PROCEDURE FOR DETERMINING THE PARAMETERS FOR AN ELECTRIC DRIVE CONTROLLING A SYNCHRONOUS ELEVATOR MOTOR WITH PERMANENT MAGNETS

Abstract: A procedure for determining the parameters for an electric drive controlling a synchronous elevator motor with permanent magnets, a computer controlling the operation of the electric drive being provided with a control model describing the elevator and containing settable parameters. The elevator car installed in the elevator shaft is allowed to enter a motional condition produced by the balance difference between the elevator masses; using two different loads connected to the terminals of the synchronous motor, the rotational speed, electromotive force and synchronous reactance of the synchronous motor are measured while the elevator car is in a constant motional condition, and the stator resistance is measured via a separate measurement; and a control model describing the elevator is computed and formed from these measurements.

Description: PROCEDURE FOR DETERMINING THE PARAMETERS FOR AN ELECTRIC DRIVE CONTROLLING A SYNCHRONOUS ELEVATOR MOTOR WITH PERMANENT MAGNETS The present invention relates to a procedure for determining the parameters for an electric drive controlling a synchronous elevator motor with permanent magnets, as defined in the preamble of claim 1. To allow the adjustments of a converter used in elevator control to be made at the factory, several methods and calculation programs have been developed. Generally, the converter settings are calculated based on the motor and elevator data specified in the order. This may be done relatively long before the elevator is actually delivered and installed in the shaft. The problem here is the inaccuracy and divergence of both elevator data and motor data. The parameters describing the motor are usually given as typical values. These so-called name plate values may differ from the actual properties of the motor by several percentage units. When the frequency converter has been adjusted based such values, both the frequency converter and the elevator need additional adjustment at the site of installation. Adjustments carried out at the site of installation increase the installation time, thus increasing the total manufacturing and installation costs of the elevator. In recent times, a new type of synchronous motor with permanent magnets as described in international patent application WO 95/00432 has been developed for use in elevator drives. The use of this new motor type as an elevator component brings considerable advantages. However, as a consequence of the large diameter and discoid shape of its rotor/stator , certain manufacturing tolerances must have larger values. This in turn leads to a larger range of variation in the performance characteristics of the motors manufactured than in the case of conventional asynchronous motors. As this new type of elevator motor generally forms an integral part of the hoist- ing machinery of the elevator, the installation assembly containing the motor is relatively heavy, so it is difficult to handle, move or mount on a test bench. This makes it still more difficult to adjust the frequency converters in factory. The object of the present invention is to eliminate the drawbacks mentioned above. A specific object of the invention is to disclose a new type of method by which the parameters for the electric drive of an elevator already installed can be determined and set as sim- ply, quickly and economically as possible. As for the features characteristic of the invention, reference is made to the claims. The procedure of the invention is based on an arrangement in which the elevator car is installed in the elevator shaft before any precise adjustments are made, so the adjustments are carried out in the actual operating conditions of the elevator. According to the invention, after the elevator car has been installed in the elevator shaft, the car is allowed to move freely as driven by the forces resulting from the elevator masses, mainly from the imbalance between the masses of the elevator car and counterweight . Once the elevator car has reached a constant motional condition, the rotational speed, electromotive force and synchronous reactance of the synchronous motor are measured for two different loads connected to the terminals of the synchronous motor. In addition, a separate measurement is carried out to determine the stator resistance. From these measurements, an actual control model describing the elevator is then calculated and formed. The two measurements are preferably performed using connections previously provided in the motor. Thus, one of the measurements can be carried out with a normal braking resistance connected to the motor terminals and the other with the motor short-circuited. However, other loads can also be used in the measurements. The measurements to be made in a constant motional condition are preferably carried out separately, i.e. first a given connection is made between the motor terminals, whereupon the first measurement is carried out. After this, the connection is changed and the second measurement is carried out. In a particularly preferred case, the elevator is allowed to enter a free motional condition from the same point in the elevator shaft and the measurements are performed at the same place in the elevator shaft while the elevator is in a constant motional condition. This allows any variations in the friction between the elevator car and the elevator shaft to be eliminated from the measurements. However, it is also possible to carry out the measurements during a single free motional condition of the elevator car by changing the connection while the car is moving. The stator resistance can be determined before- hand with a relatively good accuracy and stored in the memory of the computer controlling the frequency converter. On the other hand, it can also be measured e.g. by means of the current sensor of the frequency converter using direct current. The procedure of the invention has significant advantages as compared with prior art. The procedure allows simpler processes in the manufacture of the elevator machinery and in elevator delivery. Larger divergences are permitted in the parameters of the elevator machinery than traditionally, or alternatively the testing of the machinery can be simplified. In the elevator delivery process, the amounts of calculations and factory settings as well as documentation can be reduced. Reliability of the elevator is increased and its operating characteristics improved because the adjustment values of the system are in better accordance with the particular machinery and elevator shaft. Significant advantages are also gained by apply- ing the procedure of the invention e.g. in conjunction with regular maintenance of the elevator. The characteristics of the frequency converter can thus be easily modified in accordance with the changes in mechanical properties caused by ageing or wear of the elevator. By adjusting the parameters, the elevator can also be adapted for optimal operation in situations involving various changes in external conditions. Such changes might be e.g. seasonal variations in temperature and humidity, which occur in most buildings in spite of or due to heating or cooling. In the following, the invention will be described in detail by referring to the attached drawings, in which Fig. 1 is a schematic representation of a system in which the procedure of the invention is used, and Fig. 2 presents an equivalent circuit representing a synchronous elevator motor. The procedure of the invention can be used e.g. in a system as illustrated by Fig. 1. In this system, the elevator motor 1 is operated using a frequency converter drive 2 controlled by a control computer 3. The control computer 3 receives from a tachometer 4 a speed signal 5 representing the rotational speed of the motor. Another control signal supplied to the control computer 3 is a current feedback signal 6 obtained from the braking re- sistors 7. A synchronous motor with permanent magnets can be described with sufficient accuracy by an equivalent cir- - cuit as shown in Fig. 2. The equivalent circuit consists of the electromotive force E, stator resistance R 3 and synchronous reactance X of the motor. The stator resistance can be determined beforehand with a relatively high accuracy and stored in the memory of the computer 3 controlling the frequency con- verter 4. To determine the electromotive force and synchronous reactance, at least two additional measurements are needed. With the elevator car installed in the elevator shaft, one of the measurements can be carried out using the normal braking resistance 7 at the motor terminals. When the brake 8 of the elevator is released, the elevator car will move at a constant speed. In this situation, the following equation applies: E: /ι = RyR J + i *X l where E α <= nι*e, i = k * n.ι*L, n = speed of rotation and k = constant. The other measurement can be carried out with the motor short-circuited, in which case the following equation applies: /,= R. + i *Xι where E 2 = n 2 *E and X 2 = k * n 2 *L. Since the electromotive force and synchronous reactance are directly proportional to the speed of rota- tion measured by the tachometer 4, the dependence of "" the electromotive force on rotational speed e and the dependence of the synchronous reactance on rotational speed L -can be solved from the two equations presented above. From the data obtained by the method described above, it is possible to create a motor model that relatively accurately describes the newly installed system, allowing easy adjustment of the system. For example, the motor power can be calculated from the electromotive force and the current component acting in the same direction. On the other hand, if the required torque is known, then the current needed to generate it can be calculated. From the above-mentioned measurement results, it is also possible to calculate the friction of the diverting pulleys because the speed reached during the measurements depends on the friction. This makes it possible to change the control parameters so that the shaft properties, such as friction, are taken into account. The fric- tion could be compensated e.g. by increasing the current reference. In the foregoing, the invention has been described by way of example by referring to the attached drawings, but different embodiments of the invention are possible within the scope of the inventive idea defined by the claims.

Claims: CLAIMS 1. Procedure for determining the parameters for an electric drive controlling a synchronous elevator mo- tor with permanent magnets, a computer controlling the operation of the electric drive being provided with a control model describing the elevator and containing settable parameters , charac teri s ed in that - the elevator car, installed in an elevator shaft, is allowed to enter a motional condition produced by the balance difference between the elevator masses; - using two different loads connected to the terminals of the synchronous motor, the rotational speed, electromotive force and synchronous reactance of the syn- chronous motor are measured while the elevator car is in a constant motional condition, and the stator resistance is measured via a separate measurement; and - a control model describing the elevator is calculated and formed from the measurements . 2. Procedure as defined in claim 1, char a c t e r i s ed in that one of the measurements is performed while the elevator car is in a constant motional condition, using the normal braking resistance at the motor terminals. 3. Procedure as defined in claim 1, charac t e r i s e d in that one of the measurements is carried out while the elevator car is in a constant motional condition, with the motor short-circuited. 4. Procedure as defined in claim 1, charac - teri s ed in that the stator resistance is measured via a separate resistance measurement. 5. Procedure as defined in claim 1, charac t eri s ed in that the speed of rotation of the motor is measured using a tachometer. 6. Procedure as defined in claim 1, charac t eri s ed in .that the motor power is calculated from the electromotive force and the current component acting in the same direction with it. 7. Procedure as defined in claim 1, charac teri s ed in that the current needed to generate a desired torque is calculated from the measurement results. 8. Procedure as defined in claim 1, charac t eri s ed in that the friction values of the elevator shaft and diverting pulleys are determined from the measurement results, and that, based on said friction values, the current reference, which is one of the control parameters, is increased to compensate for the friction. 9. Procedure as defined in any one of claims 1 - 8, charac t e r i s e d in that the procedure is applied in conjunction with the original installation of an elevator, elevator modernisation, maintenance operations and/or when the elevator is being adapted to changed circumstances . 10. Procedure as defined in any one of claims 1 - 9, charac t e r i s ed in that the defined parameters are set in the computer controlling the operation of the electric drive of the elevator.

Inventors: JAHKONEN PEKKA, SAARIKOSKI TAPIO, JAHKONEN, PEKKA, SAARIKOSKI, TAPIO
Applicants: JAHKONEN PEKKA, KONE CORP, SAARIKOSKI TAPIO, JAHKONEN, PEKKA, KONE CORPORATION, SAARIKOSKI, TAPIO
Application year: 1998
Main classification: B66B1
IPC codes: B66B1, H02P6