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ÖZET Bu çalışma, DGM (Darbe genişlik Modülasyonu) gerilim dalgaları ile beslenen asenkron motorun, harmonik akımları ile etkilerini incelemek için hazırlanmıştır. Amaç, zaman harmonikleri tarafından bozulan motor performansının artırılması için, motor eşdeğer devre parametreleri ile gerilim harmonikleri arasında ilişki kurmaktır. DGM evirici ile beslenen asenkron motordaki harmonik momentleri, doyma olmayan çalışmada hesaplanmıştır. Farklı iki asenkron motorda, önceden seçilen çalışma şartlarını sağlamak için, temel bileşen üzerine etki eden harmonik momentleri kullanıldı. Asenkron motorun eşdeğer devresi, zaman harmonikleri için düşünülerek eşit süreli 2, 4, 8 DGM'li gerilim dalgaları motor terminallerine uygulandı. Seçilen asen kron motorlar, aynı güç, gerilim, frekans ve kutup sayısına sahip olmasına rağmen, farklı firmalar tarafından üretilmişlerdi ve aynı kayma değerinde farklı momentler üretiyorlardı. Motorlar aynı olmamasına rağmen, harmonik momentleri yardımıyla çalışma şartlarının eşitliği (moment ve kayma), gerektiği gibi seçilen DGM'li dalgalarla belirli kayma değerlerinde elde edilebildiği gösterildi. Bu analizlerin sonucu olarak Darbe genişlik terimlerindeki eşdeğer devre parametrelerinin fonksiyonları verilen moment ve kayma değeri için elde edildi. Aynı kayma değerinde, çıkış momentleri arasında büyük farklar bulunan asenkron motorlara bu yöntem, istenilen çalışma şartlarını elde etmede uygulanamazken, bu asenkron motorların devrilme kaymaları ve devrilme momentleri birbirlerine eşitlenerek, benzer değişimlere sahip Moment-Kayma eğrileri elde edildi. THE ANALYSIS OF PWM-HARMONIC EFFECTS IN SELECTING TWO INDUCTION MOTORS FOR INVERTER DRIVE SYSTEMS SUMMARY The performance of an induction machine when sub jected to a nonsinusoidal voltage waveform has been analy sed by many authors. It has been found that the destruc tive effects of the time marmonics decrease the efficiency of the drive system due to increased additional losses. Many authors have worked upon the construction of waveforms and inverter electronics to eliminate the low order harmo nics which cannot be filtered by the machine impedance. These works have become succesful and found practical app lications. In [1 ], it was shown that the effects of PWM strategy upon the performance characteristics of optimised total harmonic distortion. A sample modulating wave and triangular carrier wave were used for modulating technique and intersection of them were employed to produce the switching edges of PWM wave at the output of the inverter. While in [-2.1, the crest factor of the current waveform induced by a PWM sequence was used as a measure of its op- timality and shown that 250-300 Hz switching frequency re gion would be preferable. Analytical and experimental investigation on steady state and transient behavior of an induction motor fed from nonsinusoidal power supplies is presented in [31. The analytical investigations are based on a direct three phase model developed for this purpose. Simulation proce dure for computing the exact nature obtained from a pulse with modulated (PWM) inverter is described. Transient xxstudies exhibiting the efects of specific PWM pattern changing on the induction motors are outlined. The ability of the developed model to represent faulty inverter conditions such as single phasing is described and analysed. Finally key results are verified experimentally on a PWM inverter fed induction motor. The total losses of an induction motor were calculated by using superposition of separate harmonic currents and voltage effects. The losses of the rotor and the stator were separately estimated and combined for frequencies from 100 to 20000 Hz. The loss model of the motor was developed and defined as the function of frequency for different power ratings by using empirical datas obtained experimentally in [4. J. While in [5]> the analysis of torque generation were dedicated in the induction machines. The general conditions concerning the existance of synchronous and asynchronous torques were presented. The results of that analysis were illustrated by numerical examples and verified width experimental investigation. The modified equivalent circuit and the present torque analysis are general for the specialist in asynchronous machines who can handle them without any complications. In [6 3, traditional PWM AC motor drives perform well over a large speed range and have many positive features demonstrated with their simplicity. However, the waveforms used are significantly less than ideal at high modulation depths and low switching rates, especially with regard to harmonically induced motor losses. An developed strategy for digitally producing PWM based on simple triangulation methods is presented. A new technique for the decdeasing the harmonic losses resulting from sinusoidal PWM waveforms is analysed in depth and realised on a 40 kVA inverter. Tests with this inverter on 7,5 kW and 15 kW motors confirm that the inverter's xiiperformance is significantly enhanced for certain operating conditions without any significant sacrifies. On the other hand, in reference l7J, a new PWM algorithm for battery-source three-phase inverters is described. The concept of the algorithm is to determine the pulse widths by equating the areas of the segments of the sinusoidal referans with the related output pulse areas. The algorithm is especially suitable to handle a non-constant voltage source with good harmonic suppresion. Since the pulse widths are computable in real time width minimal storage requirement as well as compact hardware and software. It is particularly suitable for single-chip microcomputer Intel 8095-based battery source inverter can control a 3 kW synchronous motor drive satisfactorily over a frequency range of 2 to 100 Hz. In references [8J. [ 9 ] and [10J PWM voltage waveforms were analysed for a motor drive application. The switching patterns were developed in single and three- phase half-bridge inverters. The approach was based upon the minimising the harmonic content of the current flowing into the motor. In ill J, `2] and [13.1 harmonic elimination methods have been discussed in PWM voltage waveforms for an AC motor-drive using a six-thyristorised full-bridge inverter. In [141, it was shown that the hysterisis and eddy-current losses which produced in an AC machine, when subjected a nonsinusoidal voltage waveform, as PWM, have changed with pulse duration. Although, the amount of change was insignificant in hysterisis losses, there was a substantial increase in eddy-current losses. PWM waveforms were analysed and obtained loss- optimal PWM waveforms for variable speed induction motor drives. PWM waveforms were introduced differently and novel waveforms were demonstrated. Effects of supply voltage waveforms upon iron losses were examined in an induction motor in references [151, [16 J and [17 J. xiiiIn this study, firstly equivalent circuit of the induction machine has been explained obviously and the equations of output torque and electromagnetic torque of an an induction machine has been obtained, besides producing harmonic torques in a motor and measures against them in the cofguration of the machine have been mentioned. In section 3, the structure of an inverter, its driving and three-phase bridge-inverter has been described. The harmonic equivalent circuit and the magnitude of voltage harmonic torques has been formulated by using the methods of harmonic analysis. The harmonic elimination methods in PWM output voltage waveforms of a three-phase inverter have been suggested and in order to increase motor performance by destructing time harmonics, the corelation between motor parameters and voltage harmonics has been set up. In this paper the inverter and the induction motor are considered as a system. It is well known that the machine parameters for the same frame size and revolution are different as depending upon the manufacturers. Therefore, the copper losses and iron losses occured in the machine will have different values, for the same frame size. Considering this fact, the minimasition of the total losses cannot be only related to the harmonic content of the voltage waveform. Therefore, a particular waveform selected would produce different losses and efficiencies in two different motors. This mean that, the harmonic analysis of a nonsinusoidal voltage wave cannot always be succesfull to minimise the motor losses, even if it has the minimum harmonic content. The pulse duration is increased to reduce the low order harmonics, but on the other side, iron losses are increased substantially. This shows that the decdeasing the harmonic content of a voltage waveform does not essentially cause a reduction in the total losses of an induction motor. It is because of this fact that both members of xivthe drive system must be considered as a whole. Hence the analysis of the system is to be based upon two important and direct variables which are as the pulse duration, total losses and torques. The former is vital component, since the number and the total duration of pulses exist in one cycle determine the harmonic content. The second is the result obtained during the drive and end of manufacturing process and has two values in two different motors subjected to same voltage waveform. In this paper the aim is to developed relations between the losses and torques of the motor and the pulse duration of the supply voltage waveform. General equations are developed for the calculation of a particular harmonic. It is also presented that the losses associated with a harmonic can be eliminated when pulse duration is set to the value shown in fiqures. The total losses, excluding the aditional losses are obtained by employing superposition method for unsaturated oparation. Since the manufacturers have different criterias the equivalent circuit parameters of same rating motors will have different values. As a result of this, their torque-speed curves will not be idintical. Therefore, the motors fed by PWM voltage waveforms will have to run at different slips for a given torque. In order to run these motors at the same drive conditions, the efects of equivalent circuit parameters upon the torque have to be known in advance. Secondly, the harmonic torques produced by voltage harmonics have tobe used to change the total torque. For this reason two same rating induction motors are subjected to 2, 4 and 8 PWM voltage waves. In some slip points for the torques of two motors, common driving area is occured by changing the harmonic content of the supply waveform. After achieving the equality in torques and slips by changing pulse durations, those are once more xvobtained by altering the motor parameters against pulse duration. The analysis is proved that an inverter-driven induction motor replaced by a spare motor will certainly necessetate to alter the drive conditions. The curves of the torque-slip of two different motors are approached one another by equating their stalling torques and stalling slips. In order to avoid such changes to maintain the previous torque and slip values as they were, either the supply waveform or the equivalent circuit parameters must necessarily have new values. All of these are presented in this?paper. xvx 91