Coupling inductors are the most commonly utilized filtering option in grid-connected direct power control (DPC)-based active front-end rectifiers integrated into three-phase adjustable-speed drives (ASDs). Inductor faults, e.g., common interturn short circuits, can drive the whole system to failure. In this paper, a novel strategy is proposed for the early detection of incipient faults in the coupling inductors of the aforementioned ASDs. The proposed method enables a fast identification of the defective phase. The strategy also provides an accurate estimation of the inductance value of the coupling inductors that improves the performance of the DPC method. Simulations and experimental tests demonstrate the validity of this detection and estimation strategy.

A strategic use of a static synchronous compensator (STATCOM) for providing dynamic reactive power management of a hot rolling mill plant along with active mitigation of harmonics is considered in this paper. More specifically, the behavior of a cascaded H-bridge (CHB) converter-based STATCOM is assessed. The impact of the steel to be milled and the specific features of the plant on the design of the STATCOM is discussed. The proposed strategy is analyzed from the point of view of reactive power flow management, active power loss reduction and voltage control at the coupling point, as well as harmonics reduction and decrease of unscheduled shutdowns in the event of a trip in the passive filtering system. The study is based on real plant measurements, simulation tests and results from an experimental platform built at scale, and represents the first stage of an ambitious plan to renew this type of plants aimed at transforming them into active elements for electrical energy management.

The main drawback of unmanned aerial systems (UAS) is that almost their entire field of application is autonomous in terms of energy. Flights beyond 50 min are nearly impossible when using conventional energy storage systems (lithium-ion polymer or lithium-ion batteries). Several commercial products have been developed using hybrid systems (H-UAS). Although the improvement they have provided is undeniable, H-UAS in the present market are strongly limited by their low thrust vs. weight ratio, which is caused by limited electrical power generation and a non-optimal energy conversion with relatively low efficiencies. This paper reviews these systems to show the preliminary results of a prototype of hybrid generator which state-of-the-art electronics as well as a new approach using a supercapacitor (SC) array are used to save fuel, increase the thrust vs. weight ratio, optimize losses during conversion and prevent the overheating of the internal combustion unit (ICU). Whereas current generators mostly operate with the ICU at a constant speed, delivering maximum power, the presented prototype includes a throttle control system, and the engine works with a variable regime according to the power demand. Thus, fuel consumption is reduced, as well as heating and wear. The lifespan of the engine is also increased, and the time between maintenance operations is lengthened. The designed system provides almost twice the power of the hybrid current generators. The reduction in the RPM regime of the engine is achieved by means of a supercapacitor array that provides the necessary energy to keep the DC output power constant during the engine acceleration when the flight envelope experiences a perturbation or a sudden manoeuvre is performed by the pilot. To obtain maximum efficiency, the diode rectifiers and conventional converters used in the reviewed products are replaced by synchronous converters and rectifiers. The whole system is controlled by means of a FPGA where a specific control loop has been implemented for every device: ICU’s throttle, DC bus converter, charge and discharge of the SC’s array, cooling and monitoring of temperature for the cylinders heads, and on-line transmission, by means of a XBEE™ module, of all the monitored data to the flight ground station.

The aging of supercapacitors (SCs) depends on several factors, with temperature being one of the most important. When this is high, degradation of the electrolyte occurs. The impurities generated in its decomposition reduce the accessibility of the ions to the porous structure on the surface of the electrode, which reduces its capacity and increases its internal resistance. In some applications, such as electric vehicles whose storage system consists of SCs, fast chargers, which supply very high power, are used. This can lead to an increase in temperature and accelerated aging of the cells. Therefore, it is important to know how the temperature of the SCs evolves in these cases and what parameters it depends on, both electrical and thermal. In this contribution, mathematical formulae have been developed to determine the evolution of the temperature in time and its maximum value during the transient state. The formulae for obtaining the mean and maximum temperature, once the thermal steady state (TSS) has been reached, are also shown, considering that the charger cells are recharged from the grid at a constant current. Based on this formulation, the thermal analysis of a specific case is determined.

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 article proposes a coordinated management of electrical energy in a steelworks and a wind farm that are connected to the same distribution network. The suggested solution seeks to improve the efficiency of the hot rolling mill, to reduce greenhouse gas emissions, to minimize the cost of the electrical energy utilized in the manufacture of steel coils, to increase the power system chargeability, and to guarantee power quality. The proposal consists of constituting a virtual plant (comprising the wind farm and the rolling mill) to be managed by a single operator. The approach is mainly focused on the management of the virtual plant reactive power. The algorithm proposed to optimize this reactive power is based on the so-called particle swarm optimization. Three optimization strategies are analyzed: minimization of losses in the distribution network, minimization of the voltage deviation at two of its nodes, and maximization of the displacement factor in both the rolling mill and the wind farm. Energy losses are reduced by up to 20% when adopting the first strategy in comparison to the least efficient case. Voltage variations are kept at less than 1% at both nodes when using the second strategy, whereas deviations between 1% and 5% are obtained when implementing the other two strategies. The study is based on actual measurements and simulation tests.