Variable-speed System Research Articles

Longitudinal Ventilation for Smoke Control and Evacuation in High-Temperature Tunnel Fires

When high-temperature geothermal conditions occur within road tunnels, the safety of emergency exits becomes more challenging, especially in cases of fire. The high background temperature increases the speed of the smoke stratification process, and therefore, is unfavorable for people rescue and safety evacuation. In China, longitudinal ventilation systems are widely used to control the smoke within road tunnels during emergency fire events and help ensure safety evacuation. This paper aims to evaluate the performance of the longitudinal ventilation system when applied to a high-temperature road tunnel. The results show that the high-temperature geothermal in the tunnel will result in an accelerated stratification of the smoke layer, and the ventilation speed must be reasonably adjusted to meet the demands of smoke control. Under an optimal ventilation setting, the smoke density in the passage was reduced and the visibility was dramatically improved, which tremendously increased the evacuation efficiency. Overall, this study provides some practical suggestions for tunnels exposed to high geothermal temperatures, including the potential for variable-speed ventilation systems and localized smoke extraction strategies.

Comparative evaluation of Z source / quasi Z-source direct and indirect matrix converters for PMG based WECS

The present era sees the dominance of wind energy conversion systems as a leading technology in renewable energy. Various technologies have been devised to harness wind energy, with variable speed systems emerging as particularly advantageous. Consequently, these systems are designed to operate at specified speeds using power electronic interfaces, maximizing power extraction from the wind. The integration of Permanent Magnet Generators (PMGs), directly linked to the wind turbine lacking a gearbox, allows operation at minimum speeds. To stabilize the continuously fluctuating output voltage of the PMG, power electronic converters are extensively utilized in Wind Energy Conversion Systems (WECS), ensuring a consistent voltage and frequency output. The voltage gain of Traditional matrix converters (MCs) is limited to less than 0.866. In turn, the Z-source (ZS) and discontinuous QZSDMC, as well as ZS IMCs, topologies have achieved voltage gains exceeding 0.866. However, the former provides complicated commutation issues from DMC, while the latter incorporates a Z source network in the DC link, resulting in a non-all-silicon solution. A novel continuous QZSDMC and QZSIMC are suggested, wherein a qZS network incorporates the grid-side filtering function. This design eliminates the need for an additional input filter in the proposed system. Three newly introduced topologies of ZSDMC, QZSDMC and QZSIMC are thoroughly compared across various parameters including voltage gain, current and voltage ripples, inductor current and capacitor voltage stresses, filtering capabilities, input current, and output voltage Total Harmonic Distortion (THD), finally efficiency. The paper presents their control and modulation methods to achieve the desired performance levels. Experimental comparisons validate the theoretical analysis and demonstrate the potential of the proposed QZSDMC as a promising topology.

A validated model for variable-speed multi-chillers to assess different operation modes

Environmental protection drives the replacement of environmentally harmful refrigerants with potentially flammable alternatives, necessitating efficient cooling strategies for varying loads. Legislation limits flammable refrigerant charge, leading to the adoption of multi-chiller systems with smaller charges and therefore also smaller loads per chiller. However, operating such systems requires complex strategies, addressable through fast and reliable models. This study presents a semi-empirical model predicting the behaviour of variable-speed multi-chiller systems. The model focuses on predicting cooling capacity and coefficient of performance (COP) for cooling, with input parameters of evaporation and condensation temperatures, and compressor speed. Experimental validation of the parameterized model shows COP predictions within 3 % for a two-module system using R-290 (propane) under different conditions and compressor speeds. The model assesses various operation strategies, including the conventional mode with fewer chiller modules running at high speed, compared to modes where all chillers run but at reduced speeds. Comparing COP values in these modes reveals energy-saving potentials of up to 14.57 % for constant condensation temperatures. Moreover, strategies involving condensation temperature reduction, or a combination with compressor speed reduction are analysed for energy-saving potentials. Reducing the condensation temperature by 3 K results in savings of up to 13.25 % and combined with the compressor speed reduction savings of up to 23.54 % are feasible. These findings emphasize the importance of considering compressor speed when operating multi-chiller systems to maximize energy savings. The presented model effectively evaluates various strategies and implements variable-load control in multi-chiller systems, serving as a valuable tool for optimising energy efficiency and promoting environmentally friendly cooling practices.

Comparison of Variable Speed Wind Turbine Control Strategies.

Variable speed operation of wind turbines presents certain advantages over constant speed operation. Basically, variable speed wind turbines use the high inertia of the rotating mechanical parts of the system as a flywheel; this helps to smooth power fluctuations and reduces the drive train mechanical stress. Also, variable speed systems could lead to maximise the capture of energy during partial load operation. In this paper alternative control strategies for variable speed operation are considered and compared from the point of view of energy yield and power quality. Control aim is always maximum power generation. Maximum power tracking and power fluctuation will be analysed when exciting the different configurations with a particular wind profile. Also fixed speed wind turbine are considered for the comparison.

Variable-Speed Operation of Micro-Hydropower Plants in Irrigation Infrastructure: An Energy and Cost Analysis

Micro-hydropower plants have now become a way to decarbonise the power generation system. Older micro-hydropower plants generally operate at a fixed speed. When there is a lack of rainfall, these plants operate outside their design flow causing various problems (such as the occurrence of the phenomenon of cavitation, decreased turbine performance, and decreased operating hours), especially in micro-hydropower plants installed in irrigation infrastructure, where the priority for water use is crops. This study aims to carry out a comparative evaluation of several indicators (cavitation, investment costs, electricity production and economic benefit) of two types of control system on an asynchronous electric generator (a fixed speed control system (scenario 1) and a variable-speed control system (scenario 2)) at the same micro-hydropower plant. The Rebolluelo micro-hydropower plant (Spain) is used for this purpose as a case study. This micro-hydropower plant uses a semi-Kaplan turbine coupled to an asynchronous electric generator through a gearbox. The results show the advantages of using a variable-speed control system. The use of variable-speed technology: (i) eliminates the possibility of cavitation, (ii) increases the power output ratio (from 35.87% to 93.03%), and (iii) increases the economic benefit (from 29.31% to 108.72%). There are also, of course, disadvantages, such as an 11.96% increase in cost. This work demonstrated the superiority of variable speed technology at micro-hydropower plants for three of the four indicators evaluated. This work could be of assistance when making decisions regarding future micro-hydropower plant installations.

Design and Optimization of Low Impact Shift Control Strategy for Aviation Transmission Power System Based on Response Surface Methodology

The utilization of a variable-speed power system significantly improves the forward flight speed and cruising range of the helicopter. Nevertheless, the shock of speed and torque during the shift process brings stability and safety problems that cannot be ignored. Thus, swift and stable shift control is a key issue in the research on aviation power systems. This study focuses on the design and optimization of low-impact shift control strategies for a variable-speed power system, which involves multiple control variables, long adjustment times, and uncontrollable risks due to the nonsteady state. A comprehensive power system model that integrates the engine, a two-speed dual-clutch transmission system, and the main rotor was proposed. By selecting the engine fuel flow, friction clutch hydraulic pressure, and rotor pitch angle as input signals, regression fitting models between the input signals’ starting time points and speed or torque shock were obtained using Response Surface Methodology (RMS). The interaction effect of multiple time series was analyzed, and four kinds of low-impact nonlinear programming multi-objective optimized models for speed or torque are proposed. The results indicate that the P values of the RMS fitting models at upshift and downshift are less than 0.0001 and 0.05, respectively, which are highly significant and can effectively predict the shift dynamic response; under the optimized upshift and downshift control strategy, the speed and torque shock are reduced by 5–10%.

Tracking control for a position-dependent periodic signal in a variable-speed rotational system

This paper concerns the problem of tracking a position-related periodic signal for an uncertain nonlinear rotational system. Applying the additive-state-decomposition (ASD) technique decomposes the original uncertain nonlinear system into two subsystems: A primary linear time-invariant system that performs spatial repetitive control, and a secondary nonlinear system that ensures robust stability of the whole system with respect to unknown nonlinear dynamics and exogenous disturbances. This method has four features: (i) The ASD technique provides an effective way to deal with the coupling between the spatial periodicity and other factors (temporal and state-dependent uncertainties and disturbances) in a rotational system. This technique ensures satisfactory tracking and disturbance rejection performance; (ii) A real-time digital implementation of a spatial repetitive controller enables repetitive control with an exact period in the position. This ensures the synchronous execution of repetitive control in the position domain and robust stability in the time domain; (iii) The method of accurate phase compensation in a spatial repetitive controller leads to a significant improvement in steady-state tracking performance; and (iv) An extended-state observer precisely estimates the overall effect of disturbances. Integrating a disturbance estimate into a control input effectively compensates for disturbances. Stability criteria and design algorithms are presented in detail. Finally, experiments of a rotational speed-control system demonstrate the effectiveness of this method.

Multivariate Approach to Peak-Period Models for Crash Types and Severities in Variable Speed Systems on Freeways

According to current research, safety performance functions (SPFs) based on traditional annual average daily traffic are less suitable for addressing crash risk in traffic-management strategies that typically operate for short time intervals (e.g., peak period). Variable speed limit (VSL)/variable advisory speed (VAS) is a traffic-management strategy which is deployed to achieve speed harmonization typically during the peak hours of weekdays. However, peak-period SPFs for VSL/VAS-implemented freeways considering different crash types and severity levels are still unexplored. Therefore, in this study the multivariate Poisson lognormal (MVPLN) method was applied to estimate the different crash-type and severity-level models. The results showed that by addressing correlations among different crash types and severity levels, MVPLN models outperformed individual univariate Poisson lognormal crash-type and -severity models. From the developed models, several traffic- and roadway-related attributes—such as volume, average speed, standard deviation of speed, segment type (merge, diverge, and weaving), higher number of lanes, and so forth—could be identified as the potential crash-risk factors. Also, the proposed models were successful in capturing the spatial effects of segments (differences between segments downstream and upstream of the location of interest) on crash frequency. Further, the implementation of VSL/VAS strategy was found to be effective in reducing rear-end crashes in the crash-type model as well as property-damage-only (PDO) and C (non-incapacitating) crash severity levels in the crash-severity model. Policymakers and practitioners could benefit from this study in incorporating safety aspects into developing VSL/VAS algorithms.

가변속 DFIM 시스템의 가상관성 모델링

The variable-speed DFIM system is a next-generation energy storage technology in which a rotor is connected to a back-to-back converter to adjust the active and reactive power of the device to compensate for the output variability of renewable energy sources. However, general DFIM has less inertia than synchronous generators to support the system when a disturbance occurs in the system, and requires an active technology to assist it. In this paper, a steam turbine governor with droop characteristics was modeled to explain the power control of the existing variable speed DFIM and simulate the drop in system frequency, and a virtual inertia controller was used for the variable speed DFIM system. The current and active power of the DFIM and the frequency change is compared by distinguishing the before and after using the virtual inertia. DFIM, which operates as a variable load after using virtual inertia, reduces the rotor current and reduces the active power absorbed from the system from 1p.u to 0.78p.u by using the virtual inertial active power. Accordingly, it was confirmed that the rotor speed was variable, and it was confirmed that the virtual inertia loop using kinetic energy operated effectively. When disturbance occurs in the system frequency due to the dropout of the power source of the system, the frequency nadir point drops to 48.5Hz. When the system frequency inertia was supported using virtual inertia, the frequency nadir increased from 48.5Hz to 48.76Hz, confirming that the system frequency nadir was improved by mimicking the inertial characteristics of the synchronous generator even during pump operation.

Wind farm active power dispatching algorithm based on grey incidence

This study proposes a wind farm active power dispatching (WFAPD) algorithm based on the grey incidence method, which does not rely on an accurate mathematical model of wind turbines. Based on the wind turbine start-stop data at different wind speeds, the weighting coefficients, which are the participation degrees of a variable speed system and a variable pitch system in power regulation, are obtained using the grey incidence method. The incidence coefficient curve is fitted by the B-spline function at a full range of wind speeds, and the power regulation capacity of all wind turbines is obtained. Finally, the WFAPD algorithm, which is based on the regulating capacity of each wind turbine, is compared with the wind speed weighting power dispatching (WSWPD) algorithm in MATLAB. The simulation results show that the active power fluctuation of the wind farm is smaller, the rotating speed of wind turbines is smoother, and the fatigue load of high- speed turbines is effectively reduced.

Thermal-Fluid-Solid Coupling Simulation and Oil Groove Structure Optimization of Wet Friction Clutch for High-Speed Helicopter

Wet friction clutch is the key functional component of the high-speed helicopter variable-speed transmission system, which is used to change the power transmission path. In the engagement process of wet friction clutch, the driving/driven disc will produce drag torque under the shearing of lubricating oil, which reduces the transmission efficiency. This unnecessary drag torque reduces efficiency and increases clutch temperature. The temperature increase promotes the wear of gears and bearings and the aging deformation of friction plates, which leads to local wear and reduces the service life of the clutch. From the principle of wet friction clutch, the oil groove structure is directly related to the drag torque and the temperature rise of friction disc. It is very important for the long-distance flight and service life of high-speed helicopters to obtain the groove structure with low drag torque and low temperature rise. In order to solve this problem, taking the wet friction clutch of a high-speed helicopter as the research object, based on the radial and annular compound groove, the thermal-fluid-solid coupling simulation model of the wet friction clutch is established to obtained the flow characteristics and temperature field distribution of the lubricating oil in the friction disc oil groove, and to analyze the influence law of the oil groove structure parameters on the drag torque and temperature field. In order to improve the transmission efficiency and the service life of friction disc, Taguchi experiment and non-dominated neighborhood immune algorithm were used to optimize the structural parameters of the oil grooves. The comparison results show that the optimized structural can effectively reduce the drag torque and the temperature rise. This work can provide a theoretical reference for the structure design of a wet friction clutch.

Investigating critical model input features for unitary air conditioning equipment

A variable-speed air-conditioning system provides more control than single-or multi-stage units, resulting in increased energy efficiency and more precise temperature control. Current commercial and residential direct expansion (DX) equipment testing standards require the embedded control placed on variable-speed equipment to be deactivated during performance testing and instead the fan and compressor speeds are fixed. For this reason, the test and field performances differ, creating a performance as well as an energy consumption gap. This paper presents a machine learning-based approach to investigate critical features from the air and refrigerant side influencing the cooling capacity of unitary air conditioning equipment. High-fidelity experimental data obtained from 4 different state-of-the-art high-efficiency units, 1 fixed-speed 35.2(10) kW(tons) commercial and 3 variable-speed residential unitary equipment of 12.3(3.5), 14(4), and 17.6(5) kW(tons) of cooling capacity have been analyzed by utilizing a feature selection methodology, Elastic Net (EN). Influential features with higher relevance scores corresponding to the total cooling capacity are fed into a supervised Artificial Neural Network (ANN), formulated as a predictive model to evaluate the validity of features selected. Results show that the proposed method of feature selection when applied, ANN is able to predict the equipment cooling capacity with a mean absolute percent error of less than 2% for all tested units, thus approving the proposed input features. The findings may be used as recommendations for the development of a semi-empirical model for better cooling capacity and COP predictions.

Efficiency of a Six-Phase Induction Generator Employing a Static Excitation Controller to Generate AC Power for Wind Energy

The most widely applied six phase induction generator (SPIG) leads to insufficient frequency regulation ability of power system. A six phase induction generator (SPIG) Combined with appropriate capacitors and a motor, it produces an induction generator that is self-excited. The advantage of this generator, which has recently caught the interest of various experts, particularly in the field of wind energy, combines the advantages of multiphase devices. This study aims to offer a technique for regulating the voltage of a wind-powered SPIG. The methodology suggests two different compensation setups for (V-f) control, involving two switching capacitors. Different setups’ performance constraints, controls, and features will be closely scrutinized and contrasted. The performance limits of the suggested system will be contrasted. to those of variable speed and variable capacity systems after being modelled and simulated. The results show that using the optimal capacitances for each configuration improves voltage and frequency regulation significantly. The preferable option, however, is short-shunt compensation since it regulates the output voltage and frequency with the fewest capacitances and the least amount of necessary duty fluctuation.

G-Reactor at Micro-Plan

The stirrer reactor govern the industrial pharmaceutical productions up to the present, however the complex transmission systems may increase the costs exponentially with the power rates and the hermetic rector sealing. G-reactor improves the analogous reactors with simple pneumatic power device to heavy duty performances at high technological risks by pathogens and per substitution of complex transmissions by own-design; a single compression unit produces the sterile air to the power input of micro-plants and the oxygen of aerobic processes; important economic technical profits is foreseen; microplants distinguishes by small installations for compressed air and the services with overall automatic control available; the reliable performance for the human health, variable speed and standard impeller system, simple sterilization, safe sampling and supplies, foam-breaks to avoiding chemicals and simple automatic flow control distinguish the installations. The mathematical simulation of G-reactor performances to the mixing operations at gas-liquid systems to mass-transfer is shown; a solved example to a specific process illustrates the calculus fundamentals; the software enables the calculus of consumption parameters to the reactor scale-up and micro-plants of maximum capacity; the descriptive data analysis is discussed for the primary technical evaluations and general conclusions. The innovation is proposed for the small production scale of drugs and the unit operations of the chemical industry; a brief technical description of micro-plants and the production of sterile air may lead to the process engineering and the preliminary analysis of costs. The prophylactic treatment of the residual gas flow is shown.

DESIGN AND ANALYSIS OF THE CHAMELEON SCHEDULING ALGORITHM FOR RECONFIGURABLE COMPUTING

Conventional power generation is the source of widespread worry over the depletion of nonrenewable energy sources and the environmental difficulties that this would inevitably cause. As a direct consequence of this, an increasing number of people are gravitating toward renewable energy sources like as photovoltaic boards and wind generators. Wind power is being put to use for a vast array of applications, some of which include the charging of batteries, the pumping of water, the generation of electricity for homes, the heating of swimming pools, the operation of satellite power systems, and many more. However, despite the fact that they do not need any sort of upkeep and do not result in any kind of pollution, their installation costs are high in many different contexts. Wind energy is quickly becoming a more significant contributor to the total installed power capacity around the globe. In the field of wind energy, the PMSG-based wind turbine equipped with a variable-speed and variable-pitch control system are the most common type of wind power generator. This device is capable of operating either independently or while linked to an existing grid. It is necessary to have a complete understanding of the machine's modelling, control, dynamic, and steady-state analyses in order to obtain the maximum possible amount of power from the wind, researchers must make an accurate prediction of the machine's performance in either mode of operation. The complexity of the systems, the sensors required, the speed of combination, the cost, the breadth of effectiveness, the technology employed, and the popularity of the systems all vary. Multiple control computations are performed on the Wind Energy Conversion System (WECS) in order to produce maximum power in a variety of wind speed scenarios. This is done so that the system can respond appropriately. The purpose of this work is to suggest several methodologies for obtaining dynamic features from the WECS integrated grid. The first technique makes use of the Firefly Algorithm (FA) as well as the Artificial Neural Network (ANN) methods. Both are classification algorithms. By utilizing the most effective parameters for design, the design of the grid-integrated power system design was able to achieve a voltage THD of 11.47 percent.

Influence of interval type-2 fuzzy control approach for a grid-interconnected doubly-fed induction generator driven by wind energy turbines in variable-speed system

This paper suggests a developed control technique using an interval type-2 fuzzy logic control (FLC) tuned PI for optimum torque adjustment for wind turbines operated by doubly fed induction generator (DFIG). The suggested control regulates the error of the mechanical rotor speed to enhance the performance of the torque and the output power results in the study system's overall performance improving. The suggested control combines the advantages of the two techniques: fast response of conventional PI control and adaptively properties of interval type-2 FLC. The studied system is a wind farm of 9 MW composed of 6 wind turbines of 1.5 MW each. Wind speed functions of several types are studied such as step change, extreme change, and constant high speed. The results indicate how the power and optimal torque have fast response with interval type-2 FLC tuned PI compared to the type-1 fuzzy tuned PI and conventional PI control. The simulated results deduce that the suggested interval type-2 FLC can enhance the wind energy system's stability and reliability in a better manner compared to the type-1 FLC and conventional PI.

A INVESTIGATION OF EFFICIENCY OF SERVO MOTOR DRIVE HYBRID PRESS BRAKE SYSTEM: A COMPARATIVE STUDY WITH A TRADITIONAL APPLICATION

In this study, an experimental investigation of the conventional valve-controlled and variable speed pump-controlled control of the press brake system with two hydraulic double-acting actuators was carried out. The system envisaged on the 80-ton press brake, which is one of the press machines in which hydraulic systems are widely used, has been applied. In conventional valve-controlled systems, the flow rate in the system is adjusted with the help of a proportional valve, while the required flow in the variable-speed pump-controlled system is provided by changing the pump speed with the help of a servo motor. From the results obtained, it has been seen that 54% energy saving can be achieved in 100 cycles. The amount of oil used has also been reduced.

Laboratory load-based testing and performance rating of residential heat pumps in heating mode

Improving the energy efficiency of air conditioners and heat pumps is crucial for reducing the effects of continuously rising energy demands for space conditioning. One of the effective and tested approaches for achieving this goal has been to set energy efficiency benchmarks based on minimum energy performance standards which drive technological innovation and implementation in the market. For heat pumps, a testing and rating procedure that estimates equipment seasonal performance from laboratory measurements forms the technical basis for these standards. However, with current residential heat pumps rating standards, significant differences have been observed between efficiency measured in the lab and actual operational performance in field applications. One of the reasons for this is that with current rating approaches, the test unit native controls are overridden when measuring performance in the laboratory. As an alternative, a load-based testing approach has been developed that captures dynamic interactions of the integrated controls, equipment and building with the goal of better-representing field application conditions. In this paper, a load-based testing approach previously developed for air-conditioners is extended for heat–pump heating-mode and demonstrated for a variable-speed system. Climate-specific heating seasonal performance ratings were determined by propagating the test results through a temperature-bin method.

A variable wind harvesting based induction generator using variable voltage and variable frequency converter for renewable energy applications

ABSTRACT This paper proposes the design and development of a power electronic converter intended for induction generator (IG) to harvest the power generated from variable wind in a wind energy conversion system (WECS). The squirrel cage induction generator (SCIG) is anticipated for fairly fixed speed operation, while its speed should be super-synchronous with respect to the synchronous speeds corresponding to the frequency of the receiving alternating current bus bar. In the existing WECS, SCIG requires a minimum wind velocity below which generation is not possible. The novelty of the proposed method is that the range of wind velocities can be selected over which generation is possible. To achieve this, the proposed system makes use of a variable voltage and variable frequency converter (VVVFC). Depending upon the wind velocity, the frequency of the VVVFC is adjusted such that the speed of the turbine and hence the IG are virtually maintained at super synchronous speeds with respect to the frequency of the AC side of the VVVFC. In addition, the perturb and observe-based maximum power point tracking (MPPT) scheme is also implemented. The proposed methodology also includes a series compensated buck–boost converter (SCBBC) inserted between the battery and the direct current link of the final inverter that feeds an RL load. Simulation in the MATLAB Simulink environment is carried out, and an experimental prototype has also been developed to validate the proposed method. Based on the results, it is found that the proposed variable speed system with the integration of VVVFC, SCBBC, and MPPT harvests is 78% greater than the conventional fixed speed system.

Fuzzy optimization strategy of the maximum power point tracking for a variable wind speed system

Wind power systems are gaining more and more interests; in order to diminish dependence on fossil fuels. In this paper, we present a variable speed-wind energy global system based on a synchronous generator with permanent magnetic (PMSG). The major goal of this study is to track the maximum power that is present in the turbine. An examination of control methods to extract the MPPT point, from a wind energy conversion system (WECS) under variable speed situations is presented. An intelligent controller based on the fuzzy logic control (FLC) is proposed for regulating permanent magnetic synchronous generator (PMSG) output power, in order to improve tracking performance. The principle of this maximum power point tracking (MPPT) algorithm consists in looking for an optimal operating relation of the maximum power, then tracking this last. We simulated our system with MATLAB-Simulink software. The found results will be debated to elucidate performance of the global system.