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Showing papers on "Voltage regulation published in 2017"


Journal ArticleDOI
TL;DR: An extended state observer (ESO) based second-order sliding-mode (SOSM) control for three-phase two-level grid-connected power converters and experimental results are presented to validate the control algorithm under a real power converter prototype.
Abstract: This paper proposes an extended state observer (ESO) based second-order sliding-mode (SOSM) control for three-phase two-level grid-connected power converters. The proposed control technique forces the input currents to track the desired values, which can indirectly regulate the output voltage while achieving a user-defined power factor. The presented approach has two control loops. A current control loop based on an SOSM and a dc-link voltage regulation loop which consists of an ESO plus SOSM. In this work, the load connected to the dc-link capacitor is considered as an external disturbance. An ESO is used to asymptotically reject this external disturbance. Therefore, its design is considered in the control law derivation to achieve a high performance. Theoretical analysis is given to show the closed-loop behavior of the proposed controller and experimental results are presented to validate the control algorithm under a real power converter prototype.

414 citations


Journal ArticleDOI
TL;DR: In this article, a coordinated voltage regulation method based on soft open point (SOP) was proposed for active distribution networks (ADNs) to minimize operation costs and eliminate voltage violations of ADNs.
Abstract: The increasing penetration of distributed generators (DGs) exacerbates the risk of voltage violations in active distribution networks (ADNs). The conventional voltage regulation devices limited by the physical constraints are difficult to meet the requirement of real-time voltage and VAR control (VVC) with high precision when DGs fluctuate frequently. However, soft open point (SOP), a flexible power electronic device, can be used as the continuous reactive power source to realize the fast voltage regulation. Considering the cooperation of SOP and multiple regulation devices, this paper proposes a coordinated VVC method based on SOP for ADNs. First, a time-series model of coordinated VVC is developed to minimize operation costs and eliminate voltage violations of ADNs. Then, by applying the linearization and conic relaxation, the original nonconvex mixed-integer nonlinear optimization model is converted into a mixed-integer second-order cone programming model which can be efficiently solved to meet the requirement of voltage regulation rapidity. Case studies are carried out on the IEEE 33-node system and IEEE 123-node system to illustrate the effectiveness of the proposed method.

262 citations


Journal ArticleDOI
TL;DR: An extended droop control (EDC) strategy to achieve dynamic current sharing autonomously during sudden load change and resource variations for hybrid energy storage system is proposed.
Abstract: Power allocation is a major concern in hybrid energy storage system. This paper proposes an extended droop control (EDC) strategy to achieve dynamic current sharing autonomously during sudden load change and resource variations. The proposed method consists of a virtual resistance droop controller and a virtual capacitance droop controller for energy storages with complementary characteristics, such as battery and supercapacitor (SC). By using this method, battery provides consistent power and SC only compensates high-frequency fluctuations without the involvement of conventionally used centralized controllers. To implement the proposed EDC method, a detailed design procedure is proposed to achieve the control objectives of stable operation, voltage regulation, and dynamic current sharing. System dynamic model and relevant impedances are derived and detailed frequency domain analysis is performed. Moreover, the system level stability analysis is investigated and system expansion with the proposed method is illustrated. Both simulations and experiments are conducted to validate the effectiveness of the proposed control strategy and analytical results.

255 citations


Journal ArticleDOI
TL;DR: In this article, a small-signal model is proposed to understand VSC external characteristics based on motion equation concept also featured in synchronous generator (SG), which can hold the main behaviors of concern.
Abstract: With the increasing use of voltage source converters (VSCs) in power electronics dominated power systems, oscillation phenomena in DC-link voltage control (DVC) timescale (around 10 Hz) among multiple VSCs have occurred. Several studies have tried to analyze these oscillation problems, but all associated with the single VSC situation. To consider the dynamic interactions between VSCs in DVC timescale, especially in the weak grid condition, this paper presents a small-signal model to understand VSC external characteristics based on motion equation concept also featured in synchronous generator (SG). Comparisons of time-domain simulation responses and eigenvalues show that the proposed model can hold the main behaviors of concern. The form of the model is very similar to the rotor motion equation in SG, with which power engineers have been very familiar. In addition, by establishing the relationship between the unbalanced powers and state variables of internal voltage (viz., VSC output voltage), the modeling idea introduced in this paper can be applied to other power electronic devices.

211 citations


Journal ArticleDOI
TL;DR: In this article, a multi-timescale coordinated stochastic voltage/var control method for high renewable-penetrated distribution networks is proposed, which utilizes multiple devices to counteract uncertain voltage fluctuation and deviation.
Abstract: This paper proposes a multi-timescale coordinated stochastic voltage/var control method for high renewable-penetrated distribution networks. It aims to utilize multiple devices to counteract uncertain voltage fluctuation and deviation. In the hourly timescale (first stage), capacitor banks and transformer tap changers are scheduled before stochastic renewable output and load variations are realized. In the 15-min timescale (second stage), inverters that interface the renewable energy resources provide var support to supplement the first-stage decision after uncertainty is observed. The coordination is model as a two-stage stochastic programming problem with scenario reduction. It is then converted to a deterministic mixed-integer quadratic programming equivalence model and solved by commercial solvers combined. Compared with existing methods, the proposed volt/var control can achieve lower expected energy loss and can sustain a secure voltage level under random load demand and renewable power injection. The proposed method is verified on the IEEE 33-bus distribution network and compared with existing practices.

210 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a design procedure for the smart transformer architecture, which is composed of at least two power stages, each of which provides ancillary services to the distribution and transmission grids to optimize their performance.
Abstract: The solid-state transformer (SST) was conceived as a replacement for the conventional power transformer, with both lower volume and weight. The smart transformer (ST) is an SST that provides ancillary services to the distribution and transmission grids to optimize their performance. Hence, the focus shifts from hardware advantages to functionalities. One of the most desired functionalities is the dc connectivity to enable a hybrid distribution system. For this reason, the ST architecture shall be composed of at least two power stages. The standard design procedure for this kind of system is to design each power stage for the maximum load. However, this design approach might limit additional services, like the reactive power compensation on the medium voltage (MV) side, and it does not consider the load regulation capability of the ST on the low voltage (LV) side. If the SST is tailored to the services that it shall provide, different stages will have different designs, so that the ST is no longer a mere application of the SST but an entirely new subject.

207 citations


Journal ArticleDOI
TL;DR: In this article, a local voltage regulation technique that utilizes very short-term (15 s) PV power forecasts to circumvent imminent upper voltage limit violation or an overvoltage scenario is proposed.
Abstract: Distribution voltage profiles are subjected to overvoltage limit violations from high penetration of grid-connected photovoltaic (PV) systems. Such voltage rises seen at the point of PV interconnection can be mitigated by adaptively changing the active and/or reactive power injection from the PV inverter. This work proposes a local voltage regulation technique that utilizes very short-term (15 s) PV power forecasts to circumvent imminent upper voltage limit violation or an overvoltage scenario. To provide these PV generation forecasts, a hybrid forecasting method is formulated based on Kalman filter theory, which applies physical PV generation modeling using high-resolution (15 s) data from on-site measurements. The proposed algorithm employs an active power curtailment based on these PV power forecasts, when the reactive power estimate given by a droop-based method cannot provide the desired voltage regulation within predefined power factor limits. The curtailment threshold values are calculated in such a way that this voltage regulation technique can reduce possible voltage limit violations. The effectiveness of the proposed method is demonstrated with case studies developed on a standard test feeder with realistic load and PV generation profiles.

206 citations


Journal ArticleDOI
TL;DR: In this article, a dual-bridge LLC resonant converter for wide input applications is proposed and the topology is an integration of a half-bridge (HB) LLC circuit and a full-bridge circuit.
Abstract: This paper proposes a dual-bridge (DB) LLC resonant converter for wide input applications. The topology is an integration of a half-bridge (HB) LLC circuit and a full-bridge (FB) LLC circuit. The fixed-frequency pulsewidth-modulated (PWM) control is employed and a range of twice the minimum input voltage can be covered. Compared with the traditional pulse frequency modulation (PFM) controlled HB/FB LLC resonant converter, the voltage gain range is independent of the quality factor, and the magnetizing inductor has little influence on the voltage gain, which can simplify the parameter selection process and benefit the design of magnetic components as well. Over the full load range, zero-voltage switching (ZVS) and zero-current switching (ZCS) can be achieved for primary switches and secondary rectifier diodes, respectively. Detailed analysis on the modulation schedule and operating principle of the proposed converter is presented along with the converter performance. Finally, all theoretical analysis and characteristics are verified by experimental results from a 120-V to 240-V input 24 V/20 A output converter prototype.

167 citations


Journal ArticleDOI
TL;DR: This study presents an overview of various control schemes used for voltage and frequency regulation in standalone and transition mode operation of hybrid microgrid and some recommendations are presented for future research.
Abstract: Microgrids have become an attractive option for distributed generation (DG) with increase in renewable energy sources (RES) and storage systems. The existence of both AC and DC microgrids has led to a new concept of hybrid AC/DC microgrid which consists of both AC and DC grids tied by an interlinking converter (ILC). Such hybrid AC/DC microgrid has the advantages of both AC and DC with increased efficiency and less cost since the conversion between AC and DC is reduced. The management of power in such a grid becomes important for voltage and frequency control. Different voltage and frequency control strategies have been successfully implemented within AC and DC grids, but the control of hybrid microgrid requires further attention with focus on ILC. This study presents an overview of various control schemes used for voltage and frequency regulation in standalone and transition mode operation of hybrid microgrid. A detailed study on hybrid grid structure is presented with different modes of operation. Various ILC strategies based on droop and communication-based control are presented. Based on the analysis, some recommendations are presented for future research.

154 citations


Journal ArticleDOI
TL;DR: In this article, a new control scheme is proposed to control the power sharing between batteries and supercapacitors to match the generation-demand mismatch and regulate the grid voltage, which not only improves the dc grid voltage regulation capability but also reduces the stress levels on the battery and hence increases the life span of the battery.
Abstract: The power generation from renewable power sources is variable in nature, and may contain unacceptable fluctuations in case of the wind power generation. High fluctuations in power generation may negatively impact the voltage stability of the microgrid. This problem can be alleviated by using hybrid energy storage system consisting of batteries and supercapacitors (SCs) at dc grid. A new control scheme is proposed to control the power sharing between batteries and SCs to match the generation-demand mismatch and hence to regulate the grid voltage. In the proposed control strategy, the SC supplies error component of the battery current in addition to the fast transient power demand. This added feature not only improves the dc grid voltage regulation capability but also reduces the stress levels on the battery and hence increases the life span of the battery. The main advantage of the scheme is that, the uncompensated power due to slow dynamics of the battery is diverted to the SC and keeps the state of charge within the limits for longer duration, as compared to the conventional strategy. The proposed scheme is validated through detailed experimental studies.

148 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the problem of high-parasitic capacitances produced by large overlapping layers in planar transformers (PTs) and proposed mitigation strategies to improve the performance of $LLC$ converters with PTs.
Abstract: The use of $LLC$ resonant converters has gained popularity in multiple applications that require high conversion efficiency and galvanic isolation. In particular, many applications like portable devices, flat TVs, and electric vehicle battery chargers require demanding slim-profile packaging and enforce the use of planar transformers (PTs) with low-height, low leakage inductance, excellent thermal characteristics, and manufacturing simplicity. The main challenge in successfully designing $LLC$ converters with PT resides in controlling high-parasitic capacitances produced by large overlapping layers in PT windings. When the parasitic capacitances are not controlled, they severely impair the converters’ performance and regulation, and limit the application of PTs in high-frequency $LLC$ converters. This paper characterizes the PT capacitance issue in detail and proposes mitigation strategies to improve the performance of $LLC$ converters with PTs. A systematic analysis is performed, and six PT winding layouts are introduced and benchmarked with a traditional design. As a result of the investigation, an optimized structure is obtained, which minimizes both the interwinding capacitance and ac resistance, while improving the regulation performance of $LLC$ converters. Experimental measurements are presented and show a significant reduction of parasitic capacitance by up to 21.2 intra- and 16.6 interwinding capacitances, without compromising resistance. This substantial capacitance reduction has a tangible effect on the regulation performance of $LLC$ resonant converters. Experimental results of the proposed PT structure in a 1.2 kW $LLC$ resonant converter show a reduction in common-mode noise, extended output voltage regulation, and improved overall efficiency of the converter.

Journal ArticleDOI
TL;DR: In this paper, a mixed integer non-linear optimization problem is formulated to optimally determine the siting and sizing of SOPs based on the typical operation scenarios generated by Wasserstein distance.

Journal ArticleDOI
TL;DR: The proposed controller offers various advantages, such as allowing the integration of significant levels of intermittent renewable resources in isolated/islanded microgrids without the need for large energy storage systems, providing fast and smooth frequency regulation with no steady-state error, regardless of the generator control mechanism.
Abstract: This paper presents a frequency control mechanism for an isolated/islanded microgrid through voltage regulation. The proposed scheme makes use of the load voltage sensitivity to operating voltages and can be easily adopted for various types of isolated microgrids. The proposed controller offers various advantages, such as allowing the integration of significant levels of intermittent renewable resources in isolated/islanded microgrids without the need for large energy storage systems, providing fast and smooth frequency regulation with no steady-state error, regardless of the generator control mechanism. The controller requires no extra communication infrastructure, and only local voltage and frequency is used as feedback. The performance of the controller is evaluated and validated through various simulation studies in the PSCAD/EMTDC software environment based on a realistic microgrid test system, using small-perturbation stability analysis to demonstrate the positive effect of the proposed controller in system damping.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the stability of digitally voltage-controlled voltage-source inverters (VSIs) with the linear voltage regulators and proposed an enhanced voltage control approach with a widened stability region, and a step-by-step design method of the proposed controller was developed based on the root contours in the discrete z-domain.
Abstract: This paper analyzes the stability of digitally voltage-controlled voltage-source inverters (VSIs) with the linear voltage regulators. It is revealed that the phase lags, caused by using the resonant controller and the time delay of a digital control system, can stabilize the single-loop voltage control without damping of the LC -filter resonance. The stability region for the digital single-loop resonant voltage control is then identified, considering the effects of different discretization methods for the resonant controller. An enhanced voltage control approach with a widened stability region is subsequently proposed, and a step-by-step design method of the proposed controller is developed based on the root contours in the discrete z -domain. Simulations and experimental tests of a 400-Hz VSI system validate the stability analysis and the performance of the proposed control approach.

Journal ArticleDOI
TL;DR: In this paper, a two-phase interleaved LLC (iLLC) resonant converter with hybrid rectifier is proposed for wide output voltage range applications, where the primary sides of the two LLC converters are in parallel, and the connection of the secondary windings can be regulated by the hybrid rectifiers according to the output voltage.
Abstract: A family of two-phase interleaved LLC (iLLC) resonant converter with hybrid rectifier is proposed for wide output voltage range applications. The primary sides of the two LLC converters are in parallel, and the connection of the secondary windings in the two LLC converters can be regulated by the hybrid rectifier according to the output voltage. Variable frequency control is employed to regulate the output voltage and the secondary windings are in series when the output voltage is high. Fixed-frequency phase-shift control is adopted to regulate the configuration of the secondary windings as well as the output voltage when the output voltage is low. The output voltage range is extended by adaptively changing the configuration of the hybrid rectifier, which results in reduced switching frequency range, circulating current, and conduction losses of the LLC resonant tank. Zero voltage switching and zero current switching are achieved for all the active switches and diodes, respectively, within the entire operation range. The operation principles are analyzed and a 3.5 kW prototype with 400 V input voltage and 150–500 V output voltage is built and tested to evaluate the feasibility of the proposed method.

Journal ArticleDOI
TL;DR: In this article, the optimal location and size of a battery energy storage system (BESS) for voltage regulation in a distribution system while increasing the battery lifespan was found for voltage control.
Abstract: The lifespan of a battery in battery energy storage systems (BESSs) is affected by various factors such as the operating temperature of the battery, depth of discharge, and magnitudes of the charging/discharging currents supplied to or drawn from the battery In this study, the optimal location and size of a BESS are found for voltage regulation in a distribution system while increasing the lifespan of the battery Various factors that affect the lifespan of a battery are considered and modelled The problem is formulated as a multi-objective optimisation problem with two-objective functions The first objective function calculates the energy losses in the system, whereas the second objective function represents the total investment cost of the distributed generator (DG) and BESS installations Wind and solar DGs with uncertainties in their output powers are also considered with the BESSs An elitist non-dominated sorting genetic algorithm-II with a utopian point method is used to solve the optimisation problem Furthermore, an IEEE 906 bus European low-voltage test feeder and eight test cases are considered for this study The results show reduced losses and cost, improvement in the voltage profile, and extended lifespan of the batteries

Journal ArticleDOI
TL;DR: In this paper, the transient response of three-phase VSCs under practical grid voltage dips is studied and a catastrophic bifurcation phenomenon is identified in the system. And a set of design-oriented stability boundaries in some chosen parameter space are verified by cycle-bycycle simulations and experimental measurement on a practical grid-connected VSC prototype.
Abstract: Three-phase voltage source converters (VSCs) are commonly used as power flow interface in ac/dc hybrid power systems. The ac power grid suffers from unpredictable short-circuit faults and power flow fluctuations, causing undesirable grid voltage dips. The voltage dips may last for a short time or a long duration, and vary the working conditions of VSCs. Due to their nonlinear characteristics, VSCs may enter abnormal operating mode in response to voltage dips. In this paper, the transient response of three-phase VSCs under practical grid voltage dips is studied and a catastrophic bifurcation phenomenon is identified in the system. The converter will exhibit an irreversible instability after the dips. The expanded magnitude of ac reactive current may cause catastrophic consequence for the system. A full-order eigenvalue analysis and a reduced-order mixed-potential-theory-based analysis are adopted to reveal the physical origin of the large-signal instability phenomenon. The key parameters of the system are identified and the boundaries of instability are located. The bifurcation phenomenon and a set of design-oriented stability boundaries in some chosen parameter space are verified by cycle-by-cycle simulations and experimental measurement on a practical grid-connected VSC prototype.

Journal ArticleDOI
TL;DR: In this article, a real-time simulation model is developed for a full-transit battery electric buses (BEB) operation in order to quantify the energy demands, design the required infrastructure of the charging station, test the transit operation feasibility, and generate the charging load profile.

Journal ArticleDOI
TL;DR: A hybrid control method combining pulse frequency modulation (PFM) and pulse width modulation is proposed to overcome the limited frequency resolution issue and improve voltage regulation performance for LLC resonant converters.
Abstract: High switching frequency is an effective method to improve power density for LLC resonant converters. However, conventional digital controllers, such as general-purpose digital signal processors and microprocessors, have limited frequency resolution, which induces high primary- and secondary-side current variation and leads to poor output voltage regulation. In this paper, a hybrid control method combining pulse frequency modulation (PFM) and pulse width modulation is proposed to overcome the limited frequency resolution issue. The proposed hybrid control method focuses on steady-state operation, and its operating principles are introduced and analyzed. In addition, the proper magnetizing inductance and dead time duration are derived to ensure that the power mosfet s achieve zero voltage switching with the proposed control method. The improved voltage regulation performance is compared with the conventional PFM control and verified through simulation and experimental results using a 240 W prototype converter operating at a switching frequency of 1 MHz.

Journal ArticleDOI
TL;DR: It is shown that an inverter-interfaced microgrid under plug-and-play (PnP) functionality of distributed generations (DGs) can be cast as a linear time-invariant system subject to polytopic-type uncertainty.
Abstract: This paper proposes a decentralized control strategy for the voltage regulation of islanded inverter-interfaced microgrids. We show that an inverter-interfaced microgrid under plug-and-play (PnP) functionality of distributed generations (DGs) can be cast as a linear time-invariant system subject to polytopic-type uncertainty. Then, by virtue of this novel description and use of the results from theory of robust control, the microgrid control system guarantees stability and a desired performance even in the case of PnP operation of DGs. The robust controller is a solution of a convex optimization problem. The main properties of the proposed controller are that: 1) it is fully decentralized and local controllers of DGs that use only local measurements; 2) the controller guarantees the stability of the overall system; 3) the controller allows PnP functionality of DGs in microgrids; and 4) the controller is robust against microgrid topology change. Various case studies, based on time-domain simulations in MATLAB/SimPowerSystems Toolbox, are carried out to evaluate the performance of the proposed control strategy in terms of voltage tracking, microgrid topology change, PnP capability features, and load changes.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a new method of generating higher number of levels in the voltage waveform by stacking multilevel converters with lower voltage space vector structures, which can find extensive applications in electric vehicles since direct battery drive is possible.
Abstract: This paper proposes a new method of generating higher number of levels in the voltage waveform by stacking multilevel converters with lower voltage space vector structures. An important feature of this stacked structure is the use of low voltage devices while attaining higher number of levels. This will find extensive applications in electric vehicles since direct battery drive is possible. The voltages of all the capacitors in the structure can be controlled within a switching cycle using the switching state redundancies (pole voltage redundancies). This helps in reducing the capacitor size. Also, the capacitor voltages can be balanced irrespective of modulation index and load power factor. To verify the concept experimentally, a nine-level inverter is developed by stacking two five-level inverters and an induction motor is run using V/f control scheme. Both steady state and transient results are presented.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a dynamic voltage support (DVS) capability as a function of PV inverters to improve the short-term voltage stability in PV power generation systems.
Abstract: The large integration of photovoltaic (PV) power generation systems into power systems causes deterioration in power system stability. In our previous work, we showed that reactive power control using the inverters of PV systems, known as dynamic voltage support (DVS) capability, is a promising approach to improve the short-term voltage stability in power systems. In this paper, we propose a novel DVS capability as a function of PV inverters. In contrast to the conventional DVS capability, the proposed method uses both active and reactive power injection to improve the short-term voltage stability. Numerical examples show that the proposed DVS capability further improves the short-term voltage stability compared with the conventional DVS capability. Furthermore, the proposed method can alleviate a frequency drop after a fault caused by interruption in PV systems.

Journal ArticleDOI
TL;DR: The proposed converter is designed as a series resonant converter with nominal-input voltage and operates under two additional modes: a boost converter with low- input voltage and a buck converter with high-input Voltage.
Abstract: A microconverter serves as a front-end dc–dc stage of a microinverter to convert the power from a photovoltaic module to a dc bus. These front-end microconverters require isolation, high-boost ratio, wide-input voltage regulation, and high efficiency. This paper introduces an isolated resonant converter with hybrid modes of operation to achieve wide-input regulation while still maintaining high efficiency. The proposed converter is designed as a series resonant converter with nominal-input voltage and operates under two additional modes: a boost converter with low-input voltage and a buck converter with high-input voltage. Unlike conventional resonant converters, this converter operates at discontinues conduction mode with a fixed frequency, simplifying the design and control. In addition, this converter can achieve zero-voltage switching (ZVS) and/or zero-current switching (ZCS) of the primary-side MOSFETs, ZVS and/or ZCS of the secondary-side MOSFETs, and ZCS of output diodes under all operating conditions. Experimental results using a 300-W prototype achieve a peak efficiency of 98.1% and a California Energy Commission efficiency of 97.6% including all auxiliary and control power at nominal-input voltage.

Journal ArticleDOI
TL;DR: In this article, a dc-dc modular multilevel converter (dc-dc MMC) with a medium-frequency ac-link transformer is proposed for the modern electric ship medium voltage dc power system to provide galvanic isolation, flexible voltage regulation, and fault ride through ability.
Abstract: The dc-dc modular multilevel converter (dc-dc MMC) with a medium-frequency ac-link transformer is a promising candidate for the modern electric ship medium voltage dc power system to provide galvanic isolation, flexible voltage regulation, and fault ride through ability. However, the steady states and dynamics of such an isolated dc-dc MMC are rather complicated because it contains many state variables. Moreover, the on-ship requirements further complicate the system design. This paper thus proposes the modeling and control of such a dc-dc MMC. Based on the fact that such a dc-dc MMC is controlled by the phase-shifted operation, the fundamental period averaging (FPA) method is applied to obtain the steady-state and small-signal models, and based on the on-ship requirements, the modulation index control as well as the simple but efficient competitive dual closed loops (a voltage loop for normal condition and a current loop for overload condition) are designed. It is proved that the FPA method can preserve the necessary model information about the dc-dc MMC, and the proposed controllers can be well designed based on the steady-state and small-signal FPA models by compromising the on-ship requirements. The analysis and design results are verified by the simulations and experiments.

Journal ArticleDOI
TL;DR: In this paper, an experimentally analyzed whether series-produced EVs, adhering to contemporary standard and without relying on any vehicle-to-grid capability, can mitigate line voltage drops and voltage unbalances by a local smart charging algorithm based on a droop controller.
Abstract: As electric vehicles (EVs) are becoming more widespread, their high power consumption presents challenges for the residential low voltage networks, especially when connected to long feeders with unevenly distributed loads. However, if intelligently integrated, EVs can also partially solve the existing and future power quality problems. One of the main aspects of the power quality relates to voltage quality. The aim of this work is to experimentally analyze whether series-produced EVs, adhering to contemporary standard and without relying on any vehicle-to-grid capability, can mitigate line voltage drops and voltage unbalances by a local smart charging algorithm based on a droop controller. In order to validate this capability, a low-voltage grid with a share of renewable resources is recreated in SYSLAB PowerLabDK. The experimental results demonstrate the advantages of the intelligent EV charging in improving the power quality of a highly unbalanced grid.

Journal ArticleDOI
TL;DR: In this article, the authors present challenges and potential impacts of photovoltaic (PV) integration in the lowvoltage downtown secondary networks (downtown networks) and propose a solution based on differential currents to upgrade the network protector relays in order to avoid false trips due to excessive PV power.
Abstract: This paper presents challenges and potential impacts of photovoltaic (PV) integration in the low-voltage downtown secondary networks (downtown networks). In the conventional secondary networks, substation feeders are the sole source of electric power and establish unidirectional power to the downtown network. The network protectors prevent the flow of power from inside the network to the upstream feeder by disconnecting the circuit to protect the feeder transformer against upstream faults. The assumption of unidirectional power flow can be violated by PV generation due to the possibility of excess power inside the network. It is shown in this paper that a large number of network protector trips can occur and, thus, voltage collapse may follow even in low PV penetration levels. In addition, it is demonstrated that the reclose action of the network protector relays is adversely affected by the PV power. Other adverse effects of such distributed-generation units, such as voltage profile, line overloads, and flicker, are also briefly discussed. Finally, a solution is proposed, based on differential currents, to upgrade the network protector relays in order to avoid false trips due to excessive PV power. Part of the New Orleans downtown network is modeled and the study is performed through simulations.

Journal ArticleDOI
TL;DR: A case study dealing with long-term voltage instability in systems hosting active distribution networks (DN) anticipates future situations with high penetration of dispersed generation (DG), where the latter are used to keep distribution voltages within desired limits, in complement to load tap changers.
Abstract: A case study dealing with long-term voltage instability in systems hosting active distribution networks (DN) is reported in this paper. It anticipates future situations with high penetration of dispersed generation (DG), where the latter are used to keep distribution voltages within desired limits, in complement to load tap changers. The interactions between transmission and active DN are investigated on a 3108-bus test system. It involves transmission grid, large generators, and 40 DN, each with DG steered by a controller inspired by model predictive control. The reported simulations show the impact of distribution network voltage restoration, as well as the benefit of load voltage reduction actuated by the dispersed generators.

Journal ArticleDOI
TL;DR: The cooperative performance of a novel proportional-integral-derivative (PID) control scheme for PV interfacing inverter based on intelligent adaptive neuro-fuzzy inference system (ANFIS) and an ANFIS-based supervisory storage energy management system (EMS) for regulating the voltage of three-phase grid-connected solar PV system under any nonlinear and fluctuating operating conditions is evaluated.
Abstract: In this paper, the voltage regulation problem in low-voltage power distribution networks integrated with increased amount of solar photovoltaics (PV) has been addressed. This paper proposes and evaluates the cooperative performance of a novel proportional-integral-derivative (PID) control scheme for PV interfacing inverter based on intelligent adaptive neuro-fuzzy inference system (ANFIS) and an ANFIS-based supervisory storage energy management system (EMS) for regulating the voltage of three-phase grid-connected solar PV system under any nonlinear and fluctuating operating conditions. The proposed ANFIS-based PID control scheme (ANFISPID) dynamically controls the PV inverter to inject/ absorb appropriate reactive power to regulate the voltage at point of common coupling (PCC) and provides robust response at any system worst case scenarios and grid faults. And the proposed ANFIS-based supervisory EMS controls the charge/discharge of the energy storage system when there is voltage deviation to cooperate with ANFISPID in PCC voltage regulation. The proposed ANFISPID-based PV inverter control scheme and ANFIS-based supervisory EMS are developed and simulated in MATLAB/ Simulink environment and their dynamic cooperative performances are compared with cooperative performances of conventional PID-based PV inverter control scheme and state-based EMS.

Journal ArticleDOI
TL;DR: A small-signal stability/eigenvalue analysis of a grid-connected PV system with the complete linearized model is performed to assess the robustness of the controller and the decoupling character of the grid- connected PV system.
Abstract: For utility-scale photovoltaic (PV) systems, the control objectives, such as maximum power point tracking, synchronization with grid, current control, and harmonic reduction in output current, are realized in single stage for high efficiency and simple power converter topology. This paper considers a high-power three-phase single-stage PV system, which is connected to a distribution network, with a modified control strategy, which includes compensation for grid voltage dip and reactive power injection capability. To regulate the dc-link voltage, a modified voltage controller using feedback linearization scheme with feedforward PV current signal is presented. The real and reactive powers are controlled by using $dq$ components of the grid current. A small-signal stability/eigenvalue analysis of a grid-connected PV system with the complete linearized model is performed to assess the robustness of the controller and the decoupling character of the grid-connected PV system. The dynamic performance is evaluated on a real-time digital simulator.

Journal ArticleDOI
TL;DR: In this paper, a cost effective control algorithm for standalone batteryless photovoltaic (PV) systems is presented based on the linearization of the dynamic model of the entire system which consists of PV panel, Cuk converter, and motor load.
Abstract: This paper presents a cost effective control algorithm for standalone batteryless photovoltaic (PV) systems. The control is driven by a fuzzy-based maximum power point tracker which has the capabilities to maintain high-energy conversion efficiency under different weather and load conditions. General design considerations are presented based on the linearization of the dynamic model of the entire system which consists of PV panel, Cuk converter, and motor load. For our particular fuzzy-MPPT controller, these design considerations are combined with an artificial intelligent technique to achieve the optimum control design. Furthermore, the developed control algorithm has voltage regulation capability to protect the load from overvoltage during light load conditions and a fast digital overload protection. The transient and steady-state performance of the entire system was modeled by a nonlinear state-space representation. The proposed control is simulated in MATLAB and experimentally tested under the fast variation of climatic conditions for verification purposes A very good agreement has been shown between theoretical, simulations, and experimental results