Showing papers by "Juan C. Vasquez published in 2018"
TL;DR: In this article, a distributed nonlinear controller is presented to achieve both accurate current-sharing and voltage regulation simultaneously in dc microgrids considering different line impedances effects among converters, and an improved event-triggered principle for the controller is introduced through combining the state-dependent tolerance with a nonnegative offset.
Abstract: A distributed nonlinear controller is presented to achieve both accurate current-sharing and voltage regulation simultaneously in dc microgrids (MGs) considering different line impedances effects among converters. Then, an improved event-triggered principle for the controller is introduced through combining the state-dependent tolerance with a nonnegative offset. In order to design the event-triggered principle and guarantee the global stability, a generalized dc MG model is proposed and proven to be positive definite, based on which Lyapunov-based approach is applied. Furthermore, considering the effects from constant power loads, the damping performance of proposed controller is further improved which is comparative with the traditional $V\hbox{--}I$ droop controller. The proposed event-triggered-based communication strategy can considerably reduce the communication traffic and significantly relax the requirement for precise real-time information transmission, without sacrificing system performance. Experimental results obtained from a dc MG setup show the robustness of the new proposal under normal, communication failure and communication delay operation conditions. Finally, communication traffic under different communication strategies is compared, showing a drastic traffic reduction when using the proposed approach.
135 citations
TL;DR: Steady-state performance analysis assures the global voltage regulation, frequency synchronization, and proportional active/reactive power sharing of ac microgrids.
Abstract: This paper proposes a fully distributed control methodology for secondary control of ac microgrids. The control framework includes three modules: 1) voltage regulator; 2) reactive power regulator; and 3) active power/frequency regulator. The voltage regulator module maintains the average voltage of the microgrid distribution line at the rated value. The reactive power regulator compares the local normalized reactive power of an inverter with its neighbors’ powers on a communication graph and, accordingly, fine-tunes Q-V droop coefficients to mitigate any reactive power mismatch. Collectively, these two modules account for the effect of the distribution line impedance on the reactive power flow. The third module regulates all inverter frequencies at the nominal value while sharing the active power demand among them. Unlike most conventional methods, this controller does not utilize any explicit frequency measurement. The proposed controller is fully distributed; i.e., each controller requires information exchange with only its neighbors linked directly on the communication graph. Steady-state performance analysis assures the global voltage regulation, frequency synchronization, and proportional active/reactive power sharing. An ac microgrid is prototyped to experimentally validate the proposed control methodology against the load change, plug-and-play operation, and communication constraints such as delay, packet loss, and limited bandwidth.
134 citations
TL;DR: The second-order-generalized-integrator-based freq-uency-locked loop (SOGI-FLL) is a well-known tool for filtering and synchronization purposes in the power and energy applications, but has a limited ability in rejecting the grid voltage disturbances.
Abstract: The second-order-generalized-integrator-based freq-uency-locked loop (SOGI-FLL) is a well-known tool for filtering and synchronization purposes in the power and energy applications. The SOGI-FLL, nevertheless, has a limited ability in rejecting the grid voltage disturbances. To deal with this problem, two advanced SOGI-FLLs have been proposed recently. In the first one, a SOGI-based filter is included inside the standard SOGI-FLL control loop, and in the second one, a SOGI-based filter is employed as the prefiltering stage of the SOGI-FLL. The small-signal modeling, tuning procedure, and detailed performance comparison of these advanced SOGI-FLLs have not been carried out yet. The aim of this paper is to cover these issues.
120 citations
TL;DR: A thorough survey is done on power quality enhancement devices with emphasis on ancillary services of multi-functional DGs and a couple of thorough comparisons are done between the available techniques considering the nature, capabilities, advantages and implementation costs.
Abstract: It is obvious that power quality is an important characteristic of today's distribution power systems as loads become more sensitive on the other hand nonlinear loads are increasing in the electrical distribution system. Considering the distributed nature of harmonic loads, the need for distributed power quality improvement (PQI) is inevitable. From years ago, researchers have been working on various kinds of filters and devices to enhance the overall power quality of power system, but today the nature of distribution system has been changed and power electronic based DGs play an important role in distribution grids. In this paper, a thorough survey is done on power quality enhancement devices with emphasis on ancillary services of multi-functional DGs. A literature review is also done on microgrids concept, testbeds and related control methods. Although there were some applications of DGs for PQI improvement these applications were not defined multi-functional DGs. Various control methods are studied and categorized regarding different viewpoints in the literature. Finally, a couple of thorough comparisons are done between the available techniques considering the nature, capabilities, advantages and implementation costs.
108 citations
TL;DR: In this paper, the authors review several types of energy storage devices that have been extensively used to improve the reliability, fuel consumption, dynamic behavior, and other shortcomings for shipboard power systems and highlight the challenges of integrating the ESS in the shipboard microgrids.
Abstract: In recent years, concerns about severe environmental pollution and fossil fuel consumption has grabbed attention in the transportation industry, particularly in marine vessels. Another key challenge in ships is the fluctuations caused by high dynamic loads. In order to have a higher reliability in shipboard power systems, presently more generators are kept online operating much below their efficient point. Hence, to improve the fuel efficiency of shipboard power systems, the minimum generator operation with N-1 safety can be considered as a simple solution, a tradeoff between fuel economy and reliability. It is based on the fact that the fewer the number of generators that are brought online, the more load is on each generator such that allowing the generators to run on better fuel efficiency region. In all-electric ships, the propulsion and service loads are integrated to a common network in order to attain improved fuel consumption with lesser emissions in contrast to traditional approaches where propulsion and service loads are fed by separate generators. In order to make the shipboard power system more reliable, integration of energy storage system (ESS) is found out to be an effective solution. Energy storage devices, which are currently being used in several applications consist of batteries, ultra-capacitor, flywheel, and fuel cell. Among the batteries, lithium-ion is one of the most used type battery in fully electric zero-emission ferries with the shorter route (around 5 to 10 km). Hybrid energy storage systems (HESSs) are one of the solutions, which can be implemented in high power/energy density applications. In this case, two or more energy storage devices can be hybridized to achieve the benefits from both of them, although it is still a challenge to apply presently such application by a single energy storage device. The aim of this paper is to review several types of energy storage devices that have been extensively used to improve the reliability, fuel consumption, dynamic behavior, and other shortcomings for shipboard power systems. Besides, a summary is conducted to address most of the applied technologies mentioned in the literature with the aim of highlighting the challenges of integrating the ESS in the shipboard microgrids.
101 citations
TL;DR: A novel grid voltage modulated direct power control strategy for a grid-connected voltage source converter is proposed to control the instantaneous active and reactive powers directly and guarantees not only the convergence rate but also the steady-state performance of the system.
Abstract: A novel grid voltage modulated direct power control (GVM-DPC) strategy for a grid-connected voltage source converter is proposed to control the instantaneous active and reactive powers directly. The GVM-DPC method consists of a nonlinear GVM controller, a conventional controller (feedforward and PI feedback), and nonlinear damping. The proposed control strategy shows a relationship between DPC and voltage-oriented control methods designed in $d$ - $q$ frame. The main advantage is that the proposed method makes the system be a linear time-invariant system, which enables us to apply various control methods easily. The GVM-DPC guarantees not only the convergence rate but also the steady-state performance of the system. Moreover, it is ensured that the closed-loop system is exponentially stable. Finally, simulation and experimental results using a 2.2-kVA VSC are provided to validate the tracking performance and robustness of the proposed control architecture. In addition, the total harmonic distortion of the current is 1.9 $\%$ which is much less than the requirement for grid operation.
101 citations
TL;DR: In this paper, an adaptable energy management system implemented in an online scheme, as well as an evaluation framework to quantitatively assess the enhancement attained by different online energy management strategies is presented.
Abstract: Microgrids are energy systems that can work independently from the main grid in a stable and self-sustainable way. They rely on energy management systems to schedule optimally the distributed energy resources. Conventionally, the main research in this field is focused on scheduling problems applicable for specific case studies rather than in generic architectures that can deal with the uncertainties of the renewable energy sources. This paper contributes a design and experimental validation of an adaptable energy management system implemented in an online scheme, as well as an evaluation framework to quantitatively assess the enhancement attained by different online energy management strategies. The proposed architecture allows the interaction of measurement, forecasting and optimization modules, in which a generic generation-side mathematical problem is modeled, aiming to minimize operating costs and load disconnections. The whole energy management system has been tested experimentally in a test bench under both grid-connected and islanded mode. Also, its performance has been proved considering severe mismatches in forecast generation and load. Several experimental results have demonstrated the effectiveness of the proposed EMS, assessed by the corresponding average gap with respect to a selected benchmark strategy and ideal boundaries of the best and worst known solutions.
87 citations
TL;DR: In this article, a decentralized current-sharing control strategy is proposed to endow fast transient response to paralleled dc-dc converters systems, such as dc microgrids or distributed power systems.
Abstract: This paper proposes a decentralized current-sharing control strategy to endow fast transient response to paralleled dc–dc converters systems, such as dc microgrids or distributed power systems. The proposed controller consist of two main control loops: an external voltage droop control for current-sharing proposes and an internal current loop. The external droop control loop is designed as a voltage loop with embedded virtual impedance, which avoids the use of a slow voltage loop and a separate extra virtual impedance loop that may limit the system bandwidth. The internal current loop, thanks to the external control loop simplification, plays a major role in the system bandwidth, so that an adaptive proportional-integral (PI) controller is proposed for this matter. In the paper, two different droop control methods have been modeling, designed, simulated, and tested: The conventional virtual-impedance-loop based V–I droop and the proposed embedded-virtual-impedance based I–V droop. In order to compare the dynamic response performances between two droop controllers, their state-space models have been developed and analyzed in this paper. The results show that the dynamic response of the I–V droop control is faster than that of the conventional V–I droop control. Furthermore, by analyzing the effects from I–V droop control parameters, the errors can be reduced faster by enlarging the proportional terms, but with no fluctuations, and then completely eliminated by restoring back to small proportional values. Meanwhile, there exists a tradeoff phenomenon between the fast dynamic response and good steady-state performance; thus, an adaptive PI controller is proposed to both improve dynamic response and guarantee good steady-state performance simultaneously. Experimental results are shown to verify the accuracy of the models and the effectiveness of the proposed control framework.
83 citations
TL;DR: Experimental results from a grid-connected lab-scale microgrid system are presented to prove effectiveness and robustness of the proposed model predictive control based on power/voltage smoothing strategy.
Abstract: Random fluctuation in photovoltaic (PV) power plants is becoming a serious problem affecting the power quality and stability of the grid along with the increasing penetration of PVs. In order to solve this problem, by the adding of energy storage systems (ESS), a grid-connected microgrid system can be performed. To make this system feasible, this paper proposes a model predictive control (MPC) based on power/voltage smoothing strategy. With the receding horizon optimization performed by MPC, the system parameters can be estimated with high accuracy, and at the same time the optimal ESS power reference is obtained. The critical parameters, such as state of charge, are also taken into account in order to ensure the health and stability of the ESSs. In this proposed control strategy, communication between PVs and ESS is not needed, since control command can be calculated with local measured data. At the same time, MPC can make a great contribution to the accuracy and timeliness of the control. Finally, experimental results from a grid-connected lab-scale microgrid system are presented to prove effectiveness and robustness of the proposed approach.
73 citations
TL;DR: A novel passivity-based coordinated control strategy is proposed for an islanded AC microgrid including renewable energy source and energy storage system units and the asymptotical stability of the whole microgrid can be guaranteed by using the passivity principle when the heterogeneous renewable energy sources are integrated into the microgrid.
61 citations
TL;DR: In this paper, an enhanced state observer-based controller is proposed to regulate the dc-link voltage of three-phase ac/dc converters, which does not require the dclink current measurement and offers a "plug and play" capability, a rather high disturbance rejection ability and robustness against the dc link capacitance parameter variation.
Abstract: To regulate the dc-link voltage of three-phase ac/dc converters, an enhanced state observer-based controller is presented in this letter. The proposed controller, contrary to the traditional ones, does not require the dc-link current measurement and offers a “plug and play” capability, a rather high disturbance rejection ability and robustness against the dc-link capacitance parameter variation. The design procedure of the suggested controller is discussed, and its effectiveness is verified using experimental results.
TL;DR: A state-of-the-art of the IoT-based energy systems is presented to review the recent activities on every component of IoT in energy systems.
Abstract: The Internet of Things (IoT) is beginning to shape the future of many industries and emerging markets. One of the target markets for IoT is the energy systems. IoT is a matter of producing, transferring, and processing information, therefore all parts of the system including software and hardware parts should be considered as a whole. In this paper, a state-of-the-art of the IoT-based energy systems is presented to review the recent activities on every component of IoT in energy systems. Challenges in this subject area are discussed, and some solutions are presented thereafter.
TL;DR: The proposed voltage modulated direct power control for three-phase pulsewidth modulated rectifier has guaranteed that the closed system is globally exponentially stable.
Abstract: In this paper, a voltage modulated direct power control for three-phase pulsewidth modulated rectifier is proposed. With the suggested method, the differential equations describing the rectifier dynamics are changing from a linear time-varying system into a linear time-invariant one. In this way, conventional feedback and feedforward controllers are applicable for the independent control of active and reactive powers. The proposed method has guaranteed that the closed system is globally exponentially stable. A feedback linearization method is also employed for generating the active power reference of inner loops. Finally, some experimental tests are conducted to verify its effectiveness.
TL;DR: A dynamic consensus algorithm (DCA)-based coordinated secondary control with an autonomous current-sharing control strategy is proposed in this paper for balancing the discharge rate of energy storage systems (ESSs) in an islanded ac microgrid.
Abstract: A dynamic consensus algorithm (DCA)-based coordinated secondary control with an autonomous current-sharing control strategy is proposed in this paper for balancing the discharge rate of energy storage systems (ESSs) in an islanded ac microgrid. The DCA is applied for information sharing between distributed generation (DG) units to regulate the output power of DGs according to the ESS capacities and state-of-charge (SoC). Power regulation is achieved by adjusting the virtual resistances of voltage-controlled inverters with an autonomous current-sharing controller. Compared with existing methods, the proposed approach can provide higher system reliability, expandability, and flexibility due to its distributed control architecture. The proposed controller can effectively prevent operation failure caused by over-current and unintentional outage of DGs by means of balanced discharge rate control. It can also provide fast response and accurate current sharing performance. A generalizable linearized state-space model for ${n}$ -DG network in the ${z}$ -domain is also derived and proposed in this paper; the model includes electrical, controller, and communication parts. The system stability and parameter sensitivity have been analyzed based on this model. To verify the effectiveness of the proposed control approach, this paper presents simulation results from a ten-node network and a comparison between experimental results obtained from the conventional power sharing control and the DCA-based SoC coordinated control in a setup with three 2.2 kW DG units.
TL;DR: In this paper, the authors proposed a coordination architecture for islanded ac microgrids, which considers the appropriate charge profiles for battery-based energy storage systems and uses only local measurements for determining the operation mode of each unit independently.
Abstract: For reliable operation of an islanded microgrid, at least one of its distributed resources should assume the responsibility of forming the off-grid power system. This responsibility is usually assumed by energy storage systems based on their capability of compensating the unbalance between generation and consumption. However, the storage units lose this capability when they reach the maximum and minimum limits of charge. Under these conditions, the regulation of the power grid may be assumed by another unit with enough capability or the power balance should be adjusted coordinately. This paper proposes a coordination architecture for islanded ac microgrids, which considers the appropriate charge profiles for battery-based energy storage systems. The architecture is based on distributed decision-making mechanisms, which use only local measurements for determining the operation mode of each unit independently. The coordination relies on a bus-signaling method, which enables the distributed units to have a global perception about the operation of the microgrid, without any communication infrastructure. The proposed architecture includes cooperative operation between distributed energy storage systems for achieving the equalization of the states of charge. Experimental results in a lab-scale microgrid with network configuration validate the proposed strategy under different operational conditions.
TL;DR: Based on a structural resemblance between a resonant current regulator and second-order generalized integrator-based frequency-locked loop, a frequency-adaptive resonant controller is presented and some experimental results are presented to verify its effectiveness.
Abstract: The proportional-resonant (PR) controller is highly popular for controlling grid-connected voltage source converters. The resonant part of this controller provides an infinite gain at the nominal frequency and, in this way, ensures a zero steady-state tracking error when the grid frequency is at its nominal value. In the presence of frequency drifts, nevertheless, a zero tracking error may not be guaranteed. To deal with this problem, the resonance frequency of the PR controller may be updated using the frequency estimated by the synchronization unit, which is often a phase-locked loop. In recent years, however, there is a growing attention toward eliminating the need for a dedicated synchronization unit and designing integrated synchronization and control structures as they benefit from a simpler and more compact structure. In this letter, based on a structural resemblance between a resonant current regulator and second-order generalized integrator-based frequency-locked loop, a frequency-adaptive resonant controller is presented. The tuning procedure of the proposed controller is discussed, and some experimental results are presented to verify its effectiveness.
TL;DR: In this paper, the authors classify community grids responsible for the electrification of developing regions based on architecture, type of generation, and mode distribution, and propose an off-grid solution for achieving higher efficiency and reliability on a village scale.
Abstract: There is a worldwide focus on the electrification of developing regions, as is evident from the sustainable development goals (SDGs) of the United Nations. In particular, the aim of SDG 7 is to ensure universal access to affordable, reliable, sustainable, and modern energy services for all by 2030. Because of these sustained efforts, more than 1 billion people worldwide have gained access to electricity since 2000. During this course, the electrification architecture of developing regions has taken different forms, ranging from extensive utility grid extensions to limited off-grid solutions. Off-grid solutions generally offer cost-effective and lower up-front cost alternatives in comparison to utility grid extensions and are deemed more suitable for developing economies. In developing economies, these off-grid electrification solutions have evolved from individual solar home-based systems to community-based microgrids in pursuit of achieving higher efficiency and reliability on a village scale. Community grids responsible for the electrification of developing regions are further categorized based on architecture, type of generation, and mode distribution.
TL;DR: It is demonstrated that some supposedly different PLLs using the steady-state linear Kalman filter are actually equivalent to some well-known SRF-PLL structures and, therefore, provide no advantage compared to them.
Abstract: In three-phase power and energy applications, the synchronous reference frame phase-locked loop (SRF-PLL) is a popular tool for synchronization purposes. The SRF-PLL can be easily and effectively customized for different scenarios by changing its loop filter. Recently, some supposedly different PLLs using the steady-state linear Kalman filter have been developed. The main aim of this letter is to analyze these PLLs. It is demonstrated that they are actually equivalent to some well-known SRF-PLL structures and, therefore, provide no advantage compared to them.
TL;DR: Blackbox models are proposed as a tool to foresee the effect of these complex interactions, overcoming the lack of detailed information about the power converters, and large-signal strategies are proposed in order to consider nonlinearities in the static and dynamic behavior of the converters.
Abstract: Maritime applications have found in the integration of the electric power system a way to further improve efficiency and reduce the weight of new electric ships. This movement has led scientists to integrate smart management systems to optimize the overall behavior of the grid. In this context, power electronics play a key role in linking the different elements of the power architecture. Moreover, the transition toward a dc distribution, which has already been established in other applications, is being regarded as a promising alternative to ease the integration of renewable sources, batteries, and the ever increasing number of dc loads. In this paper, blackbox models are proposed as a tool to foresee the effect of these complex interactions, overcoming the lack of detailed information about the power converters. Large-signal strategies are proposed in order to consider nonlinearities in the static and dynamic behavior of the converters. An accurate model of the physical layer is essential to allow intelligent systems to take the most out of the system performance. This approach offers the opportunity to study the dynamic response of complex interconnected systems, tune the system-level controllers, design protections, or assess the compliance of the system dynamics with the standards. Experimental results are included in order to validate the proposed method.
TL;DR: The aim of this letter is to develop an effective OLS technique for single-phase power and energy applications that benefits from a straightforward implementation, a fast dynamic response, and a complete immunity against the dc component in the grid voltage.
Abstract: From the control point of view, synchronization techniques are divided into two major categories: open-loop and closed-loop methods. Roughly speaking, open-loop synchronization (OLS) approaches are not as popular as closed-loop ones, probably because they suffer from a poor performance in the presence of frequency drifts. This is particularly true in single-phase applications, where the lack of multiple independent input signals makes the implementation of the synchronization technique difficult. The aim of this letter is to develop an effective OLS technique for single-phase power and energy applications. The proposed OLS method benefits from a straightforward implementation, a fast dynamic response (a response time less than two cycles of the nominal frequency), and a complete immunity against the dc component in the grid voltage. In addition, the designed OLS method totally blocks (significantly attenuates) all harmonics up to the aliasing point under a nominal (off-nominal) frequency. The effectiveness of the designed OLS technique is verified using comparative experimental results.
TL;DR: An improved open loop strategy which is based on non-linear least square (NLS) approach can extract the fundamental voltage and estimates its phase within only half cycle, even in the presence of odd harmonics and dc offset.
TL;DR: The results show that the proposed TCB-DPWM can effectively simplify the implementation of modulation and improve system efficiency.
Abstract: This paper proposes a triangle carrier-based discontinuous pulsewidth modulation (TCB-DPWM) implement method for three-level neutral-point-clamped (3L-NPC) inverters. The function equivalent relationship of the proposed TCB-DPWM and space vector-based DPWM (SVB-DPWM) is mathematically analyzed in this paper. The proposed TCB-DPWM method effectively simplified the implementation of the SVB-DPWM by injecting twice common mode voltages (CMVs) to original modulation signals, where different DPWM methods can be easily obtained in a unified scheme by setting different values of the proportional allocation factor for small vectors in different sectors. In addition, a TCB-DPWM-based neutral-point voltage balancing method is investigated to demonstrate its application. The polarity of the CMV injection is regulated according to the polarity of the proportional allocation factor to realize the neutral-point voltage balancing. Finally, the proposed TCB-DPWM and the neutral-point voltage balancing method are both verified by simulation and experimental results. The results show that the proposed TCB-DPWM can effectively simplify the implementation of modulation and improve system efficiency.
TL;DR: In this paper, a distributed hierarchical control architecture for voltage and frequency stabilization and reactive power sharing in AC islanded microgrids is presented, where each generation unit is equipped with a local regulator for voltage stability acting on the corresponding voltage-source converter.
TL;DR: The tuning procedure and analysis of some well-known single-phase and three-phase PLLs are considered and the main aim of this paper is to cover the gap in small-signal modeling of a variable-length delay-based PLL.
Abstract: In power and energy applications, implementing a large number of phase-locked loops (PLLs) involves using transfer delays. These delays are employed for different control and filtering purposes, such as creating a fictitious orthogonal signal (which is required for the frame transformation in single-phase PLLs) and filtering harmonics, dc offset, and other disturbances. Depending on the application in hand and the expected variation range of the grid frequency, the length of these delays may be variable or fixed. Roughly speaking, the variable-length delays are often preferred for applications where large frequency drifts are anticipated and a high accuracy is required. To the best of authors’ knowledge, the small-signal modeling of a variable-length delay-based PLL has not yet been conducted. The main aim of this paper is to cover this gap. The tuning procedure and analysis of these PLLs are also presented. As design examples, some well-known single-phase and three-phase PLLs are considered.
TL;DR: In this paper, an adaptive current controller was proposed for three-phase grid-connected converters by using a conventional SRF phase-locked loop, in which the current controller and synchronization part are merged into a single unit, which results in a simpler and more compact structure.
Abstract: The current control of three-phase grid-connected converters is typically carried out by using a proportional-resonant controller or synchronous reference frame (SRF) proportional-integral regulator. The implementation of these controllers often requires knowledge of the grid voltage frequency/phase angle, which is typically provided by a synchronization unit. It implies that dynamics and possible inaccuracies of the synchronization unit have a considerable impact on the current controller performance. The aim of this letter is to design an adaptive current controller by using a conventional SRF phase-locked loop. In this way, the current controller and synchronization part are merged into a single unit, which results in a simpler and more compact structure. The effectiveness of the proposed controller is verified using experimental results.
TL;DR: In this paper, a nonadaptive MAF-based QSG with some error compensators is suggested to reduce the implementation complexity while maintaining a good performance, which is briefly referred as the non-adaptive maf-based PLL, and verified using experimental results.
Abstract: The rectangular window filter, typically known as the moving average filter (MAF), is a quasi-ideal low-pass filter that has found wide application in designing advanced single-phase phase-locked loops (PLLs). Most often, the MAF is employed as an in-loop filter within the control loop of the single-phase PLL. The in-loop MAF, however, causes a large phase delay and, hence, makes the PLL dynamic response slow. Recently, using MAFs as a prefilter/quadrature signal generator (QSG) before the PLL input has been suggested. As the MAFs are outside the PLL control loop, the problem of slow dynamic response is avoided. Nevertheless, the PLL implementation complexity considerably increases as MAFs are frequency-adaptive and, therefore, they require an additional frequency detector for estimating the grid frequency. To reduce the implementation complexity while maintaining a good performance, using a nonadaptive MAF-based QSG with some error compensators is suggested in this letter. The effectiveness of the resultant PLL, which is briefly called the nonadaptive MAF-based PLL, is verified using experimental results.
TL;DR: A voltage detection based harmonic compensator (HC) for CCM converters is proposed that realizes seamless interface of HC with inner fundamental current control loop and offers better performance because of directly harmonic voltage regulation.
Abstract: Harmonics have been considered as one of the major issues in future power grids. With the increasing demand in advanced control functions, power electronic converter interfaced distributed generators (DGs) are expected to perform harmonic compensation when necessary. It has been demonstrated in a number of studies that DG converters operating in voltage-controlled mode can be easily configured to realize voltage harmonic compensation utilizing naturally embedded voltage control loop. While for DGs operating in current-controlled mode (CCM), such function was rarely studied. Considering that CCM is commonly used in renewable energy based generators and energy storage systems, it has certain significance to achieve the same function with CCM converters. Aiming at such objectives, this paper proposes a voltage detection based harmonic compensator (HC) for CCM converters. The novelty and main advantages of the proposed method include the following. It realizes seamless interface of HC with inner fundamental current control loop. Compared with a conventional active power filtering method, it does not require remote load harmonic current measurement since it is local voltage detection based. Compared with a conventional voltage detection based method, it offers better performance because of directly harmonic voltage regulation. Experimental results are presented to demonstrate the effectiveness of the method.
TL;DR: In the last decade, new energy policies have boosted the integration of renewable energy sources (RESs) into the electrical power system in an attempt to reduce fossil fuel consumption and move toward a cleaner and more sustainable energy system.
Abstract: In the last decade, new energy policies have boosted the integration of renewable energy sources (RESs) into the electrical power system in an attempt to reduce fossil fuel consumption and move toward a cleaner and more sustainable energy system. A good example of this is the 2020 and 2030 energy strategy of the European Union. The established goals of this policy require a 40% cut in greenhouse gas emissions and at least a 27% increase of shared renewable energy consumption and a 27% increase in energy savings.
TL;DR: An improved consensus-based distributed controller is proposed to alleviate the overshoot issue during the transient process in voltage amplitude and frequency restoration and increase the system reliability and robustness.
Abstract: In this paper, a dc-link voltage protection (DCVP) control method is proposed to address the dc-link overvoltage issue due to power backfeeding in a parallel uninterruptible power supply (UPS) system. The proposed control method is able to protect the inverter against the excessive dc-link voltage, which increases the system reliability and robustness. Moreover, a current sharing control strategy is proposed by online regulating the virtual resistance of each UPS module. The proposed current sharing control strategy is able to address the circulating fundamental and harmonic currents caused by the line impedance mismatching or power backfeeding issue in the UPS system. In addition, an improved consensus-based distributed controller is proposed to alleviate the overshoot issue during the transient process in voltage amplitude and frequency restoration. Finally, the feasibility of the proposed methods is verified by experimental results from the parallel UPS prototypes.
16 Oct 2018
TL;DR: In this paper, the integration of microgrid technologies in conventional seaports aims to become the initial step to the future “green port.” Furthermore, microgrids research has significantly increase self-sustainability for the future port because of their efficient on-site integration and coordination of renewable energy sources such as photovoltaic systems, wind turbines, and energy storage system.
Abstract: The issue is mostly attributable to the growth of maritime, inland shipping, waterborne transport and trade demand in the freight sector. This fundamental problem is being a key concern for the European Commission because it leads to adverse health and environmental effects. To solve the emission issues, shore-side-power emerges as an initial solution to mitigate the unwanted environmental impact of ships at berth. In addition to this, port development must be in line with the emerging ships technologies as most of the ships are moving forward All-Electric-Ship (AES) concept. However, the use of shore-side-power is still new, although the international standard was recently available, shore-side-power still facing technical challenges like power supply/demand power, different voltage, and frequency level on the ship and port side. Therefore, the integration of microgrid technologies in conventional seaports aims to become the initial step to the future “green port.” Furthermore, microgrids research has significantly increase self-sustainability for the future port because of their efficient on-site integration and coordination of renewable energy sources such as photovoltaic systems, wind turbines, and energy storage system. This challenging solution will provide more benefits to end-users as well as fuel cost savings and high system reliability.