Elevator
Battery based emergency power supplies are needed to power the elevator to be
able to rescue people from an elevator car during sudden power outages, for
example, during a sudden blackout. Typically, such devices are powered from
batteries which must be replaced before the lifetime of the batteries is exceeded or
otherwise there-is a risk of failing the emergency rescue operation.
Batteries, especially valve regulated lead acid (VRLA) or Li-ion batteries, are prone to
aging, i.e., the available capacity from a fully charged battery tends to decrease over
time. Factors affecting on aging are charging and discharging cycles and
temperature. For VRLA batteries, a 10°Crise in temperature halves the expected
lifetime.
Nowadays, emergency device batteries are replaced approximately every two or
three years, and this replacing intervalmay varydepending on the environment.
However, in most cases, the full capacity and lifetime of the batteries is not used. At
the worst batteries are already at the end of their lifetime when emergency rescue
function would be required to operate. To avoid these situations some kind of battery
health or chargemonitoring is needed.
It is difficult to measure the health state of a battery. An open circuit voltage
measurement across battery terminals indicates a rough estimate ofthe state of
charge of the battery. However, the health stateof the battery cannot be accurately
determined based on the open circuit voltage measurement, excluding the rare cases
of short circuited or fully dead batteries. Some techniques whichestimate the health
state(or the state of charge) of the battery according tothe measurement of an AC or
. DC resistance of the battery. As the battery ages, AC and DC resistances increase.
However, this is still not a reliable indicator of the state of health by itself because of
large tolerances of those resistances. There are also some methods to observe the
health state of a battery during a charging process. One is to measure residual
current flowing into the battery when the battery is fully charged and the charger is
applying a constant float charging voltage. This method is also not accurate enough
by itself.
In order to determine the functional state of a battery, there is also amethod where
a load is connected across the battery terminals. In some basic techniques battery
testing is done by connecting a power resistor to the battery terminals for a short
period of time and monitoring how much the battery terminal voltage drops.

Basically, this test is very similar to DC resistance measurement and the accuracy is
not sufficiently good. The test resistor has to be rated for high power which means
that it is big and takes some space in the device itself. Furthermore, if the device is
able to operate with different type of batteries, for example, with 12V, 24V or 48V
batteries, then having a single test resistor means that battery test current differs
between each battery type.
It is therefore object of the invention to provide an elevator and a method for
monitoring of an emergency power supply battery which allow a reliable detection of
the functional battery state and thus the issue of a replacement signal for the
elevator or maintenance company.
The object is solved with an elevator according to claim 1 as well as with a method
according to claim 8. Preferred embodiments of the invention are subject-matter of
the dependent claims. Advantageous embodiments of the invention are also
described in the description as well as in the drawings.
The basic configuration of the inventive elevator comprises an elevator control
having a motor drive for an elevator motor driving an elevator car along a typically
vertical movement path. The motor drive comprises a frequency converter with a
rectifier bridge designed to be connected to mains, a converter bridge for feeding the
elevator motor and an intermediate DC circuit located in-between them. The elevator
further comprises a brake drive for supplying energy to at least one motor brake,
regularly atleast two motor brakes, with the brake drive being connected to the
intermediate DC circuit. The elevator further comprises an emergency power supply
battery designed to allow safe release of passengers in the case of a power outage.
The capacity of the emergency power supply battery has therefore to be large
enough to allow the drive of the elevator motor via the motor drive and the
energization of the brake drive to release the motor brake.
According to the invention, the battery is connected to the intermediate DC circuit
and the elevator control has a measuring circuit connected to the intermediate DC
circuit. Further, the elevator control has a battery test module which is configured to
apply a defined load to the battery and to measure the voltage and/or current of the
DC circuit and thus of the battery itself for a defined time period. In this connection it
has to be carried out that the defined time period is preferably dependent on the
capacity of the battery. The time period should be chosen long enough so that at
least 20% of the battery charge runs over the load applied to the intermediate DC

circuit. The defined load is preferably the converter bridge in which case the
semiconductor switches are controlled to allow a certain current flow between the
positive and negative branch of the DC circuit. Another possibility of a load is a brake
chopper in which case a chopper switch, usually a regulating semiconductor switch
connected in series with the brake resistor of the brake chopper is controlled to allow
a current flow via the brake resistor leading to heat dissipation in the brake resistor.
A third possibility for a load is the connection of the brake drive which energizes-at
least one, preferably one of the motor brakes so that the current flows into the brake
coil releasing the brake. In this case, preferably, only one of the brakes of the
regularly two motor brakes is energized so that the other motor brake holds the
elevator car during the battery test process. Of course, the above-mentioned three
alternative loads may be used in combination with each other.
Further, the battery testing module comprises a comparator for comparing the
measured voltage and/or current and/or power with at least one stored first
threshold value, whereby the elevator control is configured to issue a replacement
signal for the battery dependent on the signal of the comparator. From the
measurement of the current flowing between the battery terminals and thus between
the positive and negative branch of the intermediate DC circuit as well as the voltage
it is easily possible to calculate the power discharged during the measurement. The
power can be set in relation to the nominal capacity of the battery and thus the
measuring time can be defined to be a fixed portion of the capacity, e.g. 20%. Via
the measurement of the voltage over the time a voltage profile is obtained which can
be compared with the voltage profiles over the health state as it is shown in Fig. 2.
By a comparison of the voltage curve with these voltage profiles stored as a
reference value the health state of the battery can be reliably retrieved, and if the
current profile exceeds a certain threshold profile, which could be e.g. 70%
remaining capacity, a battery replacement signal is issued. If the profile exceeds a
further lower threshold value, which could be e.g. 50% remaining capacity, the
elevator may be taken out of order by the elevator control as this remaining capacity
may be insufficient to release trapped passengers.
In summary, the invention offers the use of a load realized by components of the
motor and brake drive which are obligatory in an elevator system, as e.g. the
converter bridge being controlled to connect the positive and negative branch of the
intermediate DC circuit, the brake driveenergizing a motor brake coil, or the brake
chopper to allow a current flow between the positive and negative branch of the DC
circuit leading to a dissipation of the energy in the brake resistor of the brake

chopper. Therefore, no separate battery test load has to be applied or provided in
the inventive elevator. Furthermore, the fact that the voltage is monitored over a
defined longer time period of several seconds, preferably up to five minutes, most
preferably from 30 seconds, advantageously from one minute to three minutes,
ensures that the functional battery status is reliably determined. The defined time
period is thereby preferably dependent on the circumstances of current flow between
the positive and negative branch of the intermediate. DC circuit as well as onthe
rated capacity of the battery to be tested. Preferably, the defined time period is set
to a value that allows at least 20% of the rated battery power flowing through the
load connected to the intermediate DC circuit.
The invention provides the best and most straightforward test method is to apply a
test load that has equivalent power adapted to the power of an emergency rescue
device. The discharge time should be advantageously so long that at least 80% state
of charge is reached. This is because the battery voltage starts to drop more rapidly
as the state of charge is decreased. It is very difficult to tell the difference between
good and bad battery if we can only monitor the beginning of the discharge curve,
which is shown in Fig. 2,
In one preferred embodiment of the invention, a battery pack of an emergency
power supply consists of 4 pieces of 12V 12Ah VRLA batteries connected in series.
They are being discharged approximately at the rate of 24...36A. This means that
they will last only for about ten minutes. In terms of power the batteries are
discharged via the emergency rescue device, e.g. via energizing the elevator motor
to move the car and energizing the motor brakes to release the carwith a power
requirement ofabout 1.5 kW. In order to make a battery test preferably this nominal
power of the emergency rescue device should be used. The load connected to the
battery should therefore in the above case preferably lead to a power consumption of
1,5 kW. The defined measuring time should proceed until the charge of the battery
has dropped to about 80%. Thus, in general cases the battery is discharged with a
load leading to a power consumption of 1.5 kW for 2 minutes.
The emergency power supply may advantageously also consist of Li-ion batteries
which have a high efficiency and only need minor space for installation.
In a preferred embodiment the invention works as follows:

Batteries are connected to the emergency braking device which is galvanically
connected to the intermediate circuit of the motor drive using relays. The emergency
braking device and the motor drive communicate with each other using a serial-link
or a parallel interface.
The fact that batteries are directly connected to drive intermediate DC-circuit enables
a facilitated battery testing using existing components of the motor and/or brake
without the necessity to use a dedicated battery test resistor. The test load can be
applied to the battery by
opening one brake with brake controller,
supplying power to the motor without creating torque or
usirrg brake chopper to load the battery.
If the motor drive or brake drive are being used the elevator safety chain has to be
closed. The emergency braking device can request a battery test from the motor
drive which then forwards this request to elevator control. If the elevator safety
chain is closed, then elevator control can request that the safety inputs for the motor
and brake drive to be closed allowing the motor drive to open, i.e. to energize the
motor brakes or to supply power to the motor to apply the load between the positive
and negative branch of the intermediate DC circuit and thus to the battery itself. If
the motor and brake drive is ready to control the brakes or to supply power to the
motor, then it will respond a'ready condition' to the emergency braking device which
can then connect battery to the drive intermediate circuit by closing the relays. And
then, the emergency braking device can request how much power shall be drawn
from the batteries to perform the battery test. During the battery test, the
emergency braking device will monitor the battery terminal voltage and the current
flow and decide if the battery Is in good condition or not via comparison with
reference or threshold values. In case battery needs replacement, the emergency
braking device will inform the motor drive as well as the elevator control to issue a
replacement signal. In the worst case the elevator is prohibited from being taken into
use,
If a braking chopper is used, then there is no need to communicate with elevator
controller. Instead, the motor and brake drive itself can control a braking chopper
semiconductor switch to supply power to braking resistor.
The advantages of the invention comprise i.e.:

- If the battery is being used rarely the battery replacement interval can be
increased using condition-based maintenance.
- The batteries can be replaced as soon as usable battery lifetime has been
exceeded.
- More sophisticated type of battery testing will avoid causing unnecessary request to
replace batteries.
~= Bulky battery test resistors can be avoided"
In a preferred embodiment of the invention, the elevator control comprises a power
or current monitoring device and the elevator control is configured to disable the
measurement circuit in the connection of the load after the measured power or
current during the voltage measurement exceeds a certain second threshold value.
With these features it can be ensured that the time period is long enough so that a
certain amount of current or power is flowing during the voltage measurement which
enables a quite reliable information about the real status of the battery.
Preferably, the second threshold value is dependent on the rated capacity of the
battery. This allows the setting of the time period to an exact value portion of the
rated capacity of the battery. For example, the status of a battery can be determined
the better the longer the voltage measurement takes whereby at least 20% of the
battery charge should be flowing via the load during the measurement. The
measurement of the profile of the voltage drop in the above sense allows information
about the functional battery status. The initial voltage measurement with full charge
battery is not a very reliable value for the battery status. Therefore, according to the
invention, the voltage of the battery is measured over the remaining battery capacity
which better considers the natural voltage behaviour of a battery during discharge.
Such a behaviour is indicated in Fig. 2 where the profile of the battery terminal
voltage is shown via the discharge time for different health states of the battery and
thus via the really remaining functional battery capacity. It can be clearly seen that
the voltage drop in each profile clearly takes place only after a certain time period
which ensures that at least an essential portion of the battery charge, preferably at
least 20% of the battery charge, is discharged so that 80% of the rated battery
charge remain at the most. With recording this initial discharge profile of the battery
the health state of the battery is reliably tested.
In a preferred embodiment of the invention, the measuring circuit is configured to
disable the elevator motor and to ensure that at least one of the motor brakes is de-

energized. Via this measure it can be ensured that the elevator is kept in piaceduring
the voltage measurement. Accordingly, the battery test does not affect the security
of the elevator. Accordingly the elevator control may communicate with an elevator
safety controller to ensure stop of-the elevator car during the battery test.
In a preferred embodiment of the invention, the elevator is a traction sheave
elevator and the elevator motor drives a traction sheave which co-aets with elevator
ropes connected to the elevator car. This type of elevator is most convenient and
comprises the components mentioned above. Of course, the invention also works
with a toothed belt as suspension means for the car and counterweight, in which
case the drive sheave connected to the elevator motor combs the toothed belt.
Preferably, the battery is a valve regulated lead acid battery (VRLA). This type of
battery has the discharge behaviour which is depicted in Fig. 2. Accordingly, the
inventive elevator and monitoring method for the battery is preferably designed for
said type of battery which on the other hand provides enough capacity to allow at
least a short time run of the elevator motor and the simultaneous release of the
motor brakes. In this case it is to be mentioned that the windings of the motor
brakes have to be energized to allow the motor brakes to be released. This is a
safety measure'obligatory in elevator regulations around the world.
The present invention also refers to a method for monitoring an emergency power
supply battery in an elevator comprising an elevator control having a motor drive of
an elevator motor, driving an elevator car on a movement path. The motor drive
comprises a frequency converter with a rectifier bridge designed to be connected to
mains, a converter bridge for feeding the elevator motor and an intermediate DC
circuit located in-between. The elevator further comprises a brake drive for supplying
energy to at least two motor brakes which are required by regulations. The brake
drive is also connected to the intermediate DC circuit. Finally, the elevator comprises
an emergency power supply battery for allowing the release of trapped passengers
during a power outage.
According to the inventive method, the function of the battery is tested by
connecting it for a certain time period to a load connected to the intermediate DC
circuit to which also the battery is connected. The load may be
a brake chopper,
theenergization of at least one of the motor brakes via the brake drive or

- the control of at least some semiconductor switches of the converter bridge to be
leading between the two branches of the intermediate DC circuit.
The elevator control- has a measuring circuit connected to the intermediate DC
circuit. As current is flowing via the load between the positive and negative branch of
the intermediate DC circuit, a voltage drop is measured whereby the voltage drop is
measured'for a defined time period. The measured voltage is compared withrat least
one stored first threshold value, whereby a replacement signal for the battery is
issued when the threshold value is exceeded.
The first threshold value is for example a discharge curve over the time which is
present wheh the capacity of the battery has gone down to for example 70% of the
rated load. The drop of the battery capacity to this value is then deemed as a signal
for a battery replacement. The monitoring of the actual remaining battery capacity is
based on the measurement of the voltage drop over the defined time period which
time period is selected so that an essential amount of the battery charge is
dissipated over the load, preferably at least 20%, most preferably up to 40%.
Accordingly, the invention provides a very reliable tool for replacing a battery which
capacity has dropped to an extent so that the performance of a safety run of the
elevator car to release trapped passengers is no longer ensured.
In a preferred embodiment of the method, during the voltage measurement, the
power dissipation over the load or the current flowing over the load is measured and
the time period is defined by the amount of power or current exceeding a
predetermined second threshold value which is a portion of the rated capacity of the
battery. The time period can therefore be defined by the power or current flow in
relation to the rated battery capacity. This allows the voltage measurement until a
certain portion of the battery capacity is dissipated via the load. Preferably, this
portion is at least 10%, preferably 15%, or at least 20%, most preferably at least
25%.
The inventive method could also be described that the initial discharge profile of the
battery of at least 10%, preferably at least 15%, most preferably at least 20% of the
rated battery capacity is recorded and compared with at least one reference
profilesof the battery for a defined health state, e.g. 70% remaining functional
capacity as first threshold or reference value.

It shall be clear for the skilled person that the above-mentioned embodiments of the
invention can be combined arbitrarily.
The invention is described hereinafter by means of an example in the annexed
drawings. In these drawings:
Fig. 1 shows a schematic diagram of a part of the inventive elevator,and
Fig. 2 a battery discharge curve of a valve regulated lead acid battery with the
terminal voltage of the battery over the discharge time for different
functional battery states.
Fig. 1 shows a part of an elevator 10 comprising an elevator control 12 having three
optional microprocessor parts 12a, 12b and 12c.
The elevator further comprises a motor and brake drive 14 as well as an battery
testing module 15 comprising an emergency power supply battery 16, e.g. a VLRA or
Li-ion battery.
The motor and brake drive 14 comprises a motor drive 17 with rectifier bridge 18
connected to mains 20 via a separator switch 22 controlled by the elevator control
12. Further, the motor drive 17 comprises a converter bridge 24 which converter
bridge 24 is connected to the rectifier bridge 18 via an intermediate DC circuit 25.
The converter bridge 24 is in drive connection to the elevator motor 26.
The motor and brake drive 14 further comprises a brake drive 28 which is connected
to the intermediate DC circuit 25 of the motor drive 17 optionally via a DC/DC
inverter 30. The brake drive 28 controls two motor brakes 32a,b. The battery 16 of-
the battery testing module is connected to the intermediate DC circuit 25 via a safety
switch 34 which is controlled via a microprocessor part 12c of the elevator control
12.
The motor and brake drive 14 further comprises a part 12b of the elevator control as
well as a brake chopper 36 which comprises a brake resistor 38 connected in series
with a semiconductorchopper switch 40 controlled by the elevator control 12.
The battery testing module 15 comprises a measuring circuit 44 with a shunt 42 for
current measurement. The measuring circuit measures via the third microprocessor
part 12c of the elevator control 12 the voltage and current flowing during the

measurement, which allows the determination of the power flow during the
measurement.
The invention works as follows:
In case the elevator 10 is not used and the elevator control 12 requires the
performing of a functional battery test, the elevator control 12 opens via the first
microprocessor part 12a in connection with separator switch 22 the connection
between the rectifier bridge 18 and mains 20. Furthermore, the elevator motor is de-
energized and at least one of the motor brakes is de-energized to keep it in gripping
position.
The elevator control or a part of it connects the load, e.g. the brake resistor 38
and/or switches of the converter bridge 24 and/or the motor brake 32a,b between
the positive and negative branch of the intermediate DC circuit 25, and the third
microprocessor part 12c of the elevator control 12 closes the safety switch 34 to
connect the battery 16 with the intermediate DC circuit 25. Simultaneously the
measuring circuit 44 is activated to measure the current flow as well as the voltage
over the battery terminals. Via this measure the power consumed during the
measurement is calculated. The measurement is performed over a defined time
period which calculates e.g. by a power amount corresponding to 20% of the rated
battery capacity. Thus, an essential part of the discharge profile of the battery is
measured which allows exact information about the functional or health state of the
battery. The measured profile is e.g. compared with stored profiled according to Fig.
2 to obtain the health state of the battery. If the detected state exceeds a first
threshold value, e.g. only 70% of the rated capacity left, a replacement signal is
issued by the elevator control, e.g. to a remote maintenance center of the elevator
or to another monitoring facility of the elevator company, maintenance company or
building owner.
Preferably, the elevator control comprises on this behalf a memory with the values of
the discharge profiled as shown in Fig. 2 as reference values. By comparing the
voltage drop in correlation to the discharged power, it is therefore able to reliably
give an estimation about the remaining actual capacity of the battery and of course
about the necessity of a replacement of the battery. Accordingly, the elevator control
may if the first threshold values according to the discharge characteristics are
exceeded issue a replacement signal.

It is optionally furthermore possible that after the third microprocessor part of the
elevator control realizes a capacity loss which affects the usability of the battery it
triggers for example the elevator safety circuit to set the elevator out of operation
■ and issue a maintenance signal.
The microprocessor parts 12a, 12b, 12c of the elevator control are used for clarity
reasons in-the drawings and are-optional. The corresponding components can be
directly connected to the elevator control. At least parts of the battery testing
module and of the elevator control may be realised or organized in an emergency
rescue device of the elevator control. Different modules and components of the
elevator control may be integrated or provided as separate components. The motor
drive and brake drive can be realized in separate devices/
The described embodiment should not be understood as limiting the invention but
the invention can be carried out within the scope of the appended patent claims.

List of reference numerals
10 elevator
12 elevator control
12 a, b, c microprocessor parts of the elevator control
motor and brake drive
battery testing module
battery (VRLA)
motor drive (frequency converter)
rectifier bridge
20 mains (public AC source)
'22 separator switch
converter bridge
intermediate DC circuit
elevator motor
28 brake drive (brake controller)
30 DC/DC coupler (optional)
32a,b motor brakes
34 safety switch of the battery testing module
36 brake chopper
38 brake resistor
40 chopper switch (semiconductor switch)
42 measurement resistor for current measurement
44 measuring circuit

Claims
1. Elevator comprising an elevator control (12) having a motor drive (17) of an
elevator motor (26)-driving an elevator car on a movement path, which motor drive
(17) comprising a frequency converter with a rectifier bridge designed to be
connected to mains, a converter bridge for feeding the elevator motor (26) and an
intermediate DC circuit (25) located in between, the elevator further comprising a
brake drive (28) for supplying energy to at least two motor brakes (32a, 32b) with
the brake drive (28) being connected to the intermediate DC circuit (25) as well as
an emergency power supply battery (16) designed to allow safe release of
passengers in case of a power outage,
characterized in that the battery (16) is connected to the intermediate DC circuit
(25), and that the elevator control (12) has a measuring circuit (44) connected to
the intermediate DC circuit (25) and that the elevator control (12) has a battery
testing module (15) which is configured to apply a defined load to the battery (16)
and to measure the voltage of the DC circuit (25) for a defined time period,
and that the battery testing module (15) comprises a comparator for comparing the
measured voltage with at least one stored first threshold value, whereby the elevator
control (12) is configured to issue a replacement signal for the battery (16)
dependent on the signal of the comparator.
Elevator according to claim 1, wherein the load is the converter bridge controlled
in a conducting state and/or the brake drive (28) energizing a brake and/or a brake
chopper.
Elevator according to one of the preceding claims, characterized in that the
elevator control (12) comprises a power and/or current monitoring device, and that
the elevator control (12) is configured to disable the measuring circuit (44) after the
measured current/power during the voltage measurement exceeds a certain second
threshold value.
4. Elevator according to claim 3, characterized in that the second threshold value is
dependent on the rated capacity of the battery (16), preferably at least 10%,
advantageously 15%, most preferably at least 20% of the rated battery capacity.

5. Elevator according to one of the preceding claims, characterized in that the
measuring circuit (44) is configured to disable the elevator motor (26) and to ensure
that at least one of the motor brakes (32a, 32b) is de-energized.
6. Elevator according to one of the preceding claims, characterized in that the
elevator is a traction sheave elevator and the elevator motor (26) drives a traction
sheave which co-acts with elevator ropes~connected to the elevator car.
Elevator according to one of the preceding claims, characterized in that the
battery (16) is a valve regulated lead acid battery (VRLA) or a Li-ion battery.
Method for monitoring an emergency power supply battery (16) in an elevator
comprising an elevator control (12) having a motor drive (17) of an elevator motor
(26), driving an elevator car on a movement path, which motor drive (17)
comprising a frequency converter with a rectifier bridge designed to be connected to
mains, a converter bridge for feeding the elevator motor (26) and an intermediate
DC circuit (25) in-between, the elevator further comprises a brake drive (28) for
supplying energy to at least two motor brakes (32a, 32b) with the brake drive (28)
being connected to the intermediate DC circuit (25) as well as the emergency power
supply battery (16) ,
characterized in that the function of the battery (16) is tested by connecting it for a
certain time period to a load connected to the intermediate DC circuit (25), and that
the elevator control (12) has a measuring circuit (44) connected to the intermediate
DC circuit (25), which load is the converter bridge controlled in a conducting state
and/or the bake drive energizing a brake and/or a brake chopper controlled to be
connected to the DC intermediate circuit, that the voltage over the DC circuit (25) is
measured for a defined time period,
and that the measured voltage is compared with at least one stored first threshold
value, whereby a replacement signal for the battery (16) is issued when the
threshold value is exceeded.
9. Method according to claim 8, wherein during the voltage measurement the power
dissipation over the load is measured and the time period is defined by integrating
the dissipated power over the time and the voltage measurement is stopped when
the integral exceeds a predetermined second threshold value.
10. Method according to claim 9, wherein the second threshold value is at least 10%,
preferably at least 15%, most preferably at least 20% of the rated battery capacity.

Method according to one of claims 8 to 10, wherein at least one of the motor
brakes (32a, 32b) is kept de-energized during the voltage measurement.
Method according to one of claims 8 to 11, wherein during the voltage
measurement a separation switch (22) is activated to separate the rectifier bridge
from mains.
Method according to one of claims 8 to 12, wherein the measuring circuit (44)
measures the voltage of the intermediate DC circuit (25) as well as the current flow
between the two branches of the intermediate DC circuit (25).
Method according to one of claims 8 to 13, wherein the initial discharge profile of
the battery (16) of at least 10%, preferably at least 15%, most preferably at least
20% of the rated battery capacity is recorded and compared with at least one
reference profiles of the battery (16) for a defined health state, e.g. 70% remaining
functional capacity.
15. Method according.to one of claims 8 to 14 performed in an elevator according to
one of claims 1 to 7.