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Low-voltage grid-connected microgrids rely on the exploitation of inverter-interfaced distributed energy resources (DERs) in order to feed loads and to achieve bidirectional power flow controllability at their point of common coupling (PCC) with the upstream grid. However, adverse operational conditions, such as the existence of DERs of different operation natures, DERs of non-equal power ratings, as well as the occurrence of non-steady and non-sinusoidal grid voltage scenarios, bring complications to microgrid energy management. Consequently, control strategies employed to coordinate DERs in dispatchable microgrids need to be resilient to such non-ideal conditions. Hence, this paper demonstrates that a multi-purpose strategy, so-called the Generalized Current-Based Control (GCBC) approach, is capable of steering DERs under such adverse operational scenarios, ensuring proportional current sharing among them while also regulating the microgrid power dispatchability at the PCC. The discussions are supported by an extensive experimental validation on a laboratory-scale single-phase microgrid prototype, demonstrating that the GCBC approach allows DERs of different operational natures to be coordinated, respecting their power ratings, and allowing the single-controllable microgrid to endure operation under distorted voltages and support voltage ride-through conditions. [ABSTRACT FROM AUTHOR]

The presence of single-phase distributed generators unevenly injecting active power in three-phase microgrids may create undesired upstream current unbalance. Consequently, voltage asymmetry and even active power curtailment may occur in such networks with negative economic impact. Thus, this paper proposes an optimal multiobjective approach to regulate the active and reactive power delivered by distributed generators driven by a three-layer hierarchical control technique in low-voltage microgrids. This method does not require previous knowledge of network parameters. The multiobjective algorithm is implemented in the secondary level achieving optimal dispatch in terms of maximizing the active power generation, as well as minimizing the reactive power circulation and current unbalance. By the existence of a utility interface three-phase converter placed at the point-of-common-coupling, the proposed control can regulate the power circulating among the microgrid phases, and the microgrid structure can withstand grid-connected and islanded operating modes. The path for interphase power circulation through the DC-link of the utility interface allows the multiobjective algorithm to achieve better results in terms of generation and compensation compared to the system without utility interface. The proposed method is assessed herein by computational simulations in a three-phase four-wire microgrid under realistic operational conditions. [ABSTRACT FROM AUTHOR]

This paper presents a complete wave-to-wire approach to the modeling of wave energy farms. It captures all the main peculiarities of such applications, from the variability of sea waves to the issues related to the grid integration of a multi-MW wave farm, including the hydrodynamic modeling of wave energy converters (WECs). The paper specifically discusses the different levels of control of a wave farm and their integration and coordination. These are crucial to meet the power quality requirements at the point of common coupling (PCC) and ensure the efficiency of the power transfer from the waves to the main electric grid. A specific real-time technique for the centralized control of a wave farm is also proposed, which is exemplified with reference to the PCC voltage control in the real test case of bimep. Critical cases of weaker grids are also considered to extend the validity of the analysis. [ABSTRACT FROM PUBLISHER]

The Conservative Power Theory (CPT) emerged in recent decades as a theoretical framework for coping with harmonically distorted and unbalanced electric networks of ac power systems with a high participation of converter interfaced loads and generation. The CPT measurements are intrinsically linked to moving averages (MA) over one period of the grid. If the CPT is to be used in a low-inertia isolated-grid scenario, which is subjected to frequency variations, adaptive moving averages (AMA) are necessary. This paper reviews an efficient way of computing MAs and turns it into an adaptive one. It shows that an easily available variable time delay block, from MATLAB, causes steady-state errors in the measurements when the grid frequency varies. A new variable time delay block is, thus, proposed. Nonetheless, natural pulsations in the instantaneous power slip through MAs when the discrete moving average window does not fit perfectly the continuously varying period of the grid. A method consisting of weighing two MAs is reviewed and a new and effective hybrid AMA is proposed. The CPT transducers with the different choices of AMAs are compared via computer simulations of a single-phase voltage source feeding either a linear or a nonlinear load. [ABSTRACT FROM AUTHOR]

This paper proposes a preliminary design tool for active power filters' (APFs) solutions to be applied in offshore oil and gas platforms, where power quality indices are typically low, and reactive power compensation and current harmonic mitigation are often desired. The proposed approach considers that APF selection and rating is a trade-off between performance and size, and that both component and system aspects need to be optimized to achieve a well-tailored solution. As size and weight are critical constraints in offshore applications, possible benefits of using Silicon Carbide (SiC) switches for the APF implementation are investigated. Moreover, different compensation strategies are compared, varying the connection point of the APF between two different voltage levels and assigning the APFs different compensation goals. Improvements in power quality indices, as well as APFs rating, number of components, power losses, and filter size, have been considered for both SiC and Silicon-based solutions to identify the best trade-offs suitable for the considered, energy intensive industrial application. [ABSTRACT FROM AUTHOR]

This paper investigates power quality issues in a wind-powered offshore oil and gas platform operating in island mode. Topics of interest are the negative effects that load and wind power variability have on the electrical system frequency and voltage; and how those influence the gas turbine operation. The authors discuss how smart load management together with energy storage can mitigate those effects, and propose a control algorithm for that. Simulations in MATLAB/Simulink demonstrate that the proposed energy storage controller reduces frequency and voltage variations in a case study. Moreover, the paper presents a methodology to derive a simplified model of the hybrid energy system that reduces simulation time in at least two orders of magnitude. The latter can be a useful tool for optimization algorithms evaluating a huge number of scenarios, especially those dealing with economical dispatch of generators or sizing of energy storage systems. [ABSTRACT FROM AUTHOR]

Considering the high penetration of distributed generators in low-voltage grids, establishing a coordinated operation of their grid-tied inverters has become imperative to move towards the implementation of smart grids. Yet, knowing that mitigation of power quality issues such as reactive power, current unbalance and harmonics is of importance within such a context, this work proposes a master/slave control approach, which uses a communication means of low-bandwidth, to flexibly coordinate four-leg inverters dispersed in three-phase four-wire networks. Their coordination is attained by means of a current-based approach, allowing the sharing of active, reactive, harmonic and unbalance currents drawn by loads. The control strategy also regulates the power flow at the point of common coupling of the low-voltage network, while proportionally steering inverters according to their nominal capabilities. In addition to the offering of selective harmonic mitigation, the control approach provides distributed and decoupled unbalance compensation, in partial or total portion, based on concepts from the Conservative Power Theory. Consequently, extraction of sequence components or implementation of virtual impedance control loops are not required. The proposed strategy is evaluated based on multiple simulation results, considering the CIGRE's European low-voltage distribution benchmark, including six distributed inverters, as well as linear and nonlinear loads. • Distributed and decoupled unbalanced compensation in low-voltage networks. • Distributed and selective harmonic mitigation through parallel inverters. • Fully-controllable power flow control at the network's point of common coupling. • Coordinated control of four-leg inverters in three-phase four-wire networks. • Proportional current sharing among four-leg inverters. [ABSTRACT FROM AUTHOR]