JP3336756B2 - Method of detecting islanding operation of grid-connected inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a system in which a distributed power supply is connected to a distribution system or the like, for use in a distributed power supply such as a fuel cell power generation system or a solar power generation system. The present invention relates to a state in which an inverter disconnects from a higher power system during grid connection and continues to supply power to the load of the power distribution system, that is, a so-called islanding operation detection method of a grid connection inverter that detects islanding. .

[0002]

2. Description of the Related Art Conventionally, this type of islanding detection method detects the islanding operation of a grid-connected inverter by using a method of interrupting transfer or a method of monitoring voltage or frequency. These methods will be described with reference to FIG. FIG. 2 is a block diagram showing a configuration of a conventional power system and a distributed power supply.

In FIG. 2, an infinite bus 1 and a higher system transmission line 2 are connected to a distribution system 5 as a power system via a distribution transformer 3 and a system side circuit breaker 4. Fuel cell main body 11 as distributed power supply and system interconnection inverter 1
The fuel cell power generation system 12 composed of 0 is connected to the power distribution system 5 via the inverter-side circuit breaker 9 for system interconnection, the circuit breaker 8 for power reception, and the power receiving point 7 as a system interconnection point.
The on-site load 15 is connected to the power distribution system 5 via the power receiving circuit breaker 8 and also connected to the system interconnection inverter 10 via the system interconnection inverter-side circuit breaker 9. The external load 6 of the power distribution system 5 is also connected to the system interconnection inverter 10 via the power receiving circuit breaker 8 and the system interconnection inverter-side circuit breaker 9.

In the method of detecting the independent operation of the system interconnection inverter 10 which is connected to the power distribution system 5 as a power system and operates in parallel in this manner, the detection of the isolated operation by the transfer interruption method is performed by the system-side circuit breaker. 4, when the system interconnection inverter 10 is disconnected from the upper system side (the infinite bus 1, the upper system transmission line 2 and the power distribution transformer 3) to be in an isolated operation state, the system side circuit breaker This is a method of interrupting the transfer of the power receiving circuit breaker 8 by the transfer interruption signal 16 from the control unit 4.

In the method of monitoring voltage and frequency,
The voltage and frequency of the distribution system 5 are monitored by an over / under voltage relay or over / under frequency relay (not shown) installed at the power receiving point 7 or at the output of the grid interconnection inverter 10 to detect that they have changed to a set value or more. In this method, a protection device (not shown) on the power receiving circuit breaker 8 and the grid connection inverter 10 side is operated to passively detect the islanding operation.

[0006]

However, in the above-described conventional islanding detection method, the method of detecting islanding by the method of interrupting transmission requires the use of a dedicated line for transmitting the transmission interruption signal 16, which will not be possible in the future. When the number of distributed power supplies increases, the capacity of the dedicated line needs to be increased. Also, the transfer cutoff signal 1
The use of line sharing and wireless transmission for transmission of 6 is not realistic and economically problematic.

Further, in the method of detecting the isolated operation by monitoring the voltage and the frequency, the load amount (external load 6 and internal load 15) of the power distribution system 5 and the grid connection inverter 10
If the isolated operation occurs in a state where the power generation amount is balanced, there is a problem that the voltage and frequency of the distribution system 5 do not change and it is difficult to detect them. Therefore, an object of the present invention is to eliminate the need for transmission equipment such as a dedicated line for a cutoff signal, and to detect the isolated operation of the grid interconnection inverter only by providing a simple method on each distributed power supply side. An object of the present invention is to provide a method for detecting an isolated operation of a grid interconnection inverter.

[0008]

SUMMARY OF THE INVENTION According to the present invention, an islanding operation detection for detecting that an inverter for system interconnection of a dispersed type power source is disconnected and becomes an isolated operation during interconnection between a power system and a distributed type power source. In the method, the reactive power setter of the grid interconnection inverter is given a periodic small change to constantly change the reactive power at the receiving point, and the frequency change of the grid interconnection point or the grid interconnection inverter is monitored. If the deviation between the monitored frequency and the predetermined reference frequency is equal to or greater than a certain value,
After a lapse of a predetermined time, the amplitude of the periodic disturbance of the receiving point reactive power is amplified for a predetermined minute time, and the isolated operation is determined by monitoring the frequency deviation of the amplified grid connection point or the grid connection inverter. It is characterized by doing.

Alternatively, in an islanding operation detection method for detecting that a system interconnection inverter of a distributed power source is disconnected and becomes an isolated operation during interconnection between a power system and a distributed power source, The periodic change in the receiving point reactive power is always given by giving the reactive power setting device a small periodic change, and the frequency change of the grid connection point or the grid connection inverter is monitored. When the deviation from the reference frequency is equal to or greater than a certain value, the amplitude of the periodic change in the reactive power at the receiving point is amplified for a predetermined minute time, and the frequency of the amplified grid connection point or the grid-connected inverter is amplified. Monitoring is performed via an imperfect differential filter, and when a predetermined set value and a settling time of the imperfect differential filter are exceeded, it is determined that the system interconnection inverter is disconnected from the power system and has been operated independently.

[0010]

Further, in any one of the above-described methods for detecting an isolated operation of a grid interconnection inverter, the predetermined reference frequency may be an average value of frequency values several seconds in the past.
Further, the method for detecting the islanding operation of the grid interconnection inverter according to the present invention detects that the grid interconnection inverter of the distributed power supply is disconnected and becomes an isolated operation during the interconnection between the power system and the distributed power supply. In the islanding detection method, the reactive power setter of the grid interconnection inverter is given a periodic minute change to constantly change the reactive power at the power receiving point to periodically change the power at the receiving point. The frequency change is monitored, and the frequency deviation between the monitored frequency and a predetermined reference frequency is integrated over a certain period of time, and when the integrated value of the frequency deviation exceeds a predetermined value, the grid interconnection inverter solves the power grid. It is determined that the vehicle has been operated in an isolated state.

[0012]

In the islanding operation detection method according to the first aspect, a periodic change is always given to the reactive power at the power receiving point by giving a periodic minute change to the reactive power setting device of the inverter for grid connection, and The frequency change of the system point or the grid connection inverter is monitored, and when the deviation between the monitored frequency and the predetermined reference frequency is equal to or greater than a predetermined value, the amplitude of the periodic disturbance of the receiving point reactive power after a predetermined time has elapsed. By amplifying for only a predetermined short period of time and monitoring the deviation of the system interconnection point or the system interconnection inverter after the amplification, it is possible to prevent malfunction of the islanding operation detection.

Further, in the islanding detection method according to the present invention, the reactive power at the power receiving point is always periodically changed by giving a small periodic change to the reactive power setting device of the grid interconnection inverter. The frequency change of the grid connection point or the grid connection inverter is monitored, and when the deviation between the monitored frequency and a predetermined reference frequency is equal to or more than a predetermined value, the amplitude of the periodic change in the reactive power of the power receiving point is set to a predetermined value. By amplifying for a short time and monitoring the frequency of the system interconnection point or the system interconnection inverter after amplification through an imperfect differential filter, it increases the sensitivity of islanding detection and causes fluctuations in system frequency. It is possible to prevent the erroneous detection of the isolated operation state to be obtained.

Further, in the islanding detection method according to the third aspect, the predetermined reference frequency in the first or second aspect is not set to a constant value of 50 Hz or 60 Hz of the commercial frequency, but instead of a frequency value several seconds in the past. As an average,
It is possible to prevent erroneous detection of the islanding operation state that may be caused by a change in the system frequency.

Further, in the islanding detection method according to the present invention, the reactive power setting device of the grid interconnection inverter is periodically subjected to a minute change so that the reactive power at the receiving point is constantly changed periodically. Monitoring the frequency change of the grid connection point or the grid connection inverter due to the above, integrates the frequency deviation between the monitored frequency and the predetermined reference frequency for a certain period of time, and monitors the integrated value of this frequency deviation to operate independently. Can be detected.

[0016]

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a method for detecting an isolated operation of a system interconnection inverter according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram of an isolated operation detection device for a power system, a distributed power supply, and a system interconnection inverter of the distributed power supply according to an embodiment of the present invention. 1, for convenience of explanation, the same components as those in the block diagram showing the configuration of the conventional power system and the distributed power source shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted. .

That is, FIG. 1 differs from the conventional example in that the output of the isolated operation detection device 14 via the frequency converter 13 is input to the grid interconnection inverter 10.
The islanding operation detecting device 14 of the system interconnection inverter of the present invention thus configured operates as follows. The load amount of the distribution system 5 (the external load 6 and the internal load 15) and the power generation amount of the system interconnection inverter 10 are balanced, and the higher system side (the infinite bus 1, the higher system transmission line 2, and the distribution transformer 3) are balanced. ) And the distribution system 5, the reactive power at the power receiving point 7 periodically and minutely fluctuates based on the reactive power set value of a reactive power setting unit (not shown) of the grid interconnection inverter 10 in order to prevent a power flow between the power distribution system 5 and the power distribution system 5. In such a manner, the periodic reactive power fluctuation signal 17 is actively supplied from the islanding operation detection device 14 to the grid interconnection inverter 10 so that there is always a power flow. During this time, the islanding operation detection device 14 inputs the power receiving point 7 detected by the frequency detector 13 or the frequency of the grid interconnection inverter 10, and inputs this frequency, an average value within an arbitrary time in the past, and a reference frequency ( For example, the frequency deviation from the power system frequency (50 Hz or 60 Hz) is continuously monitored. As a result, it is possible to detect a power receiving point or a change in the frequency of the grid interconnection inverter that occurs when the system-side circuit breaker 4 of the power distribution system 5 is cut off. Therefore, when the frequency deviation exceeds a predetermined value, the system It is determined that the system inverter is disconnected from the power system and is in the islanding operation state, and the islanding operation of the system interconnection inverter 10 is detected.

FIG. 3 is a diagram for explaining the detection operation of the first embodiment of the method for detecting the isolated operation of the system interconnection inverter according to the present invention, in which (A) reactive power and (B) a power receiving point or system interconnection. It is a correlation diagram of the frequency deviation of a system inverter, (C) a small deviation detection signal, and (D) an islanding operation detection signal.
As shown in FIG. 3A, a minute fluctuation of the reactive power occurs due to the periodic reactive power fluctuation signal described above. FIG.
In FIG. 3 (B), a small deviation detection signal shown in FIG. 3 (C) in which the deviation of the frequency of the power receiving point 7 or the frequency of the grid interconnection inverter 10 is slightly confirmed starts an erroneous detection prevention timer (not shown). This erroneous detection prevention timer is for cooperating with another protection device. After a predetermined erroneous detection prevention timer time Ts elapses, the periodic reactive power minute fluctuation a is amplified for a predetermined minute time as shown in FIG. 3A, and the sensitivity is increased as the reactive power fluctuation b is large. . Then, a deviation between the subsequent power receiving point 7 or the frequency of the system interconnection inverter 10 and a predetermined reference frequency (for example, the frequency of the power system 50 Hz or 60 Hz) is continuously monitored, and the frequency deviation is determined to be a predetermined fixed value. If the value exceeds the value, it is determined that the grid interconnection inverter 10 is disconnected from the power distribution system 5 at that time and the islanding operation is performed, and an islanding operation detection signal is output as shown in FIG.

FIG. 4 is a diagram for explaining a detection operation according to the second embodiment of the method for detecting the isolated operation of the grid interconnection inverter according to the present invention, in which (A) the receiving point or the frequency of the grid interconnection inverter and (B) is a correlation diagram of a small deviation detection signal, (C) an output value of an incomplete differential filter, and (D) an isolated operation detection signal. Also in this embodiment, the load amount of the distribution system 5 (the external load 6 and the internal load 15) and the power generation amount of the system interconnection inverter 10 are balanced, and the higher system side (the infinite bus 1, the higher system transmission line 2, In order to prevent a state in which there is no power flow between the distribution transformer 3) and the distribution system 5, the receiving point reactive power is periodically reduced based on a setting value of a reactive power setting device (not shown) of the grid interconnection inverter 10. As fluctuates,
Periodic reactive power fluctuation signal 1 from islanding detection device 14
As in the first embodiment, 7 is provided actively so as to always have a current.

The independent operation detection shown in FIG. 4 is different from the detection shown in FIG. 3 in that a deviation in the frequency of the power receiving point 7 or the frequency of the grid interconnection inverter 10 in FIG. The small reactive detection signal shown in FIG. 4B amplifies the periodic minute reactive power fluctuation for a predetermined short time (not shown), thereby increasing the reactive power to increase the sensitivity. Then, the frequency of the subsequent power receiving point 7 or the frequency of the system interconnection inverter 10 is continuously monitored via the incomplete differential filter as shown in FIG.

This imperfect differential filter has a transfer function representation of sT / (1 + sT), where T is represented by a filter time constant, and a set value d of a predetermined fixed value of the imperfect differential filter. If it exceeds and the settling time Te is exceeded, it is determined at that time that the grid interconnection inverter 10 is disconnected from the power distribution system 5 as a power system and is in an isolated operation, and as shown in FIG. By outputting the islanding detection signal, islanding can be reliably detected with high sensitivity without erroneous detection of a transient frequency change. Since they are performed at the same time, the reliability of this type of device is improved.

The above-mentioned predetermined reference frequency is not a constant value of the power system frequency 50 Hz or 60 Hz but a frequency value several seconds in the past so as not to erroneously detect the isolated operation state due to the fluctuation of the frequency on the power system side. Average values can be used. FIG. 5 is a diagram for explaining a detection operation according to a third embodiment of the method for detecting the islanding operation of the grid interconnection inverter according to the present invention, in which (A) a power receiving point or a deviation of the frequency of the grid interconnection inverter; It is a correlation diagram of (B) integral value of a frequency deviation, and (C) islanding operation detection signal. Also in this embodiment, the load amount of the distribution system 5 (the external load 6 and the
5) and the power generation amount of the system interconnection inverter 10 is balanced, and there is no power flow between the upper system side (the infinite bus 1, the upper system transmission line 2 and the distribution transformer 3) and the distribution system 5. In order to prevent the above problem, the periodic reactive power fluctuation signal from the islanding operation detection device 14 is set so that the receiving point reactive power slightly fluctuates periodically based on the set value of a reactive power setting device (not shown) of the grid interconnection inverter 10. In the same manner as in the first embodiment, 17 is provided actively so as to always have a tidal current.

The independent operation detection shown in FIG. 5 is different from the detection shown in FIG. 3 in that the frequency deviation of the frequency of the power receiving point or the grid connection inverter shown in FIG. Integrate with time. As shown in FIG. 5B, the integrated value of the frequency deviation of the power receiving point or the grid interconnection inverter is monitored, and if the deviation of the integrated value of the frequency deviation in one direction exceeds the islanding detection range c, the system It is determined that the interconnection inverter 10 is disconnected from the power distribution system 5 as an electric power system and is in an isolated operation, and outputs an isolated operation detection signal as shown in FIG. This detection can be performed simultaneously with the detection in the embodiment of FIG. 3, and in this case, the detection of the isolated operation can be reliably performed without erroneous detection, so that the reliability of this type of device is improved.

[0025]

As is apparent from the above-described embodiment, according to the present invention, in order to detect the isolated operation state of the system interconnection inverter, the exclusive use of the interruption signal required in the conventional transfer interruption method is required. No transmission equipment such as lines is required,
Since simple operation can be easily detected simply by providing a simple method on each of the distributed power sources, there is a realistic and economically excellent effect.

Further, even if the load and the power generation amount of the grid interconnection inverter are balanced and there is no tidal current, the isolated operation detection method of the present invention cannot be detected by the conventional voltage and frequency monitoring methods. The active reactive power setter of the grid interconnection inverter is given active periodic microfluctuations, so that the reactive power at the receiving point periodically fluctuates slightly based on the set value of the reactive power setter. By enabling the detection of operation, amplifying the fluctuation value of the reactive power of the receiving point and switching it step by step, using an erroneous detection prevention timer, and using an incomplete differential filter, the erroneous detection of the isolated operation state can be performed. Can be prevented.

In addition, the method for detecting the islanding operation of the system interconnection inverter according to the present invention by monitoring the integrated value of the frequency deviation between the system interconnection inverter and a predetermined reference frequency is described below.
Since the deviation of the integral value of the frequency deviation is monitored, the isolated operation can be reliably detected, and the reliability can be improved.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various design changes can be made without departing from the spirit of the present invention. It is.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of a method for detecting an isolated operation of a grid interconnection inverter according to the present invention;

FIG. 2 is a configuration diagram of a conventional method for detecting an islanding operation of a grid interconnection inverter.

FIG. 3 is a diagram for explaining a detection operation according to the first embodiment of the method for detecting the isolated operation of the grid interconnection inverter according to the present invention;

FIG. 4 is a diagram for explaining a detection operation according to a second embodiment of the method for detecting the isolated operation of the system interconnection inverter according to the present invention;

FIG. 5 is a diagram for explaining a detection operation according to a third embodiment of the method for detecting the isolated operation of the system interconnection inverter according to the present invention;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Infinite bus, 2 ... Upper system transmission line, 3 ... Distribution transformer, 4 ... System side circuit breaker, 5 ... Distribution system, 6 ... External load,
Reference numeral 7: power receiving point, 8: power receiving circuit breaker, 9: system interconnection inverter-side circuit breaker, 10: system interconnection inverter, 11: fuel cell body, 12: fuel cell power generation system, 13: frequency detector, 14 ... islanding detection device, 15 ... internal load,
16: transfer cutoff signal, 17: reactive power fluctuation signal

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02J 3/00-5/00

Claims (4)

(57) [Claims] An isolated operation detection method for detecting that a grid-connected inverter of a distributed power supply is disconnected and becomes an independent operation during the connection between a power system and a distributed power supply. The periodic change in the receiving point reactive power is always given by giving the reactive power setting device a small periodic change, and the frequency change of the grid connection point or the grid connection inverter is monitored. When the deviation from the reference frequency is equal to or greater than a predetermined value, the amplitude of the periodic disturbance of the receiving point reactive power is amplified for a predetermined minute time after a predetermined time has elapsed, and the amplified grid connection point or grid connection point is amplified. A method for detecting an islanding operation of an inverter for system interconnection, wherein an islanding operation is determined by monitoring a frequency deviation of the inverter. 2. An isolated operation detection method for detecting that an inverter for system interconnection of a distributed power supply is disconnected and becomes an independent operation during interconnection between a power system and a distributed power supply. The periodic change in the receiving point reactive power is always given by giving the reactive power setting device a small periodic change, and the frequency change of the grid connection point or the grid connection inverter is monitored. When the deviation from the reference frequency is equal to or greater than a certain value, the amplitude of the periodic change in the reactive power at the receiving point is amplified for a predetermined minute time, and the frequency of the amplified grid connection point or the grid-connected inverter is amplified. Monitoring through an imperfect differential filter, and when the predetermined set value and settling time of the imperfect differential filter are exceeded, it is determined that the grid interconnection inverter is disconnected from the power system and is operated independently. Characterized by Method for detecting the islanding operation of a grid connection inverter. 3. The method according to claim 1, wherein the predetermined reference frequency is an average value of frequency values several seconds in the past. Method for detecting the isolated operation of a grid-connected inverter. 4. An isolated operation detection method for detecting that a grid-connected inverter of a distributed power supply is disconnected and becomes an isolated operation during connection between a power system and a distributed power supply. The periodic change in the receiving point reactive power is always given by giving the reactive power setting device a small periodic change, and the frequency change of the grid connection point or the grid connection inverter is monitored. Integrate the frequency deviation from the reference frequency for a certain period of time, and when the integrated value of this frequency deviation exceeds a predetermined value, determine that the grid interconnection inverter is disconnected from the power system and determined to be in isolated operation. Characteristic method of detecting islanding of inverters for grid interconnection.