• Energy Research

This paper describes a solid-state asymmetric bridge resonant topology to increase the energy efficiency of switching pulse modulators. The solid-state resonant topology will replace an existing pulse transformer and thyratron-based resonant modulator to supply the 60-kV target potential for the ion acceleration of the On-Line Isotope Mass Separator ISOLDE accelerator. An experimental prototype is tested in order to validate the proposed concept, including a low auxiliary voltage power supply to compensate the losses in the circuit. The design of the circuit components and the experimental results for a 6-kV prototype are presented and discussed, as well as the design procedure and parameters for the 60-kV modulator, including a high-voltage gapped coil core.

Robust sliding mode on-line space vector controllers, designed for output current control in multilevel three-phase power inverters are described. Capacitor voltage divider equalisation is included using the same approach. Using two four-level comparators, simulation and experimental results show no steady state-errors, very fast dynamics and robustness against power supply variations and load unbalances.

This paper proposes a Direct Matrix Converter operating as a Unified Power Flow Controller (DMC-UPFC) with an advanced control method for UPFC, based on the Lyapunov direct method, presenting good results in power quality assessment. This control method is used for real-time calculation of the appropriate matrix switching state, determining which switching state should be applied in the following sampling period. The control strategy takes into account active and reactive power flow references to choose the vector converter closest to the optimum. Theoretical principles for this new real-time vector modulation and control applied to the DMC-UPFC with input filter are established. The method needs DMC-UPFC dynamic equations to be solved just once in each control cycle, to find the required optimum vector, in contrast to similar control methods that need 27 vector estimations per control cycle. The designed controller’s performance was evaluated using Matlab/Simulink software. Controllers were also implemented using a digital signal processing (DSP) system and matrix hardware. Simulation and experimental results show decoupled transmission line active (P) and reactive (Q) power control with zero theoretical error tracking and fast response. Output currents and voltages show small ripple and low harmonic content.

Research on renewable energy sources and power electronic converters has been increasing due to environmental concerns. Many countries have established targets to decrease CO2 emissions and boost the proportion of renewable energy, with solar power being a prominent area of investigation in the recent literature. Techniques are being developed to optimize the energy recovered from PV cells and increase system efficiency, including modeling PV cells, the use of converter topologies to connect PV systems to high-power inverters, and the use of MPPT methods. Certain MPPT algorithms are intricate and demand high processing power. The literature describes several MPPT methods; however, the number of hardware resources required by MPPT algorithms is typically not disclosed. This work proposes a novel MPPT technique based on integral feedback conductance and incremental conductance error, considering the current dynamics of the boost converter. This MPPT algorithm is compared to the most widely used techniques in the literature and evaluates each method’s efficiency, performance, and computational needs using an HIL system. Comparisons are made with well-known MPPT algorithms, such as perturb and observe, incremental conductance, and newer techniques based on fuzzy logic and neural networks (NNs). As the NN that is most widely used in the literature depends on irradiation and temperature, an additional NN that is trained using the proposed method is also investigated.

Abstract A new non-isolated DC-DC converter for photovoltaic systems is proposed in this paper. This converter topology is characterized by an integration of the classical Boost and Cuk DC-DC converters. The proposed topology requires only a single power semiconductor switch, reduces voltage stress across diodes and power semiconductor switch while providing a continuous input current. Further, this topology allows extending the voltage static gain when compared with the conventional Boost converter. The new converter is regulated by a PWM technique at constant frequency that can be associated to a maximum power point tracking algorithm. Herein, the design considerations of this power converter are presented, and the characteristics of the proposed topology are confirmed by simulations and experiment results from a laboratory prototype.

This work presents an islanded microgrid energy system that uses backstepping control applied to neutral point clamped (NPC) multilevel converters coupled with batteries to behave as virtual generators, able to absorb surplus renewable energy, therefore increasing the penetration of renewable energy sources. Additionally, on a charged battery the virtual generator allows turning-off the backup diesel generator set (GenSet). Aside from improving energy efficiency, the battery-connected multilevel converter aims to regulate frequency, improves power quality, and keeps the microgrid operational in the event of a GenSet failure. The backstepping controlled NPC multilevel converter emulates a virtual generator injecting power to perform as the primary and secondary microgrid frequency controller. Additionally, AC voltage control is implemented, which enables running the islanded microgrid only with multilevel converters, supplied by the battery while integrating solar and wind energy sources. Energy demand and renewable energy forecasts are used to manage the battery state-of-charge. Simulation results, obtained from switched and phasor models show that energy storage and the backstepping frequency control enables the compensation of power fluctuations from renewable energy sources. Furthermore, in the event of the main GenSet failure, the controlled virtual generator keeps the microgrid running for a few minutes, until another GenSet is ready to supply the microgrid. Therefore, the microgrid integration of the battery-connected multilevel converter results in a significant boost in energy efficiency by allowing the disconnection of the backup GenSet.

This paper presents a backward Euler stabilized-based control strategy applied to a neutral point clamped (NPC) back-to-back connected five level converters. A generalized method is used to obtain the back-to-back NPC converter system model. The backward Euler stabilized-based control strategy uses one set of calculations to compute the optimum voltage vector needed to reach the references and to balance the voltage of the DC-bus capacitors. The output voltage vector is selected using a modified cost functional that includes variable tracking errors in the functional weights, whereas in classic approaches, the weights are considered constant. The proposed modified cost functional enables AC current tracking and DC-bus voltage balancing in a wide range of operating conditions. The paper main contributions are: (i) a backward Euler stabilized-based control strategy applied to a double, back-to-back connected, five level NPC converter; (ii) the use of cost functional weight varying as a function of the controlled variable tracking errors to enforce the controlled variables and to balance the DC capacitor voltages; and (iii) the demonstration of system feasibility for this type of converter topology and control strategy, ensuring a high enough computational efficiency and extending the modulation index from 0.6 to 0.93. Experimental results are presented using a prototype of a five level NPC back-to-back converter.

Matrix converters have been extensively investigated in academia over the last 3 decades. Several review works targeting matrix converter topologies, commutation strategies, modulation and control techniques have been published. However, to the best of the authors’ knowledge, a review on the potential contributions of matrix converters for applications that are shaping the electric power sector transition towards decarbonization is lacking, namely applications on smart grids, sustainable transportation and electrical drives. This paper presents an extensive literature review on the more relevant research works targeting applications of matrix converters as an enabling key technology for smart and resilient grids, sustainable transportation, and innovation in variable speed electric drives.

Backstepping controllers are obtained for distributed hybrid photovoltaic (PV) power supplies of telecommunication equipment. Grid-connected PV-based power supply units may contain dc–dc buck–boost converters linked to single-phase inverters. This distributed energy resource operated within the selfconsumption concept can aid in the peak-shaving strategy of ac smart grids. New backstepping control laws are obtained for the single-phase inverter and for the buck–boost converter feeding a telecom equipment/battery while sourcing the PV excess power to the smart grid or to grid supply the telecom system. The backstepping approach is robust and able to cope with the grid nonlinearity and uncertainties providing dc input current and voltage controllers for the buck–boost converter to track the PV panel maximum power point, regulating the PV output dc voltage to extract maximum power; unity power factor sinusoidal ac smart grid inverter currents and constant dc-link voltages suited for telecom equipment; and inverter bidirectional power transfer. Experimental results are obtained from a lab setup controlled by one inexpensive dsPIC running the sampling, the backstepping and modulator algorithms. Results show the controllers guarantee maximum power transfer to the telecom equipment/ac grid, ensuring steady dc-link voltage while absorbing/injecting low harmonic distortion current into the smart grid. -10.13039/501100003176-Ministerio de Educación, Cultura y Deporte of Spain. -10.13039/501100001871-Fundação para a Ciência e a Tecnologia (FCT) (Grant Number: UID/CEC/50021/2013) Departamento de Ingeniería Eléctrica y Térmica Departamento de Ingeniería Electrónica, de Sistemas Informáticos y Automática