Cascaded H-bridge multilevel (CHB-ML) inverters are an attractive alternative for supplying power to ac grids as they have high reliability and offer an acceptable quality of voltage at their output terminals. In order to achieve efficient operation in these CHB-ML inverters, they must work at low switching frequencies. The finite-control set model predictive control (FCS-MPC) scheme is a very intuitive strategy for controlling this type of converter, but traditional FCS-MPC algorithms generally have a steady-state error when operating at low sampling frequencies and/or if there are parameters mismatch in the prediction model, regarding those of the real system. In this article, a grid-connected CHB-ML inverter that uses an improved FCS-MPC scheme is proposed. The proposed strategy eliminates the steady-state error in an MPC operating at low sampling frequencies and maintains correct operation when a change in the control reference occurs. Experimental results from a grid-connected CHB-ML inverter with three units (seven levels) demonstrate the feasibility of the proposal.

Hybrid Distribution Transformers (HDTs) offer a compelling alternative to traditional low-frequency transformers (LFTs), providing auxiliary services in addition to standard functionalities. By integrating LFTs with power converters, HDTs enhance the operational capabilities of the system. The specific configuration in which converters are connected to the transformer allows for the provision of multiple services. This can not only prevent network failures but also extend the lifespan of its components, an outcome that is highly desirable in a distribution grid. This article discusses an HDT developed to mitigate voltage fluctuations in the grid and to decrease the reactive power drawn from the secondary side of traditional LFTs. A finite-control-set model predictive control (FCS-MPC), in conjunction with linear controllers, is utilized for the effective management of the HDT converters. Two separate control loops are established to regulate voltage and reactive power on the secondary side of the transformer. Results from Hardware-in-the-Loop (HIL) testing affirm the proficiency of HDT in reducing grid voltage variations by 15% and in cutting reactive power consumption by up to 94%. The adopted control strategy and topology are demonstrated to be effective in stabilizing voltage and reactive power fluctuations while concurrently facilitating the charging of the converters’ DC link directly from the grid.

This paper compares two finite-control-set model predictive control (FCS-MPC) strategies in the context of a grid-connected single-phase quasi-Z source inverter (SP-qZSI). Both schemes use discrete-time models of the inductor current and capacitor voltage for the DC side, as well as the output current on the AC side. To enhance the converter’s performance, given the non-minimum phase characteristics of the DC side, a long prediction horizon is implemented for the predictive control. However, a horizon of this nature can be highly demanding in terms of processing load, rendering it inapplicable for some microcontrollers. To address this issue and mitigate the processing load, an alternative control strategy is presented that divides the total number of candidate solutions to be evaluated into smaller segments. The performance of the two control strategies is compared using total harmonic distortion (THD) and simulation times as evaluation metrics. The results indicate that the proposed strategy achieves significantly shorter simulation times than the compared control strategy when increasing the prediction horizon. Additionally, a reduction in the THD was observed in the proposed strategy, reaching an average of 2.8%, which is lower than the compared strategy that exhibited THD close to 3.5%.

The objective of this article is to validate a dynamic output-feedback (DOF) control synthesis methodology to be implemented through digital signal processors in the scope of electrical microgrid applications. The DOF controller, originally designed in continuous-time, is developed aiming to comply with strict transient behavior requirements associated with electrical systems, by using an adaptation of the $\mathcal {D}$-stability concept to handle linear systems affected by time-varying parameters (linear parameter varying model). In order to allow a digital implementation of the control action, a discrete-time equivalent representation of the continuous-time DOF controller is obtained from the Taylor series expansion of the exponential terms associated with the discretization. Additional contributions of this article include: the use of a formulation based on differential linear matrix inequalities to ensure the stability of the hybrid system (composed of the analog plant and the digital controller), and the validation of the redesigned controller performance when applied to a real-time simulation of a three-phase inverter with a grid-supporting configuration emulated via hardware-in-the-loop device. The results demonstrate that the controlled system has achieved a regular operation for all the load cases investigated after the anomalies presented, even regulating a voltage drop of 20%. The proposed method was compared with a method in the literature, showing a decrease of 17.5% in the harmonic distortion of the currents holding similar voltage distortion.

This paper explores the use of series compensated low frequency transformers (SCLFT), operating in parallel to traditional low frequency transformers (LFT), to attenuate harmonic distortion caused by nonlinear loads in electrical networks. The proposed strategy achieves harmonic cancellation through a controlled phase shift between the SCLFT and LFT voltages, emulating the behavior of multi-pulse transformers. By integrating power converters into the LFT, the SCLFT’s operation is optimized to maximize system efficiency and implement a robust control algorithm for precise output voltage regulation. The effectiveness of the proposed approach is validated through hardware-in-the-loop (HIL) simulations and experimental testing, demonstrating a significant reduction in current harmonic distortion. These results position series-compensated SCLFTs as a viable solution for enhancing power quality in distribution grids. This technology offers a promising alternative to modernizing electrical infrastructure and paves the way for future applications in microgrid optimization and large-scale distribution systems.