Abstract
The operation modes of the TVC-AM electric drive in which the power losses can be reduced were mathematically described. It was defined more precisely that what was at issue is the continued operation of an asynchronous motor at artificial characteristics in the region of nominal slip with an energetics better than at the working section of the natural mechanical characteristic. The system of automatic minimization of power losses of asynchronous motors was developed. It was shown that under conditions of feeding the electric drive from a source with asymmetrical voltage, it is necessary to use phase-by-phase control which requires the use of three control channels and three feedback channels. The logic of the feedback action is that when the load on the AM shaft decreases, it reduces the output voltage of the TVC and the motor currents. As a consequence, it becomes possible to maintain equality of the load angles of all phases to the optimum value. This makes it possible to solve the problem of minimizing the AM losses in a case of equality of the load angles to the optimal value and symmetrization due to equality of load angles by the phases of the motor. The quantitative indices of power loss decrease as well as the symmetrization indices when the electric drive is powered from a source with an asymmetric voltage were shown. The features of the power loss minimization system and the ways of improvement of its efficiency were illustrated. It was shown that the use of the proposed control system led to an improvement in both the power and dynamic parameters of the asynchronous electric drive. A 5 to 45 % reduction of power losses in the range of operating moments of 0£М£М bo relative to losses during operation at the main mechanical characteristic was recorded. The symmetrization effect was characterized by a 1.5 to 6 times reduction of the current asymmetry coefficients. The use of a thyristor voltage converter makes it possible to realize controlled transient start-up and braking modes. Symmetrization of the acting currents of the asynchronous motor results in an 80–150 % reduction of vibrational components of the electromagnetic moment in a steady-state regime
Highlights
A trend to building-up mass production of controlled electric drives (ED) is observed in the current world practice
The region limited by the section a–b of the natural characteristic, the axis of slips and the line of equal losses 4 is the region in which modes can be formed with asynchronous motors (AM) power losses smaller than at the natural characteristic
The results show that the loss minimizing system (LMS) provides a significant reduction of AM losses in the range of operating moments 0£М£Мbo
Summary
A trend to building-up mass production of controlled electric drives (ED) is observed in the current world practice. According to the data of economically developed countries, ED with asynchronous motors (AM), mainly with a squirrel-cage rotor, account for 80 % to 90 % of the total amount of electric power consumed by ED. This is due to their relatively low cost, less need for scarce materials in comparison with electric motors of other types, cost effectiveness, simplicity, and reliability of operation. The TVC-AM electric drives are characterized by low cost, simplicity, good weight-to-size indicators, high reliability, and wide functionality (especially when used in closedloop systems) [2]. It is important to develop electromechanical systems aimed at compensation for the negative properties associated with impairment of the power source quality indicators
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