EP0198249A1 - AC control drive, in particular for a lift - Google Patents

Abstract

An electric three-phase AC control drive, in particular a lifting-gear drive for use in lifts, contains an asynchronous motor (12), a frequency converter (18) with a transistor pulse inverter, a microcomputer-guided control unit (24) as well as an incremental shaft encoder (16) which is connected to the rotor. The three-phase AC system produced by the converter and adjustable within wide limits has a low harmonic content and is guided by the control unit (24) in such a way that optimum current conduction, displacement and speed control meeting the requirements and also a smooth starting and braking movement are ensured. <IMAGE>

Description

The invention relates to an electrical three-phase control drive, in particular a hoist drive for use in elevators, with a three-phase motor, a frequency converter and a control unit.

It is known to operate three-phase motors controlled by a control unit by means of a frequency converter as three-phase control drives. The primary side of the frequency converter is fed from the normal 220/380 V AC or three-phase network with a frequency of 50 Hz. The converter contains a rectifier section and an inverter section as well as the control electronics. In the inverter part of the converter, alternating or three-phase current of the desired frequency is composed from the direct voltage obtained. The three-phase motor is operated with this alternating or three-phase network of the desired and adjustable frequency on the secondary side. The control unit determines the setpoints for guiding and steering the converter and thus the motor, in accordance with external requirements and loads on the drive.

Three-phase control drives, especially hoist drives for lifts, are used in a variety of ways. The problem occurs with the drive in the car, particularly when used in elevators or, generally speaking, the load of entering the stops precisely and bringing them to a standstill. This is often not possible with different loads. The suspension cable is stretched differently so that there are differences in height between the boarding platform and the floor of the car when stopping or moving off.

Another problem is the starting and braking or stopping process. Often, the vehicle is only started with a jerk, that is, from standstill it switches to the operating speed with one step, then to the operating speed almost suddenly in a further step. This is not noted as comfortable. Furthermore, when entering the stopping position, the system switches suddenly from operating speed to lower speed, so-called creep speed, from which the vehicle then stops suddenly. This is an attempt to achieve a more precise positioning in the breakpoint. In addition to doubtful success in positioning, the jerky shutdown is felt to be uncomfortable.

The object of the present invention is to design the electric three-phase control drive according to the preamble of claim 1 in such a way that jerk-free starting and stopping is made possible, as is the precise reaching of the stopping point regardless of the load. This is to be achieved with relatively small, very adaptable and energy-saving means.

The object on which the present invention is based is achieved in a very advantageous manner in the said three-phase electric control drive by applying the features set out in the characterizing part of claim 1.

The advantages thus achieved are particularly as follows. A smooth start and stop is made possible. These "soft" start-up and stopping processes, which can be easily optimized, result in very low network peak currents and thus low network loads, which enables low connection costs. You can even limit the peak current to the nominal current. If an asynchronous motor is used, the field weakening range can be exploited, i.e. Achieve high torques at low speeds and low torques at high speeds and thus achieve high tightening torques without high currents and still provide the required lifting capacity from the converter. The stopping point can be reached precisely in position without creep speed. This results in a self-contained driving process that ensures comfortable driving with economical use of energy.

Another particular advantage of using the three-phase control drive designed according to the invention as an elevator drive is that a much simpler gear, in particular a spur gear, can be used instead of a more expensive and energy-consuming worm gear. This means that the overall efficiency, consisting of the electric drive and gearbox, can be increased from 35% to 40% to approx. 70%.

Advantageous further developments and refinements of the invention are set out in the subclaims. The advantages that can be achieved in this way are either obvious or are given below in connection with the specific description.

• Fig. 1 schematisch den Gesamtaufbau des erfindungsgemäß gestalteten Drehstromregelantriebs am Beispiel der Anwendung als Hebzeugantrieb für einen Aufzug;
• Fig. 2 schematisch als Blockbilddarstellung den verwendeten Frequenzumrichter mit seinen wesentlichen Ein- und Ausgängen;
• Fig. 3 schematisch in drei Diagrammen, jeweils in Abhängigkeit von der Zeit, ein Profil der Beschleunigung a, der Geschwindigkeit v und der Lage x der vom Motor zwischen zwei Positionen bewegten Last;
• Fig. 4 schematisch ein Schaubild zur Gewinnung der Lage-Sollwerte x_s; und
• Fig. 5 schematisch in einem Blockdiagramm den Zusammenhang der Generierung der Lage- Sollwerte und der Motorführung.

The invention is explained in more detail below with reference to a special exemplary embodiment shown in the drawing. The figures in the drawing show in detail:

• Figure 1 schematically shows the overall structure of the three-phase control drive designed according to the invention using the example of the application as a hoist drive for an elevator.
• Fig. 2 shows schematically as a block diagram the frequency converter used with its essential inputs and outputs;
• 3 schematically in three diagrams, each as a function of time, a profile of the acceleration a, the speed v and the position x of the load moved by the motor between two positions;
• 4 schematically shows a diagram for obtaining the nominal position values x _s ; and
• Fig. 5 shows schematically in a block diagram the relationship between the generation of the position setpoints and the motor control.

In Fig. 1, the overall structure of the three-phase control drive 10 according to the invention is shown schematically using the example of the application as a hoist drive for an elevator. The three-phase control drive 10 drives via a shaft 13, a transmission 30. Its output shaft 32 is connected to a cable guide roller 34, via which the support cable 35 of the car F of the elevator is guided. The other end of the support cable 35 is connected to the counterweight G.

The three-phase control drive 10 consists, for example, of a synchronous motor or, as shown, an asynchronous motor 12, which is preferably a low-scatter cage run ^g r asynchronous gate. The asynchronous motor 12 is ver via its rotor shaft 14 with an angle encoder 16 bound. Another essential component of the drive 10 is the frequency converter 18 and the control unit 24.

The frequency converter 18, which is designed as a transistor pulse inverter, feeds the motor 12 via the lines 20 with a three-phase system adjustable in frequency from 0 Hz to maximum frequency. This three-phase system has a low harmonic content due to the design and the type of control of the transistor pulse inverter. On the primary side, the converter is powered by the usual 220 V or 380 V network 22.

The control unit 24 is connected to the transistor pulse inverter 18 via a bus 26. Setpoints for controlling and regulating the motor 12 are supplied to the converter 18 via this collecting line. At the same time, feedback is made available via the collecting line of the control unit 24. The control unit 24 continues to be supplied with the pulses of the angle stepper 16 via a line 15. The pulses from the angular step encoder 16 provide information about the position of the rotor of the motor 12 or about the angular position of the shaft 14. Both the angular position and the speed of the rotor can be determined from these signals. In addition, these signals can also be used for distance measurement if a suitable calibration has been carried out. Primarily, the pulses from the angle stepper 16 are used and processed for optimal and dynamic guidance of the motor 12 within the control unit 24.

The control unit 24 is supplied with initiator signals via the line Ixo and via the line Ixu. External superordinate setpoint signals are supplied to the control unit 24 via a further input 28 to be understood as a collective input.

The lines Ixu and Ixo are outputs of O-circuits 37 and 39, respectively. The inputs of the D-circuit 37 are signals from the initiators I _2u , 1 _3u and I _4u . These signals always occur when the car F of the elevator travels with its lower edge 40 at initiator points from bottom to top to the floors labeled two, three and four. Such initiator position sensors are provided within the elevator shaft at precisely defined points below the stop lines. If the stops are approached from above, then there are pulses at the initiator positions I ₁₀ , 12o and I ₃₀ , which are combined via the OR circuit 39 and supplied to the control circuit 24 on the line I _xo . These signals also occur when the car F, with its lower edge 40 coming from above, has approached the stopping point of the stock values three, two and one in each case up to a certain distance. These signals Ixo and Ixu then each initiate the braking process in order to stop car F exactly on floors one to four.

Figure 2 shows schematically as a block diagram the frequency converter 18 used with its essential parts and with its essential inputs and outputs. The converter 18 contains a part GR / NT with rectifier and low-voltage power supply. The rectifier supplies the DC voltage to the transistor inverter WR. The low-voltage power supply supplies the converter electronics. Both the GR / NT part and the WR inverter part are managed by the control and regulating electronics SR. The main inputs of the control and regulating part are the control inputs UE for switching on the converter and UA for switching off the converter as well as IF as pulse enable for the inverter and FS as an error signal, signals that enable a two-phase setpoint specification are connected via the Rund S connections. The actual phase current values can be removed at the connections R _i , S., T _i .

The inverter WR, which is designed as a transistor pulse inverter, supplies the three strings U, V, W of the motor supply lines 20. Since the inverter WR is operated with an interrogation frequency of up to 100 kHz, its branches can not only generate almost purely sinusoidal phase currents, but can also carry direct currents or rapid phase current changes force. This is essential for dynamic guidance of the squirrel-cage asynchronous motor.

If an asynchronous motor is used, the field weakening range can be exploited, i.e. Achieve high torques at low speeds and low torques at high speeds and thus achieve high tightening torques without high currents and still provide the required lifting capacity from the converter.

The control and regulating electronics SR of the converter 18 is designed so that four-quadrant operation is possible. Furthermore, it enables either phase current or phase voltage regulation with two-phase setpoint specification. The current limitation is adjustable so that the mains peak currents do not exceed the desired or permissible level.

The control unit 24 is provided with a microcomputer. This is used for optimal current control, for displacement or speed control and for generating jerk-free starting and braking or stopping movements of the asynchronous motor 12. In addition, the microcomputer-controlled control unit 24 generates setpoints as a function of and in accordance with supplied actual values, superordinate setpoint signals, external position signals and internally specified control parameters. Such higher-order setpoint signals are, for example, the requirements for driving the drive supplied via connection 28

Elevator to a specific location from a specific location. The actual values supplied can be the position; the current actual values for the individual phases R, S and T can also be involved. External position signals are, for example, the lower or upper initiator position signals from the elevator shaft that are supplied via lines Ixu and I _xo . As an example for internally specified control parameters, max. Acceleration, max. permissible speed and max. To name currents and voltages.

The distinction made in the microcomputer ^g eführten control unit 24 generating the target values will be explained with reference to FIGS. 3 to 5 in more detail below. 3 shows three diagrams as a function of time t. A profile of the acceleration a for a specific movement cycle is plotted in the uppermost diagram in FIG. 3. The acceleration increases linearly in a first area, then remains at the max. permissible value and then decreases to zero. Then the acceleration becomes negative, i.e. it increases linearly in the sense of braking, then remains at a constant negative maximum value for a while and then increases linearly again to the value zero.

The diagram shown in the middle in FIG. 3 shows the profile of the speed v over the time t for the acceleration profile shown in the first diagram. In the range tD to t _{1, the} speed roughly follows the shape of a parabola, that is, this corresponds to the linearly increasing part of the acceleration between times t _D to t ₁ . Then the speed increases linearly between t1 and t2. Then in the range between t2 and t _{3 the on} slowed down The speed increased parabolically, in order to then remain constant at the maximum value Vmax in the range between t ₃ and t4. In accordance with the linear negative of acceleration a between times t4 and t5, the speed decreases parabolically, then decreases linearly between times t5 and t ₆ , in order to continue to decrease in the range between t ₆ and t7 following a parabola, in order to decrease the value at time t ₇ To reach 0.

The bottom diagram in FIG. 3 shows the position X over the time t between the times t0 and t7 in accordance with the acceleration profile a and the speed profile v at the corresponding times. The position profile x corresponds, for example, to the course and the respective location depending on the time of the elevator cage F between the second floor and the third floor. The lower line, corresponding to the time axis t, corresponds to the stop line of the second floor and the upper dashed line corresponds to it the stop line of the floor three, as shown in Fig. 1. The course of the location of the position of the basket, this corresponds to curve X _s , rises gently following a curve from time t0 to time t ₃ , at which the speed reaches its max. Has reached value. Between the point in time t ₃ and the point in time t ₄ , that is to say at a constant speed, the course of the location is linear. Subsequently, between time t ₄ and time t ₇ , the car approaches stop line 3 in a smooth transition with decreasing speed in a smooth transition. The actual position is indicated by dashed lines approximately parallel to the curve marked X _s , X _i . The actual position of the car F follows the generated setpoint X _{s with a} time delay, as can be seen from the curve.

The time at which the initiator _signal 1 _3u (cf. also FIG. 1) occurs is shown in the linear region of the position diagram shown in FIG. 3 with the aid of an arrow. This signal I _3u indicates that when the car F travels between two floors and three floors, the lower initiator point is reached before the third floor by the lower edge 40 of the car. From there, there is still a defined way to travel Xinit. In practice, this can correspond to the distance of 1 m. From this value and the stored value of the necessary braking distance, the control unit 24 calculates those further setpoints that can still be output in a linear manner until braking is initiated.

In FIG. 4, in addition to the three diagrams of FIG. 3, the sequence in which each individual position setpoint X _{s is created is} schematically explained. In a cyclic sequence with a suitable frequency, a summation process is carried out for a specific Δ a of the acceleration profile, which leads to an acceleration value a. This acceleration value a must be less than the maximum. From this, the associated speed value V is determined by summation or integration, which is also less than the permissible maximum speed V _max . A further summation is used to determine the value for the initial Δ a and, accordingly, the current target value X _s for the position at the specific point in time of the car F. As already mentioned, this process is carried out cyclically in a certain cycle.

5 shows schematically in the block diagram the relationship between the generation of the position setpoints X _s and the control of the motor by the converter. In the setpoint generator of the control unit 24, the position setpoints X _{s are} determined in accordance with the starting conditions and the occurrence of the initiator pulses 11 ₀ to I ₄ u .

These position setpoints X are fed to a position controller. The two phase setpoints Rs and Ss are then available at the output, which either specify the phase current or the phase voltage according to the setpoint. These values are fed to the converter, which uses them to output the motor phase currents with the aid of its control and regulating electronics SR.

During each starting process, the control unit 24 determines a specific starting target path Xs during the starting process between the time to t ₃ , as shown in FIG. 3, in particular in the lower diagram. This approach path or the individual setpoints determined in the process are stored as the braking distance and are used in reverse order as setpoints in the braking process for the braking distance during the subsequent braking process. This ensures a braking distance analogous to the approach path. The braking process is initiated when the signal I _xo or I _xu comes at a specific position before the stopping point. The control unit then determines when the braking process must be initiated. The braking process is carried out in the same way as the start-up process and then initiated after the initiator pulse when the car position corresponds to the total distance minus the approach path. Approach and braking distance are those routes on which, as can be seen from the diagrams in FIG. 3, a change in speed of the load or. of the car F occurs.

The position setpoints X _s for the drive guided in the position are generated by the microcomputer-controlled control unit 24 in such a way that a continuous movement is achieved from the time of starting, t _D to the time of complete stopping at time t ₇ . Fig. 3 shows this continuous jerk-free course, which ensures particularly pleasant driving comfort.

Claims (10)

1. Electrical three-phase control drive, in particular a hoist drive for use in elevators, with a three-phase motor, a frequency converter and a control unit, characterized in that a) an angular step encoder (16) is connected to the rotor of the three-phase motor (12), _b ) the frequency converter (18) contains a transistor pulse inverter, which supplies a three-phase system with low harmonic content that is adjustable within wide limits, c) the control unit (24) is provided with a microcomputer for optimal current and flow control, for path or speed control and for producing jerk-free starting and braking or holding movements of the three-phase motor (12), and d) the control unit (24) generates position setpoints (X _s ) or phase setpoints (R _s , S _s ) as a function of and in accordance with supplied actual values, superordinate setpoint signals, external position _signals (I _xu , I _xo ) and internally predetermined control parameters ( a, amax, v _max ). 2. Drive according to claim 1, characterized in that the control unit (24), which is guided by a microcomputer, generates a speed profile (v) from an internally predetermined time-dependent profile of the acceleration (a) and a further position-dependent position profile (x) by further summation. is generated, the individual values (x _s ) of which serve as setpoints for the position control, the summation being carried out cyclically at a high frequency. 3. Drive according to claim 1 or 2, characterized in that the setpoints generated during the starting process for the approach path (x _s ) are stored and used as setpoints in the braking process in the reverse order for the braking distance. 4. Drive according to claim 3, characterized in that the braking process is carried out analogously to the starting process and then initiated when that position is reached which corresponds to the total path minus the respective approach path. 5-. Drive according to claim 3 or 4, characterized in that the approach and braking distance is the route on which a speed change of the load (F) occurs. 6. Drive according to one of claims 3 to 5, characterized in that the microcomputer-controlled control unit (24) generates the position setpoints (x _s ) in such a way that the start-up movement and the braking movement take place continuously, ie jerkily from or to a standstill, and likewise the transition to constant as well as from constant speed. 7. Drive according to one of the preceding claims, characterized in that the rotor position angle signals of the with the rotor of the three-phase motor (12) connected angle encoder (16) can be used both for dynamically optimal guidance of the three-phase motor (12) and for distance measurement. 8. Drive according to one of the preceding claims, characterized in that a squirrel-cage motor asynchronous motor (12) is provided as a three-phase motor. 9. Drive according to claim 8, characterized in that the squirrel cage asynchronous motor (12) is low in scatter and thus has a large field weakening range. 10. Drive according to one of claims 1-7, characterized in that a synchronous motor is provided as a three-phase motor.

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