Rotational speed

About: Rotational speed is a research topic. Over the lifetime, 23327 publications have been published within this topic receiving 151696 citations. The topic is also known as: speed of revolution & revolution rate.

Static synchronous generators

Abstract: The invention is concerned with a device and a method for controlling an inverter associated with a power source, which typically will be a distributed power source. The role of an inverter is to modulate the electrical power output, e.g. to provide a three phase AC electrical output at suitable voltage, where the output is to be supplied to a conventional power distribution, grid. The invention involves modelling the behaviour of a synchronous electrical generator. Variables represent the angular position and rotational speed of the virtual rotor (14) of this virtual synchronous generator. The torque electromagnetically exerted on the rotor is calculated from a measured inverter output current, and from a variable representing excitation current in the rotor. Allowing for this and for a notional drive torque applied to the virtual rotor (which in the physical analogue would be supplied by some prime mover such as an engine), as well as for the virtual inertia of the rotor, the angular speed of the virtual rotor is calculated, Using the angular position and rotational speed of the virtual rotor, and allowing for the aforementioned excitation current, it is possible to obtain the cmf induced in stators of the virtual generator. On this basis a control signal is generated which causes the inverter to produce an AC output corresponding to that which would be provided by the virtual synchronous generator. A synchronous generator must be regulated, as too must the virtual synchronous generator of the present invention. To this end, the invention provides a feedback loop in which deviation of the rotational speed of the virtual generator rotor from a reference angular speed is detected and is used to adjust the virtual drive torque, thereby to regulate the rotational speed of the rotor and hence the frequency of the AC output and the real power supplied by it.

The critical rotational speed of circular saw: simple measurement method and its practical implementations

Abstract: Operation safety during sawing operations as well as dimensional accuracy and surface roughness depend on circular saw dynamic features among other factors such as circular saw blade accuracy and static/dynamic properties of the machine tool Manufacturers of saw blades have an obligation to mark tools with a value stating the maximum allowed rotational speed for each saw However, in some cases the value indicated on the saw corresponds to the critical rotational speed or is dangerously close to this critical value Saw operation at the critical rotational speed is inadvisable and may result in serious injury or depreciation of product quality This report outlines a simple methodology for evaluation of circular saw critical rotational speed The assessment was conducted with a camera vision technique on the basis of an impulse test Results are compared with theoretically calculated critical rotational speeds and the marks on saw blades

Variable speed induction generator-motor with controllable excitation frequency

Abstract: A variable velocity apparatus includes a wound-rotor induction machine having a primary winding connected to a power system having a power system frequency, a secondary winding excited by an alternating current (AC), a generator-motor shaft, and a load united with the generator-motor shaft. The apparatus includes a frequency detection element for detecting a change in the power system frequency, and a controller for changing a rotational speed of the induction machine based on the detected change in the power system frequency. The change in the rotational speed is made substantially equivalent to the detected change in the power system frequency, so as to maintain a slip frequency of the induction machine essentially constant when the power system frequency changes.

Robust Speed Control of Ultrasonic Motor Based on H.INF. Control with Repetitive Compensator.

Abstract: A constant speed control system of an ultrasonic motor(USM)is designed based on H∞ control with a repetitive compensator. Generally driving mechanism of USM uses frictional force. It comes the following disadvantages of the motors : (1)the dynamic response shows non-linear natures and depends on the operating temperature ; (2)the average rotational speed gradually decreases with temperature rise ; (3)the speed fluctuates periodically synchronizing with rotation. To tackle the problems, multiplicative uncertainties are introduced into the plant model to represent the non-linearity and the temperature dependency. The decrease and the fluctuation in speed are treated as a step and a periodic disturbance respectively. The control system is designed as follows. Firstly, and integral type H∞ controller is designed which guarantees robust stability against the uncertainties. Secondly, a repetitive compensator is attached to the system without loosing stability to attenuate the periodic disturbance. Experiments confirm the validity of the proposed control system.