Distributed Power Generation Systems Research Articles

[formula omitted] gain-scheduled dynamic output feedback control with transient performance applied to electrical microgrid

This paper introduces an approach for designing gain-scheduled dynamic output feedback controllers for continuous-time Linear Parameter-Varying (LPV) systems. The aim is to improve transient response by incorporating both D-stability and H∞ criteria into the synthesis conditions. We achieve this by employing changes of variables and congruence transformations, which lead to new synthesis conditions expressed as linear matrix inequalities. Additional fine-tuned scalar parameters can be used to enhance further the controller performance in terms of less conservative H∞ guaranteed costs. To assess the effectiveness of our proposed synthesis procedure, we conduct computational experiments in the context of a microinverter-based distributed power generation system. These experiments take into account real-world operational characteristics, providing a comprehensive evaluation of our approach. The results demonstrate that the designed controller effectively ensures the desired closed-loop system behavior, even when dealing with state noise and discretization errors originating from digital implementation.

Application of Fractional Order PI/PID Voltage Controllers for Three-Phase Voltage Source Inverter with Dynamic Load

Purpose: With the depletion of fossil fuels, the landscape of electrical energy generation has witnessed a transformative shift towards alternative sources such as fuel cells and photovoltaic (PV) systems that produce direct current (DC) electricity. In the realm of distributed power generation, three-phase voltage source inverters (VSIs) are extensively utilized for converting energy from DC sources to alternating current (AC) for the grid or loads. The pivotal objective of this study is to investigate and compare the performance of fractional-order Proportional-Integral (PI) and Proportional-Integral-Derivative (PID) control structures against their integer-order counterparts in the voltage control loop of a VSI connected to a dynamic load system.
 Materials and Methods: The research employs frequency response analysis to design and implement both fractional-order PI/PID and integer-order PI/PID control structures for the voltage control loop. The simulation of the controlled system is conducted using MATLAB/Simulink, considering two distinct test scenarios – unstable and stable dynamic load conditions. The primary focus is on analyzing the inverter output voltage in the d-q axis under these scenarios.
 Findings: The analysis of the simulation results reveals noteworthy distinctions between the fractional-order and integer-order PI/PID controllers in the context of controlling the inverter system with dynamic loads. These findings shed light on the advantages of employing fractional order controllers, particularly in dynamic load scenarios, showcasing superior performance in comparison to their integer-order counterparts.
 Implications to Theory, Practice and Policy: The study's outcomes hold significant implications for the theory and practice of voltage control in distributed power generation systems. The superiority of fractional-order PI controllers underscores their potential for enhancing power quality, especially in systems with unstable and time-varying dynamic loads. These insights can inform the development of more effective control strategies for voltage source inverters, influencing both theoretical frameworks and practical applications. Policymakers may consider these findings when formulating regulations and incentives to promote the adoption of advanced control strategies in the evolving landscape of electrical energy generation.

Power quality disturbance mitigation in grid connected photovoltaic distributed generation with plug-in hybrid electric vehicle

In the last twenty years, electric vehicles have gained significant popularity in domestic transportation. The introduction of fast charging technology forecasts increased the use of plug-in hybrid electric vehicle and electric vehicles (PHEVs). Reduced total harmonic distortion (THD) is essential for a distributed power generation system during the electric vehicle (EV) power penetration. This paper develops a combined controller for synchronizing photovoltaic (PV) to the grid and bidirectional power transfer between EVs and the grid. With grid synchronization of PV power generation, this paper uses two control loops. One controls EV battery charging and the other mitigates power quality disturbances. On the grid connected converter, a multicarrier space vector pulse width modulation approach (12-switch, three-phase inverter) is used to mitigate power quality disturbances. A Simulink model for the PV-EV-grid setup has been developed, for evaluating voltage and current THD percentages under linear and non-linear and PHEV load conditions and finding that the THD values are well within the IEEE 519 standards.

Impact of Grid-Connected Inverter Parameters on the Supraharmonic Emissions in Distributed Power Generation Systems

In this paper, a mathematical analysis is presented to show the effect of grid-connected inverter (GCI) parameters on its emissions in the supraharmonic range. This analysis is extended to explain the effect of asymmetry on the emissions of parallel-connected GCIs on distributed power generation systems. The switching harmonics of a GCI appear as bands around the switching frequency and its multiples. A MATLAB/Simulink model is built to perform two studies. In the first study, we use one GCI to examine the effect of the parameters on the emissions, while in the second study, we examine the effect of the asymmetry of two parallel-connected GCIs on the total emission toward the grid. An actual setup is built to verify the results of the mathematical analysis and the simulation study. It is found that the SHs of single-phase GCI amplitude are strongly dependent on the DC-link voltage and the coupling inductor, while the phases of the sideband harmonics only change with changing the injected power. The variation of the injected power does not have any tangible effect on the carrier harmonics.

Power factor control for inverters under high penetration of distributed generation

AbstractThe paper proposes a method to select a power factor for an inverter of distributed power generation systems to keep appropriate voltage of a power system with the high penetration of inverter‐interfaced generation. The increase of inverter‐interfaced power sources, such as wind and photovoltaic power generation, arouses concerns on the voltage fluctuations in a power system. While constant power factor control of an inverter has been studied as a means to stabilize the voltage of a power system, there still remains room to improve the control. The proposed method in the paper selects the power factor based on the R/X ratio of the looking‐back impedance into the interconnected power system. By normalizing the related variables, a general formula is derived for the power factor, and the resultant relationship between the apparent power and voltage of an inverter becomes identical irrespective of the R/X ratio with the control. Sample studies show that, by operating an inverter with the power factor, voltage fluctuations are effectively suppressed even for a power system with the high penetration of inverter‐interfaced generation.

Ultra-low emission power generation utilizing chemically stabilized waste plastics pyrolysis oil in RCCI combustion concept

Emission standards in European Union, designed to reduce the environmental impact of power generation, present a significant challenge for fast-response distributed power generation systems based on internal combustion engines. Regulated emissions, such as NOx and particulate matter present a major concern due to their adverse number of environmental and health effects. Simultaneously, European Union strives towards sustainable management of plastic waste and seeks the ways for its upcycling and production of new fuels and chemicals. As an answer to the presented challenges, the present experimental study addresses the potential for use of chemically stabilized Waste Plastics Oil (WPO), a product of pyrolysis process of waste plastics in a Reactivity Controlled Compression Ignition (RCCI) combustion concept. To establish a reactivity-controlled combustion, the study uses a combination of methane (a model fuel for biomethane) and WPO to a) simultaneously reduce NOx and particulate matter emissions due to low local combustion temperatures and a high degree of charge homogenization and b) address waste and carbon footprint reduction challenges. Through experiments, influence of direct injection timing and energy shares of utilized fuels to in-cylinder thermodynamic parameters and engine emission response were evaluated in engine operating points at constant indicated mean effective pressure. Acquired results were deeply investigated and benchmarked against compression ignition (CI) and RCCI operation with conventional diesel fuel to determine potential for WPO utilization in an advanced low-temperature combustion concept. Results show that chemically stabilized WPO can be efficiently utilized in RCCI combustion concept without adaptation of injection parameters and that with suitable control parameters, ultra-low emissions of NOx and PM can be achieved with utilized fuels. For diesel/methane mix, NOx and PM emissions were reduced compared to conventional CI operation for 82.0% and 93.2%, respectively, whereas for WPO/methane mix, NOx and PM emissions were reduced for 88.7% and 97.6%, respectively, which can be ascribed to favourable chemical characteristics of WPO for the utilized combustion concept. In the least favourable operating point among those studied, indicated mean effective pressure covariance was kept below 2.5%, which is well below 5% being considered the limit for stable engine operation.

Fractional‐order LC filter modeling, implementation, and analysis for distributed power generation system

SummaryThis paper proposes a comprehensive mathematical modeling and analysis considering fractional‐order LC filters (FOLCF) in the utility grid‐connected mode (UGCM) and the standalone mode (SM) of operation for the distributed power generation system. The fractional‐order behavior of LC filter elements helps to more properly depict a practical inductor or capacitor than the integer‐order LC filters (IOLCF) in the distributed power generation system. The fractional‐order model of UGCM and SM is obtained in the synchronously rotating reference frame using coordinate transformation. A detailed stability and time domain analysis is performed on the developed FO UGCM and SM mathematical models. The stability of fractional‐order LC filters increases for orders less than 1, based on the performance evaluation of the FO and IO mathematical models for UGCM and SM with the corresponding designed controller gains. The FOLCFs are approximated using the constant phase element method, which gives a compact and exact approximation of the fractional‐order inductor and capacitor elements. The implementation of FOLCF with UGCM and SM operations verifies the effectiveness of the proposed model in real‐time simulation. The results show the FOLCF model provides better dynamic tracking and disturbance rejection response than the IOLCF model. Hence, the FOLCF model imparts immunity against local load disturbances to regulate the point of common coupling voltage and frequency in standalone mode. Furthermore, a significant improvement in % total harmonic distortion is also observed in grid current and load voltage.

Towards Energy Sustainability in University Campuses: A Case Study of Beirut Arab University

Lebanon has been suffering from severe challenges in its electric sector for decades owing to chronic supply shortages and faults in its aging power grid infrastructure. The deplorable situation of the Lebanese electric sector has been made worse by the economic meltdown that started in 2019, which eventually led to total power blackouts across the country. In this paper, we present a case study on the design and implementation of a solar microgrid system for Beirut Arab University, Lebanon. As a first step, simulation software for a microgrid and a distributed generation power system is used to compare different design scenarios. Considering the available installation area and the fact that the greatest demand occurs during the daytime, when both the educational and managerial facilities are running, it is found that a 500-kW photovoltaic system tied to the university’s already present diesel generators is the optimal solution in terms of return on investment. The second step details the actual implementation of the system in the Beirut campus and the evaluation of the system’s performance in terms of diesel cost savings and emissions reduction. We expect that the results of this case study will encourage other institutions and communities to adopt sustainable and renewable energy sources.

Predicting NOx Distribution in a Micro Rich–Quench–Lean Combustor Using a Variational Autoencoder

Micro gas turbines are widely used in distributed power generation systems. However, the combustion of gas turbine combustors produces a large amount of nitrogen oxides (NOx), which pollute the environment and endanger human life. To reduce environmental pollution, low-emission combustors have been developed. In recent years, there has been an increasing focus on the use of low-heat-value gas fuels, and it is necessary to study the NOx emissions from low heat value gas fuel combustors. Data-driven deep learning methods have been used in many fields in recent years. In this study, a variational autoencoder was introduced for the prediction of NOx production inside the combustor. The combustor used was a micro rich-quench-lean combustor designed by the research group using coal bed gas as a fuel. The internal NO distribution contour was obtained as the dataset using simulation methods, with a size of 60 images. The model architecture parameters were obtained through hyperparameter exploration using the grid search method. The model accurately predicted the distribution of NO inside the combustor. The method can be applied in the prediction of a wider range of parameters and offers a new way of designing combustors for the power industry.

Research on a DC–DC Converter and Its Advanced Control Strategy Applied to the Integrated Energy System of Marine Breeding Platforms

The deep-sea aquaculture industry will become one of the important pillars of the future marine economy. However, the application of clean energy in the new scenario needs to be strengthened for platform operation. For this kind of renewable-energy distributed-generation system, an energy storage system is essential. A bidirectional DC–DC converter is essential for distributed power generation systems. It connects a variety of renewable energy sources with energy storage cells. A high-gain bidirectional Cuk circuit with zero ripple is proposed in the paper. It is characterized by a simple structure, zero ripple, low voltage stress of semiconductor power devices, and high voltage gain. A passivity-based control with linear active disturbance rejection is proposed to solve the problems of the large steady-state error. The zero steady-state error, strong robustness, and whole-range stability have been obtained for the proposed control strategy. Finally, a simulation was carried out. A 100 W, 48 V/400 V prototype was built to verify the validity of the theoretical analysis for the proposed circuit. The improved passivity-based control strategy was verified to solve the contradiction between rapidity and overshoot. It can be realized to improve the dynamic performance of the proposed converter and achieve robust control.

Resonant hybrid flyback: A novel topology with wide voltage range for DC microgrid applications

DC microgrids are becoming very popular due to the increasing deployment of distributed power generation systems. This presents new challenges for power converters, including how to achieve a wide range of input and output voltages in a small volume. State-of-the-art solutions include flyback-based and LLC-based converters. The first ones are bulky due to the large size of magnetic required to store the energy and their efficiency is limited by their capability to recycle the energy from parasitic elements. The second ones offer good efficiency but a limited range for input and output voltage, and may involve a large number of semiconductors. This paper studies the application of a novel topology, the asymmetrical half-bridge flyback, whose hybrid operation principle combines the advantages of forward and flyback converters while keeping a small number of switches. A design process to accomplish the outstanding requirements with the topology is presented. The theoretical analyses are supporter by a 240 W DC–DC prototype with an input range of 320 V–400 V and an output range of 5 V–24 V. A peak efficiency of 97.6 % is measured. The achieved power density of the converter is 65 W/inch3 uncased. Finally, a comprehensive numerical comparison with the LLC and flyback converters in the state of the art is carried out to show the potential of the proposal.

Overview of Single-Stage High-Frequency Isolated AC–DC Converters and Modulation Strategies

The single-stage high-frequency (HF) isolated ac–dc converter has the advantages of high-power density, long life, and high efficiency. It has a broad application prospect in distributed power generation, ac microgrid, and energy storage system. In this article, its topologies are classified according to the energy storage components. The structure and operating principle of various topologies are introduced. Furthermore, the development of extended multiport single-stage HF isolated ac–dc converter is introduced. On this basis, the advantages and disadvantages, typical characteristics, cost, and power loss of various topologies are analyzed and summarized. Finally, the key issues that need to be solved are pointed out and the development trends are explored. This article aims to provide a reference for the subsequent research on single-stage HF isolated ac–dc converters and the advancement of their practicability.

A novel ultra-high step-up interleaved DC–DC converter based on the three-winding coupled inductor for distributed generation power system

Abstract In this paper, a non-isolated DC–DC converter with three-winding coupled inductors and switched capacitor cells is introduced. More output voltage is acquired without imposing any extreme duty cycle and high turns ratio. With the help of a two-phase interleaved technique, the input current ripple is reduced efficiently. The leakage inductance of coupled inductors causes the reverse recovery problem of circuit diodes to be solved and alleviates them. Leakage energy is also absorbed by switched capacitor cells. One of the advantages of this converter is the reduction of voltage stress of power switches, which leads to a reduction of conduction losses. In this way, low-voltage rated power switches can be used. Creating soft-switching conditions on power switches and high efficiency are also the prominent features of this structure. Laboratory and experimental results were produced and presented by making a prototype of 350 W–18 V/480 V. Their analysis indicates the effective performance of the proposed topology.

A Robust Nonlinear Sliding Mode Controller for a Three-Phase Grid-Connected Inverter with an LCL Filter

In distributed power generation systems, grid-connected inverters are becoming an attractive means of delivering the energy generated from renewable sources into the grid. However, the performance of the current controller drastically decreases in the presence of model uncertainty, grid harmonics, filter parametric, and grid impedance variations, which can jeopardize the entire system’s stability. This paper presents a novel design of a super-twisting integral sliding mode control (ST-ISMC) strategy for the first time in the application of a three-phase voltage source grid-connected inverter. The designed controller has shown robustness and maintains a low total harmonic distortion (THD) in the presence of filter parameters drift, grid impedance variation, and grid harmonics distortion. The super-twisting action is added to remove the chattering problem associated with the conventional SMC strategy, and integral action is adopted to improve the grid’s current steady-state error. The modeling and simulation of a complete system are carried out using MATLAB/SIMULINK. Finally, a real-world hardware prototype system is fabricated to demonstrate the performance and effectiveness of the proposed controller.

An alternative control synthesis for stability enhancement of digital-controlled LCL-filtered grid-connected inverter

• A control synthesis is proposed to damp capacitor current resonance for LCL-filtered GCI. • The stability and performance characteristics are analyzed and compared with methods from the literature. • Intuitive design, wider stable damping region, better dynamic performance, and higher parametric robustness are the potential benefits of the proposed control synthesis. In distributed power generation systems, the inherent resonance phenomena of LCL -filtered grid-connected inverter is one of the major challenges faced by the integration of renewable energy resources with the electric power grid. In this context, the capacitor current based multi-loop active damping method is employed due to lossless resonance damping and flexible control design. However, the damping loop with the feedback compensation design suffers from relatively higher parameters sensitivity unless employed with the reduced digital delays. The filter parameters fluctuation causes a shift in resonance frequency, which leads to ineffective damping at the critical resonance frequency and may risk the control loop stability. Therefore, an alternative linear control synthesis is proposed to design the capacitor current damping loop in order to reduce the filter parameters sensitivity. The proposed design realizes the equivalent virtual impedance in an alternative manner to suppress the resonance peak and enhanced the stability characteristics of the grid-connected inverter. A detailed stability and performance analysis have been done to show the widened stable damping region and high parametric robustness of the suggested design as compared to the literature method. Simulations and experimental results are presented to confirm the theoretical findings.

Secondary Voltage Collaborative Control of Distributed Energy System via Multi-Agent Reinforcement Learning

In this paper, a new voltage cooperative control strategy for a distributed power generation system is proposed based on the multi-agent advantage actor-critic (MA2C) algorithm, which realizes flexible management and effective control of distributed energy. The attentional actor-critic message processor (AACMP) is extended into the MA2C method to select the important messages from all communication messages adaptively and process important messages efficiently. The cooperative control strategy trained by centralized training and decentralized execution frame will take over the responsibility of the secondary control level for voltage restoration in a distributed manner. The introduction of the attention mechanism reduces the amount of information exchanged and the requirements of the communication network. Finally, a distributed system with six energy nodes is used to verify the effectiveness of the proposed control strategy.

Flexible control of grid-connected renewable energy systems inverters under unbalanced grid faults

The sustainable energy opportunity of the future lies in the renewable energy-based distributed Power Generation systems (DPGSs). However, there are different concerns and integration issues that surround them. To increase the rate at which renewable energy can be used, this paper focuses on an integrated utility grid system. A novel strategy to control the grid side inverter is developed for a DPGS when considering an unbalanced grid. First, an analysis of the consequences of the occurrence of a fault on the grid is performed. Secondly, a control strategy is proposed to ensure the operation of the DPGS connected to the grid even if the latter is unbalanced. The proposed approach consists in developing control loops for each of the three symmetrical sequences in a specific reference frame to ensure the operation of the grid-connected DPGS even during asymmetrical grid voltage fault. The found results are promising in terms of the guarantee of service continuity during faulty conditions.

Distributed Generation Power Systems in Wastewater Management

The article concerns the energy security of a wastewater treatment process caused by unforeseen situations related to the risk of electrical power outages. In this case, renewable energy sources based on distributed generation power systems can solve this problem in each wastewater treatment plant. The article highlights e related challenges and proposes the direction of solutions in this regard based on Czech conditions. The first part of the paper deals with the consequences of long-term outage of wastewater treatment plants on the population and the environment. There are several solutions presented for blackout conditions, and model calculations are made based on data from a Czech wastewater treatment plant. Diesel engine-generators, biogas as a cogeneration source of heat and electricity, solar panels with storage systems and combined biogas and solar systems were considered as approaches to provide energy autonomy during a blackout in a wastewater treatment plant. Special attention was paid to a combination of CHP units with solar panels and batteries. The results were evaluated for three different locations for this combination. It was concluded that biogas combustion in the CHP unit was the most profitable option, allowing the production of electricity independently of the grid for its own consumption and possibly for other operations. The last part of the paper deals with the transition to island operation, which must occur during a blackout. This transition is more difficult for both solar panels and cogeneration units if they were to supply electricity to the grid before a blackout. The transition to energy island operation could be ensured by frequency relay and processor devices to control the circuit breaker. Then, to maintain island operation, it would be necessary to have an automatic load shedding/application system.

A robust controller design procedure for LCL‐type grid‐tied proton exchange membrane fuel cell system in harmonics‐polluted network

AbstractProton exchange membrane fuel cell (PEMFC), due to its high efficiency and good stability, is one of the most efficient and effective sources of alternative renewable energy. The LCL filters are utilized to attenuate the harmonics caused by inverter‐based distributed power generation systems (DPGS). In this paper, a systematic robust control design is presented for an LCL‐type grid‐tied PEMFC inverter. The proposed nested control includes the capacitor current feedback and the outer grid current loops, considering the computational delays. The proposed control results in more accurate and realistic modeling to transfer the power of PEMFC and inject a high‐quality current into a weak and harmonics‐polluted network. Also, by utilizing the proposed method, the computational delays that affect the damping capability are eliminated, and the performance of the control system is improved. In addition, designing a virtual series and parallel impedances strengthens the phase and amplitude of the inverter output impedance. As a result, the robust operation of the inverter for significant changes in network impedance is improved, and the system well attenuates the mains voltage harmonics. The simulation results in Matlab/Simulink environment confirm the performance of the control system and the suitable quality of the injected current of the PEMFC system into the weak and harmonic‐polluted network.

A Novel Method of Islanding Detection in a Distributed Power Generation System Integrated with Photovoltaic-Array

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