Electric power conversion systems – Current conversion – Including automatic or integral protection means
Reexamination Certificate
2003-05-23
2004-10-05
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
Including automatic or integral protection means
C363S097000, C363S109000, C363S132000, C363S071000, C307S030000
Reexamination Certificate
active
06801442
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a power conversion apparatus, power conversion system, and islanding operation detection method and, more particularly, to a power conversion apparatus which converts a DC power into to an AC power and outputs the AC power to a system power supply, a power conversion system which has a plurality of power conversion apparatuses, and an islanding operation detection method in the apparatus or system.
BACKGROUND ART
In recent years, since problems of global warming due to carbon dioxide emission by use of fossil fuel and radioactive contamination by nuclear power plant accidents and radioactive waste have become serious, interests in global environment and energy are growing. Under these circumstances, solar power generation that uses solar light as an inexhaustible and clean energy source, geothermal power generation using the geothermal energy, wind power generation using the wind power, and the like have been put into practice all over the world.
A DC power generated by such a natural energy is converted into an AC power by a power conversion apparatus called an inverter and supplied to, e.g., a commercial power system.
FIG. 5
is a block diagram showing a general arrangement of a solar power generation system. Referring to
FIG. 5
, reference numeral
1
denotes a solar battery;
10
, a system interconnection inverter apparatus (to also be simply referred to as an inverter hereinafter);
3
, a circuit breaker;
4
, an AC system; and
5
, a load.
The inverter
10
is mainly constituted by a power conversion means
21
, removal means
22
, control means
25
, and active scheme implementation means
103
. The power conversion means
21
is formed from a known converter circuit and inverter circuit to convert a DC power output from the solar battery
1
into an AC power and output the AC power to the system
4
. The removal means
22
removes the inverter
10
from the system
4
in accordance with a removal signal output from the control means
25
. The control means
25
controls the entire inverter
10
.
The active scheme implementation means
103
has a means
231
(to also be simply referred to as an implementation means or a variation generation means hereinafter) for detecting that power supply from the system is stopped, and islanding operation starts in accordance with an active scheme that gives a small variation to the output current, frequency, phase, or the like. The inverter
10
implements an active power variation scheme by the implementation means
231
.
As active schemes, an active power variation scheme which outputs a power instruction value (to be referred to as a fluctuation instruction value hereinafter) that superposes a fluctuation component having a predetermined period on an output current so as to generate, in the output current from the inverter
10
, a variation having the predetermined period with respect to the output voltage, a reactive power variation scheme which outputs a signal (to be referred to as a phase shift signal hereinafter) obtained by adding a phase difference &Dgr;&phgr; to a phase signal at a predetermined period so as to generate the predetermined phase difference &Dgr;&phgr; in the output current from the inverter
10
every predetermined period, and a reactive power variation scheme which outputs a phase shift signal for setting a phase advance or delay in accordance with the frequency of a detected output so as to change the output frequency of the inverter
10
are known. These schemes are described in, e.g., Japanese Patent Laid-Open Nos. 8-70534, 9-98539, and 7-245876, respectively.
FIG. 12
is a block diagram showing another arrangement of the solar power generation system. Referring to
FIG. 12
, reference numeral
1
denotes a solar battery;
8
, a system interconnection inverter;
3
, a circuit breaker;
4
, an AC system; and
5
, a load. The same reference numerals as in the solar power generation system shown in
FIG. 5
denote the same parts in FIG.
12
.
The inverter
8
is mainly constituted by a power conversion means
21
, removal means
22
, control means
26
, and passive scheme implementation means
83
. The power conversion means
21
is formed from a known converter circuit and inverter circuit to convert a DC power output from the solar battery
1
into an AC power and output the AC power to the system
4
. The removal means
22
removes the inverter
8
from the system
4
upon receiving a removal signal output from the control means
26
. The control means
26
controls the entire inverter
8
.
The passive scheme implementation means
83
has a means
331
(to be referred to as a power failure detection means
331
hereinafter) for implementing, of islanding operation detection schemes, a voltage phase jump detection scheme as a passive scheme which detects islanding operation by detecting a power failure. The inverter
8
implements the voltage phase jump detection scheme by the power failure detection means
331
.
As passive schemes, a voltage phase jump detection scheme which detects a jump in instantaneous phase of an output voltage, thereby determining a power failure in the system, a third harmonic voltage distortion abrupt increase detection scheme which detects an abrupt increase in third harmonic distortion of the output voltage of the inverter, which occurs at the time of a power failure, thereby determining a power failure in the system, and a frequency change rate detection scheme which detects an abrupt change in frequency of the output voltage of the inverter, which occurs at the time of a power failure, thereby determining a power failure in the system are known. These schemes are described in, e.g., Japanese Patent Laid-Open Nos. 2001-169565, 9-84251, and 10-336903, respectively.
It is reported that in an inverter having a single passive or active scheme as described above, when parallel operation of a plurality of inverters of the same model (to be referred to as a multiple inverter parallel operation hereinafter) is executed under conditions that almost balance the output power of the inverter and load power consumption, islanding operation continuously takes place.
To prevent such continuous islanding operation, in executing multiple inverter parallel operation of system interconnection inverters, a master inverter
10
′ and remaining inverters
10
are connected by master-slave cables
12
to execute synchronous operation of the inverters, as shown in
FIG. 6
, in order to eliminate mutual interference of the active scheme for detecting islanding operation, as disclosed in, e.g., Japanese Patent Laid-Open No. 2000-152506 or Japanese Patent No. 3028205.
However, to execute multiple inverter parallel operation based on master-slave connection as described above, master-slave connection cables are necessary. This increases the cost, complicates install operation, and decreases the degree of freedom in installation.
On the other hand, as is reported in Kitamura et al., Paper No. 32, Power & Energy Society of the Institute of Electrical Engineers of Japan (2000), when parallel operation is executed using a plurality of inverters of different types, the duration of islanding operation shortens unless mutual interference occurs because the inverters have different dead bands for the active scheme or passive scheme, and also, the generation conditions are limited, unlike parallel operation of a plurality of inverters of the same model.
However, to execute parallel operation of a plurality of inverters by directly referring to the above report, a plurality of inverters of different types must be prepared. This greatly increases the labor and cost.
In addition, for example, when parallel operation is to be executed by installing home solar power generation systems in neighboring houses, it is substantially impossible to grasp the islanding operation schemes of the inverters of the respective houses. Even inverters of different types are also hard to prepare. Especially, if a system interconnection system which requires no prior application t
Suzui Masaki
Takehara Nobuyoshi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Han Jessica
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