Monica-Adela Enache

Aspects regarding optimal design of high power squirrel cage asynchronous motors

The lately important development of some high precision electrical drives with great response speed, as well as the fact that the electrical machines exploitation is closer and closer to limit of stability have led to intense preoccupations, in the whole world and in our country, for the precise determination of the asynchronous motors parameters and the operation characteristics. This paper has got a novelty character, emphasizes the role of the electromagnetic stresses and the constructive dimensions in the total cost optimization for high power asynchronous motors; it is based on the utilization of the modern numerical methods and the afferent software. There have been performed significant simulations, which bring quantitative and qualitative information necessary for finding the final optimum solution, by considering the customers restrictive conditions regarding the machine gauge. The optimization study has been done by the minimum total cost criterion, by considering twelve variables: A - the current sheet; B - the air gap magnetic induction; J1, J2b, J2i - the current densities into the stator winding, rotor winding and the short-circuit ring; Bj1, Bj2 - the magnetic inductions in the stator and rotor yoke; D - the machine diameter; δ - the air gap; βc1, βc2, βi - the form factors for the stator slot, the rotor slot and the short-circuit ring. The optimization advantages are emphasized by the simultaneous presentation of the three variants of motors: Vm - the existing variant of motor; Vo - the optimum variant; Vd - the unfavourable variant (which has the maximum total cost). The total cost of the optimized motor decreased with 12,2% in comparison to the existing motor (designed by using the known method) and with 27,5% in comparison to the unfavourable variant. Since there are many such motors in use it appears that the saving is significant.

Aspects Regarding Dynamic Regimes of Induction Motors Control by the Stator Flux

In this paper there are presented the equations defining the mathematical model of the saturated induction machine when considering the magnetising current and the stator flux as state variables. By their means there is analysed the influence of the induction motors parameters upon the transient states duration of the converter-motor assembly when controlling by the stator flux with the implementation of a voltage inverter that is commanded in current.

Method and device of synchronization for determination of squirrel cage asynchronous motors parameters

This paper presents a method for the squirrel cage asynchronous motors parameters determination, which is the object of a invention proposal. The method involves monitoring a direct-on-line starting and processing, by minimizing an objective function, the data recorded during starting. There are also presented the experimental results obtained, with accent on the synchronization device, which is the object of an invention demand, too.

Aspects regarding design of squirrel cage asynchronous motors for mining excavators

This paper aims at emphasizing the importance of the electromagnetic stresses and constructive dimensions in the starting characteristics optimization in case of high power squirrel cage asynchronous motors used for surface mining excavators. Since the motor drives a high capacity excavator, the inertia moment is high and a significant increase of the starting period results. Several significant simulations are presented in this paper; they bring information which is necessary for determining the final optimum constructive solution, where a very low starting current is considered, so that the motor is able to cope with it, during the starting period. The restrictive gauge conditions imposed by the place where the motor is assembled are also considered when the optimum constructive solution is established. The optimization study has been made by the customers criterion - minimum starting current - by using twelve variables: current loading, air-gap magnetic induction, stator and rotor winding current densities, stator and rotor yoke magnetic induction, machine diameter, air-gap, shape factors for the stator and rotor slots, rotor slot isthmus dimensions. The optimized motor has a starting current Ip=2,85*IN (lower by 12,2% in comparison with the limit value imposed by customer) and the total cost (of fabrication and exploitation) is lower by 3,5 % in comparison with the real existing motor of the excavator.

Considerations regarding modelling, simulation and monitoring of dynamic regimes for asynchronous motors

This paper presents a few aspects regarding the modelling, simulation and monitoring of dynamic regimes for asynchronous motors. There are presented the two-axes mathematical model of these motors, the Simulink simulation program, the simulation results for the case of direct on-line starting, as well as a few experimental results (which confirm the simulations). The research originality derives from the utilization of the mathematical model considering the saturation written as an original form, a relatively complicated one, but very easily to implement in Simulink. With its help, a simulation program, which is also original, has been conceived.

Transitory processes determined by the shunt-reactors in the high voltage networks. Theoretical synthesis and simulation

This paper analyzes some transient processes specific to high voltage electric networks. There are followed especially the electric stresses in disconnecting shunt reactors. Analytical and numerical determinations are taken into account. The simulations confirm the analytical conclusions.

Reluctance synchronous motors modelling and analysis

This paper presents a possibility for the theoretical and experimental modelling and analysis of the reluctance synchronous motors asynchronous starting. In the first part of the paper the two axes theory mathematical model of the reluctance synchronous motor is presented. The accent is laid on the model written in matrix form, which is easy to implement in Matlab. An original Matlab program has been conceived with the help of this model (detailed in this paper); it makes possible the analysis of the asynchronous starting dynamic regime when the motor parameters are modified (resistances, inductivities and inertia moment). The simulations obtained with the help of this program and the conclusions emerging from them are presented. There are detailed the dependences of the current, speed and torque versus time and the mechanical characteristics obtained for the cases when the rotor resistance and the inertia moment are modified in turn. Finally, there are presented the test stand and the experimental determinations, which confirm the theoretical conclusions validity. A special attention is paid to the test stand structure, which contains a high speed data acquisition board assembled inside a computer. In order to confirm the conclusions obtained theoretically, there are presented the curves of the phase current and the rotor angular speed versus time.

Possibilities for reluctance synchronous machines parameters experimental determination

A few methods for the experimental determination of the reluctance synchronous machines parameters are detailed in this paper. Since this paper is not a reluctance synchronous machine (RSM) test handbook, all the tests will not be described, certain references being recommended for this purpose. In the first part of the paper there is presented an experimental stand for the reluctance synchronous machines parameters determination. The stand includes a data acquisition board KPCI 3102. In the second part, there are presented the experimental tests, performed with a flux barriers machine rated at 1,2 kW. There have been considered the determination of the stator resistance, the longitudinal synchronous inductance, the transversal synchronous inductance, the leakage inductances, the longitudinal and transversal magnetization inductances and the sub-transient reactances. It is called the attention to the modern method for obtaining the longitudinal and transversal synchronous inductances. The longitudinal and transversal synchronous inductances have been determined by means of a method consisting in a direct current decreasing through the stator winding, the rotor being at rest and positioned so that the longitudinal axis coincides with the axis of the phase A. Finally there are presented the conclusions emerging by experimental tests, conclusions which confirm the theory presented in the literature. It is emphasized that the reluctance synchronous motors parameters can be determined easy and quickly by means of the test stand we conceived and built.

Aspects regarding electromagnetic torque of brushless direct current motors

Interest paid lately to brushless direct current motors made the researches regarding the optimum design and construction of these motors to be very present. The study carried out, by the simulations we presented, shows that these motors have high torque oscillations in a complete rotation. There are identified the slots which create high torques, respectively low torques, in a complete rotation, thus justifying the oscillations. In this paper there is emphasized that the optimum variant of maximum torque involves a supply by six pulses per period in direct direction, also indicating the value of the control angle. The most unfavourable variant occurs at brushless direct current motor supplied by three pulses per period and reverse succession of phases, where the average value of the torque decreases by 56.7% over the optimum machine. An almost constant torque cannot be obtained for brushless direct current motor, but we can draw near this requirement.

Simulation of some dynamic regimes specific to permanent-magnet motors used for electrical motor-scooters

This paper presents a series of dynamic regimes specific to the operation of permanent-magnet synchronous motors used for electrical motor-scooters. On this purpose, there is presented the mathematical model of the motor. By means of this model, there has been carried out a programs package of simulation (in Matlab); a part of these simulations are presented in this paper. There have been considered three particular situations: dynamic processes in the absence of the permanent magnet and weak damping, dynamic processes in the absence of the permanent magnet and strong damping and dynamic processes in the presence of the permanent magnet. The paper ends by conclusions obtained from the simulations analysis.