This paper presents two hybrid filter topologies applied to a hot strip mill electrical system with cycloconverters, to evaluate the harmonic compensation and damping of harmonic resonance. In addition, an evaluation of the performance of hybrid filters in reducing the current rating of the passive filter is also presented. The most relevant waveforms of the system and its harmonic spectrum are analyzed, to assess the performance of each filtering structure in improving the power quality. The results obtained through digital simulation show that a series hybrid filter provides harmonic damping and allows enhancing the harmonic compensation characteristics of the passive filtering system, using an active filter of lower rated power compared to a parallel hybrid filter. However, the series hybrid filter does not present good filtering characteristics in the high frequency range, what can be performed by a parallel hybrid filter with a higher rating.

Voltage regulation in low-voltage (LV) distribution grids is essential to increase the penetration of photovoltaic (PV) rooftop units. Hence, PV inverters are commonly embedded with volt-var (VV) and volt-watt (VW) control functions to support the grid voltage regulation within the grid codes. Such an approach usually increases the LV grid hosting capacity (HC) by 1.5 to 2 times at the cost of energy curtail. Thus, the use of decentralized battery energy storage systems (BESS) near to nodes sensible to overvoltage become appealing, as it stores energy without creating current circulation within the grid. However, there are still gaps in sizing of decentralized BESSs and in quantifying their improvement in terms of HC. Thus, this paper contributes with a comprehensive study that evaluates the HC of a generic LV grid comprised of PV units with embedded VV and VW control functions, and proposes a methodology to guide the sizing of small decentralized BESS used to increase the grid HC. Using OpenDSS software, the VV and VW control functions are evaluated and compared with a base scenario where PV units operate at a unity power factor. The active power curtailment is used to size decentralized BESS to absorb excess energy, avoiding PV active power derating. Results show that BESS units, sized at about 5-10% of the PV power capacity, can reduce revenue impacts and increase HC by over 30% in LV grids.

Distributed energy sources, mainly from renewable energy, have been increasingly applied to commercial facilities and residences. The power control of the various distributed sources is a fundamental task and is being studied in several recent papers. Among the current works many have explained the use the so called synchronverter control strategy to regulate the active and reactive power flow for three-phase distributed generators. Nevertheless, none of them have addressed a proposal for single-phase synchronverter power systems. In this paper, a brief review of synchronverters is presented. Thereupon, it is proposed a single-phase synchronverter for residential distributed generators, such as photovoltaic power system. The proposed single-phase model is based on the conventional structure of the three-phase control model. Simulation results are shown in order to validate the single-phase synchronverter, including evaluating performance in the presence of power quality issues, such as voltage sag and grid harmonic distortion, in both grid-connected and islanded mode.

The power system is experiencing an expansion of distributed generators connected to the low voltage network. In this context appears the so-called microgrid, which consists of a group of electrical microsources, loads and storage elements controlled as a single unit whose may operate either connected to or islanded from the main grid. The microgrid can be arranged in a centralized structure, e.g., master-slave architecture, where the centralized converter, i.e., grid-forming converter plays a crucial role. It must promptly respond to load and grid variations, manage the transition from grid-connected to islanded mode, and define the voltage and frequency during islanded operation. This paper proposes a repetitive control tuned at even harmonic orders applied to a grid-forming converter instead of repetitive control tuned at odd harmonics as usual. Such grid-forming is devised in synchronous reference frame and applied to a centralized AC microgrid, particularly under islanded operation. Such microgrid is composed of linear and nonlinear load, a photovoltaic inverter and the grid-former converter itself. Through simulation results the microgrid power flow and power quality are analyzed evaluating the grid-forming converter operation.