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In this paper, a modified transformerless inverter topology for photovoltaic (PV) applications is presented. This proposal is capable to produce a nine-level AC output from a single low DC voltage source with an efficiency of 95.59%, making it ideal as a micro-inverter. This is achieved by an elevation phase that generates two isolated DC outputs from a single source, using a redesigned DC/DC parallel boost converter that elevates up to ten times the input with no extreme duty cycles and performing it with fewer components compared to similar capacities topologies. These two isolated voltages are employed to feed an asymmetrical cascade cells DC/AC inverter. The theoretical fundaments and both simulation and experimental results presented in this paper validate the proposed topology.

This paper presents a practical approach for the real-power economic dispatch of AC/DC power transmission systems formed by VSC-HVDC equipment. It uses the Lagrange multipliers method combined with a comprehensive representation of the AC/DC power system. The power losses of the AC systems, DC grid and power converters are considered in this novel formulation by using incremental transmission loss factors. For realistic solutions, the different control strategies of the power converters forming any VSC-based power grid are considered. Interestingly, this approach permits to conclude that the AC grids coupled to converters charged with DC voltage control define the nodal marginal prices in the DC network, and in turn, the energy prices in the VSC-connected passive grids are inherited from the DC network. Overall, this modelling approach yields great flexibility to model any arbitrary VSC-based HVDC power grid interconnecting various AC systems. The developed method has been validated using a two-terminal VSC-HVDC network interconnecting two otherwise independent AC grids. Its results are compared against those obtained by the sequential quadratic programming method available in the optimisation toolbox of Matlab©, with both solutions exhibiting differences inferior to 0.30% in the total generation costs, therefore concurring very well between each other. The practicality of this approach is also demonstrated by carrying out the real-power economic dispatch of an AC/DC transmission system comprising seven VSC units which give rise to a thirteen-node DC grid.

Mexico's national electric grid comprises ten regional systems, with one isolated in the south of the Baja California Peninsula. In addition, providing electricity access remains a challenge in the country. Therefore, distributed renewable energy solutions are relevant to satisfy the electricity demand and promote grid development. Distributed renewable energy access (DREA) based on a wind energy conversion system integrated into low-voltage direct current (LVDC) networks is presented. The DREA is analysed and simulated under wind speed conditions measured and recorded for one year at Baja California Sur. A representative variability is applied to five type-4 wind turbines based on wind speed turbulence intensity analysis. The generated power is transferred through a bidirectional dual active bridge converter, controlled by a novel small-signal model using a single closed-loop proportional-integral control, owing to its modularity, power density, and ability to transfer power from LVDC to high-voltage direct current. The effectiveness and robustness of the proposed DREA are assessed via a complete mathematical model, corroborated by the simulation results in MATLAB-Simulink®, and validated by experimental results using the real-time simulator Opal-RT Technologies® and laboratory prototyping. The results indicate a DC-link voltage compensation and integration of a power capacity of 150 kW in the LVDC networks with an efficiency of 94%.

The presence of harmonic currents in three-phase distribution networks and the stochastic behavior of unbalanced loads with different power factors are undoubtedly responsible for power quality problems. This paper proposes a novel solution named Cross Phases Hybrid Transformer (CPHT) to address those issues. The CPHT incorporates a conventional distribution transformer into an AC/AC power electronic stage referred to as cross phase module. This new hardware configuration allows to achieve continuous three-phase energy supply of distinct loads as well as high energy quality indexes for diverse distribution networks. The proposed solution has been numerically and experimentally validated by means of simulations carried out in Simulink and with a scaled-down laboratory prototype respectively. The validations consider distinct case studies to show the operative advantages of the CPHT with respect to other topologies reported in the literature.

This work introduces the Proportional-Values Modulation (PVM), an advanced technique for modulating DC–DC DAB converters. The relative advantages of this technique are: (i) Full elimination of reactive power throughout the bidirectional operating range of the DAB; (ii) reduction of the apparent power in the high-frequency transformer, HFT, while maintaining the harmonic distortion low, and (iii) the output capacitance is lower than the one obtained using Single-Phase-Shift Control (SPSC) and Dual-Phase-Shift Control (DPSC) methods, while the AC and DC current peaks are not incremented. This set of advantages increases the overall technical efficiency and power density flow of the converter. As additional characteristics of interest, the technique uses a single feedback PI loop and no complex control rules are implemented. Both features increase the computational efficiency of the PVM above other proposals.

This paper presents and details the H-Bridge PFC rectifier control scheme. This control is a step forward in sensorless current control schemes for performance improvements of single-phase bidirectional rectifiers. The H-Bridge PFC rectifier is designed based on a single PI controller loop fed by DC reference signals. Regarding dynamic operating conditions, the proposed control can maintain a regulated DC voltage under varying conditions at input (voltage sags) and output (load step changes) ports while maintaining an unitary power factor (PF) and constant THD current input at any of these conditions. Different to other investigations, this control proposal uses SPWM, does not require a variable transformation into the dq0 reference frame, and the complex compensators accompanying to the PI controller stage are no longer needed. Therefore, this proposal is aimed to reduce the complexity of the control scheme and to improve the overall dynamic response of the PFC rectifier. The experimental results obtained from the scaled-down prototype setup, which was built for research purposes, validate the control law, mathematical model and quantitative comparison between simulation and experiment, both considering the parasitic resistances of the inductor and semiconductor switches.

The electric arc phenomenon associated with high impedance faults (HIFs) in distribution systems is an exciting subject that directly impacts over the reliability of electrical utilities, because fault currents are very small and present non-linearity and asymmetrical waveforms. Therefore, HIFs may be an undetectable phenomenon by overcurrent protections like fuses, re-closers, and relays. A HIF entails a challenge for its detection and location. In this sense, more realistic high impedance models, as well as reliable signal processing techniques, are needed to extract all transient characteristics aiming to detect HIFs in distribution networks. In this work, an efficient Resistive-HIF model is proposed and implemented into the Alternative Transients Program of the Electromagnetic Transients Program (ATP/EMTP) software to represent the main characteristics of HIFs. The model is compared against well-prove models by using two multiresolution approaches based on the Hermite transform and the Wavelet transform considering different frequency bands.

This paper introduces a PV system model useful for steady-state power flow studies of practical electrical networks. This multi-array PV system model features a comprehensive representation of the three main stages taking part in solar energy conversion systems: (i) PV arrays for the solar-to-electrical energy conversion, (ii) the DC boost converter useful for establishing the MPPT strategy and for stepping up the output voltage of the PV arrays, and (iii) the DC-to-AC power conversion by the voltage source converter (VSC) used to link the PV system with the AC grid. The derived PV system model is flexible and modular as it permits to consider any desired number of PV arrays with different irradiance conditions each. For validation purposes, a 1.5-MW PV system coupled to a 3-bus AC network was simulated. Its steady-state power flow results were compared against those obtained by a highly-detailed switching-based PV model implemented in Simulink©. It is shown that the proposed model retains sufficient accuracy since the computed relative errors were inferior to 2% between both fundamentally different methods. The IEEE 57-bus test grid is also used to incorporate five PV plants, thus showing the practicality of the introduced modeling approach for distributed PV systems.

This paper proposes an improved Multilevel Boost Converter, also known as Multiplier Boost Converter, in which the spike-type current among capacitors is eliminated through one resonant inductor, achieving some resonant-type current waveforms. Experimental results demonstrate the applicability of the proposition.