore, be regarded as a reliable tool to aid in the design of rectangular-shaped air-core magnetic couplers with applications in the contactless transfer power that are not necessarily limited to vehicle electrification.

The continuous monitoring of voltage characteristics in electric power systems, such as in microgrids, is required for power quality assessment, grid control, and protection purposes. Due to the presence of disturbances in the grid voltage, such as harmonics, imbalances, noise, and offsets introduced by the instrumentation, among others, the frequency-estimation process has to be robust against all these disturbances to obtain an accurate estimation of the frequency value. This paper presents a fast and accurate method to estimate the fundamental frequency of an electric power system. The estimation method works properly in balanced and imbalanced three-phase systems, and even in single-phase systems. The proposed solution is based on an algebraic method, which is able to calculate the frequency of a pure sinusoidal signal using three samples. A filtering stage is used to increase the robustness of the algorithm against disturbances in a wide frequency range. Simulation and experimental results show the good performance of the method for single- and three-phase systems with a high level of harmonic distortion, even in the presence of amplitude, phase, and frequency changes.

This paper presents a two degrees of freedom (2DOF) control scheme for voltage compensation in a dynamic voltage restorer (DVR). It commences with the model of the DVR power circuit, which is the starting point for the control design procedure. The control scheme is based on a 2DOF structure implemented in a stationary reference frame (α-β), with two nested controllers used to obtain a passband behavior of the closed-loop transfer function, and is capable of achieving both a balanced and an unbalanced voltage-sag compensation. The 2DOF control has certain advantages with regard to traditional control methods, such as the possibility of ensuring that all the poles of the closed-loop transfer function are chosen without the need for observers and reducing the number of variables to be measured. The use of the well-known double control-loop schemes that employ feedback current controllers to reduce the resonance of the plant is, therefore, unnecessary. A simple control methodology permits the dynamic behavior of the system to be controlled and completely defines the location of the poles. Furthermore, extensive simulations and experimental results obtained using a 5-kW DVR laboratory prototype show the good performance of the proposed control strategy.

The control of grid-connected power converters, such as in photovoltaic generation systems, requires a fast, accurate, and robust synchronization method, particularly during faults and when operating under highly disturbed conditions. This paper presents a method to estimate the frequency, amplitude, and phase of the positive- and negative-sequence components. A filtering stage in a rotating reference frame based on a particular type of notch filter is designed to reject the most relevant disturbances, including voltage sags, frequency variations, phase jumps, voltage imbalances, and harmonics. Furthermore, an accurate estimation of the grid frequency is also carried out. Extensive simulation and experimental results are provided to show the performance of the estimation method in different scenarios considering the aforementioned disturbances. The method is able to precisely provide the estimated values between one and one and a half cycles of the fundamental frequency. Furthermore, the computational cost of implementation of the notch filters employed is considerably small.

This paper presents a discrete-time domain control scheme for balanced voltage sag compensation using a Dynamic Voltage Restorer (DVR), which is recognized to be an appropriate and economical power electronic device with which to ameliorate these disturbances. The proposed control method is implemented in the synchronous reference frame (SRF), with two nested regulators, one of which includes an integral action. This algorithm has some advantages with respect to other control algorithms, such as the fact that the proposed methodology permits all the closed-loop poles of the DVR system to be placed in the desired locations in order to define the dynamical behavior with a reduction in the number of the electrical magnitudes to be measured and without the need for state observers, as occurs in traditional control methods. What is more, the well-known inner current loop implemented in other control schemes, which is employed to attenuate the resonance of the plant, is unnecessary. Furthermore, the unbalanced voltage sag compensation can be achieved by adding a “plug-in” controller and following the same methodology presented for balanced voltage sags to design the controller. The good performance of the proposed control scheme is validated by means of simulation and experimental results carried out with a 5 kW DVR laboratory prototype. The discrete-time control method is also compared with two control schemes previously proposed in literature.

People suffering from rheumatoid arthritis are normally prescribed with physical exercises. The realization of these exercise routines should be supervised to prevent wrongly adopted postures or bad movements that end up harming the affected articulations. The motivational component associated with a supervised session is also important. On the contrary, having access to qualified supervision is not always possible due to different reasons, such as tight schedules, limited mobility, or economic reasons. This article presents a system for at-home rehabilitation, based on Microsoft Kinect, that resembles the role played by the physiotherapist during the supervision of an exercise session. The system not only supervises the realization of exercises but it also collects and manages information about the exercise-session history. Additionally, and despite affecting young people, rheumatoid arthritis is a disease that mainly affects seniors. For this reason, the system provides a natural interface to ease the interaction. Finally, the performance of the proposed system has been evaluated using a three-dimensional dynamic measurement system as a gold standard to validate the accuracy of the measurements. Obtained results demonstrate the potential of the Kinect-based system for at-home rehabilitation exercise routines.