Special Issue "Control and Nonlinear Dynamics on Energy Conversion Systems"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "Energy Fundamentals and Conversion".

Deadline for manuscript submissions: closed (30 September 2018).

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Dr. Herbert Ho-Ching Iu
E-Mail Website
Guest Editor
School of Electrical, Electronic and Computer Engineering, The University of Western Australia, Perth, WA 6009, Australia
Interests: power electronics; chaos, smart grid; renewable energy; nonlinear dynamics
Special Issues and Collections in MDPI journals
Prof. Dr. Abdelali El Aroudi
E-Mail Website
Guest Editor
Department of Electronic, Electrical and Automatic Engineering (DEEEA), Universitat Rovira i Virgili, Carrer de l`Escorxador, s/n, 43003 Tarragona, Spain
Interests: control of power conditioning systems for 
autonomous systems; power factor correction; stability problems; nonlinear 
phenomena; bifurcations and control
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

Power electronics such as switching power converters are probably the most commonly used electronic devices, as they can be found in applications ranging from simple domestic applications to military and space systems. The ever-increasing need for higher efficiency, smaller size, and lower cost make the analysis, understanding, and design of such converters extremely important, interesting, and even imperative. One of the most neglected features in the study of such systems is the effect of the inherent nonlinearities on the stability of the converter. Due to these nonlinearities, these devices may exhibit undesirable and complex dynamics, which are the focus of many researchers. Even though a lot of research has taken place in this area during the last 20 years, it is still an active research topic to the mainstream power engineer. That research has demonstrated that switched mode power converters for conventional applications can become unstable with a direct result in increased losses, extra subharmonics, and even uncontrollability/unobservability. Furthermore, the detailed study of these systems can help in the design of smaller, lighter, and less expensive converters that are particularly important in emerging areas of research like electric vehicles, smart grids, renewable energy sources, and others. The aim of this Special Issue is to cover control and nonlinear aspects of instabilities in switching converters: theoretical, analysis modelling, and practical solutions for such emerging applications. In this Special Issue, we wish to solicit novel research work in the area of control and nonlinear dynamics on energy conversion systems which will be of highly interest to both academics and industrialists.

The topics include but are not limited to:

  • Nonlinear dynamics of power converters used in renewable energy systems and electric vehicle applications;
  • High conversion ratio power converters for renewable energy applications and electric vehicles;
  • Stability analysis techniques of switching converters with applications to renewable energy interfaces for nano and micro-grid applications;
  • Control and design of switching converters for light emitting diodes (LEDs);
  • New techniques to avoid undesired nonlinear phenomena;
  • Nonlinear dynamic and stability analysis of wind energy conversion system;
  • Nonlinear dynamic and stability analysis of MPPT controllers;
  • Stability analysis of grid-connected power generation systems;
  • Active and reactive power control of energy conversion systems;
  • Nonlinear control of wind energy conversion system based on Control-Lyapunov function;
  • Voltage stability analysis of grid-connected energy conversion systems with FACTS;
  • Energy conversion systems architectures and technologies;
  • Power electronics integrated with renewables;
  • Energy conversion systems modelling, remote monitoring and diagnosis;
  • Power electronic systems-converters and emerging technologies;
  • Control methodologies of energy conversion systems;
  • Nonlinear dynamics, bifurcation, and chaos in energy conversion systems;
  • Reliability and fault tolerance, safety critical operation;
  • Modeling and simulation of electrical power systems;
  • Load management, power quality, distribution reliability, distributed and islanded power systems, communication and control;
  • Emerging topics in energy conversion systems;
  • Optimization and advanced heuristics, adaptive systems, robust control.

Prof. Dr. Herbert Ho-Ching Iu
Prof. Dr. Abdelali El Aroudi
Guest Editors

Manuscript Submission Information

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Keywords

  • Energy conversion systems architectures and technologies
  • Power electronics integrated with renewables
  • Energy conversion systems modelling, remote monitoring and diagnosis
  • Power electronic systemsconverters and emerging technologies
  • Control methodologies of energy conversion systems
  • Nonlinear dynamics, bifurcation, and chaos in energy conversion systems
  • Reliability and fault tolerance, safety critical operation
  • Modeling and simulation of electrical power systems
  • Load management, power quality, distribution reliability, distributed and islanded power systems, communication and control
  • Renewable energy systems
  • Emerging topics in energy conversion systems
  • Optimization and advanced heuristics, adaptive systems, robust control

Published Papers (21 papers)

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Open AccessArticle
Influences of the Load of Suspension Point in the z Direction and Rigid Body Oscillation on Steel Catenary Riser Displacement and Frequency Under Wave Action
Energies 2019, 12(2), 273; https://doi.org/10.3390/en12020273 - 16 Jan 2019
Abstract
The rigid body swing is an important problem for steel catenary risers (SCRs). In addition to many other important issues, the transverse flow direction response is studied in this paper. By extending the load terms of the large deflection slender beam equation, the [...] Read more.
The rigid body swing is an important problem for steel catenary risers (SCRs). In addition to many other important issues, the transverse flow direction response is studied in this paper. By extending the load terms of the large deflection slender beam equation, the load of suspension point in the z direction, Morison and rigid body swing are superimposed on the beam equation. On the basis of the above work, a Cable3d subroutine is written to complete the task. Then the structural response is simulated and verified by the Lissajous phenomenon and spectral phase analysis. On the basis of verification, the response is analyzed from an angle of three-dimensional space and the influence coefficient is adopted to evaluate the effect of rigid body swing. The importance of loads is determined by spectral analysis. Phase curve and the change of vibration direction are analyzed by higher orders of frequency. The results show the verification of Lissajous and spectral phase analysis are feasible. The analysis of the spatial response shows the vibration direction of the 140th node is in the same direction as the rigid body swing vector, so the interaction is relatively of more intensity and the influence coefficient is relatively larger. This influence interval of rigid body swing displacement statistical analysis is −0.02 to 0.02 and the effect is weak. The spectrum analysis indicates there is no resonance between the main load and the bending vibration, and the analysis also shows the main influence load of the transverse flow response in this paper is the top load in the z direction. According to phase analysis, the load has a high order effect on the spectral phase curve of the structure. This paper has drawn a conclusion that rigid body swing has limited effect on transverse flow response, however, it has a relatively strong impact on the middle region of the riser, so it plays an influential role on the safety of the riser to some extent. The key point for this paper is to provide qualitative standards for the verification of rigid body swing through Lissajous graphs, which are central factors to promote the development of rigid body swing. It is hoped that the above research can provide some reasonable suggestions for the transverse flow response simulation of the steel catenary riser. Full article
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Open AccessArticle
Analysis of Nonlinear Dynamics of a Quadratic Boost Converter Used for Maximum Power Point Tracking in a Grid-Interlinked PV System
Energies 2019, 12(1), 61; https://doi.org/10.3390/en12010061 - 25 Dec 2018
Cited by 1
Abstract
In this paper, the nonlinear dynamics of a PV-fed high-voltage-gain single-switch quadratic boost converter loaded by a grid-interlinked DC-AC inverter is explored in its parameter space. The control of the input port of the converter is designed using a resistive control approach ensuring [...] Read more.
In this paper, the nonlinear dynamics of a PV-fed high-voltage-gain single-switch quadratic boost converter loaded by a grid-interlinked DC-AC inverter is explored in its parameter space. The control of the input port of the converter is designed using a resistive control approach ensuring stability at the slow time-scale. However, time-domain simulations, performed on a full-order circuit-level switched model implemented in PSIM© software, show that at relatively high irradiance levels, the system may exhibit undesired subharmonic instabilities at the fast time-scale. A model of the system is derived, and a closed-form expression is used for locating the subharmonic instability boundary in terms of parameters of different nature. The theoretical results are in remarkable agreement with the numerical simulations and experimental measurements using a laboratory prototype. The modeling method proposed and the results obtained can help in guiding the design of power conditioning converters for solar PV systems, as well as other similar structures for energy conversion systems. Full article
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Open AccessArticle
Dynamic Analysis of a Permanent Magnet DC Motor Using a Buck Converter Controlled by ZAD-FPIC
Energies 2018, 11(12), 3388; https://doi.org/10.3390/en11123388 - 03 Dec 2018
Cited by 5
Abstract
This paper presents the dynamic analysis of a permanent magnet DC motor using a buck converter controlled by zero average dynamics (ZADs) and fixed-point inducting control (FPIC). Initially, the steady-state behavior of the closed-loop system was observed and then transient behavior analyzed while [...] Read more.
This paper presents the dynamic analysis of a permanent magnet DC motor using a buck converter controlled by zero average dynamics (ZADs) and fixed-point inducting control (FPIC). Initially, the steady-state behavior of the closed-loop system was observed and then transient behavior analyzed while maintaining a fixed ZAD control parameter and changing the FPIC parameter. Other behaviors were studied when the value of the ZAD control parameter changed and the FPIC parameter was maintained at the initial value. Besides, bifurcation diagrams were built with one and two delay periods by changing the control parameter of the FPIC and maintaining fixed ZAD parameters while some disturbances were carried out in the electric source. The results show that the ZAD-FPIC controller allowed good regulation of the speed for different reference values. The ZAD-FPIC control technique is effective for controlling the buck converter with the motor, even with two delay periods. The robustness of the system was checked by changing the voltage of the source. It was shown that the system used a fixed switching frequency because the duty cycle was not saturated for certain ranges of the control parameters shown in the research. This technique can be used for higher order systems with experimental phenomena such as quantization effects, time delays, and variations in the input signal. Full article
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Open AccessArticle
Efficiency Optimization of a Variable Bus Voltage DC Microgrid
Energies 2018, 11(11), 3090; https://doi.org/10.3390/en11113090 - 08 Nov 2018
Cited by 1
Abstract
A variable bus voltage DC microgrid (MG) is simulated in Simulink for optimization purposes. It is initially controlled with a Voltage Event Control (VEC) algorithm supplemented with a State of Charge Event Control (SOCEC) algorithm. This control determines the power generated/consumed by each [...] Read more.
A variable bus voltage DC microgrid (MG) is simulated in Simulink for optimization purposes. It is initially controlled with a Voltage Event Control (VEC) algorithm supplemented with a State of Charge Event Control (SOCEC) algorithm. This control determines the power generated/consumed by each element of the MG based on bus voltage and battery State of Charge (SOC) values. Two supplementary strategies are proposed and evaluated to improve the DC-DC converters’ efficiency. First, bus voltage optimization control: a centralized Energy Management System (EMS) manages the battery power in order to make the bus voltage follow the optimal voltage reference. Second, online optimization of switching frequency: local drivers operate each converter at its optimal switching frequency. The two proposed optimization strategies have been verified in the simulations. Full article
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Open AccessArticle
Control of a DC-DC Buck Converter through Contraction Techniques
Energies 2018, 11(11), 3086; https://doi.org/10.3390/en11113086 - 08 Nov 2018
Cited by 5
Abstract
Reliable and robust control of power converters is a key issue in the performance of numerous technological devices. In this paper we show a design technique for the control of a DC-DC buck converter with a switching technique that guarantees both good performance [...] Read more.
Reliable and robust control of power converters is a key issue in the performance of numerous technological devices. In this paper we show a design technique for the control of a DC-DC buck converter with a switching technique that guarantees both good performance and global stability. We show that making use of the contraction theorem in the Jordan canonical form of the buck converter, it is possible to find a switching surface that guarantees stability but it is incapable of rejecting load perturbations. To overcome this, we expand the system to include the dynamics of the voltage error and we demonstrate that the same design procedure is not only able to stabilize the system to the desired operation point but also to reject load, input voltage, and reference voltage perturbations. Full article
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Open AccessArticle
Pulse-Current Sources for Plasma Accelerators
Energies 2018, 11(11), 3057; https://doi.org/10.3390/en11113057 - 07 Nov 2018
Cited by 1
Abstract
The pulse source for plasma-accelerators supply operates under the conditions of nonlinear growth of load inductance, which complicates the matching of the source and the load. This article presents experimental studies of the use of both traditional pulse-energy sources based on capacitive storage [...] Read more.
The pulse source for plasma-accelerators supply operates under the conditions of nonlinear growth of load inductance, which complicates the matching of the source and the load. This article presents experimental studies of the use of both traditional pulse-energy sources based on capacitive storage and alternative ones based on explosive magnetic generators (EMG). It is shown that the EMG with the special device of the current-pulse formation more effectively matches with such a plasma load as the pulse plasma-accelerator (PPA). This device allows a wide range to manage the current-pulse formation in a variable load and, consequently, to optimize the operation of the power source for the specific plasma load. A mathematical model describing the principle of operation of this device in EMG on inductive load was developed. The key adjustable parameters are the current into the load, the residual inductance of the EMG, and the sample time of the specified inductance and the final current in the load. The device was successfully tested in experiments with the operation on both one and two accelerators connected in parallel. In the experiments, the optimal mode of device operation was found in which the total energy inputted to a pair of accelerators in one pulse reached 0.55 MJ, and the maximum current reached about 3.5 MA. A comparison with the results of experiments performed with capacitive sources of the same level of stored energy is given. The experiments confirmed not only the principal possibility of using EMG with a special device of current-pulse formation for operation with plasma loads in the MJ energy range but also showed the advantages of its application with specific types of plasma load. Full article
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Open AccessArticle
Slope Compensation Design for a Peak Current-Mode Controlled Boost-Flyback Converter
Energies 2018, 11(11), 3000; https://doi.org/10.3390/en11113000 - 01 Nov 2018
Cited by 1
Abstract
Peak current-mode control is widely used in power converters and involves the use of an external compensation ramp to suppress undesired behaviors and to enhance the stability range of the Period-1 orbit. A boost converter uses an analytical expression to find a compensation [...] Read more.
Peak current-mode control is widely used in power converters and involves the use of an external compensation ramp to suppress undesired behaviors and to enhance the stability range of the Period-1 orbit. A boost converter uses an analytical expression to find a compensation ramp; however, other more complex converters do not use such an expression, and the corresponding compensation ramp must be computed using complex mechanisms. A boost-flyback converter is a power converter with coupled inductors. In addition to its high efficiency and high voltage gains, this converter reduces voltage stress acting on semiconductor devices and thus offers many benefits as a converter. This paper presents an analytical expression for computing the value of a compensation ramp for a peak current-mode controlled boost-flyback converter using its simplified model. Formula results are compared to analytical results based on a monodromy matrix with numerical results using bifurcations diagrams and with experimental results using a lab prototype of 100 W. Full article
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Open AccessFeature PaperArticle
A Novel Step-Up Converter with an Ultrahigh Voltage Conversion Ratio
Energies 2018, 11(10), 2693; https://doi.org/10.3390/en11102693 - 10 Oct 2018
Abstract
A new step-up converter with an ultrahigh voltage conversion ratio is proposed in this paper. Two power switches of such a converter, which conduct synchronically, and its output voltage, which has common ground and common polarity with its input voltage, lead to the [...] Read more.
A new step-up converter with an ultrahigh voltage conversion ratio is proposed in this paper. Two power switches of such a converter, which conduct synchronically, and its output voltage, which has common ground and common polarity with its input voltage, lead to the simple control circuit. No abrupt changes in the capacitor voltage and the inductor current of the proposed step-up converter mean that it does not suffer from infinite capacitor current and inductor voltage. Two input inductors with different values can still allow the proposed step-up converter to work appropriately. An averaged model of the proposed step-up converter was built and one could see that it was still fourth-order even with its five storage elements. Some theoretical derivations, theoretical analysis, Saber simulations, and circuit experiments are provided to validate the effectiveness of the proposed step-up converter. Full article
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Open AccessArticle
Vibration Characteristics Analysis of Planetary Gears with a Multi-Clearance Coupling in Space Mechanism
Energies 2018, 11(10), 2687; https://doi.org/10.3390/en11102687 - 09 Oct 2018
Cited by 2
Abstract
Multi-clearance is the main cause for the performance and reliability decline of complicated mechanical systems. The increased clearance could induce contacts and impacts in joints, and consequently affect control accuracy. A nonlinear dynamic model of planetary gears with multi-clearance coupling is proposed in [...] Read more.
Multi-clearance is the main cause for the performance and reliability decline of complicated mechanical systems. The increased clearance could induce contacts and impacts in joints, and consequently affect control accuracy. A nonlinear dynamic model of planetary gears with multi-clearance coupling is proposed in the current study to investigate the mechanism of influence of clearance on the dynamic performance. In addition, the coupling relationship between radial clearance and backlash is integrated into the multi-body system dynamics. The vibration characteristics of planetary gears with the changes of rotational velocity, clearance size and inertia load are explored. The numerical simulation results show that there are complex coupling relations in planetary gear systems, due to the multi-clearance coupling. The phenomenon of system resonance may occur with the changes of rotational velocities and clearances’ sizes. Multi-clearance coupling can significantly increase the resonant response of planetary gear systems in empty-load or light-load states. Full article
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Open AccessArticle
A New Bridgeless High Step-up Voltage Gain PFC Converter with Reduced Conduction Losses and Low Voltage Stress
Energies 2018, 11(10), 2640; https://doi.org/10.3390/en11102640 - 02 Oct 2018
Cited by 2
Abstract
Bridgeless power factor correction (PFC) converters have a reduced number of semiconductors in the current flowing path, contributing to low conduction losses. In this paper, a new bridgeless high step-up voltage gain PFC converter is proposed, analyzed and validated for high voltage applications. [...] Read more.
Bridgeless power factor correction (PFC) converters have a reduced number of semiconductors in the current flowing path, contributing to low conduction losses. In this paper, a new bridgeless high step-up voltage gain PFC converter is proposed, analyzed and validated for high voltage applications. Compared to its conventional counterpart, the input rectifier bridge in the proposed bridgeless PFC converter is completely eliminated. As a result, its conduction losses are reduced. Also, the current flowing through the power switches in the proposed bridgeless PFC converter is only half of the current flowing through the rectifier diodes in its conventional counterpart, therefore, the conduction losses can be further improved. Moreover, in the proposed bridgeless PFC converter, not only the voltage stress of power switches is lower than the output voltage, but the voltage stress of the output diodes is lower than the conventional counterpart. In addition, this proposed bridgeless PFC converter features a simple circuit structure and high PFC performance. Finally, the proposed bridgeless PFC converter is analyzed and designed in the discontinuous conduction mode (DCM). The simulation results are presented to verify the effectiveness of the proposed bridgeless PFC converter. Full article
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Open AccessFeature PaperArticle
Full-Speed Range Encoderless Control for Salient-Pole PMSM with a Novel Full-Order SMO
Energies 2018, 11(9), 2423; https://doi.org/10.3390/en11092423 - 13 Sep 2018
Cited by 3
Abstract
For salient-pole permanent magnet synchronous motor (PMSM), the amplitude of extended back electromotive force (EEMF) is determined by rotor speed, stator current and its derivative value. Theoretically, even at extremely low speed, the back EEMF can be detected if the current in q [...] Read more.
For salient-pole permanent magnet synchronous motor (PMSM), the amplitude of extended back electromotive force (EEMF) is determined by rotor speed, stator current and its derivative value. Theoretically, even at extremely low speed, the back EEMF can be detected if the current in q-axis is changing. However, it is difficult to detect the EEMF precisely due to the current at low speed. In this paper, novel full-order multi-input and multi-output discrete-time sliding mode observer (SMO) is built to detect the rotor position. With the proposed rotor position estimation technique, the motor can start up from standstill and reverse between positive and negative directions without a position sensor. The proposed method was evaluated by experiment. Full article
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Open AccessArticle
A Novel Adaptive Neuro-Control Approach for Permanent Magnet Synchronous Motor Speed Control
Energies 2018, 11(9), 2355; https://doi.org/10.3390/en11092355 - 06 Sep 2018
Cited by 1
Abstract
A speed controller for permanent magnet synchronous motors (PMSMs) under the field oriented control (FOC) method is discussed in this paper. First, a novel adaptive neuro-control approach, single artificial neuron goal representation heuristic dynamic programming (SAN-GrHDP) for speed regulation of PMSMs, is presented. [...] Read more.
A speed controller for permanent magnet synchronous motors (PMSMs) under the field oriented control (FOC) method is discussed in this paper. First, a novel adaptive neuro-control approach, single artificial neuron goal representation heuristic dynamic programming (SAN-GrHDP) for speed regulation of PMSMs, is presented. For both current loops, PI controllers are adopted, respectively. Compared with the conventional single artificial neuron (SAN) control strategy, the proposed approach assumes an unknown mathematic model of the PMSM and guides the selection value of parameter K online. Besides, the proposed design can develop an internal reinforcement learning signal to guide the dynamic optimal control of the PMSM in the process. Finally, nonlinear optimal control simulations and experiments on the speed regulation of a PMSM are implemented in Matlab2016a and TMS320F28335, a 32-bit floating-point digital signal processor (DSP), respectively. To achieve a comparative study, the conventional SAN and SAN-GrHDP approaches are set up under identical conditions and parameters. Simulation and experiment results verify that the proposed controller can improve the speed control performance of PMSMs. Full article
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Open AccessArticle
Sliding-Mode Control of Distributed Maximum Power Point Tracking Converters Featuring Overvoltage Protection
Energies 2018, 11(9), 2220; https://doi.org/10.3390/en11092220 - 24 Aug 2018
Cited by 3
Abstract
In Photovoltaic (PV) systems with Distributed Maximum Power Point Tracking (DMPPT) architecture each panel is connected to a DC/DC converter, whose outputs are connected in series to feed a grid-connected inverter. The series-connection forces the output voltage of those converters to be proportional [...] Read more.
In Photovoltaic (PV) systems with Distributed Maximum Power Point Tracking (DMPPT) architecture each panel is connected to a DC/DC converter, whose outputs are connected in series to feed a grid-connected inverter. The series-connection forces the output voltage of those converters to be proportional to the converter’ output power; therefore, under mismatched conditions, the output voltage of a highly-irradiated converter may exceed the rating (safe) value, causing an overvoltage condition that could damage the converter. This paper proposes a sliding-mode controller (SMC) acting on each converter to regulate both the input and output voltages, hence avoiding the overvoltage condition under partial shading. The proposed control strategy has two operation modes: maximum power point tracking (MPPT) and Protection. In MPPT mode the SMC imposes to the PV panel the voltage reference defined by an MPPT technique. The Protection mode is activated when the output voltage reaches the safety limit, and the SMC regulates the converter’ output voltage to avoid overvoltage condition. The SMC has a bilinear sliding surface designed to provide a soft transition between both MPPT and Protection modes. The SMC analysis, parameters design and implementation are presented in detail. Moreover, simulation and experimental results illustrate the performance and applicability of the proposed solution. Full article
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Open AccessArticle
Improvement of the Response Speed for Switched Reluctance Generation System Based on Modified PT Control
Energies 2018, 11(8), 2049; https://doi.org/10.3390/en11082049 - 07 Aug 2018
Cited by 2
Abstract
The Switched Reluctance Generator (SRG) is suitable for wind power generation due to its good reliability and robustness. However, The SRG system adopting the conventional control algorithm with Pulse Width Modulation (PWM) method has a drawback, low response speed. The pulse train (PT) [...] Read more.
The Switched Reluctance Generator (SRG) is suitable for wind power generation due to its good reliability and robustness. However, The SRG system adopting the conventional control algorithm with Pulse Width Modulation (PWM) method has a drawback, low response speed. The pulse train (PT) control has been widely used in dc/dc power converters operating in the discontinuous conduction mode due to its advantages of simple implementation and fast response. In this paper, for the first time, the PT control method is modified and adopted for controlling the output voltage of SRG system in order to achieve fast response. The capacitor current on the output side is sampled and combined with the output voltage to select the pulse trains and the low frequency oscillation cased by PT can be suppressed by tuning the feedback coefficient of the capacitor current. Also, good performance can be guaranteed with a wide range of voltage regulations, fast response, and no overshoot. The experimental platform of an 8/6 SRG system is built, and the experimental results show that the PT control can be used for SRG system with good practicability. Full article
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Open AccessArticle
Experimental Study of Flow-Induced Whistling in Pipe Systems Including a Corrugated Section
Energies 2018, 11(8), 1954; https://doi.org/10.3390/en11081954 - 27 Jul 2018
Abstract
When air flows through pipe systems that include a corrugated segment, a whistling tone is generated and increases in intensity with increasing flow velocity. This whistling sound is related to the particular geometry of corrugated pipes, which is in the form of alternating [...] Read more.
When air flows through pipe systems that include a corrugated segment, a whistling tone is generated and increases in intensity with increasing flow velocity. This whistling sound is related to the particular geometry of corrugated pipes, which is in the form of alternating cavities. This whistling is an environmental noise problem as well as a possible structural danger because of the resulting induced vibration. This paper studies the whistling behavior of various pipe systems with a combination of smooth and corrugated pipes through a series of experiments. The considered pipe systems consist of two smooth pipes attached at the upstream and downstream ends of a corrugated segment. Experiments with smooth and corrugated pipes, which had inner diameters of 15.25 and 16.5 mm, respectively, and various lengths, were performed for flow velocities of up to approximately 30 m/s. The minimum and maximum Strouhal numbers (St) obtained during our experiments were 0.25 and 0.38, respectively. For all pipe configurations investigated in this study, the lowest Mach number at which whistling was observed was 0.017, and the maximum was 0.093. The lowest frequency at which whistling was detected in our experiments was 650 Hz, and the highest was 3080 Hz. The results presented in the form of different variables and dimensionless parameters, including the frequency, Mach number, Strouhal number, and Helmholtz number. The average mode gap and number of excited acoustic modes were also taken into account for all considered configurations. The pipe systems with longer corrugated segments had broader whistling ranges than did configurations with shorter segments, indicating that the number of cavities inside the corrugated pipe has a direct effect on whistling. Increasing the smooth pipe length (either upstream or downstream) resulted in a decrease in the average mode gap between successive modes. The number of excited acoustic modes was primarily related to the corrugated segment length, but the smooth pipe length also had a pronounced effect on the excited modes for a constant corrugation length. The highest number of excited modes (13) was seen in the case of corrugated length 450 mm and smooth pipe length (either upstream or downstream) 400 mm while the lowest number of excited modes (1) was observed for corrugated length 250 mm and smooth pipe length (downstream) 300 mm and 400 mm. Full article
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Open AccessArticle
Passivity-Based Robust Output Voltage Tracking Control of DC/DC Boost Converter for Wind Power Systems
Energies 2018, 11(6), 1469; https://doi.org/10.3390/en11061469 - 06 Jun 2018
Cited by 2
Abstract
This paper exhibits a passivity-based robust output voltage controller for DC/DC boost converters for wind power system applications. The proposed technique has two features. The first one is to introduce a nonlinear disturbance observer for estimating the disturbances arising from the load and [...] Read more.
This paper exhibits a passivity-based robust output voltage controller for DC/DC boost converters for wind power system applications. The proposed technique has two features. The first one is to introduce a nonlinear disturbance observer for estimating the disturbances arising from the load and parameter variations. The second one is to derive a proportional-type passivity-based output voltage tracking controller incorporating the disturbance observer output, which simplifies the control algorithm by removing the use of tracking error integrators and an anti-windup algorithm. These two features constitute the useful closed-loop properties called the performance recovery and offset-free properties. Numerical simulation results confirm the efficacy of the proposed scheme, where a wind power system including the proposed controller is emulated using the PowerSIM software. Full article
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Open AccessArticle
Modeling and Control of a Combined Heat and Power Unit with Two-Stage Bypass
Energies 2018, 11(6), 1395; https://doi.org/10.3390/en11061395 - 30 May 2018
Cited by 1
Abstract
This paper presents a non-linear dynamic model of a combined heat and power (CHP) unit with two-stage bypass for the first time. This model is derived through an analysis of the material and energy balance of the CHP unit. The static parameters are [...] Read more.
This paper presents a non-linear dynamic model of a combined heat and power (CHP) unit with two-stage bypass for the first time. This model is derived through an analysis of the material and energy balance of the CHP unit. The static parameters are determined via the design data of the CHP unit, and the dynamic parameters refer to model parameters of same type of units in other references. Based on the model, an optimized control scheme for the coordination system of the unit is proposed. This scheme introduces a stair-like feedforward-feedback predictive control algorithm to solve the control problem of large delays in boiler combustion, and integrates decoupling control to reduce the effect of external disturbance on the main steam pressure. Simulation results indicate that the model effectively reflects the dynamics of the CHP unit and can be used for designing and verifying its coordinated control system; the control scheme can achieve decoupling control of the CHP unit; the fluctuation of main steam pressure is considerably reduced; and the adjustment of coal feed flow is stable. In this case, the proposed scheme can guarantee the safe, stable and flexible operation of the unit and lay the foundation for decoupling the heat load-based constraint of CHP units, thereby expanding the access space of wind power in northern China. Full article
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Open AccessArticle
A Comprehensive Strategy for Accurate Reactive Power Distribution, Stability Improvement, and Harmonic Suppression of Multi-Inverter-Based Micro-Grid
Energies 2018, 11(4), 745; https://doi.org/10.3390/en11040745 - 26 Mar 2018
Cited by 4
Abstract
Among the issues of accurate power distribution, stability improvement, and harmonic suppression in micro-grid, each has been well studied as an individual, and most of the strategies about these issues aim at one inverter-based micro-grid, hence there is a need to establish a [...] Read more.
Among the issues of accurate power distribution, stability improvement, and harmonic suppression in micro-grid, each has been well studied as an individual, and most of the strategies about these issues aim at one inverter-based micro-grid, hence there is a need to establish a model to achieve these functions as a whole, aiming at a multi-inverter-based micro-grid. This paper proposes a comprehensive strategy which achieves this goal successfully; since the output voltage and frequency of micro-grid all consist of fundamental and harmonic components, the strategy contains two parts accordingly. On one hand, a fundamental control strategy is proposed upon the conventional droop control. The virtual impedance is introduced to solve the problem of accurate allocation of reactive power between inverters. Meanwhile, a secondary power balance controller is added to improve the stability of voltage and frequency while considering the aggravating problem of stability because of introducing virtual impedance. On the other hand, the fractional frequency harmonic control strategy is proposed. It can solve the influence of nonlinear loads, micro-grid inverters, and the distribution network on output voltage of inverters, which is focused on eliminating specific harmonics caused by the nonlinear loads, micro-grid converters, and the distribution network so that the power quality of micro-grid can be improved effectively. Finally, small signal analysis is used to analyze the stability of the multi-converter parallel system after introducing the whole control strategy. The simulation results show that the strategy proposed in this paper has a great performance on distributing reactive power, regulating and stabilizing output voltage of inverters and frequency, eliminating harmonic components, and improving the power quality of multi-inverter-based micro-grid. Full article
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Open AccessArticle
Nonlinear Modeling and Inferential Multi-Model Predictive Control of a Pulverizing System in a Coal-Fired Power Plant Based on Moving Horizon Estimation
Energies 2018, 11(3), 589; https://doi.org/10.3390/en11030589 - 08 Mar 2018
Cited by 4
Abstract
Fuel preparation is the control bottleneck in coal-fired power plants due to the unmeasurable nature or inaccurate measurement of key controlled variables. This paper proposes an inferential multi-model predictive control scheme based on moving horizon estimation for the fuel preparation system in coal-fired [...] Read more.
Fuel preparation is the control bottleneck in coal-fired power plants due to the unmeasurable nature or inaccurate measurement of key controlled variables. This paper proposes an inferential multi-model predictive control scheme based on moving horizon estimation for the fuel preparation system in coal-fired power plants, i.e., the pulverizing system, aimed at improving control precision of key operating variables that are unmeasurable or inaccurately measured, and improving system tracking performance across a wide operating range. We develop a first principle model of the pulverizing system considering the nonlinear dynamics of primary air, and then employ the genetic algorithm to identify the unknown model parameters. The outputs of the identified first principle model agree well with measured data from a real pulverizing system. Thereafter we derive a moving horizon estimation approach to estimate the desired, but unmeasurable or inaccurately measured, controlled variables. Estimation constraints are explicitly considered to reduce the influence of measurement uncertainty. Finally, nonlinearity of the pulverizing system is analyzed and a multi-model inferential predictive controller is developed using the extended input-output state space model to achieve offset-free performance. Simulation results show that the proposed soft sensor can provide improved estimates than conventional extended Kalman filter, and the proposed inferential control scheme can significantly improve performance of the pulverizing system. Full article
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Open AccessArticle
Development of a Data-Driven Predictive Model of Supply Air Temperature in an Air-Handling Unit for Conserving Energy
Energies 2018, 11(2), 407; https://doi.org/10.3390/en11020407 - 09 Feb 2018
Cited by 6
Abstract
The purpose of this study was to develop a data-driven predictive model that can predict the supply air temperature (SAT) in an air-handling unit (AHU) by using a neural network. A case study was selected, and AHU operational data from December 2015 to [...] Read more.
The purpose of this study was to develop a data-driven predictive model that can predict the supply air temperature (SAT) in an air-handling unit (AHU) by using a neural network. A case study was selected, and AHU operational data from December 2015 to November 2016 was collected. A data-driven predictive model was generated through an evolving process that consisted of an initial model, an optimal model, and an adaptive model. In order to develop the optimal model, input variables, the number of neurons and hidden layers, and the period of the training data set were considered. Since AHU data changes over time, an adaptive model, which has the ability to actively cope with constantly changing data, was developed. This adaptive model determined the model with the lowest mean square error (MSE) of the 91 models, which had two hidden layers and sets up a 12-hour test set at every prediction. The adaptive model used recently collected data as training data and utilized the sliding window technique rather than the accumulative data method. Furthermore, additional testing was performed to validate the adaptive model using AHU data from another building. The final adaptive model predicts SAT to a root mean square error (RMSE) of less than 0.6 °C. Full article
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Review

Jump to: Research

Open AccessReview
Review of Electromagnetic Vibration in Electrical Machines
Energies 2018, 11(7), 1779; https://doi.org/10.3390/en11071779 - 06 Jul 2018
Cited by 10
Abstract
Electrical machines are important devices that convert electric energy into mechanical work and are widely used in industry and people’s life. Undesired vibrations are harmful to their safe operation. Reviews from the viewpoint of fault diagnosis have been conducted, while summaries from the [...] Read more.
Electrical machines are important devices that convert electric energy into mechanical work and are widely used in industry and people’s life. Undesired vibrations are harmful to their safe operation. Reviews from the viewpoint of fault diagnosis have been conducted, while summaries from the perspective of dynamics is rare. This review provides systematic research outlines of this field, which can help a majority of scholars grasp the ongoing progress and conduct further investigations. This review mainly generalizes publications in the past decades about the dynamics and vibration of electrical machines. First the sources of electromagnetic vibration in electrical machines are presented, which include mechanical and electromagnetic factors. Different types of air gap eccentricity are introduced and modeled. The analytical methods and numerical methods for calculating the electromagnetic force are summarized and explained in detail. The exact subdomain analysis, magnetic equivalent circuit, Maxwell stress tensor, winding function approach, conformal mapping method, virtual work principle and finite element analysis are presented. The effects of magnetic saturation, slot and pole combination and load are discussed. Then typical characteristics of electromagnetic vibration are illustrated. Finally, the experimental studies are summarized and the authors give their thoughts about the research trends. Full article
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