Variable Speed Control System Research Articles

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.

An improved approach to model compressors, condenser/gas cooler and their control system in refrigeration systems with R404A and R744 based on physical principles

This study introduces an improved methodology to evaluate with accuracy the performance of a conventional system with R404A and a Booster system with R744. Reciprocating and scroll compressors are modeled with improved semi-empirical approaches, and their operation is ideally controlled to maintain the required refrigerant mass flow rate with an On/Off and variable speed control system. The R744 gas cooler is modeled with a four-zones model and the R404A condenser with a three-zones model. The R744 condenser is modeled with the superheated zone discretized into eight zones to avoid unrealistic results due to the variation of its thermophysical properties and the two-phase and subcooled zones with one zone respectively. In line with the design, the Booster condenser enters into the pseudo-critical zone at an ambient temperature of 23 °C, while the gas cooler is activated after 31 °C. The compressor models present errors lower than 10%, while the Booster model presents mean deviations lower than 2.3%. The Booster system presents better COPs than the conventional at ambient temperatures lower than 15ºC. At higher ambient temperatures, the COPs of both systems are similar: the conventional system overperforms the Booster up to 6%, being in disagree with the literature results where these differences increase up to 30%. The proposed methodology allows to reduce the overall model error by 3% with respect to a thermodynamic cycle-based model; allowing to improve the comparison between the Booster system with R744 and the conventional one with R404A, which leads to more transparent results than the reported common comparisons.

Research on Power Regulation Schedule Control System for Turboprop Engine

Abstract A method of variable speed control system for turboprop engine is presented in this paper. Firstly, the steady operation state of turboprop engine is analyzed, and the operating line is figured out in the steady state characteristic diagram, which is the design basis of Engine Thrust Management System (ETMS). Secondly, the reference model sliding mode multivariable control is used to design the control law to follow the speed instructions given by ETMS. Finally, the optimization of the minimum fuel consumption operating curve is realized, and the control system designed is applied to a numerical model of a turboprop engine. The simulation results show that compared with the constant speed control system, the variable speed control system can reduce the specific fuel consumption by 2.37 % on average and 3.1 % in steady state conditions. Furthermore, the method can enable the pilot to manipulate the turboprop aircraft by using only one throttle lever, which can greatly reduce the pilot operation burden.

System Design and Characteristic Analysis of Variable Frequency Hydraulic Crane

The hydraulic crane widely used at present has low efficiency, high noise and maintenance cost; it is difficult to meet the requirements of the development of energy conservation and environment protection. The hydraulic variable frequency speed regulation makes use of variable frequency motor to adjust the working speed of the quantitative pump, thereby regulating the output flow of the quantitative pump, and solving the problem of power matching from the source. The motor system is always in an efficient working state, thus avoiding the high-speed continuous operation of the motor and the hydraulic pump, improving the reliability, the service life and the energy utilization rate of the equipment. The design scheme of variable frequency hydraulic speed control system are put forward and its operating characteristics are analyzed in this paper.

Variable Speed Control of Wind Turbines Based on the Quasi-Continuous High-Order Sliding Mode Method

The characteristics of wind turbine systems such as nonlinearity, uncertainty and strong coupling, as well as external interference, present great challenges in wind turbine controller design. In this paper, a quasi-continuous high-order sliding mode method is used to design controllers due to its strong robustness to external disturbances, unmodeled dynamics and parameter uncertainties. It can also effectively suppress the chattering toward which the traditional sliding mode control method is ineffective. In this study, the strategy of designing speed controllers based on the quasi-continuous high order sliding mode method is proposed to ensure the wind turbine works well in different wind modes. First, the plant model of the variable speed control system is built as a linearized model; and then a second order speed controller is designed for the model and its stability is proved. Finally, the designed controller is applied to wind turbine pitch control. Based on the simulation results from a simulation of 1200 s which contains almost all wind speed modes, it is shown that the pitch angle can be rapidly adjusted according to wind speed change by the designed controller. Hence, the output power is maintained at the rated value corresponding to the wind speed. In addition, the robustness of the system is verified. Meanwhile, the chattering is found to be effectively suppressed.

Special issue: emerging technologies for intelligent transportation

Special issue: emerging technologies for intelligent transportation

Modeling of High Power Water Resistor Speed Control System of Wound Rotor Induction Motor

A variable value water resistor speed control system for rotor winding induction motor is introduced. On the basis of the structure about the water resistance and the governor principle, the steady-state mathematical model and the dynamic mathematical models are established. The effect of temperature changes on the resistance of the electrolyte solution is discussed, and temperature compensation is proposed. Simulation results show that the water resistance speed control system is feasible.

Variable Speed Wind Turbine with External Stiffness and Rotor Deviation Observer

Often in prominent literature, the appearance of external stiffness in wind turbine dynamical model has been neglected. The ignorance of external stiffness eliminates the presence of rotor-side angular deviation in the system dynamic. In order to give more practical look of the variable speed control system structure, we develop a linear observer to estimate the rotor angular deviation. We use Linear Quadratic Regulator (LQR) to design the observer gain, as well as the estimation error gain. To facilitate observer design, the system is linearized around its origin by using Jacobian matrix. By using the estimated rotor angular deviation, we design a variable speed control via Lyapunov and Arstein to enhance power output from the turbine.

Exploratory analysis of an optimal variable speed control system for a recurrently congested freeway bottleneck

SummaryThis study presents two models for proactive variable speed limit (VSL) control on a recurrently congested freeway segment. The proposed model uses embedded traffic flow relations to predict the evolution of congestion patterns over the projected time horizon, and then computes the time‐varying optimal speed limit to smooth traffic flows. To contend with the uncertainties associated with drivers' responses to VSL control, this study has also proposed an advanced model that further adopts Kalman Filter to enhance the traffic state estimation. Both models have been investigated with two control objectives—travel time minimization and speed variance minimization. Our extensive simulation analysis with a VISSIM simulator, calibrated with field data from our previous VSL field demonstration, has revealed the benefits of the proposed VSL control models. Also, the experimental results indicated that the proposed advanced models with both control objectives can significantly reduce the travel time over the recurrent bottleneck locations. With respect to several selected measure of effectiveness (MOEs), such as average number of stops and average travel time, the research results confirm that the control models with the objective of minimizing speed variance can offer the promising properties for field implementation. Copyright © 2014 John Wiley & Sons, Ltd.

A Gain Scheduled Method for Speed Control of Wind Driven Doubly Fed Induction Generator

This paper proposes a gain scheduled control method for a doubly fed induction generator driven by a wind turbine. The purpose is to design a variable speed control system so as to extract the maximum power in the region below the rated wind speed. Gain scheduled control approach is applied in order to achieve high performance over a wide range of wind speed. A double loop configuration is adopted. In the inner loop, the rotor speed is used as the scheduling parameter, while a function of wind and rotor speed is used as the scheduling parameter in the outer loop. It is verified in simulations that a high tracking performance has been achieved.

NREL 5MW 풍력터빈의 제어시스템 설계

This paper introduces a methodology for NREL 5MW wind turbine, which is the variable speed and variable pitch(VSVP) control system. This control strategy maximizes the power extraction capability from the wind in the low wind speed region and regulates the wind turbine power as the rated one for the high wind speed region. Also, pitch control efficiency is raised by using pitch scheduling.Torque schedule is made of torque table depending on the rotor speed. Torque control is used for vertical region in a torque-rotor speed chart. In addition to these, mechanical loads reduction using a drive train damper and exclusion zone on a torque schedule is tried. The NREL 5MW wind turbine control strategy is comprised by the generator torque and blade pitch control. Finally, proposed control system is verified through GH Bladed simulation.

Modeling and Simulation of Parameter Self-Tuning Fuzzy PID Controller for DC Motor Speed Control System

The establishment of DC motor system model is an important part of its control system analysis, this paper introduces the traditional method of modeling and the application of parameter self-tuning fuzzy logic PID control in the simulation and experimental research of variable speed control system for DC electric motor. In MATLAB / SMULINK simulation environment, high robustness and precision are obtained. The simulation results show that fuzzy logic PID control strategy has better performances than traditional controllers.

상태공간 모델링에 의한 공작기계용 수냉각기의 최적제어기 설계

ABSTRACT:Typical temperature control methods of a cooler for machine tools are hot-gas bypass and compressor variable speed control. The hot-gas bypass system has been widely used to control the cooler temperature in many general industrial fields. On the contrary, the compressor variable speed control is focused on special fields such as aerospace and high precision machine tools which need high precision control. The variable speed control system usually has two control variables such as target temperature and superheat. In other words, the variable speed control sys-tem is basically multi-input multi-output(MIMO) system. In spite of MIMO system, the proportional integral derivative(PID) feedback control methodology that based on single-input single-output (SISO) system is generally used for designing the variable speed control system. Therefore, it is inevitable to describe transfer functions for dynamic behaviors of every controlled variables and decide the PID gains with tremendous iteration process. Moreover, the designed PID gains do not provide optimum system performances. To solve these problems, high performance controller design method based on a state space model is suggested in this paper. An optimum controller is designed to minimize both control errors and energy inputs. This method was more simple to describe dynamic behaviors and easier to design the cooler controller which is MIMO system.Keywords:Water cooler(수냉각기), Optimum control(최적제어), State space model(상태공간 모델), Compressor variable speed control(압축기 가변속 제어), Multi-input multi- output system(다입력 다출력 시스템), State variable(상태변수)

Development of Clemson variable-rate lateral irrigation system

Crops in the Southern United States are generally produced in fields which are known to have a high degree of variability in soil type, water holding capacity, infiltration rates, and other major factors which affect crop production. In these fields, the ability to turn irrigation water on or off or apply variably to different segments of the field is advantageous over the conventional uniform application. A variable-rate lateral irrigation (VRLI) system was developed for site-specific application of water to match field variability. The system consists of solid-state relays controlled by custom software, air-actuated diaphragm valves, a forward speed control system and a GPS receiver. The Clemson VRLI system applies variable-rate water utilizing the nozzle-pulsing technique and variable speed control system. This system could monitor and apply water based on the actual soil moisture content, pan evaporation data, or the U.S. Climate Reference Network (CRN) data. Uniformity tests show that the system is able to control the irrigation rate from 0 to 2.5 cm of irrigation water and can control the forward speed between 145 and 29 m/h. The pulsing technique to deliver variable amounts of irrigation had little adverse effect on system uniformity and nozzle flow rate with an average application error of less than 2%.

Development and Performance Evaluation of a Conveyor Belt Type Animal Treadmill

A portable conveyor belt type animal treadmill has been designed and developed at CIAE, Bhopal for laboratory studies on work performance and fatigue of draught animals. The treadmill consists of a portable frame, conveyor belt, railings, advance variable speed control system, transport cum inclination changing wheels, a loading device for animal with suitable harnessing system and inclined platforms to help the test animal to climb up for the experiment. The speed of conveyor belt can be adjusted in the range of 0 - 2.5 km/h and draft load on the animals can be exerted from 0 -15% of body weight. The treadmill was tested for its performance with Malvi breed of bullocks on draft loads equivalent to 6, 6.5, 7 and 7.5 %body weight of bullock at belt speed of 1.6, 1.8,2. I and 2.24 km/h. The power requirement to operate the treadmill ranged from 1.1 to 2.70 kW at belt speed of 0.5 to 2.5 km/h with and without load respectively.

Design and partial load exergy analysis of hybrid SOFC–GT power plant

This paper presents a full and partial load exergy analysis of a hybrid SOFC–GT power plant. The plant basically consists of: an air compressor, a fuel compressor, several heat exchangers, a radial gas turbine, mixers, a catalytic burner, an internal reforming tubular solid oxide fuel cell stack, bypass valves, an electrical generator and an inverter. The model is accurately described. Special attention is paid at the calculation of SOFC overpotentials. Maps are introduced, and properly scaled, in order to evaluate the partial load performance of turbomachineries. The plant is simulated at full-load and part-load operation, showing energy and exergy flows trough all its components and thermodynamic properties at each key-point. At full-load operation a maximum value of 65.4% of electrical efficiency is achieved. Three different part-load strategies are introduced. The off-design operation is achieved handling the following parameters: air mass flow rate, fuel mass flow rate, combustor bypass, gas turbine bypass, avoiding the use of a variable speed control system. Results showed that the most efficient part-load strategy corresponded to a constant value of the fuel to air ratio. On the other hand, a lower value of net electrical power (34% of nominal load) could be achieved reducing fuel flow rate, at constant air flow rate. This strategy produces an electrical efficiency drop that becomes 45%.

Design and part-load performance of a hybrid system based on a solid oxide fuel cell reactor and a micro gas turbine

This paper addresses the design and off-design analysis of a hybrid system (HS) based on the coupling of a recuperated micro gas turbine (MGT) with a high temperature solid oxide fuel cell (SOFC) reactor. The SOFC reactor model is presented and discussed, taking into account the influence of the reactor lay-out, the current density, the air utilisation factor, the cell operating temperature, etc. The SOFC design and off-design performance is presented and discussed; the design and off-design models of a recuperated micro-gas turbine are also presented. The operating line, the influence of the micro gas turbine “variable speed” control, and the efficiency behaviour at part load are analysed in depth. Finally, the model of the hybrid system obtained by coupling the MGT and the SOFC reactor, considering the compatibility (technological constraints) of the two systems, is presented. The model allows the evaluation of the design and off-design behaviour of the hybrid system, particularly when the MGT variable speed control system is considered. The thermal efficiency of the hybrid system, taking into account its size (250/300 kW e), is noteworthy: higher than 60% at design point, and also very high at part load conditions. Such a result is mainly due to the simultaneous positive influence of SOFC off-design behaviour and MGT variable speed control. Moreover, it is possible to recover the waste heat from the gas at the MGT recuperator outlet ( T gas is about 250°C) for cogeneration purposes.

A Robust Controller for a Novel Variable Speed Wind Turbine Transmission

A hybrid mechanical-electrical variable speed transmission for wind turbines is presented. The concept consists of a planetary differential transmission in which one input is driven by the variable speed rotor and the second by the variable speed control system, both driving the main generator at a constant speed. The increase in the energy output is estimated to be of about 15 percent–20 percent using the new transmission with the same rotor. The control system, designed to operate efficiently at the entire anticipated wind speed range, varies the rotor speed to provide optimal output power for slow wind speed variations and to attenuate high frequency shaft torque fatigue damage in gusty wind operation. The net result is a cost effective system compared to contemporary variable speed solutions. Dynamic simulations are presented to demonstrate the improved system performance.

High Precision Control for Electrical Machine with Periodical Disturbances based on Optimal Repetitive Control.

It is well known that the speed control system, even though which is constructed with an excellent control method, has an unexpected steady speed error when it is suffered by a periodical load disturbance. As the method of eliminating the speed fluctuation caused by such kind of disturbance, a repetitive control is the most effective. But the repetitive control method is only adoptive for a constant speed control system.In this paper, a novel control system designing method which is effective to both the constant speed control system and variable speed driving system is shown. The fact that a periodical disturbance depends on time function and also rotational angle is utilized to design the control system. From the result, the numerical modeling of the controlled object is derived in the rotational angle function domain. For the obtained numerical model, an extended state variable equation based on the original system is presented by using the control technique named “Error System Technique”. And then the optimal feedback gains are decided by solving the optimal regulator problem for the extended state equation. Therefore, a stability of the system is ensured.The proposed control method is applied to DC motor variable speed control system and the experimental setup is constructed. Finally, the effectiveness of the proposed method is confirmed by the result of simulations and experiments.

New design for the high‐performance drive system for DC brushless motor

AbstractThe dc brushless motor, permanent magnet‐type synchronous motor (PM motor), has been used widely in industrial robots, the machine tools for factory, and factory automations. Therefore, it is more desirable to improve the performance of the PM motor variable speed control system. Although only the torque component current is adjusted as the control method for the PM motor, so‐called Vector Control, it is expected that the developed characteristics will be added to the PM motor.In this paper, new driving methods for the PM motor and a new design method for the variable speed control system are presented. The new motor driving methods which bring to the PM motor a new driving performance, e.g., a quick transient response or high‐efficiency motor driving, can be implemented by controlling not only the torque component current, but also the magnetizing component current. A developed optimal control theory, i.e., the error system technique, is employed for designing the control system. The control law is endowed with a steady robustness against the variation of the system parameters and the ability of compensating the delay time due to the control processing.The effectiveness of the proposed method is confirmed by simulations and experiments.