Step Load Change Research Articles

Management and Distribution Strategies for Dynamic Power in a Ship’s Micro-Grid System Based on Photovoltaic Cell, Diesel Generator, and Lithium Battery

Combining new energy technology with electric propulsion technology is an effective way to decrease the pollution of water resources caused by cruise ships. This study examines the stable parallel operation of a ship’s micro-grid system through a dynamic power management strategy involving a step change in load. With cruise ships in mind, we construct a micro-grid system consisting of photovoltaics (PV), a diesel generator (DG), and a lithium battery and establish a corresponding simulation model. We then analyze the system’s operating characteristics under different working conditions and present the mechanisms that influence the power quality of the ship’s micro-grid system. Based on an analysis of the power distribution requirements under different working conditions, we design a power allocation strategy for the micro-grid system. We then propose an optimization allocation strategy for dynamic power based on fuzzy control and a load current feed-forward method, and finally, we simulate the whole system. Through this study we prove that the proposed power management strategy not only verifies the feasibility and correctness of the ship’s micro-grid structure and control strategy, but also greatly improves the reliability and stability of the ship’s operation.

Power Quality Performance Evaluation of Multilevel Inverter With Reduced Switching Devices and Minimum Standing Voltage

Multilevel inverters (MLIs) have been extensively employed to improve the power quality of the photovoltaic (PV) systems. However, the need for large number of components, higher standing voltage, and high harmonic content in the output of a conventional MLI greatly affects the system efficiency. Asymmetrical MLIs have been therefore developed as a suitable alternative to address these issues. This article aims at developing such a hybrid asymmetrical structure suitable for PV application that has a high level per component ratio and minimum standing voltage. The proposed MLI is assembled using a reduced switch H-bridge-based (RSHB) MLI structure with n asymmetrical repeating units and different level doubling circuit (LDC) combinations. The two dc sources used in the repeating units are in the ratio of 1: n voltage ratio, and using n such units, the proposed MLI structures, i.e., PS1 and PS2 can synthesize 4 n + 5 and 4 n + 7 levels, respectively, at the output instead of 2 n + 3 levels with only RSHB MLI. Comparative analysis reveals that both PS1 and PS2 have fewer switches, low standing voltage, less power loss, and lower cost. A 3.9-kW standalone solar PV system is considered for performance evaluation of the PS1 structure applying both the selective harmonic elimination and carrier-based pulsewidth modulation control schemes. In light of this, dc-link voltage balancing and self-voltage balancing mechanism of the LDC are warranted. Extensive simulation of the proposed MLI is performed in MATLAB/Simulink platform under a change in modulation index, sudden load change, frequency change, and step change in solar insolation. Furthermore, theoretical and simulation findings are validated experimentally by performing similar tests on a prototype of the proposed 17-level MLI.

Modeling of the transient behavior of a slurry bubble column reactor for CO2 methanation, and comparison with a tube bundle reactor

In this publication, the performance of a slurry bubble column reactor (SBCR) and a tube bundle reactor (TBR) are compared for steady-state and transient Power-to-Gas (PtG) operation. Transient PtG conditions are modeled using gas load step changes between 25 and 100% of the reactor maximum capacities in 1 s.For steady-state operation the TBR facilitates much higher gas hourly space velocities (GHSV) as compared to the SBCR. A sensitivity analysis shows that the TBR is limited by heat transfer, while the SBCR is limited by gas/liquid mass transfer.For transient PtG operation the TBR undergoes significant temperature changes within a short time resulting in out of specification product gas qualities and unacceptable temperature hot spots; the SBCR temperature shows marginal changes upon transient operating conditions, and the outlet gas composition sticks to the gas quality requirements.Finally, measures to improve the efficiency of both reactors are proposed considering dimensionless numbers. The GHSV of the SBCR can be enhanced by increasing the specific interfacial area controlling gas/liquid mass transfer, while the transient behavior of the TBR can be improved by reducing the catalyst concentration/activity or by mixing the catalyst with high heat capacity inert material in detriment of the GHSV.

Fuzzy Logic Controlled Current Source- Quasi ZSI Fed IM

Quasi ZSI are used for induction motors operating at low input voltage. This work deals with comparison of FLC & PI controlled current fed quasi ZSI fed IMdrive systems. Open loop and closed loop systems are simulated by considering step change in load. The results of open loop and closed loop systems are compared. The objective of this work is to improve the dynamic response of CFQZSI using FLC. The time responses of PI and FLC controlled closed loop systems are also compared. Fuzzy logic controlled system is proposed to improve the dynamic response of CFQZSI fed induction drive system. Design and simulation results are presented to demonstrate the new features. FLC is observed to provide better control the another controllers and it also has improved damping characteristics.

Dynamical and operational performance of shunt and permanent-magnet DC motors powered by lead–acid batteries for pumping applications

This paper presents some dynamical and operational performance of shunt and permanent-magnet DC motors powered by lead–acid batteries for water pumping applications. Starting from fully charged battery, the dynamical analysis includes the starting of fully loaded DC motors and the response of the system after successive step changes in the pumping capacities. The strong nonlinearities of the lead–acid battery model are taken into account based on simulating the electrochemical interaction by the electrical equivalent circuit. The dynamics of the thermal part of the electrolyte of the cell is considered. Additionally, the nonlinearities of the dynamical model of the motors have also been included along with that of their ferromagnetic material. The state-of-charge (SOC), variation of the efficiency and internal resistance of the batteries are outlined. It is concluded that the lead–acid battery can effectively start a fully loaded shunt and permanent-magnet DC motors within a settling time of more than 1 h following direct switching. It can also run them steadily at different loading conditions and can withstand step changes in the mechanical loads coupled to motors. It is observed that about 25% of the SOC of the battery is consumed for starting. The energy efficiency of the battery at starting and running conditions for the two motors has been addressed. All of the study is conducted assuming an ambient temperature of 25 $$^{\circ }$$C. All numerical simulations are carried out using MATLAB software package by building the code required.

Effect of Prime Mover's Characteristics on the Survivability of a Synchronous Generator-Based Distributed Energy Resource During Transient Overload Conditions

Recently, prime-mover stalling phenomenon was observed in a synchronous generator-based distributed energy resource (DER) for large step load changes during experimental testing at the Consortium for Electric Reliability Technology Solutions Microgrid. It is found to highly impact the generator's survivability during transient overload conditions. The stalling occurs in synchronous generator-based DER because of a sustained imbalance between electrical load demand and mechanical power available from the prime mover, thus depleting the generator's stored kinetic energy. In particular, mechanical power capability of the prime mover and stored kinetic energy in the rotating mass are the causal factors. This article evaluates two different types of prime movers—reciprocating engine and combustion gas turbine—for the DER survivability. The characteristics of these two commonly used prime movers are investigated during transient overload conditions by simulation case studies using PSCAD/EMTDC software.

Frequency control of islanded wind‐powered microgrid based on coordinated robust dynamic droop power sharing

This study proposes a new frequency control of islanded and storage independent wind-powered microgrid based on coordinated robust dynamic droop power sharing. The islanded microgrid includes wind turbine as undispatchable distributed generation (DG) and fuel cell as dispatchable DG. In the first layer of control, the reverse and direct droop controls are considered for wind turbine and fuel cell, respectively. Accordingly, the outputs of reverse droop control are active and reactive powers, which are used for wind turbine. Simultaneously, the outputs of direct droop control are frequency and voltage, which are used for the fuel cell. Since the generated power of wind turbine is not constant, so the coordinated dynamic droop coefficients for both DGs are modified as a function of available wind power. Then in the second layer, robust sliding mode control is designed for setpoints tracking of both DGs to control the frequency and voltage of islanded microgrid. The effectiveness evaluation of the proposed control scheme is performed by simulation studies on the islanded microgrid in different conditions such as single-phase fault, load step change and variety of wind speeds in MATLAB/Simulink environment. Finally, results are validated experimentally through the implementation of real-time hardware-in-the-loop system.

A Novel Hybrid Control Method for Single-Phase-Input Variable Frequency Speed Control System With a Small DC-Link Capacitor

A novel hybrid control method, which consists of dual-frequency tracking control (DFTC) and virtual inertia control (VIC), is proposed for single-phase-input variable frequency speed regulation system with a small dc-link capacitor. Because of lacking a large-capacity energy storage device, the dc-link voltage is a pulsating dc, which causes a strong power coupling relationship between the rectifier and inverter side. The instantaneous power and dq -axis currents of the inverter contain both ac and dc components at the same time, which cannot be controlled well using traditional proportional-integrational (PI) controllers. Herein the DFTC that is based on a PI-resonant controller is proposed to accurately track ac and dc components of the instantaneous power and dq -axis currents respectively. With higher open-loop gain at both low frequency and the specified resonant frequency, the proposed DFTC ensures accurate tracking of the ac and dc components of power and dq -axis currents, high-power-factor, and low total harmonic distortion (THD) of input grid current. To maintain the stability of the dc-link voltage under step changes of load, a VIC is proposed. Subsequently, the input power factor and the fluctuation of dc-link voltage can be improved in the system. Simulations and experimental results are given to provide further validation of the proposed DFTC and VIC under different operating scenarios.

Optimal Controller Design for Interconnected Power Networks With Predetermined Degree of Stability

A novel procedure for the design of an optimal controller with a predetermined degree of stability to enhance damping of interarea oscillations in interconnected power networks is presented in this paper. The proposed approach includes a feedback controller, which is independent of internal disturbances as a stabilizer. A tuning parameter is also provided, which treats load changes as disturbances. The gains of the proposed controller are calculated based on moving the dominant poles to the left on the S plane to obtain a desired stability margin and provide a prescribed degree of stability. In order to better validate the performance of the proposed controller, a multiarea power system is considered with different step load changes that are applied successively in simulations. The time responses and eigenvalue analysis are presented and discussed thoroughly. It is shown in the results that the developed optimal controller can effectively damp the frequency and tie-line power deviations in interconnected power systems.

An intelligent approach for dynamic load frequency control with hybrid energy storage system

ABSTRACTOne of the important factors to be considered in an electric power system is to maintain the frequency constant, so that power stations run satisfactorily in synchronise among the connected pool of power generation systems. The main purpose of load frequency control (LFC) is to reduce the frequency deviation and net interchange of power flow between electrical power generating units and for achieving steady-state error to be zero. This research paper proposes the way to improve the LFC by employing energy storage systems (battery energy storage systems and superconducting magnetic energy storage (SMES)) during change in load demand. The energy storage devices are acting quickly and they are effectively damp electro mechanical oscillations in a power system. Moreover, they provide storage capacity and the kinetic energy of the generator shares the sudden changes in power requirement. An integrated hybrid BES and SMES energy storage systems along with LFC minimise the deviation of frequency by contribution of additional power requirement. Investigating the performance of the LFC with storage system under step change of load (∆Pd) has been analysed by employing proportional-integral (PI) and fuzzy logic controller (FLC) for frequency regulation and load tracking. Even, the PI controller attains zero steady-state error in system frequency, it has unsatisfied dynamic (overshoots and settling time) performance followed by disturbances. The mismatch power in the power system makes frequency deviation followed by the change in load demand and electrical power generation and it is balanced by employing of an energy storage system with proper controller. The simulation results are illustrated that the performance of LFC system is enhanced by BES storage system which effectively reduces frequency deviation than SMES system. The comparative analysis has been made for LFC with BES, SMES and hybrid storage system employing FLC and PI controller design also. A significant improvement in the frequency profile has been obtained with FLC controller than PI controller followed by the step load changes.

Stability analysis model for multi-node undersea observation networks

Cabled undersea observation networks have been attracting increasing research attention due to the abilities of abundant power distribution and broad bandwidth communication. Stability of their power supply systems is crucial for their normal operation. However, rare studies were carried out on stability analysis of such multi-node undersea power supply systems. This paper focuses on analyzing the steady-state characteristics of multi-node tree topology power supply system for regional coastal ocean observation network. Firstly, the equivalent model of power delivery submarine cable is introduced, as well as the cable parameters calculating method. Then, based on features of the power network, simplified model of constant power load (CPL) and voltage algorithm of multi-node tree topology network are proposed and built respectively, to obtain each node voltage of a given network. The algorithm was carried out on MATLAB, and simulation model of the observatory network was set in Pspice based on CPL theory. Full-response time-domain method was proposed to analyze the dynamic process at scenarios of startup and load step change. Simulations and experiments were carried out, from which results showed good consistence, verifying the theoretical methods.

Optimal AGC Design for a Hybrid Power System Using Hybrid Bacteria Foraging Optimization Algorithm

This paper proposes a hybrid optimization algorithm developed through the novel combination of particle swarm optimization (PSO) oriented bacteria foraging optimization algorithm (BFOA) for finest tuning of proportional integral derivative (PID) controllers for load frequency control problem of hybrid power system comprising of photovoltaic (PV) system and thermal generators. In order to prevent the solution from sub-optimal condition and to accelerate the convergence time of the problem the PSO is merged with BFOA to solve the LFC problem of the hybrid system. To check the power of the proposed strategy initially the hybrid system is evaluated for step load change and the results are compared with some powerful optimization algorithms such as BFOA, PSO, and flower pollination algorithm (FPA) based PID in terms of computed gains and achieved value of error. The results obtained show the cost and control efficacy of the proposed design. The study is extended to investigate the performance of proposed design with dead-band of governor and generation rate constraint non-linearity. Finally, the robustness of the proposed design is evaluated for random load change, sinusoidal load change and for extensive parametric variations from the typical plant values and the application results are presented.

Power applications for fuel-cell using switching regulators

<p><strong> </strong></p>Generally the switch mode power supply input voltage source is constant or shows insignificant little varieties.in any case, when fuel call used input source the last assumption is not valid. A fuel cell stack is give a details of low and not controlled DC output voltage, moreover, when the demanded current increases the output voltage becomes low in a nonlinear form; from now on, suitable controller is required to taken the previously mentioned issues. In this article, a normal current-mode controller is planned to using a joined model for an energy unit stack and a boost converter; besides, the resolving control method increasing the system stability and output voltage regulation.. The proposed energy system utilizes an energy component power (polymer electrolyte film fuel cell) and a boost converter passing on power of 900 W. the proposed controller execution for output voltage regulation by means of closed loop gain estimations and step load changes. What's more, a correlation amongst open-and closed- loop estimations is made, where the controller robustness is tried for vast load varieties and fuel cell stack output voltage changes are shows on simulation results.

Power quality improvement of distribution system with photovoltaic and permanent magnet synchronous generator based renewable energy farm using static synchronous compensator

This paper presents power quality improvement for effective power transfer in a grid-integrated solar photovoltaic-wind energy hybrid system. The hybrid system constitutes a renewable energy farm, based on photovoltaic energy generation system and wind energy conversion system. The system experiences frequent disturbances in AC loads and power output from the renewable farm. This creates reactive power mismatch and raises voltage instability and power quality issues. This gap can be eliminated using an adjustable reactive power source i.e. static synchronous compensator. Three case scenarios of the hybrid system, i.e. hybrid system in (I) standalone mode, (II) grid-integrated mode and (III) grid-integrated mode with STATCOM, are tested to compare their dynamic and transient performances. Results show that scenario-III best fulfilled the dynamic compensation requirement among all cases. Under this scenario, load bus voltage is regulated at around 1.0 p.u. and total harmonic distortion in voltages/currents are maintained at around 1%. Furthermore, this scenario demonstrated superior transient response towards a step change in reactive power load, significantly reducing maximum peak deviation by 73.4% and settling time by 75% in load voltage compared to the worst case of scenario-I.

Modeling of the tensometric measuring system

Article deals with the design of a model of a tensometric measuring system. Authors in this article describes the procedure for measuring the system response to a step change in load and then the procedure creating a model. The article shows a graphical comparison between the measured ones system characteristics and simulated system characteristics. The conclusion is given calculated errors between measured system characteristics and simulated system characteristics.

Nonsingular Terminal Sliding Mode Control Based on Binary Particle Swarm Optimization for DC–AC Converters

This paper proposes an improved feedback algorithm by binary particle swarm optimization (BPSO)-based nonsingular terminal sliding mode control (NTSMC) for DC–AC converters. The NTSMC can create limited system state convergence time and allow singularity avoidance. The BPSO is capable of finding the global best solution in real-world application, thus optimizing NTSMC parameters during digital implementation. The association of NTSMC and BPSO extends the design of classical terminal sliding mode to converge to non-singular points more quickly and introduce optimal methodology to avoid falling into local extremum and low convergence precision. Simulation results show that the improved technique can achieve low total harmonic distortion (THD) and fast transients with both plant parameter variations and sudden step load changes. Experimental results of a DC–AC converter prototype controlled by an algorithm based on digital signal processing have been shown to confirm mathematical analysis and enhanced performance under transient and steady-state load conditions. Since the improved DC–AC converter system has significant advantages in tracking accuracy and solution quality over classical terminal sliding mode DC–AC converter systems, this paper will be applicable to designers of relevant robust control and optimal control technique.

A new structure of three‐phase five‐level inverter with nested two‐level cells

SummaryThis paper presents a new structure of three‐phase five‐level inverter with a single direct current (DC) source for low‐ and medium‐voltage applications. The proposed configuration is built with a cascade connection of two‐level cells in a nested form and owns the advantages of a reduced number of passive components, total blocking voltage of the switches, and isolated DC sources. In order to make this topology attractive, a comparison is made with five‐level inverter topologies proposed for low‐ and medium‐voltage applications in recent years. The proposed circuit is powered using a single DC source and an auxiliary voltage‐balancing circuit (AVBC) to maintain the desired DC‐link capacitor voltages. A sinusoidal pulse width modulation (SPWM) scheme is implemented in field‐programmable gate array (FPGA), using Xilinx blocks developed in MATLAB/SIMULINK environment, to control the inverter switches. The performance of the proposed topology is verified through MATLAB simulation and prototype model for a step change in load. Finally, the experimental results are presented to validate the effectiveness of the proposed topology.

Operating-Point Tracking Method for Sensorless Induction Motor Stability Enhancement in Low-Speed Regenerating Mode

The stability of adaptive full-order observer (AFO) can be improved by feedback gain tuning and speed adaptive scheme modification for sensorless induction motor (IM) drives in low-speed regenerating mode. However, few research concern this problem with attention to IM operating point changes. To cope with this problem, this paper proposes an operating-point tracking method to design feedback gain and speed adaptive scheme for AFO. Compared with the existing approaches, lower synchronous speed can be accessible during step speed and load changes in low-speed regenerating mode without signal injection. Addressing the operating point changes, the estimated flux error is derived by adapting the projection of estimated current error with respect to speed and torque. The derivative estimated flux error with changing parameters is taken as an additional variable to design feedback gain. Meanwhile, the speed adaptive scheme is modified by the operating-point tracking expression. As a result, the proposed method acquires the capacity to track the operating point in real time. The experimental results on a 2.2-kW IM experimental setup confirm the effectiveness of the proposed method.

Automatic Generation Control Incorporating Electric Vehicles

Electrical vehicles (EVs) enjoying the new technology known as vehicle-to-grid have presented new opportunities to control and planning of power grids. Bidirectional connection capability of converters in EVs’ structure makes them a secure backup for frequency support. This paper applies EVs as one of the foremost controllable loads along with other conventional generation units for frequency control after disturbances in a multi-area power system. Application of tilt-integral-derivative (TID) controller for EVs has been addressed for the first time in this paper. In this regard, artificial bee colony optimization algorithm is employed for optimal tuning parameters of TID controllers in EV and automatic generation control structures. In order to achieve accurate and realistic results, physical limitations of generation rate constraint, non-linearity, and governor dead-band effect are included in the analysis. Eventually, three scenarios including step and random load changes, and sensitivity analysis are selected to illustrate the efficiency of the proposed coordinated control in terms of settling time, peak time, peak overshoot, and the integral of time multiplied squared error performance index in frequency and tie-line power deviations. The results are compared with particle swarm optimization and genetic algorithm based TID controllers.

An Inductor Current Estimator for Digitally Controlled Synchronous Buck Converter

Inductor current is an important feedback parameter in synchronous buck converters (SBCs). It is used for overcurrent protection, current sharing among interleaved modules, and current-mode feedback regulation, among others. While implementing a digital controller, inductor current is sensed and fed into the controller through a high sampling frequency analog to digital converter (ADC). As the switching frequency of the converter becomes higher, the need for an even higher sampling frequency ADC also goes up, which is a distinct disadvantage in terms of the overall cost. This paper discusses a simple current estimation technique that avoids use of any expensive current sensor and high sampling frequency ADCs. The paper shows that in a buck converter, inductor current can be estimated by tracking the width of the switch node voltage. Implementation and limitations of the proposed current estimation scheme are discussed in detail. The proposed method is validated using a 3.3 V–15 A SBC prototype and results show the estimation technique is accurate within 5% with a converter switching frequency of 800 kHz. In order to prove the effectiveness of the technique in feedback regulation, the current estimation technique is used to implement average current mode and hysteretic current mode control on a SBC. To prove the effectiveness of the proposed current estimation scheme, it is used in closed-loop control of the SBC to verify the dynamic responses, such as start-up transient, step change in load, and reference.