This paper presents novel control algorithms for a transformerless hybrid active filter without current sensors. The hybrid active filter is composed of a shunt active filter in series with a passive filter tuned nearby 5th harmonic frequency. This structure allows reducing the DC-Link voltage, which is very important when the connection of hybrid active filters to power grids at medium voltage level is desirable. The control algorithms employed to determine the 5th harmonic current are derived from the instantaneous reactive power theory, pq-theory, together with a PLL circuit. Previous works introduced control algorithms for providing selective harmonic filtering with the active filter acting as a current-controlled voltage source. Dissimilarly, this work conceives the active filter operating as a voltage-controlled voltage source, besides providing selective harmonic filtering. Based on the proposed algorithms, the number of inputs is reduced and the algorithms to determine the 5th harmonic current becomes more simple. In a comparative analysis, simulation results considering the active filter as a current-controlled voltage source and voltage-controlled voltage source, in transient and steady-state conditions, are presented.

The modular multilevel converter (MMC) is a keystone of modern energy transmission systems. Consequently, there is an ongoing pursue for mathematical models to represent it under different configurations and control approaches. In short, this paper introduces an analytical Thévenin-equivalent model for representing the MMC when it is controlled with inner current- and an outer voltage-loop altogether. The model is based on a linearized representation of the converter and conveys the dynamics of passive components, such as submodule capacitors and arm reactors, as well as both control loops. Besides that, the proposed model is divided into a close-loop transfer matrix and the equivalent impedance matrix, both of which represent the relationships between the ac-side dq voltages and currents. We also propose a framework for implementing electromagnetic–transient simulations using the impedance model of this power electronic converter. The framework reduces a multi-bus power grid to a multi-input multi-output (MIMO) feedback system where impedance/admittance matrices of the MMC and other grid elements compose its loops. For validation purposes, it is considered a three-bus power grid comprising one MMC and another two grid-connected VSC. The proposed model was validated by comparing its results with a switching-level PSCAD model of the system.

A power electronic interface that integrates a photovoltaic string with a single-phase grid to feed a three-phase induction motor, while driving a fan-type load, is presented. The inte ...

This paper addresses a novel control algorithm for a selective active filter compensating specific harmonic currents and the fundamental negative-sequence component of the load current. The proposed control algorithm combines the resonant controller with a PLL circuit to determine the current references in αβ frame. Previous works introduced control algorithms for a selective active filter connected to radial grid, in dq frame, where the load currents were no longer used to determine the current references. However the transient performance of the active filter was compromised, once the current references are indirectly determined and, moreover, due to the presence of low-pass filters. Now, this work proposes an algorithm where the low-pass filters is removed, therefore the overall control algorithm becomes simpler to be implemented with the active filter presenting a faster transient response. Simulation results are presented to evaluate the proposed algorithm with the active filter compensating symmetrical harmonic currents under transient- and steady-state conditions.

This paper aims at improving the Enhanced-PLL (E-PLL) to mitigate the transient low-frequency oscillations, which is inherent to single-phase circuits. These improvements resulted in a new PLL configuration, designated here as the Double-Frequency Mitigation SOGI-EPLL, or simply DFM-SOGiEPLL. We integrate the EPLL with a Second-Order Generalized Integrator (SOGI), by modifying the computation of the internal error signals of the phase-and-frequency loop and the amplitude loop. Thus, the proposed DFM-SOGiEPLL is able to extinguish transient low-frequency oscillations, in a short time period, in comparison to the conventional EPLL. A dynamic model approach of both EPLLs, including four different test-cases, was implemented through numerical simulations and hardware experiments to verify the better performance of the proposed one.