The invention relates to method for testing a capacity of a drive rescue battery for
driving an electric motor of a transportation system in a rescue operation mode, a
software program, and a testing arrangement.
When a power sag or power loss occurs, a transportation system such as an elevator, an
escalator, a moving walkway or the like my come to an unintended halt concerning a
safety of passengers using the transportation system. An elevator may become stalled
between floors in the elevator hoistway until the power supply returns to the nominal
operating voltage range. In conventional systems, passengers in the elevator may be
trapped until a maintenance worker is able to release a brake for controlling cab
movement upwardly or downwardly to allow the elevator to move to the closest floor.
To improve this situation, elevator systems employing automatic rescue operation have
been introduced. These elevator systems include electrical energy storage devices, e.g.
in the form of a drive rescue battery, that are controlled after power failure to provide
power to move the elevator to the next floor for passenger disembarkation. An
integrated rescue feature of new generation drives for elevators thus enables battery
discharging to drive internal loads such as moving the trapped elevator car up or down
to the closest floor.
However, many current automatic rescue operation systems are complex and expensive
to implement, and may provide unreliable power to the elevator drive after a power
failure. For example, battery capacity will decrease over time and use. It is extremely
important to replace the rescue battery with a new one before a given capacity, i.e.
stored electric charge, of the battery is too small to complete the rescue operation
leading to a situation that the rescue operation may fail.
Previous attempts to safeguard a sufficient capacity of the drive rescue battery rely on an
external load resistor or braking resistor which may have been used as a load resistor.

The LCL filter (LCL stands for inductor L - capacitor C - inductor L) is used to reduce
higher-order harmonics caused by the switching frequency of electronically switchable
switching means of the rectifier circuit, e.g. in the form of insulated gate bipolar
transistors (IGBTs). LCL filters in T-form are low pass filters especially designed to reduce
harmonics of current absorbed by power converters, with a rectifier input stage such as
the rectifier circuit of the frequency converter. Mainly, LCL filters are made of a parallel-
series combination of reactors or inductors and capacitors adapted to reduce the Total
Harmonic Distortion of the current, abbreviated THD(I), of rectifiers. They are especially
designed to reduce the THD(I) to values of approximately 8%, in order to comply with
IEC-61000-3.4 and 1EEE-519 standards. The LCL-filter may be disconnected from the AC
mains downstream of an EMI-filter (EMI is the short form of electromagnetic
Interference) which is connected to the AC means.
The rectifier circuit may be in the form of an Active Front End (AFE). Rather than using
diodes in the rectifier circuit to convert the incoming AC voltage to a DC voltage, in the
Active Front End IGBTs are used to convert the incoming AC power to DC. Other
electronically switchable switching means than IGBTs may be used, it is possible by
means of the AFE to monitor an input current waveform and to shapes it to be
sinusoidal, reducing total harmonic distortion (THD) to 5 percent or less, where the
THD is only measured for lower-order harmonics. The inventive method may thus
executed by means of an Active Front End and the LCL-filter as a test load / power sink
for testing that the drive rescue battery has adequate capacity to fulfil a rescue operation.
The first, second, and third phases are defined in the following as the power phases of
an AC means supply to supply electric power to a consumer for driving the
transportation system, such as a hoisting motor of an elevator. Each phase's voltage,
current, and power is offset from the voltage, current, and power of another phase by
120°. Each phase is associated with an electric main, e.g. in form of an electric wire or
an electric path of whatever sort, e.g. a conducting layer attached to a substrate like a
PCB (printed circuit board), of its own which is conducted from the AC means through
the LCL-filter to the rectifier circuit isolated from the electric mains associated with the

a capacity sufficient for a rescue operation is thus provided. At the same time, the
inventive method is energy efficient for the electric motor not being required to move to
represent the test load.
The method is preferably executed by further comprising:
modulating, e.g. by pulse width modulation (PWM), electronically switchable
switching means of the rectifier circuit which are connected to the first and
second phases to generate an AC-voltage from the DC supply voltage supplied
by the drive rescue battery, which AC-voltage is applied to the test load.
The electronically switchable switching means of the rectifier circuit may be insulated
gate bipolar transistors. Gates of the electronically switchable switching means may be
modulated to generate the AC-voltage from the DC supply voltage supplied by the drive
rescue battery.
In a further embodiment, the modulating of the first and second phases of the rectifier
circuit comprises the steps:
operating the high side electronically switchable switching means of the rectifier
circuit connected to the first phase and the low side electronically switchable
switching means of the rectifier circuit connected to the second phase to be
closed while operating the other electronically switchable switching means of
the rectifier circuit connected to the first and second phases to be open, and
operating the high side electronically switchable switching means of the rectifier
circuit connected to the second phase and the low side electronically switchable
switching means of the rectifier circuit connected to the first phase to be closed
while operating the other electronically switchable switching means of the
rectifier circuit connected to the first and second phases to be open.
Both steps may occur subsequently to each other, wherein the second step can be
executed before or after the first step. Intermediate steps are possible as long both steps
are executed during testing of the capacity of the drive rescue battery. The first step
leads to a current running from a high side of the DC supply voltage to a low side
thereof. The second first step leads to a current running in the opposite direction of the
first step, i.e. from the low side of the DC supply voltage to the high side thereof.

When a battery test is requested, a drive main circuit including the LCL-filter and the
rectifier circuit of the frequency converter is isolated from the AC mains power supply to
be able to use LCL-filter and the rectifier circuit, e.g. in the form of the Active Front End
for loading the drive rescue battery. A battery negative terminal may be connected to a
low side of the DC supply voltage, which may be labeled DC-link minus potential. A
battery positive terminal may be connected to the inductor of the LCL-filter connected to
the third phase, which inductor acts as boost converter storage choke. A boost converter
may be formed by the low side electronically switchable switching means of the rectifier
circuit connected to the third phase as switch and a diode switched in parallel to a high
side electronically switchable switching means of the rectifier circuit connected to the
third phase, as a boost rectifier.
It is thus preferred that the boost converter is formed by the low side electronically
switchable switching means of the rectifier circuit connected to the third phase as a
boost converter switch, the diode, which is switched in parallel to the high side
electronically switchable switching means of the rectifier circuit connected to the third
phase, as a boost rectifier, and a capacitive intermediate device of the frequency
converter for leveling the DC supply voltage as a boost converter capacitor. The high
side and low side electronically switchable switching means of the rectifier circuit may
be IGBTs.
As stated above, it is preferred that the negative terminal of the drive rescue battery is
connected to the DC-link minus potential of the DC supply voltage and the positive
terminal of the drive rescue battery is connected to the inductor of the LCL-filter
connected to the third phase. Alternatively, the positive terminal of the drive rescue
battery may be connected to a DC-link plus potential of the DC supply voltage and the
negative terminal of the drive rescue battery may be connected to the inductor of the
LCL-filter connected to the third phase.
. It is particularly preferred that a local drive unit of the frequency converter and / or an
external server initiate(s) and / or execute(s) the testing of the capacity of the drive
rescue battery and / or analyse(s) results of the testing of the capacity of the drive rescue

different threshold levels discussed above. Also, the analysis of the results of the testing
of the capacity of the drive rescue drive could be done alternatively to an external server
such as a cloud server or in work sharing with such a server locally in a battery
management system that would have a required energy / charge level of the battery to
perform the worst case scenario rescue operation of the transportation system, e.g.
elevator system, stored in its memory. Then, the battery management system may send
the maintenance need information to the cloud server, the service unit, and / or the
maintenance person.
Another aspect of the invention is a software program realizing the methods according
to the invention when executed on a computer. In the aforementioned software program
the computer is preferably a distributed computing system wherein part of the
computing system is located / arranged / operated in a cloud computing system. The
software program may be embodied as a computer program product or a data carrier
carrying data representing the software program.
The invention also relates to a testing arrangement for testing a capacity of a drive
rescue battery configured to drive an electric motor of a transportation system in a
rescue operation mode. The testing arrangement comprises
the drive rescue battery and measuring means configured to measure a voltage, a
current, a voltage decrease over time, e. g. 10 minutes, and / or a current decrease over
time of the drive rescue battery,
first, second, and third phases of AC-means which are configured to supply
power from the AC-means via a low pass LCL-filter to a frequency converter configured
to drive the electric motor in normal operation mode,
the LCL-filter,
a rectifier circuit of the frequency converter configured to provide a DC supply
voltage,
a first switching device configured to disconnect the AC means from the LCL-
filter,
a second switching device configured to disconnect an inductor of the LCL-filter
connected to the third phase, wherein the inductor is connected downstream of a

switching means are opened and the third switching device is closed, the inductor of
the LCL-filter connected to the third phase forms a boost converter storage choke in the
rescue operation mode. This way, the battery is able to supply electric power / charge to
the capacitive intermediate device of the frequency converter for leveling the DC supply
voltage, i.e. the DC-link, directly or via one or several converters which is able to further
supply electric power / charge to the rectifier circuit, e.g. the AFE, and the LCL-filter. As
explained above for the first and second switching devices, several phases may by
switched, e.g. together and simultaneously, by the third switching device.
In a preferred embodiment, the inductor of the LCL-filter connected to the third phase is
connected to a link connecting a low side electronically switchable switching means
and a high side electronically switchable switching means of the rectifier circuit
connected to the third phase such that the inductor such that the inductor forms a boost
converter storage choke in the rescue operation mode. The boost converter may then be
formed by the low side electronically switchable switching means of the rectifier circuit
connected to the third phase as a boost converter switch, the diode switched in parallel
to the high side electronically switchable switching means of the rectifier circuit
connected to the third phase, as a boost rectifier, and the capacitive intermediate device
of the frequency converter for leveling the DC supply voltage as a boost converter
capacitor.
Further embodiments of the inventive method, the inventive software program, and the
testing arrangement according to the invention include that
the transportation system is formed by one of an elevator, escalator and a
moving sidewalk and / or
the rectifier circuit is formed by an Active Front End (AFE) and / or
at least one the high side and low side electronically switchable switching
means of the rectifier circuit connected to the first, second, and third phases are formed
by an Insulated Gate Bipolar Transistor. The transportation system is thus selected with
advantage from one of an elevator, an escalator, and a moving walkway. It is further
possible to select the transportation system from one of a cablecar, a railway
locomotive, a railcar, a roller coaster, a conveyor, a crane, a positioning unit, and

Now, exemplary embodiments of the invention will be described in further detail.
Fig. 1 shows an electric diagram of the motor and brake drive section of an elevator
system including a drive rescue battery 10 and a battery charger 11 for the drive rescue
battery 10. The motor and brake drive section is supplied with electric AC power in
normal operation mode by AC means 2 which supply power over a first phase P1, a
second phase P2 and a third phase P3 via a low pass LCL-filter 4 to a frequency
converter 8 for driving an electric motor 9 for moving an elevator car of the elevator
system. The phases PI, P2, P3 provide AC-voitage offset by approximately 120 degrees
to each other with respect to ground G. An EMI filter may be inserted between the AC
means 2 and the LCL-filter 4 as shown in the figure. The frequency converter 8
comprises a rectifier circuit 5 for providing a DC supply voltage, a capacitive
intermediate device 6 for leveling the DC supply voltage, and an output inverter 7 for
generating the AC power supplied to the electric motor 9 as required to control a
movement of the elevator car of the elevator system. The rectifier circuit 5 is in the form
of an Active Front End comprising electronically switchable switching means T1 to T6
with diodes, e.g. diode D6 of IGBT of T6, switched in parallel thereto functioning as
freewheeling diodes. The electronically switchable switching means T1 to T6 are
embodied as IGBTs with the IGBTs T1, T3, and T5 at a low side LS of the DC supply
voltage, which may be labeled DC-link minus potential, and the IGBTs T2, T4, and T6
at a high side HS of the DC supply voltage. IGBTs T1, T2 are linked to each other and
connected to the first phase PI, IGBTs T3, T4 are linked to each other and connected to
the second phase P2, and IGBTs T5, T6 are linked to each other and connected to the
third phase P3. A corresponding arrangement of electronically switchable switching
means as that of the rectifier circuit 5 in the form of IGBTs 17 to T12 is set up in the
output inverter 7 for generating the AC-voltage for the motor 9.
The battery charger 11 is not only connected to the DC plus terminal of the drive rescue
battery but also to the high side HS and low side LS of the DC supply voltage. The
battery charger can therefore also supply DC-voltage to the capacitive intermediate
device 6 and to redundant machinery brake controllers and thus brakes of the
machinery brake controllers and brakes 12. Moreover, the capacitive intermediate

Switches SI" and S2 are controlled by switch control unit SC2. If the first switches S1,
ST, SI" and the second switch S2 are opened, inductors L2, L2' and capacitors C1, C2
of the LCL-filter 4, wherein L2 and C1 are connected to the first phase P1 and L2# and
C2 are connected to the second phase P2, form a test load for testing the capacity of the
drive rescue battery 10. Inductor L1 of the LCL-filter 4, which is connected to the first
phase P1 upstream of the capacitor C1, and inductor L1' of the LCL-filter 4, which is
connected to the second phase P2 upstream of the capacitor C2, are not part of a closed
electric circuit and thus not operating. In contrast to L1 and L1', inductors L2 and L2' are
connected via capacitors C1 and C2 in a series connection to the rectifier circuit
connected to the first phase Pa1 and the second phase P2 to be supplied with AC-
voltage by modulating the gates of the IGBTs T1 to T4 for constituting the test load of
the drive rescue battery 10. To this end, inductor L2 of the LCL-filter 4, which is
connected to the first phase P1 and downstream of the capacitor C1 of the LCL-filter 4
connected to the first phase P1 to the rectifier circuit 5, the capacitors C1, C2 of the
LCL-filter 4 connected to the first phase P1 and the second phase P2, and the inductor
L2' of the LCL-filter 4 which is connected to the second phase P2 and downstream of
the capacitor C2 of the LCL-filter 4, which is connected to the second phase P2, to the
rectifier circuit 5 form the series connection as the test load for the battery 10.
A third switch S3 is configured to disconnect a DC plus terminal of the drive rescue
battery 10 from the inductor L2" of the LCL-filter 4 connected to the third phase P3
upstream of the inductor L2", wherein, if the first switches SI, SV, SI" and the second
switch S2 are opened and the third switch S3 is closed, the inductor L2" of the LCL-filter
4 connected to the third phase P3 forms a boost converter storage choke in the rescue
operation mode and in the inventive method for testing the capacity of the battery 10.
The switch S3 is controlled by switch control unit SC3. When the switch S1" and S2 are
opened by switch control unit SC2, inductor L1" of the LCL-filter 4, which is connected
to the third phase P3 upstream of the capacitor C3, and capacitor C3 of the LCL-filter 4,
which is connected to the third phase P3 upstream of the inductor L2", are not part of a
closed electric circuit and thus not operating. When first switches S1, S1, S1" and
second switch S2 are opened and the third switch S3 is closed, a boost converter is
formed by

of the first phase P1, LV of the second phase P2, and L1" of the third phase P3 are not
used in boost operation or as the test load of the drive recue battery 10.
Fig. 3 is a simplified electric diagram of the testing arrangement 1 of Fig. 2 for driving
the electric motor 9 of the elevator system in a rescue operation mode according to the
invention. Once the first switches S1, SV, S1" and the second switch S2 are opened, the
electric diagram of Fig. 2 can be simplified into that of Fig. 3. Modulation of the gates
G1 of IGBT 1 and G2 of IGBT T2, each of which is connected to the first phase P1, and
of the gates G3. of IGBT 3 and G4 of IGBT T4, each of which is connected to the second
phase P2, results in providing AC-voltage for the test load being the series connection of
inductor L2, capacitor C1, capacitor C2, and inductor L2'. First, the switches S1, S1, S1
and S2 are opened. Thereafter, switch S3 is closed to set the battery 10 into boost
operation mode. Then, the gates G1 to G4 of the IGBTs T1 to T4 may be modulated for
a test load of an AC-voltage generated by the series connection of devices L2, C1, C2,
and L2' being applied to the battery 10. According to the invention, a control unit of the
frequency converter 8 may be responsible for initiating, executing and analysing the
testing without the intervention of an elevator controller.
The motor 9 (see Fig. 1) must not run during the test of the capacity of the drive rescue
battery 10. During this test only the two phases P1 and P2 can be modulated to provide
constant AC-discharge power and the third phase P3 can be used for the boost operation
of the battery 10. Inductor L2" is essential only for the boost operation of the battery 10,
not for the test load operation of the series connection of L2, C1, C2, L2'. In case the
battery 10 is connected in some other way to the DC-link, e.g. when the positive
terminal of the drive rescue battery may be connected to the DC-link plus potential of
the DC supply voltage and the negative terminal of the drive rescue battery may be
connected to the inductor of the LCL-filter connected to the third phase, the inductor
L2" may not be participating in a closed electric circuit and thus not operate.
Consequently, the inventive method of testing the capacity of the battery 10 by using
the devices L2, C1, C2, L2" of the LCL-filter 4 as a test load of the battery 10 may not
require the battery to operate in the boost operation mode. To resemble the test load
with that of the motor 9 when running, it is preferred to modulate the gates G1 to G4 of

10 is boost converted into the high side HS and the low side LS of the DC supply
voltage (DC-link plus potential and DC-link minus potential). The gates G1 to G4 of
ICBTs T1 to T4 are pulse width modulated to generate an AC-voltage over inductor L2,
capacitors C1, C2, and inductor L2' connected in series. The resulting test load of the
battery 10 is for example 230 V, 10 A at 1000 Hz. Intervals in time 45, 45', 45", 45'",
45"" indicate states in which the high side IGBT T2 connected to the first phase P11
and the low side IGBT T3 connected to the second phase P2 are conducting for current
to flow technically from the high side to the low side of the DC supply voltage. IGBTs
T1, T4 are not conducting and therefore do not have an impact on the current flow.
During the time intervals 45 to 45"" there is a positive voltage in a range 46 between
approximately 200 and 230 V to be supplied by the battery 10. In time intervals 47, 47',
47", 47'", 47"" states are indicated in which the low side IGBT T1 connected to the
first phase P1 and the high side IGBT T4 connected to the second phase P11 and are
conducting for current to flow technically from the low side to the high side of the DC
supply voltage, i.e. the opposite direction of the current which is flowing during time
intervals 45 to 45"". IGBTs T2, T3 are not conducting when IGBTs T1, T4 are
conducting and thus do not have an impact on current flow. During the time intervals
47 to 75"" there is a negative voltage in the range 48 ranging between approximately
-200 and -230 V to be supplied by the battery 10. The operation of the gates G1 to G4
comprises according to Fig. 4 other switching patterns of the IGBTs T1 to T4 as well,
e.g. after an interval of closed IGBT T2 and IGBT T3 and opened IGBT T1 and IGBT T4
at t=O,0992 s (see time interval 45"), it follows an interval of closed IGBT T2 and IGBT
T4 and opened IGBT T1 and IGBT T3 at t = 0,09923 s before the following interval of
closed IGBT T2 and IGBT T3 and opened IGBT T1 and IGBT T4 again at t = 0,09925 s
(see time interval 45'").
The fundamental frequency of 1000 Hz and voltage level of 230 V over the LCL-filter
capacitors C1, C2 are controlled to keep a constant discharge power by using a P
(Proportional) or PI (Proportional Integral) controller. A PID (Proportional Integral
Differential) controller is also possible. First a discharge power reference value is set to
e.g. 200 W. Then a battery current and voltage measurement is utilized to acquire a
(real) discharge power value, which is subtracted from the discharge power reference

PATENT CLAIMS
1. Method for testing a capacity of a drive rescue battery (10) for driving an electric
motor (9) of a transportation system in a rescue operation mode, wherein in normal
operation mode AC means (2) supply power over first (P1), second (P2) and third phases
(P3) via a low pass LCL-filter (4) to a frequency converter (8) for driving the electric
motor (9), wherein the frequency converter (8) comprises a rectifier circuit (5) for
providing a DC supply voltage, wherein the method comprises the steps:
disconnecting the LCL-filter (4) from the AC mains (2);
using inductors (L2, L2') and capacitors (C1, C2) of the LCL-filter (4), each of
which being connected to the first (P1) or second phase (P2), as a test load for
testing the capacity of the drive rescue battery (10), wherein the inductor (L2) of
the LCL-filter (4), which is connected to the first phase (PI) and downstream of
the capacitor (C1) of the LCL-filter (4), which is connected to the first phase (P1),
to the rectifier circuit (5), the capacitors (C1, C2) of the LCL-filter (4) connected
to the first (P1) and second phases (P2), and the inductor (L2') of the LCL-filter (4)
which is connected to the second phase (P2) and downstream of the capacitor
(C2) of the LCL-filter (4), which is connected to the second phase (P2), to the
rectifier circuit (5) form a series connection as the test load; and
determining at least one value of a voltage or a current of the drive rescue
battery (10) resulting from the test load.
2. Method of claim 1, further comprising:
modulating, e.g. by pulse width modulation (PWM), electronically switchable
switching means (T1 - T4) of the rectifier circuit (5) which are connected to the
first (P1) and second phases (P2) to generate an AC-voltage from the DC supply
voltage supplied by the drive rescue battery (10), which AC-voltage is applied to
the test load.
3. Method of claim 2, wherein the modulating of the first (P1) and second phases
(P2) of the rectifier circuit (5) comprises the steps:

LCL-filter (4) connected to the third phase (P3), to the third phase (P3) of the
rectifier circuit (5), upstream of the inductor (L2") from the rest of the LCL-filter
(4); and
connecting one terminal of the drive rescue battery (10) to the inductor (L2") of
the LCL-filter (4) connected to the third phase (P3) such that the inductor (L2")
forms a boost converter storage choke in the rescue operation mode.
7. Method of claim 6, wherein a boost converter is formed by a low side (LS)
electronically switchable switching means (T5) of the rectifier circuit (5) connected to
the third phase (P3) as a boost converter switch, a diode (D6), which is switched in
parallel to a high side (HS) electronically switchable switching means (T6) of the rectifier
circuit (5) connected to the third phase (P3), as a boost rectifier, and a capacitive
intermediate device (6) of the frequency converter (8) for leveling the DC supply voltage
as a boost converter capacitor.
8. Method of claim 6 or claim 7, wherein either a negative terminal of the drive
rescue battery (10) is connected to a DC-link minus potential (LS) of the DC supply
voltage and a positive terminal of the drive rescue battery (10) is connected to the
inductor (L2") of the LCL-filter (4) connected to the third phase (P3) or the positive
terminal of the drive rescue battery (10) is connected to a DC-link plus potential (HS) of
the DC supply voltage and the negative terminal of the drive rescue battery (10) is
connected to the inductor (L2") of the LCL-filter (4) connected to the third phase (P3).
9. Method of any of the preceding claims, wherein a local drive unit of the
frequency converter (8) and / or an external server initiate(s) and / or execute(s) the
testing of the capacity of the drive rescue battery (10) and / or analyse(s) results of the
testing of the capacity of the drive rescue battery (10), e.g. at least one value of at least
one measurement of the voltage, the current, a voltage decrease over time, e.g. 10
minutes, and / or a current decrease over time of the drive rescue battery (10) to
determine an energy / charge level of the drive rescue battery (10) for comparison with a
required energy / charge level which is indicated by a threshold or several thresholds

of the drive rescue battery (10), wherein the inductor (L2) of the LCL-filter (4), which is
connected to the first phase (P1) and downstream of the capacitor (C1) of the LCL-filter
(4) connected to the first phase (P1) to the rectifier circuit (5), the capacitors (C1, C2) of
the LCL-filter (4) connected to the first (P1) and second phases (P2), and the inductor
(L2') of the LCL-filter (4) which is connected to the second phase (P2) and downstream
of the capacitor (C2) of the LCL-filter (4) connected to the second phase (P2) to the
rectifier circuit (5) form a series connection as the test load.
12. Testing arrangement (1) of claim 11, wherein the inductor (L2) of the LCL-filter
(4) connected to the first phase (P1) is connected to a link connecting a low side (LS)
electronically switchable switching means (T1) and a high side (HS) electronically
switchable switching means (T2) of the rectifier circuit (5) connected to the first phase
(P1) and the inductor (L2') of the LCL-filter (4) connected to the second phase (P2) is
connected to a link connecting a low side (LS) electronically switchable switching
means (T3) and a high side (HS) electronically switchable switching means (T4) of the
rectifier circuit (5) connected to the second phase (P2).
13. Testing arrangement (1) of claim 11 or claim 12, further comprising
a third switching device (S3) configured to disconnect one terminal of the drive
rescue battery (10) from the inductor (L2") of the LCL-filter (4) connected to the third
phase (P3) upstream of the inductor (L2"), wherein, if the first (S1, ST, S1") and second
switching means (S2) are opened and the third switching device (S3) is closed, the
inductor (L2") of the LCL-filter (4) connected to the third phase (P3) forms a boost
converter storage choke in the rescue operation mode.
14. Testing arrangement (1) of claim 13, wherein the inductor (L2") of the LCL-filter
(4) connected to the third phase (P3) is connected to a link connecting a low side (LS)
electronically switchable switching means (T5) and a high side (HS) electronically
switchable switching means (T6) of the rectifier circuit (5) connected to the third phase
(P3).