DE2327672A1 - BRAKE CIRCUIT ARRANGEMENT FOR AN ASYNCHRONOUS MACHINE ALSO WORKING IN FIELD LOW OPERATION - Google Patents

Description

Brake circuit arrangement for a also working in field weakening mode Asynchronous machine The invention relates to a brake circuit arrangement for an asynchronous machine that also works in field shaft operation, which is supplied by a feeder device is fed with a voltage ton of variable frequency There are electrical machine drives, especially train and vehicle drives that are controlled so that the drive torque decreases with increasing speed. The machine can operate in field weakening mode work. For a frequency-controlled asynchronous machine, this means that their Terminal voltage no longer increases proportionally to frequency with increasing frequency is, but kept constant by a predetermined frequency limit value at z Bo The motor overturning moment of this Asynohronmaschine then goes with increasing Frequency corresponding to the square of the ratio between terminal voltage and Frequency back. The feed device9 z Bo a converter or a speed-controlled one The synchronous generator and the asynchronous machine are then to be designed in such a way that at the highest Frequency, the breakdown torque is just slightly greater than the required drive torque. If you now brake at the highest frequency, i.e. at the highest speed, 9 stands for the braking process, the generator breakdown torque is available as the maximum braking torque This generator breakdown torque is only slightly greater than the motor breakdown torque Frequently is now one of such an electric machine drive with an asynchronous machine Requires significantly greater braking torque than the generator breakdown torque is equivalent to. In order to meet this requirement, the machine drive would have to be oversized which require a considerable additional economic outlay The invention is based on the object 9 for a field growth operation working Åsynchronmaschine 9 from a supply device with a voltage variable frequency is fed to specify a braking circuit arrangement by which avoids oversizing of the feed device and / or asynchronous machine This brake circuit arrangement is intended in particular in the case of an electric traction vehicle, its asynchronous traction motor from a converter with variable output frequency fed is 9 used The invention is based on the consideration that this task can be achieved if it is possible through circuit measures, a significant increase in the generator breakdown torque and thus the maximum braking torque to achieve The stated task is achieved by a first brake circuit arrangement solved9 which according to the invention is characterized9 that in at least one connecting line between the machine-side output of the feed device and the asynchronous machine an ohmic resistor is arranged, which by means of a switch when driving This series connection of asynchronous machine and ohmic resistor can be short-circuited is possible with single-phase as well as multi-phase asynchronous machines0 What is important in any case9 is that through the additional insertion of the ohmic resistor and the resulting voltage drop is the voltage; at the output of the feeder different from the terminal voltage on the asynchronous machine is 0 Part of the Braking energyO that of the asynchronous machine working as a generator is supplied, is converted into heat in the braking resistor. The rest of the Braking energy must either be fed back into the feed device or in a additional braking resistor, which in principle can be arranged at any point can also be converted into heat. It is a three-phase synchronous machine provided, it is useful if one in each of the three connecting lines ohmic resistance is arranged9 and if the ohmic resistances are equal As a result, a symmetrical braking behavior of the asynchronous machine is achieved.

The aforesaid object is also achieved by a second brake circuit arrangement solved, which is characterized according to the invention that in the area between Braking resistor and asynchronous machine at least between two connecting cables At least one capacitor is switched, which is activated by means of a switch while driving can be switched off. This second embodiment can preferably be used together with the first Embodiment can be realized. In the three-phase case, a star or delta connection can be used of capacitors can be provided, which are all equally sized.

This development has a further increase in the overturning moment Asynchronous machine result. Because by the additional arrangement of the capacitor you can turn the phase position of the current in said ohmic resistance so that the terminal voltage on the asynchronous machine is significantly greater than the AC output voltage the dining facility. With a suitable dimensioning of the resistor and the capacitor can even be achieved that the Ilemmensspannung on the asynchronous machine assumes maximum value, which is determined by arithmetic addition of the voltage drop at the ohmic resistance with the output AC voltage of the converter.

Embodiments of the brake circuit arrangement according to the invention are explained in more detail below with reference to the accompanying figures.

FIG. 1 shows an exemplary embodiment of the invention for a three-phase Asynchronous machine, Figure 2 characteristic frequency diagrams of a vehicle drive used frequency-controlled asynchronous machine, Figure 3 is a circle diagram for a synchronous machine upstream of which a resistor is connected in braking operation, FIG 4 shows an equivalent circuit diagram for a phase winding of the asynchronous machine, the upstream ohmic resistance and an intermediate capacitor are taken into account are, and Figure 5 is a phasor diagram for an asynchronous machine in the braking mode a resistor and a capacitor are connected upstream.

According to Figure 1 is a three-phase asynchronous machine 2, the terminals with R, S, T are designated, via connecting lines 3, 4 and 5 to the output a feed device, which in the present case is a converter 6. This converter 6 contains (not shown) controlled main valves, in particular Thyristors in a known manner via a control input 7 with ignition pulses are supplied. The converter 6 is connected to its DC voltage terminals 89 9 a (not shown) DC voltage source connected. As a DC voltage source a battery is used in the present case. Instead, you can also use a DC voltage network or a controlled or uncontrolled rectifier, which is fed from an alternating voltage network can be used.

In the latter case, between the rectifier and the converter 6 still has an intermediate circuit choke and an intermediate circuit capacitor arranged sein0 The converter 6 can be operated in both energy directions. While driving it works as an inverter and in braking mode as a rectifier.

The three-phase asynchronous machine 2 is in particular for driving a electric traction vehicle9 zO Bo in railway traffic9 provided9 which is a generator should be braked.

In the connecting lines 39 4 and 5 between the machine-side Output of the converter 6 and the terminals R9 59 T of the three-phase asynchronous machine 2 each ohmic resistors 10, 11 and 12 are arranged. These resistances 109 11.

and 129, which could also be called series resistors, are 9 preferably of the same size to ensure symmetrical conditions in braking operation To get 0 Each braking resistor 109 11 ved 12 is a switch 13, 14 or 15 connected in parallel9 whose switching contacts are open in braking mode. While driving the switching contacts are closed9 so that the braking resistors 109 11 and 12 are short-circuited and are therefore ineffective. In the present case, the switches 139 14 and 15 are components a contactor 169 that can be switched over via its control input 170 It can be seen from FIG. 1 that in braking operation between the connecting lines 3, 4 and 5, a star connection of capacitors 189 19 and 20 is preferably also connected is. The capacitors 18, 19 and 20 are in particular dimensioned to be the same size To achieve symmetrical relationships, instead of the star connection could be there also a (not shown) delta connection of the same size, in particular, but then differently sized capacitors can be provided. It is in both cases make sure that the star or delta connection of the capacitors is in the area between the braking resistors 10, 11 and 12 on the one hand and the terminals R, S, T of the three-phase asynchronous machine 2 is arranged on the other hand. While driving can the capacitors 189 19 and 20 by means of the switches 21, 22 or 23, the each in series with one of these Capacitors 18, 19, 20 are arranged are to be switched off.

These switches 21, 22 and 23 can also contactor in a switching be summarized.

In the case of the brake circuit arrangement in FIG. 1, it was specifically assumed that that a three-phase three-phase asynchronous machine 2 is provided. The invention can also be used in connection with a higher-phase, a two-phase or also implement a single-phase asynchronous machine 0 With a single-phase asynchronous machine a single resistor in one of the two connecting lines is sufficient Converter and asynchronous machine and, if necessary, an additional capacitor, which is connected in parallel to the input of the asynchronous machine.

As will be explained in more detail later, FIG. 9 is used in the braking circuit arrangement In Figure 1, part of the electrical braking energy generated by the generator in braking operation working three-phase asynchronous machine 2 is supplied in the resistors 10, 11 and 12 converted into heat. The remaining part of the braking energy must now also can be removed from the three-phase asynchronous machine 2. There are different ones Possibilities: a) Is the converter 6 with its DC voltage terminals 8, 9 in the manner already mentioned, but not shown, via a direct current intermediate circuit, which contains an intermediate circuit capacitor and / or an intermediate circuit choke If a rectifier is connected, it can be used between the two direct current lines a braking resistor can be arranged in the DC link. This is in braking mode by a switch, in particular a thyristor or a DC power controller, switched on permanently or pulsed. A corresponding brake circuit is e.g. known from German Offenlegungsschrift 1 513 532 - VPA 65/1672. The additional in the DC link, so on the DC side of the The braking resistor arranged by the converter takes over the remaining part of the braking energy.

b) Is the converter z. B. to a non-absorbent DC voltage source connected, a braking circuit can be used in which at least two of the connecting lines 3, 4 and 5 via a series connection of a braking resistor with a controllable valve, in particular with a thyristor, connected to each other are. This brake circuit has the advantage that a Tösch arrangement for the controllable valve is not required. Such a brake circuit is z. B. off the German Offenlegungsschrift 1 638 611 - VPA 67/1505 known. Also here takes over the additional 9 braking resistor arranged on the AC voltage side of the converter the remaining part of the braking energy.

c) It is also possible to use a braking resistor and a controllable Brake valve also existing brake circuit between the machine-side Connect the output of the converter 6 and one of the DC voltage terminals 8, 9. Such a braking circuit is z. B. from German Offenlegungsschrift 1 763 871 - VPA 68/1209 known. In this case, too, the remaining part of the braking energy is used converted into heat in the braking resistor.

d) However, it is not necessary to include any of the additional Use brake circuits if the connected to the DC voltage terminals 8, 9 DC voltage source for the three-phase asynchronous machine via the converter 6 2 regenerated energy can be absorbed, This condition is met -a battery, which is provided in the brake circuit arrangement according to FIG. 1 as an equal voltage source is. A special braking circuit is therefore not shown in FIG.

To explain the mode of operation of the brake circuit arrangement shown in FIG it is initially assumed when considering Figure 2 that the switches 13, 14 and 15 are also closed during braking and the capacitors 18, 19 and 20 are removed are, so that a common machine drive z. B.

for a vehicle.

In FIG. 2 there are diagrams of some sizes which, in the case of such a path or vehicle drive with converter and asynchronous machine are important, applied. The individual sizes are each to a maximum value, which is through marked the index o.

The electric drive is first controlled in such a way that the terminal voltage U (see also FIG. 1) increases proportionally to the output frequency f of the converter 6. The input power P of the asynchronous machine 6 also increases accordingly indicated by the rising dashed straight line. The drive torque Ma has its maximum value Mao (Ma / Mao = 1 applies). From a frequency ratio f / fo = a, to which an equally large speed ratio n / no = a corresponds with increasing frequency f, the drive torque Ma is reduced. The driving torque Ma is roughly proportional to the reciprocal frequency 1 / f. This course is in Figure 2 is shown with a solid curve. For the asynchronous machine 2, this means that their terminal voltage U has a frequency ratio f / fO = b on is kept constant at the maximum value UO (U / UO = 1 applies), which results from the dashed horizontal lines can be seen. The input power runs accordingly P. A field weakening operation is therefore carried out from b on. The motor overturning moment Mkm of the three-phase asynchronous machine 6 corresponds to the square of the ratio between the maximum value UO of the terminal voltage U and frequency f. The relationship So Mkm / Mao is proportional to (Uo / f) 2.

This is indicated in Figure 2 by the dash-dotted curve.

The feeding converter 6 and dießsyndhronmaschine 6 are like this designed, that at the maximum value f0 of the frequency f (it applies f / fO = 1) the motor tilting moment Mkm is a small value greater than the required drive torque Ma This The value is so small that it is not visible at point A in FIG.

At the maximum value fO of the frequency f, i.e. at the maximum value nO of the speed n the three-phase asynchronous machine 6, the vehicle should now by reducing the Frequency f can be braked.

As a result, the three-phase asynchronous machine 2 goes into the generator mode Operation over. As is known, the maximum braking torque then stands for the braking process the regenerative pull-out torque Mkg is available at the maximum value n0 of the speed n.

This generator breakdown torque Mkg (fo) is only slightly larger as the corresponding drive torque Ma (fo), its related to the maximum value Mao Ratio Ma / Eao - as shown - at point A z. B. is 0.25. For many For purposes, however, a larger maximum braking torque Mb is required for the maximum value f0, which is larger, for example, by a factor of 3, so that a on the maximum value Mao related ratio Mb / Mao of z. B. 0.75, see point B in Figure 2. This high braking torque Mb should z. B. from the maximum value n0 of the speed n up to Speed n = 0 can be kept constant. This requirement is also shown in Figure 2 as a dash-dotted horizontal straight line running through point B.

The brake circuit arrangement shown in Figure 1 ensures that during the transition from driving mode to braking mode, a braking torque Mb z. B. accordingly Mb / Mao = 0.75 (see point B) and not e.g. B. corresponding to Mb / Mao = 0.25 (cf. Point A) is available. The distance between the two points A and B is a Measure for the braking power converted into heat in the ohmic resistors 10, 11 and 12, In other words: The ohmic resistors 109 11 and 12 are designed in such a way that that they absorb the power corresponding to the distance A-B and convert it into heat capital.

To explain the operation of the brake circuit arrangement of FIG 1, FIG. 3 is considered next. Here is a pie chart plotted, in the way it is usual for asynchronous machines. Let it be in this one Connection, for example, to the textbook "Electrical Machines" from the Bödefeld sequence, Springer Verlag Vienna 1952, pages 171 to 175, especially Fig. 252 on page 175 pointed out. The following formulas apply to the pie chart: tg to = X1 / R1 (1) tg to = # X1 / R1 (2) D = (1- U1 / # X1 (3) with # = 1 - Xh2 / (X1 # + Xh) (X2 # + Xh) (4) and X1 = X1 # + Xh. (5) #o is the angle for the idle point Po, # @@ the angle for the infinity point P @, X1 an arithmetic variable, R1 the ohmic resistance of the stand, # another calculation variable, D is the diameter of the circle K in Figure 3, U1 the phase voltage, Xh the main field reactance, X1 # the primary leakage reactance or stator leakage reactance, and X2 # the secondary leakage reactance or rotor leakage reactance.

For a more detailed description, reference is made to FIG. 4, in which an equivalent circuit diagram for one strand of the three-phase asynchronous machine 6 is shown. The designation is independent of whether there is a delta or star connection of the windings. R is the ohmic resistance per string connected upstream according to the invention, and C is the capacitor per strand, s the slip of the asynchronous machine 2, 11 the strand current, and 1 the Magnetizing current.

It is well known that in a pie chart the distances between the straight line that can be drawn through the points PO and P, on the one hand and the two parallel tangents to the circle K, on the other hand, the motor tilting moment Mkm or the generator breakdown torque Mkg To increase the breakdown torque Mkg, which corresponds to the maximum achievable braking torque, the points Po and Po must be in the direction shown along the arrows F0 9 yoO wander around the circumference. That is according to formula (1) and (2) by magnification the angles #o and «9 d. H. by increasing the effective ohmic stator resistance 111 reached. The effective stator resistance R1 is shown in Figure 1 by the series connection of the resistors 10, 11 and 12 with the stator windings enlarged. The diameter of the circle D is retained. While the straight line PO - P @@ in the usual regenerative Braking operation runs practically exactly through the center of the circle K is according to FIG. 3 this straight line PO shifted by switching on the resistors 10, 11 and 12, that the generator breakdown torque Mkg is considerably greater than the motor Overturning moment Mkm.

The effect created by the additional arrangement of the capacitors 18, 19 and 20 in FIG. 1 and the capacitor C in the equivalent circuit diagram in FIG. 4 is achieved, results from Figure 5. In the lower part is a phasor diagram of the currents defined by FIG. The phase current Ii then settles vectorially composed of two components, namely the current IR through the resistor R and the current IC through the capacitor C.

With an insertion of the capacitor C or a change in its capacitance The value is the size and phase position of the current IC in the capacitor C and the current 1R changed in the connected ohmic resistor R. With an additional arrangement it capacitor C can therefore rotate the phase position of the current IR so that the Phase voltage Uq, which in an asynchronous machine with windings connected in a delta the terminal voltage U corresponds to 9 is significantly greater than the output alternating voltage Uw of the converter 6. This increases the diameter D des according to equation (3) Circle K in Figure 3 and thus also the generator breakdown torque Mkg significantly.

The optimal state is shown in FIG. The phase angle between the voltage drop IRR across the resistor R and the AC output voltage To the converter 6 was rotated so that their vector sum equal the arithmetic sum and therefore maximum. The output alternating voltage Uw and the voltage drop IRR thus have the same direction.

So around the optimal value shown in a brake circuit arrangement According to Figure 1, one becomes the capacitance of the capacitors 18, 19 and 20 change until the phase voltage U1 (see FIG. 4), which is the case with a synchronous machine with delta winding measured directly as terminal voltage U (see FIG. 1) or until the sum of the voltage drop across the resistor 10, 11 or 12 and voltage UW at the corresponding output terminals of the inverter 6 Has reached the maximum. The capacity value determined in this way has the consequence that the asynchronous machine 2 can be braked with maximum braking torque Mb.

5 claims 5 figures

Claims (5)

Claims 1. Brake circuit arrangement for a field weakening operation working asynchronous machine supplied by a supply device with a voltage is fed by a variable frequency, characterized in that in at least a connecting line (3, 4, 5) between the machine-side output of the feed device (6) and the asynchronous machine (2) an ohmic resistor (10, 11 or 12) is arranged is, which can be short-circuited while driving by means of a switch (13, 14 or 15) is. 2. Brake circuit arrangement according to claim 1 for a three-phase Asynchronous machine, characterized in that in each of the three connecting lines (3, 4, 5) an ohmic resistor (10, 11, 12) is arranged, and that the ohmic Resistors (10, 11, 12) are dimensioned the same. 3. Brake circuit arrangement for a working in Peldschwächbetrieb Asynchronous machine supplied by a supply device with a voltage of changeable Frequency is fed, in particular according to claim 1 or 2, characterized in that that in the area between ohmic resistance (10, 11, 12) and asynchronous machine (2) at least one capacitor between two connecting lines (3, 4, 5) (18, 19, 20) is switched, which by means of a switch (21, 22, 23) can be switched off. 4. Brake circuit arrangement according to claim 3 for a three-phase Asynchronous machine, characterized in that three capacitors (18, OK) in triangular or star connection are provided, which are of the same size. 5. brake circuit arrangement according to one of claims 1 to 4, characterized characterized in that the switch (13, 14, 15; 21, 22, 23) is a contactor (16) is provided.