GB2121557A

GB2121557A - A.C. lift control system

Info

Publication number: GB2121557A
Application number: GB08309316A
Authority: GB
Inventors: Takanobu Hatakeyama; Katsu Komuro; Sadao Hokari; Toshiro Narita; Morio Kanesaki; Yasunori Katayama
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1982-04-07
Filing date: 1983-04-06
Publication date: 1983-12-21
Also published as: GB2121557B; SG26087G; JPS58177864A; KR900008057B1; GB8309316D0; HK63687A; JPS6315231B2; KR840004023A

Abstract

In an AC lift control system in which the voltage and frequency applied from an inverter unit (3) to an induction motor (4) driving a lift car (9) are controlled to control the operation of the car in a normal operation mode, a battery (18) is connected to the DC input terminals of the inverter unit for use in an emergency such as sudden service interruption, and a switching signal generator (16) operating in an emergency operation mode generates a switching signal for controlling the output of the inverter unit (3) in such a manner that the number of switching is smaller than that in the normal operation mode and the duty factor per unit switching is larger than that in the normal operation mode. Therefore, a battery (18) of low voltage and small size can be used. <IMAGE>

Description

SPECIFICATION A.C. elevator control system This invention relates to a system for controlling an AC elevator car driven by an induction motor.

The operation of an elevator car is classified into a normal operation mode and an emergency operation mode. In the normal operation mode, the elevator car is driven under control of a normal-operation control apparatus controlling the acceleration and deceleration of the elevator car in usual manner, while, in the emergency operation mode, the elevator car is driven under control of an emergency-operation control apparatus provided to deal with an emergency such as sudden service interruption.

In an AC elevator system including an elevator car driven by a three-phase induction motor, such a normal-operation control apparatus and such an emergency-operation control apparatus have been separately provided so that the former can be switched over to the latter in the case of an emergency.

An example of an AC elevator control system including the former apparatus is disclosed in U.S. Patent No.3,876,918 (issued April 8, 1975). In the disclosed system, a controller composed of control elements such as thyristors is provided for controlling the elevator car in the normal operation mode so that, depending on the error between the speed command signal and the speed feedback signal, the primary voltage of an induction motor can be controlled when the elevator car is accelerated or running at the rated speed, while the DC braking current supplied to the primary winding of the induction motor can be controlled when the elevator car is decelerated, whereby both of the motoring torque and the DC braking torque can be controlled to satisfactorily control the acceleration and deceleration of the elevator car.

In such an elevator control system, the operation mode is switched over to an emergency operation mode as described below in the case of an emergency, such as sudden service interruption.

(a) An emergency DC power source such as a battery and an inverter unit converting DC power into three-phase AC power are provided so as to drive the induction motor by the inverter unit.

(b) As proposed in British Patent No.2,020,926 (issued August 1982), an emergency DC power source such as a battery and a small-sized DC motor supplied from the DC power source are provided so as to drive the elevator car by the small-sized DC motor.

However, in each of (a) and (b) above described, a battery and an inverter unit or a small-sized DC motor have been required besides the aforementioned normal-operation control apparatus, resulting in a bulky and expensive system.

On the other hand, in the normal operation mode, the induction motor is controlled to operate in the range of large slip during both of acceleration and deceleration. Therefore, a large rotor loss and large power consumption have been inevitable.

A method solving these problems is known from, for example, British Patent No. 2,081,534 (issued February 17, 1982). According to the cited British patent, an inventor unit is used to control an induction motor driving an elevator car. This inverter unit controls the induction motor in such a manner as to maintain constant the relation between the voltage and the frequency applied to the induction motor, as is commonly known. For example, the pulse-width modulation (PWM) control is well known as this type of control. In this case, the induction motor can be controlled to operate in the range of small slip so that efficient operation can be ensured.

Further, since this inverter unit operates with DC power, this DC power can be obtained by converting AC power from an AC power source by a converter in the normal operation mode, while DC power supplied from a DC power source such as a battery can be directly used in the emergency operation mode. That is, in the case of an emergency, the emergency operation can be effected by merely connecting the inverter unit to a DC power source such as a battery.

Also, as is commonly known, the inverter unit which controls the induction motor is primarily designed to operate on the DC voltage provided by rectifying the AC voltage supplied from the AC power source.

Therefore, when the inverter unit is connected to the battery or like DC power source supplying a low DC voltage, the torque generated by the induction motor is inevitably lowered. On the other hand, a torque (an unbalance torque) determined by the difference between this weight of the elevator car and that of the counterweight is imposed as a load of the induction motor, and this load varies greatly depending on the number of passengers in the elevator car. That is, a great unbalance torque is applied in the down direction when the elevator car is fully loaded, while such a torque is applied in the up direction when the number of passengers in the elevator car is small. Therefore, when the torque generated by the induction motor is small, the unbalance torque becomes dominant to such an extent that the control of the elevator car becomes impossible resulting in a great danger.

In order to avoid a dangerous situation as above described, the emergency DC power source such as the battery is required to supply a very high voltage of the value close to that of the DC voltage obtained by rectifying the AC voltage supplied from the AC power source. Because of the above requirement, the increase in the cost and scale has been unavoidable in the prior art control system.

It is therefore a first object of the present invention to provide an AC elevator control system in which an emergency DC power source of a low voltage can be used to simply drive an elevator car in the case of an emergency.

A second object of the present invention is to provide an AC elevator control system which can improve the reliability of the emergency operation.

A third object of the present invention is to provide an AC elevator system which can improve the comfortableness to ride and the accuracy of landing at stopping floors even in the case of an emergency.

It is a first feature of the present invention that, in an AC elevator control system in which the frequency and voltage applied from an inverter unit to an induction motor driving an elevator car are controlled to control the elevator car in the normal operation mode, an emergency DC power source supplies a DC voltage to the inverter unit in an emergency operation mode, and the inverter unit is controlled in the emergency operation mode by such a switching signal that the duty factor, relative to the same frequency, of the output of the inverter unit differs from that in the normal operation mode.

According to a second feature of the present invention, the switching signal applied to the inverter unit in the emergency operation mode is generated from a unit provided separately from the unit generating the switching signal applied to the inverter unit in the normal operation mode.

According to a third feature of the present invention, the emergency-operation switching signal above described is generated in response to the generation of a speed command signal commanding the running speed of the elevator car in the emergency operation mode.

Other objects and features of the present invention will be apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings, in which: Figure 1 to 12 illustrate a preferred embodiment of the present invention wherein: Figure lisa block diagram showing the general structure of the AC elevator control system; Figure 2 is a circuit diagram showing the structure of the main circuit of the inverter unit shown in Figure 1; Figure 3 is a graph showing the relation between the voltage and the frequency applied to the induction motor from the inverter unit; Figure 4 shows the waveform of the output voltage generated from the inverter unit in a high frequency range; Figure 5 shows the waveform of the output voltage generated from the inverter unit in a low frequency range;; Figure 6 shows the torque characteristic of the induction motor controlled by the inverter unit; Figure 7 is a block diagram showing the structure of the normal-operation switching signal generating unit generating the switching signal in the normal operation mode; Figure 8 is a signal waveform diagram for illustrating the operation of various parts of the switching signal generating unit shown in Figure 7; Figure 9 shows the waveform of the output voltage generated from the inverter unit in the normal operation mode; Figure 10 shows the waveform of the output voltage generated from the inverter unit in the emergency operation mode; Figure 11 is a block diagram showing the structure of the emergency-operation switching signal generating unit generating the switching signal in the emergency operation mode; and Figure 12 is a signal waveform diagram for illustrating the operation of various parts of the switching signal generating unit shown in Figure 11, and Figure 13 is a block diagram showing the general structure of another preferred embodiment of the AC elevator control system according to the present invention.

Preferred embodiments of the present invention will now be described in detail with reference to the drawings.

The present invention is applicable to all of the cases in which an elevator car must be driven by DC power supplied from a DC power source since it is no more capable of normal operation under control of an elevator control unit due to occurrence of abnormal situations including sudden service interruption, accidental stoppage of the elevator car between floors for some unidentified reason and operational failure of the elevator control unit. Such abnormal situations are detected by individual abnormality detecting means, and it is apparent that such means are constructed to detect corresponding abnormal conditions respectively. In the following description, preferred embodiments of the present invention are adapted to deal with occurrence of sudden service interruption, by way of example.

Figure lisa block diagram showing the general structure of a preferred embodiment of the AC elevator control system according to the present invention.

Referring to Figure 1, an elevator car 9 and a counterweight 10 are suspended from the both ends respectively of a rope 6 trained around a traction sheave 7. The elevator car 9 is driven by a three-phase AC induction motor 4through an electromagnetic brake 5 and a reduction gearing 6. A service interruption detecting unit 19 detects sudden interruption of AC power supply from a three-phase AC power source 1 functioning as a power source in the normal operation mode. The output signal from this service interruption detecting unit 19 is applied to an elevator sequence controller unit 22 which functions to turn on-off main circuit contacts 20, 21 and control circuit contacts 20a1, 20a2 and 21 a1, 21 a2 depending on the presence or absence of service interruption detected by the service interruption detecting unit 19.

In the normal operation mode, the contacts 20, 20at and 20a2 are in their closed position, while the contacts 21,21 a1 and 21 a2 are in their open position. A converter unit 2 converts the three-phase AC voltage into a DC voltage VDC which is applied to an inverter unit 3. This inverter unit 3 has a known structure as shown in Figure 2 and is composed of transistors Tri to Tr6 and diodes D1 to D6. The transistors Tri to Tre are subject to switching control to convert the DC voltage VDe into a three-phase AC voltage which is applied to the induction motor 4.

In response to the application of an elevator-car operation start signal from the sequence controller unit 22, the electromagnetic brake 5 is released, and a speed commanding unit 13 generates a speed command signal whose level rises with time. The speed command signal from the speed commanding unit 13 is applied to a comparator 14 together with the detected speed signal applied from a tachometer generator 12 coupled to the three-phase induction motor 4 driving the elevator car 9. The comparator 14 compares the detected speed signal with the speed command signal to find the difference or error therebetween, and the error signal is applied from the comparator 14 to a normal-operation switching signal generating unit 15 which generates a switching signal used for the PWM control of the inverter output in the normal operation mode.

This switching signal generating unit 15 is provided for controlling the transistors Tri to Tr6 shown in Figure 2 so that the ratio between the voltage and the frequency applied to the induction motor 4 can be maintained constant. The number of switching and duty factor of the output of the inverter unit 3 are controlled depending on the error between the speed command signal and the detected speed signal.

For the purpose of ensuring efficient operation of the elevator car 9, it is necessary to control the voltage V and frequency f applied to the induction motor 4 so that the ratio V/f therebetween can be maintained constant as shown in Figure 3. Therefore, in a low frequency range in which the period is long, the output of the inverter unit 3 is controlled in a manner as shown in Figure 4. It will be seen in Figure 4 that the number of switching (referred to hereinafter as the number of pulses N) in the half cycle is large, and the duty factor Tp/T of the pulses is small, where T is the half cycle time and Tp is the pulse width. On the contrary, in a high frequency range in which the period is short, the output of the inverter unit 3 is controlled in a manner as shown in Figure 5.It will be seen in Figure 5 that the number of pulses N is small, and the duty factor Tp/T of pulses is large. This manner of control is called the pulse-width modulation (PWM) control. When the voltage applied to the induction motor 4 is controlled in the manner above described, the torque characteristics of the induction motor 4will be as shown in Figure 6. By controlling the speed of the elevator car 9 by driving it by the induction motor 4 having the torque characteristic shown in Figure 6, the elevator car 9 can be efficiently driven since the induction motor 4 operates in the range of small slip.

Figure 7 shows one form of the practical structure of the switching signal generating unit 15. Referring to Figure 7, the switching signal generating unit 15 includes an oscillator 31, a 1/2 frequency divider 32, a sexenary ring counter 33, a PWM signal producing circuit 34, a pulse number changer 35, a differentiator 36, a sawtooth waveform generating circuit 37 and a comparator 38. This switching signal generating unit 15 is constructed so that the number of pulses in the half cycle is changed over between the three values, N1, N2 and 1, depending on the frequency of the output from the inverter unit 3.

Figure 8 shows waveforms appearing from the various parts of the switching signal generating circuit 15 when the number of pulses N1 in Figure 7 is selected to be N1 = 8.

A frequency command signal d2 which is a control input to the switching signal generating unit 15 is provided generally by adding the error between the speed command signal and the speed feedback signal to the speed command signal or the speed feedback signal.

Therefore, the oscillator 31 generates a pulse signal a having a frequency proportional to the frequency command signal d2 as shown in Figure 8. This pulse signal a is applied through the pulse number changer 35 to the differentiator 36 to produce a pulse signal c as shown in Figure 8. The pulse signal c thus obtained is applied to the sawtooth waveform generating circuit 37 to produce a sawtooth pulse signal d, and, then, this pulse signal d1 is compared with the frequency command signal d2 in the comparator 38 to produce a pulse signal e as shown in Figure 8.

In the meantime, the output pulse signal a from the oscillator 31 is applied to the 1/2 frequency divider 32 to produce a pulse signal a1 which is frequency-divided by the factor of 2 as shown in Figure 8, and this pulse signal a1 is applied to the sexenary ring counter 33 to produce pulse signals bo to b5 which are different in phase by 60 from each other.The pulse signals bo to b5 are applied together with the pulse signal e and its inverted signalS to the PWM signal producing circuit 34 which carries out the AND and OR operations on the signals bo to b5, e and e to produce pulse signals g1 = b0 + b1 S + b2 + b4 e, g2 = b2 + bo e + b4 buzz + b3 S, and g3 = bo + b2. e + b4 + b5 S, as shown in Figure 8. These pulse signals g1, g2, g3 and their inverted signals g1, g2r 9 3 (not shown) are used as the switching signals (pulse signals) for the PWM control.

The pulse signals g1 to g3 and g1 to g 3 above described are amplified by a pulse amplifier unit 17 shown in Figure 1. The pulse signals G1 and G1 obtained by amplifying the pulse signals g1 and g, are applied to the bases of the transistors Tri and Tr2 shown in Figure 2 respectively. Similarly, the pulse signals G2 and G2 obtained by amplifying the pulse signals g2 and g2 are applied to the bases of the transistors Tr3 and Tr4 respectively, and the pulse signals G3 and G3 obtained by amplifying the pulse signals g3 and g3 are applied to the bases of the transistors Tr5 and Tr6 respectively. Thus, depending on the error between the speed command signal and the detected speed signal, the frequency is progressively increased to control the motoring torque of the induction motor 4 so as to control the acceleration of the elevator car 9 through the reduction gearing 6, sheave 7 and rope 8.

As soon as the elevator car 9 accelerated in the manner above described reaches a predetermined position short of the floor landing point after having travelled a predetermined distance, a position detector 11 mounted on the elevator car 9 detects the position of the elevator car 9 from the floor landing point and applies a signal indicative of the detected position to the speed commanding unit 13.

The speed commanding unit 13 generates a speed command signal decreasing depending on the position of deceleration of the elevator car 9, and the frequency command signal d2 corresponding to the error between this speed command signal and the speed feedback signal from the tachometer generator 12 is applied to the switching signal generating unit 15 as described with reference to Figure 7.

Therefore, by the function of the switching signal generating unit 15 above described, the frequency is progressively decreased as commanded by the frequency command signal d2 while maintaining constant the relation between the voltage V and the frequency f, and the regenerative braking torque of the induction motor 4 is controlled to control the deceleration of the elevator car 9.

The regenerative power in this case may be returned to the power source or consumed by an external resistor as is customarily done in this field.

As soon as the elevator car 9 being decelerated reaches the floor landing point, a signal indicative of arrival of the elevator car 9 at the floor landing point is applied to the sequence controller unit 22, and a stop signal is generated from the sequence controller unit 22 to activate the electromagnetic brake 5 thereby stopping and holding the elevator car 9 at the target floor.

When service interruption occurs in the AC power source 1 in such an elevator control system, the elevator car 9 is operated in a manner as will be described now.

When service interruption occurs while the elevator car 9 is situated within the door open zone in which the door of the elevator car 9 can be opened because the elevator car 9 is situated at one of the floors, the elevator car 9 is not operated until power supply is restored. On the other hand, only when service interruption occurs while the elevator car 9 is running, and the elevator car 9 is stopped outside of the door open zone, rescue operation is done to avoid confinements of passengers in the elevator car 9. In such a case, it is advantageous from the aspects of economy and safety to run the elevator car 9 at a speed considerably lower than the rated speed.

Referring to Figure 1 again, in the event of occurrence of sudden service interruption in the AC power source 1, the service interruption detecting unit 19 detects occurrence of service interruption and acts to open the contacts 20, 20a1 and 20a2 and close the contacts 21,21awl and 21 a2.

As a consequence, an emergency DC power source 18 such as a battery is connected to the DC input terminals of the inverter unit 3. At the same time, this emergency DC power source 18 is connected to the input terminals of an emergency-operation switching signal generating unit 176, pulse amplifier unit 17, sequence controller unit 22 and service interruption detector unit 19. Thus, the DC power source 18 supplies power now to the individual units, and the emergency-operation switching signal generating circuit 16 operates now in lieu of the normal-operation switching signal generating circuit 15 thereby completing or establishing an emergency operation circuit.

Let fa and Va be the output frequency and output voltage respectively of the inverter unit 3 corresponding to the running speed of the elevator car 9 in the emergency operation mode. Then, the emergency-operation switching signal generating unit 16 is required to generate such pulse signals that the relation Va/fa satisfies the f-V characteristic shown in Figure 3.

Therefore, in order that the power supply voltage Va of the inverter unit 3 in the emergency operation mode can be set to be lower than the power supply voltage Vnj in the normal operation mode, the output voltage of the inverter unit 3 relative to the same frequency is preferably controlled in such a manner that the number of pulses in the normal operation mode is, for example, 9 as shown in Figure 9 and the number of pulses in the emergency operation mode is, for example, 2 as shown in Figure 10, so that the effective voltage is equal in both of these cases.

That is, the number and duty factor of pulses in the output generated from the inverter unit 3 under control of the switching signals applied from the normal-operation and emergency-operation switching signal generating units 15 and 16 are selected to satisfy the following relations: Number of pulses: normal operation > emergency operation Duty factor of pulses: normal operation < emergency operation Further, when the effective output voltage relative to the same frequency is set to be equal in both of these cases, the induction motor 4 generates torques as shown as in Figure 6 thereby satisfactorily driving the elevator car 9 in the emergency operation mode.

Figure 11 shows one form of the practical structure of the emergency-operation switching signal generating unit 16. The emergency-operation switching signal generating unit 16 includes an oscillator 40, a sexenary ring counter 41, a PWM signal producing circuit 42, a differentiator 43, a sawtooth waveform generating circuit 44 and a comparator 45. The operating principle of this unit 16 is substantially the same as that of the normal-operation switching signal generating unit 15 shown in Figure 7.

Figure 12 shows the waveforms appearing from the various parts of the emergency-operation switching signal generating unit 16 when it is adapted to generate two PWM control pulses in the half cycle. Referring to Figures 11 and 12, an emergency-operation speed command signal (frequency signal) k2 for driving the elevator car 9 at a low speed is applied from the sequence controller unit 22 to the oscillator 40, and a pulse signal h having a frequency proportional to that of the speed command signal k2 as shown in Figure 12 is generated from the oscillator 40. This pulse signal h is differentiated by the differentiator 43 to produce a pulse signal j as shown in Figure 12, and this pulse signal j is applied to the sawtooth waveform generating circuit 44 to produce a sawtooth pulse signal k1 as shown in Figure 12.This signal ka is compared with the speed command signal k2 in the comparator 45 to produce a pulse signal e as shown in Figure 12.

In the meantime, the output pulse signal h from the oscillator 40 is applied to the sexenary ring counter 41 to produce pulse signals mO to m5 which are different in phase by 60 from each other. These pulse signals mO to mS are applied together with the pulse signal '0and its inverted signal e to the PWM signal producing circuit 42 which carries out the AND or OR operations on the signals mO to m5,'0 C and C to produce pulse signals q1 = m0 + m1 '0+ m2 + m4 q2 = m2 + m0 "0 C + m4 + m3 '0, and q3 = m0 + m2 '0 + m4 + m5 '0 as shown in Figure 12. These pulse signals q1, q2, q3 and their inverted signals q1, q2, q3 (not shown) are used as the PWM switching signals in the emergency operation mode.

The pulse signals q1 to q3 and q1 to q3 above described are amplified by the pulse amplifier unit 17 shown in Figure 1, and the output pulse signals from the unit 17 are applied to the bases of the transistors Tri to Tr2 respectively in the inverter unit 3 as described already with reference to Figure 7.

In response to the appearance of an emergency-operation starting signal from the sequence controller unit 22, the emergency-operation switching signal generating unit 16 generates the pulse signals corresponding to the running speed of the elevator car 9 in the emergency operation mode, and these pulse signals are applied through the pulse amplifier unit 17 to the inverter unit 3 to drive the elevator car 9.

As soon as the running elevator car 9 reaches the floor landing point, a stop signal is generated from the sequence controller unit 22 to deactivate the inverter unit 3 and activate the electromagnetic brake 5 thereby stopping and holding the elevator car 9 at the target floor.

In the embodiment of the present invention shown in Figure 1, an emergency power source such as a battery is connected, in the case of an emergency such as sudden service interruption, to the DC terminals of the inverter unit provided for the control of the induction motor driving the elevator car in the normal operation mode, and switching signal generating means for the PWM control of the inverter unit in the emergency operation mode is provided separately from the switching signal generating means provided for the PWM control of the inverter unit in the normal operation mode.Further, the switching signals generated from the emergency-operation switching signal generating means are such that, when the frequency applied from the inverter unit to the induction motor is the same for both of the normal and emergency operation modes, the number of pulses in the inverter output is smaller than that generated in the normal operation mode, and the duty factor of the pulses is larger than that of pulses generated in the normal operation mode.

Therefore, the DC power supply voltage of the inverter unit can be reduced in the emergency operation mode.

Therefore, the size and cost of the emergency power source can be greatly reduced to provide an economical AC elevator control system.

Figure 13 shows another embodiment of the present invention in which the speed feedback control is also applied during acceleration and deceleration of the elevator car in the emergency operation mode.

In Figure 13 showing a modification of the AC elevator control system shown in Figure 1, reference numerals 23 and 24 designate an emergency-operation speed commanding unit and a comparator respectively, and the same reference numerals are used to designate the same parts shown in Figure 1.

Since the operation of the system in the normal operation mode is the same as that described with reference to Figure 1, any description thereof is unnecessary.

In the emergency operation mode, the speed commanding unit 23 generates a speed command signal which is a function of time when the elevator car 9 is being accelerated, while it generates a speed command signal which is a function of the position of the elevator car 9 when the elevator car 9 is being decelerated.

The comparator 24 detects the difference or error between the speed command signal from the speed commanding unit 23 and the speed feedback signal from the tachometer generator 12, and the emergency-operation switching signal generating unit 16 generates PWM-control switching signals corresponding to the speed control error detected by the comparator 24 to control the speed of the elevator car 9 in the emergency operation mode.

The embodiment shown in Figure 13 is advantageous in that the capacity of the battery 18 can be further reduced since the current of smaller value flows through the induction motor 4 during acceleration and deceleration of the elevator car 9 in the emergency operation mode.

The second embodiment is further advantageous in that the application of the speed feedback control during acceleration and deceleration of the elevator car 9 can also greatly improve the accuracy of floor landing.

When the elevator car 9 is run at a very low speed, the floor landing error is expected to be unappreciable.

In such a case, therefore, the speed feedback control may not be done, and a speed command signal incresing or decreasing with a substantially constant acceleration or deceleration may be generated to control the inverter unit 3 for suppressing the current flowing through the induction motor 4 thereby reducing the capacity of the battery 18.

In the embodiments shown in Figures 1 and 13, the PWM-control signals are described to include equal pulses having the same pulse width. However, known unequal pulses having different pulse widths may be used in lieu of the equal pulses. In such a case, the waveform of the output voltage of the inverter unit 3 becomes closer to the sinusoidal waveform, and such a waveform provides the advantage that the noise and heat generated from the induction motor 4 can be reduced.

The switching signal generating units 15 and 16 shown in Figures 1 and 13 may be replaced by a microcomputer having both of the normal-operation switching signal generating function and the emergency-operation switching signal generating function, and these functions may be switched over to generate the required switching signals. By the use of such a microcomputer, the system can be made smaller in size, and the switching signals can make more delicate control of the speed of the elevator car.

Further, the normal-operation switching signal generating unit 15 only may be replaced by an elevator-control microcomputer, and the emergency-operation switching signal generating unit 16 may be left to serve exclusively its scheduled function. In such a case, the emergency operation of the system can be reliably performed even when the microcomputer is disabled, and the safety can be more reliably ensured.

It will be understood from the foregoing detailed description of the present invention that, in the case of an emergency such as sudden service interruption of AC power supply from the AC power source, a DC power supply voltage from an emergency DC power source is applied to the inverter unit provided for the control of the elevator car in the normal operation mode, and the inverter unit is controlled by switching signals so that its output includes pulses having a duty factor larger than in the case of the normal operation mode, when the frequency applied to the induction motor from the inverter unit in both of the normal and emergency operation modes is the same. Therefore, the DC power supply voltage to be applied to the inverter unit in the emergency operation mode can be reduced, and the small-capacity and economical DC power source can be used to safely run the AC elevator car in the emergency operation mode. When, for example, a battery is used as this emergency DC power source, the effect becomes more marked considering the fact that the battery must be periodically inspected and replaced.

Claims

1. An AC elevator control system including an AC power source, an induction motor driving an elevator car, an inverter unit receiving DC power obtained by converting the AC power as its input and supplying an output of a variable voltage and a variable frequency to said induction motor, speed commanding means for commanding the speed of said elevator car, speed detecting means for detecting the speed of said elevator car, and normal-operation switching signal generating means for generating a switching signal for controlling the frequency and duty factor of the output of said inverter unit depending on the error between the speed command and the detected speed of said elevator car in a normal operation mode, said AC elevator control system comprising an emergency DC power source, abnormal-condition detecting means for detecting occurrence of an abnormal condition in said AC elevator control system, and emergencyoperation switching signal generating means for generating such a switching signal in an emergency operation mode that the duty factor relative to the same frequency, of the output of said inverter unit in the emergency operation mode differs from that in the normal operation mode, whereby, when occurence of said abnormal condition is detected, said emergency DC power source supplies DC power to the DC input terminals of said inverter unit, and said emergency-operation switching signal generating means controls the output of said inverter unit.

2. An AC elevator control system as claimed in Claim 1, wherein said emergency-operation switching signal generating means generates such a switching signal that, for the same frequency, the number of switching is smaller than that in the normal operation mode, and the duty factor per unit switching is larger than that in the normal operation mode.

3. An AC elevator control system as claimed in Claim 1, wherein said abnormal-condition detecting means includes means for detecting service interruption of said AC power source.

4. An AC elevator control system as claimed in Claim 1, wherein said abnormal-condition detecting means includes means for detecting accidental stoppage of said elevator car between the floors.

5. An AC elevator control system as claimed in Claim 1, wherein said abnormal-condition detecting means includes means for detecting an operational failure of said elevator car.

6. An AC elevator car system as claimed in Claim 1, further comprising emergency-operation speed command generating means, so that said emergency-operation switching signal generating means generates a switching signal corresponding to the speed command generated from said emergencyoperation speed command generating means.

7. An AC elevator control system as claimed in Claim 6, further comprising means for detecting the error between said emergency-operation speed command and said detected speed so that said emergencyoperation switching signal generating means generates a switching signal corresponding to said error.

8. An AC elevator control system as claimed in Claim 6, wherein said emergency-operation speed command is so set that the acceleratoin and deceleration are substantially constant.

9. An AC elevator control system as claimed in Claim 1, wherein said emergency DC power source supplies DC power to other units in addition to said inverter unit.

10. An AC elevator control system as claimed in Claim 1, wherein said emergency-operation switching signal generating means dispose independently of said normal-operation switching signal generating means.

11. An AC elevator control system as claimed in Claim 10, further comprising switch-over means for disconnecting said normal-operation switching signal generating means from said inverter unit when occurrence of said abnormal condition is detected and connecting said emergency-operation switching signal generating means to said inverter unit in an emergency operation mode.

12. An AC elevator control system as claimed in Claim 10, wherein said emergency-operation switching signal in response to a speed command generated from speed command generating means disposed independently of said speed commanding means associated with said normal-operation switching signal generating means.

13. An AC elevator control system as claimed in Claim 1, wherein said AC power source is a three-phase AC power source.

14. An A.C. elevator control system constructed and arranged to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.