Rotational Speed Control System Research Articles

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.

A Novel MPC with Actuator Dynamic Compensation for the Marine Steam Turbine Rotational Control with a Novel Energy Dynamic Model

The conventional modeling method of the marine steam turbine rotational speed control system (MSTRSCS) is based on Newton’s second law, constructing the mechanical equations between the rotational acceleration and the resultant torque. The disadvantages of this are nonlinearity, a complex structure and an infinite point of discontinuity in the rotational acceleration when the rotational speed is close to 0. Taking the kinetic energy of MSTRSCS as the output variable by using the kinetic energy theorem in this paper, we convert the complex nonlinear model of MSTRSCS into a linear one, since kinetic energy and rotational speed are homeomorphic. Model predictive control (MPC) adopts a discrete-time model, whereas the real system is time-continuous. Hence, poor performance is obtained in the real system when the time-discrete control law is applied to the MSTRSCS through the actuator. In case of high requirements for system accuracy and control performance, conventional MPC (CMPC) cannot meet the engineering requirements. In order to lessen the impact of this phenomenon, this paper proposes a novel MPC with actuator dynamic compensation (ADCMPC), in which the dynamics of the actuator are quantified and the system performance is improved. Compared with other control techniques such as CMPC, the performance of the ADCMPC strategy in MSTRSCS is successfully validated.

Counter-rotating type tidal stream power unit: Excellent performance verified at offshore test

A counter-rotating type tidal stream power unit, composed of tandem propellers and a peculiar generator with double rotatable armatures, was provided for verification tests at offshore. The front propeller with diameter of 1 m has three blades, and the rear propeller with diameter of 0.95 m has five blades. The blade profiles were optimized with the blade element-momentum theory and CFD, and then covered with CFRP. The front and the rear propellers connect to inner and outer armatures in a synchronous type generator with net output 1.5 kW, whose efficiency was improved by heat pipes and the modification of the armature profiles. The shafts are equipped with mechanical seals to protect electric circuits from seawater. A rotational speed control system was also prepared not only to adjust the output but also to overcome the static friction torque due to bearings, slip rings and mechanical seals while starting-up. The power unit takes the maximum output with excellent efficiency at the relative tip speed ratio specified in the unit design. The unit can start-up after maintenance works and the output can be adjusted smoothly in the stream.

Control strategy of PMSG based wind energy conversion system under strong wind conditions

This paper presents a control approach for the Permanent Magnet Synchronous Generator (PMSG) based Wind Energy Conversion Systems (WECS) under a wide range of wind speeds. Generally, most of the wind turbines are turned-off and disconnected from the power grid, in case wind velocity is gone over 25 m/s. It may cause wind power supply shortage from wind farms. This research introduces a pitch angle controller as well as a rotational speed control system so that the PMSG based WECS can generate power if the wind speeds are above 25 m/s. The proposed method reduces the mechanical stress of the wind turbine by preferential reducing of the rotational speed rather than the mechanical torque during strong wind condition. As a result, the chance of turning-off the is reduced compared to the conventional control system because the PMSG based WECS can temporarily tolerate the wind speed up to 35 m/s. A 2 MW WECS with the electrical and mechanical characteristics is modeled in the MATLAB/SimPowerSystems® to verify the proposed research.

Rotational speed control system of water driven spindle considering influence of cutting force using disturbance observer

The water driven spindle has been developed for use in an ultra-precision machine tool for producing precision parts. In order to achieve high machining accuracy and generate high-quality surfaces, precise rotational accuracy and a constant machine tool spindle speed are necessary in ultra-precision machine tools. However, the rotational speed of the spindle inevitably changes due to the influence of the cutting forces during machining process. In order to deal this problem, this paper describes the development of a rotational speed control system. In particular, the control system is designed such that the influence of the cutting forces is effectively reduced. In this paper, mathematical models of the water-driven spindle and the flow control valve are introduced to develop a feedback control system. The effectiveness of the developed feedback control system is then verified through simulation and experimental tests. In addition, the disturbance observer is added to the designed feedback control system in order to minimize the influence of the cutting forces. Turning tests are then carried out in order to verify the effectiveness of the disturbance observer. As a results, the developed feedback control system with the disturbance observer is verified to successfully reduce the change in the rotational speed.

Investigating the simulated control of the rotational speed of roadheader cutting heads, relating to the reduction of energy consumption during the cutting process

The main responsibilities carried out by roadheaders are cutting rock heading faces of drilled headings or tunnels. This process, especially when drilling headings in hard rock, has been characterized to date by high energy consumption. It is a highly complex process due to its physical nature, as well as, a variety of other factors which it is impacted by. This article presents the possibilities for reducing energy consumption from cutting with transverse roadheader cutting heads, by adapting the rotational speed of the cutting heads to the current conditions of the cutting process at hand. The solution is addressed through automatic rotational speed control of cutting heads and an algorithm of a computer simulated operation of an automatic cutting head rotational speed control system with a PID controller. The computer simulations conducted enabled the assessment of the operational efficiency of the proposed automatic control system in regard to reducing energy consumption when cutting hard rocks.

Comparative CFD study of the effect of the presence of downstream turbines on upstream ones using a rotational speed control system

The effect of a downstream turbine on the production of a turbine located upstream of the latter is studied in this work. This is done through the use of two CFD simulation codes, namely OpenFOAM and EllipSys3D, which solve the Navier-Stokes equations in their incompressible form using a finite volume approach. In both EllipSys3D and OpenFoam, the LES (Large Eddy Simulation) technique is used for modelling turbulence. The wind turbine rotors are modelled as actuator disks whose loading is determined through the use of tabulated airfoil data by applying the blade-element method. A generator torque controller is used in both simulation methods to ensure that the simulated turbines adapt, in terms of rotational velocity, to the inflow conditions they are submited to. Results from both simulation codes, although they differ slightly, show that the downstream turbine affects the upstream one when the spacing between the turbines is small. This is also suggested to be the case looking at measurements performed at the Lillgrund offshore wind farm, whose turbines are located unusually close to each other. However, for distances used in today's typical wind farms, this effect is shown by our calculations not to be significant.

Aperiodic Disturbance Rejection in Repetitive-Control Systems

A repetitive control system (RCS) provides good control performance for periodic signals, but it may not satisfactorily reject aperiodic disturbances. Our solution is an equivalent-input-disturbance (EID)-based RCS in which aperiodic disturbances are estimated by an EID estimator and rejected by incorporation of the estimate into the repetitive control law. A stability criterion and a design algorithm have been developed, and the validity of the method has been demonstrated through simulations and experiments on a rotational speed control system. A comparison of the disturbance rejection performance of this method, proportional-integral-differential control, conventional repetitive control, and H∞ repetitive control demonstrates the superiority of this method.

B26 切削負荷による外乱を考慮したウォータドライブスピンドルの回転数制御モデルの検討(OS2 最新機械要素技術(2))

Recently, various precision parts are produced by ultra-precision machining. For the ultra-precision machining, the precise rotation accuracy, high-bearing stiffness and thermal stability are required to the spindle of the ultra-precision machine tool. Thus, the water driven spindle was developed in previous research. This spindle has the rotor driven mechanism by water flow and has water hydrostatic bearings. However, in the case of actual ultra-precision machining, the rotational speed changes under the influence of cutting forces. This degrades the surface quality of the workpiece. In order to solve this problem, the mathematical model of the water driven spindle is developed and the rotational speed control system is proposed. Effectiveness of this proposed rotational speed control system was verified by simulation tests.

Test sequencing problem arising at the design stage for reducing life cycle cost

Previous test sequencing algorithms only consider the execution cost of a test at the application stage. Due to the fact that the placement cost of some tests at the design stage is considerably high compared with the execution cost, the sequential diagnosis strategy obtained by previous methods is actually not optimal from the view of life cycle. In this paper, the test sequencing problem based on life cycle cost is presented. It is formulated as an optimization problem, which is non-deterministic polynomial-time hard (NP-hard). An algorithm and a strategy to improve its computational efficiency are proposed. The formulation and algorithms are tested on various simulated systems and comparisons are made with the extant test sequencing methods. Application on a pump rotational speed control (PRSC) system of a spacecraft is studied in detail. Both the simulation results and the real-world case application results suggest that the solution proposed in this paper can significantly reduce the life cycle cost of a sequential fault diagnosis strategy.

Design of equivalent-input-disturbance estimator using a generalized state observer

In this paper, we present a design method based on the concept of equivalent input disturbance (EID) to reject disturbances for a linear time-invariant system. A generalized state observer (GSO) is used to estimate an EID of the external disturbances, and the pole-assignment algorithm is employed to select the matrices of the GSO. Simulation and experimental results of a rotational speed control system demonstrate the validity of our method.

Neural rotational speed control for wave energy converters

Among the benefits arising from an increasing use of renewable energy are: enhanced security of energy supply, stimulation of economic growth, job creation and protection of the environment. In this context, this study analyses the performance of an oscillating water column device for wave energy conversion in function of the stalling behaviour in Wells turbines, one of the most widely used turbines in wave energy plants. For this purpose, a model of neural rotational speed control system is presented, simulated and implemented. This scheme is employed to appropriately adapt the speed of the doubly-fed induction generator coupled to the turbine according to the pressure drop entry, so as to avoid the undesired stalling behaviour. It is demonstrated that the proposed neural rotational speed control design adequately matches the desired relationship between the slip of the doubly-fed induction generator and the pressure drop input, improving the power generated by the turbine generator module.

Wave energy plants: Control strategies for avoiding the stalling behaviour in the Wells turbine

This study analyzes the problem of the stalling behaviour in Wells turbines, one of the most widely used turbines in wave energy plants. For this purpose two different control strategies are presented and compared. In the first one, a rotational speed control system is employed to appropriately adapt the speed of the double-fed induction generator coupling to the turbine, according to the pressure drop entry. In the second control strategy, an airflow control regulates the power generated by the turbine generator module by means of the modulation valve avoiding the stalling behaviour. It is demonstrated that the proposed rotational speed control design adequately matches the desired relationship between the slip of the double-fed induction generator and the pressure drop input, whilst the valve control using a traditional PID controller successfully governs the flow that modulates the pressure drop across the turbine.

Angular Position Control of Fluid-Driven Bi-Directional Motor

This paper describes the design of a rotational speed-control system and an angular position-control system for a fluid-driven bi-directional motor. The fluid-driven bi-directional motor has a driving principle similar to that of the fluid-driven spindle, which is designed for use in ultra-precision machine tools. The fluid-driven bi-directional motor was designed so that it is driven by low viscosity oil flow power. In this paper, the rotational speed controller for the motor is first discussed. In order to reduce the influence of external load torque on the rotational speed, a conventional disturbance observer is combined with the rotational speed-control system. The angular position-control system, which possesses the rotational speed feedback loop with the disturbance observer in the angular position feedback loop, is then discussed. The designed rotational speed and angular position-control systems are conventional I—P control and proportional control systems, respectively. The performance of the designed rotational speed-control system and the angular position-control system is studied via simulations and experiments. The performance of the designed control system is tested by the step response method as well as by the frequency response method, respectively. The simulation and experimental results show that the rotational speed and the angular position of the motor can be controlled by the rotational speed controller and angular position controller, respectively. In addition, the influence of the external load torque acting on the motor is successfully compensated for by means of the disturbance observer. The experimental result shows that the designed angular position-control system suppresses the steady-state positioning error to less than 0.02°, even if external constant load torque acts on the motor.

Hybrid System Test Rig: Start-up and Shutdown Physical Emulation

The University of Genoa (TPG) has designed and developed an innovative test rig for high temperature fuel cell hybrid system physical emulation. It is based on the coupling of a modified commercial 100 kW recuperated micro gas turbine to a special modular volume designed for the experimental analysis of the interaction between different dimension fuel cell stacks and turbomachines. This new experimental approach that generates reliable results as a complete test rig also allows investigation of high risk situations with more flexibility without serious and expensive consequences to the equipment and at a very low cost compared with real hybrid configurations. The rig, developed with the support of the European Integrated Project “FELICITAS,” is under exploitation and improvement in the framework of the new European Integrated Project “LARGE-SOFC” started in January 2007. The layout of the system (connecting pipes, valves, and instrumentation) was carefully designed to minimize the pressure loss between compressor outlet and turbine inlet to have the highest plant flexibility. Furthermore, the servocontrolled valves are useful for performing tests at different operative conditions (i.e., pressures, temperatures, and pressure losses), focusing the attention on surge and thermal stress prevention. This work shows the preliminary data obtained with the machine connected to the volume for the test rig safe management to avoid surge or excessive stress, especially during the critical operative phases (i.e., start-up and shutdown). Finally, the attention is focused on the valve control system developed to emulate the start-up and shutdown phases for high temperature fuel cell hybrid systems. It is necessary to manage the flows in the connecting pipes, including an apt recuperator bypass, to perform a gradual heating up and cooling down as requested during these phases. It is an essential requirement to avoid thermal stress for the fuel cell stack. For this reason, during the start-up, the volume is gradually heated by the compressor outlet flow followed by a well managed recuperator outlet flow and vice versa for the shutdown. Furthermore, operating with a constant rotational speed control system, the machine load is used to reach higher temperature values typical of these kinds of systems.

184 流体駆動スピンドルの回転数制御系の設計(生産加工・工作機械I,一般講演)

184 流体駆動スピンドルの回転数制御系の設計(生産加工・工作機械I,一般講演)