DE1463513A1 - Method and device for controlling the speed of asynchronous motors - Google Patents

Description

Method and device for controlling the speed of asynchronous motors Of the various known methods for controlling the speed of asynchronous machines In practice, especially those who deal with energy destruction have prevailed work. The procedure is as follows: 1. Turning on resistors in the running circuit, with the machinist additionally operating a mechanical brake becomes, the latter especially with pulling load (negative torque). To this Way you can, albeit cumbersome, any speed in sub-synchronous Set range.

This method is not suitable for automatic systems. 2. Switching on a mechanical brake, the brake disc of which is mostly on. the motor shaft is seated and its lifting motor is fed by the idufer frequency. This means that a speed of about 20 ib of the nominal speed can be set automatically for all load cases, ie for positive and negative torques. However, one is bound to a frequency or speed which is around 20% of the nominal frequency or nominal speed; the effort for this method is relatively low. 3.: Coupling of a controllable brake generator (collector machine ne) to the motor, whereby the n "= otor additional variable Braking torques can be applied. Therewith are characteristic curves reached those of the Leonard-Schaltuni; are very similar and coat the entire speed range. Engine and braking rator work on resistors. - The brake machine has about the same performance as four r°.r@tor, soda: - the financial outlay very green, i is. This procedure has proven itself to be the case with the Leonard not enforced. 4. A three-phase motor for a hoist is driven by a stands burdened and when lowering the hast (negative moment) than grerr.sdynario acting «leictistrorr-Feihenscl? lui -, - r @ iaschine coupled. At Einl eibunt, the lowering operation occurs a disruptive, jerky wise falling through the load. % urch an additional, about Rectifier-fed external line from the braking machine can be lost largely avoid the initial dropping of the load because after switching on the Brerrrsstufe compared to the self-excited 'liderätands-Bremsmaschine sefcrt the brake comes into effect, soda., - i even at: er speeds a braking force is procreated. The additional excitation can also come from an additional the lifting motor's position rotation: the! rectifier fed where the number of ampere turns of the: rickluns for the foreign excitation is chosen so that. the braking machine is working stably. Here, too, an additional DC machine (collector machine machine) required; furthermore, the design of the three-phase motors because of the additional ones accommodated in the stand routes Winding from the normal construction, which mainly contributes to because: i could not enforce this system. Coupling of a collector and slip ringless brake machine ari the M ^ tor. The braking machine consists of a direct current excited and controllable Jielpol stand and a short circuit rotor and <erbe it @ a to some extent;, en as a synchronous generator on the pseudo s. There are therefore no external contradictions : vidcrstand of the rotor cage Stäii (le with associated switchgear required, slip rings and i,: nllectors do not exist. The resulting dependency ter 7) reh7a111 from the load, - at least it remains large and. is C- ir automatic luit drives not suitable. The invention; refers to a procedure and facilities FOR controlling the speed of asynchronous motors when loaded with negative or positive load mo- cient.eii, with the inclusion of resistors in (Ion rotor circuit, especially for the operation of rope conveyor systems, and. solves the Task, such a to create that is full ; iiiton: rttisclien operation suitable for the whole control range can be used wall-free and no special design of the asynchronous Motors with additional windings and the like. Requires, so that the Costs remain within tolerable limits. First of all, based on the diagram of FIG. 1, the problem to be solved Problem can be made further understandable, the diagram shows the typical characteristics of a resistance-controlled asynchronous Engine. On the right of the abscissa axis are the positive torques ( pulled load) and on the left the negative torques (pulling toots) both related to the nominal torque of the motor (M / Mn) and to the Ordinate axis the associated speeds, based on the synchronous speed (n / n1) applied. The solid line a represents the characteristic curve when the rotor is short-circuited, the less solid lines b, c, d, e and f show the operating states for increasing resistances connected to the rotor circuit.

From Fig. 1 you can see the known fact that the speeds only reasonably even in the vicinity of the positive nominal torque (abscissa +1) react to the switching on of the resistors. For small moments (below +1) lie With the resistances shown, the speeds are too high and with negative torques if the rotor resistance increases, they rise far above the synchronous speed at.

The inventive method for controlling the speed of asynchronous motors is that to change the speed, especially when lowering the speed below the nominal speed, in addition to the inclusion of resistors in the rotor circuit A braking torque of such magnitude is also applied to the motor shaft is brought that the sum of the load and braking torque is close to that moment which is the desired speed according to the characteristic curve that corresponds to the one that is switched on Resistance corresponds, is assigned. The motor therefore works while the speed is changing usually roughly in the area indicated by hatching in FIG. 1.

The devices according to the invention essentially consist of the following Share: A measuring device for the torque present on the engine. ment (e.g. B. Torque meter or wattmeter to determine the Torque at nominal speed or active ammeter or, in the simplest case, ordinary ammeters) and from a braking device (e.g. brake motor; brake disc for friction brake; hydraulic brake, etc.), which is preferably automatic in a manner known per se sn can be set that the motor is usually during the control process is loaded with approximately the positive nominal torque. In the simplest case, this can be additional Braking torque can be generated by a mechanical brake, - To generate the braking torque An electric brake machine can also be used, as well as hydraulic devices and the like can be used. The process runs for the simplest case as follows: The engine is in operation at its rated speed; the command "Slower" switches on the braking device, which automatically starts from zero for as long is adjusted increasing until the nominal current is reached; the resistances in the rotor circuit are switched on until the desired lower speed is reached.

It can also be the difference between the actual value of the torque and the positive nominal load torque with the help of one of the known control devices be used to prepare the size of the braking effect automatically, so that when Occurrence of the command "lower the speed" of the motor with approximately the nominal torque is charged. The size of the braking effect can also be determined by a wattmetric relay to get prepared. It is advisable to adjust the setting while slowing down the brake. mostly nothing more changed. When controlling the speeds according to this method, the advantage is achieved that the liiert for the delay or acceleration remains constant with sufficient accuracy under all loads and thus the effect of this process comes very close to that of the direct current process, but the effort is much lower and the machines used are much less are more robust and no regulators are necessary. Further objects of the invention go from those explained in more detail below with reference to the drawing figures 2 to 4 Embodiments emerge.

Fig. 2 of the drawing shows the circuit diagram of a control device according to the invention, Fig. 3 is a diagram showing the relationship between speed and Braking torque of an electrical brake machine shows and FIG. 4 shows the diagram of a mechanical one Brake with adjustable braking torque.

In the embodiment according to the circuit diagram shown in FIG 1 is the asynchronous motor with slip rings 2 and variable resistor 3. It relates the energy from the network 4 via the switch 5 and drives via the clutch 6, the can also be designed as a torque measuring device, the 'Lindwerk 7 with the Pulley 8 on. On the motor shaft sits the electric brake machine 9, the is excited via a rectifier 10 from the 11 AC side. The excitement the braking machine and thus the braking torque is with the help of the resistor 11 on adjustable in different ways. The contacts 12 ″ 13, 14 each bridge parts of resistance 11. The device 15 measures this on the motor existing torque and actuates the connection line in a manner known per se 16 the contacts 12, 13, 14, so that over parts of the resistor 11 the electrical Brake machine 9 is the more excited, the further the vorhr.ndene torque from the greatest positive nominal torque of motor 1 deviates.

From the rope 17, the device 18 with several centrifugal contacts driven; at a speed of 120% based on 100% nominal speed, the Main brake 19 actuated, at 110 the intermediate brake 20, at around 100% is in each case the rotor of the motor 1 short-circuited, regardless of the position of the starting resistor 3 has reached, so that the motor 1 is supported on the network 4 even when the load is pulling can without the starting resistor 3 must have arrived at the output stage.

Further centrifugal force contacts can be provided in device 18 be that when a certain speed is reached, which has been driven for a long time should be and the starting resistor would heat up too much for this Switch on motors 21 or 22 built at speeds (e.g. 50%).

The motor 21 can, for example, have a nominal speed of 150 t / min and four-pole, whereas the motor 22 e.g.

runs at 750 t / min and has eight poles. Should the drive pass from motor 21 to motor 22, the rotor circuit of motor 21 a resistor switched on and at the same time a brake applied until the speed is reduced to 750 t / min @, whereupon the motor 22 is switched on and the motor 21 is switched off. The motor 22 is only switched on, for example: when the crawl speed of 2 to 3% is reached, the motor 22 can also are permanently connected to the network and when the creep speed is reached by a Clutch 22a can be switched to the shaft.

It may be useful to use one of the brakes 19 or 20 as a regulating brake train, which is fed by the rotor frequency and a speed of approx. 20%. The switch 5a-is closed as soon as a speed change is initiated shall be. In many cases it is not necessary when increasing the speed to adhere to a certain value for the acceleration. When a negative moment is present, the speed increases automatically; when then the rated speed is reached a speed monitor (e.g. centrifugal switch) can be operated by a contactor that short-circuits the rotor windings. - It is therefore in many cases not absolutely necessary to know the load torque when increasing the speed, especially since it cannot be measured precisely when the engine is at a standstill. On the other hand, can Measure the existing load torques in a simple way before lowering the speed. In practice, when lowering the speed, it is particularly important to adjust the load torque to know and take into account: so that the speed is not too fast or too slow decreases.

In most cases it is sufficient to split the additional braking torque into three to subdivide up to six levels. Of these stages, the more switched on the further the existing load torque deviates from the largest positive load torque. Will requires that one or more intermediate speeds be run for a longer period of time, so it is most appropriate for this speed or speeds, machines with the to provide corresponding nominal speeds on the same shaft, which in each case Be switched on when the associated speed is reached. The excess braking torque, which is available to destroy the kinetic energy during the braking process, must be, can be determined with sufficient precision for each system by setting. That Setting consists in following the work area shown in FIG moved to the right or left of +1 and thus a greater or lesser delay achieved. As a rule, however, the setting to +1 is sufficient, as shown in FIG. 1.

Is e.g. the normally running engine with a negative load torque (pulling load) is loaded by half the nominal torque, as a rule an additional positive load torque (braking torque) of approximately 1.5 times Nominal torque is applied to the motor and the resistance in the rotor circuit is increased for as long until the desired speed is reached.

In FIG. 3, on the same scale as in FIG. 1, the relationship between the braking torque MB of the electric brake machine and the speed n is shown as a function of various direct current excitations g, h and i. If, for example, the excitation h is switched on, then when the motor 1 is idling, the rotor resistors can be used to regulate it back to half the nominal speed. If there is a pulling load (negative moment), the excitation is switched on. - From Fig. 3 it can be seen that the braking effect of the electrical brake machine is reduced to zero at low speeds. A mechanical brake avoids this disadvantage (Fig. 4).

The. in Fig. 4 sketched mechanical brake works as follows: The Drive pulley 20 (or 19) is from the brake shoes 23, which are on the linkage 24 seated, braked. This engages the brake shoes via the joints 26 and 27 Linkage 28, indirectly via the thinker 25 on linkage 24 or directly on the linkage 24. The brake weight 29 is arranged displaceably on the linkage 28. The shifting is done by a Gall's chain 30 on the counter disk 31 from Motor 32 causes. The motor 32 is in a manner known per se from the device 15 (Fig. 2) controlled. Limit switches can also be attached to the linkage 28, which are actuated accordingly by the brake weight 29. The pawl 33 is swiveled out, as soon as a speed change is to be initiated. In the disengaged state; the The pawl can pivot the linkage 28 about the pivot points 26 and 27 and so a the position of the weight 29 apply braking torque corresponding to the position of the weight.

All of the circuits mentioned can also be automatically flawless make.

For the construction of the operating points that result from the described procedure set, let the following be said: In Fig. 1, carry on the abscissa from the zero point from the respective existing load torque according to size and direction, add to it to the right the size of the additionally applied braking torque, e.g. after a of curves g, h, i from FIG. 3, and determine the points of intersection of the abscissa obtained with the straight lines a to f, which correspond to the individual rotor resistances. These Then make intersections the operating points that arise A contact wattmeter can be used as device 15 in FIG Contacts the excitation of the braking machine or the position of the braked weight 29 in Fig. 4 controls. The wattmeter is best designed as a mirror galvanometer, whereby the light beam according to the positive or negative load photosensitive Controls cells. The relays are latched until the next relay is excited.

Claims (7)

P atent ans pr ü che r 1. A method for controlling the speed of asynchronous motors when loaded with negative or below the nominal torque positive load torques, with the inclusion of resistors in the rotor circuit, especially for the operation of cable conveyor systems, characterized in that to change the Speed and especially when lowering the speed below the nominal speed, in addition to the inclusion of resistors in the rotor circuit on the motor shaft, a braking torque of such magnitude is brought into effect that the sum of the fast and braking torque is close to that positive torque, which is assigned to the desired speed according to the characteristic curve (a to f), which corresponds to the resistor that is switched on, and which is in the vicinity of the positive nominal torque. 2. The method according to claim 1, characterized in that to achieve a certain speed first the applied to the shaft braking torque is changed until in the Usually the rated current of the motor is reached and then switched on a suitable resistor, the desired speed is forced. 3. Device for carrying out the method according to claim 1, characterized by a mechanical braking device, which allows the setting of braking torques of various sizes, as they are to be assigned to the individual load torques in the control of the motor, by hand or automatically as a function of a device measuring the load torque enables. 4. Device for through the method according to claim 1, characterized characterized in that for the generation of the braking torque an adjustable one Electric braking machine, in particular with a multipolar DC excited stator and squirrel cage, whose ohmic and impedance represents the load, is provided. 5. Device according to claim 4, characterized in that it ' a measuring device for the respective existing load torque aueeiot, through which the electric brake machine in the sense of the generation of what is to be pushed onto the motor Braking torque is excited. 7th 6. Device according to claim 3, characterized in that it has a measuring device for the respective load torque present, by means of which a torque-influencing member of the mechanical braking device is adjusted by, for example, a brake weight moved along a lever arm, the tension of a spring or the pressure a hydraulic device is changed; 7. Device for performing the method according to claim 1, characterized in that one or more further drive motors (21, 22) are connected to the shaft of the main drive motor (9) via clutches which have lower nominal speeds than the main drive motor and which optionally the drive take over if you want to drive at a lower speed for a longer period of time.