This paper proposes an online grid impedance estimation method for AC Grids under the presence of grid-tied converters. A novel modelling approach in the α,β,0 reference frame is proposed, including the relationship with the instantaneous power theory. The proposed modelling framework considers both balanced and unbalanced conditions and operation in the four quadrants. For the impedance identification, a Pulsed Signal Injection (PSI) approach together with a Recursive Least Square (RLS) algorithm is used. The proposed modelling and identification method is thoroughly evaluated by simulation and experimental results. The work presents a contribution for the optimization of the distribution grid operation with high-dynamic impedance changes due to the integration of distributed resources.

A set of analytical equations for the calculation of the temperature in supercapacitors operating in constant-power applications is presented in this paper. Although the main operation modes of supercapacitors are constant-current and constant-power charge and discharge, this study was focused on the latter, since both sources and loads act as constant-power systems in a wide range of power conversion facilities. The starting point of this study is the classical supercapacitor model based on electrical and thermal parameters provided by manufacturers or also obtained by experimental means. The proposed mathematical analysis is based on the so-called incomplete gamma function that presents two major advantages over previously existing methods. Firstly, it is not necessary to solve any differential equations system by means of numerical methods, which reduces the required computational effort. Secondly, no simplifications to relief the calculations are made in the computation of any variable. The new formulation renders valid solutions even for high-power demand situations. Moreover, the temperature of the supercapacitor can be expressed as a function of time or any other electrical variable in the charging and discharging processes. Therefore, the proposed formulas are especially remarkable for the electrical and thermal dimensioning of supercapacitors.

This contribution explores the possibility of improving the global efficiency of three-phase inverter-based distributed resources (DR) embedded in low-voltage distribution feeders, by the adaptation of their switching frequency (SF) to the operation point of both the converter and local loads. The core of this proposal lies on the fact that in a good number of applications, in both services and residential sectors, the owner of the DR is also in charge of the losses caused in the local electric power system. This fact leaves room for a global optimization of the power losses, i.e, converter losses will be considered together with those losses caused by the current harmonics injected into the local grid. A dynamic adaptive SF frame of the DR is considered in this proposal to allow its operation beyond its rated frequency at light loads, subjected to the thermal constraints of the device. Simulation results obtained using PLECS software as well as an experimental validation of the method are included.

This article proposes a passive and an online estimator of the dc bus parameters (series resistance $R_s$ , inductance $L_s$ , and capacitance $C$ ) used in doubly fed induction machines for wind applications. This kind of machines is widely adopted as generators for wind applications, where predictive maintenance is an important cost-reduction driver. Two implementations are described, plug-in or parallel, depending on whether the algorithm runs in the application digital control platform or as a standalone diagnostic device. Neither requires maintenance shutdown or dc current measurements to estimate bus parameters. In the plug-in operation, the proposed method relies only on the electrical quantities required by the control system, i.e., stator-side and rotor-side voltages and currents. Conversely, in parallel mode, dedicated external voltage and current sensors are used. In both cases, the series $RLC$ estimation is based on a recursive least squares algorithm that works for the full speed range of regular operation required in wind energy applications. In this way, the replacement of deteriorated capacitors can be performed by monitoring the estimated parameters. The validity of the proposal is discussed based on a theoretical analysis, simulation results, and experimental validations.

In this article, a new methodology for the sizing of a fast-charging station for electric vehicles is presented. The proposed method is applicable to public service vehicles on urban journeys. Its use has been conceived for vehicles equipped with an energy storage system based on supercapacitors (SCs), which are already functional in several countries. The proposed charging station also uses a bank of SCs of variable capacitance. During the study, mathematical expressions will be obtained for the electrical variables involved in vehicle charging: instantaneous current, peak current, charging time, dissipated energy, and the efficiency of energy transference. From these, each of the components of the system will be dimensioned: the capacitance of the charger with its different variable steps, the initial voltage of the charger, and the current smoothing inductor. The proposed charger presents the advantage of allowing energy to be evacuated to the electric vehicle very quickly and with high performance, all without using an external power source or high-power converters. The proposed architecture minimizes the disturbances that, with conventional methods, would appear on the electrical grid, preventing the installation of fast-charging stations at many grid nodes, as is currently the case. Finally, the charger control algorithm is considerably simplified as it only depends on the initial voltage of the vehicle’s accumulator.

The phenomenon known as the Biefeld-Brown effect or ionic wind has been the subject of study since its discovery with the aim of being applied to aircraft propulsion. Electrohydrodynamic (EHD) thrusters have been developed in a thorough and detailed way since 2000. Subsequently, some attempts have been made to extend them to electric-powered atmospheric aircrafts. This paper is framed in this field by performing a rigorous and detailed analysis of the energy efficiency, measured as the ratio of thrust to energy consumed, for both EHD systems and conventional electric propulsion. This is done using simple EHD thruster configurations together with accurate measurements of the current consumed under controlled environmental conditions. The results are not only compared with the performance of an electric propulsion motor-propeller set, but also consider future research, summarizing the issues that arise to scale them. Future designs of low weight, high performance thrusters might allow this technology to be applied to manned or remotely piloted aircrafts.