MINIMIZATION OF ELECTRICAL CONSUMPTION OF A FREQUENCY-REGULATION INDUCTION MOTOR WITH A FAN LOAD IN START-BRAKING REGIMES

Abstract

Purpuse. To minimize the total power consumption in start-braking regimes by a three-phase squirrel-cage frequency-regulated induction motor, loaded a centrifugal fan (or smoke exhauster), and also to obtain analytical dependencies for calculating the optimal durations of acceleration and deceleration times, corresponding to minimizing the total energy consumption of this motor in start-braking regimes with the indicated type of load. Metodology. Based on the methods of calculus of variations and numerical solution of non-linear differential equations, the quasi-optimal type of trajectories of speed change (tachograms) of the motor with the considered load in start-braking regimes is determined. Using the methods of mathematical analysis and similarity, the acceleration and deceleration times of an induction motor with a fan load were optimized for different (linear, parabolic and quasi-optimal) types of tachograms. Using the method of computer simulation, the energy consumption in the start-braking regimes of an induction motor with the indicated load for these types of tachograms was quantified. Results. Refined analytical dependencies are obtained for calculating the consumed active power and energy in start-braking regimes by a frequency-regulated induction motor with a fan load for the mentioned various types of tachograms. Analytical optimization of the consumption of active energy of this motor in start-braking regimes has been carried out. The change at the optimal durations for the starting-braking regimes and the corresponding it’s total energy consumption of the motor with varying the maximum value of the motor speed in these regimes has been researched. A quantitative assessment of transient electromechanical and energy processes in the considered motor with a fan load has been carried out. For this motor, as applied to the non-regenerative version of the static frequency converter, a scalar automatic control system is proposed, by means of which the motor accelerates with a constant rotor flux linkage with a given (linear, parabolic or quasi-optimal) speed trajectory and brakes on freewheel. The expected annual saving of active energy by an induction motor, loaded with a smoke exhauster, in starting and braking regimes, achieved by optimizing the form of the tachograms and the duration of the acceleration and deceleration times, is determined. Originality. Analytical dependencies are obtained for calculating the optimal durations of the acceleration and deceleration times of an induction motor with a fan load, corresponding to minimizing the energy consumption of this motor in start-braking regimes. The "U"-shaped form of dependences of the total energy, consumed during acceleration (or the total generated energy during braking) of the induction motor in function the duration of the deceleration (or braking) times is established. An analytical dependence is obtained for changing the speed of a motor loaded by a fan or a smoke exhauster during the freewheel braking regime, and an analytical expression is proposed for determining the duration of the indicated braking time. Practical value. On the example of an induction motor loaded by a smoke exhauster, the possibility of saving the total energy consumption in start-braking regimes was identified: from 77 to 90 % – due to the use of the proposed quasi-optimal tachogram and the use of practically realizable optimal acceleration and deceleration times, and also in the amount of 10 % – through the transition from freewheel braking to regenerative braking. Figures 6, tables 6, references 22.