AN ELEVATOR LINE BRIDGE FILTER FOR COMPENSATING REAC-
TIVE POWER IN A GRID
BACKGROUND OF THE INVENTION
Field of the invention:
The invention relates to hoisting machines,
and hoisting machine power supply. Particularly, the
invention relates to an elevator line bridge filter
for compensating reactive power in a grid.
Description of the Related Art:
An elevator does work also when an elevator
car is braked. The work done is usually lost as heat.
The braking may be used to produce electrical power.
Currently, the electrical power produced is not uti-
lized.
In a power supply system loads may also have
a combination of resistive, capacitive or inductive
nature. Power may also flow towards the source. For
example, electrical motors and lighting equipment have
inductive coils which function as inductive load. The
power caused by inductive or capacitive loads is re-
ferred to as reactive power. When reactive power is
present, there is a phase difference between voltage
and current. Reactive power causes rise in current
value in the internal grid of the building and there-
fore causes heating in power transmission lines and
all kinds of power supply lines of the building.
A building automation system controls a plu-
rality of electricity consuming subsystems in a build-
ing. The building automation system monitors and con-
trols several subsystems of the building such as
lighting, heating, air-conditioning and security. A
building automation system comprises at least one com-
puter, which is referred to as a building automation
server. The server is connected to a plurality of sen-

sors that monitor the proper functioning of the afore-
mentioned subsystems. The building automation system
may also measure use of electrical power in the afore-
mentioned subsystems. Some of the aforementioned sub-
systems may have reactive or inductive loads which
give rise to reactive power, which returns to the pow-
er source such as a grid unless it compensated. The
building automation system may also measure reactive
power.
Therefore, it would be beneficial to have a
solution which enables a building automation system to
perform compensation for reactive power. It would be
beneficial if an elevator system was able to compen-
sate reactive power produced by a plurality of build-
ing subsystems.
SUMMARY OF THE INVENTION:
According to an aspect of the invention, the
invention is a method comprising: determining, by a
controller of an electrical converter, a first reac-
tive power produced by a smoothing filter using pre-
determined information on impedance of the smoothing
filter, the smoothing filter being electrically con-
nected via a three-phase electrical connection to a
converter matrix of the electrical converter of an
elevator, the smoothing filter being electrically con-
nected via a three-phase connection to a grid, the
converter matrix producing pulse width modulated
three-phase output voltages to the smoothing filter;
and requesting, by the controller, the electrical con-
verter to make a plurality of first compensative elec-
trical connections in the converter matrix to compen-
sate the first reactive power.
According to a further aspect of the inven-
tion, the invention is an electrical converter of an
elevator, the electrical converter comprising: a
smoothing filter configured to smooth three-phase out-

put currents, the smoothing filter being electrically
connected via a three-phase electrical connection to a
converter matrix, the smoothing filter being electri-
cally connected via a three-phase electrical connec-
tion to a grid; a converter matrix configured to pro-
duce the pulse width modulated three-phase output vol-
tages to the smoothing filter, to make a plurality of
connections in the converter matrix to compensate
reactive power; and a controller configured to deter-
mine a first reactive power produced by a smoothing
filter using pre-determined information on impedance
of the smoothing filter and to request the electrical
converter to make the plurality of first compensative
connections in the converter matrix to compensate the
first reactive power.
According to a further aspect of the inven-
tion, the invention is an elevator comprising the
electrical converter.
According to a further aspect of the inven-
tion, the invention is an elevator group comprising
the elevator.
In one embodiment of the invention, the con-
verter may be a line bridge in which the converter ma-
trix is replaced with a plurality of IGBT transistors
of the line bridge. The IGBT transistors may be seen
to form a matrix of the line bridge.
In one embodiment of the invention, the me-
thod further comprises: receiving, by the controller,
information on a second reactive power from a remote
node over a communication channel, the second reactive
power being produced to the grid; adding, by the con-
troller, the first reactive power and the second reac-
tive power to yield a total reactive power; and re-
questing, by the controller, the electrical converter
to make a plurality of second compensative connections
in the converter matrix to compensate the total reac-
tive power.

In one embodiment of the invention, the con-
troller is configured to receive information on a
second reactive power from a remote node over a commu-
nication channel, the second reactive power being pro-
duced to the grid, to add the first reactive power and
the second reactive power to a yield a total reactive
power, and to request the electrical converter to make
a plurality of second compensative connections in the
converter matrix to compensate the total reactive pow-
er.
In one embodiment of the invention, the step
of determining the first reactive power further com-
prises: measuring a phase to neutral voltage by the
controller in the grid; measuring a phase current by
the controller in at least one of the grid and the
three-phase electrical connected between the smoothing
filter and the converter matrix; and determining, by
the controller, the first reactive power using the
pre-determined information on impedance of the smooth-
ing filter, the phase to neutral voltage and the phase
current.
In one embodiment of the invention, the
smoothing filter is an LCL filter. The LCL filter may
comprise a plurality of inductors (L) and a plurality
of capacitors (C).
In one embodiment of the invention, the grid
is an internal grid of a building, an factory, or a
ship.
In one embodiment of the invention, the re-
mote node is a building automation system server.
In one embodiment of the invention, the
second reactive power is produced to the grid by at
least one building electrical subsystem.
In one embodiment of the invention, the at
least one building electrical subsystem comprises
lighting, heating, air circulation and access control.

In one embodiment of the invention, the me-
thod further comprises: determining a voltage drop in
a voltage of the grid; and making a plurality of con-
nections in the converter matrix to regulate the vol-
tage of the grid.
In one embodiment of the invention, the first
reactive power is determined for three phases, the in-
formation on the second reactive power comprises in-
formation on three-phases and the total reactive power
is computed for three phases.
In one embodiment of the invention, the con-
verter matrix is electrically connected to an inverter
bridge via a direct current connection and the inver-
ter bridge is electrically connected to an electrical
motor of the elevator.
The embodiments of the invention described
hereinbefore may be used in any combination with each
other. At least two of the embodiments may be combined
together to form a further embodiment of the inven-
tion. A method, an electrical converter and an eleva-
tor to which the invention is related may comprise at
least one of the embodiments of the invention de-
scribed hereinbefore.
It is to be understood that any of the above
embodiments or modifications can be applied singly or
in combination to the respective aspects to which they
refer, unless they are explicitly stated as excluding
alternatives.
The benefits of the invention are related to
possibility of utilizing an elevator electrical con-
verter to compensate for reactive power in a grid.
BRIEF DESCRIPTION OF THE DRAWINGS:
The accompanying drawings, which are included
to provide a further understanding of the invention
and constitute a part of this specification, illu-
strate embodiments of the invention and together with

the description help to explain the principles of the
invention. In the drawings:
Fig. 1 is a block diagram illustrating an
elevator line bridge controller configured to communi-
cate with a building automation system computer node
in one embodiment of the invention;
Fig. 2 illustrates an elevator reactive power
compensation system in one embodiment of the inven-
tion; and
Fig. 3 is a flow chart illustrating a method
for reactive power compensation in one embodiment of
the invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS:
Reference will now be made in detail to the
embodiments of the present invention, examples of
which are illustrated in the accompanying drawings.
Figure 1 is a block diagram illustrating an
elevator line bridge controller configured to communi-
cate with a building automation system computer node
in one embodiment of the invention.
In Figure 1 there is illustrated an electric-
al system 100. The system comprises an external grid
102. Grid 102 may be the grid of a power company or
other commercial or non-commercial electricity dis-
tributor. There is also a switch 104 which connects
electrically external grid 102 to an internal grid
108. External grid 102 may be a three-phase electrical
grid. To switch 104 is electrically connected to a
filter 154 via electrical connection 106. Electrical
connection 106 may be a three-phase electrical connec-
tion. Filter 154 may be an LCL filter. Filter 154 is
configured to provide three-phase electrical current
to electrical connection 106. Filter 154 may receive a
pulse-width modulated three-phase electrical current
from a line bridge 152 of elevator 160. Filter 154
performs smoothing of the pulse-width modulated three-

phase electrical current and outputs a smoothed three-
phase electrical current to electrical connection 106
to switch 102. Line bridge 152 has a Direct Current
(DC) electrical connection to an inverter bridge 150
of elevator 160. Inverter bridge 150 has a three-phase
electrical connection 166 to an electrical motor 164
that may drive a traction sheave 178 of elevator 160.
Elevator 160 comprises a hoistway 162 in which an ele-
vator car 170 is hoisted. In hoistway 162 there is al-
so a counterweight 172 and traction means 174 looped
over traction sheave 178 and connected to elevator car
17 0 on one end and to counterweight 172 on the other
end. Traction means 174 may comprise a plurality of
traction ropes or a traction belt.
Line bridge 152 is controlled by a line
bridge controller 156. Line bridge controller 156 is
configured to control a plurality of Insulated-Gate
Bipolar Transistors (IGBT) transistors in line bridge
152. Line bridge controller 156 is connected to line
bridge 152. Line bridge controller 156 provides in-
structions to line bridge 152 to switch a plurality of
IGBT transistors in line bridge 152. The instructions
may be in the form a signal from a Pulse Width Modula-
tion (PWD) comparator circuit (not shown), which com-
pares a modulating signal to a carrier signal. Line
bridge 152 may control the gate voltages of the IGBT
transistors based on the instructions. Line bridge
controller 156 is also configured to measure phase to
neutral voltage UF in electrical connection 106. Line
bridge controller 156 is also configured to measure
phase current IF in the electrical connection between
filter 154 and line bridge 152. Line bridge controller
156 may also measure phase current IF alternatively in
electrical connection 106. Line bridge controller 156
is preconfigured with information on inductive and ca-
pacitive components and their connections in filter
154, for example, impedance of filter 154. Line bridge

controller 156 determines reactive power due QF to
filter 154 based on the impedance of filter 154, cur-
rent IF and voltage UF. Line bridge controller 156 is
able to determine necessary compensation for reactive
power QF. To perform the compensation line bridge con-
troller 156 is configured to control the plurality of
IGBT transistors in line bridge 152 via connection
148. Line bridge 156 may send gate control signals in
the form of PWM modulation to line bridge 152. The
gate control signals specifies which transistors in
line bridge 152 must be switched on to achieve compen-
sating connections in line bridge 152 that compensate
reactive power QF.
Line bridge controller 156 is connected via a
message bus 142 or other communication channel to a
Building Automation System (BAS) server 140. Server
14 0 may also be any computer node, which is communica-
tively connected to line bridge controller 156. Server
140 is communicatively connected to a controller 122
over communication channel 146. Server 140 is also
communicatively connected to controller 12 6 over com-
munication channel 144. Communication channels 144 and
14 6 may be wired or wireless communication channels,
for example, wired or wireless local area networks or
message busses. Controller 122 controls a first sub-
system 120 in the building automation system, whereas
controller 126 controls a second subsystem 124 in the
building automation system. Examples of types of sub-
systems comprise lighting, heating, ventilation and
access control. First subsystem 120 is electrically
connected to internal grid 108 via three-phase elec-
trical connection 110. Second subsystem 124 is electr-
ically connected to internal grid 108 via three-phase
electrical connection 112.
In Figure 1 line bridge controller 156 is
configured to control the plurality of IGBT transis-
tors in line bridge 152 to compensate for reactive

power QG measured to be present in internal grid 108.
Line bridge 152 obtains the information on reactive
power in internal grid 108 in order to control the
plurality of transistors in line bridge 152. Line
bridge 152 obtains the information on reactive power
in internal grid 108 from server 140.
The starting point for determining the neces-
sary reactive power compensation is that controllers
122 and 126 measure reactive power produced in their
respective subsystems 120 and 124. Controller 122 pro-
vides information on the measured reactive power pro-
duced in subsystem 120 to server 140 over communica-
tion channel 146. Similarly, controller 126 provides
information on the measured reactive power produced in
subsystem 124 to server over communication channel
144. Server 140 determines the overall reactive power
QG produced to internal grid 108 by summing the reac-
tive powers produced in subsystems 120 and 124. Server
140 provides information on the overall reactive power
in internal grid 108 to line bridge controller 156.
Line bridge controller 156 sums the overall reactive
power QG and reactive power QF produced by filter 154.
Line bridge controller 156 is able to determine neces-
sary compensation for reactive power QF + QG. To perform
the compensation line bridge controller-156 is confi-
gured to control the plurality of transistors in line
bridge 152 via connection 148. Line bridge controller
156 may send a control signal over connection 148 to
line bridge 152. The control signal specifies which
transistors in line bridge 152 must be switched on to
achieve compensating connections in line bridge 152
that compensate reactive power QF + QG.
Figure 2 illustrates an elevator reactive
power compensation system 200 in one embodiment of the
invention.
In Figure 2 there is a supply grid 202.
Supply grid 202 may comprise at least one subsystem

(not shown) which produces reactive power. The reac-
tive power produced must be compensated. In Figure 2
there is also illustrated filter 154, which also pro-
duces reactive power due to reactive load in filter
154. Filter 154 may be an LCL filter. Filter 154 may
comprise inductors LI for three phases, capacitors Cf
for three phases and inductors L2 for three phases.
Supply grid 202 is connected to filter 154 via three-
phase electrical connection 204. Filter 154 is con-
nected to line bridge 152 via three-phase electrical
connection 206. Line bridge 152 is connected via a DC
electrical connection 208 to inverter bridge 150. Line
bridge 152 may also be referred to as an electrical
converter, which comprises a converter matrix, to
which filter 154 is connected via three-phase elec-
trical connection 206, and, to which inverter bridge
150 is connected via DC electrical connection 208. In-
verter bridge 150 is connected via three-phase elec-
trical connection 210 to electrical motor 164. Inver-
ter bridge 150 comprises a plurality of IGBT transis-
tors such as transistors 240 and 242. The plurality of
IGBT transistors such as transistors 240 and 242 may
be referred to as a converter matrix. Line bridge 152
is controlled by line bridge controller 156 via a com-
munication channel 220, which may be a message bus.
Line bridge controller 156 is configured to control a
plurality of IGBT transistors such as transistors 230
and 232 in line bridge 152 via communication channel
220. Line bridge 152 is controlled by PWM control
pulses from line bridge controller 156 to determine
target states for the plurality of transistors. Line
bridge 152 supplies gate voltages to the plurality of
IGBT transistors based on the PWM control signals. The
gate voltage causes the transistors to turn on or off
depending on the voltage level. For example, a posi-
tive gate voltage, for example, +15 V, may cause a
transistor to turn on and negative gate voltage, for

example, -5 V, may cause the transistor to turn off.
Line bridge controller 156 comprises a communication
channel interface 250, for example, a message bus in-
terface. Communication channel interface 250 may be
used to communicate with a building automation system,
which may comprise a server. Line bridge controller
156 is configured to receive via communication channel
interface 250 at least one message, which comprises
information on reactive power in supply grid 202. Line
bridge controller 156 is also configured to measure
phase to neutral voltage UF in three-phase electrical
connection 204. Line bridge controller 156 is also
configured to measure phase current IF in the three-
phase electrical connection 206 between filter 154 and
line bridge 152. Line bridge controller 156 may also
measure phase current IF alternatively in electrical
connection 204. Line bridge controller 156 may be pre-
configured with information on inductive and capaci-
tive components and their connections in filter 154,
for example, impedance of filter 154. Line bridge con-
troller 156 determines reactive power QF due to filter
154 based on the impedance of filter 154, current IF
and voltage UF. Line bridge controller 156 is able to
determine necessary compensation for reactive power
produced by filter 154. To perform the compensation
line bridge controller 156 is configured to control
the plurality of transistors in line bridge 152 via
connection 220. Line bridge controller 156 may sum
reactive powers in supply grid 202 and reactive power
produced by filter 154 to obtain total reactive power.
To perform the compensation for the total reactive
power, line bridge controller 156 is configured to
control the plurality of IGBT transistors in line
bridge 152 via connection 220.
The embodiments of the invention described
hereinbefore in association with Figures 1 and 2 may
be used in any combination with each other. Several of

the embodiments may be combined together to form a
further embodiment of the invention.
Figure 3 is a flow chart illustrating a me-
thod for reactive power compensation in one embodiment
of the invention.
At step 300 a reactive power produced by a
smoothing filter is determined by a controller of an
electrical converter. The determination may use pre-
determined information on impedance of the smoothing
filter. The smoothing filter may be electrically con-
nected via a three-phase electrical connection to a
converter matrix of the electrical converter. The
smoothing filter may also be electrically connected
via a three-phase electrical connection to a grid. The
converter matrix may produce pulse width modulated
three-phase output voltages.
At step 302 the controller requests the elec-
trical converter to make a plurality of compensative
connections in the converter matrix to compensate the
first reactive power.
In one embodiment of the invention, the con-
troller receives from a remote node over a communica-
tion channel information of a second reactive power.
The second reactive power may be produced to the grid
by at least one subsystem connected to the grid. The
first reactive power is added to the second reactive
power to yield a total reactive power. The controller
requests the electrical converter to make a plurality
of compensative second connections in the converter
matrix to compensate the total reactive power.
In one embodiment of the invention, the steps
may be performed in numeric order.
The embodiments of the invention described
hereinbefore in association with Figures 1, 2 and 3
and the summary of the invention may be used in any
combination with each other. At least two of the embo-

diments may be combined together to form a further em-
bodiment of the invention.
It is to be understood that the exemplary em-
bodiments are for exemplary purposes, as many varia-
tions of the specific hardware used to implement the
exemplary embodiments are possible, as will be appre-
ciated by those skilled in the hardware art(s). For
example, the functionality of one or more of the com-
ponents of the exemplary embodiments can be imple-
mented via one or more hardware devices, or one or
more software entities such as modules.
While the present inventions have been de-
scribed in connection with a number of exemplary embo-
diments, and implementations, the present inventions
are not so limited, but rather cover various modifica-
tions, and equivalent arrangements, which fall within
the purview of prospective claims.
It is obvious to a person skilled in the art
that with the advancement of technology, the basic
idea of the invention may be implemented in various
ways. The invention and its embodiments are thus not
limited to the examples described above; instead they
may vary within the scope of the claims.

CLAIMS:
1. A method, comprising:
determining, by a controller of an electrical con-
verter, a first reactive power produced by a smoothing
filter using pre-determined information on impedance
of the smoothing filter, the smoothing filter being
electrically connected via a three-phase electrical
connection to a converter matrix of the electrical
converter of an elevator, the smoothing filter being
electrically connected via a three-phase connection to
a grid, the converter matrix producing pulse width
modulated three-phase output voltages to the smoothing
filter; and
requesting, by the controller, the electrical con-
verter to make a plurality of first compensative elec-
trical connections in the converter matrix to compen-
sate the first reactive power.
2. The method according to claim 1, the me-
thod further comprising:
receiving, by the controller, information on a
second reactive power from a remote node over a commu-
nication channel, the second reactive power being pro-
duced to the grid;
adding, by the controller, the first reactive pow-
er and the second reactive power to yield a total
reactive power; and
requesting, by the controller, the electrical con-
verter to make a plurality of second compensative con-
nections in the converter matrix to compensate the to-
tal reactive power.
3. The method according to claim 1 or claim
2, the step of determining the first reactive power
further comprising:
measuring a phase to neutral voltage by the con-
troller in the grid; and
measuring a phase current by the controller in at
least one of the grid and the three-phase electrical

connection between the smoothing filter and the con-
verter matrix; and
determining, by the controller, the first reactive
power using the pre-determined information on imped-
ance of the smoothing filter, the phase to neutral
voltage and the phase current.
4. The method according to any of the claims
1-3, wherein the smoothing filter is an LCL filter.
5. The method according to any of the claims
1 - 4, wherein the grid is an internal grid of a
building.
6. The method according to any of the claims
1 - 5, wherein the remote node is a building automa-
tion system server.
7. The method according to any of the claims
1-6, wherein the second reactive power is produced
to the grid by at least one building electrical sub-
system.
8. The method according to claim 7, wherein
the at least one building electrical subsystem com-
prises lighting, heating, air circulation and access
control.
9. The method according to any of the claims
1-8, the method further comprising:
determining a voltage drop in a voltage of the
grid; and
making a plurality of connections in the converter
matrix to regulate the voltage of the grid.
10. The method according to any of the claims
1-9, wherein the first reactive power is determined
for three phases, the information on the second reac-
tive power comprises information on three-phases and
the total reactive power is computed for three phases.
11. The method according to any of the claims
1 - 10, wherein the converter matrix is electrically
connected to an inverter bridge via a direct current

connection and the inverter bridge is electrically
connected to an electrical motor of the elevator.
12. An electrical converter of an elevator,
the electrical converter comprising:
a smoothing filter configured to smooth three-
phase output currents, the smoothing filter being
electrically connected via a three-phase electrical
connection to a converter matrix, the smoothing filter
being electrically connected via a three-phase elec-
trical connection to a grid;
a converter matrix configured to produce the pulse
width modulated three-phase output voltages to the
smoothing filter, to make a plurality of connections
in the converter matrix to compensate reactive power;
and
a controller configured to determine a first reac-
tive power produced by a smoothing filter using pre-
determined information on impedance of the smoothing
filter and to request the electrical converter to make
the plurality of first compensative connections in the
converter matrix to compensate the first reactive pow-
er.
13. The electrical converter of claim 12,
wherein the controller is configured to receive infor-
mation on a second reactive power from a remote node
over a communication channel, the second reactive pow-
er being produced to the grid, to add the first reac-
tive power and the second reactive power to a yield a
total reactive power, and to request the electrical
converter to make a plurality of second compensative
connections in the converter matrix to compensate the
total reactive power.
14. An elevator comprising the elevator elec-
trical converter according to claim 12.
15. An elevator group comprising the elevator
according to claim 14.

ABSTRACT

The invention relates to a me
thod and an electrical converter of an
elevator. In the method a controller of
the electrical converter determines a
first reactive power produced by a
smoothing filter using pre-determined
information on impedance of the smooth
ing filter. The controller may also re
ceive information on a second reactive
power from a remote node over a communi
cation channel, the second reactive pow
er being produced to a grid. The con
troller adds the first reactive power
and the second reactive power to yield a
total reactive power. The controller re
quests the electrical converter to make
a plurality of compensative connections
in the converter matrix to compensate
the first reactive power or the total
reactive power.