Apparatus for controlling an elevator

An elevator control system connected to a source of three-phase alternating current which is rectified by a converter to direct current which is converted to a variable-voltage variable-frequency A.C. voltage which, in turn, drives the elevator hoist motor. A resistor and a switch are connected across the D.C. terminals of the converter. When the motor is operating in the regenerative mode, the switch is closed to permit the regenerated circuit to flow through the resistor which dissipates or consumes the regenerated power. When the regenerated power being consumed by the resistor is detected to exceed a predetermined value, the excess regenerated power is returned to the A.C. source through a regenerative inverter.

BACKGROUND OF THE INVENTION 
The present invention relates to an elevator controlling apparatus which 
employs variable-voltage and variable-frequency control (referred to as 
"VVVF control", hereinafter) and, more particularly, to the handling of 
electric power regenerated by the elevator hoist motor. 
FIG. 4 shows a known apparatus for controlling an elevator. 
Referring to FIG. 4, a converter 1 is constituted by a diode rectifier 
which converts the alternating current from three-phase AC mains R, S, T 
into a direct current. A smoothing capacitor 2 is connected to the DC side 
of the converter 1. A known PWM type inverter 3 is also connected to the 
DC side of the converter 1. The inverter 3 is constituted by a transistor 
3a and a diode 3b in this example such as to convert a constant DC voltage 
into a VVVF AC voltage by pulse-width control. A three-phase induction 
hoist motor 4 is connected to the inverter 3. A hoist 5 is connected to 
the motor 4 through a shaft 4a. A brake 6 is adapted to brake the hoist 5. 
A main rope 7 is passed over the hoist 5. A cage 8 and a counterweight 9 
are respectively connected to opposite ends of the main rope 7. The 
reference numerals 10 and 11 respectively denote a speedometer and a 
current transformer which detects the current flowing through the motor 4. 
A controller 12, to which signals from the speedometer 10 and the current 
transformer 11 are input, controls the voltage and frequency of the output 
of the inverter 3. A resistor 13 is provided to consume electric power 
which is regenerated by the motor 4, while a series-connected switching 
transistor 14 controls the on/off operation of the resistor 13 by either 
blocking or permitting current flow therethrough. A regenerated 
power-detecting means in the form of a voltage detector 15 is adapted to 
detect the voltage across the smoothing capacitor 2 via leads or probes 
15a. The means 15 is actuated when the voltage across the smoothing 
capacitor 2 exceeds a predetermined value such as to make the transistor 
14 conductive, thereby turning on resistor 13. The regenerated power 
detecting means 15 has heretofore been constituted by an overvoltage 
detector which is actuated whenever electric power is regenerated. (An 
apparatus similar to the above-described one has been shown in the 
specification of Japanese Patent Laid-Open No. 163276/1984). 
The operation of the elevator controlling apparatus shown in FIG. 4 will 
now be described. 
Whether an elevator is operating in a powered-running state or in a 
regenerative-running state is decided by the relationship between the 
weight of the cage 8 including passengers, and that of the counterweight 9 
and by the running direction. More specifically, when the cage 8 is raised 
while bearing a load which corresponds to its fixed capacity, the motor 4 
is in the powered-running state. In such as case, the motor 4 is supplied 
with electric power from the converter 1, and there is no possibility of 
the overvoltage detector 15 being actuated. On the other hand, when the 
cage 8 is lowered while bearing a load corresponding to its fixed 
capacity, the motor 4 is in the regenerative state. 
Since the converter 1 is constituted by a diode rectifier, it is not 
possible to return the regenerated power to the power source R, S, T. For 
this reason, when electric power is regenerated, the voltage across the 
smoothing capacitor 2 rises and actuates the overvoltage detector 15 such 
as to make the transistor 14 conductive. When transistor 14 is conductive, 
current flows through the resistor 13 which dissipates or consumes the 
regenerated power. Since the regenerated power is thus consumed or 
absorbed, cage 8 is run at a predetermined speed without any fear of its 
being lowered at an excessive speed. 
However, the resistor 13 is generally installed in a machine room (not 
shown) where the motor 4 and other devices may be housed. As a 
consequence, the heat generated from the resistor 13 undesirably raises 
the temperature of the machine room. When the capacity of the motor 4 is 
relatively small, this heat problem is not extremely serious. However, as 
the speed or carrying capacity of the cage 8 increases, the capacity of 
the motor 4 must be increased. As the rated load or capacity of the motor 
4 is increased, the power regenerated thereby also increases, and the 
generation of heat in the machine room also increases. 
Consequently, the air-cooling capacity required to cool the machine room 
also undesirably increases, which fact disadvantageously involves an 
increase in the consumption of energy in the building as a whole. 
Another known elevator controlling apparatus is shown in FIG. 5. 
In FIG. 5, the same members or portions as those in FIG. 4 are denoted by 
the same reference numerals. A converter 20 is constituted by a thyristor 
rectifier. The converter 20 is fired by a firing circuit 20a. A 
regenerative inverter 21, which is adapted to return the regenerated power 
to the power source R, S, T, is constituted by six thyristors 21t. A 
firing circuit 21a is adapted to fire the regenerative inverter 21. A 
reactor 22 is connected to the DC side of the regenerative inverter 21. 
The reactor 22 is employed to protect the regenerative inverter 21 when 
the converter 20 becomes inoperative as a result of an undesirable 
stoppage of current from the power source R, S, T. An autotransformer 23 
is provided to make reliable the commutation of the regenerative inverter 
21. The voltage of the autotransformer 23 on its regenerative inverter 21 
side is slightly higher than the voltage of the power source R, S, T. 
In the elevator controlling apparatus shown in FIG. 5, the overvoltage 
detector 15 also is not actuated when the motor 4 is in a powered-running 
state, in a manner similar to that of the apparatus shown in FIG. 4. As a 
consequence, the firing circuit 20a actuates the converter 20 such as to 
supply electric power. On the other hand, when the motor 4 is in a 
regenerative state, the overvoltage detector 15 is actuated such as to 
make the firing curcuit 20a inoperative and to cause the firing circuit 
21a to fire the regenerative inverter 21. This firing allows the 
regenerated power to be returned to the power source R, S, T via the 
regenerative inverter 21 and the autotransformer 23. 
In the elevator controlling apparatus shown in FIG. 5, the thyristors 21t 
are required to possess a capacity large enough to return the regenerated 
power to the power source R, S, T, which fact disadvantageously involves 
an increase in cost. 
Another known regenerated power handling apparatus has been disclosed in 
the specification of Japanese Patent Laid-Open No. 154380/1983 (U.S. 
patent application Ser. No. 470,955, filed Mar. 1, 1983). This regenerated 
power handling apparatus is arranged such that, in a first stage of 
regeneration of power, the regenerated power is employed as a power source 
for various controllers of the elevator, and as the regenerated power 
further increases in amount, it is also consumed by a resistor, thereby 
eliminating any need to provide an inverter for regeneration of electric 
power. 
In practice, however, there are cases where it is not possible to use the 
above-described arrangement wherein no power regeneration inverter is 
employed. Therefore, it is not always possible to say that such an 
arrangement is adequate for practical use. 
Further, utilization of regenerated power at a power failure is disclosed 
in the specification of U.K. Patent Application Publication No. GB No. 
2,111,251A (U.S. patent application Ser. No. 440,350, filed Nov. 9, 1982). 
According to the disclosure, at the time of a power failure various 
control circuits for an elevator are driven by the use of regenerated 
power such that the elevator is stopped at the nearest floor. 
In an apparatus having the above-described arrangement, however, the 
regenerated power in a normal operation is handled in a regenerative 
inverter and returned to a power source. In a consequence, this apparatus 
also disadvantageously requires a regenerative inverter which is high in 
cost, such as that described in relation to FIG. 5. 
U.S. Pat. No. 4,503,940, assigned to the assignee of this application, 
disclosed a VVVF elevator control system in which the regenerated power is 
normally returned to the A.C. mains through a regenerative inverter. 
However, when an emergency generator becomes the A.C. source upon failure 
of the main A.C. source, the regenerative inverter is blocked and the 
regenerated power is absorbed or consumed by a resistor. 
As will be understood from the above description, known elevator 
controlling apparatuses have suffered various problems, that is, an 
excessive rise in the temperature in the machine room in the case where 
regenerated power is consumed in a resistor, and an increase in the cost 
because of the regenerative inverter in the case where the regenerated 
power is return to the power source. 
SUMMARY OF THE INVENTION 
In view of the above-described problems of the prior art, it is a primary 
object of the present invention to allow regenerated power to be handled 
with a low-cost apparatus by providing an arrangement wherein a part of 
the regenerated power is consumed in the machine room and the rest is 
returned to the power source. 
To this end, the present invention provides, in an elevator controlling 
apparatus in which an alternating current is converted into a direct 
current which is further converted into a VVVF alternating current for 
controlling the hoist of an elevator, an improvement characterized by 
comprising: a resistor connected to the DC circuit such as to consume any 
electric power regenerated by a hoist motor; and a regenerative inverter 
adapted to return excess regenerated power to the power source when the 
amount of the regenerated power being consumed by the resistor exceeds a 
predetermined value. 
Thus, in the elevator controlling apparatus according to the present 
invention, any regenerated power less than the predetermined value is 
consumed by the resistor, and any regenerated power which exceeds the 
predetermined value is returned to the power source by the regenerative 
inverter.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows the arrangement of the whole of one embodiment of the elevator 
controlling apparatus according to the present invention. As will be clear 
from FIG. 1, this embodiment is arranged as follows. The alternating 
current supplied from the AC power source R, S, T is converted into a 
direct current by the converter 1, and this direct current is further 
converted into an alternating current by the inverter 3 so as to be 
employed to control the hoist motor 4. In this elevator controlling 
apparatus, when the regenerated power detecting means 15 detects the fact 
that the hoist motor 4 is regenerating electric power, the regenerated 
power is supplied to the resistor 13 and consumed thereby; when the amount 
of the power thus consumed exceeds a predetermined value, a consumed power 
detecting means 40 is actuated such as to cause a regenerative inverter 30 
to return the regenerated power to the AC power source R, S, T. 
FIG. 2 is a circuit configuration of the embodiment of the elevator 
controlling apparatus shown in FIG. 1, while FIG. 3 is a flow chart of a 
program employed in the embodiment. 
Referring first to FIG. 2, the same reference numerals as those in FIGS. 4 
and 5 denote the same or corresponding members or portions. The 
regenerative inverter 30 is formed in a three-phase bridge by employing 
six pairs of transistors 30t and diodes 30d, each transistor and its 
associated diode being connected in parallel such as to be opposite to 
each other in polarity. A firing circuit 30a is adapted to fire the 
regenerative inverter 30. A detector 31 detects the current flowing 
through the resistor 13. An input port 32 (referred to as an "I/P", 
hereinafter) is adapted to convert a signal from the detector 31 and a 
signal representing the voltage across the smoothing capacitor 2 into 
respective digital signals. A microcomputer 33 processes signals from the 
I/P 32. The microcomputer 33 is composed of: a central processing unit 33u 
(referred to as a CPU, hereinafter); a random-access memory 33a (referred 
to as a RAM, hereinafter) for storing external data and results of 
calculation; and a read-only memory 33m (referred to as a ROM, 
hereinafter) in which the program shown in FIG. 3 and various reference 
values have been stored. An output port 34 (referred to as an O/P, 
hereinafter) is adapted to actuate the firing circuit 30a in accordance 
with the result of calculation carried out by the microcomputer 33. In 
addition, an O/P 35 is adapted to run on, or render conductive, the 
transistor 14, and operates in a manner similar to that of the O/P 34. 
The operation of this embodiment will now be described with reference to 
FIG. 3. 
(1) Powered-Running Operation: 
When the cage 8 is raised while bearing a load corresponding to its fixed 
capacity, the motor 4 is supplied with electric power from the AC power 
source R, S, T such as to perform a powered running operation. In this 
state, the value detected by the detector 15a is read out in a process 
step 100 shown in FIG. 3, and a comparison is made in a step 101 between 
the value read out and a reference voltage value previously stored in the 
ROM 33m. In such a powered running operation, there is no possibility of 
the value read out from the detector exceeding the reference voltage 
value. Therefore, the answer of the judgment made in the step 101 is "NO", 
and the process proceeds to a step 102. In the step 102, such signals are 
delivered as making both the transistor 14 and the regenerative inverter 
30 nonconductive, and the process then returns to the step 100. As a 
consequence, the electric power is neither consumed by the resistor 13 nor 
returned to the AC power source R, S, T. 
(2) Regenerative-Running Operation: 
When the cage 8 is raised while empty, for example, the motor is the 
regenerative running state (because of the effect of the counterweight). 
More specifically, in such a case, the value detected by the voltage 
detector 15a exceeds the reference voltage value. As a consequence, the 
answer of the judgment made in the step 101 becomes "YES", and the process 
proceeds to a step 103, in which the transistor 14 is made conductive 
through the O/P 35. The transistor 14 being conductive allows the 
regenerated power to be consumed or dissipated by the resistor 13. The 
value detected by the detector 31 is read out in a step 104. Further, a 
comparison is made in a step 105 between the value read out and a 
reference consumed power value previously stored in the ROM 33m. If the 
read-out value is not in excess of the reference consumed power value, the 
answer of the judgment is "NO", and the process returns to the step 100. 
If the reference consumed power value is exceeded, the answer is "YES", 
and the process proceeds to a step 106. In the step 106, a signal is 
delivered through the O/P 34 such that the firing circuit 30a is actuated 
to cause the regenerated inverter 30 to return the regenerated power to 
the power source R, S, T. 
According to the above-described embodiment, since a part of the 
regenerated power is consumed by the resistor 13, the amount of 
regenerated power which is returned to the power source R, S, T is reduced 
correspondingly. This reduction in the amount of the regenerated power 
advantageously decreases the required capacity of a transformer (not 
shown) employed to constitute the power source R, S, T. When the power 
source R, S, T is supplied by a non-utility power generator in particular, 
such as an emergency engine-generator, it is frequently necessary for 
substantially all of the regenerated power to be dissipated or consumed as 
a generator loss, since such a generator generally involves a small loss 
and has a small load connected thereto. For this reason, the rated 
capacity of the generator is determined so that the generator is able to 
absorb the regenerated power, which fact conventionally requires a 
generator which has an otherwise unnecessarily large capacity. According 
to the present invention, however, the regenerated power is consumed by 
the resistor 13; therefore, it is possible to reduce the required capacity 
of the generator and, consequently, to lower the cost. 
Further, since the amount of the regenerated power which is to be converted 
by the regenerative inverter 30 is reduced by an amount corresponding to 
that which is consumed by the resistor 13, the required capacities of the 
transistors 30t and the diodes 30d are also favorably reduced. Also, since 
six pairs of transistors 30t and diodes 30d are employed to constitute the 
regenerative inverter 30, the capacities of all the transistors and diodes 
for six pairs are reduced, so that the degree of reduction in the cost of 
these components is favorably larger than the increase in the cost caused 
by the employment of the resistor 13 and other members. 
Furthermore, since the elevator controlling apparatus shown in FIG. 2 
employs the transistors 30t, the apparatus is advantageously made free 
from any irregularity in the voltage waveform (the phenomenon in which 
notches are formed in the waveform), whereas the conventional apparatus 
(shown in FIG. 5) which employs the thyristors 21t undesirably involves 
such irregularity. 
As has been described above, according to the present invention, in an 
elevator controlling apparatus in which an alternating current is 
converted into a direct current which is further converted into a VVVF 
alternating current for controlling the hoist motor of the elevator, a 
resistor is connected to the DC circuit such that, when the hoist motor 
regenerates electric power, it is consumed by this resistor, and when the 
amount of the regenerated power being consumed by the resistor exceeds a 
predetermined value, a regenerative inverter is actuated such as to return 
the regenerated power to the power source. Therefore, the generation of 
heat by the resistor is advantageously suppressed, and it is consequently 
possible to prevent any abnormal rise in the temperature in the machine 
room. Additionally, it is possible to reduce the required capacity of the 
regenerative inverter by an amount corresponding to the amount of the 
regenerated power which is consumed by the resistor, so that it is 
favorably possible to lower the cost of the apparatus as a whole. 
Random-access memory 33a may be an Intel 2148H, 1024.times.4 Bit Static 
RAM, read-only memory 33m an Intel 2708, 8K(1K.times.8) UV Erasable PROM, 
and central processing unit 33u an Intel 8086, 16 Bit HMOS Microprocessor. 
Because of the 16 Bit CPU 33u, four of the 2148H RAMs and two of the 2708 
ROMs are needed.