GB2146187A

GB2146187A - Procedure and means for controlling the direct current motor of a lift

Info

Publication number: GB2146187A
Application number: GB08421454A
Authority: GB
Inventors: Osmo Ivanto; Matti Kahkipuro
Original assignee: Elevator GmbH
Current assignee: Elevator GmbH
Priority date: 1983-08-26
Filing date: 1984-08-23
Publication date: 1985-04-11
Also published as: DE3429722A1; JPS60106391A; BR8404237A; GB2146187B; FI833051A0; GB8421454D0; FR2551276A1

Abstract

In a lift d.c. motor drive arrangement an alternating supply current (Us) is rectified in a manner known in itself in prior art. In order to eliminate the drawbacks of conventional four-quadrant thyristor bridges, the d.c. voltage that is formed is conducted to an energy storage battery (2) supplying the main drive energy for the d.c. motor (3), and the drive voltage (Uz) for the d.c. motor (3) is formed from the constant, or intermediate, voltage (Uv) of the energy storage (2) by pulse-width modulating it by means of switching elements (4,5,6,7), known in themselves in prior art, which enable the motor (3) to be controlled in four quadrants. <IMAGE>

Description

SPECIFICATION Procedure and means for controlling the direct current motor of a lift The present invention concerns a procedure and a means for forming the control voltage for the direct current motor of a lift, in said procedure the alternating supply current being rectified in a manner known in itself in prior art.

In lift technology, the characteristics of the direct current motor make it superior in quality to an alternating current motor. By quality is in this connection meant freedom from vibration and accuracy of the speed control.

Therefore, particularly the gearless high speed lifts are constructed using exclusively d.c.

motors.

In lift technology, the classical Ward-Leonard technology has been replaced in the control of d.c. motors by the four-quadrant thyristor bridge. The novel technology is advantageous in use e.g. owing to its high efficiency. Drawbacks particularly encumbering high speed lifts are, however, poor power factor, high starting currents and harmonics entering the mains. Moreover, d.c. motor controlling lift operating systems carried out with power semiconductors, drawing energy from the mains, present the drawback that mains failure may cause the fuses to blow and people to be imprisoned in the lift between floors.

The object of the present invention is to eliminate the drawbacks of a lift with d.c.

motor mentioned in the foregoing. For accomplishing said advantageous effect, the procedure of the invention is mainly characterized in that the direct voltage formed by rectifying is conducted to an energy storage supplying the main drive energy of the d.c. motor, and that the control signal for the d.c. motor is formed of the constant or intermediate voltage of the energy storage by pulse width modulation, using switching elements known in themselves in the art which enable the motor to be controlled in four quadrants. The most important advantages of the invention are as follows: -the mains power rating required is low because energy also goes to the energy storage when the lift is stationary.Since this charging current of the storage is rather low, neither power factor nor superharmonics will become a problem.

-the starting current imposes no load on the mains, whereby the mains only provide to the system the uniform energy-storage charging current.

-the lift has reserve power (the energy storage) at all times, and therefore no fuses will blow in the event of mains failure, nor any persons remain captive in the lift.

An advantageous embodiment of the procedure of the invention is also characterized in that from the d.c. motor energy is supplied to the storage when the motor is braking, at any speed of rotation, at low speeds by utilizing the inductance of the rotor circuit and/or using an extra inductance. When the speed of the d.c. motor is low, for instance at the beginning of braking, whereby the voltage across the terminals is also low (lower than the constant voltage of the energy storage), the energy released in braking the motor can even in this case be supplied into the storage by boosting the energy to be returned in the high inductance of the rotor circuit, whereby the voltage across the motor rises to be high enough to enable a current to pass to the energy storage.

The means applying the procedure of the invention, comprising a rectifying unit with control electronics known in itself in the art, is characterized in that the means consists of one or several storage batteries serving as energy storage and of a pulse modulation circuit controlling the d.c. motor, by the aid of which the control voltage is produced for the d.c. motor. It is easy by the aid of pulse modulation to control the mean power of the constant voltage d.c. current supplied to the consumer means, without changing the voltage level. In addition, a storage battery is a commonly available and simple energy storage. It has to be pointed out that a very small storage battery intended for industrial use is fully sufficient to do the job.

An advantageous embodiment applying the procedure of the invention is characterized in that the pulse modulation circuit has been carried out as a thyristor circuit of the socalled McMurray type, which is known in the art. By the McMurray circuit, it is possible to set up a simple and reliable pulse modulation system requiring no special components.

The invention is described in the following more in detail by the aid of an example, referring to the drawing attached, wherein: Figure 1 presents a circuit applying the invention, Figure 2 presents a design representing the state of art, Figure 3a illustrates the principle of pulse modulation, and Figure 3b shows the use of a semiconductor switch in applying the principle, Figure 4 presents an advantageous embodiment of the pulse modulation circuit.

It is thus understood that Fig. 1 presents a d.c. motor controlling means according to the invention. The supplying mains Us supply single or multiple phase a.c. current to a rectifier 1, the output of which is a constant intermediate voltage Uv. The storage battery 2 serving as energy storage has been connected in parallel with the rectifier 1. Of the intermediate voltage Uw is by the aid of semi-conductor switching elements 4, 5, 6, 7 formed the control voltage for the d.c. motor 3. The elements 4-7 constitute a pulse width modulation circuit, which is commonly employed in the control of a d.c. motor.

Fig. 2 illustrates the controlling of a d.c.

motor operating a lift, by the aid of prior art.

Power supply is from three-phase mains RST.

The thyristors constitute a four-quadrant rectifying bridge, by which the lift motor 3 is controlled. The thyristors are so-called anglecontrolled thyristors and they are commutated by the aid of the mains voltage, and therefore the d.c. component of the control voltage U, of the lift can be controlled by controlling the time of ignition. The group 10 of three thyristors T1, T2 and T3 isolated by dotted lines constitutes one half of the two six-thyristor bridges required for four-quadrant operation.

Depending on the direction of the current, only one of the two bridges is on, its different halves (e.g. 10) being conductive on the different half-waves of the supply current RST.

Since the voltage U, obtained from the thyristor bridge is alternating, it is not possible to connect to it for instance a storage battery.

Fig. 3a shows how pulse width modulation can be applied to make the constant d.c.

voltage adjustable. With the working cycle length, determined by the pulse width, equalling T and with k representing the degree of modulation, proportional to the required power, in the present instance from the intermediate voltage Uv is obtained by pulse width modulation a mean voltage U2, which at the same time is the load-controlling voltage. It is now understood that the value of U2 can be controlled by varying the degree of modulation k. Since now the intermediate voltage Uv is fixed, it is possible to connect a storage battery to this voltage.

In Fig. 3b is shown in a simplified manner how modulation as in Fig. 3a can be effected with one switch.

In Fig. 4 has been shown the known socalled McMurray circuit, which can be used as a thyristor-based pulse width modulator. It is composed of thyristors T4-Tl 1, diodes D1-D4, capacitors C1 and C2 and inductances L1 and L2. The storage battery 2 and the d.c. motor 3 are connected to the modulator as shown in the figure. With reference to Fig. 1, e.g. the switching elements 5 and 7 can be separated from the circuit diagram as indicated with dotted lines. It is to be noted that the components C2 and L2 are common to both elements. The state of the magnetizing circuit M of the motor 3 is not an essential matter in this connection: its voltage can be assumed to be constant, for instance.

It is expedient that the d.c. motor operates in four quadrants, because the motor can then be made to rotate in both directions, and in each direction of rotation a positive as well as a negative torque is obtained when this is required by the load. In Fig. 4, the switching elements 4-7 may then consist, in this case, of power transistor, thyristor or GTO thyristor circuits. In the thyristor circuit of Fig. 4, forced commutation has been employed, wherein switching off of the thyristor is accomplished with a resonance circuit composed of a capacitor and a choke (e.g. C2, L2).

Forced commutation circuit technology is a matter well familiar to a person skilled in the art, and therefore nothing more is said here concerning the operation of the circuit in Fig.

4.

In the following shall be examined the operation of a means as taught by the invention, in its proper service environment.

When the lift starts moving upward, the d.c. motor 3 requires a heavy starting current, which the storage battery or another equivalent energy storage has to be able to supply.

No current is taken from the a.c. mains at all through the rectifying bridge 1 for running the motor, all the energy which the motor needs being instead supplied from the storage battery 2. It has however been found than an industrial storage battery of even very small size is fully adequate to serve the purpose, and therefore no difficulties will be encountered in finding a suitable energy storage. The energy drawn from the a.c. mains is only required for charging the energy storage to make up for various losses, since the motor 3 operates as a generator restoring the energy consumed in hoisting just as much as it operates as a motor, when the left is moving up and down.

Let us assume that the current passes through the d.c. motor 3 through the rectifying switching elements 4 and 5 in Fig. 1 as the motor moves the lift upward. The elements 6 and 7 are then in non-conductive state, and the pulse code modulation takes place in the elements 4 and 5. When the left descends, the motor 3 begins to operate as a generator. As soon as the voltage of the motor is high enough, the switching elements 4 and 5 begin to operate as alternators with the aid of the diodes D1 and D4, and the pulse width modulation circuit then supplies energy from the load through the motor 3 to the storage battery 2. It is thus understood that the apparatus never feeds back energy to the supplying mains as do the circuits of existing art.

The voltage of the motor is always lower than the voltage Uv of the storage battery.

Regardless of the low motor voltage, the current is forced to pass through the high inductance of the rotor circuit, where the voltage value increases to be such that the switching elements 4 and 5 shift to the alternating mode. Hereby the advantage is gained that the d.c. motor 3 is able at any speed to push energy into the storage battery 2-this may appear peculiar, seeing that as a rule current cannot be conducted from a lower to a higher potential.

If the storage battery 2 is fully charged, there is in the embodiment of Fig. 1 a resistance R connected across the storage battery and a switch c, which switches the resistance R on, to dissipate the extra charging energy, as required.

It is obvious to a person skilled in the art that various embodiments of the invention are not exclusively confined to the example presented in the foregoing but may vary within the claims stated below.

Claims

1. A procedure for forming the control voltage for a lift d.c. motor, wherein the alternating supply current (Us) is rectified in a manner known in itself in the art, characterized in that the d.c. voltage thus obtained is conducted to an energy storage (2) giving off the main drive energy for the d.c. motor (3) and that a control signal (U2) for the d.c.

motor (3) is formed of the constant, or intermediate, voltage (Uv) of the energy storage (2) by pulse-width modulating it with the aid of switching elements (4, 5, 6, 7) known in themselves in the art, which enable the motor (3) to be controlled in four quadrants.

2. A procedure according to claim 1, characterized in that from the d.c. motor (3) energy is fed to the storage (2) when the motor (3) is braking, at any speed of rotation thereof, at low speeds using as an aid the inductance of the rotor circuit and/or extra inductance.

3. A means for carrying out a procedure according to claim 1, comprising a rectifying unit known in itself with control electronics (1), characterized in that the means consists of one or more storage batteries (2) serving as energy storage and of a pulse width modulation circuit (4, 5, 6, 7) controlling the d.c.

motor (3), by the aid of which the control voltage (U2) of the d.c. motor (3) is formed.

4. A means according to claim 3, characterized in that the pulse width modulation circuit (4, 5, 6, 7) has been carried out by the known, so-called McMurray-type thyristor circuit.

5. A means for carrying out a procedure as claimed in Claim 3 substantially as described with reference to Fig. 1 or Fig. 4 of the accompanying drawings.