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Smart transformers offer the possibility to reduce the costs related to the integration of renewables and charging station into the grid and are gaining industrial interests. Grid system operators request modularity for easy maintenance and power scalability. Normally, the power is shared equally in the modular structure. However, differences in electrical and thermal parameters of the individual cells result in a nonoptimal efficiency and reliability characteristics with equal power sharing. In this article, a generalized approach for system-level modeling of modular converters with graph theory is presented. Graph theory simplifies the power flow management in modular architectures to a network flow problem, thereby facilitating the routing of power among the cells for optimizing reliability and efficiency. A power routing algorithm based on convex cost flow optimization is discussed, and case studies are presented to demonstrate the potential of the proposed method. [ABSTRACT FROM AUTHOR]

Currently, the necessity of efficient and reliable power systems is also increasing because of the strict requirements that standards and regulations impose, but still costs have to remain low. The monitoring and control of the components' lifetime can lead to reduce maintenance costs.However, overcoming the related challenges is not a straightforward task, as it involves knowledge of power device physics, smart management of electrical quantities, and optimal maintenance planning and scheduling. It represents a multidisciplinary issue being faced in the last decade. [ABSTRACT FROM AUTHOR]

The smart transformer (ST) is a potential solution for an upgrade of the electric distribution grid, which enables to provide services to the grid and dc connectivity. However, the power electronics within the system are challenged by high reliability requirements. One possible solution to increase the reliability is to employ prognosis to predict the failures and avoid down times of the system. Traditional maintenance scheduling is based on the remaining useful lifetime (RUL) of the individual components or the forecasted failure probability. For a further increase of the time to the next maintenance, it is desired to have similar wear out of all components, which need to be maintained or exchanged. In this article, it is proposed to route the power internally in a modular power converter consisting of a cascaded H-bridge connected to dual active bridges in order to influence the RUL of its building blocks. Therefore, a thermal stress based wear-out control is designed for addressing the processed power dependent failures of the devices in the building blocks of the ST. Compared to the conventional power routing methods, the impact of the proposed system-level control considering electrical and thermal parameter variations is demonstrated using Monte Carlo analysis. [ABSTRACT FROM AUTHOR]

Grid-forming converters enable an asynchronous connection of grids, which opens new opportunities for the power system management. This includes the potential to control the amplitude and the frequency of the grid voltage to vary the power consumption of the loads and the generation in the grid. Depending on the load sensitivity to voltage and frequency, the power transfer of the grid-forming converter changes. Remarkably, this has an impact on the power semiconductors by means of thermal stress, which is limiting the lifetime of the devices. This article aims to investigate and mitigate the thermal stress in grid-forming converters by applying a load voltage-sensitivity control. Depending on the nature of the loads, their power consumption varies with the voltage. This response is dependent on the connected loads and can be characterized by constant power (independent from the voltage), constant current (linearly dependent on the voltage), and constant impedance behavior (squared-dependent on the voltage). The sensitivity to voltage is exploited to control the load power consumption, reducing the junction temperature fluctuations and, thus, the power semiconductors stress. [ABSTRACT FROM AUTHOR]

With the goal to decrease weight and increase overall efficiency, power electronics is proliferating in the aircraft applications. The conventional mechanical, pneumatic, and hydraulic systems are substituted with on-board electrical distribution systems. The new power electronics based distribution architectures should comply with the airworthiness standards by providing adequate redundancy to operate even under multiple failures. However, each redundant system adds to more weight and cost, and hence optimizing redundancy without compromising safety still remains a challenge. In this scenario, modular power converters offer a promising solution for obtaining reliable operation. Apart from ensuring availability and operation of the system, the modular converters enable controlling the stress for the individual converter cell and therefore their wear-out. This paper considers the failure mechanisms of the most sensitive devices in the system, the power semiconductors, and predicts their remaining useful lifetime (RUL). Based on this RUL, an optimization of the system loading is performed in order to delay the wear-out based failures in the system without reducing the mean lifetime of the building blocks. A study case is shown in order to demonstrate the lifetime extension of the system with the proposed algorithm. [ABSTRACT FROM AUTHOR]

The use of a smart transformer-based electrical distribution could be an effective approach to reorganizing the electric grid and solving the problems and challenges of distributed generation systems and active loads. While lower efficiency and higher cost compared with the conventional transformer are well known and investigated limiting factors, the required higher maintenance, related to the use of electronics systems in the electric grid, is seldom targeted. In fact, high maintenance cost would make the use of smart transformers inapplicable even if new services could justify higher initial cost and new semiconductor development could increase the overall efficiency. This work proposes a modular repairable system based on condition monitoring, which aims at equalizing the lifetime consumption of the single modules to make possible prognostic maintenance. [ABSTRACT FROM PUBLISHER]

The thermal stress of power electronic components is one of the most important causes of their failure. Proper thermal management plays an important role for more reliable and cost-effective energy conversion. As one of the most vulnerable and expensive components, power semiconductor components are the focus of this paper. Possible approaches to control the semiconductor junction temperature are discussed in this paper, along with the implementation in several emerging applications. The modification of the control variables at different levels (modulation, control, and system) to alter the loss generation or distribution is analyzed. Some of the control solutions presented in the literature, which showed experimentally that the thermal stress can be effectively reduced, are reviewed in detail. These results are often mission-profile dependent and the controller needs to be tuned to reach the desired cost-benefit tradeoff. This paper analyzes also the many open questions of this research area. Among them, it is worth highlighting that a verification of the actual lifetime extension is still missing. [ABSTRACT FROM PUBLISHER]

A smart transformer (ST) can take over an important managing role in the future electrical distribution grid system and can provide many advanced grid services compared to the traditional transformer. However, the risk is that the advanced functionality is balanced out by a lower reliability. To address this concern, this work conducts thermal stress analysis for a modular multilevel converter (MMC), which is a promising solution for the medium voltage stage of the ST. The focus is put on the mission profiles of the transformer and the impact on the thermal stress of power semiconductor devices. Normal operation at different power levels and medium voltage grid faults in a feeder fed by a traditional transformer are considered as well as the electrical and the thermal stress of the disconnection and the reconnection procedures. For the validation, the thermal stress of one MMC cell is reproduced on a laboratory setup with high-speed temperature measurement. It is concluded that the investigated conditions, including inrush currents and power variations, do not cause a significant lifetime reduction. [ABSTRACT FROM AUTHOR]

In the last years, the optimization of the energy harvesting of photovoltaic systems during fast variable irradiance conditions has been an active area of research and of competition among the companies. The proposed fast maximum power point tracking (MPPT) algorithms can produce extremely variable loading of the power semiconductors resulting in a decrease of the system lifetime, which in consequence can nullify the economic advantage of higher energy harvesting. This work analyzes the problem with a deep theoretical and laboratory work. Then, a multiobjective MPPT, which limits the positive temperature gradient and the maximum junction temperature of the power semiconductors, is introduced and fully validated in the laboratory with a mission profile emulating variable irradiance conditions. [ABSTRACT FROM PUBLISHER]

Active thermal control for power modules can potentially extend the lifetime of the converter. This paper investigates the trade-off between the lifetime extension or de-rating and its cost due to the efficiency reduction. A short review on the existing approaches using control to reduce thermal stress of power modules is presented. Based on a given junction temperature profile, a method to evaluate the active thermal control's trade-off is presented. The concept is validated on a laboratory setup, where active thermal control is implemented by adapting the switching frequency. A discussion of the possible lifetime extension at the efficiency's expense is finally given. [ABSTRACT FROM AUTHOR]