t
Technical Field
[0001] The present invention relates to a power conversion device, and a control
5 and communication device as well as a communication error detecting
method, both of which are used for the power conversion device.
Background of Invention
[0002] In recent years, the introduction of distributed power sources, typified by
a solar power generation, into the power distribution system has been
10 actively promoted, but as a result, increasing voltage variation of the power
distribution system is becoming a problem. It is effective to apply a reactive
power compensator for improving the stability of such a power distribution
system, and in particular, application of a cascade-connection type SVC
(Static Var Compensator) is proposed.
15 In Patent Literature 1, a technique of a cascade"connection type SVC is
disclosed, wherein single-phase power converters, having N units per phase,
are serially connected at the AC side and configured to be capable of
outputting multi-level voltages.
When the single-phase power converters (hereinafter, referred to "cells"
20 as appropriate) are controlled by a PWM (Pulse Width Modulation) method,
and if a phase of a triangular carrier wave to be supplied to each of the cells
is shifted properly, it is possible for output power waveforms of the SVCs to
approximate sine waves at multi-levels, thereby suppressing harmonic
components.
25 In Patent Literature 2, an operation method is disclosed, wherein, in
order to control a plurality of cells by a PWM method, by constituting a
distributed control system consisting of. a central control unit installed in a
position at a distance from the cells; and cell control units installed in the
vicinity of each of the cells, and by including a PWM synchronization signal,
30 as well as a voltage command value and a PWM pattern command, in a
2
signal to be transmitted from the master to the slaves, a PWM generator is
reset every time the synchronization signal is outputted.
Prior Art Literature
[0003] Patent Literature:
5 1. Japanese Laid-Open Patent Application No. 2007-280358
2. Japanese Laid-Open Patent Application No. 2002-345252
Summary of Invention
Problems to be Solved
[0004] However, as a potential of each of the cells is different from one another
10 in the cascade-connection type SVC and some cells may have high ground
potentials, the central control unit at the grounded potential and each of the
cell control units need to be connected with a special optical fiber cable
provided with a dielectric strength to withstand the potential difference
between the two.
15 Further, as there is a possibility of a communication error such as a cable
short circuit due to insulation deterioration, a feature to detect such a
communication error need to be also provided. However, there is a problem
that the number of bits of the control signal frame increases when the
communication error detection feature is incorporated into the control signal
20 frame, and it takes longer time.
An optical fiber cable having a dielectric strength is more expensive as an
insulation performance increases. Therefore, it is assumed to shorten the
length of the optical fiber cable requiring high insulation performance in the
entire system, by connecting the central control unit and each of the cell
25 control units with a daisy chain through the optical communication means.
With the daisy chain connection, as the control signal frame transmitted
from the central control unit includes the information for controlling all the
cells, it takes longer time for the control signal frame, thus revealing the
aforesaid problem notably.
30 [0005] Accordingly, the present invention is intended to solve these problems,
with the purpose of providing a power converter configured to perform error
3
II
detection at low cost and easily for inability to transmit from the control unit of
each of the single"phase power converters, communication interruptions due to
disconnection or short circuit of the optical fiber cable, or the like.
Means for solving Problems
5 [0006] In order to solve the aforesaid problems and attain the purpose of the
present invention, a configuration is made as follows.
That is, a power conversion device includes: a plurality of cascade"
connection type single"phase power converters; and a first control unit that
controls the plurality of single "phase power converters, wherein each of the
10 plurality of the single"phase power converters has a second control unit, and
the first control unit and the plurality of the second control units are
connected via a communication means having a daisy"chain configuration,
wherein the second control unit transmits and receives a control signal via
the communication means having the daisy"chain configuration, as well as a
15 specific pattern signal, other than a control signal frame, which can be
distinguished from the control signal frame, and determines a communication
error due to not receiving the specific pattern signal at the second control
unit, or an inconsistency between the received signal and the specific pattern
signal.
20 Effects of Invention
[0007] According to the present invention, it is possible to provide a power
converter configured to perform error detection at low cost and easily for
inability to transmit from the control unit of each of the single"phase power
converter, communication interruptions due to disconnection or short circuit
25 of the optical fiber cable, or the like.
Brief Description of Drawings
[0008] FIG. 1 is a diagram showing a configuration of an optical serial signal
frame provided with a control signal and a specific pattern signal of a first
embodiment of the present invention.
4
..
FIG. 2 is a diagram showing a circuit configuration of a cascadeconnection
type SVC according to the first embodiment of the present
invention.
FIG. 3 is a diagram showing a circuit configuration of a single-phase
5 power converter (cell) in the cascade-connection type SVC according to the
first embodiment of the present invention.
FIG. 4 is a diagram showing a configuration of an optical serial signal
frame including a signal indicating presence or absence of a communication
error in upstream cells and a communication error cell number according to a
10 second embodiment of the present invention.
FIG. 5 is a diagram showing a configuration of an optical serial signal
frame including a common-for-all-cell control signal according to a third
embodiment of the present invention.
FIG. 6 is a diagram showing the configuration of an optical serial signal
15 frame as a comparative reference.
FIGS. 7A and 7B are diagrams showing a circuit configuration of a
modular multilevel converter as a reference, where FIG. 7A shows a
schematic configuration of a modular multilevel converter and FIG. 7B shows
a circuit configuration of a cell used in FIG. 7A.
20 Embodiments of Invention
[0009] Hereinafter, embodiments for implementing the present invention will
be described with reference to drawings.
First Embodiment
[0010] A first embodiment of the present invention will be described with
25 reference to FIGS. 1 to 3.
FIG. 1 is a diagram showing a configuration of an optical serial signal
frame provided with a control signal and a specific pattern signal used for the
first embodiment of the present invention.
FIGS. 2 and 3 are diagrams showing circuit configurations of a cascade-
30 connection type SVC which is a power conversion device that applies the
5
optical serial signal frame used in the first embodiment of the present
invention.
A feature of the first embodiment of the present invention is in the
configuration of an optical serial signal frame provided with a control signal
5 and a specific pattern signal in FIG. 1, but for the purpose of easy
understanding why such a configuration of a signal frame is being applied, a
circuit configuration of a power conversion device that applies an optical
serial signal frame used in the first embodiment of the present invention will
be described first with reference to FIGS. 2 and 3, then the configuration of
10 the optical serial signal frame in FIG. 1 will be described.

[0011] In FIG. 2, the power conversion device according to the first embodiment
(cascade-connection type Static Var Compensator) 23 is interconnected to a
three-phase power system 21 via a transformer 22, and an AC power is
15 transferred between the two (21 and 23). Each converter arm of the power
conversion device 23 is configured with cascade"connection of cells 24 which
are a plurality of single-phase power converters.
[0012] That is, a first converter arm has cells Cn"C1n cascade"connected, a
second converter arm has cells C21-C2n cascade-connected, and a third
20 converter arm has cells C31-C3n cascade "connected, thereby constituting a
three-phase converter arm out of the first to third converter arms.
In addition, one end of each of the first to third converter arms is
connected to the secondary side of the transformer 22 via an AC reactor 29.
The other end of each of the first to third converter arms is commonly
25 connected.
It should be noted that the circuit configuration of the power conversion
device 23 in FIG. 2 is called a Cascade-Multilevel Converter (CMC).
[0013] A central control unit (first control unit) 26 is configured to include a
central controller 27 and an optical communication master 28, for controlling
30 the power conversion device 23.
6
As will be described later, each cell 24 of a plurality of single"phase power
converters includes a cell control unit (second control unit, or single"phase
power converter control unit) 37 (FIG. 3) and an optical communication slave
38 (FIG. 3).
5 The central control unit 26 transmits an optical serial signal (frame) to
the optical communication slave 38 (FIG. 3) of each cell 24 via an optical fiber
cable 25, by the central controller 27 and the optical communication master
28, and receives a signal from the optical communication slave 38 (FIG. 3) of
each cell 24.
10 However, it does not mean that the optical communication master 28 and
an optical communication slave 38 (FIG. 3) of each cell 24 are directly
connected via an optical fiber cable 25. It will be described below what
configuration is used for connecting the two.
[0014] In FIG. 2, the optical communication master 28 is connected to the cell
15 Cll of a cell 24 via the optical fiber cable 25, the cell Cll is connected to the
cell C12 via the optical fiber cable (25), and likewise cells are connected in
series up to the cell C1n, which is a terminal of the first converter arm, via
the optical fiber cable (25).
Further, the cell C2n, which is a terminal of the second converter arm, is
20 connected to the cell C1n via the optical fiber cable (25), and the cell C2n up
to the first cell C21 of the second converter arm are sequentially connected in
series via the optical fiber cable (25).
Furthermore, the cell C31, which is a first cell of the third converter arm,
is connected to the cell C21 via the optical fiber cable (25), and the cell C31 up
25 to the cell C3n, which is a terminal of the third converter arm, are
sequentially connected in series via the optical fiber cable (25).
Lastly, the cell C3n is connected to the optical communication master 28
via the optical fiber cable (25).
[0015] As shown above, by the optical communication master 28 of the central
30 control unit 26 controlling the optical communication slaves 38 (FIG. 3) of the
plurality of the cells 24, the central control unit 26 and the cells 24 of a
7
plurality of single-phase power converters relationally constitute a daisy
chain.
It should be noted that the central control unit 26 as well as the neutral
point of the secondary side of the transformer 22 are generally configured to
5 have the grounded potential, but not necessarily.

[0016] FIG. 3 is a diagram showing a circuit configuration of a cell 24 of a
single-phase power converter.
In FIG. 3, a main circuit 34 as a single-phase power converter is a full-
10 bridge circuit configured with switching elements 35A, 35B, 36A and 36B,
each of which is composed of an IGBT (Insulated Gate Bipolar Transistor). In
addition, a DC capacitor 39 is provided in the main circuit 34.
By turning on/off switching elements 35A, 35B, 36A, 36B, an AC voltage
which the cell 24 of a single-phase power converter is in charge thereof is
15 outputted across a first and second terminals 241,242 of the main circuit 34
having a full-bridge configuration.
[0017] The cell control unit 37 generates a pulse (gate pulse) of the control
signal which turns on/off the switching elements 35A, 35B, 36A, 36B of the
main circuit 34. In the cell control unit 37, a digital signal which has been
20 converted into a PWM pulse is outputted, by comparing a modulation
waveform of a sine wave with a carrier signal of a triangular wave
(triangular carrier wave). That is, functions of an AID (Analog/Digital)
conversion and a PWM conversion are provided.
[0018] In response to signals from the cell control unit 37, the gate driver 33
25 controls the switching elements 35A, 35B, 36A, 36B of the main circuit 34.
In addition, the driver power supply 31 supplies power to the gate driver
33 and the cell control unit 37.
Further, by detecting a voltage across the DC capacitor 39 of the main
circuit 34, a voltage sensor 32 sends a detected signal to the cell control unit
30 37. The cell control unit 37 transmits the information from the voltage sensor
32 as an item of a DC capacitor voltage 6 (FIG. 1) in the control signal frame
8
8A (FIG. 1) included in the optical serial signal frame, that will be described
later, via the optical communication slave 38.
[0019] The optical communication slave 38 receives optical serial signals
(frames) transmitted from the optical communication master 28 of the central
5 control unit 26, via the optical fiber cable 25. As well as transmitting control
signals contained in the optical serial signals (frames) to the cell control unit
37, the optical communication slave 38 receives signals indicating the state of
the cell control unit 37, as described above. Then, the optical communication
slave 38 transmits the information to other cells (24) or the central control
10 unit 26, via the optical fiber cable 25.
[0020] As described above, by the cells 24 of the plurality of single"phase power
converters
[0021] As described above, FIG 1 is a diagram showing a configuration of an
optical serial signal frame.
A signal transmitted from the central control unit 26 (FIG. 2) to the cell
control unit 37 (FIG. 2) is configured with an optical serial signal frame. An
20 optical serial signal frame is configured to include a control signal frame 8A
and a specific pattern 1.
In FIG. 1, the control signal frame 8A, for instance, includes: a signal
start mark (START) 2; a synchronized carrier number 3; a subject cell
number (Subject cell number) 4, a modulation factor for each cell (Modulation
25 factor) 5; a voltage signal of each DC capacitor or dummy voltage information
(DC capacitor voltage) 6; and a signal end mark (END) 7.
[0022] Here, each of the items (2-7) included in the control signal frame 8A
above is expressed in FIG. 1, in the words indicated in parentheses as
described above. In addition, as (l"k-N) pieces are present for each of the
30 items above, a suffix number is appended in sequence to each of the items.
9
Further, the control signal frame 8A and the specific pattern 1 are
transmitted from the central control unit 26 at a substantially constant
frequency.
[0023] «Normal communication case»
5 In the case the communication is normal, each cell control unit 37 (FIG.
3) or each cell 24 (FIG. 2) behaves as follows, with the control signal frame 8A
in FIG.!.
Assuming that a cell 24 (FIG. 2) which receives a control signal at the kth
order from the central control unit 26 (FIG. 2) is the k-th cell, the k-th cell
10 retrieves the modulation factor 5 for itself, by referencing to the subject cell
number 4 of the control signal frame 8A received from the (k-I)-th cell.
Further, the k-th cell generates a new control signal frame 8A, by
replacing the dummy information of the DC capacitor (DC capacitor voltage
6) with the actual DC capacitor voltage signal of its own, and transmits the
15 new control signal frame 8A to the (k+ I)-th cell.
It should be noted that the main circuit (34, FIG. 3) of the k-th cell (24,
FIG. 3) is operated with the retrieved modulation factor 5. The voltage of the
DC capacitor (39, FIG. 3) is detected by the voltage sensor (32, FIG. 3) as
described above.
20 [0024] Further, if the synchronized carrier number 3 received from the (k-I)-th
cell and the carrier number of its own are consistent, the triangular carrier
wave generated by itself is forcibly reset to a predetermined value, when
duration of a cell-dependent adjustment time (time to approximately align
the signal transmission delay time from the central control unit 26 to each of
25 the cells Cll-Cln, C2I-C2n, C3I-C3n) is elapsed since the signal end mark
(END 7) was received.
[0025] As described above, using the control signal frame 8A in FIG. 1, a control
signal composed of an optical serial signal frame is transmitted from the
optical communication master (28, FIG. 2) of the central control unit (26, FIG.
30 2) to each of the cell control units (37, FIG. 3) via each of the optical
communication slaves (38, FIG. 3) of each of the cells (ell-Cln, C2I-C2n,
10
C31-C3n, FIG. 2). By transmitting and receiving control signals of the control
signal frame 8A, each of the cells (en-C1n, C21-C2n, C31-C3n, FIG. 2) which
is a single-phase power converter, operates integrally in collaboration. Thus
the power converter (23, FIG. 2) works.
5 [0026] «Communication error detection»
As a cause that an optical serial signal frame is not transmitted correctly
to the cell controller 37, a communication error due to disconnection of the
optical fiber cable 25 or a failure at a transceiver (not shown) in the optical
communication slave 38 is possible.
10 In case of the circuit configuration in FIG. 2, since the potential of each of
the cells 24 is different from one another, it is necessary that the optical fiber
cable 25 has a dielectric strength to withstand the potential difference
between each of the cells 24 with one another or between each of the cells and
the central control unit 26, and the possibility of not only disconnection but
15 also short circuit due to insulation degradation must be considered.
[0027] The control signal frame 8D in FIG. 6, shown for reference, includes a
synchronization pattern 11, wherein it is assumed that, due to not receiving a
synchronization pattern 11 or inconsistency therebetween, a communication
error of out-of-sync such as inability to transmit from the previous cell and
20 disconnection of the optical fiber cable 25 (FIG. 2) has occurred.
However, the synchronization pattern 11 caused a long transmission time
(sync time), as well as long control signal frame 8D.
[0028] Therefore, as shown in FIG. 1, a specific signal pattern 1 is included
during the time other than the control signal frame 8A, instead of the
25 synchronization pattern 11 (FIG. 6), and if a specific pattern 1 is not received
or there is an inconsistency between the received signal and the specific
pattern 1, it is determined that a communication error due to out-of-sync has
occurred.
It should be noted that a specific pattern 1 is a predetermined pattern
30 which can be distinguished from the control signal frame 8A.
11
[0029] In this way, by inserting a specific pattern 1 between the control signal
frames 8A, which time was originally unused, and verifying the
synchronization deviation therewith, it is possible to shorten the time length
of the control signal frame 8A.
5 FIG. 1 shows a case where there is one control signal frame 8A per one
control cycle, but there may be multiple control signal frames 8A per one
control cycle and more effects are expected from applying the present
invention.
Further, as signals of the specific patter 1 are transmitted and received
10 during the time when there is no control signal frame 8A, some signals are
always in communication, thereby having an advantage that out-of-sync
becomes less likely to occur.
Second Embodiment
[0030] Next, a second embodiment of the present invention will be described.
15 An optical serial signal frame and a control signal frame 8B included therein
in the second embodiment are shown in FIG. 4 , and there are various
methods to use the control signal frame 8B (FIG. 4). Then, a first and second
usages of the second embodiment will be described in this order.

20 [0031] FIG. 4 is a diagram showing a configuration of an optical serial signal
frame in which a signal indicating presence or absence of a communication
error at upstream cells
25 [0034] Next, a second usage of the second embodiment will be described. As in
the first usage of the second embodiment, the control signal frame 8B in the
second usage of the second embodiment is the configuration shown in FIG. 4.
In the first usage of the second embodiment, the communication error
presence signal 12 indicating the presence of an error at an upstream cell and
30 the communication error cell number 13 were made to have the same signals,
13
regardless of the communication error detection result for the specific pattern
1 at the (k+ l)-th cell and beyond.
However, in the second usage of the second embodiment, by rendering a
specific pattern 1 of a new control signal frame to be transmitted from the k-
5 th cell same as the specific pattern 1 to be transmitted when there is no
communication error, a communication error detected at the (k+ l)-th cell and
beyond due to not receiving the specific pattern 1 or inconsistency thereof is
assumed to be included in the communication error cell number 13.
[0035] That is, at the k-th cell, signals other than the communication error
10 presence signal 12 indicating the presence of an error at an upstream cell and
the communication error cell number 13 are transmitted as if there was no
communication error virtually. Then, when detecting a new communication
error due to not receiving the special pattern 1 or inconsistency thereof, it is
possible to transmit all cell numbers having a communication error to the
15 central control unit 26 (FIG. 1), by independently including information of the
cell number currently in error into the information that has been transmitted
as the communication error cell number 13, therefore it is very useful when
multiple cells 24 or optical fiber cables 25 fail at the same time.
[0036] The abovementioned method need to increase the number of bits
20 allocated to the communication error cell number 13 as the number of cells
(24, FIG. 1) is increased, therefore when the number of cells (24, FIG. 2) is
large, there is a concern that the time lengths of the control signal frames 8A
(FIG. 1) and 8B (FIG. 4) become longer, but even therewith the time lengths
of the control signal frames 8A and 8B become shortened as compared to that
25 according to the method in FIG. 6, which will be described later, because
detection of a communication error is performed by utilizing the specific
pattern 1 which is not included in the control signal frames 8A and 8B,
thereby having higher possibility of being implemented even for a case when
a control cycle time 9 is short.
30 Third Embodiment
[0037] Next, a third embodiment of the present invention will be described.
14
FIG. 5 is a diagram showing a configuration of an optical serial signal
frame including a common-for-all-cell control signal 14 in the third
embodiment.
The control signal frame SC in FIG. 5 is obtained by including the
5 common-for-all-cell control signal 14 into the control signal frame SA that
does not contain a synchronization pattern shown in the first embodiment. A
specific pattern 1 is provided between pluralities of the control signal frames
SC.
At the k-th cell, when a communication error due to not receiving the
10 specific pattern 1 or inconsistency between the received signal and the
specific pattern 1 is detected, the control signal is set to tum off the switching
elements (35A, 35B, 36A, 36B, FIG. 3) of each of the cells (24, FIG. 2) in the
common-for-all-cell control signal 14, and a new control signal frame is
generated, then the new control signal frame is transmitted to the (k+1)-th
15 cell.
[003S] Further, all switching elements (35A, 35B, 36A, 36B, FIG. 3) of its own
(the k-th cell) are turned off. At the (k+1)-th cell and beyond, by receiving the
common-forall-cell control signal 14 including a control signal to turn off
switching elements (35A, 35B, 36A, 36B, FIG. 3), control to turn off all
20 switching elements (35A, 35B, 36A, 36B, FIG. 3) of its own is executed, and
the control signal frame SC is transmitted to the next cell as it is.
As a result, at the cells from the k-th cell up to the N-th cell, all switching
elements (35A, 35B, 36A, 36B, FIG. 3) are turned off.
[0039] In addition, the central control unit 26 (FIG. 2), which received the
25 common-for-all-cell control signal 14 including the control signal to turn off
switching elements (35A, 35B, 36A, 36B, FIG. 3) from the N-th cell, also
transmits the common-for-all-cell control signal 14 portion to the first cell as
it is.
As well as the k-th cell through the N-th cell, the first cell through the (k-
30 1)-th cell executes the control to turn off all switching elements of its own, by
receiving the common-for-all-cell control signal 14 including a control signal
15
to turn off the switching elements, then transmits the control signal frame 8C
to the next cell as it is.
[0040] Thus, once the control signal frame 8C is transmitted up to the (k-l)-th
cell, all switching elements (35A, 35B, 36A, 36B, FIG. 3) are turned off, and
5 thereby it is possible to protect the device (power conversion device 23, FIG.
2).
In the present embodiment, as the specific pattern 1 is used for turning
off all switching elements, the synchronization pattern 11 (FIG. 6) is not
required. Therefore, as the synchronization pattern 11 (FIG. 6) is not
10 included in the control signal frame 8C, it is possible to transmit a signal for
turning off all switching elements (35A, 35B, 36A, 36B, FIG. 3) to all cells 24
(eU-C1n, C21-C2n, C31-C3n, FIG. 2) in a short time, as compared to the
method in FIG. 6 as a comparison reference, which will be described later. In
other words, there is an effect that will enable protection of the device (power
15 conversion device 23) in a short period of time since detecting a
communication error.
Other Embodiments
[0041] It should be noted that a circuit configuration assuming a Static Var
Compensator is shown in the first embodiment of the present invention, but
20 the scope of the present invention is not limited to a Static Var Compensator,
and applicable to cascade-connection type power conversion devices in
general. That is, the circuit configuration of the power conversion device 23
may be not only the cascade multilevel converter (CMC) shown in FIG. 2 but
also a circuit configuration such as a modular multilevel converter (MMC)
25 shown in FIGS. 7A and 7B.
[0042] FIGS. 7A and 7B are diagrams showing a configuration of a modular
multilevel converter 73 as a reference, where FIG. 7A shows a schematic
configuration of a modular multilevel converter 73, and FIG. 7B shows a
circuit configuration ofa cell 74 for use in FIG. 7A.
30 In FIG. 7A, the modular multilevel converter 73 is interconnected to a
three-phase power system 71 via a transformer 72. The modular multilevel
16
converter 73 is composed of two sets, top and bottom, of multilevel converter
in FIG. 7A. In each of the multilevel converters, a plurality of cells 74, each of
which is a single-phase power converter, are connected in series (cascade
connection) respectively for each of a first to third arms, which constitute a
5 three-phase arm, wherein one end of each of the first to third arms is
connected to the secondary side of the transformer 72. Also, the other end of
each of the first to third arms is connected to a common line 70A or common
line 70B, respectively, via an AC reactor 79. In addition, the common line 70A
and the common line 70B are DC-linked.
10 It should be noted that FIG. 7B shows a circuit configuration of the cell 74
for use in FIG. 7A as described above, which cell is composed of IGBTS 75, 76
and a DC capacitor 78.
[0043] The cell 24 in FIGS. 2 and 3, depicted as the first embodiment, may be
provided with a storage battery in place of the DC capacitor 39 (FIG. 3).
15 Likewise, the cell 24 in FIG. 7B may be provided with a storage battery in
place of the DC capacitor 78.
[0044] Further, in the cell 24, a single-phase power converter, of the first
embodiment, a converter portion of the main circuit 34 (FIG. 3) was described
as configured with a full bridge circuit using IGBTS, but it is also possible to
20 use a bidirectional chopper circuit instead of the full bridge circuit (main
circuit 34). However, it is necessary to change a control circuit of the gate
driver 33 (FIG. 3) to the one corresponding to the bidirectional chopper circuit.
[0045] Furthermore, in the cell 24, a single-phase power converter, of the first
embodiment, a converter portion of the main circuit 34 was described as
25 using a switching element consisting of the IGBTS, but it is also possible to
use other switching element.
That is, a switching element for on-off control, such as a GTO (Gate-TumOff
thyristor) and a MOSFET (Metal-Oxide Semiconductor Field-Effect
Transistor) is also applicable.
17
[0046] Although not shown in FIG. 1, it is acceptable to include a checksum
(Check Sum, one of error-detecting codes), CRC (Cyclic Redundancy Check),
or the like in the control signal frame SA (SB, SC).
[0047] Further, in the control signal frame SB of the second embodiment, the
5 communication error diagnostic information signal was described as
consisting of the communication error presence signal 12 and the
communication error cell number 13, but other elements may be added to
form the communication error diagnostic information signal. For example, it
may be added with a cause of the error, severity, date and time, or the like in
10 the form of a digital signal.
[004S] Furthermore, it was described that the power conversion device of the
present embodiment in FIG. 2, controlled with the control signal frame SA
(SB, SC) and the specific pattern 1 in FIG. 1, is used as a reactive power
compensator, but its application is not limited thereto. By changing a control
15 method of a signal, the power conversion device may be applicable to a power
inverter or a power converter, and in such cases a method using the control
signal frame SA (SB, SC) and the specific pattern 1 in FIG. 1 is effective.
Optical Serial Signal Frame as Comparative Reference
[0049] FIG 6 is a diagram showing a configuration of an optical serial signal
20 frame including a frame control signal SD, as a comparative reference.
The control signal frame SD in FIG. 6 includes a synchronization pattern
11. In addition, there is a "no signal" section 101, during which a signal is not
transmitted, in the optical serial signal frame. The control signal frame SD is
configured, assuming that, due to not receiving a synchronization pattern 11
25 or inconsistency therebetween, a communication error of out-of-sync such as
inability to transmit from the previous cell and disconnection of the optical
fiber cable 25 (FIG. 2) has occurred.
However, as described above, there is a problem that, by including the
synchronization pattern 11 in the control signal frame SD in this way, a
30 control signal frame SD becomes longer, and a time required for its
transmission (synchronization time) takes longer.
18
Supplement for Present Invention and Embodiment
[0050] The present embodiment is summarized that a power conversion device
functioning as a reactive power compensator is configured with a plurality of
single-phase power converters (cells) in cascade"connection, and a central
5 control unit that controls the cells. Further, the central control unit and the
plurality of the single"phase power converters (control units) are configured
in a daisy-chain structure. Then, by constituting an optical serial signal
frame, for controlling the plurality of the single-phase power converters, with
a control signal frame and a specific pattern of signal that can be
10 distinguished from the control signal frame, and by transmitting and
receiving thereof, it is intended to determine communication errors.
With the configuration and method described above, the detection of
communication errors such as inability to transmit from a control unit of each
of the single-phase power converters and communication interruptions due to
15 disconnection or short circuit of the optical fiber cable, or the like can be
performed easily and at low cost, without increasing the length of the control
signal frame.
Legend for Reference Numerals
[0051] 1 Specific pattern, (Specific pattern to detect communication error)
20 2 START, Signal start mark
3 Synchronized carrier number
4 Subject cell number, (Cell number to be subjected)
5 Modulation factor, (Modulation factor signal)
6 DC capacitor voltage, (DC capacitor voltage signal or DC capacitor
25 voltage dummy information), (String of signals composed of DC capacitor
voltage signal or DC capacitor voltage dummy information)
7 END, Signal end mark
8A, 8B, 8C, 8D Control signal frame (one frame)
9 Control cycle time
30 10 Time without Control signal frame
11 Synchronization pattern
19
..
12 Communication error presence signal, Signal indicating presence
or absence of communication error at upstream cells,