Analyzing High Efficiency Asynchronous Motors Using Scalar Control Technique

In industry, more than half of the total electrical energy produced in developed countries is converted into mechanical energy by electric motors. The usage rate of asynchronous motors is estimated to be 90% of all electric motors. For these motors, an improvement in efficiency may result in huge savings. These electric motors which have minimized losses can be improved with speed control drives to be more efficient in terms of energy consumption and performance. In speed control drives of asynchronous motors widely used in industry; scalar, vector control and direct torque control are used. In this study, in a Matlab/Simulink environment, high efficiency and standard asynchronous motors with the same characteristics were driven with scalar control technique and the simulations were compared in detail. From the point of view of both speed control performance and energy saving, it observed that high efficiency motors have more advantages.


I. INTRODUCTION
ORLD industrial production mostly relies on electric motors and electric motors are performing the work of billions of people.Therefore, it is of great importance that the electric motor is highly efficient.Efficiency improvements can provide big savings.By minimizing the losses in the motor, the obtained high-efficiency motors, can not only prevent heat loss, but also minimizes any other losses.Other big advantages of high efficiency motors are that when used with variable speed drive they have advanced control characteristic [1][2][3][4].

II. HIGH EFFICIENCY ASYNCHRONOUS MOTORS
It is known that the industry is the biggest electricity consuming sector in a country.In the industry of advanced countries three-quarters of the energy consumed is used in electric motors.Efficiency improvements in these motors can provide big savings.
In the production phase electric motors are generally manufactured in three classes.These classes are named according to European standards as High Efficiency Motor Class (EFF1), Standard Efficiency Motor Class (EFF2) and Low Efficiency Motor Class (EFF3).Nowadays EFF3 class motors, totally or partially disappeared from production and EFF1 and EFF2 have been used mostly in industry.In our study, subjects will be motors of these two classes.
Two different Technologies are used in the manufacture of high efficiency motors.Extending the length of the packet motor sheet is raising efficiency, and the other design is made by using higher quality sheet metal and copper.In addition, motors with rotors produced with copper injection technique do also step forward as new generation high-efficiency motors.Also in this type of motor the fan structure is designed specifically to provide better cooling.Thus the heat losses to the energy are minimized.
An electric motor cannot convert the entire energy it draws from the network which it's connected into mechanical energy.The useful power from the electric motor shaft; losses from the power drawn from the mains power out of the state.Energy losses in the motor during operation of the engine are converted into heat energy.The high efficiency motors gained from minimization of these losses, not only prevents heat loss, but also minimizes any other losses [1][2][3][4][5][6][7][8][9][10][11].

III. SCALAR CONTROLS
Due to the ease of implementation, scalar control nowadays is the best known and most widely used method of speed control for variable speed motor drives.The essential feature of this method; at speeds from zero to the rated value is that the voltage applied to the stator frequency (V / F) ratio, and thus the flux and induced torque is kept constant.At speeds above the rated speed, the increase in frequency and the voltage is kept constant; therefore, the attenuation of the flux through the rate control can be performed.Asynchronous Motor (ASM) speed drive systems using scalar methods of control have a good variable dynamic steady-state performance, but the dynamic response is not good answered.Oscillations in the air flow Analyzing High Efficiency Asynchronous Motors Using Scalar Control Technique H.Uzun, O.Akar, A.Demirci, M.C.Akuner, and U.K. Terzi W range worsens dynamic response and causes electromagnetic torque oscillation.In high-performance drive systems, oscillations in torque and speed are not required.In this type of application, high accuracy, fast position and speed control is required.If the flux and torque are controlled separately, these problems can be overcome.A method of controlling the flux and torque individually is called the vector control (field oriented control) [6,[12][13][14][15][16][17][18].

IV. STUDIES
In this section, studies performed in the MATLAB/ Simulink environment are described.In the simulation study performed with MATLAB/Simulink blocks asynchronous motors with scalar control methods have been proposed.For the realization of these simulations of both efficiency classes of the Gamak motor brand and tag information of the motor equivalent circuit parameters were utilized.In Table 1 and Table 2, the tag information and equivalent circuit parameters of the motor are given.For scalar control experiment, the block diagram given in Figure 1 is used.After entering the motor tag information and equivalent circuit parameters from Table 1 and Table 2 and entering appropriate settings, the stator current and rotor speed graphics were obtained from the screen.In order to measure the response of asynchronous motor during loading, the motor speed reference of 3000 rpm including 0-1 sec in the range of load (ie.0 Nm) and 1-2 sec in the range of nominal motor torque with 3.7 Nm load reference has been entered.In Figure 2, It can be seen that the current drawn of EFF1 efficient motor at the very beginning is higher than the current drawn by the EFF2 motor.In Figure 3, EFF1 efficient motor 1 sec at 3.7 Nm loads the implementation of the reduction by reference speed of the rotor speed is less than EFF2 efficient motor.To monitor the response of the asynchronous motor against variable speed references, under no load conditions, speed references; 2000 rpm for duration of 0-1 sec, 3000 rpm for duration of 1-2 sec, 3500 rpm for duration of 2-3 sec, 2500 rpm for duration of 3-4 sec and 1000 rpm for duration of 4-5 sec were applied to motors.Figure 4 shows that at the start up stage, EFF1 motors with no load draw more current than the efficient EFF2 motor.In Figure 5, the responses of EFF1 and EFF2 efficient motors to variable speed references are seen.It can be seen that fluctuations of high efficiency motor while reaching to reference speed are less than those in the standard motor.Performed in this paper, a study was done on the standard motors and highly efficient asynchronous motors which have same characteristics (power, voltage, speed) and their stator currents and speeds were compared.In the simulation study done, it is observed that the starting current in the EFF1 efficient motor is higher than the starting current of the EFF2 efficient motor.This shows that the highly efficient motor start-up torque is higher.It is also observed that the current of the efficient motor, after getting the steady state, is lower.This means that less energy is spend in continuous operation.On the other hand, it is seen that EFF1 efficient motor response to changes in motor speed is faster than the EFF2 efficient motor and fluctuations were less.This also shows that speed control characteristic in highly efficient motors is better.Generally, this study shows that high efficiency asynchronous motors are superior to standard motors in terms of energy saving and speed controlling characteristic.However, because the starting current in the EFF1 efficient motor is higher than the starting current of the EFF2 efficient motor, this situation causes using more sensitive protection devices.

Fig. 2 .
Scale Control in The Idle and 3.7 Nm Load Current in The Stator a) EFF1 Motor b) EFF2 Motor (a) (b) Fig.3.In The Idle and 3.7 Nm Load Variation of Rotor Speed for Scale Control a) EFF1 Motor b) EFF2 Motor

Fig. 4 .
Stator Current Changes in The Mixed Speed Reference for Scale Control a) EFF1 Motor b) For EFF2 Motor (a) (b) Fig.5.Variations of rotor speed in The Mixed Speed Reference for Scale Control a) For Eff1 Motor b) For EFF2 Motor V. CONCLUSION

TABLE I HIGH
EFFICIENCY MOTOR INFORMATION (EFF1 YIELD CLASS)