GB2157512A

GB2157512A - Electric motor control system

Info

Publication number: GB2157512A
Application number: GB08409707A
Authority: GB
Inventors: Matti Kahkipuro; Pertti Saransaari
Original assignee: Elevator GmbH
Current assignee: Elevator GmbH
Priority date: 1982-10-15
Filing date: 1984-04-13
Publication date: 1985-10-23
Also published as: FR2534747B1; DE3337272A1; JPS60219998A; FI823519L; GB8409707D0; FR2534747A1; FI823519A0

Abstract

An electric motor control system comprises a two-phase AC motor (6) supplied with 2-phase current from an electronic power control circuit 7, 8, for use in a gearless elevator drive. The circuits 7, 8 are controlled to provide the required phase shift between the two phases. Power is fed back to the power source during braking. <IMAGE>

Description

SPECIFICATION Electric motor control systems This invention is concerned with electric motor control systems more particularly but not exclusively for gearless elevator applications and utilising a two-phase AC motor and electronic power control units.

As electronic power control systems are becoming more sophisticated, it is common to accomplish electric motor speed control by using AC motor frequency control. In gearless elevator applications the AC motor is controlled by three electronic power control units, each of which produces an electronic phase for the motor.

Operating on the current regulation principle, the control system supplies a pre-determined threephase current in which the phase shift between the different phases is 120 degrees, producing a rotating magnetic field. Motor speed can be controlled by adjusting the frequency of a command variable. The problem associated with existing systems is their complexity and, consequently, high cost.

The object of this invention is to eliminate the aforesaid problem by making the motor control system simpler. Characteristic of a system according to the invention is that the main circuit of the unit incorporates two phase-production circuits, and the control circuit is programmed to give the command variable to effect the phase shift, and during braking, power is fed back to the three-phase supply network. In this way, one third of the expensive electronics, including its control system, is rendered unnecessary.

Furthermore, in a system according to the invention the frequency of the main circuit current as well as the motor speed can advantageously be controlled by means of the command variable.

The invention will now be described by way of example and with reference to the accompanying drawings, in which Fig. 1 shows a block circuit diagram of a conventional motor control system.

Fig. 2 shows a block circuit diagram of a motor control system according to the invention, and Fig. 3 shows in more detail the electronic control units forming the electronic power control circuit of the system of Figure 2.

Conventionally, as shown in Figure 1, the main circuit of an AC motor consists of three electronic power control circuits 2,3 and 4. Each of these units produces one electronic phase for the poles of the motor 1. The detecting and control element 5 provides a 3-phase command variable for the current, and there is a 120-degree phase shift between the different phases to produce a rotating magnetic field. Motor speed is controlled by adjusting the frequency of the command variable.

A system based on the invention is shown by way of example in Figure 2 embodies a two-phase motor 6. Thus only two electronically produced phases are needed in the main circuit; these are provided by electronic power control units 7 and 8. The control element 9 provides a command variable which determines the phase shift as 90 degrees, and motor speed is controlled by adjusting the frequency of the command variable.

Although the motor is of the two-phase type, the load on the three-phase supply network is symmetricaL This is because each electronically produced phase of the current utilizes all the three phases RST of the supply as can be seen in Fig. 2.

The system of Figure 2 is suitable for the motor of a gearless elevator drive because: a) The two-phase motor is well known and it can be modified to perform like a three-phase motor, and b) Particularly, in the low-speed gearless machinery of the elevator, a three-phase motor in a direct-feeding three-phase supply network cannot be run even in its reserve mode of operation; this is so because the nominal frequency of the motor is in this case much lower than that of the mains supply and, therefore, elevator motors are always special motors, and a three-phase standard offers no advantages.

Fig. 3 illustrates how the control system for a twophase motor can be constructed by using two shunted four-quadrantal six-pulse thyristor connections. This switching can be called a twophase cyclon converter. A three-phase cyclon converter is a known device. The construction shown in Fig. 3 is particularly suitable for fourquadrantal motor operation when it is required that power be also fed back into the supply system when necessary. The electronic power control units 2, 3 and 4 used in three-phase operation are replaced by two four-quadrantal duty braking thyristor units 7 and 8.

CLAIMS:

1. An electric motor control system comprising a two-phase AC motor and an electronic power control circuit, for example in a gearless elevator application, characterised in that the power control circuit includes phase-production connections for two phases, and that a control circuit is programmed to provide a command variable to effect the desired phase shift, and that during braking power is fed back into the supply network.

2. A system according to claim 1, characterised in that the frequency of the supply provided by the power control circuit and thus the speed of the motor is controlled by the command variable.

3. A system substantially as hereinbefore described with reference to Figure 2 or Figures 2 and 3 of the accompanying drawings.

Amendments to the claims have been filed, and have the following effect: *(a) Claims 1 to 3 above have been deleted *(b) New claims have been filed as follows: 1. In a gearless elevator, an electric motor control system comprising a two-phase AC motor and an electronic power control circuit, characterised in that the power control circuit includes phaseproduction connections for two phases, and that a control circuit is programmed to provide a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electric motor control systems This invention is concerned with electric motor control systems more particularly but not exclusively for gearless elevator applications and utilising a two-phase AC motor and electronic power control units. As electronic power control systems are becoming more sophisticated, it is common to accomplish electric motor speed control by using AC motor frequency control. In gearless elevator applications the AC motor is controlled by three electronic power control units, each of which produces an electronic phase for the motor. Operating on the current regulation principle, the control system supplies a pre-determined threephase current in which the phase shift between the different phases is 120 degrees, producing a rotating magnetic field. Motor speed can be controlled by adjusting the frequency of a command variable. The problem associated with existing systems is their complexity and, consequently, high cost. The object of this invention is to eliminate the aforesaid problem by making the motor control system simpler. Characteristic of a system according to the invention is that the main circuit of the unit incorporates two phase-production circuits, and the control circuit is programmed to give the command variable to effect the phase shift, and during braking, power is fed back to the three-phase supply network. In this way, one third of the expensive electronics, including its control system, is rendered unnecessary. Furthermore, in a system according to the invention the frequency of the main circuit current as well as the motor speed can advantageously be controlled by means of the command variable. The invention will now be described by way of example and with reference to the accompanying drawings, in which Fig. 1 shows a block circuit diagram of a conventional motor control system. Fig. 2 shows a block circuit diagram of a motor control system according to the invention, and Fig. 3 shows in more detail the electronic control units forming the electronic power control circuit of the system of Figure 2. Conventionally, as shown in Figure 1, the main circuit of an AC motor consists of three electronic power control circuits 2,3 and 4. Each of these units produces one electronic phase for the poles of the motor 1. The detecting and control element 5 provides a 3-phase command variable for the current, and there is a 120-degree phase shift between the different phases to produce a rotating magnetic field. Motor speed is controlled by adjusting the frequency of the command variable. A system based on the invention is shown by way of example in Figure 2 embodies a two-phase motor 6. Thus only two electronically produced phases are needed in the main circuit; these are provided by electronic power control units 7 and 8. The control element 9 provides a command variable which determines the phase shift as 90 degrees, and motor speed is controlled by adjusting the frequency of the command variable. Although the motor is of the two-phase type, the load on the three-phase supply network is symmetricaL This is because each electronically produced phase of the current utilizes all the three phases RST of the supply as can be seen in Fig. 2. The system of Figure 2 is suitable for the motor of a gearless elevator drive because: a) The two-phase motor is well known and it can be modified to perform like a three-phase motor, and b) Particularly, in the low-speed gearless machinery of the elevator, a three-phase motor in a direct-feeding three-phase supply network cannot be run even in its reserve mode of operation; this is so because the nominal frequency of the motor is in this case much lower than that of the mains supply and, therefore, elevator motors are always special motors, and a three-phase standard offers no advantages. Fig. 3 illustrates how the control system for a twophase motor can be constructed by using two shunted four-quadrantal six-pulse thyristor connections. This switching can be called a twophase cyclon converter. A three-phase cyclon converter is a known device. The construction shown in Fig. 3 is particularly suitable for fourquadrantal motor operation when it is required that power be also fed back into the supply system when necessary. The electronic power control units 2, 3 and 4 used in three-phase operation are replaced by two four-quadrantal duty braking thyristor units 7 and 8. CLAIMS:

Amendments to the claims have been filed, and have the following effect: *(a) Claims 1 to 3 above have been deleted *(b) New claims have been filed as follows:

1. In a gearless elevator, an electric motor control system comprising a two-phase AC motor and an electronic power control circuit, characterised in that the power control circuit includes phaseproduction connections for two phases, and that a control circuit is programmed to provide a command variable to effect the desired phase shift, and that during braking power is fed back into the supply network.