RESTRICTION OF OUTPUT OF ELECTRICAL DRIVE AND PROTECTION OF
AN ELEVATOR
Field of the invention
The object of the invention is a method for restricting the output of an electrical
drive as defined in the preamble of claim 1, a protection of an elevator as
defined in the preamble of claim 5, and a method for protecting an elevator as
defined in the preamble of claim 13.
Prior art
In electrical drives the motor current is restricted e.g. by stopping the operation
of the electrical drive in an overcurrent situation. The maximum of the motor
voltage in electrical drives is determined according to the maximum output
voltage of the power supply appliance of the motor, and the ending of the
voltage is seen via the distortion of the output voltage also as distortion of the
motor current, which has caused vibration of the motor and noise problems.
When restricting the current or the voltage of an elevator motor in elevator
drives, the operation of the elevator drive is stopped e.g. on the basis of
overcurrent monitoring or on the basis of speed monitoring. In this case the
speed monitoring is activated when the reference value of the speed of the
elevator car and the speed measurement differ from each other e.g. by five
percentage points.
Purpose of the invention
The purpose of this invention is to disclose a restriction of the output of an
electrical drive as well as a protection of an elevator integrated into the
restriction of the output of an electrical drive. As presented in the invention, the
operation of the electrical drive, such as of an elevator drive, continues in a
controlled manner if the current or the voltage of the elevator motor is restricted.

As further presented in the invention, restriction of the current or of the voltage
does not cause distortion of the motor current.
Characteristic features of the invention
The method for restricting the output of an electrical drive according to the
invention is characterized by what is disclosed in the characterization part of
claim 1. The protection of an elevator according to the invention is characterized
by what is disclosed in the characterization part of claim 5. The method
according to the invention for protecting an elevator is characterized by what is
disclosed in the characterization part of claim 13. 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.
In the protection of an elevator according to the invention the elevator
comprises a machinery brake, a safety brake of the eievator car, and an
electrical drive, which electrical drive comprises an elevator motor and also a
power supply appliance of the elevator motor. The protection of an elevator
comprises: a determination of the limit value for the stator voltage and/or the
stator current of the elevator motor; a restriction of the output of the electrical
drive, in which the output of the electrical drive is restricted on the basis of the
limit value for the stator voltage and/or stator current; at least one determination
of the limit value for permitted movement of the eievaior car; and aiso a
restriction of the movement of the elevator car, in which the movement of the
elevator car is restricted on the basis of at least one determined limit value for
permitted movement. At least one limit value for permitted movement of the

elevator car is determined at least partly on the basis of the limit value for the
stator voltage and/or the stator current of the elevator motor, and the elevator
car is fitted to move with a restricted movement during the aforementioned
restriction of the movement of the elevator car.
In the method for protecting an elevator according to the invention: an electrical
drive is fitted into the elevator, to which electrical drive an elevator motor and a
power supply appliance of the elevator motor is fitted; a machinery brake and
also a safety brake of the elevator car is fitted to the elevator; a limit value for
the stator voltage and/or the stator current is determined; the output of the
electrical drive is restricted on the basis of the limit value for the stator voltage
and/or the stator current; and also a limit value for the permitted movement of
the elevator car is determined; and the movement of the elevator car is
restricted on the basis of the limit value for permitted movement; at least one
limit value for the permitted movement of the elevator car is determined at least
partly on the basis of the limit value for the stator voltage and/or the stator
current of the elevator motor; and the elevator car is moved with a restricted
movement during the aforementioned restriction of movement of the elevator
car.
In one method according to the invention for restricting the output of an
electrical drive the electrical drive comprises a motor and the power supply
appliance of the motor. In the method according to the invention an unlimited
stator voltage vector is determined; the length of the unlimited stator voltage
vector is determined, and when the length exceeds the determined limit value
for voltage, the length of the stator voltage vector is restricted essentially to its
aforementioned limit value restricting only that component of the stator voltage
which is perpendicular with respect to the rotor flux. Motor in this context refers
generally to a polyphase alternating current motor, such as a synchronous
motor. Power supply appliance of a motor in this context refers generally to an
appliance with which the output of the motor can be controlled. This kind of
appliance can be e.g. a frequency converter. Stator voltage vector refers
generally to the stator voltage of the motor or to the reference value for voltage,

which can be described in vector format. Unlimited stator voltage vector or
stator current vector refers the stator voltage or the stator current set by the
control of the motor according to its control principle or to reference value for
the stator current or stator voltage, which is thus not limited with the restriction
principle according to the invention.
In one method according to the invention an unlimited stator voltage vector is
determined in the d, q coordinate system fixed to the rotor; the length of the
unlimited stator voltage vector is determined, and when the length exceeds the
determined limit value for voltage, the length of the stator voltage vector is
restricted essentially to its aforementioned limit value restricting only the
component that is in the direction of the q axis of the stator voltage. Determining
the voltage vector and the current vector in the d, q coordinate system fixed to
the rotor refers to describing the vector components in the moving coordinate
system of the rotor, which is in itself prior art. Here the d axis of the coordinate
system is determined as the direction of the magnetic flux of the rotor and the q
axis is defined as perpendicular with respect to the magnetic flux of the rotor, in
which case the q axis can also be called the torque axis. The q axis is in this
case also parallel with its source voltage, which as the rotor moves is induced
by the magnetic field produced by the rotor magnetization. When the voltage
vector and the current vector A are restricted essentially to their limit value
restricting only the component Aq in the direction of the q axis of the vector, the
total length |A| of the vector is calculated from the component Ad in the direction
of the d axis as well as from the component Aq in the direction of the q axis with
the equation:

and if the total length |A| exceeds the limit value, the component Aq in the
direction of the q axis is reduced such that the total length |A| of the vector
remains essentially at the magnitude of the aforementioned limit value. The
aforementioned voltage vector or current vector can also be fixed to the stator
coordinate system, in which case the position of the voltage vector or current

vector is however determined in the same way on the basis of the position of
the magnetic flux of the rotor, and restriction occurs in the same way
perpendicularly with respect to the magnetic flux of the rotor.
In one embodiment of the invention the aforementioned limit value Ullimt of
voltage is selected by means of the intermediate circuit voltage Ud of the power
supply appliance of the motor according to the equation presented:

In one method according to the invention after the component in the direction of
the q axis of the limited stator voltage is reduced to zero, the length of the stator
voltage vector is restricted to essentially its limit value restricting only the
component in the direction of the d axis of the stator voltage. Limited stator
voltage refers to the reference value of the stator voltage or of the voltage,
which is limited with the restriction principle according to the invention.
In one method according to the invention an unlimited stator current vector is
determined in the d, q coordinate system fixed to the rotor; the length of the
unlimited stator current vector is determined, and when the length exceeds the
determined limit value for current, the length of the stator current vector is
restricted essentially to its aforementioned limit value restricting only the
component that is in the direction of the q axis of the stator current.
In one protection of an elevator according to the invention determination of the
limit values comprises the determination of at least one limit value for the output
of the electrical drive, and in the same connection the determination of at least
one limit value for the permitted movement of the elevator car. The limit value
for permitted movement refers to the limit value of permitted movement of some
movement parameter of the elevator car, such as the limit value for the position,
speed or acceleration of the elevator car.

The limit values for the output of one electrical drive according to the invention
comprise the limit value for the length of the stator voltage vector, which limit
value is determined using at least one of the following determination criteria:
on the basis of the machinery parameters of the motor
on the basis of the appliance parameters of the power supply
appliance of the motor
on the basis of the determination of the network voltage or of the
intermediate circuit voltage
on the basis of the determination of the speed of the motor
on the basis of the determination of the speed of the elevator car
The machinery parameters of the motor refer here to the motor-specific
parameters that can generally be measured from a motor, such as the stator
resistance, rated output, rated current, rated voltage, rated speed or reactance
at the rated speed, or the source voltage. The appliance parameters of the
power supply appliance of the motor refer generally to the parameters
expressing the accuracy of the capacity or power control of the power supply
appliance, such as the current endurance or voltage endurance of power
semiconductors, the switching losses or line losses of power semiconductors,
the warm-up time constants of the power supply appliance, the accuracy of
setting the current or the voltage, or distortion of the set current or set voltage of
the power supply appliance. Network voltage refers to the voltage of the supply
network of the elevator system. Intermediate circuit voltage refers to e.g. the
voltage of the intermediate circuit of the frequency converter. The determination
of the network voltage or of the intermediate circuit voltage refers to, for
instance, the computational estimation of the voltages or the measurement of
the voltages with some voltage measurement according to prior art. The
intermediate circuit voltage can also in some cases be estimated on the basis of
the measurement of the network current, or wee versa. Determination of the
speed of the motor refers to estimation of the speed of the motor e.g. on the

basis of an estimate of the source voltage of the motor, or if a synchronous
motor is in question the speed of the motor can also be estimated e.g. on the
basis of the current of the motor or the supply frequency of the voltage.
Furthermore the speed of the motor can be measured e.g. by means of a
tachometer or pulse encoder installed with tractive friction onto the rotating shaft
of the motor or onto the frame of the motor. The speed of the elevator car can
be determined e.g. by means of a tachometer or a pulse encoder installed
between the guide rail of the elevator car and the elevator car, or e.g. by means
of a tachometer or a pulse encoder fitted in connection with the rope pulley of
the overspeed governor.
The limit values for the output of one electrical drive according to the invention
comprise the limit value for the length of the stator current vector of the motor,
which limit value is determined using at least one of the following determination
criteria:
on the basis of the machinery parameters of the motor
on the basis of the appliance parameters of the power supply
appliance of the motor
on the basis of the determination of the imbalance of the loading of
the elevator
on the basis of the determination of the temperature of the motor or
of the power supply appliance of the motor
on the basis of the determination of the temperature of the elevator
shaft
The determination of imbalance of the loading of the elevator refers e.g. to
measuring the load of the elevator car with some prior-art ioad weighing sensor
fitted in connection with the elevator car or with the roping of the elevator car, in
which case the imbalance can be evaluated by means of both the
aforementioned measurement of the loading of the elevator car and by means

of the masses of the elevator car and the counterweight. The elevator according
to the invention can however also be one without counterweight. The imbalance
of the loading of the elevator can also be evaluated e.g. by determining the
motor current or the motor torque, or the reference value of current or torque,
that is needed to keep the elevator car in its position with the machinery brake
open. The temperature of the motor or of the power supply appliance of the
motor can be determined e.g. by calculation on the basis of the motor currents,
or temperature sensors can be installed in the elevator motor or in the power
supply appliance. In this case the temperature sensor can be fitted e.g. onto the
stator of the elevator motor or onto the heat sink of the power semiconductors
of the power supply appliance of the motor. The temperature of the elevator
shaft can be determined e.g. by installing a temperature sensor in the elevator
shaft.
In one protection of the elevator according to the invention at least one limit
value for permitted movement of the elevator car is determined at least partly on
the basis of at least one determined limit value for the output of the electrical
drive. If, for example, the limit value of the stator voltage or the current of the
motor is changed for some reason, such as e.g. when the network voltage
decreases or the temperature of the motor increases, it is possible to determine
a change in the permitted movement of the elevator car corresponding to the
change in the limit value of the stator current or the stator voltage.
In one protection of an elevator according to invention at least one limit value for
permitted movement of the elevator car is determined at least partly on the
basis of the determination of imbalance of the loading of the elevator.
One protection of an elevator according to the invention comprises a
determination of the movement of the elevator car. The restriction of movement
of the elevator car is in this case fitted to compare the determined value of the
movement of the elevator car to the limit values for permitted movement of the
elevator car and when the determined value of movement of the elevator car
deviates outside the range defined by the limit values for permitted movement,

the protection of the elevator is fitted to activate the emergency stop. In this
case it is also possible to activate emergency stops of different levels according
to the severity of the problem detected. In one embodiment of the invention in
this case at least the machinery brake and possibly also the safety brake of the
elevator car is activated and also at the same time the power supply to the
motor is prevented e.g. by opening the main circuit of the power supply
appliance of the motor or by otherwise preventing the operation of the power
supply appliance such as by disconnecting the control of the controllable
switches of the power supply appliance. Activation of the machinery brake or of
the safety brake of the elevator car means in this context controlling them into a
braking state. In another embodiment of the invention it is also possible to
perform an emergency stop by controlling the elevator car to stop with the
electrical drive in a situation where a detected problem does not require
stopping the elevator car with a mechanical brake.
In one protection of the elevator according to the invention the limit values for
permitted movement of the elevator car comprise first limit values, with which a
first range of permitted movement is set, as well as second limit values, with
which a second range of permitted movement is set. The second range of
permitted movement is in this case defined to be closer to the extreme limits of
safe movement in the elevator shaft than the first range of permitted movement.
When the determined value of movement of the elevator car deviates outside
the first range of permitted movement, the protection of the elevator is fitted to
activate the machinery brake, and when the determined value of movement of
the elevator car further deviates outside the second range of permitted
movement, the protection of the elevator is fitted to activate the safety brake of
the elevator car.
In one method according to the invention the limit values, with their
determination criteria, for the output of the electrical drive are determined, and
also at least one limit value for permitted movement of the elevator car is
determined at least partly on the basis of at least one limit value for the output
of the electrical drive.

In one method according to the invention at least one limit value for permitted
movement of the elevator car is determined at least partly on the basis of the
determination of imbalance of the loading of the elevator.
In one method according to the invention the movement of the elevator car is
determined; the movement of the elevator car is compared to the limit values for
permitted movement of the elevator car and when the determined value
deviates outside the range defined by the limit values for permitted movement,
the emergency stop is activated.
In one method or protection according to the invention at least one
aforementioned limit value is formed from a plurality of instantaneous limit
values that are consecutive to each other or can be described as a continuous
limit value curve in relation to time.
In the method or the protection according to the invention the aforementioned
electrical drive can also be intended to move the transport appliance of a
transport system. A transport appliance refers in this context to a part of a
transport system, which is used to move passengers or goods. This kind of
transport system can be, for instance, an elevator system, an escalator system,
a travelator system or a crane system.
One motor according to the invention is a synchronous motor, such as a
permanent-magnet motor.
Movement of the elevator car refers to e.g. a change in the location of the
elevator car, the speed of the elevator car, the acceleration of the elevator car
and the deceleration of the elevator car.
Advantages of the invention
With the invention at least one of the following advantages is achieved:
- When the output of the electrical drive is restricted as presented in the
invention, the voltage or the current of the motor does not distort, in

which case the torque of the motor does not distort either, and in this
case it is possible to avoid the noise problems and vibration problems of
prior art.
- When the limit values for the output of the electrical drive are determined
on the basis of the machinery parameters or of the appliance parameters
of the power supply appliance of the motor, it is possible to prevent
overloading of the motor or of the power supply appliance and at the
same time to ensure that the operation of the electrical drive continues in
a controlled manner.
- When the limit value for the length of the stator voltage vector is
determined on the basis of the movement of the elevator car or, for
instance, on the basis of the speed of the elevator motor, it is possible to
restrict movement of the elevator car to a safe range of movement. If a
limit value is determined on the basis of a comparison of the speed of the
motor and the movement of the elevator car, it is possible to determine a
limit value on the basis of a determination of movement that is doubly
verified, which improves the reliability of the determination of the limit
value.
- When the limit value for the length of the stator voltage vector is
determined on the basis of the determination of the network voltage or of
the intermediate circuit voltage of the power supply appliance, it is
possible to prevent distortion of the output voltage of the power supply
appliance e.g. when the network voltage decreases.
- When the limit value for the length of the stator current vector of the
motor is determined based on the imbalance of the loading of the
elevator, the limit value can be reduced e.g. with a balancing load of the
elevator.
- When the limit value for the length of the stator current vector is
determined on the basis of the determination of the temperature of the

motor or of the power supply appliance of the motor, the aforementioned
limit value can be reduced e.g. in a situation in which the temperature of
the motor or of the power supply appliance rises. On the basis of the
reduction of the limit value for the length of the stator current vector
based on the temperature of the motor, it is possible in this case to
prevent overloading of the motor or of the power supply appliance.
- When the limit value for the permitted movement of the elevator car is
determined on the basis of a determined limit value for the output of the
electrical drive, it is possible to ensure that the movement of the elevator
car continues in a controlled manner also when restricting the output of
the electrical drive. The permitted movement of the elevator car can be
restricted according to the operating situation determined by the
restriction of the voltage or of the current of the elevator motor, in which
case e.g. when the current or the voltage is restricting movement of the
elevator motor in the heavy load direction, deceleration of the movement
of the elevator car can be permitted by setting the range of permitted
movement of the elevator car to cover the aforementioned lower speed
range.
When the limit value for permitted movement of the elevator car is
determined also on the basis of the determination of imbalance of the
loading of the elevator, the accuracy of the determination of the limit
value for permitted movement can be improved in a situation in which the
output of the electrical drive is restricted. In addition the heavy loading
drive direction of the movement of the elevator motor can be determined
from the imbalance of the loading, and the information can be used in the
determination of the limit values for permitted movement.
When the limit values for the permitted movement of the elevator car are
determined on the basis of the output of the electrical drive as presented
in the invention, it is possible to accurately determine the safe movement
of the elevator car in different operating situations of the electrical drive.

The limit values for permitted movement can comprise a number of limit
values, which determine the distance of the permitted movement of the
elevator car to the extreme limits for safe movement in the elevator shaft.
If for example the elevator car arrives in the proximity of the end zone of
the elevator shaft, the protection of the elevator can activate emergency
stops of different levels based on different exceedances of the limit
values for permitted movement. Depending on the limit values for
permitted movement and on the position of the elevator car in the
elevator shaft, the protection of the elevator can activate an emergency
stop, in which case the elevator car is stopped with a deceleration ramp
under the control of the electrical drive; the protection can also activate
the machinery brake to stop the elevator car, or when the movement of
the elevator car continues further towards the extreme limits for safe
movement, the protection can activate the safety brake of the elevator
car, such as the wedge brake or the guide rail brake. When the output of
the electrical drive is restricted during a run of the elevator and the speed
of the elevator car in this case changes, the protection of the elevator
can activate different levels of emergency stops when the speed of the
elevator car decreases or increases outside the different ranges of
permitted movement. Likewise when the output of an electrical drive is
restricted the limit values of permitted movement can be changed during
the run e.g. such that deceleration of the speed of the elevator car is
permitted, in which case the elevator does not necessarily make an
emergency stop when the speed decelerates but instead drives normally,
which improves the service of the elevator.
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 an elevator system according to the invention

Fig. 2 presents a determination of the limit values according to the
invention
Fig. 3 presents a restriction of movement according to the invention
Fig. 4 presents the stator voltage defined in a system of d, q coordinates
Fig. 5 presents the stator current defined in a system of d, q coordinates
Fig. 6 presents the determined speed of the elevator car and also the limit
values for permitted movement when restricting the output of the
electrical drive
Fig. 7 presents the determined speed of the elevator car and also the limit
values for permitted movement when restricting the output of the
electrical drive
Fig. 8 presents the determined speed of the elevator car and also the
determination criteria of the limit value for permitted movement
Fig. 1 presents an elevator system in which a protection of the elevator
according to the invention can be fitted. The elevator motor 3 is here a three-
phase synchronous motor, the rotor of which comprises permanent magnets.
Power is supplied to the elevator motor 3 with a frequency converter 2 from a
network supply 6. The elevator motor moves the elevator car 10 and the
counterweight 11 in the elevator shaft via elevator ropes connected
mechanically to the traction sheave of the elevator motor 3. The control 4 of the
frequency converter sets the speed of the elevator motor by means of the
speed measurement 5 of the motor and/or by means of the speed
measurement 9 of the elevator car. The speed of the motor is measured with a
motor encoder 5 fitted with tractive friction to the rim of the traction sheave, and
the speed of the elevator car is measured with a car encoder 9 connected to the

guide rail of the elevator car. The loading of the elevator car can be measured
with the load weighing device sensors 36 of the car. The movement of the
elevator car can, if necessary, be stopped with the machinery brake 7
connected to the traction sheave or with the guide rail brake connected to the
guide rail of the elevator car. Limit values for permitted movement are
determined in the elevator shaft e.g. in the proximity 12 of the landings, and
also in the proximity 13, 14 of the ends of the elevator shaft.
Fig. 2 presents a determination 15 of the limit values according to the invention.
The aforementioned determination of the limit values comprises the
determination 16 of the limit values for the output of the electrical drive, as well
as the determination 17 of the limit values for the permitted movement of the
elevator car derived from this. The determination 15 of the limit values
determines the limit values of the output 1 of the output of the electrical drive
and also the limit values of the restriction 18 of movement of the elevator car. If
the limit values for the output of the electrical drive are changed, the limit values
for the permitted movement of the elevator car also change correspondingly.
For example when the network supply voltage 6 decreases the limit value 27 for
the stator voltage of the motor is reduced correspondingly, in which case
distortion of the supply voltage of the motor is prevented, and at the same time
noise and vibration problems resulting from this are prevented. In this case
when the network voltage 6 decreases the drive quality of the elevator remains
good, even though the speed of the elevator car in the heavy load drive
direction decelerates. When the limit values for permitted movement of the
elevator car are changed correspondingly to the change in the limit value for the
stator voltage, the range of permitted movement for smaller speeds is
expanded, in which case it is possible to drive in a controlled manner with the
elevator also when the speed is restricted in the drive direction of heavy loading
owing to the restriction of stator voltage. Correspondingly, if the limit value 28
for stator current is reduced e.g. as a result of warming of the motor, the limit
value for permitted movement is changed according to the change in the limit
value for the stator current.

Fig. 3 presents a restriction of movement according to the invention. The
restriction of movement here comprises an unintended movement governor 18,
which is formed from an electrical unintended movement governor circuit. The
unintended movement governor 18 restricts the movement of the elevator car
according to the set limit values 15 for permitted movement. The unintended
movement governor 18 reads the movement signal of the elevator car 10 from
the car encoder 9 and also the movement signal of the elevator motor from the
motor encoder 5. These encoders give a pulse-shaped signal at constant angle
intervals as the encoder rotates. The unintended movement governor 18
compares the movement signal of the car encoder that it reads to the
movement signal of the motor encoder. In this case it is possible with the
comparison of the movement signals to detect e.g. slipping of the ropes of the
elevator car on the traction sheave, or a breakage of the ropes. A confirmed
speed signal is obtained as the result of the comparison of the movement
signals. The unintended movement governor 18 also determines the position of
the elevator car in the elevator shaft by integrating the pulses of the car encoder
9. The determined position data is corrected on the basis of the position data of
the position sensors of the floor level. The unintended movement governor 18
compares the confirmed movement signal to the limit values 13,14,30,31,32 for
permitted movement of the elevator car and when the movement of the elevator
car deviates outside the range defined by the limit values for permitted
movement, the unintended movement governor aciivates emergency stops of
different levels. If, on the basis of the determination of position, the elevator car
is positioned in the middle of the elevator shaft, the unintended movement
governor sends to the frequency converter 2 a control command, on the basis
of which the frequency converter stops the elevator car in a controlled manner
with a deceleration ramp. If, on the basis of the determination of the position,
the elevator car is positioned in the proximity of the end zone of the elevator
shaft, when the distance from the end decreases to the first limit value 13 the
unintended movement governor controls the machinery brake 7 by opening the
coil of the machinery brake with the safety circuit-breaker 37 of the power
supply circuit and additionally disconnects the three-phase power supply circuit

of the frequency converter 2 at all poles with a similar safety circuit-breaker 37.
Safety circuit-breaker refers here to a controllable circuit-breaker, which
disconnects the power supply circuit at all poles but at least at two different
points. Disconnection of the three-phase supply at all poles however requires
three disconnector switches. This kind of safety circuit-breaker can comprise
e.g. at least two controllable mechanical switches connected in series, or it can
also comprise at least two corresponding semiconductor switches integrated
into the power supply circuit to be disconnected. If despite the engagement of
the machinery brake the elevator car further continues its journey towards the
end of the elevator shaft, when the distance of the elevator car from the end
decreases to the second limit value 14, the unintended movement governor 18
controls in addition the guide rail brake 8 of the elevator car by disconnecting
the power supply circuit of the coil of the guide rail brake with the safety circuit-
breaker 37.
Fig. 4 presents the stator voltage determined in the d, q coordinate system fixed
to the rotor. The axis of magnetization of the rotor is in the direction of the d
axis. In this case the source voltage 22 of the motor is in the direction of the q
axis. Since in this embodiment of the invention the stator current is in the
direction of the q axis lq, the component 20 of the stator voltage in the direction
of the q axis is formed from the source voltage 22 as well as from the voltage
dissipation R*lq 23 of the stator resistance. The component 21 of stator voltage
in the direction of the d axis is the control voltage w*L*lq needed to rotate the
current vector of the stator, where w is the speed of rotation of the current
vector of the stator and L is the inductance of the stator winding. The stator
voltage 19 is determined as the resultant of the components that are in the
direction of the d and q axes.
When the frequency converter 2 sets the stator voltage for setting the speed of
the elevator motor 3, the stator voltage begins to distort e.g. when the network
voltage 6 decreases. The aforementioned distortion is prevented by restricting
the stator voltage to the set limit value. The length of the stator voltage vector
19 is measured, and the component 20 of the stator voltage in the direction of

the d axis is restricted according to the limit value. At the same time the
component 21 of the stator voltage in the direction of the d axis is permitted to
change feely on the basis of the criteria for setting the speed of the motor. The
limit value for the length of the stator voltage is in this case determined on the
basis of the measurement of the intermediate circuit voltage of the frequency
converter. Since the changeover switches of the frequency converter fitted to
the supply of the motor connect the windings of the motor between the voltage
potentials of the positive and the negative intermediate circuit busbar of the
frequency converter, when the intermediate circuit voltage decreases also the
voltage range of the stator voltage of the motor decreases. The limit value for
the length of the stator voltage vector 19 is in this case determined to
correspond to the maximum undistorted stator voltage.
Fig. 5 presents the stator current 24 of the motor determined in the d, q
coordinate system. In this embodiment of the invention the stator current
comprises, in addition to the component 25 in the direction of the q axis, also a
component 26 in the direction of the d axis, which is of the opposite direction to
the rotor magnetization and thus weakens the rotor magnetization. In
permanent-magnet motors this component 26 in the direction of the d axis is
often set at zero, and thus permanent-magnet motors are not used in this kind
of field weakening state. In a field weakening state the output voltage 22 of the
motor weakens and in this case the stator voltage 19 needed also often
decreases, in which case the possible operating speed range of the motor
increases. The stator current is restricted to the set limit value 28. By reading
the temperature sensors fitted to the stator of the motor the temperature of the
motor is determined and when the temperature increases, the limit value 28 for
the length of the stator current vector 24 is reduced. The length of the stator
current vector is determined, and when the length exceeds the determined limit
value the stator current vector is restricted to the limit value by restricting only
the component 25 of the current in the direction of the q axis.
Fig. 6 presents the determined speed 29 of the elevator car and also the limit
values 30 for permitted movement as a function of the position of the elevator

car in the elevator shaft s when restricting the output of the electrical drive at the
time 39, when the elevator is driving in the direction of heavy loading of the
elevator motor. At the time 39 the output of the electrical drive is restricted e.g.
as result of a reduction in the network voltage 6 or of wanning of the motor 3. In
this case correspondingly the limit value 27, 28 for the output of the electrical
drive changes, and the limit value 30 for permitted speed of the elevator car
also changes on the basis of the change in the limit value 27, 28 for the output
of the electrical drive. As a result of the restriction of the output of the electrical
drive, the determined speed 29 of the elevator car also starts to decrease. The
elevator can in this case, however, continue its run in a controlled manner
because the reduction of the limit value for permitted speed allows deceleration
of the speed of the elevator car. At the time 38 however the speed of the
elevator car decreases further below the lowermost limit value 30 for permitted
speed, and the unintended movement governor 18 in this case stops the
elevator by controlling the machinery brake 7 and also by disconnecting the
power supply circuit of the frequency converter 2.
Fig. 7 further presents the determined value 29 of the speed of the elevator car
and also the limit values 30, 31, 32 for permitted speed as a function of the
position of the elevator car in the elevator shaft s when restricting the movement
of the elevator car. In this embodiment of the invention the limit values for
permitted speed determine three different ranges of permitted speed. The limit
values 31 and 32 determine two different ranges for the maximum permitted
speed of the elevator car. At the time 39 the limit values 27, 28 for the output of
the electrical drive change and the limit values for permitted speed are changed
based on the change in the limit values for the output of the electrical drive. The
determined speed 29 of the elevator car decelerates, and the ranges of
permitted speed change correspondingly, in which case the movement of the
elevator car is controlled and the overspeed governor 18 reacts quickly to
changes in the speed of the elevator car. When the elevator car approaches the
terminal floor the motor 3 starts to decelerate the speed of the elevator car with
the control of the frequency converter 2. Also the limit values for permitted

speed decrease towards the terminal floor. If the speed of the elevator car does
not in this case decelerate sufficiently, when the speed exceeds the first limit
value 31 for permitted speed at the time 40 the overspeed governor 18 controls
the machinery brake 7 and also disconnects the power supply circuit of the
frequency converter 2. If the movement of the elevator car continues farther
towards the end of the elevator shaft, the overspeed governor additionally
controls the guide rail brake of the elevator car at the time 41.
Fig. 8 presents a graph of the determined speed of the elevator car in the
situation according to Fig. 7. The line 33 presents the speed of the elevator car
with deceleration according to the control of the frequency converter 2. The
distance 34 describes in this case the deviation of the control of the frequency
converter from the set target point for stopping. The limit values of the elevator
shaft for permitted movement in the end zone 13, 14 of the elevator shaft are
determined in the invention such that the braking distance of the machinery
brake 7 of the elevator and if necessary of the safety brake of the car 8 is
shorter than the distance from the end of the elevator shaft determined by the
limit values for permitted movement. When calculating the limit values in this
case the determined value of the speed of the elevator car must also be taken
into account in the proximity of the end of the elevator shaft.
In one embodiment of the invention data about the imbalance of the loading of
the elevator is also used in the determination of the limit values 13,14,30,31,32
for permitted movement of the elevator car. Imbalance is determined by
measuring the load of the elevator car with the car load weighing device 36. The
imbalance is typically at its greatest with a full car or with an empty car. The
drive direction of heavy loading of the elevator motor varies in this case
according to the loading such that with an empty elevator car the drive direction
of heavy loading is downwards and with a full car upwards. The run direction of
heavy loading can in this case be determined by measuring the load of the
elevator car. The limit values for permitted movement of the elevator car are in
this case determined separately according to the heavy and to the light drive
direction, e.g. so that when the output of an electrical drive is restricted the

speed of the elevator car decreases differently in the heavy drive direction than
when driving in the drive direction of light loading.
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. Protection of an elevator, in which the elevator comprises a machinery
brake (7), a safety brake (8) of the elevator car, and an electrical drive (1),
which electrical drive comprises an elevator motor (3) and also a power
supply appliance (2) of the elevator motor, and which protection of an
elevator comprises:
determination of the limit value (27,28) for the stator voltage
and/or the stator current of the elevator motor
restriction of the output of the electrical drive (1), in which the
output of the electrical drive is restricted on the basis of the
limit value (27,28) for the stator voltage and/or the stator
current
determination of at least one limit value (13,14,30,31,32) for
permitted movement of the elevator car
restriction of the movement (12, 29) of the elevator car, in
which the movement of the elevator car is restricted on the
basis of at least one determined limit value (13,14,30,31,32)
for permitted movement
characterized in that at least one limit value (13,14,30,31,32) for
permitted movement of the elevator car is determined at least partly on the
basis of the limit value (27,28) for the stator voltage and/or stator current
of the elevator motor, and in that the elevator car is fitted to move with a
restricted movement during the aforementioned restriction of the
movement of the elevator car.
2. Protection of an eievator according to ciaim 1, characterized in ihat the
determination of the limit values comprises:

determination of the limit value (27, 28) for stator voltage
and/or the stator current of the elevator motor and in the
same connection
determination of at least one limit value (13,14,30,31,32) for
permitted movement of the elevator car
3. Protection of an elevator according to any of the claims above,
characterized in that the limit value (27) for the length of the stator
voltage vector is determined using at least one of the following
determination criteria:
on the basis of the machinery parameters of the motor (3)
on the basis of the appliance parameters of the power
supply appliance (2) of the motor
on the basis of the determination of the network voltage (6)
or the intermediate circuit voltage (35)
on the basis of the determination (5) of the speed of the
motor
on the basis of the determination (9) of the speed of the
elevator car
4. Protection of an elevator according to any of the claims above,
characterized in that the limit value (28) for the length of the stator
current vector is determined using at least one of the following
determination criteria:
on the basis of the machinery parameters of the motor (3)
on the basis of the appliance parameters of the power
supply appliance (2) of the motor

on the basis of the determination (36) of the imbalance of the
loading of the elevator
on the basis of the determination of the temperature of the
motor (3) or of the power supply appliance (2) of the motor
on the basis of the determination of the temperature of the
elevator shaft
5. Protection of an elevator according to any of the preceding claims
characterized in that at least one limit value (13,14,30,31,32) for
permitted movement of the elevator car is determined at least partly on the
basis of the determination (36) of the imbalance of the loading of the
elevator.
6. Protection of an elevator according to any of the preceding claims,
characterized in that the protection of an elevator comprises a
determination (5,9) of the movement of the elevator car and in that a
restriction (18) of the movement of the elevator car is fitted to compare the
determined value of movement of the elevator car to the limit values
(13,14,30,31,32) for permitted movement of the elevator car. and in that
when the determined value of the movement of the elevator car deviates
outside the range defined by the limit values for permitted movement, the
protection of the elevator is fitted to activate the emergency stop.
7. Protection of an elevator according to claim 6, characterized in that the
limit values for permitted movement of the elevator car comprise first limit
values (13,30,31), with which a first range of permitted movement is set,
as well as second limit values (14,32), with which a second range of
permitted movement is set, and in that the second range of permitted
movement is defined to be closer to the extreme limits of safe movement
in the elevator shaft than the first range of permitted movement, and in
that when the determined value of movement of the elevator car deviates
outside the first range for permitted movement (13,30,31) the protection of

the elevator is fitted to activate the machinery brake (7), and in that when
the determined value of movement of the elevator car deviates outside the
second range for permitted movement (14,32) the protection of the
elevator is fitted to activate the safety brake (8) of the elevator car.
8. Method for protecting an elevator, in which method:
an electrical drive (1) is fitted into the elevator,
to which electrical drive an elevator motor (3) and a power
supply appliance (2) of the elevator motor are fitted,
a machinery brake (7) and a safety brake (8) of the elevator
car are fitted to the elevator
a limit value (27, 28) for stator voltage and/or stator current
is determined
the output of the electrical drive is restricted on the basis of
the limit value (27, 28) of stator voltage and/or stator current
and
a limit value (13,14,30,31,32) for permitted movement of the
elevator car is determined
the movement (12, 29) of the elevator car is restricted on the
basis of the limit value (13,14,30,31,32) for permitted
movement
characterized in that:
at least one limit value (13,14,30,31,32) for permitted
movement of the elevator car is determined at least partly on
the basis of the limit value (27,28) of the stator voltage
and/or the stator current of the elevator motor

the elevator car is moved with a restricted movement during
the aforementioned restriction of the movement of the
elevator car
9. Method according to claim 8, characterized in that
at least one limit value (13,14,30,31,32) for permitted
movement of the elevator car is determined at least partly on
the basis of the determination (36) of the imbalance of the
loading of the elevator
10. Method according to claim 8 or 9, characterized in that:
the movement (12, 29) of the elevator car is determined
the movement of the elevator car is compared to the limit
values (13,14,30,31,32) for permitted movement of the
elevator car and when the determined value deviates outside
the range defined by the limit values for permitted
movement,
the emergency stop is activated
11. Method or protection according to any of the preceding claims,
characterized in that at least one aforementioned limit value
(13,14,27,28,30,31,32) is formed from a plurality of instantaneous limit
values that are consecutive to each other or can be described as a
continuous limit value curve in relation to time.

The invention discloses a protection of an elevator and a method for protecting an elevator, in which the elevator
comprises a machinery brake (7), a safety brake (8) of the elevator car (10), and an electrical drive (1) comprising an elevator motor
(3) and a power supply appliance (2) of the elevator motor (3). The protection of the elevator comprises restriction of the output of
the electrical drive (1) on the basis of the determined limit value (27, 28) for the stator voltage and/or the stator current of the elevator
motor (3) and restriction of the movement (12, 29) of the elevator car (10) on the basis of at least one determined limit value (13,
14, 30, 31, 32) for permitted movement of the elevator car (10). At least one limit value for permitted movement of the elevator car
(10) is determined at least partly on the basis of the limit value (27, 28) for the stator voltage and/or the stator current of the elevator
motor (3) and the elevator car (10) is fitted to move with a restricted movement during the restriction of the movement of the elevator
car (10).