JP2017051063A - Isolated operation detection system for distributed power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an isolated operation detection system capable of surely detecting an isolated operation state of a distributed power supply in a short time.SOLUTION: An isolated operation detection system comprises frequency detection means 12, frequency deviation calculation means 13, reactive power calculation/injection means 14, and isolated operation detection means 16 and injects reactive power in which, with respect to a frequency deviation, a frequency deviation calculated next to the frequency deviation varies by a predetermined ratio, into a system 21 through an inverter 11. The isolated operation detection means 16 calculates a ratio of the present frequency deviation's increase/decrease from a past frequency deviation, as a frequency deviation ratio and determines to be in an isolated operation state when the number of times of the frequency deviation ratio having exceeded a first threshold supposed from injected reactive power has exceeded a second threshold; or when, at the time of an injected reactive power amount exceeding a threshold, the number of times of the frequency deviation ratio having exceeded a third threshold has exceeded a fourth threshold, or when the number exceeds a fifth threshold and the absolute value of the frequency deviation exceeds a sixth threshold or a system frequency exceeds a seventh threshold or is lower than an eighth threshold.SELECTED DRAWING: Figure 4

Description

  In the present invention, when a distributed power source such as a solar power generation system, a wind power generation system, or a fuel cell power generation system is connected to an electric power system via an inverter, the distributed power source is The present invention relates to an isolated operation detection system that detects that the system has been disconnected from the system and has entered an isolated operation state.

  When a distributed power source connected to the power system is in a single operation state and the power supply from the system power source stops, the electric shock and power distribution equipment are damaged due to the reverse charging of the distribution line by the distributed power source. There is a risk. For this reason, it is required to quickly detect isolated operation of the distributed power source and to ensure safety by separating the inverter and the distributed power source from the power system.

  This type of isolated operation detection system is a passive method that detects isolated operation by detecting changes in voltage, phase, etc. that occur when the distributed power source is disconnected from the interconnection state with the power system and transitions to the isolated operation state. A fluctuation factor is given to the output of the inverter connected to the power supply, and the influence of the fluctuation does not appear at the time of interconnection operation. It can be roughly divided into the active method.

As the above-mentioned active method, there is known a method in which reactive power is injected into a system to change the output of an inverter, and the change is detected, and an isolated operation is detected using a deviation of the system frequency as a determination condition.
For example, there is one that calculates a deviation between the latest system frequency and a past system frequency, and determines that the islanding operation is performed when the deviation exceeds a predetermined threshold.
FIG. 9A is an explanatory diagram of the principle for detecting the isolated operation of the distributed power supply when the frequency deviation exceeds the threshold value once or a plurality of times, and “●” indicates a sampling point at a constant period. Indicates frequency deviation.

Further, Patent Document 1 discloses a conventional technique in which a threshold value for monotonously increasing / decreasing monotonically is set in a stepwise manner, and an isolated operation is detected when the frequency deviation exceeds the above stepwise threshold value at a plurality of sampling points. Yes.
Here, FIG. 10 is a configuration diagram of the isolated operation detection device 50 described in Patent Document 1, and this detection device 50 is connected between the distributed power supply 60 and the system power supply 70. In FIG. 10, 51 is a control device that controls the interconnection relays 54 and 55 by measuring the frequency of the system, and 52 is an inverter that controls the inverter 53 based on the command from the control device 51 and the voltage and current of the system. It is a control unit.

FIG. 11 is a block diagram of the control device 51 in FIG. The control device 51 includes a measurement unit 51a that measures the frequency of the system, a frequency feedback unit 51b that generates corrected reactive power according to the fluctuation state (frequency deviation) of the measurement frequency during a predetermined period, and the reactive power periodically. A periodic variation unit 51c that varies, an addition unit 51d that adds the reactive power that periodically varies and the corrected reactive power, a change pattern generation unit 51e that generates a change pattern according to a frequency deviation in a predetermined period, and a frequency deviation And a change pattern to determine whether or not an independent operation is performed, and a determination unit 51f that drives the interconnection relays 54 and 55 based on the determination output.
FIG. 12A is an explanatory diagram of the principle of detecting an isolated operation with the above-described configuration. When the frequency deviation exceeds a stepped threshold (change pattern) at a plurality of sampling points, the isolated operation is detected. Yes.

JP 2007-215392 A (paragraphs [0041] to [0062], FIG. 1, FIG. 2, FIG. 5, etc.)

As described above, in the method of detecting the isolated operation by comparing the frequency deviation with the threshold value, if a system disturbance occurs such that the frequency deviation changes with a large change with respect to the threshold value, the frequency deviation is determined during the determination. Even if there is a point where the rate of change is reversed and the frequency deviation becomes smaller thereafter, it may be erroneously detected as an isolated operation even if it is not an isolated operation.
FIG. 9B and FIG. 12B show such a false detection state. In any case, the frequency fluctuates instantaneously due to the disturbance of the system, and then the frequency deviation gradually decreases in the process of returning to the original frequency, but it does not fall below the preset threshold value. Incorrect operation will be detected.

In order to avoid the above-described erroneous detection of isolated operation, it is necessary to finely adjust the threshold value or to set a larger threshold value with a margin.
However, it is difficult to eliminate false detection completely only by finely adjusting the threshold, and if there is a margin in the threshold, it will not be possible to detect isolated operation unless the frequency deviation becomes large. Decreases and the time required for determination becomes longer. That is, as a result, the single operation state of the distributed power source continues for a long time, and there is a problem that safety is lowered.
Accordingly, an object of the present invention is to provide an isolated operation detection system capable of reliably detecting an isolated operation state of a distributed power supply in a short time.

  In order to solve the above-described problem, the present invention injects reactive power into a system through an inverter, and thus the frequency deviation increases according to the injected reactive power amount, and the frequency deviation assumed from the injected reactive power amount. The islanding operation is detected based on the change of.

First, the behavior of the frequency deviation due to the reactive power injection into the system will be described with reference to FIGS.
In FIG. 6, assuming that the frequency deviation detected at time t1 is Δf, the reactive power injected into the system at time t1 is expected to generate a frequency deviation (2 × Δf) twice Δf at the next sampling point t2. Ideally, the frequency deviation detected at time t2 is (2 × Δf). Further, assuming that the frequency deviation detected at time t2 is (2 × Δf), the reactive power injected into the system at time t2 is twice the frequency deviation (4 × Δf) at (2 × Δf) at the next sampling point t3. Assuming that Δf) is expected to occur, ideally, the frequency deviation detected at time t3 is (4 × Δf).
In the present invention, the distributed power source is based on comparing the ratio of frequency deviations between consecutive sampling points expected to be caused by the injection reactive power (“2.0” in the example of FIG. 6) with a predetermined threshold. Is detected.

  FIG. 7 is a diagram showing the relationship between the frequency deviation and the injection reactive power. There may be a case where the polarity of the injection reactive power is negative. Here, a case where the polarity is positive will be described. In addition, when the polarity of the injection reactive power is negative, the characteristics are symmetrical to those in FIG.

An ideal state will be described for a case where the polarity of the injection reactive power is positive.
In FIG. 7, first, when the frequency deviation Δf1 is detected, the reactive power Q2 that is expected to generate twice the frequency deviation Δf2 (= 2 × Δf1) is injected. Then, the frequency deviation Δf2 generated by the injection of the reactive power Q2 is detected. Next, when the frequency deviation Δf2 is detected, reactive power Q3 that is expected to generate twice the frequency deviation Δf3 (= 2 × Δf2) is injected. Then, the frequency deviation Δf3 generated by the injection of the reactive power Q3 is detected.
Thereafter, similarly, when the frequency deviation Δfn is detected, reactive power Qn + 1 that is expected to generate a frequency deviation Δfn + 1 (= 2 × Δfn) that is twice that frequency deviation is injected.

By injecting reactive power into the system according to the above procedure, the frequency deviation gradually increases. In other words, if the next expected frequency deviation is, for example, (2 × Δf) with respect to the detected frequency deviation Δf, the next frequency deviation increases as Δf increases, and the next frequency deviation decreases as Δf decreases. .
Focusing on this point, in the present invention, a threshold value fluctuation method is used in which the threshold value for detecting the isolated operation is varied according to the change state of the frequency deviation.

FIG. 8 is a conceptual diagram for explaining the threshold value fluctuation method in the present invention. In the present invention, when the frequency deviation is small as shown in FIG. 8A, the frequency deviation expected next is also small, so the threshold value, which is the ratio of the frequency deviation, becomes small, and conversely, FIG. When the frequency deviation is large as described above, the next expected frequency deviation is also large, so that the threshold value, which is the ratio of the frequency deviation, varies so as to increase.
For this reason, in the present invention, as shown in FIG. 9B and FIG. 12B, when the frequency deviation greatly fluctuates due to the disturbance of the system, the threshold for the next frequency deviation is increased. However, if the frequency deviation subsequently decreases from the previous value and does not reach the expected value, the ratio of the frequency deviation is less than the increased threshold. Misdetection is avoided because it is not considered.

That is, the invention according to claim 1 is an isolated operation detection system for a distributed power supply that detects that the distributed power supply is in an isolated operation state without being connected to an electric power system via a power converter,
A frequency detecting means for detecting a system frequency; a frequency deviation calculating means for calculating a frequency deviation of a predetermined period from the system frequency; and a frequency deviation of a next predetermined period changes at a predetermined ratio with respect to the frequency deviation of the predetermined period. Reactive power calculation / injection means for calculating reactive power to be injected into the system via the power converter, and reactive power injected into the system by the frequency deviation of the predetermined period and the reactive power calculation / injection means And an isolated operation detecting means for determining whether or not the distributed power supply is in an isolated operation state based on
The isolated operation detecting means includes
When the injection reactive power to the system is greater than or equal to a predetermined value, the ratio of increase / decrease of the current frequency deviation from the past frequency deviation is calculated as a frequency deviation ratio, and the frequency deviation ratio is assumed as a ratio threshold assumed from the injection reactive power When the number of times exceeding the first threshold value exceeds the second threshold value as the frequency threshold value, it is determined that the distributed power source is in a single operation state,
When the injection reactive power calculated by the reactive power calculation / injection means exceeds an injection amount threshold,
The reactive power calculation / injection means limits the injection reactive power to the injection amount threshold,
The isolated operation detecting means includes
When the ratio of increase / decrease of the current frequency deviation from the past frequency deviation is calculated as the frequency deviation ratio, and the number of times the frequency deviation ratio exceeds the third threshold as the ratio threshold exceeds the fourth threshold as the frequency threshold Alternatively, when the frequency deviation ratio exceeds the third threshold exceeds a fifth threshold as a frequency threshold, and the absolute value of the frequency deviation of the system exceeds a sixth threshold, the distributed power supply It is determined that the vehicle is in a single operation state.

The invention according to claim 2 is an isolated operation detection system for a distributed power source that detects that the distributed power source is in an isolated operation state without being connected to a power system via a power converter,
A frequency detecting means for detecting a system frequency; a frequency deviation calculating means for calculating a frequency deviation of a predetermined period from the system frequency; and a frequency deviation of a next predetermined period changes at a predetermined ratio with respect to the frequency deviation of the predetermined period. Reactive power calculation / injection means for calculating reactive power to be injected into the system via the power converter, and reactive power injected into the system by the frequency deviation of the predetermined period and the reactive power calculation / injection means And an isolated operation detecting means for determining whether or not the distributed power supply is in an isolated operation state based on
The isolated operation detecting means includes
When the injection reactive power to the system is greater than or equal to a predetermined value, the ratio of increase / decrease of the current frequency deviation from the past frequency deviation is calculated as a frequency deviation ratio, and the frequency deviation ratio is assumed as a ratio threshold assumed from the injection reactive power When the number of times exceeding the first threshold value exceeds the second threshold value as the frequency threshold value, it is determined that the distributed power source is in a single operation state,
When the injection reactive power calculated by the reactive power calculation / injection means exceeds an injection amount threshold,
The reactive power calculation / injection means limits the injection reactive power to the injection amount threshold,
The isolated operation detecting means includes
When the ratio of increase / decrease of the current frequency deviation from the past frequency deviation is calculated as the frequency deviation ratio, and the number of times the frequency deviation ratio exceeds the third threshold as the ratio threshold exceeds the fourth threshold as the frequency threshold Or when the frequency deviation ratio exceeds the third threshold exceeds a fifth threshold as a frequency threshold and the system frequency exceeds the seventh threshold or less than the eighth threshold. Is determined to be in the single operation state.

  In addition, as described in Claim 3, it is desirable that the isolated operation detection means determines the number of comparisons with the first threshold based on the transition of the frequency deviation ratio.

The present invention is an isolated operation detection system in which reactive power injected into a system is associated with a frequency deviation caused thereby, and even if the appearance of the frequency deviation caused by reactive power injection varies depending on the load condition, the initial frequency This is a detection system in which the isolated operation detection works effectively even when the fluctuation is small and the rise is slow, and conversely, the initial frequency fluctuation is large and the limit value of the injection reactive power is reached quickly. .
According to the present invention, it is possible to detect a single operation of a distributed power supply in a short time, and it is possible to immediately take measures to prevent accidents by quickly opening the interconnection relay.
Also, a single operation detection operation determined based on the frequency deviation ratio of the system according to the injection reactive power and a single operation detection operation determined based on the injection reactive power, thereby providing a highly accurate single operation with no detection omission. A driving detection system can be realized.
Furthermore, by using a judgment condition that combines the frequency deviation ratio and the frequency deviation or system frequency and their change time, even if the upper limit value of the reactive power injected into the system is changed, the isolated operation is erroneously detected. In addition, there is an effect that a fine adjustment of a threshold value for determination is not necessary, while ensuring a function of reliably detecting without any problem.

1 is a configuration diagram of a grid interconnection system to which an embodiment of the present invention is applied. It is a flowchart which shows the process of the independent operation detection means in FIG. It is a flowchart which shows the process of the independent operation detection means in FIG. It is a flowchart which shows the process of the independent operation detection means in FIG. It is a flowchart which shows the process of the independent operation detection means in FIG. It is a figure which shows the behavior of the frequency deviation by the reactive power injection | pouring to a system | strain. It is a figure which shows the relationship between a frequency deviation and injection reactive power. It is a conceptual diagram for demonstrating the threshold value fluctuation | variation method in this invention. It is explanatory drawing of the independent operation | movement detection principle by a prior art. It is a block diagram of the isolated operation detection apparatus described in patent document 1. It is a block diagram of the control apparatus in FIG. It is explanatory drawing of the independent operation detection principle by patent document 1. FIG.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a system interconnection system of distributed power sources to which this embodiment is applied.
This interconnection system converts the DC power of the distributed power supply 1 into AC power by the power conditioner 10, and synchronizes this AC power with the power supplied from the system power supply 20 via the system 21. Or the like to be supplied to the load 30.

In FIG. 1, a distributed power source 1 is a DC power source provided in a solar power generation system or a wind power generation system, and supplies DC power to a power conditioner 10.
The power conditioner 10 includes an inverter 11 for converting DC power supplied from the distributed power supply 1 into AC power synchronized with the system power supply 20, frequency detection means 12 for detecting the system frequency, and current frequency detection means 12. The frequency deviation calculating means 13 for calculating the frequency deviation from the system frequency of the system and the past system frequency held therein, and the reactive power to be injected into the system 21 for causing the frequency fluctuation based on the frequency deviation are calculated. The distributed power source 1 is in a single operation state based on the reactive power calculation / injection means 14 to be output and the frequency deviation from the frequency deviation calculation means 13 and the information on the reactive power calculation / injection means 14. And the independent operation detection means 16 that outputs the determination result and the frequency information from the frequency detection means 12 Injecting reactive power information from the power calculating and injecting means 14, and, based on the independent operation information from the independent operation detecting means 16, and inverter control means 15 that drives and controls the inverter 11, and is composed of.
Reference numeral 17 denotes an interconnection relay that disconnects the inverter 11 (distributed power source 1) from the system 21 by a detection signal output from the isolated operation detection means 16.

The frequency deviation calculated by the frequency deviation calculating means 13 may be a deviation in a single cycle, but may be a value calculated from a moving average value for several cycles in order to eliminate the influence of measurement errors and noise errors.
The reactive power calculation / injection unit 14 calculates the reactive power injected into the system 21 separately for the first stage gain and the second stage gain according to the frequency deviation sent from the frequency deviation calculation unit 13. Here, the reactive power injected when the frequency deviation is smaller than a gain threshold, which will be described later, is detected frequency deviation × first stage gain, and the reactive power injected when the frequency deviation is larger than the gain threshold is detected frequency deviation × second stage. Calculated as gain.

  The gain threshold value for determining the first stage gain / second stage gain used for the reactive power calculation is, for example, a frequency deviation of 0.01 [Hz]. Further, as the value of each gain, by making the second stage gain larger than the first stage gain, when the frequency deviation is small, the injection reactive power is reduced by the first stage gain to suppress the influence on the system 21; When the frequency deviation increases, the injection reactive power is increased by the second-stage gain so that the change becomes more remarkable.

  The injection reactive power determined by the reactive power calculation / injection means 14 is provided with an injection amount threshold value, and reactive power exceeding the injection amount threshold value cannot be injected. A state where the injection reactive power reaches the injection amount threshold is referred to as a reactive power injection limit state.

Next, the processing of the isolated operation detection means 16 in this embodiment will be described with reference to FIGS. The processing of the isolated operation detecting means 16 shown in these figures is started at a regular cycle.
In the following description, “inspection” is defined as an inspection mode for detecting whether or not the vehicle is in an isolated operation state, and a flag indicates that inspection is in progress.

First, in FIG. 2, the islanding operation detection means 16 refers to the in-inspection flag, and if inspecting (YES in step S1), the process in FIG. Migrate to
When the inspection is not in progress (NO in S1), it is determined based on information from the reactive power calculation / injection means 14 whether or not the injection reactive power is at the level of the second stage gain (S2). When the injection reactive power is at a level based on the second stage gain (S2 YES), it is determined that a frequency deviation that satisfies the detection condition has started to occur, and each process for starting the process based on the first isolated operation detection condition is performed. The counters (ratio excess counter 1 and ratio excess counter 2) are cleared (S3).

  Here, the ratio excess counter 1 is a counter that counts the number of times that the ratio between the current frequency deviation and the past frequency deviation (frequency deviation ratio) exceeds the first threshold (ratio threshold 1), and the ratio excess counter 2 is It is a counter that counts the number of times that the ratio between the current frequency deviation and the past frequency deviation (frequency deviation ratio) exceeds the third threshold (ratio threshold 2) in the reactive power injection limit state.

Next, a frequency deviation ratio is obtained from the current and past frequency deviations sent from the frequency deviation calculation means 13 of FIG. 1 (S4), and this frequency deviation ratio is assumed from the reactive power calculation / injection means 14 injected reactive power. It is determined whether or not the first threshold value (ratio threshold value 1), for example, “2.0” is exceeded (S5).
Here, the basis of “2.0” given as an example of the first threshold is that injection is performed in the expectation that a deviation of four times the detected frequency deviation will appear when reactive current is injected, and the frequency for two cycles If the frequency deviation is calculated by averaging the values, the assumed frequency deviation is based on the fact that the frequency deviation is “2.0”, which is half of four times. It goes without saying that this may allow for margins.

  When the frequency deviation ratio exceeds the first threshold value (S5 YES), the in-inspection flag is set and the ratio excess counter 1 is incremented to start the processing based on the first islanding detection condition (S6, S6). S7) By holding the past frequency deviation input from the frequency deviation calculating means 13 as the previous value (S8), the current process is terminated.

  In step S5, when the frequency deviation ratio does not exceed the first threshold (NO in S5), the ratio (frequency deviation ratio) between the current frequency deviation and the past frequency deviation is the third threshold (ratio threshold 2). For example, it is determined whether or not “1.2” is exceeded (S9). When the frequency deviation ratio exceeds the third threshold value (S9 YES), the in-inspection flag is set and the ratio excess counter 2 is incremented to start the processing based on the second islanding operation detection condition (S10, S11) After shifting to step S8, the current process is terminated.

In step S9, if the frequency deviation ratio does not exceed the third threshold (NO in S9), it is determined that the isolated operation detection condition is not satisfied, and the in-inspection flag is not set, and the process proceeds to step S8. The current process is terminated after the migration.
Furthermore, if the injection reactive power is not at a level corresponding to the second-stage gain in step S2 (S2 NO), there is no frequency deviation that satisfies the isolated operation detection condition, and the process proceeds to step S8. To end the current process.

  Next, the process when it is determined in step S1 that the inspection is being performed (S1 YES) will be described with reference to FIG. The process of FIG. 3 is a process based on the first isolated operation detection condition.

In FIG. 3, first, it is determined based on information from the reactive power calculation / injection means 14 whether or not the injection reactive power is at the level of the second-stage gain (S12).
If the injection reactive power is at the level of the second-stage gain (YES in S12), it is determined that a frequency deviation that satisfies the detection condition has occurred, and the detection operation is continued. Based on the output information of the frequency deviation calculation means 13 The current and past frequency deviation ratios are calculated (S13).

  Next, the presence / absence of the count value of the ratio excess counter 1 is determined (S14). If there is a count value (YES in S14), the frequency deviation ratio calculated in step S13 is injected by the reactive power calculating / injecting means 14. It is determined whether or not a first threshold value (ratio threshold value 1) assumed from reactive power, for example, “2.0” is exceeded (S15). When the frequency deviation ratio exceeds the first threshold (S15 YES), the ratio excess counter 1 is incremented (S16), and the count value of the ratio excess counter 1 exceeds the second threshold (number threshold 1). It is determined whether or not (S17).

When the count value of the ratio excess counter 1 exceeds the second threshold value (S17 YES), the first islanding operation detection condition is satisfied by the occurrence of a predetermined number of changes in the frequency deviation according to the injection reactive power. It is determined that the distributed power source 1 is in a single operation state. That is, the isolated operation detection flag is set (S18), the in-inspection flag is cleared to cancel the inspection state (S19), and the current process is terminated.
Simultaneously with the setting of the isolated operation detection flag (S 18), the interconnection relay 17 of FIG. 1 is opened to disconnect the inverter 11 from the system 21.

In step S12, if the injection reactive power is not at the level due to the second stage gain, the inspection start condition is not satisfied, so the in-inspection flag is cleared (S21), and the frequency deviation input from the frequency deviation calculating means 13 is calculated. The previous value is held (S22), and the current process is terminated.
Further, if the count value of the ratio excess counter 1 does not yet exist in step S14, and if the frequency deviation ratio does not exceed the first threshold value in step S15, the first islanding operation detection condition is not satisfied. As a result, the ratio excess counter 1 is cleared (S20), and the process proceeds to FIG.
Furthermore, when the count value of the ratio excess counter 1 does not exceed the second threshold value in step S17, the process proceeds to the process of FIG. 4 while continuing the process based on the first isolated operation detection condition.

Next, processing based on the second islanding operation detection condition will be described with reference to FIG.
It is in the reactive power injection limit state, and it is determined whether the ratio of the current frequency deviation and the past frequency deviation (frequency deviation ratio) exceeds the third threshold (ratio threshold 2) (S23), If both of these conditions are satisfied (S23 YES), the ratio excess counter 2 is incremented (S24).

  Then, it is determined whether or not the count value of the ratio excess counter 2 has exceeded the fourth threshold value (number of times threshold value 2) (S25). If it has exceeded (S25 YES), the frequency deviation is sufficiently large. Since the increasing tendency continues, it is determined that the second isolated operation detection condition is satisfied, and it is determined that the distributed power source 1 is in the isolated operation state. That is, the isolated operation detection flag is set (S26), and then the in-inspection flag is cleared to cancel the inspection state (S27), thereby terminating the current process. Simultaneously with the setting of the isolated operation detection flag, the interconnection relay 17 in FIG. 1 is opened to disconnect the inverter 11 from the system 21.

  In the isolated operation detection system that injects reactive power into the system according to the frequency deviation, the distributed power supply injects reactive power even when the system frequency is disturbed by factors other than the occurrence of isolated operation. Become. There is no problem when the system is strong against the distributed power supply, but when the system is vulnerable to the distributed power supply, the distributed power supply injects reactive power to further promote disturbance of the system. Therefore, the upper limit value of the reactive power that the distributed power source injects into the system is set low.

In this way, when the upper limit value of reactive power injected into the system by the distributed power source is set low, the reactive power injection amount changes according to the frequency deviation, or the reactive power upper limit value is set high. As compared with, since the increase in the frequency after reaching the reactive power injection limit state is suppressed by the small frequency deviation, the frequency deviation ratio is rapidly reduced.
That is, since the time during which the frequency deviation ratio exceeds the third threshold is shortened in step S23, the count value of the ratio excess counter 2 does not exceed the fourth threshold as the frequency threshold in step S25 (NO in S25). There is a risk that isolated operation cannot be detected.

In this case, if the third threshold value is set low, the time during which the frequency deviation ratio exceeds the third threshold value becomes longer, and the count value of the ratio excess counter 2 exceeds the fourth threshold value to detect an isolated operation. Is possible. However, if this is done, there is a risk of erroneous detection as isolated operation even when system frequency disturbances occur due to factors other than the occurrence of isolated operation.
Therefore, fine adjustment of the third threshold value is necessary to reliably detect an isolated operation, but as a result, a new problem that versatility is reduced occurs.

Therefore, in the present embodiment corresponding to claim 1, even if the frequency deviation ratio exceeds the third threshold value (S23 YES), the fourth threshold value for determining that the count value of the ratio excess counter 2 is the single operation is set. A determination step (S101) for not exceeding (NO in S25) is provided.
That is, when the count value of the ratio excess counter 2 does not exceed the fourth threshold value (S25 NO), the count value exceeds the fifth threshold value (number of times threshold value 3), and the absolute value of the frequency deviation is It is determined whether the sixth threshold is exceeded (S101). If the count value exceeds the fifth threshold value, that is, if the absolute value of the frequency deviation exceeds the sixth threshold value in a state where a single operation is assumed to some extent (YES in S101), it is determined that the single operation is performed. An operation detection flag is set (S26).

The fifth threshold value and the sixth threshold value in step S101 are the frequency calculated from the frequency fluctuation in the FRT (continuous operation during system disturbance) requirement obtained in the system connected to the distributed power source or the frequency fluctuation waveform at the actual system disturbance. What is necessary is just to set based on the value which added the margin to the deviation.
By providing this step S101, it is possible to set the third threshold without fine adjustment so as not to erroneously detect isolated operation within the range where the distributed power source is required to continue operation.

  When the determination condition of step S101 is not satisfied (NO in S101), the frequency deviation input from the frequency deviation calculation means 13 in FIG. 1 is held as the previous value while continuing the processing based on the second isolated operation detection condition ( S28), the current process is terminated.

If the determination condition in step S23 is not satisfied (NO in S23), it is determined that the second islanding operation detection condition is no longer satisfied, and the ratio excess counter 2 is cleared (S29). Next, the presence / absence of the count value of the ratio excess counter 1 for performing the first isolated operation detection operation is determined (S30), and if there is no count value of the ratio excess counter 1 (S30 NO), the first isolated operation is performed. Since the detection conditions are not already satisfied and the first and second isolated operation detection conditions are not satisfied, the in-inspection flag is cleared and the inspection state is released (S31). Then, the frequency deviation input from the frequency deviation calculating means 13 of FIG. 1 is held as the previous value (S32), and the current process is terminated.
In step S30, if there is a count value of the ratio excess counter 1 (YES in S30), the process under the first isolated operation detection condition is continued, so the in-inspection flag is not cleared and step S32 is executed. After this, the current process is terminated.

Here, as shown in FIG. 5, step S102 is provided instead of step S101, and when the count value of the ratio excess counter 2 does not exceed the fourth threshold value (S25 NO), the count value is the fifth value. It may be determined whether the threshold (number threshold 3) is exceeded and the system frequency exceeds the seventh threshold or the system frequency is less than the eighth threshold. This embodiment corresponds to claim 2.
That is, if the count value of the ratio excess counter 2 does not exceed the fourth threshold value (NO in S25), the count value exceeds the fifth threshold value (number threshold value 3), and the system frequency is the seventh threshold value. Or whether the system frequency is less than the eighth threshold (S102). When the count value exceeds the fifth threshold value, that is, when the system frequency exceeds the seventh threshold value or the system frequency is less than the eighth threshold value in a state where a single operation is assumed to some extent (YES in S102). Then, it is determined as an isolated operation, and an isolated operation detection flag is set (S26).
The fifth threshold value, the seventh threshold value, and the eighth threshold value in step S102 may be set based on the system frequency in the FRT requirement or the value obtained by adding a margin to the system frequency at the time of actual system disturbance.
Also in this embodiment, the third threshold value can be set without fine adjustment.

Next, the frequency deviation ratio calculation process (step S4 in FIG. 2) in the isolated operation detection means 15 in FIG. 1 will be described.
Now, if the increase rate of the frequency deviation is large, the reactive power injection limit state is reached quickly, so that the increase rate reaches its peak and the first isolated operation detection condition cannot be satisfied. Therefore, the determination accuracy of the first isolated operation detection condition is increased by dividing the determination of whether or not the first isolated operation detection condition is satisfied into two stages.

  Here, as an example, it is assumed that the system frequency is detected every 5 [ms], that is, four times per period with respect to the system power having a frequency of 50 [Hz] (period is 20 [ms]). The number of comparisons with the first threshold (ratio threshold 1) at this time is, for example, as follows.

(1) When a high ratio state in which the rate of increase in frequency deviation exceeds “3.0” continues four times in one cycle, the total value of the number of comparisons with the first threshold is set to one and a half. Corresponding 6 times.
(2) In other cases, the total value of the number of comparisons with the first threshold value is 9 times corresponding to a little over 2 cycles.
In both cases (1) and (2), the cumulative frequency deviation ratio (increase rate) is “18.0” or more.
In addition, each numerical value shown here is an example to the last, and this invention is not limited to these numerical values at all.

1: distributed power supply 10: power conditioner 11: inverter 12: frequency detection means 13: frequency deviation calculation means 14: reactive power calculation / injection means 15: inverter control means 16: isolated operation detection means 17: interconnection relay 20: system power supply 21: System 30: Load

Claims (3)

An isolated operation detection system for a distributed power source that detects that the distributed power source is in an isolated operation state without being connected to an electric power system via a power converter,
A frequency detecting means for detecting a system frequency; a frequency deviation calculating means for calculating a frequency deviation of a predetermined period from the system frequency; and a frequency deviation of a next predetermined period changes at a predetermined ratio with respect to the frequency deviation of the predetermined period. Reactive power calculation / injection means for calculating reactive power to be injected into the system via the power converter, and reactive power injected into the system by the frequency deviation of the predetermined period and the reactive power calculation / injection means And an isolated operation detecting means for determining whether or not the distributed power supply is in an isolated operation state based on
The isolated operation detecting means includes
When the injection reactive power to the system is greater than or equal to a predetermined value, the ratio of increase / decrease of the current frequency deviation from the past frequency deviation is calculated as a frequency deviation ratio, and the frequency deviation ratio is assumed as a ratio threshold assumed from the injection reactive power When the number of times exceeding the first threshold value exceeds the second threshold value as the frequency threshold value, it is determined that the distributed power source is in a single operation state,
When the injection reactive power calculated by the reactive power calculation / injection means exceeds an injection amount threshold,
The reactive power calculation / injection means limits the injection reactive power to the injection amount threshold,
The isolated operation detecting means includes
When the ratio of increase / decrease of the current frequency deviation from the past frequency deviation is calculated as the frequency deviation ratio, and the number of times the frequency deviation ratio exceeds the third threshold as the ratio threshold exceeds the fourth threshold as the frequency threshold Or when the frequency deviation ratio exceeds the third threshold exceeds the fifth threshold as the frequency threshold, and the absolute value of the frequency deviation of the system exceeds the sixth threshold,
A distributed power supply isolated operation detection system, wherein the distributed power supply is determined to be in an isolated operation state. An isolated operation detection system for a distributed power source that detects that the distributed power source is in an isolated operation state without being connected to an electric power system via a power converter,
A frequency detecting means for detecting a system frequency; a frequency deviation calculating means for calculating a frequency deviation of a predetermined period from the system frequency; and a frequency deviation of a next predetermined period changes at a predetermined ratio with respect to the frequency deviation of the predetermined period. Reactive power calculation / injection means for calculating reactive power to be injected into the system via the power converter, and reactive power injected into the system by the frequency deviation of the predetermined period and the reactive power calculation / injection means And an isolated operation detecting means for determining whether or not the distributed power supply is in an isolated operation state based on
The isolated operation detecting means includes
When the injection reactive power to the system is greater than or equal to a predetermined value, the ratio of increase / decrease of the current frequency deviation from the past frequency deviation is calculated as a frequency deviation ratio, and the frequency deviation ratio is assumed as a ratio threshold assumed from the injection reactive power When the number of times exceeding the first threshold value exceeds the second threshold value as the frequency threshold value, it is determined that the distributed power source is in a single operation state,
When the injection reactive power calculated by the reactive power calculation / injection means exceeds an injection amount threshold,
The reactive power calculation / injection means limits the injection reactive power to the injection amount threshold,
The isolated operation detecting means includes
When the ratio of increase / decrease of the current frequency deviation from the past frequency deviation is calculated as the frequency deviation ratio, and the number of times the frequency deviation ratio exceeds the third threshold as the ratio threshold exceeds the fourth threshold as the frequency threshold Or, when the frequency deviation ratio exceeds the third threshold exceeds the fifth threshold as the frequency threshold, and the system frequency exceeds the seventh threshold or less than the eighth threshold,
A distributed power supply isolated operation detection system, wherein the distributed power supply is determined to be in an isolated operation state. In the isolated operation detection system of the distributed power supply according to claim 1 or 2,
The isolated operation detection system for a distributed power source, wherein the isolated operation detection means determines the number of comparisons with the first threshold based on a transition of the frequency deviation ratio.

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