Smart microgrids offer a new challenging domain for power theories and compensation techniques, because they include a variety of intermittent power sources, which can have dynamic impact on power flow, voltage regulation, and distribution losses. When operating in the islanded mode, low-voltage smart microgrids can also exhibit considerable variation of amplitude and frequency of the voltage supplied to the loads, thus affecting power quality and network stability. Due to limited power capability in smart microgrids, the voltage distortion can also get worse, affecting measurement accuracy, and possibly causing tripping of protections. In such context, a reconsideration of power theories is required, since they form the basis for supply and load characterization, and accountability. A revision of control techniques for harmonic and reactive compensators is also required, because they operate in a strongly interconnected environment and must perform cooperatively to face system dynamics, ensure power quality, and limit distribution losses. This paper shows that the conservative power theory provides a suitable background to cope with smart microgrids characterization needs, and a platform for the development of cooperative control techniques for distributed switching power processors and static reactive compensators.

Penetration rate of grid-connected photovoltaic (PV) generation to the existing utility grid is rapidly increasing over the years. Since the power generated from PV systems fluctuate according to the weather condition, e.g., cloud passing, this can significantly disturb the stability of a weak utility grid. The integration of energy storage devices and its ramp-rate control technique are required to reduce the impact of PV systems output fluctuations and augment the stability of the utility grid. In this paper, ramp-rate control is applied to the direct connection of energy storage devices in PV generation system configuration. The direct connection of supercapacitors string and battery combination scheme is proposed to reduce the number of power converters so that the efficiency of the system is increased. In this work, the PV system output is controlled by directly control the energy storage system (ESS) to limit the changing rate of PV output to desired ramp-rate value. Hence, reducing the battery charge/discharge cycles and extending the expected lifetime of the ESS. The performance of the proposed direct connection scheme of ESS and its ramp-rate control strategy is verified using a 1-kW PV system prototype.

This paper presents a flexible control technique for power electronics converters, which can function as an active power filter, as a local power supply interface, or perform both functions simultaneously. Thus, it can compensate for current disturbances while simultaneously injecting active power into the electrical grid, transforming the power converter into a multifunctional device. The main objective is to use all the capacity available in the electronic power converter to maximize the benefits when it is installed in the electricity grid. This objective is achieved by using the orthogonal current decomposition of the conservative power theory. Each current component is weighted by compensation coefficients (k _i ), which are adjusted instantaneously and independently, in any percentage, by means of load conformity factors ( λ _i ), thus providing online flexibility with respect to the objectives of compensation and injection of active power. Finally, simulated and experimental results are presented to validate the effectiveness and performance of the proposed approach.

Four-wire microgrids (MGs) and distribution systems are inherently unbalanced with the presence of negative and zero sequence components in voltages and currents. In small autonomous systems, the imbalance, in addition to the harmonic distortion produced by nonlinear loads, can significantly affect the power quality, loadability, and stability of the system. Furthermore, in isolated networks with significant generation from intermittent renewable energy sources, the stiffness of the system is reduced and this could amplify the effects of imbalance on the stability and power quality. To mitigate some of these problems, a novel methodology based on the application of a four-leg active power filter is proposed in this paper. The control of the compensator is based on the conservative power theory augmented by resonant controllers. The behavior of the proposed system is demonstrated using an experimental prototype deployed in a laboratory scale MG.

Ln recent years, the concept of decentralising power generation through the deployment of distributed generators (DGs) has been widely accepted and applied, driven by the growing market of renewable energy sources. These DGs are normally equipped with a switching power interface, acting as front end with the grid. This paper proposes a multi‐task control strategy for distributed generation systems that simultaneously allows the DG to inject the available energy, as well as to work as a voltage drop compensator or as an active power filter, mitigating load current disturbances and improving power quality of the grid. The main contribution of the proposed system, with respect to other solutions in the literature, is that the proposed control loops are based on the Conservative Power Theory decompositions. This choice provides decoupled power and current references for the inverter control, offering a very flexible, selective and powerful control strategy for the DG. The paper also discusses the choice of the current waveform for injecting/absorbing active power into/from the grid, and both sinusoidal and resistive references have been compared in terms of damping capability. Finally, simulation and experimental results are provided in order to validate the proposed functionalities of the DG control system.

Smart grids offer a new challenging domain for power theories and compensation techniques, because they include a variety of intermittent power sources which can have dynamic impact on power flow, voltage regulation, and distribution losses. When operating in the islanded mode, smart micro-grids can also exhibit considerable variation of amplitude and frequency of the voltage supplied to the loads, thus affecting power quality and network stability. Due to the limited power capability of smart micro-grids, voltage distortion can also get worse, affecting measurement accuracy and possibly causing tripping of protections. In such a context, a reconsideration of power theories is required, since they form the basis for supply and load characterization and accountability. A revision of control techniques for harmonic and reactive compensators is also required, because they operate in a strongly interconnected environment and must perform cooperatively to face system dynamics, ensure power quality and limit distribution losses. This paper shows that the Conservative Power Theory (CPT) provides a suitable background to cope with smart grids characterization needs, and a platform for the development of cooperative control techniques for distributed switching power processors and static reactive compensators.