Miguel A. Torres

This manuscript presents an energy management strategy (EMS) for a commercial smart building participating in a tertiary frequency regulation market. The building integrates non-controllable components, such as loads and photovoltaic generation, and controllable resources such as a battery storage system and a set of electric vehicle (EV) chargers that are available for customers of the smart building. The EMS is based on model predictive control due to its innate ability to deal with operational constraints and different optimization criteria, which are critical for the operation of the EMS, and consists of two stages. The first iteratively optimizes energy costs and revenues from tertiary regulation reserves and activations in order to determine the optimal operation of the smart building and the regulation offers in nominal conditions. Then, a second problem determines the operation whenever an activation request is made. Simulation-based analyses are performed to study the performance of the EMS and its financial viability in diverse scenarios relevant to the smart commercial building. The results show that profits are greater if both upward and downward regulation can be provided, for a larger number of EVs and chargers and for longer connection times. Most notably, incomes from regulation almost match operation costs for a large number of chargers and EVs (240), obtaining a deficit of only EUR 39.12 for a day of operations.

Modular multilevel converters (MMCs) have been proposed as a suitable power electronics topology for the integration of second-life batteries (SLBs) sourced from electric vehicles (EVs). The inherent parameter variations among the SLBs located in different clusters of the MMC require the implementation of control strategies to regulate battery discharge rates and prevent battery damage from overcharging or overdischarging. In this article, a decoupled modeling approach based on the $\boldsymbol{\Sigma\Delta\alpha\beta} \mathbf{0}$ transform is proposed for the SLB-MMC, and the resulting model is used to develop a decoupled nonlinear control strategy for state of charge (SoC) equalization of SLBs integrated in the MMC. The benefits of using the proposed controller are demonstrated using simulation work, moreover, the proposed control strategy is experimentally validated using an experimental rig where 18 SLBs retired from electrical scooters with capacities between 9 and 13 Ah are integrated in a three-phase MMC composed of 18 sub-modules (SMs). The experimental results demonstrate good SoC balancing performance between phases and clusters of the MMC in three scenarios comprising a discharge test, a cycling test and a charge test where reactive power is provided to the grid.

The Modular multilevel converter (MMC) is a prominent topology for medium to high-voltage, high-power conversion applications. This converter has a modular construction based on building blocks named sub-modules (SMs). However, the large number of SMs required in a typical application makes operating the MMC through a centralized control architecture difficult. Recently, distributed control schemes have been proposed to provide a modular hardware and software development solution for the MMC. This control architecture allows a two-level hierarchy, in which there are distributed low-level control tasks among local controllers (LCs) placed in the converter SMs, while central controller (CC) undertakes high-level control tasks. Under this scheme, both LCs and the CC could execute their control algorithms at different time steps, optimizing the control hardware utilization: This has not been previously reported for MMC operating with a distributed control approach. Based on that, this article proposes an event-triggered distributed control scheme for regulating the capacitor voltages in the MMC. Contrary to previously reported works, the proposal only updates the control actions of LCs when a trigger event occurs, notably reducing the LCs hardware utilization. Real-time hardware-in-the-loop simulation studies validate the proposal's effectiveness, and its performance is compared with traditional consensus-based distributed approach, showing superior performance.

Grid-connected power inverters are indispensable in modern electrical systems, playing a pivotal role in enhancing the integration of renewable energies into power grids. Their significance, primarily when functioning as grid-forming inverters, extends to maintaining the grid’s inertia and strength—a distinct advancement over traditional grid-following operations. As grid-forming inverters, these devices emulate the characteristics of synchronous generators and can act as robust voltage sources, providing essential ancillary services. This behavior is particularly relevant when integrating energy storage systems on the converters’ direct current side. Among the various inverter topologies, the current source inverter (CSI) has emerged as a promising yet underexplored alternative for grid-forming applications. CSIs, when paired with their AC output filters, can effectively operate as voltage sources, utilizing control strategies that facilitate the integration of renewable energies into the electrical system. Their design inherently manages output current fluctuations, reducing the need for restrictive current limitations or additional protective measures. This paper examines the operational region of CSIs, obtained through detailed modeling, to explore their advantages, challenges, and potential for enhancing grid-connected systems. Analyzing the operating region from the converter model verifies the limits of where the converter can operate in a plane of active and reactive powers. For a small prototype model operating with 7 amperes in DC and 120 V in AC, it is possible to supply or absorb active power exceeding 1000 W and manage maximum reactive power values around 500 VAr, as determined by its operating region. Simulations also confirm that small changes in the control reference, as little as 5%, towards the region’s right limits cause significant oscillations in the dynamic control responses. This research aims to deepen our understanding of CSIs’ operational capabilities and highlight their unique benefits in advancing grid-connected systems and promoting the integration of renewable energy using this technology.

This work presents a photovoltaic greenhouse’s design and performance evaluation as an energy hub in modern agriculture that integrates battery energy storage, an electric vehicle charging station, and non-controlled loads. The greenhouse roof comprises 48 semi-transparent photovoltaic panels with nominal transparency of 20% and 110 W capacity. The control of the photovoltaic greenhouse as an energy hub was approached as an optimization problem with the aim of minimizing the energy purchased from the grid. The simulation results indicate that the system is capable of balancing power transactions within the microgrid, thus enabling electromobility and, at the same time, achieving an average energy saving of up to 41%. Furthermore, it was found that the case of slow charging of the electric vehicle at night was less demanding on the battery system than fast charging during the day in terms of abrupt power transitions and average state of charge of the battery system, 61% vs. 53%, respectively. Empirical results also demonstrated the negative impact of soiling generated by agricultural activity on the performance of solar panels. For a period analyzed of three years, an average annual production loss of 6.8% was calculated.

This work presents the design, construction and performance evaluation of a photovoltaic greenhouse as an energy hub (EH) in modern agriculture that integrates battery energy storage (BES) and an electric vehicle charging station (EV). The greenhouse is composed of 48 semi-transparent PV panels with nominal transparency of 20% and 110 W capacity. The control of the PV greenhouse as EH was approached as an optimization problem with the aim of minimizing the cost of the energy used from the grid. Simulation results indicate that the integrated BES is capable of balancing power transactions within the microgrid. In addition, it was found that the case of slow charging of the EV at night was less demanding on the BES than fast charging during the day in terms of abrupt power transitions and average depletion of BES SOC (61% vs 53%). Empirical results also demonstrated the negative impact of dust generated by agricultural activity on the performance of solar panels. For a period analyzed of three years, an average yearly production loss of 6.8% was calculated.

Small grid-connected inverters are not friendly to the electrical grid, in the sense they do not take any action to support the grid when contingency events occur. For example, because of their relatively low power capacity, small grid-connected inverters are not designed to provide dynamic frequency support to the grid. On the other hand, it is well known that microgrids and weak grids including distributed generation would benefit significantly if all of the grid-connected converters could support and help against grid frequency disturbances. Within the family of small grid-connected converters, single-phase quasi-Z-source inverters (QZSI) have become an attractive topology, because they represent a reliable and economical alternative, and can be very efficient in applications that demand small or medium powers. However, a major disadvantage is that the control strategy must manage both direct current and alternating current variables through the same group of switches. The latter is a challenging task when implementing predictive control schemes. This paper proposes a finite control set model predictive control (FCS-MPC) strategy for a single-phase grid-supporting QZSI. The proposed predictive scheme can be easily integrated with a complementary control block to provide grid frequency support. Experimental results show evidence of the inverter operating under the proposed control strategy and providing grid frequency support, which demonstrates the feasibility of the proposal.

This paper introduces the concept of the operating region of a virtual synchronous generator (VSG). The main objective of the operating region is to help take a decision on choosing proper VSG parameters. A VSG based on a diesel generator (Genset) model was used as the study case. The theoretical analysis examined the impact of relevant genset-based VSG parameters, such as droop factor, m _dr , inertia, J, and damping, D, on the output electrical frequency. The main result of this analysis showed that it is possible to define inertia-damping surfaces which are parameterized upon different values of the droop factor. The operating region of the VSG is then defined as the locus of the triples (m _dr , J, D) where the frequency transient response satisfies certain specifications in terms of peak frequency, peak time and rate of change. Experimental results showed that the VSG achieved a satisfactory performance for different values of speed droop during a transient and also in steady-state, validating the model of the genset. In comparison with simulation results, the measured peak frequencies deviated with a mean absolute error of 0.2 % and the steady-state frequencies with a mean absolute error of 0.12 %, validating the concept of the operating region.