Wyniki wyszukiwania - Biblioteka Nauki

1

Moment silników bezzestykowych z magnesami trwałymi w stanie bez prądu

100%

Pochanke A.

|

2001

|

tom Z. 208

131-141

PL

W pracy przeprowadzono analizę wpływu zmienności punktu pracy magnesu trwałego na charakterystyki kątowe momentu elektromagnetycznego silników bezzestykowych, a w szczególności badano problematykę występowania i obliczania momentu, gdy silniki znajdują się w stanie bez prądu. Przedstawiono wyniki obliczeń symulacyjnych wpływu skosu magnesów wirnika na tętnienia momentu wypadkowego. Wykazano teoretyczne możliwości całkowitej redukcji tych tętnień.

EN

In a permanent magnet motor the basic electromagnetic torque is generated as the result of the interaction of the permanent magnet flux with the magnetomotive force of the armature. The interaction between the rotor magnets and the slotting on the stator causes the periodical variations of the permanent magnet flux. This causes the ripple of the total electromagnetic torque which have two fundamental components. The first component of the torque ripple is proportional to magnetomotive force of the armature. The second component which exists even in the absence of the stator currents, results from the modulation of the permanent flux and is called cogging torque or detent torque. The torque ripple causes additional losses, mechanical vibrations and noise. The variation of the permanent magnet flux is an obstruction in realizing constant speed control or high accuracy of position control. There are several methods for reduction of this variation of the permanent magnet flux, but one of the most effective techniques for minimization of this undesirable phenomenon is stator slot skewing or skewing the rotor magnetic field distribution via either skewed rotor magnets or skewed magnetization. In this paper the influence of skewing the rotor field distribution - via skewed mounting of discrete magnet segments on the rotor - on the cogging torque and on the ripple of the total electromagnetic torque is investigated. The finite element method has been used to calculate the magnetic field distribution and the total torque has been calculated using the Maxwell stress method. The cogging torque has been also calculated using the method of the magnetic co-energy variation.

2

Analiza układu napędowego z silnikiem indukcyjnym klatkowym przy bezpośrednim sterowaniu mocy i momentu elektromagnetycznego

80%

Pieńkowski K.

|

2001

|

tom Z. 208

119-130

PL

Przedstawiono układ napędowy z silnikiem indukcyjnym klatkowym sterowanym częstotliwościowo przez falownik napięcia. Obwód pośredniczący falownika jest zasilany z sieci prądu przemiennego przez przekształtnik AC/DC o takiej samej strukturze topologicznej jak falownik napięcia. Przedstawiono metody sterowania przekształtników energoelektronicznych w tym układzie napędowym: metodę bezpośredniego sterowania mocy elektrycznej do sterowania przekształtnika AC/DC i metodę bezpośredniego sterowania momentu i strumienia do sterowania falownika napięcia i silnika indukcyjnego. Opisano układ sterowania i omówiono wybrane wyniki symulacji cyfrowej.

EN

Voltage source inverters with direct current link and PWM control are widely used in industry to realize high dynamic control for drive systems with induction motors. The common supply for the DC link of that inverters consists of an uncontrolled rectifier bridge connected to the three phase grid. This system produces harmonic distortion in the mains and the electrical braking of induction motor with energy recovery can not be realized. These disadvantages can be avoided if a controlled reversible three-phase AC/DC power converter is used at the line side. The structure of the power electronic system considered in the paper is shown in Fig. 1. Major parts of the system are two identical voltage source inverters. The three phase grid is connected to the line-side inverter by three inductances. The DC link consists of a single capacitor bank. The squirrel-cage induction motor is directly connected to the machine-side inverter. Among all methods of induction motor control the Direct Torque Control (DTC) appears to be very atractive. Because the line-side converter has identical scheme as the voltage source converter it can be controlled in the same way. In the paper the principle of DTC control is applied to the line converter and is called as Direct Power Control (DPC). The basic idea of DTC control is based on vector equations (1)-(3) and is presented in Fig 2a). For using the principle of DTC control for line-side converter two virtual flux vectors are defined by equations (5): the grid flux vector and the inverter flux vector. The basic idea of DPC control is based on vector equations (4)-(7) and is presented in Fig. 2b). The full control scheme with application the DTC control of machine-side inverter and the DPC control of line-side inverter is presented in Fig. 3 and described in Chapter 3. The performance of the considered control scheme was tested by numerical simulations. The results of simulation are presented in Fig. 4-7 and discussed in Chapter 4. Fig. 4 shows induction motor torque waveforms for motor operation and for regenerating operation caused by the change of the mechanical load. In Fig. 5 the waveforms of phase voltage and phase current of induction motor are presented. Fig. 6 shows the line voltage and the line current for power conversion from line-side to machine-side and at a power conversion from the induction machine to the mains. Fig. 7 presents the waveforms of the dc link voltage and current for the considered states of system operation. The results of investigations show the effectiveness of the considered DPC and DTC methods of control. The DPC control enables to impose nearly sinusoidal line currents with unity power factor. The control strategies are quite simple because a coordinate transformation is not required and very fast and accurate control can be obtained.

3

Model matematyczny stanowiska do badania momentu elektromagnetycznego silników metodą reakcji stojana

60%

Pochanke A.

|

1999

|

tom Z. 201

171-182

PL

W pracy przedstawiono model matematyczny stanowiska do wyznaczania wartości chwilowej momentu elektromagnetycznego silników małej mocy metodą pomiaru siły reakcji stojana na czujnik dynamometryczny. Przeprowadzono przykładowe badania symulacyjne prowadzące do określenia wpływu wartości parametrów stanowiska na dokładność odwzorowania momentu elektromagnetycznego przez siłę reakcji stojana.

EN

The measurement of the electromagnetic torque of an electric motor is very important all the more since often this is the only way to get information about the instantaneous value of the torque. One of the methods is the method using the measurement of the angular displacement of the stator arm. For measuring this reaction of the stator the dynamometric transducers (usually piezoelectric devices) are used. The test stand realising this method is shown in Fig. 1. This is three-mass system with three degrees of freedom: angular positions of the stator, rotor and load. The dynamics equations of this system can be expressed in form (1). The operation of the test stand depends on the values of its parameters: moments of inertia, coefficients of viscosity dumping and torsional stiffnesses of the elements. On values of these parameters also depends difference between the real value of the electromagnetic torque and the instantaneous value of the torque measured by the piezoelectric device (the signal of this device is proportional to the angular displacement of the stator). The equations (1) were examined in the simulation model. The investigations were made for values of the parameters given in Table 1. The results of the simulations are shown in Fig. 2, where the thick line marks the real curve of the electromagnetic torque and the thin line marks the product of the angular displacement of the stator and the stiffness of the measuring device. The results of the simulations show that the values of the parameters of the test stand have the determined influence on the measurement of the motor torque.