This paper focuses on developing a finite element method (FEM) model for large capacitors thermal modeling and reliability analysis. Thermal modeling for capacitors is critical since the capacitor’s lifetime depends on the capacitor’s maximum temperature. Typically, capacitors have been modeled as a solid element, not considering the capacitor’s internal geometry, leading to temperature estimation errors and requiring extensive testing to adjust the model. The presented methodology to develop the model considers the internal geometry to obtain a reliable model, with sufficient simplicity to adapt the methodology to any electrolytic capacitor. To achieve good results, the capacitor’s winding is modeled as an anisotropic material to reproduce appropriately the behavior of the layers of aluminum and paper soaked in electrolyte. The results of the simulations match the experimental results closely, therefore validating the utility of the model.

Modular multilevel converters (MMC) can be used in several applications, especially (but not only) in high-voltage direct current (HVDC) and STATCOM. In order to develop experimental scaled-down test benches for lab validation, several projects have developed MMCs with a limited number of cells, but they need to use pulse width modulation (PWM) techniques to achieve acceptable power quality (because nearest level modulation (NLM), common in HVDC applications with hundreds of levels, cannot achieve sufficient power quality unless the number of cells is high enough). The present paper proposes a new concept which is based on designing arms with a single cell. This allows to have the simplest possible converter that maintains the structure of an MMC. While all the inner controllers of large-scale HVDC MMCs are included, the only remarkable difference is that PWM is used and NLM cannot be implemented. As this is also a limitation for other low voltage MMC, the proposed concept is suggested for scaled-down low voltage applications. The paper includes the design and construction of the converter, the definition and implementation of the converter controllers, and the converter testing, with detailed dynamic simulations and an experimental setup.

In this paper a 10 kVA photovoltaic emulator is presented. The system implemented generates photovoltaic V-I characteristic curves to analyse and test maximum power point tracking algorithms of real photovoltaic inverters according to the standard EN50530. The power converter used includes a three-phase ac-dc active rectifier. The power stage selected allows to minimize the harmonic current content and permits to be closed to the unity power factor with a fast response. The emulator is controlled by a digital signal processor that communicates with a human-machine-interface. It allows to emulate static and dynamic responses. Furthermore, the interface is also capable of simulating weather evolution and situations under shaded conditions.

This paper presents a reliability analysis of a three-leg four-wire inverter used to emulate non-linear loads. The converter under study can control the current per phase independently up to a maximum frequency of 650 Hz. A reliability analysis of the converter is carried out analyzing the effect of unbalanced loads and harmonic injection in the reliability of the semiconductors and capacitors. The results obtained show a faster degradation with the scenarios presented. The effect of the harmonics on the lifetime of the semiconductors is relevant and shall be considered in systems with high harmonic content. Regarding the capacitors both the harmonics and unbalanced loads reduce the lifetime estimation.

This paper investigates the application of fractional proportional–resonant controllers within the voltage control loop of grid-forming inverters. The use of such controllers introduces an additional degree of freedom, enabling greater flexibility in manipulating frequency trajectories. This flexibility can be harnessed to improve tracking error and enhance disturbance rejection, particularly in applications requiring precise voltage regulation. The paper conducts a conceptual stability analysis of ideal fractional proportional–resonant controllers using the Nyquist criterion. A tuning procedure based on robustness criteria for the proposed controller is also addressed. This tuning strategy is used to compare different controllers under the same conditions. In addition, a sensitivity analysis is provided, comparing the performance of fractional proportional–resonant controllers with traditional proportional–resonant controllers equipped with harmonic compensation. The controller’s formulation and performance are validated through simulations and tested with a 20 kVA inverter under high non-linear loads. Compared to classical control approaches, the fractional tuning parameter enhances tracking performance, reduces phase delay, and improves disturbance rejection. These improvements are achieved with a controller designed to minimise computational demands in terms of memory usage and execution time.

This article presents a reliability analysis of a 4-wire grid-tied inverter under different loading conditions, considering unbalanced loads and harmonic distortion in the current consumed. The proposed power converter is used as a case study to assess the impact of current disturbances on the semiconductors’ reliability. The 4-wire inverter analyzed is implemented with a 3-leg SiC MOSFET power module and a neutral wire connected to the midpoint of the DC-link. The analysis is founded on the reliability curves for power switches provided by the literature. As key take-home findings, the addition of harmonic content in the load current plays a dominant role in the semiconductors’ expected lifetime, especially for the low-frequency harmonics, e.g., third harmonic. Furthermore, the phase delay of the harmonic current content is revealed as a critical factor in the semiconductor’s reliability. Additionally, the existence of unbalanced loads substantially modifies the reliability of the semiconductors of the inverter. The results confirm that converters’ reliability is highly dependent on the loading conditions and harmonic content, so identifying the most critical conditions is inevitable.