Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Reexamination Certificate
2001-03-13
2003-04-08
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
C363S040000
Reexamination Certificate
active
06545885
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an isolated operation prevention device for a distributed power supply in a power system, which monitors and detects, at the customer equipment side, the interruption of the system supply due the opening of a circuit breaker at a substation and disconnects the distributed power supply from the system when the system supply is stopped to prevent isolated operation of the distributed power supply, and, to be more detailed, concerns the compensation of power fluctuations when a wind power generator, etc. is used as the distributed power supply.
2. Description of the Related Art
Conventionally, with customer equipment in factories, large-scale buildings, etc., so-called distributed power supplies have been interconnected with the power system, and shortages of the power generated by the distributed power supplies have been compensated by the system power.
In such cases, when a circuit breaker at a substation of a power company is opened due to a system fault, etc. and the system supply is stopped, the distributed power supply must be disconnected from the system and prevented from performing isolated operation in order to prevent the occurrence of electric shock accidents, etc. due to isolated operation of the distributed power supply.
As means for preventing this isolated operation without fail, the present applicant has invented, as disclosed in Japanese Patent Unexamined Publication No. Hei 10-248168 and Japanese Patent Unexamined Publication No. Hei 11-252806, isolated operation prevention devices for distributed power supply that inject an intermediate-order harmonic current, which is synchronized with the fundamental and has a frequency that is a non-integer multiple of the fundamental, into the system and disconnect the distributed power supply upon detecting the stoppage of the system supply from a change of the impedance or admittance for the injected frequency at the upstream side of the system.
Japanese Patent Unexamined Publication No. Hei 10-248168 discloses the detection of the stoppage of the system supply from a change of the amount (magnitude) of impedance or admittance itself, and Japanese Patent Unexamined Publication No. Hei 11-252806 discloses the detection of stoppage of the system supply based on a change of impedance or admittance that is equal to or a greater than a fixed value in the capacitive direction.
The above-described isolated operation prevention devices for distributed power supply are equipped only with the function of disconnecting the distributed power supply upon detection of the stoppage of the system supply.
Meanwhile, with the above-described type of customer equipment, when the voltage generated by the distributed power supply fluctuates during interconnected operation, the system voltage fluctuates due to the active and reactive power fluctuations of the distributed power supply, and especially in the case where the distributed power supply is comprised of a wind power generator, etc. with a large capacity, the flicker fluctuation (ripple fluctuation), due for example to the moment-to-moment wind power fluctuation that is overlapped onto the gradual voltage variation due to average variations of the wind power, is large and the fluctuation of the system voltage due to this fluctuation becomes a problem.
Priorly in order to restrict this fluctuation of the system voltage, a separate power compensation device was equipped in addition to the isolated operation prevention device for distributed power supply.
This power compensation device is formed, for example, in the same manner as a thyristor controlled reactor (TCR) system or an inverter (self-excited) type static VAR compensator (SVC) such as described in pp. 28-31 of the Nisshin Electric Technical Report Vol. 41, No. 3 ('96, 11) and compensates for the voltage fluctuation by phase control by the switching of a reactor or condenser or by the injection of an active or reactive compensation power by drive control of an inverter device.
Thus especially in the case of a receiving equipment equipped with a distributed power supply comprised of a wind power generator, etc., which has a large capacity and with which the generated power fluctuates, there is a need to equip a power compensation device in addition to the isolated operation prevention device for distributed power supply, thus making it necessary to make the customer equipment large in scale and requiring vast equipment investments on the part of the customer.
Examples of conventional distributed power supplies for customers, etc., which are put to interconnected operation with a system and with which a power converter, such as an inverter, etc., is connected to the system, include micro gas turbine generation systems, wind power generation systems, solar power generation systems, fuel cell systems, emergency power supply systems that use a generator, flywheel, etc., UPS, and constant-use power supply systems (cogeneration equipment).
When the system is normal, these distributed power supplies generate interconnected operation power that is synchronized with the system fundamental by means of an inverter or other power converter (power inverter) and supplies this power to the system.
When the circuit breaker of a substation is opened and the system supply is stopped, the isolated operation of the distributed power supply is detected and the distributed power supply is disconnected from the systems to prevent the occurrence of electric shock accidents, etc. due to isolated operation.
As a related art of the abovementioned isolated operation detection system, active systems described for example in pp. 24 to 25 of the literature, “Description of Technical Requirement Guidelines for Power System Interconnection '98” (3rd. edition, Denryoku Shinposha Co., Ltd., Sep. 24, 1998) are known.
Active systems can be classified largely into reactive power fluctuation systems (&Dgr;Q systems) and active power fluctuation systems (&Dgr;P systems).
(i) Reactive power fluctuation system (&Dgr;Q system)
With this system, a periodic reactive power fluctuation is added to the generated output and the periodic voltage fluctuation or current fluctuation, etc. that appears upon transition to isolated operation is detected.
(ii) Active power fluctuation system (&Dgr;P system)
With this system, a periodic active power fluctuation is added to the generated output and the periodic frequency fluctuation or voltage fluctuation, etc. that appears upon transition to isolated operation is detected.
As is clear for example from FIG.
5
(
a
) of p.25 of the above-mentioned literature, in the case of a distributed power supply, with which isolated operation is detected by a conventional active detection system, since a reactive power fluctuation or an active power fluctuation is caused by adding modulation to the system fundamental output of the power converter and the isolated operation that accompanies the stoppage of the system supply is detected from the fluctuation of the fluctuation detection signal (active signal), it has the problem of imposing ill effects, such as flicker (reactive power fluctuation) or beating (active power fluctuation), on the system.
Also as is described in the “(1) Disconnection Time Interval” section in p. 152 of the above-mentioned literature, due to the fluctuation characteristics of the above-mentioned active signal, the conventional art requires approximately 3 to 10 seconds for detection of isolated operation. Time is thus required from the stoppage of the system supply to disconnection, and for example in the case where the reclosing time of a system that is one level above the system to which the distributed power supply is connected is extremely short and is less than 3 seconds, the disconnection cannot be performed in time to accommodate for the reclosing operation.
In the case where a plurality of customers using the same system have such types of distributed power supplies and a power equipment with which a plurality of distributed pow
Asano Masakuni
Emura Tokuo
Hada Yoshihiro
Minowa Yoshifumi
Nishimura Shoji
Finnegan Henderson Farabow Garrett & Dunner LLP
Nguyen Matthew
Nissin Electric Co. Ltd.
LandOfFree
Isolated operation prevention device for distributed power... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Isolated operation prevention device for distributed power..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Isolated operation prevention device for distributed power... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3091850