Nowadays, new challenges arise relating to the compensation of power quality problems, where the introduction of innovative solutions based on power electronics is of paramount importance. The evolution from conventional electrical power grids to smart grids requires the use of a large number of power electronics converters, indispensable for the integration of key technologies, such as renewable energies, electric mobility and energy storage systems, which adds importance to power quality issues. Addressing these topics, this paper presents an extensive review on power electronics technologies applied to power quality improvement, highlighting, and explaining the main phenomena associated with the occurrence of power quality problems in smart grids, their cause and effects for different activity sectors, and the main power electronics topologies for each technological solution. More specifically, the paper presents a review and classification of the main power quality problems and the respective context with the standards, a review of power quality problems related to the power production from renewables, the contextualization with solid-state transformers, electric mobility and electrical railway systems, a review of power electronics solutions to compensate the main power quality problems, as well as power electronics solutions to guarantee high levels of power quality. Relevant experimental results and exemplificative developed power electronics prototypes are also presented throughout the paper.

The main objective of this tutorial is to present the basic concepts on the instantaneous p-q Theory and then show its applicability for controlling switching converters connected in a micro-grid. These converters can be used for connecting renewable energy sources (solar, wind, and others) to the micro-grids or for harmonic, reactive power or unbalance compensation, and even for voltage regulation. The emphasis is given on the compensation characteristics derived from the p-q Theory, and simulation results of test cases are shown. Special attention is put on the oscillating component of the instantaneous real power, as it may produce torque oscillations or frequency variations in weak systems (micro-grids) generators. This oscillating component, as defined in the p-q Theory, gives the amount of oscillating energy between the source and the load, and its compensation through a switching compensator must have an energy storage element to exchange it with the load. With the p-q Theory this energy storage element can be easily calculated as a function of the average component of the instantaneous real power, which depends on the observation period.

This paper presents a three-phase four-wire Shunt Active Filter that compensates power quality problems and can also interface renewable energy sources with the electric grid. The inverter stage of the active filter is based in a two-level four-leg inverter and its control is based in the Theory of Instantaneous Reactive Power (p-q Theory). The filter is capable of compensating power factor, unbalance, and current harmonics. Additionally it can also make the interface between renewable energy sources and the electrical system, injecting balanced practically sinusoidal currents (with low THD).

This study presents control algorithms for a new unified power quality conditioner (UPQC) without the series transformers that are frequently used to make the insertion of the series converter of the UPQC between the power supply and the load. The behaviour of the proposed UPQC is evaluated in presence of voltage imbalances, as well as under non‐sinusoidal voltage‐and current conditions. The presented algorithms derive from the concepts involving the active and non‐active currents, together with a phase‐locked‐loop circuit. Based on these real‐time algorithms, and considering the proposed hardware topology, the UPQC is able to compensate the harmonic components of the voltages and currents, correct the power factor, and keep the load voltages regulated, all of this in a dynamic way, responding instantaneously to changes in the loads or in the electrical power system. The control algorithms were distributed in a two‐DSP digital control architecture, without any communication between them. Consequently, can be increased the sampling frequency of the acquired voltages and currents and improve the UPQC performance. Furthermore, some constraints of the proposed UPQC are evidenced, particularly when the main voltages are imbalanced. Simulation and experimental results are presented to verify the UPQC performance under transient and steady state conditions.

This paper presents the comparison between two three-phase Shunt Active Power Filters (SAPFs), one with Current-Source Inverter (CSI) and the other with Voltage-Source Inverter (VSI), which are used to compensate current harmonics and to control reactive power. The control algorithm of both SAPFs is based on the Instantaneous Reactive Power Theory (p-q Theory). The comparison here presented focuses on the Total Harmonic Distortion (THD) and RMS values of the compensated currents, and in the Total Power Factor (TPF) of the installation.