Communication infrastructure (CI) in microgrids (MGs) allows for the application of different control architectures for the secondary control (SC) layer. The use of new SC architectures involving CI is motivated by the need to increase MG resilience and handle the intermittent nature of distributed generation units. The structure of SC is classified into three main categories, including centralized SC (CSC) with a CI, distributed SC (DISC) generally with a low-data-rate CI, and decentralized SC (DESC) with communication-free infrastructure. To meet the MGs’ operational constraints and optimize performance, control and communication must be utilized simultaneously in different control layers. In this survey, we review and classify all types of SC policies from CI-based methods to communication-free policies, including CSC, averaging-based DISC, consensus-based DISC methods, containment pinning consensus, event-triggered DISC, washout-filter-based DESC, and state-estimation-based DESC. Each structure is scrutinized from the viewpoint of the relevant literature. Challenges such as clock drifts, cyber-security threats, and the advantage of event-triggered approaches are presented. Fully decentralized approaches based on state-estimation and observation methods are also addressed. Although these approaches eliminate the need of any CI for the voltage and frequency restoration, during black start process or other functionalities related to the tertiary layer, a CI is required. Power hardware-in-the-loop experimental tests are carried out to compare the merits and applicability of different SC structures.

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On the Secondary Control Architectures of AC Microgrids: An Overview

This paper proposes the design of optimal and robust coordinated controller of hybrid energy storage system in a naval dc microgrid (MG) application. It is able to mitigate the negative effects of the pulsed power loads and meet the practical limitations of both converters input control and state variables signals based on IEEE standards. To do this, first, the dynamic model of the dc MG, which can represent in either all-electric aircraft or shipboard power systems, is developed. Second, a novel model predictive controller (MPC) for energy storage converters is proposed such that all of the mentioned hard constraints are guaranteed. Third, a linear matrix inequality approach is used to solve the MPC conditions. Finally, to evaluate the applicability and effectiveness of the proposed approach, some experimental tests are extracted. Obtained results verify better performance of the proposed approach over other state-of-the-art control techniques.

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Model Predictive Control of DC–DC Converters to Mitigate the Effects of Pulsed Power Loads in Naval DC Microgrids

Renewable energy resources are becoming the dominating element in power systems. Along with de-carbonization, they transform power systems into a more distributed, autonomous, bottom-up style one. We speak of Smart Grid and Microgrid when distributed energy resources take over. While being a means to improve technical and financial efficiency, planning, operations, and carbon footprint, it is these new technologies that also introduce new challenges. Reliability is one of them, deserving a new way of describing and assessing system and component reliability. This paper introduces a new reliability framework that covers these new elements in modern power systems. It can be seen that reliability assessment of modern power systems also requires introducing local reliability concepts as well as incorporating different electro-magnetic/mechanical stability issues.

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An Overview on the Reliability of Modern Power Electronic Based Power Systems

This letter proposes a new modified model predictive control (MPC) to compensate for voltage and frequency deviations with higher bandwidth for an ac shipboard microgrid (MG). The shipboard power system (SPS) and islanded MGs have a reasonable analogy regarding supplying loads with local generations. However, a great number of vital imposing pulse loads and highly dynamic large propulsion loads in the SPS make the frequency and voltage regulation a complicated issue. Conventional linear control methods suffer from high sensitivity to parameter variations and slow transient response, which make big oscillations in the frequency and voltage of the SPS. This letter addresses the problem by proposing a novel finite control set MPC to compensate for primary frequency and voltage deviations with higher bandwidth and order of magnitude faster than the state of the art. Furthermore, a single input interval type-2 fuzzy logic controller is applied in secondary level to damp the steady-state deviations with higher bandwidth. Finally, hardware-in-the-loop experimental results prove the applicability of the proposed control structure.

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Robust and Fast Voltage-Source-Converter (VSC) Control for Naval Shipboard Microgrids

Power quality of inverter-based microgrids is a challenging issue due to nonlinearities of inverters, multiple resonance modes of network impedance, and unbalanced and nonlinear loading condition. The ideal solution is to assure the best power quality at the common bus to which loads are connected, and share the negative and harmonic sequence currents between the inverters without any communication. However, it is difficult to achieve this objective with existing virtual-impedance-based methods when nonlinearities of inverters, e.g., dead time, are not negligible. In this paper, a novel cost-function-based method is proposed to solve this problem. The proposed cost functions are optimized using continuous-control-set model predictive control. As unknown nonlinearities of inverters can be observed by introducing disturbance models, even when they are not negligible, the presented method can compensate bus voltage unbalance and harmonics and share the compensated current between inverters autonomously, with neither communication nor upper level controller. Parameter tuning of the proposed method is the key to achieve the balance between bus voltage quality and current sharing, and between stability and fast response. Experimental results demonstrate that the proposed control scheme is effective even under conditions of large inverter nonlinearities.

Cost-Function-Based Microgrid Decentralized Control of Unbalance and Harmonics for Simultaneous Bus Voltage Compensation and Current Sharing

This paper proposes an improvement of the finite control set model predictive control (FCS-MPC) strategy for enhancing the voltage regulation performance of a voltage source converter (VSC) used for standalone microgrid and uninterrupted power supply (UPS) applications. The modification is based on tracking the voltage reference trajectory derivative using a single step prediction horizon. The main results are: 1) reduction of the total harmonic distortion (THD) and better tracking of fundamental voltage component compared with the conventional FCS-MPC, 2) lower computational burden compared to multi-step prediction horizon strategies, and 3) preserved fast dynamic response to abrupt load changes. These findings have been validated for both linear and nonlinear loads through experimental verification on a 15kW two-level VSC prototype.

Improved model predictive control for high voltage quality in microgrid applications

Finite control set model predictive control (FCS-MPC) methods in different power electronic applications are gaining considerable attention due to their simplicity and fast dynamics. This paper introduces an assessment of the two-level three-phase voltage source converter (2L-VSC) utilizing different MPC schemes with and without a modulation stage. In order to perform such a comparative evaluation, 2L-VSC efficiency and total harmonics distortion of the voltage (THDv) have been investigated, when considering a linear load. The results demonstrate the performance of different MPC algorithms through an experimental verification on a Danfoss converter, and a set of analyses have been studied using the PLECS and MATLAB/SIMULINK together. It can be concluded that a comparable performance is achieved by using conventional MPC (CMPC), improved MPC (IMPC), periodic MPC (PMPC), and MPC scheme with modulator (M 2 PC) controllers. The assessment is critical to classify the strategies as mentioned earlier according to their efficiency. Furthermore, it gives a thorough point of view on which algorithm is suitable for the grid-forming applications.

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Performance Assessment of Grid Forming Converters Using Different Finite Control Set Model Predictive Control (FCS-MPC) Algorithms

This paper embeds a high bandwidth distributed hierarchical control structure for a power electronic based ac microgrid. Conventionally, hierarchical linear control loops are applied to control the grid frequency and voltage. However, they suffer slow dynamic response and high sensitivity to parameter variations. In this paper, high bandwidth control approach realized with a finite control set model predictive control (FCS-MPC) scheme to control multiple voltage source converters (VSCs). Furthermore, droop control and virtual impedance are employed to share active and reactive power. At the upper level distributed secondary control can be programmed with much higher bandwidth compare to linearized cascaded control structures. Simulation and experimental results indicate that voltage and frequency have been regulated order of magnitude faster than state of the art.

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Model Predictive Control Approach for Distributed Hierarchical Control of VSC-Based Microgrids

It is well-known that the presence of non-linear loads in the distribution system can impair the power quality. The problem becomes worse in microgrids and power electronic-based power systems as the increasing penetration of single-phase distributed generation may result in a more unbalanced grid voltage. Shunt active power filters (SAPFs) are used for improving the power quality and compensating for the unbalance grid voltage. This study presents a modification of the classical control structure based on the finite control set model predictive control (FCS-MPC). The proposed control structure can retain all the advantages of FCS-MPC, while improving the input current quality. Furthermore, a computationally efficient cost function based on only a single objective is introduced, and its effect on reducing the current ripple is demonstrated. The presented solution provides a fast response to the transients as well as compensates for the unbalanced grid voltage conditions. A straightforward single loop controller is compared to the conventional way of realising the active power filters, which is based on space vector pulse width modulation. The simulation results have been obtained from MATLAB/SIMULINK environment, while the obtained experimental results, utilising a 15 kVA power converter, highlight the effective performance of the proposed control scheme and verifies the introduced MPC-based method as a viable control solution for SAPFs.

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Harmonics mitigation and non-ideal voltage compensation utilising active power filter based on predictive current control

This paper proposes an enhanced finite control set model predictive control (FCS-MPC) strategy for voltage source converter (VSC) with a LC output filter. The proposed control scheme is based on tracking the voltage reference trajectory by using only a single-step prediction within the controller horizon. Besides, the suitability of different frequency control schemes with the proposed scheme to prevent from inherent variable switching behaviour of conventional FCS-MPC is investigated. Based on that, the proposed method targets two major factors influencing power quality in grid forming applications by enhancing the output voltage harmonic distortion and also preventing variable switching behaviour of FCS-MPC. Although compared to multi-step prediction approaches, only a single-step multi-objective cost function to improve computation efficiency is utilized, the introduced control schemes are able to deliver higher power quality compared to its counterpart methods as well. Furthermore, the effect of different applied cost functions on the transient response of the system is studied and investigated for the future use of the VSC in microgrids (MGs). The effectiveness of the proposed scheme was assessed by simulation using MATLAB/SIMULINK and experiment using a 5.5 kVA VSC module and the results were in good agreement.

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M. Alhasheem

Papers

Improved model predictive control for high voltage quality in microgrid applications

Performance Assessment of Grid Forming Converters Using Different Finite Control Set Model Predictive Control (FCS-MPC) Algorithms

Model Predictive Control Approach for Distributed Hierarchical Control of VSC-Based Microgrids

Harmonics mitigation and non-ideal voltage compensation utilising active power filter based on predictive current control

Model Predictive Control of Grid Forming Converters with Enhanced Power Quality