Electric power conversion systems – Current conversion – Including automatic or integral protection means
Reexamination Certificate
2000-11-30
2001-11-20
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
Including automatic or integral protection means
C323S906000, C361S049000
Reexamination Certificate
active
06320769
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system interconnect power converter interconnected to a commercial power system (to be referred to as a “system” hereinafter) and a power generation apparatus using the same and, more particularly, to a power converter of insulated-transformerless type used in a power generation apparatus which comprises a direct current power supply such as a solar battery having a large ground capacitor and is interconnected to a low-voltage distribution system having one grounded line, and a power generation apparatus using the same.
BACKGROUND OF THE INVENTION
FIG. 2
is a block diagram showing the arrangement of a solar power generation apparatus interconnected to a low-voltage distribution system.
A solar battery array
1
is constituted by combining a plurality of solar battery modules serially/parallelly so as to obtain a desired output voltage and current. Direct current power output from the solar battery array
1
is input to a system interconnect power converter
2
(to be referred to as a “power conditioner” hereinafter) where the direct current power is converted into alternate current power. The output of the power conditioner
2
is connected to a low-voltage distribution system
4
via a customer's ground fault interrupter
3
. A load
5
is connected between the power conditioner
2
and the customer's ground fault interrupter
3
. Wiring inside the customer's premises is wiring from the customer's ground fault interrupter
3
to the power conditioner
2
and load
5
. The customer's ground fault interrupter
3
detects a ground fault current to detect an electrical leakage inside the customer's premises, and interrupts the connection between the customer's equipment and the low-voltage distribution system
4
so as not to influence the low-voltage distribution system
4
outside the customer's premises.
The solar battery array
1
has a ground capacitor
6
. As a solar battery module constituting the solar battery array
1
, built-in modules and low-profile modules have recently been developed. In some cases, a conductive member (metal plate or the like) as a reinforcing member or a conductive member such as a metal plate as a base member covers a roof. In this case, a solar battery cell and metal plate face each other at a small interval with a large area, which increases the ground capacitor
6
. If water attaches to the surface and any area of a solar battery module owing to rain or the like, the ground capacitor
6
is ocurred by the water.
On the other hand, most of the system interconnect power conditioners
2
recently adopt a so-called transformerless method having no insulated transformer in order to attain high efficiency, small size, light weight, and low cost.
The present inventors have found that when the ground capacitor
6
is large, the system interconnect power conditioner
2
is of transformerless type, and a ground fault occurs outside the customer's premises, the ground fault current flows through the ground capacitor
6
of the solar battery array
1
and the power conditioner
2
to cause unwanted interruption operation in the customer's ground fault interrupter
3
. This unwanted interruption operation generated in the customer's ground fault interrupter
3
causes a power failure inside the customer's premises though no electrical leakage occurs inside the customer's premises.
This problem is not limited to the solar power generation system. The same problem arises in a power generation system using a fuel cell if the ground capacitor is large. A ground fault outside the customer's premises causes the customer's ground fault interrupter
3
to unnecessarily perform interruption operation, which may generate a power failure inside the customer's premises.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the conventional drawbacks, and has as its object to prevent unwanted interruption operation of a customer's ground fault interrupter caused by a ground fault outside the consumer.
To achieve the object, a preferred embodiment of the present invention discloses a power converter for converting direct current power to alternate current power and supplying the alternate current power to a power system, said power converter comprising: a converter for boosting a voltage of direct current power supplied from a direct current power supply having a ground capacitor; an inverter for converting the direct current power supplied from said converter into alternate current power, wherein an input and output of said inverter are not insulated; a switch which is connected to an output terminal of said inverter and opens/closes an output of said power converter by a mechanical contact; a detector for detecting a ground fault within a shorter time than an operation time of a customer's ground fault interrupter interposed between said power converter and a power system having one grounded line; and a controller for controlling operations of said converter, said inverter, and said switch, wherein when said detector detects a ground fault, said controller changes said switch to an open state, blocks a gate of said inverter, and holds an output voltage of said converter to be higher than a peak value of an alternate current voltage of the power system until at least said switch changes to the open state.
Another preferred embodiment of the present invention discloses a power generation apparatus for supplying alternate current power to a power system and comprising a direct current power supply having a ground capacitor, and a power converter for converting direct current power into alternate current power, wherein said power converter comprises: a converter for boosting a voltage of direct current power supplied from the direct current power supply; an inverter for converting the direct current power supplied from said converter into alternate current power, wherein an input and output of said inverter are not insulated; a switch which is connected to an output terminal of said inverter and opens/closes an output of said power converter by a mechanical contact; a detector for detecting a ground fault within a shorter time than an operation time of a customer's ground fault interrupter interposed between said power converter and a power system having one grounded line; and a controller for controlling operations of said converter, said inverter, and said switch, wherein when said detector detects a ground fault, said controller changes said switch to an open state, blocks a gate of said inverter, and holds an output voltage of said converter to be higher than a peak value of an alternate current voltage of the power system until at least said switch changes to the open state.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
REFERENCES:
patent: 5548504 (1996-08-01), Takehara
patent: 5581171 (1996-12-01), Kerfoot et al.
patent: 5592074 (1997-01-01), Takehara
patent: 5669987 (1997-09-01), Takehara et al.
patent: 5869956 (1999-02-01), Nagao et al.
patent: 5892354 (1999-04-01), Nagao et al.
patent: 5923158 (1999-07-01), Kurokami et al.
Kurokami Seiji
Manabe Naoki
Takehara Nobuyoshi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Han Jessica
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