No abstract

The paradigm of smart grids has encouraged new developments of power electronics converters, for instance, in the perspective of renewables and electric mobility applications. Aligned with this perspective, this paper proposes a novel topology of a multilevel bidirectional and symmetrical (MBS) split-pi dc-dc converter. As a central distinguishing feature, it operates with three voltage levels in both dc sides (0, vdc/2, vdc), meaning that the voltage stress in each semiconductor is reduced when compared with the conventional split-pi converters, and it operates with controlled variables (voltage and current) based on the interleaved principle of operation, although it is not an interleaved split-pi converter. As demonstrated along the paper, the MBS split-pi converter can be controlled with current or voltage feedback in any of the dc interfaces, while the common dc-link voltage is controlled by the dc interface where the source is connected. The adopted current and voltage control schemes, as well as the pulse-width modulation, are presented and comprehensively explained. The validation is presented for the main operation modes, where it is possible to verify the claimed distinguishing features of the proposed MBS split-pi converter.

Nowadays, the majority of electronic equipment behave as nonlinear loads, introducing Power Quality (PQ) problems into the Power Grid (PG), namely, current harmonics and low power factor. These PQ problems contribute to the reduction of the efficiency of the transmission and distribution PG, as well as induce the malfunctioning of sensitive loads connected to the PG. Therefore, the development of equipment able to mitigate these PQ problems is extremely important. In this context, this paper presents a novel single-phase Shunt Active Power Filter (SAPF) based on a current-source converter, where the key differencing factor, when compared with the conventional approach, is the reduced dc-link. As the proposed topology requires a reduced dc-link, it represents a relevant advantage, since a typical current-source converter needs an inductor with a high inductance in dc-link, which results in higher losses, costs and component sizing. The proposed SAPF with reduced dc-link is introduced in detail along the paper and a comprehensive comparison with the conventional SAPF is established based on computer simulations. Besides, an experimental validation was carried-out with a developed laboratory prototype, validating the main advantages of the proposed SAPF with reduced dc-link.

This paper presents the experimental validation of a unified three-port topology, integrating a renewable energy source (RES) and an energy storage system (ESS) (or an electric vehicle) with the grid-interface operating as active power filter (APF). The proposed topology is based on a three-phase grid-interface (whose role is to operate as a APF grid-tied inverter capable of compensating current harmonics, imbalanced currents and low power factor), on a RES-interface for solar photovoltaic (PV) panels (whose role is to extract the maximum power from the PV panels), and on an ESS-interface for batteries (whose role is to store/inject energy according to the power management of the electrical installation). The paper presents the control algorithms for each interface within the scope of the different operation modes allowed by the unified three-port topology. Simulation and experimental results are presented in order to validate the distinguishing aspects of the proposed unified three-port topology.

Smart grids are incessantly contemplating new challenges about power electronics technologies, and this paper focuses on the application of solid-state transformers (SSTs) and the forthcoming perspective of hybrid AC/DC grids. In such perspective, a multilevel bidirectional four-port (MB4P) DC-DC converter is proposed to be integrated in a three-phase SST. It interfaces the SST through three independently ports, corresponding to the three-phases, and the other port is used to create a DC grid. The proposed MB4P DC-DC converter has as main features a multilevel operation with seven voltage levels as function of the voltages on both DC sides, as well as the interleaved operation, where the controlled variables have a ripple with a frequency six times higher than the switching frequency. Furthermore, it can operate in buck or boost modes, and with current or voltage control. Besides the voltage and current control, specific attention is given to the proposed PWM. The advanced attributes of the MB4P DC-DC converter are proven by computer simulations and by analytical description, both exploring steady-state and transient-state distinctive requirements.

DC power grids present significant advantages over AC power grids, namely higher stability and controllability, and the absence of harmonic currents and reactive power. Moreover, DC grids facilitate the interface with renewable energy sources (RES) and energy storage systems (ESS). DC grids can be either unipolar or bipolar, where the latter consists of three wires and provides higher flexibility, reliability and transmission capacity. However, failures in bipolar DC grids (especially in the power semiconductors) can occur. The consequences of these failures can result in increased costs, depending on the damage, e.g., if it occurs a wire of the DC grid or in the connected power converter. Thus, in this paper is presented a fault analysis of a non-isolated three-level DC-DC converter used to interface solar photovoltaic (PV) panels into a bipolar DC power grid. The fault analysis is conceived through computational simulations, where can be observed the performance of the presented DC-DC converter under fault conditions in each wire of the bipolar DC grid. The simulation results demonstrate the DC-DC converter operating in two different situations: steady-state and transient-state. The control strategy applied in normal and fault conditions, as well as the different operation modes, are explained in detail.

No abstract

No abstract