LIMITATION OF THE LOADING OF A POWER SOURCE
Field of the invention
The object of the invention is an arrangement for limiting power as defined in
the preamble of claim 1, an elevator system as defined in the preamble of claim
8, and a method for limiting the input power of a power supply appliance as
defined in the preamble of claim 9.
Prior art
Appliances connected to a power source, from luminaires to electric motors,
have conventionally limited their input power automatically if overloading the
power source.
Modem actively controlled power supply appliances, such as frequency
converters as well as AC/DC voltage sources, load the power source according
to their power requirements. These appliances do not take into account the
overloading of the power source, such as a network voltage or a generator
supply, as a consequence of which the operation of the power source is
jeopardized.
Publication US5861734 presents an arrangement for reducing the harmonics of
the current of a network voltage, in which case the loading of the network is
reduced.
Publication US 2004/0190211 A1 discloses a method, a system and a control
apparatus for detecting a reduction in the voltage / frequency of an electricity
supply network. When detecting a reduction in the voltage / frequency, the load
is disconnected from the electricity network.
Purpose of the invention
The purpose of this invention is to disclose a limitation of the input power of a
power supply appliance on the basis of the status of the power source. It is
endeavored with the limitation of input power to prevent overloading of the
power source and impairment of the operation of the power source as a
consequence of this.
Characteristic features of the invention
The arrangement according to the invention for limiting power is characterized
by what is disclosed in the characterization part of claim 1. The elevator system
according to the invenHon is characterized by what is disclosed in the
characterization part of claim 8. The method for restricting the input power of a
power supply appliance according to the invention is characterized by what is
disclosed in the characterization part of claim 9. Other features of the invention
are characterized by what is disclosed in the other claims. Some inventive
embodiments are also discussed in the descriptive section of the present
application. The inventive content of the application can also be defined
differently than in the claims presented below. The inventive content may also
consist of several separate inventions, especially if the invention is considered
in the light of expressions or implicit sub-tasks or from the point of view of
advantages or categories of advantages achieved. In this case, some of the
attributes contained in the claims below may be superfluous from the point of
view of separate inventive concepts.
The arrangement according to the invention for limiting power comprises a
power supply appliance fitted between the power source and the load to be
supplied, which power supply appliance is fitted to limit its input power on the
basis of the status of the aforementioned power source. The power source used
for the electricity supply according to the invention can be for instance a voltage
source or a current source supplying a direct current or an alternating current.
The power supply appliance can be e.g. an AC/DC transformer, an inverter or a
frequency converter supplying power to a motor. Input power refers in this
context to the power taken from the power source by the power supply
appliance.
In one embodiment of the invention the power supply appliance is fitted to
determine the status of the power source, and also to limit its input power in
stages on the basis of the determined status of the power source.
In one embodiment of the invention the power supply appliance is fitted to
disconnect its power supply if the determined status of the power source so
requires.
In one embodiment of the invention the power source is an alternating voltage
source, and one power supply appliance according to the invention comprises
in this case a determination of the status of the alternating voltage source on
the basis of the supply frequency of the alternating voltage source. In this case
the aforementioned power supply appliance can comprise a measurement of
voltage, in which case the power supply appliance can be fitted to determine the
frequency of the measured voltage e.g. using a phase-locked loop. The power
supply appliance can compare the measured frequency to at least one limit
value for frequency, in which case the power supply appliance can limit its input
power on the basis of the aforementioned comparison of the measured
frequency and the limit value for frequency. The status of the power source
refers to the loading state of the power source.
One power supply appliance according to the invention comprises a
determination of the status of the power source on the basis of the status signal
of the power source. In this case the power source can be fitted to generate a
status signal on the basis of its own status determination, and the power supply
appliance can comprise an input for the status signal of the power source. A
data transfer channel can be arranged between the power source and the
power supply appliance for transferring the status signal from the power source
to the power supply appliance. The aforementioned data transfer channel can
be e.g. a wireline or wireless serial interface bus. The status signal can
comprise e.g. data about the operating status of the power source, such as
information about the magnitude of the output current of the power source, the
supply frequency of the alternating voltage source or the magnitude of the
voltage of the direct voltage source. The power source can also be fitted to
determine its operational condition, and the status signal can in this case
comprise data about the operational condition of the power source. The power
supply appliance can be fitted to limit its input power on the basis of the status
signal.
In one embodimentFof the invention the power source is an alternating voltage
source, and one power supply appliance according to the invention is fitted to
limit its input power on the basis of a reduction of the frequency of the
alternating voltage source.
In one embodiment of the invention the power source is an alternating voltage
source, and one power supply appliance according to the invention is fitted to
limit its input power on the basis of the frequency integral of the alternating
voltage source. The frequency integral refers in this context to the integral of the
deviation between the reference frequency of the supply voltage and the supply
frequency of the power supply appliance.
In one embodiment of the invention the power source comprises a
determination of the status of the power source, and one such power source
according to the invention is fitted to send a status signal indicating the status of
the power source to at least one power supply appliance.
In one embodiment of the invention the power source is an alternating voltage
source, and in this case the status of the alternating voltage source is
determined on the basis of the frequency of the alternating voltage source.
The elevator system according to the invention comprises an arrangement for
limiting power, which arrangement comprises a power supply appliance fitted
between the power supply circuit of the elevator and the power source. The
aforementioned power supply appliance is fitted to limit its input power on the
basis of the status of the aforementioned power source.
In one method according to the invention for limiting the input power of a power
supply appliance the power supply appliance is connected to a power source;
and the input power of the power supply appliance is limited on the basis of the
status of the power source.
In one method according to the invention: the status of the power source is
determined with the power supply appliance; and the input power of the power
supply appliance is limited in stages on the basis of the determined status of the
power source.
In one method according to the invention the power supply of the power supply
appliance is disconnected if the determined status of the power source so
"requires.
In one method according to the invention the power supply appliance is
connected to an alternating voltage source; and the input power of the power
supply appliance is limited on the basis of the supply frequency of the
alternating voltage source.
In one method according to the invention a limit value is set for the supply
frequency of the alternating voltage source; and the input power of the power
supply appliance is limited when the supply frequency of the alternating voltage
source decreases below the aforementioned limit value for supply frequency.
In one embodiment of the invention the power supply appliance is fitted to limit
its input power in stages by reducing in stages the power supplied to at least
one load to be supplied.
Advantages of the invention
With the invention at least one of the following advantages, among others, is
achieved:
- When the power supply appliance presented in the invention is fitted to
limit its input power on the basis of the status of the power source, it is
possible to prevent overloading of the power source, in which case the
operating reliability of the power source improves and e.g. service breaks
caused by overloading decrease.
If the power supply appliance is fitted to determine the status of the
power source, the power supply appliance can be fitted to limit its input
power in stages on the basis of the determined status of the power
source. In this case also the power supply to the load can be continued
at least in a limited manner. Continuation of the power supply at least in
a limited manner is useful e.g. in different regulation processes, as well
as in transport applications and control applications that require above all
continuity from the power source. These kinds of applications are e.g.
transport systems, such as elevator drives, travelator drives, escalator
drives; as well as for instance various lighting, pumping, air-conditioning
and other building automation applications, as well as fan drives. The
invention is particularly well suited for use in applications in which the
supply network is isolated from the national grid. These kinds of
applications can be, in addition to those mentioned above, e.g. railways,
metros, factories, such as pulp mills; as well as different reserve power
drives, in which case the power supply occurs, e.g. during a power
outage, with a generator.
When the power supply appliance is fitted to limit its input power on the
basis of the supply frequency of the alternating voltage source, the
overloading of the alternating voltage source, such as a network voltage
or a generator, can be detected e.g. as a reduction in the supply
frequency, in which case by limiting the input power of the power supply
appliance it is possible to prevent oscillation of the supply frequency of
the network voltage or of the generator caused by overloading.
If the power supply appliance comprises a determination of the status of
the power source on the basis of the status signal of the power source, it
is possible by means of the status signal of the power source to centrally
control the input power of one or more power supply appliances. Since
the power supply appliances do not need in this case to comprise a
determination of the status of the power source, the arrangement is
simplified. If the operation of determined power supply appliances
incorporated in the arrangement is more important than the others, it is
possible to attempt to safeguard the operation of these determined
power supply appliances in a situation of overloading of the power
source by limiting at first the input power of only the less important power
supply appliances.
- If the power supply arrangement comprises two or more power rectifiers
connected to the same DC intermediate circuit, such as inverter
rectifiers, for instance inverters, and if the power supply from the power
source to the DC intermediate circuit occurs centrally with a network
inverter rectifier fitted between the power source and the DC
intermediate circuit, the network inverter rectifier can comprise a
determination of the status of the power source, in which case the
network inverter rectifier can limit the power taken by one or more power
transformers from the DC intermediate circuit on the basis of the status
of the power source.
Presentation of drawings
In the following, the invention will be described in more detail by the aid of a few
examples of its embodiments with reference to the attached drawings, wherein
Fig. 1 presents one arrangement for limiting power according to the
invention
Fig. 2 presents a second arrangement for limiting power according to the
invention
Fig. 3 presents a third arrangement for limiting power according to the
invention
Fig. 4 presents a determination of the input frequency of an alternating
voltage source according to the invention
Fig. 5 presents the limitation of power according to the invention as a
block diagram
Fig. 6 presents an elevator system according to the invention
Fig. 1 presents an arrangement for limiting power. The arrangement comprises
a frequency converter 1 fittea between an alternating voltage source 2 and an
electric motor 3. In the arrangement the supply voltage of the alternating voltage
source 2 is measured 4: In the arrangement the frequency converter 1 also
comprises a determination 5 of the status of the alternating voltage source 2 on
the basis of the measurement 4 of the supply voltage. In this case the frequency
of the supply voltage is determined, and the operating status of the alternating
voltage source is determined on the basis of the frequency. A decrease in the
frequency indicates overloading of the alternating voltage source, so that when
the frequency decreases the frequency converter 1 limits the input power.
Fig. 2 presents a second arrangement for limiting power. In this arrangement a
generator 2 functions as the power source. The status of the generator is
alternatively determined either by measuring the speed of rotation of the
generator with a tachometer 7, or by determining the frequency of the supply
voltage from the measurement 4 of the supply voltage. The generator
comprises a determination 5 of status, and the generator is fitted to send the
determined status signal 6 to at least two power supply appliances 1 connected
to the voltage supply of the generator. The status signal comprises data about
the frequency of the supply voltage of the generator, in which case the
aforementioned power supply appliances 1 limit their input power on the basis
of the signal indicating the frequency of the supply voltage. The status signal
can also comprise a limitation command for the input power, in which case the
aforementioned power supply appliances limit their input power according to the
limitation command. The limitation command can also require from at least one
power supply appliance 1 full disconnection of the power supply.
In the arrangement for limiting power according to Fig. 3, the arrangement
comprises two inverters 9, which independently supply variable frequency and
variable amplitude voltage to the windings of the motors 3. The inverters are
connected to a common DC intermediate circuit 10. Power supply between the
DC intermediate circuit and the network voltage 2 occurs with a network inverter
rectifier 8. The network inverter rectifier 8 measures the network voltage 4, and
deduces from the frequency of the network voltage the status of the network.
When the frequency decreases, the network inverter rectifier 8 limits the power
taken from the DC intermediate circuit by at least the second network inverter
rectifier 9.
Fig. 4 presents the determination of the supply frequency of the alternating
voltage source 2 using a phase-locked loop 11. The measured three-phase
voltages 2 are determined in a d, q coordinate system, which is in itself prior art,
fixed to the phase 16 of the network voltage. In this case the network voltage is
described as two DC voltage magnitudes, Ud and Uq, locked to the phase of
the network voltage. Ud = 0 is made to be the control criterion of the phase-
locked loop. Now it is endeavored to control the phase of the network voltage
with the frequency reference 50 Hz. The comparator 15 measures the deviation
14 of the voltage Ud from zero. From this deviation 14 it is detected whether the
supply voltage of the network deviates from the 50 Hz reference frequency. In
this case the frequency error and at the same time the status of the network
voltage is determined on the basis of the deviation 14. The determination of
supply frequency according to Fig. 4 can be used e.g. in connection with the
embodiment of one of Figs. 1-4.
Fig. 5a presents a power limitation as a block diagram. Figs. 5b and 5c are
present a power limitation described as a function of time. In the phase 17
according to Fig. 5a a fluctuation range 21 is determined for the supply
frequency of the alternating electricity source, within the scope of which the
supply frequency remains during normal operation of the alternating electricity
source. In the phase 18, the supply frequency 22 of the alternating electricity
source is measured, and if the supply frequency drops below the fluctuation
range 21 of normal operation, a transition to phase 19, in which the magnitude
of the reduction in frequency is determined, is made, and in phase 20 the power
23 taken from the alternating electricity source by the power supply appliance is
limited in stages according to the reduction in frequency, in which case the
power 23 taken from the alternating electricity source by the power supply
appliance is reduced as the supply frequency 22 of the alternating electricity
source decreases. The power 23 taken from the alternating electricity source by
the power supply appliance as presented in Fig. 5b is fitted to be reduced
according to the difference 24 between the bottom limit of the fluctuation range
21 of normal operation of the supply frequency and the supply frequency 22 of
the alternating electricity source. The time 30 when the input frequency 22 of
the alternating electricity source drops below the bottom limit of the fluctuation
range 21 of normal operation is marked in Figs. 5b and 5c. The power 23 taken
from the alternating electricity source by the power supply appliance according
to Fig. 5c is fitted to be reduced according to the frequency integral of the
difference 24 between the bottom limit of the fluctuation range 21 of normal
operation of the supply frequency and the supply frequency 22 of the alternating
electricity source. In this case if the deviation of the supply frequency 23 from
the fluctuation range 21 of normal operation continues, the power 23 taken from
the alternating electricity source by the power supply appliance gradually
approaches zero.
Fig. 6 presents an elevator system according to the invention. The elevator car
26 is moved in the elevator shaft via elevator ropes connected to the traction
sheave of the elevator motor 3. Power supply to the elevator motor occurs with
a frequency converter 1 from the three-phase alternating electricity network 2 of
the building. The control 25 of the movement of the elevator integrated into the
frequency converter 1 sets the movement of the elevator car by regulating the
electricity supply of the frequency converter. The control 25 of movement
endeavors to set the movement of the elevator car according to the reference
for determined movement.
The control 25 of the movement of the elevator measures the voltage of the
alternating electricity network 2, and determines the frequency of the network
voltage e.g. with the phase-locked loop according to the embodiment of Fig. 4.
When the frequency drops to below the minimum permitted limit value for the
frequency of the normal operation of the alternating electricity network 2, the
control of the movement starts to limit the power supplied to the elevator motor
3 from the alternating electricity network. In this case the control 25 of
movement calculates the reference for movement of the elevator car 26 again
such that the reference value for the speed and/or the acceleration and/or the
deceleration of the elevator car is reduced. After this the control 25 of
movement endeavors to set the movement of the elevator car according to a
new reference for movement determined for the lower reference value for the
speed and/or the acceleration and/or the deceleration of the elevator car, in
which case the power supplied to the elevator motor 3 from the alternating
electricity network 2 decreases. If the decrease in the supply frequency of the
alternating electricity network 2 continues further or even becomes greater, the
control 25 of the movement of the elevator car in the end disconnects the main
circuit of the frequency converter with the controllable switches 28, in which
case the power supply to the elevator motor disconnects. At the same time the
control 25 of the movement of the elevator car also closes the machinery brake
by disconnecting the power supply of the brake control coils of the machinery
brake with the brake control circuit 27.
The invention is not limited solely to the embodiments described above, but
instead many variations are possible within the scope of the inventive concept
defined by the claims below.
CLAIMS
1. Arrangement for limiting power, which arrangement comprises a power
supply appliance (1) fitted between the power source (2) and the load (3) to be
supplied, characterized in that the power supply appliance (1) is fitted to limit
its input power on the basis of the status of the aforementioned power source
(2)-
2. Arrangement according to claim 1, characterized in that the power supply
appliance (1) is fitted to determine the status of the power source (2), and to
limit its input power in stages on the basis of the determined status of the power
source (2).
3. Arrangement according to claim 1 or 2, characterized in that the power
supply appliance (1) is fitted to disconnect its power supply if the determined
status of the power source (2) so requires.
4. Arrangement according to any of the claims above, characterized in that the
aforementioned power source (2) is an alternating voltage source and in that
the power supply appliance (1) comprises a determination (5) of the status of
the alternating voltage source (2) on the basis of the supply frequency of the
alternating voltage source.
5. Arrangement according to any of the claims above, characterized in that the
power supply appliance (1) comprises a determination of the status of the
power source (2) on the basis of the status signal (6) of the power source.
6. Arrangement according to any of the claims above, characterized in that the
aforementioned power source (2) is an alternating voltage source and in that
the power supply appliance (1) is fitted to limit its input power on the basis of a
reduction of the frequency of the alternating voltage source (2).
7. Arrangement according to any of the claims above, characterized in that the
aforementioned power source (2) is an alternating voltage source and in that
the power supply appliance (1) is fitted to limit its input power on the basis of
frequency integral of the alternating voltage source (2).
8. Elevator system, which comprises an arrangement for limiting power, which
arrangement comprises a power supply appliance fitted between the power
supply circuit of the elevator and the power source, characterized in that the
power supply appliance (1) is fitted to limit its input power on the basis of the
status of the aforementioned power source (2).
9. Method for limiting the input power of a power supply appliance (1),
characterized in that
- a power supply appliance (1) is connected to the power source (2)
- the input power of the power supply appliance (1) is limited on the
basis of the status of the power source (2).
10. Method according to claim 9, characterized in that
- the status of the power source (2) is determined with the power
supply appliance (1)
- the input power of the power supply appliance (1) is limited in
stages on the basis of the determined status of the power source
(2)
11. Method according to claim 9 or 10, characterized in that
- the power supply of the power supply appliance is disconnected if
the determined status of the power source (2) so requires
12. Method according to any of claims 9-11, characterized in that
- the input power of the power supply appliance (1) is limited on the
basis of the supply frequency of the alternating voltage source (2)
13. Method according to claim 12, characterized in that
- a limit value is set for the supply frequency of the alternating
voltage source (2)
- the input power of the power supply appliance (1) is limited when
the supply frequency of the alternating voltage source (2)
decreases below the aforementioned limit value for the supply
frequency.

The invention relates
to an arrangement and a method for
limiting the input power of a power
supply appliance (1 ) fitted between a
power source (2) and a load (3). The
arrangement according to the invention
comprises a power supply appliance
(1 ) fitted between a power source (2)
and the load to be supplied (3), which
power supply appliance (1 ) is fitted
to limit its input power on the basis of
the status of the aforementioned power
source (2).