JP2017028867A - Isolated operation detection device and isolated operation detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an isolated operation detection device capable of satisfying FRT requirements, and an isolated operation detection method.SOLUTION: An isolated operation detection device 10 configured to detect an isolated operation state of a distributed power source 5 which is operated while being cooperated to a power system 3, from a sudden change in a voltage phase of the power system 3 comprises: a sample/hold circuit 13 and an A/D conversion circuit 14 for generating a sampling voltage Vi from a measured voltage Vtf that is obtained by measuring a voltage of the power system 3; a frequency measurement circuit 15 for measuring a system fundamental wave frequency (f) from the measured voltage Vtf; and an arithmetic processing part 16. If it is detected that a phase difference between a phase of a system fundamental wave voltage component in a present cycle and a phase of a system fundamental wave voltage component in a reference cycle is equal to or greater than a setting and it is detected that a sudden frequency change of a variation greater than a sudden frequency change caused by a step rise that is specified in the FRT requirements occurs, the arithmetic processing part 16 detects the isolated operation state of the distributed power source 5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an isolated operation detection device and an isolated operation detection method.

  In order to link a distributed power source (distributed power source) such as a solar power generation facility to an electric power system, various grid connection systems have been proposed. In this type of interconnected system, when the power company's substation breaker is opened due to an accident in the power system, etc., and the power system is disconnected from the commercial power supply, the distributed power supply is operated with the power system connected. When (single operation) is performed, power is supplied from the distributed power source to the power system disconnected from the commercial power source, and an electric shock accident or the like may occur due to the single operation. For this reason, in order to prevent the isolated operation of the distributed power source, the interconnected grid system includes an isolated operation detection device that detects the isolated operation state, and when the distributed power source shifts from the connected operation state to the isolated operation state. Therefore, it is required to quickly disconnect (disconnect) the distributed power source from the power system.

  Therefore, various isolated operation detection methods for detecting that the distributed power source is in an isolated operation state due to a system power failure or the like have been proposed. Such an isolated operation detection method is roughly classified into a passive method and an active method.

  A voltage phase jump detection method detection method is known as one of passive type single operation detection methods (see, for example, Patent Document 1). This detection method is based on the sudden change in the voltage phase because the voltage phase of the system changes suddenly due to the unbalance between the power generation output of the distributed power supply and the load when the distributed power supply shifts from the grid operation to the single operation due to the system stop. This is a method for detecting an isolated operation state of a distributed power source. More specifically, when the distributed power source shifts from the grid operation to the single operation due to the system stop, the load power factor of the system changes from the power factor during the grid operation. This power factor change appears as a change in the voltage phase of the system, and the phase of the system voltage (voltage phase) jumps instantaneously and changes suddenly. Then, for example, the phase of the system voltage in the current cycle is repeatedly compared with the phase of the system voltage in the reference cycle that is a predetermined cycle before the current cycle. By detecting more than once, the above-described jumping change in voltage phase is detected. When a jumping change in the voltage phase is detected, the single operation state of the distributed power supply is detected, and the distributed power supply is quickly disconnected from the power system. Accordingly, it is possible to accurately detect the single operation state of the distributed power supply while suppressing erroneous detection due to system noise, load fluctuation, and the like.

Japanese Patent No. 3518511

  By the way, in recent years, with the widespread use of solar power generation facilities and the like, the number of distributed power sources connected to the power system is increasing. When a large number of distributed power sources are connected to the power system in this way, for example, due to disturbances in the power system caused by an instantaneous voltage drop (instantaneous voltage drop) due to a transmission line accident, a large number of distributed power sources are If disconnected, the power quality of the power system may be adversely affected. For this reason, the distributed power supply has a Fault Ride Through (FRT) requirement that indicates the ability to continue operation without unnecessarily disconnecting the distributed power supply from the power system when the power system is disturbed due to an instantaneous drop or the like. It is required to satisfy. Furthermore, it is necessary to meet the FRT requirement even in an isolated operation detection device that detects an isolated operation of a distributed power source. Therefore, development of an isolated operation detection device and an isolated operation detection method that satisfy the FRT requirements is desired.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an isolated operation detection device and an isolated operation detection method that can satisfy FRT requirements.

  An isolated operation detection device that solves the above-described problem is an isolated operation detection device that detects an isolated operation state of a distributed power source that is interconnected to an electric power system from a sudden change in the voltage phase of the electric power system. Sampling voltage generating means for sampling a measurement voltage obtained by measuring the voltage at a predetermined period and A / D converting to generate a sampling voltage; and extracting means for extracting a system fundamental voltage component from the sampling voltage; , A frequency measuring means for measuring the frequency of the system fundamental wave from the measured voltage, the phase of the system fundamental wave voltage component in the current cycle of the system fundamental wave, and a reference cycle that is one cycle before the current cycle Voltage phase jump detection means for detecting whether or not a phase difference with respect to the phase of the system fundamental voltage component in the system is equal to or greater than a set value, and based on the frequency And a sudden frequency change detecting means for detecting whether or not a sudden frequency change having a larger fluctuation amount than a sudden frequency change due to a step increase defined in the operation continuation requirement at the time of an accident, and the phase difference is equal to or greater than the set value. And a single operation detecting means for detecting a single operation state of the distributed power supply when the large frequency sudden change is detected.

  According to this configuration, a change in the voltage phase greater than the set value is detected, and it has been detected that a sudden frequency change has occurred that has a larger fluctuation amount than the sudden frequency change due to the step increase specified in the accident continuation requirement. Sometimes the isolated operating state of the distributed power source is detected. In other words, when the large frequency sudden change does not occur, for example, when the step increase or ramp fluctuation specified in the operation continuation requirement at the time of accident occurs, even if there is a voltage phase change greater than the set value, the dispersion The single operation state of the power supply is not detected. This suppresses the unnecessary disconnection of the distributed power supply when a voltage phase change exceeding the set value occurs due to frequency fluctuations (lamp rise or lamp fluctuation, etc.) specified in the operation continuation requirements at the time of an accident. it can. On the other hand, when the large frequency sudden change described above occurs, that is, when the voltage phase change exceeding the set value occurs due to system stoppage, etc., the single operation state of the distributed power supply is detected, and the distributed power supply is reliably removed from the power system. Can be disconnected.

  In the above isolated operation detection device, further comprising a voltage drop detection means for detecting whether all of the three-phase line voltages of the power system are 80% or more of a rated voltage based on the system fundamental wave voltage component. The single operation detection means detects that all of the three-phase line voltages are 80% or more of the rated voltage, and detects that the phase difference is equal to or more than the set value; In addition, it is preferable to detect the single operation state of the distributed power source when it is detected that the large frequency sudden change has occurred.

  According to this configuration, when even one of the three-phase line voltages has dropped to less than 80% of the rated voltage, that is, when a two-phase short circuit accident has occurred in the system, the set value or more is exceeded. Even if there is a voltage phase change, the isolated operation state of the distributed power source is not detected. As a result, it is possible to prevent the distributed power source from being unnecessarily disconnected when a voltage phase change exceeding a set value occurs due to a voltage drop (such as a two-phase short circuit accident) specified in the operation continuation requirement at the time of the accident. .

  An isolated operation detection method that solves the above problem is an isolated operation detection method of a voltage phase jump detection method that detects an isolated operation state of a distributed power source connected to an electric power system from a sudden change in the voltage phase of the electric power system. Then, a step of sampling the measurement voltage obtained by measuring the voltage of the power system at a predetermined period and A / D converting to generate a sampling voltage, and extracting a system fundamental voltage component from the sampling voltage A step of measuring a frequency of a system fundamental wave from the measured voltage, a phase of the system fundamental wave voltage component in a current cycle of the system fundamental wave, and a reference cycle that is one cycle before the current cycle Detecting whether or not a phase difference from the phase of the system fundamental voltage component in the system is equal to or greater than a set value, and based on the frequency, A step of detecting whether or not a sudden frequency change having a larger fluctuation amount than a sudden frequency change due to a step increase that has been set is detected, and detecting that the phase difference is equal to or greater than the set value, and the large frequency sudden change occurs. And a step of detecting a single operation state of the distributed power source when the fact is detected.

  According to this method, when there is no sudden frequency change that is larger than the sudden frequency change due to the step increase specified in the accident continuation requirement, for example, the step increase or ramp specified in the accident continuation requirement When fluctuations occur, the isolated operation state of the distributed power source is not detected even if there is a voltage phase change greater than the set value. This suppresses the unnecessary disconnection of the distributed power supply when a voltage phase change exceeding the set value occurs due to frequency fluctuations (lamp rise or lamp fluctuation, etc.) specified in the operation continuation requirements at the time of an accident. it can. On the other hand, when the large frequency sudden change described above occurs, that is, when the voltage phase change exceeding the set value occurs due to system stoppage, etc., the single operation state of the distributed power supply is detected, and the distributed power supply is reliably removed from the power system. Can be disconnected.

  In the above isolated operation detection method, the method further comprises a step of detecting whether or not all of the three-phase line voltages of the power system are 80% or more of the rated voltage, based on the system fundamental voltage component. In the step of detecting the single operation state, it is detected that all of the three-phase line voltages are 80% or more of the rated voltage, and the phase difference is detected to be equal to or more than the set value, In addition, it is preferable to detect the single operation state of the distributed power source when it is detected that the large frequency sudden change has occurred.

  According to this method, if any one of the three-phase line voltages is reduced to less than 80% of the rated voltage, that is, if a two-phase short-circuit fault has occurred in the system, the set value or more is exceeded. Even if there is a voltage phase change, the isolated operation state of the distributed power source is not detected. As a result, it is possible to prevent the distributed power source from being unnecessarily disconnected when a voltage phase change exceeding a set value occurs due to a voltage drop (such as a two-phase short circuit accident) specified in the operation continuation requirement at the time of the accident. .

  In the isolated operation detection method, in the step of detecting the isolated operation state, all of the three-phase line voltages in the current cycle are 80% or more of the rated voltage, and the three-phase line in the reference cycle When detecting that all of the inter-voltage is 80% or more of the rated voltage, and detecting that the phase difference is equal to or greater than the set value, and detecting that the large frequency sudden change has occurred, It is also possible to detect the single operation state of the distributed power source.

  In addition, as an example of the step of detecting the sudden frequency change, a step of detecting whether or not a frequency fluctuation of a predetermined frequency fluctuation amount or more has occurred in a first period shorter than the n cycles can be mentioned, The predetermined frequency fluctuation amount can be set to be larger than the frequency fluctuation amount due to the step increase and smaller than the frequency fluctuation amount when the voltage phase suddenly changes by the set value.

  In the above isolated operation detection method, the method further includes the step of calculating an average frequency by averaging the latest predetermined number of the frequencies, and the step of detecting the sudden frequency change is performed in a second period shorter than the first period. The step of detecting the occurrence of a sudden change in the frequency by detecting the frequency change that changes at a larger fluctuation rate than the lamp change defined in the operation continuation requirement at the time of the accident, and the detection of the occurrence of the sudden change in the frequency. Whether or not the difference between the latest frequency and the average frequency calculated immediately before the occurrence detection of the sudden frequency change is equal to or greater than the predetermined frequency fluctuation amount during a third period shorter than one period. And detecting.

  According to this method, in the third period, it is detected whether or not the difference between the latest frequency and the average frequency calculated immediately before the occurrence detection of the sudden frequency change is greater than or equal to a predetermined frequency fluctuation amount. In this way, the difference between the latest frequency and the average frequency immediately before the frequency change is compared with a predetermined frequency fluctuation amount, not the difference between the rated frequency and the latest frequency, so the frequency before the frequency change is the rated frequency. Even if the frequency fluctuates, it can be accurately detected whether or not a frequency fluctuation equal to or greater than a predetermined frequency fluctuation amount has occurred.

  According to the isolated operation detection device and the isolated operation detection method of the present invention, the isolated operation of the distributed power source can be prevented while satisfying the FRT requirement.

It is a block diagram which shows the grid connection system containing the independent operation detection apparatus in one Embodiment. It is explanatory drawing for demonstrating the voltage phase jump detection process in one Embodiment. It is explanatory drawing for demonstrating the sampling voltage in one Embodiment. It is explanatory drawing for demonstrating the voltage phase jump detection process in one Embodiment. (A)-(c) is explanatory drawing which shows the vector of a line voltage. It is explanatory drawing for demonstrating the voltage drop detection process in one Embodiment. It is explanatory drawing for demonstrating step rise. It is explanatory drawing for demonstrating ramp fluctuation. It is a wave form diagram which shows the frequency fluctuation | variation at the time of phase fluctuation | variation. It is a wave form diagram showing frequency change at the time of phase change in one embodiment. It is a flowchart which shows operation | movement of the isolated operation detection apparatus in one Embodiment. It is explanatory drawing which shows the operation | movement sequence of the independent operation detection process in one Embodiment.

Hereinafter, an embodiment of the isolated operation detection device will be described.
As shown in FIG. 1, an electric power system (distribution line) 3 is connected to a commercial power source 1 via a circuit breaker 2 of a substation. A load 4 and a distributed power supply 5 are connected to the power system 3. The load 4 shows a large number of loads collectively. The distributed power supply 5 is operated in conjunction with the power system 3 when the system is healthy. On the other hand, when the circuit breaker 2 is opened due to some accident or the like while the distributed power supply 5 is connected to the power system 3, the distributed power supply 5 is operated alone.

  The distributed power supply 5 is connected to the power system 3 via, for example, a lead-in line 6 and a circuit breaker 7. Examples of the distributed power source 5 include a solar power generation facility, a cogeneration power generation facility, a fuel cell power generation facility, and a wind power generation facility. In addition, although the circuit breaker other than illustration, a transformer, etc. are normally connected to the lead-in wire 6, illustration is abbreviate | omitted here.

  An isolated operation detection device 10 that detects the isolated operation of the distributed power supply 5 is connected to the power system 3. For example, the isolated operation detection device 10 is connected to the power system 3 via the voltage detector 8. The voltage detector 8 measures a three-phase voltage (for example, line voltages Vab, Vbc, Vca of the system voltage) in the power system 3 at a predetermined sampling period, and the measured voltage Vt is measured as a single operation detection device 10. Output to. As the voltage detector 8, for example, a voltage transformer (VT) can be used.

  The isolated operation detection device 10 calculates the voltage value, phase, and frequency of the system voltage based on the measured voltage Vt measured by the voltage detector 8, and the distributed power source 5 determines whether the voltage value, phase, and frequency change. It detects whether or not it is in a single operation state. The isolated operation detection device 10 generates an isolated operation detection signal DS when the isolated operation state of the distributed power supply 5 is detected, and supplies the isolated operation detection signal DS to the circuit breaker 7 and the distributed power supply 5. By this isolated operation detection signal DS, the circuit breaker 7 is immediately opened, the distributed power supply 5 is disconnected from the power system 3, and the operation of the distributed power supply 5 is stopped.

  The isolated operation detection device 10 includes an auxiliary transformer 11, a low-pass filter (LPF) 12, a sample and hold circuit 13, an A / D conversion circuit 14, a frequency measurement circuit 15, a calculation processing unit (CPU) 16, A memory 17 and an input / output interface (input / output I / F) 18 are provided.

  The measurement voltage Vt is input to the auxiliary transformer (auxiliary PT) 11. The auxiliary transformer 11 converts the input measurement voltage Vt according to a predetermined PT ratio, and outputs the converted measurement voltage Vt to the LPF 12. The LPF 12 is a filter circuit that attenuates noise (here, a high frequency component) included in the measurement voltage Vt from the auxiliary transformer 11. The LPF 12 outputs the measurement voltage Vtf after the filter processing to the sample hold circuit 13 and the frequency measurement circuit 15.

  For example, the sample hold circuit 13 repeatedly samples and holds the measurement voltage Vtf at the cycle of the pulse based on the sample hold command pulse given from the arithmetic processing unit 16, and outputs the sample value every time. Is supplied to the A / D conversion circuit 14. For example, the sample hold command pulse is a pulse signal having a constant frequency. For this reason, the sample hold circuit 13 of this example samples and holds the measurement voltage Vtf by a fixed frequency sampling method.

  The A / D conversion circuit 14 A / D-converts the momentary hold output output from the sample hold circuit 13 based on the A / D conversion command pulse given from the arithmetic processing unit 16, and converts the converted digital The signal is output to the arithmetic processing unit 16 as a sampling voltage Vi. The A / D conversion circuit 14 converts the hold output (measurement voltage Vtf) from the sample hold circuit 13 into a digital sampling voltage Vi at intervals of, for example, an electrical angle of 30 degrees. That is, the A / D conversion circuit 14 generates the digital sampling voltage Vi from the hold output from the sample hold circuit 13 at a predetermined interval.

  The sampling voltage Vi is written into the RAM of the memory 17 through the arithmetic processing unit 16. The RAM 17 of the memory 17 holds the latest fixed amount, for example, the sampling voltage Vi for n cycles of the fundamental wave (system fundamental wave) of the power system 3. That is, the RAM of the memory 17 holds the sampling voltage Vi for n cycles from the latest sampling voltage Vi to the sampling voltage Vi n cycles before. Note that n can be set to a natural number of 3 or more, for example, and is set to n = 4 in this example.

  The frequency measurement circuit 15 receives the measurement voltage Vtf from the LPF 12. The frequency measurement circuit 15 measures the frequency (system fundamental frequency) f of the system voltage (for example, the line voltage Vab) from the measurement voltage Vtf. As the frequency measuring circuit 15, if it is a composite relay, it can be shared with a frequency relay (frequency relay). As the frequency relay, for example, an over-frequency relay (OFR) or an under-frequency relay (UFR) can be used. For example, the frequency measurement circuit 15 converts the measurement voltage Vtf (measurement voltage Vtf of the line voltage Vab) into a square wave, and counts how many clock pulses of the internal clock signal are included in the square wave. Then, the system fundamental frequency f is measured. Specifically, the frequency measurement circuit 15 starts a count operation at 90 ° intervals of the rated frequency (50 Hz or 60 Hz) of the system fundamental wave, and generates four count data during one cycle of the system fundamental wave. . Then, the frequency measurement circuit 15 calculates the system fundamental frequency f by calculating the average value of the four count data for each predetermined period. In addition, as a predetermined period, it can set to a period (for example, 10 ms) shorter than one period of the rated frequency of a system fundamental wave, for example. For example, the relay cycle of the frequency relay can be used as the predetermined cycle.

  The system fundamental frequency f measured by the frequency measurement circuit 15 is sequentially written into the RAM of the memory 17 through the arithmetic processing unit 16. The RAM of the memory 17 holds the latest predetermined amount, for example, m system fundamental frequency f. That is, the RAM of the memory 17 holds m system fundamental frequency f from the latest system fundamental frequency f to (m−1) previous system fundamental frequency f. The m can be set to a natural number of about 4 to 64, for example. The count data generated when calculating the system fundamental frequency f is supplied to the arithmetic processing unit 16.

  The arithmetic processing unit 16 executes various processing programs such as digital filter processing, voltage phase jump detection processing, voltage drop detection processing, and frequency sudden change detection processing held in the ROM of the memory 17. The arithmetic processing unit 16 generates an isolated operation detection signal DS when the isolated operation state of the distributed power supply 5 is detected by executing the processing program. Then, the arithmetic processing unit 16 supplies the generated isolated operation detection signal DS to the circuit breaker 7 and the distributed power supply 5 via the input / output I / F 18.

Next, various processes executed by the arithmetic processing unit 16 will be described.
In the digital filter processing, the arithmetic processing unit 16 is based on so-called discrete Fourier transform, for example, from the sampling voltage Vi to the system fundamental wave voltage components (here, three-phase line voltages Vab, Vbc, The extraction of the vector amount of Vca) is repeated. In the voltage phase jump detection process, the arithmetic processing unit 16 sets one cycle before the current cycle (latest cycle) of the system fundamental wave as n cycles (here, 4 cycles) as the reference cycle of the interconnection operation phase. The phase of the system fundamental voltage component in the current cycle (hereinafter also simply referred to as “voltage phase”) is compared with the voltage phase in the reference cycle. Then, based on the comparison result, the arithmetic processing unit 16 determines whether or not the voltage phase of the current cycle is shifted from the voltage phase of the reference cycle by a set value (set value) θ or more, that is, whether or not there is a jumping change in the voltage phase. The detection result is accumulated and held in the RAM of the memory 17. The set value θ can be set to about 2 to 20 ° (preferably 3 to 10 °), for example. In this example, the set value θ is set to 10 °.

Such digital filter processing and voltage phase jump detection processing are also described in, for example, Patent Document 1 described above. These processing will be briefly described below.
As shown in FIG. 2, first, when the cycle of interest in the system fundamental wave (measured voltage Vtf) is set to “0”, cycles preceding the cycle of interest are sequentially cycled “−1”, “−”. 2 ”,...,“ −6 ”, and cycles subsequent to the target cycle in the order of cycles“ +1 ”,“ +2 ”,. In the example of FIG. 2, the reference cycle is set to one cycle four cycles before the current cycle (n = 4). At this time, if a system stop occurs at time tx in the cycle “−1” and the voltage phase suddenly changes from the phase at the time of interconnection operation before time tx to the phase at the time of single operation, the current cycle and the reference cycle The voltage phase comparison results are as follows.

(A) When the current cycle is "-2" cycle or earlier When the current cycle is a cycle before "-2" cycle, the reference cycle is the cycle before "-6" cycle, and the current cycle and the reference cycle Both cycles are in the same phase of interconnected operation. For this reason, the comparison result of the voltage phase results in no phase jump change.

(B) When the current cycle is “−1” cycle When the current cycle is “−1” cycle and the reference cycle is “−5” cycle, the system stop occurs during the current cycle, and the voltage of the current cycle Since the phase includes a transient phenomenon, the voltage phase comparison result (the presence or absence of a phase jump change) is indeterminate.

(C) When the current cycle is “0” to “+2” cycle When the current cycle is “0”, “+1”, “+2” cycle, the reference cycle is “−4”, “−3”, “−2” cycle. In these cases, the current cycle is the single operation phase, while the reference cycle is the interconnection operation phase. Therefore, in these periods, the voltage phase between the current cycle and the reference cycle is shifted by a set value θ (for example, 10 °) or more. Therefore, the comparison result that there is a phase jump change occurs twice (two cycles) or more.

(D) When the current cycle is “+3” cycle When the current cycle is “+3” cycle and the reference cycle is “−1” cycle, system shutdown occurs during the reference cycle, and the voltage phase of the reference cycle is Since a transient phenomenon is included, the voltage phase comparison result is uncertain as in the case of (B).

(E) When the current cycle is after “+4” cycle When the current cycle is after “+4” cycle, the reference cycle is the cycle after “0” cycle, and both the current cycle and the reference cycle are It becomes the same phase of isolated operation. For this reason, the comparison result of the voltage phase results in no phase jump change.

  In this way, when a system stop occurs, a comparison between voltage phases of the current cycle and the reference cycle indicates that a plurality of cycles (here, “0” to “0”) immediately after the “−1” cycle at time tx when the system stop occurred. +2 "cycles), two or more cycles that are detected as having a phase jump change occur. In this example, the cycle difference n between the current cycle and the reference cycle is set to “4”, but by increasing this value, the number of detection cycles with a phase jump change can be increased to 3 or more.

Next, a voltage phase comparison method in each cycle will be described.
As shown in FIG. 3, in the current cycle, the measurement voltage Vtf (for example, the line voltage Vab of the system voltage) is sampled at a sampling point (see the mark ● in the figure) at a fixed interval by a fixed frequency sampling method. The sampling voltage Vi converted into is sequentially stored in the memory 17. When the number of samplings in one cycle of the fundamental system wave is 2k, if 2k sampling voltages Vi in the current cycle are stored in the memory 17, 2k sampling voltages Vi in the current cycle and the reference cycle are processed. Read by the unit 16. That is, in the example of FIG. 3, when the last sampling voltage Vi in the current cycle, that is, the latest sampling voltage Vi at time t0 is “V0”, 2k sampling voltages V0 to V2k−1 in the current cycle are stored in the memory. 17 is read out. In addition, when the last sampling voltage Vi of the reference cycle, that is, the sampling voltage Vi at time tn is “V2kn”, 2k sampling voltages V2kn to V2k (n + 1) −1 in the reference cycle are read from the memory 17.

  Based on the sampling voltage Vi of the current cycle and the reference cycle read out by the digital filter processing, the arithmetic processing unit 16 performs a system fundamental wave voltage component (here, the line voltage Vab of the line voltage Vab) for each of the current cycle and the reference cycle. The cosine component (cos component) Vc and the sine component (sin component) Vs of the vector amount are calculated. The cos component Vc and the sin component Vs can be obtained by the following equations 1 and 2 when the rated frequency of the system fundamental wave is fo and the sampling frequency is 2 k · fo.

Here, if the cos component Vc of the current cycle is Vc0 and the sin component Vs of the current cycle is Vs0, the cos component Vc0 and the sin component Vs0 are obtained from 2k sampling voltages V0 to V2k-1 in the current cycle. That is, the cos component Vc and the sin component Vs obtained by using the sampling voltage Vi in the above equations 1 and 2 as the sampling voltages V0 to V2k-1 become the cos component Vc0 and the sin component Vs0 of the current cycle, respectively. Similarly, when the cos component Vc of the reference cycle is Vcn and the sin component Vs of the reference cycle is Vsn, the cos component Vcn and the sin component Vsn of the reference cycle are 2k sampling voltages V2kn to V2k (n + 1) in the reference cycle. −1.

  However, the cos components Vc0 and Vcn and the sin components Vs0 and Vsn calculated by Equations 1 and 2 include gain variation and phase variation based on the variation when the system frequency of the power system 3 varies. For this reason, when the voltage phase is compared based on the cos components Vc0 and Vcn and the sin components Vs0 and Vsn, the comparison result includes the influence of the fluctuation of the system frequency. Therefore, the arithmetic processing unit 16 corrects the phase shift in the cos components Vc0 and Vcn and the sin components Vs0 and Vsn based on the variation of the system frequency by the following equations 3 to 6.

Δ in the above formulas 3 and 5 is a frequency fluctuation difference and can be obtained by the following formula.

“Fa” in Equation 7 is an average frequency indicating the current frequency, and can be obtained based on the frequency f measured by the frequency measurement circuit 15, for example. For example, the arithmetic processing unit 16 can calculate the average frequency fa from which a sudden change in frequency is removed by averaging the latest predetermined number of frequencies f held in the memory 17. As described above, the frequency fluctuation difference Δ indicates the fluctuation ratio of the average frequency fa (current frequency) with respect to the rated frequency fo.

  Subsequently, as illustrated in FIG. 4, the arithmetic processing unit 16 uses, as a reference, the cos component Vcn ′ and the sin component Vsn ′ of the corrected reference cycle, and the corrected cosine component Vc0 ′ of the current cycle. It is detected whether or not the phase of the vector β of the sin component Vs0 ′ is shifted by a set value θ or more in the advance direction or the delay direction. Whether the phase of the vector β of the line voltage Vab in the current cycle after the correction is shifted by a set value θ or more is determined based on the vector α of the line voltage Vab in the reference cycle after correction. Detect whether or not. That is, the arithmetic processing unit 16 detects whether or not the vector β is a vector included in the shaded area in FIG. Specifically, the arithmetic processing unit 16 determines whether or not the following Expression 8 or Expression 9 is satisfied, thereby determining whether or not the phase difference between the vector β and the vector α is greater than or equal to the set value θ, that is, It is determined whether there is a jumping change in the voltage phase.

When either one of these equations 8 and 9 is established, the phase of the vector β in the current cycle is shifted by a set value θ or more with respect to the phase of the vector α in the reference cycle, and the vector β is hatched in FIG. Located in the area of the section. For this reason, when either one of Expression 8 and Expression 9 is established, it can be determined that a phase jump greater than the settling value θ has occurred.

  As described above, in the voltage phase jump detection process, the phase shift of the system voltage due to the fluctuation of the system frequency of the power system 3 is corrected, and the voltage phase of the current cycle is compared with the voltage phase of the reference cycle. However, this voltage phase jump detection process alone cannot satisfy the FRT requirement. That is, with only the voltage phase jump detection processing, even if the disturbance of the power system 3 is within the FRT requirements, if the phase change greater than the set value θ is detected, the distributed power source 5 is unnecessarily disconnected from the power system 3. Will be. When the distributed power supply 5 is unnecessarily disconnected in this way, particularly when many distributed power supplies 5 are unnecessarily disconnected all at once, the voltage and frequency of the entire system may be affected and the stability of the system may be impaired. is there. Therefore, in the arithmetic processing unit 16 of the present embodiment, in order to prevent the distributed power source 5 from being unnecessarily disconnected due to the voltage drop and frequency fluctuation defined in the FRT requirement, in addition to the voltage phase jump detection process, the voltage drop The detection process and the sudden frequency change detection process are executed. These points will be described in detail below.

  Here, the FRT requirements are the conditions (that is, the voltage drop tolerance and the frequency fluctuation tolerance) that the power generation equipment (distributed power supply) continues to operate when a voltage drop and frequency fluctuation of the system voltage due to the grid transmission line accident occur. Default.

  First, the voltage drop tolerance in the FRT requirement will be described. For example, in the FRT requirements for photovoltaic power generation facilities, in the case of a three-phase short circuit accident in the system, the operation of the distributed power supply is continued for a voltage drop that causes the remaining voltage of the system voltage to be 20% or more, and is not disconnected The voltage drop tolerance is required. Further, in the FRT requirement of the photovoltaic power generation facility, in the case of a two-phase short circuit accident of the system, the remaining voltage of the system voltage is rated to be 52% or more and the phase change is 41 ° or less. The voltage drop tolerance is required to keep the power supply running and not to disconnect.

  FIG. 5A shows vectors of three-phase line voltages Vab, Vbc, Vca of the system voltage when the system is healthy. FIG. 5B shows vectors of three-phase line voltages Vab, Vbc, Vca at the time of a three-phase short circuit accident. FIG. 5C shows vectors of three-phase line voltages Vab, Vbc, Vca when a two-phase short circuit accident occurs, specifically, when a two-phase short circuit accident occurs between the b phase and the c phase in the Y-connection system. Is shown.

  As shown in FIG. 5 (a) and FIG. 5 (b), in the case of a three-phase short circuit accident, each line voltage Vab, Vbc, Vca is lower than the rated voltage (for example, 20% of the rated voltage), There is no phase change in the voltages Vab, Vbc, Vca. In this case, since the voltage phase jump change is not detected in the voltage phase jump detection process described above, the distributed power source 5 is not unnecessarily disconnected due to the three-phase short circuit accident.

  On the other hand, as shown in FIGS. 5 (a) and 5 (c), at the time of a two-phase short circuit accident, the line voltage Vbc is greatly reduced compared to the line voltages Vab, Vca, and the phase of the line voltages Vab, Vca is reduced. Changes. In the example of FIG. 5C, the line voltage Vbc decreases to 30% of the rated voltage, the line voltages Vab and Vca decrease to 87% of the rated voltage, and the system is healthy (see FIG. 5A). The phase change of the line voltages Vab and Vca with respect to is 21 °. In this case, since the phase change of the line voltages Vab and Vca is equal to or more than the set value θ, it is determined that there is a phase jump in the voltage phase jump detection process. For this reason, with only the voltage phase jump detection process, the distributed power supply 5 may be unnecessarily disconnected at the time of a two-phase short circuit accident defined in the FRT requirement.

  Therefore, in the arithmetic processing unit 16 of this embodiment, in addition to the voltage phase jump detection process, the voltage drop detection process is executed. In this voltage drop detection process, whether or not the voltage values of the line voltages Vab, Vbc, Vca are within a predetermined range based on the vector amounts of the line voltages Vab, Vbc, Vca extracted by the digital filter process. Determine whether. For example, when a two-phase short-circuit accident occurs, the voltage value of the line voltage that is the short-circuit portion decreases to a voltage value that is less than 80% of the rated voltage. Therefore, it is determined whether or not a two-phase short-circuit accident has occurred by determining whether or not the voltage values of the line voltages Vab, Vbc, and Vca have decreased to a voltage value that is less than 80% of the rated voltage. can do. Therefore, in the voltage drop detection process, it is determined whether all of the following formulas 10 to 12 are satisfied when the voltage value of the rated voltage is Vr.

If any one of Equations 10 to 12 is not satisfied, it can be determined that a two-phase short circuit accident has occurred in the current cycle.

  Further, in the voltage drop detection process, whether or not all of the following Expressions 13 to 15 are satisfied in order to determine whether or not a two-phase short circuit accident has occurred in the reference cycle in the voltage phase jump detection process. Is judged. In the following formulas 13 to 15, the voltage values of the line voltages Vab, Vbc, Vca in the reference cycle n cycles before the current cycle (4 cycles before in this example) are Vabn, Vbcn, Vcan, respectively.

That is, as shown in FIG. 6, in the voltage drop detection process, all vectors of the vectors of the line voltages Vab, Vbc, Vca in the current cycle and the vectors of the line voltages Vabn, Vbcn, Vcan in the reference cycle are shown. It is determined whether or not it is located within the region of the satin pattern inside. At this time, if any one of Expressions 10 to 15 is not satisfied (even if one of the six vectors shown in FIG. 6 is out of the textured area), in the current cycle or the reference cycle It can be determined that a two-phase short circuit accident has occurred. When a two-phase short-circuit accident occurs in this way, as described above, it may be detected that there is a phase jump in the voltage phase jump detection process. Therefore, the arithmetic processing unit 16 of the present example does not generate the isolated operation detection signal DS even when it is detected that there is a phase jump if any one of Expressions 10 to 15 is not satisfied. I did it. As a result, even if a two-phase short-circuit accident defined in the FRT requirement occurs in the current cycle or the reference cycle and a change in voltage phase exceeding the set value θ is detected, the distributed power source 5 is not required to be disconnected. It can suppress suitably.

  Next, frequency fluctuation tolerance in the FRT requirement will be described. For example, in the FRT requirement of photovoltaic power generation equipment, the system frequency changes in steps of +0.8 Hz (when connected to a 50 Hz system) or +1.0 Hz (when connected to a 60 Hz system) and continues for 3 cycles. For the frequency fluctuation (step increase) to be performed, the frequency fluctuation tolerance is required to continue the operation of the distributed power source so as not to be disconnected.

  That is, as shown in FIG. 7, when the rated frequency fo is 50 Hz, the system frequency changes from 50 Hz to 50.8 Hz and continues for 3 cycles (0.06 s) (see satin pattern in the figure). Therefore, it is necessary to continue the operation of the distributed power source 5. However, when the system frequency is stepped up, it appears that the voltage phase has changed before and after the step rise. In this case, since the change in the voltage phase before and after the step increase may become a set value θ (for example, 10 °) or more, it may be determined that there is a phase jump in the voltage phase jump detection process. For this reason, with only the voltage phase jump detection process, the distributed power supply 5 may be unnecessarily disconnected at the time of frequency fluctuation (step increase) defined in the FRT requirement.

  In addition, the FRT requirement of the photovoltaic power generation equipment requires a frequency fluctuation tolerance that keeps the operation against frequency fluctuations of the lamp-shaped system frequency of ± 2 Hz / s so as not to be disconnected. In this FRT requirement, when the rated frequency is 50 Hz, the upper limit of the system frequency is limited to 51.5 Hz and the lower limit is 47.5 Hz. When the rated frequency is 60 Hz, the upper limit of the system frequency is 61.8 Hz. The lower limit is limited to 57.0 Hz.

  That is, as shown in FIG. 8, when the rated frequency fo is 50 Hz, the system frequency increases to 51.5 Hz with a change rate of +2 Hz / s, and the system frequency has a change rate of −2 Hz / s. It is necessary to continue the operation of the distributed power supply 5 with respect to the frequency fluctuation (refer to the satin pattern area in the figure) that decreases to 47.5 Hz. However, when the system frequency fluctuates at a change rate of −2 Hz / s, it appears that the voltage phase has changed due to the frequency fluctuation (ramp fluctuation). In this case, since the change of the voltage phase at the time of ramp fluctuation may be equal to or larger than the set value θ, there is a possibility that it is determined that there is a phase jump in the voltage phase jump detection process. For this reason, with only the voltage phase jump detection process, the distributed power supply 5 may be unnecessarily disconnected at the time of frequency fluctuation (ramp fluctuation) defined in the FRT requirement.

  When frequency fluctuations occur in the system frequency in this way, it appears that the voltage phase of the system has changed. On the other hand, when a change occurs in the voltage phase of the system, it appears that frequency fluctuation has occurred in the system frequency.

  FIG. 9 shows how the frequency fluctuations of the system frequency appear when the step rise is +0.8 Hz and the phase jump is 3 °. As shown in FIG. 9, when the phase jump is 3 °, a frequency fluctuation of about −0.4 Hz is observed. The frequency fluctuation resulting from the 3 ° phase jump occurs instantaneously as in the step increase. That is, the system frequency changes suddenly with the occurrence of a phase jump of 3 °. The system frequency fc when suddenly changing with the phase jump can be obtained by the following equation, where θc is the changed phase.

From the above equation 16, it can be seen that a step increase of +0.8 Hz corresponds to a frequency fluctuation accompanying a phase jump of about 5.8 °. When the set value θ is set to 10 ° and the phase jump of the set value θ occurs, the system frequency suddenly changes from 50 Hz to 48.6 Hz or 51.4 Hz according to the above equation 16. I understand that. Thus, the frequency fluctuation amount (= 0.8 Hz) due to the step increase of +0.8 Hz is smaller than the frequency fluctuation amount (= 1.4 Hz) associated with the phase jump of the set value θ (= 10 °).

  On the other hand, since the frequency fluctuation amount due to the lamp fluctuation is 2.5 Hz at the maximum, it becomes larger than the frequency fluctuation quantity (= 1.4 Hz) due to the phase jump of the set value θ (= 10 °). However, the ramp fluctuation has a smaller frequency fluctuation amount per unit time than the frequency fluctuation accompanying the step increase or phase jump. For example, in the ramp fluctuation, 0.7 s (system) is varied by 1.4 Hz which is the frequency fluctuation amount associated with the phase jump of the set value θ (= 10 °) (that is, fluctuation from 50 Hz to 48.6 Hz). It takes 35 cycles of the fundamental wave). On the other hand, the frequency fluctuation due to the phase jump fluctuates (rapidly changes) from 50 Hz to 48.6 Hz in a short time of about 0.04 s (about two cycles of the system fundamental wave).

  From the above, by detecting whether or not a frequency fluctuation larger than the frequency fluctuation amount due to the step rise has occurred within a period shorter than the fluctuation time due to the lamp fluctuation, the frequency fluctuation (step) defined in the FRT requirement is detected. It can be determined whether or not a rise or ramp fluctuation has occurred. Therefore, in addition to the voltage phase jump detection process, the arithmetic processing unit 16 executes a frequency sudden change detection process for detecting whether or not a frequency sudden change corresponding to the set value θ occurs.

  As shown in FIG. 10, in the frequency sudden change detection process of this example, a frequency fluctuation equal to or greater than the frequency fluctuation amount ΔF when a phase jump of about the set value θ occurs in a predetermined minute period (first period) T1. It is determined whether or not.

  Here, the minute period T1 can be set to, for example, a time corresponding to the cycle difference n between the current cycle and the reference cycle, that is, a time shorter than the time corresponding to n cycles. For example, the minute period T1 can be set to a time of 2 to 3 cycles (40 to 60 ms) of the system fundamental wave. The frequency fluctuation amount ΔF is set to a fluctuation amount larger than the frequency fluctuation amount (= 0.8 Hz) due to the step increase defined in the FRT requirement. Further, the frequency fluctuation amount ΔF is obtained when the phase jump of the set value θ occurs so that the isolated operation state can be reliably detected when the phase jump greater than the set value θ (that is, the phase jump due to the system stop) occurs. It is preferable to set the fluctuation amount smaller than the frequency fluctuation amount. The frequency fluctuation amount ΔF in this example is set to the frequency fluctuation amount when a phase jump corresponding to the phase θb smaller than the set value θ occurs. In this case, the frequency fluctuation amount ΔF can be obtained by the following equation.

For example, when the set value θ is 10 °, the phase θb can be set to a phase of about 66% to 80% of the set value θ (that is, 6.6 ° to 8 °).

Next, an example of specific processing in the sudden frequency change detection processing will be described.
The frequency measurement circuit 15 generates count data generated when the system fundamental wave frequency f is calculated from the measurement voltage Vt, that is, count data generated at predetermined phase (90 ° in this case) intervals of the system fundamental wave. To supply sequentially. For example, the arithmetic processing unit 16 detects the occurrence of a sudden change in the system fundamental wave frequency f based on a plurality (four in this case) of count data obtained during one system fundamental wave cycle. For example, when the count difference between the minimum count value and the maximum count value in the four count data becomes equal to or greater than a predetermined value (for example, 4 to 8 counts), the arithmetic processing unit 16 performs the system fundamental frequency f. Detect sudden changes in That is, when it is detected that a large frequency fluctuation that cannot be caused by a ramp fluctuation has occurred during a period of generating four count data (here, during one cycle), an abrupt change in the system fundamental frequency f occurs. Can be detected. Here, the predetermined value is set to a count difference caused by a frequency change with a change rate larger than ± 2 Hz / s, which is the maximum change rate in the lamp change defined in the FRT requirement. Therefore, in the ramp fluctuation, since the count difference between the minimum count value and the maximum count value does not exceed the predetermined value, the occurrence of a sudden change in the system fundamental frequency f is not detected. Note that the period (second period) in which the occurrence of a sudden change in the system fundamental wave frequency f is detected is a period shorter than the minute period T1, and is set to a time corresponding to one cycle of the system fundamental wave in this example.

  In the example of step increase and phase jump shown in FIG. 10, at time t2, the difference between the minimum count value and the maximum count value becomes equal to or greater than a predetermined value, and the system fundamental frequency f suddenly changes (here, rapidly increases). Suppose that it was detected. When the sudden change in the system fundamental frequency f is detected in this way, the arithmetic processing unit 16, for example, the frequency fluctuation amount ΔF in a minute period (third period) T2 from time t2 to time t3 when the sudden change is detected. It is detected whether or not the above frequency fluctuation occurs. Here, the minute period T2 is a period shorter than the minute period T1, and can be set to a time of about 20 to 40 ms (in this example, 40 ms), for example.

  For example, in the minute period T2, the arithmetic processing unit 16 determines the system fundamental wave frequency f (see each plot point in the figure) measured by the frequency measurement circuit 15 every predetermined period (for example, 10 ms), and immediately before time t2. It is determined whether or not the difference Δf with respect to the average frequency fa calculated at (for example, the average frequency fa calculated at time t1) is equal to or greater than the frequency fluctuation amount ΔF. For this reason, in the minute period T2, the comparison between the latest system fundamental wave frequency f and the average frequency fa calculated immediately before time t2 is executed a plurality of times (here, four times). At this time, as shown in FIG. 10, the difference Δf becomes larger than the frequency fluctuation amount ΔF in the phase jump of the set value θ or more, while the difference Δf becomes larger than the frequency fluctuation amount ΔF in the step increase. Absent. For this reason, by detecting whether or not the difference Δf is equal to or greater than the frequency fluctuation amount ΔF within the minute period T2, the sudden frequency change is caused by either the phase jump or the step increase defined in the FRT requirement. It can be determined whether there is. That is, when the difference Δf that is equal to or greater than the frequency fluctuation amount ΔF cannot be detected within the minute period T2, it can be determined that a phase jump greater than the set value θ (that is, a phase jump due to a system stop) has not occurred. .

  Therefore, the arithmetic processing unit 16 of this example does not detect an isolated operation detection signal unless a frequency fluctuation equal to or greater than the frequency fluctuation amount ΔF is detected within the minute period T1 (that is, if a frequency sudden change corresponding to the settling value θ is not detected). DS is not generated. As a result, the distributed power source 5 is unnecessarily disconnected even when a frequency variation (step increase or ramp variation) defined in the FRT requirement occurs and a change in voltage phase greater than the set value θ is detected. It can suppress suitably.

  The arithmetic processing unit 16 functions as an extraction unit that extracts a system fundamental wave voltage component from the sampling voltage Vi, a voltage phase jump detection unit, a voltage drop detection unit, a frequency sudden change detection unit, and an isolated operation detection unit. .

Next, the operation of the isolated operation detection device 10 (mainly the arithmetic processing unit 16) will be described.
In step S1 shown in FIG. 11, the measurement voltage Vtf is sampled and held by the fixed frequency sampling method, the hold output of the latest sampling value is converted into the digital sampling voltage Vi, and the sampling voltage Vi is input to the arithmetic processing unit 16. Is done. Then, the arithmetic processing unit 16 writes the latest sampling voltage Vi into the RAM of the memory 17.

  Next, in step S2, the latest system fundamental frequency f is measured from the measured voltage Vtf (for example, the line voltage Vab) at predetermined intervals, and the latest system fundamental frequency f is sent to the arithmetic processing unit 16. Entered. Then, the arithmetic processing unit 16 writes the latest system fundamental wave frequency f in the RAM of the memory 17. At this time, count data generated when calculating the system fundamental frequency f is also input to the arithmetic processing unit 16.

  Subsequently, the arithmetic processing unit 16 reads the latest predetermined number of system fundamental wave frequencies f stored in the memory 17 and averages the predetermined number of system fundamental wave frequencies f to calculate the average frequency fa (step). S3).

  Next, in step S4, the arithmetic processing unit 16 reads 2k sampling voltages Vi in the current cycle from the memory 17, and from the above formulas 1 and 2, the system fundamental wave voltage component of the current cycle (here, the line voltage) The cos component Vc0 and the sin component Vs0 of Vab, Vbc, Vca) are calculated. In addition, the arithmetic processing unit 16 reads 2k sampling voltages Vi in the reference cycle from the memory 17, and derives the system fundamental wave voltage components (in this case, the line voltages Vabn, Vbcn, Cos component Vcn and sin component Vsn of Vcan) are calculated.

  Next, the arithmetic processing unit 16 calculates the frequency variation difference Δ (= (fa−fo) / fo) from the above equation 7 based on the average frequency fa calculated in the previous step S3 (step S5). Subsequently, the arithmetic processing unit 16 corrects, for example, the components Vc0 and Vs0 of the line voltage Vab to the components Vc0 ′ and Vs0 ′ based on the above formulas 3 to 6, respectively, for example, the components Vcn and Vcn of the line voltage Vabn, Vsn is corrected to components Vcn ′ and Vsn ′, respectively (step S6).

Next, the arithmetic processing unit 16 detects whether or not the distributed power source 5 is in the single operation state based on the numerical values input and calculated in the previous steps S1 to S6 (step S7).
FIG. 12 shows an operation sequence of the isolated operation detection process in step S7. As shown in FIG. 12, in the isolated operation detection process of this example, when all the conditions C1 to C6 are satisfied, one of the conditions C7 and C8 is satisfied, and the condition C9 is satisfied, It is detected that the distributed power supply 5 is in a single operation state. This isolated operation detection process will be described in detail below.

  Conditions C1 to C6 correspond to the above expressions 10 to 15, respectively, and whether the line voltages Vab, Vbc, Vca in the current cycle and the line voltages Vabn, Vbcn, Vcan in the reference cycle are within a predetermined range. This is a condition for determining whether or not. In other words, the conditions C1 to C6 are conditions for determining whether or not a two-phase short circuit accident has occurred in the system.

  In the determination processes 21 to 26, it is determined whether or not each of the conditions C1 to C6 is satisfied. For example, in the determination process 21, when the condition C1 (Equation 10) is satisfied for a predetermined number of times, it is determined that the condition C1 is satisfied. Similarly, in the determination processes 22 to 26, when the conditions C2 to C6 are satisfied for a predetermined number of times, it is determined that the conditions C2 to C6 are satisfied. In the determination process 27, when it is determined in the determination processes 21 to 26 that all the conditions C1 to C6 are satisfied, a condition C10 in which all the conditions C1 to C6 are superimposed is generated. In this case, each line voltage Vab, Vbc, Vca, Vabn, Vbcn, Vcan is within a predetermined range (0.8 Vr to 1.2 Vr), and it can be determined that a two-phase short circuit accident has not occurred. it can. On the other hand, in the determination processes 21 to 26, if it is determined that any one of the conditions C1 to C6 is not satisfied, the determination process 27 does not generate the condition C10. In this case, it can be determined that a two-phase short circuit accident has occurred.

  Conditions C7 and C8 correspond to the above equations 8 and 9, respectively, and whether or not the voltage phase of the current cycle has changed by more than a set value θ relative to the voltage phase of the reference cycle, that is, the jumping change of the voltage phase This is a condition for determining whether or not there is. In the determination process 28, when any one of the conditions C7 and C8 (Expression 8 and Expression 9) is continuously established a predetermined number of times, it is determined that any one of the conditions is satisfied. That is, as described with reference to FIG. 2, when the comparison result with the phase jump change is continuously generated twice or more, it is determined that there is a phase jump change greater than the set value θ.

  In the determination process 29, when the condition C10 is generated in the determination process 27 and it is determined in the determination process 28 that one of the conditions C7 and C8 is satisfied, the conditions C7 and C8 and the condition C10 are superimposed. Condition C11 is generated. In this case, since it is determined that the two-phase short-circuit accident has not occurred in the determination process 27 and it is determined that there is a phase jump change in the determination process 28, the phase jump not caused by the two-phase short-circuit accident It can be determined that a change has occurred. On the other hand, in the determination process 29, if the condition C10 is not generated in the determination process 27 (that is, if it is determined that a two-phase short circuit accident has occurred), it is determined in the determination process 28 that there is a phase jump change. Even in such a case, it operates so as not to generate the isolated operation detection signal DS. This is because it can be determined that the phase jump change in this case is caused by a two-phase short circuit accident. Such an operation suppresses the unnecessary disconnection of the distributed power source 5 when a voltage phase change exceeding the set value θ occurs due to a voltage drop (two-phase short circuit accident) specified in the FRT requirement. it can.

In the determination process 30, when the condition C11 is satisfied for a predetermined number of times, it is determined that the condition C11 is satisfied.
On the other hand, the condition C9 is a condition for determining whether or not a sudden frequency change corresponding to the set value θ has occurred. That is, the condition C9 is a condition that is satisfied when a frequency fluctuation equal to or greater than the frequency fluctuation amount ΔF is detected in the minute periods T1 and T2. In the determination process 31, for example, if a frequency fluctuation equal to or greater than the frequency fluctuation amount ΔF is detected even once in the micro periods T1 and T2, it is determined that the condition C9 is satisfied. In this case, since there is a frequency sudden change that cannot occur due to the step increase or the ramp variation defined in the FRT requirement, it can be determined that the step increase and the ramp variation have not occurred.

  In the determination process 32, when it is determined in the determination process 30 that the condition C11 is satisfied, and in the determination process 31, it is determined that the condition C9 is satisfied, it is determined that the distributed power source 5 is in the single operation state. To do. In this case, all of the conditions C1 to C6 are satisfied, one of the conditions C7 and C8 is satisfied, and the condition C9 is satisfied. Then, it is determined in the determination process 30 that there is a phase jump change that does not result from the two-phase short circuit accident, and it is determined in the determination process 31 that no step increase and ramp fluctuation have occurred. Therefore, in this case, it is determined that a phase jump change that is not caused by the voltage drop and frequency fluctuation (step rise and ramp fluctuation) specified in the FRT requirement, that is, the phase jump change due to the system stop has occurred. The isolated operation state of the distributed power source 5 can be detected quickly. When the isolated operation state of the distributed power supply 5 is detected (YES in step S7 in FIG. 11), an isolated operation detection signal DS is generated (step S8). Thereby, when a phase jump change occurs due to the system stop, that is, when the distributed power supply 5 is operated alone, the distributed power supply 5 can be reliably disconnected from the power system 3.

  On the other hand, in the determination process 32, when it is determined that the condition C9 is not satisfied, the single operation is performed even if it is determined in the determination processes 28 to 30 that there is a phase jump change that is not caused by the two-phase short circuit accident. It operates so as not to generate the detection signal DS (NO in step S7 in FIG. 11). This is because it can be determined that the phase jump change in this case is caused by the step increase or the ramp fluctuation defined in the FRT requirement. In such a case, when a voltage phase change greater than the set value θ occurs due to a voltage drop (two-phase short circuit accident) or frequency fluctuation (lamp rise or lamp fluctuation) specified in the FRT requirements, 5 can be prevented from being unnecessarily disconnected.

Next, characteristic effects of the present embodiment will be described.
(1) In addition to the condition for detecting the jumping change of the voltage phase, the condition for detecting the sudden frequency change corresponding to the set value θ is added to the condition for detecting the single operation state of the distributed power source 5. That is, when it is detected that there is a voltage phase change equal to or greater than the set value θ and a sudden frequency change greater than the sudden frequency change due to the step increase defined in the FRT requirements is detected, the distributed power source 5 alone The driving state was detected. In other words, when there is no large frequency sudden change, that is, when there is no frequency sudden change greater than the frequency fluctuation amount ΔF, for example, when there is a step increase or ramp fluctuation defined in the FRT requirement, a voltage greater than the set value θ. The single operation state of the distributed power source 5 is not detected even when there is a phase change. Thereby, when the voltage phase change more than the setting value (theta) resulting from the frequency fluctuation (ramp rise or ramp fluctuation) prescribed | regulated to FRT requirements, it can suppress that the distributed power supply 5 is unnecessarily disconnected. On the other hand, when a sudden frequency change greater than the frequency variation ΔF occurs, that is, when a voltage phase change greater than the set value θ occurs due to a system stop or the like, the distributed power source 5 is reliably disconnected from the power system 3. be able to.

  As described above, according to the isolated operation detection device 10, when the disturbance of the power system satisfies the FRT requirement, the operation can be continued without unnecessarily disconnecting the distributed power source 5, and the isolated operation of the distributed power source 5 can be performed. Sometimes the distributed power supply 5 can be reliably disconnected from the power system 3.

  (2) Furthermore, by adding the condition of detecting a sudden frequency change greater than or equal to the frequency fluctuation amount ΔF to the detection condition of the single operation state, the step increase is longer than the period (three cycles) defined by the FRT requirement ( (For example, 4 cycles or more) Even when the operation continues, it is possible to prevent the distributed power source 5 from being unnecessarily disconnected along with the step increase. That is, even if the step increase continues for 4 cycles or more, since the frequency sudden change more than the frequency fluctuation amount ΔF does not occur, it is possible to suppress the unnecessary disconnection of the distributed power supply 5 due to the step increase.

  (3) Further, the condition that all of the three-phase line voltages Vab, Vbc, Vca are 80% or more of the rated voltage Vr is added to the detection condition of the single operation state of the distributed power source 5. That is, it is detected that all of the three-phase line voltages Vab, Vbc, Vca are 80% or more of the rated voltage Vr, that there is a voltage phase change greater than the set value θ, and the frequency fluctuation amount When it is detected that a sudden frequency change of ΔF or more has occurred, the single operation state of the distributed power source 5 is detected. In other words, if any one of the line voltages Vab, Vbc, Vca has decreased to less than 80% of the rated voltage Vr, that is, if a two-phase short-circuit accident has occurred in the system, the set value is greater than θ. The isolated operation state of the distributed power source 5 is not detected even when there is a voltage phase change of. Thereby, when the voltage phase change more than the set value (theta) arises due to the voltage drop (two-phase short circuit accident) prescribed | regulated to FRT requirements, it can suppress that the distributed power supply 5 is unnecessary disconnection.

  (4) In the voltage drop detection process, it is detected whether or not all of the three-phase line voltages Vab, Vbc, Vca are 80% or more of the rated voltage Vr. Thereby, even if a two-phase short-circuit accident occurs in any of the a-phase, b-phase, and c-phase, the two-phase short-circuit accident can be detected. For this reason, even if a two-phase short circuit accident occurs at any location, it is possible to suppress the unnecessary disconnection of the distributed power supply 5 due to the two-phase short circuit accident.

  (5) In the frequency sudden change detection processing, the average frequency fa calculated immediately before the occurrence detection and the latest system fundamental frequency f are between the occurrence detection of the sudden change in the system fundamental frequency f and the minute period T2. Whether or not the difference Δf is equal to or greater than the frequency fluctuation amount ΔF is detected. As described above, since the difference Δf is not the amount of fluctuation from the rated frequency fo but the amount of fluctuation from the average frequency fa immediately before the occurrence detection, the system fundamental frequency f before the sudden frequency change fluctuates from the rated frequency fo. Even if it is, it is possible to accurately detect whether or not a frequency fluctuation greater than the frequency fluctuation amount ΔF has occurred.

In addition, you may change the said embodiment as follows.
The frequency sudden change detection processing in the above embodiment is not particularly limited as long as it is a method capable of detecting a sudden frequency change corresponding to the set value θ. That is, in the sudden frequency change detection process, it is only necessary to detect a sudden frequency change that cannot be caused by the step-up and ramp fluctuations defined in the FRT requirements.

  For example, in the frequency sudden change detection process of the above embodiment, it is determined whether or not the difference Δf between the system fundamental wave frequency f and the average frequency fa is equal to or greater than the frequency fluctuation amount ΔF in the minute period T2. For example, it may be determined whether or not the difference between the system fundamental frequency f and the rated frequency fo is greater than or equal to the frequency variation ΔF in the minute period T2. In this case, it is preferable to set the frequency fluctuation amount ΔF in consideration of the fluctuation of the system fundamental frequency f that may occur immediately before the occurrence of the sudden frequency change.

  In the frequency sudden change detection process of the above embodiment, whether or not a frequency fluctuation greater than or equal to the frequency fluctuation amount ΔF occurs in a predetermined minute period T2 after the occurrence of a sudden frequency change is detected based on the count data from the frequency measurement circuit 15. To detect. However, the present invention is not limited to this. For example, it is detected whether or not the difference between the minimum value and the maximum value of the plurality of system fundamental wave frequencies f generated within a predetermined minute period T1 is equal to or greater than the frequency fluctuation amount ΔF. May be. In this case, every time the latest system fundamental wave frequency f is generated, the difference between the minimum value and the maximum value is calculated and the difference is compared with the frequency fluctuation amount ΔF.

  In the voltage drop detection processing of the above embodiment, whether or not the voltage values of the line voltages Vab, Vbc, Vca, Vabn, Vbcn, Vcan are within a voltage range of 80% to 120% of the rated voltage Vr. Judgment was made. However, the voltage range is not limited to the voltage range of 80% to 120% of the rated voltage Vr. For example, the line voltages Vab, Vbc, Vca, Vabn, Vbcn, Vcan at the time of a two-phase short circuit accident or the like. If it is a voltage range which can detect the voltage drop of this, it will not specifically limit. For example, you may make it determine only whether the voltage value of each line voltage Vab, Vbc, Vca, Vabn, Vbcn, Vcan is a voltage value 80% or more of the rated voltage Vr. Further, it may be determined whether or not the voltage values of the line voltages Vab, Vbc, Vca, Vabn, Vbcn, Vcan are 75% or more of the rated voltage Vr. Even in these cases, it is possible to determine whether or not a two-phase short circuit accident has occurred in the system.

  In the above embodiment, the sampling voltage Vi is generated from the measurement voltage Vtf by the fixed frequency sampling method. For example, a so-called synchronous sampling method may be adopted instead of the fixed frequency sampling method. In this case, for example, based on the system fundamental frequency f measured by the frequency measurement circuit 15, a PLL synchronization circuit that operates in synchronization with the system fundamental frequency f is provided in the isolated operation detection device 10. Then, based on the clock pulse generated by the PLL synchronization circuit (that is, the clock pulse synchronized with the system fundamental frequency f), the sampling voltage Vi is generated at the sampling frequency synchronized with the system fundamental frequency f. Also good. In the case of this synchronous sampling method, the correction of the voltage phase accompanying the fluctuation of the system frequency can be omitted, so that the calculation load on the calculation processing unit 16 can be reduced.

  In FIG. 1, only one distributed power source 5 connected to the power system 3 is illustrated, but a plurality of distributed power sources 5 may be connected to the power system 3. In this case, different types of distributed power supplies 5 may be connected to the power system 3. Furthermore, the isolated operation detection device 10 can detect the isolated operation state of the plurality of types of distributed power supplies 5.

  DESCRIPTION OF SYMBOLS 1 ... Commercial power supply, 3 ... Power system, 5 ... Distributed power supply, 10 ... Single operation detection apparatus, 13 ... Sample hold circuit (sampling voltage generation means), 14 ... A / D conversion circuit (sampling voltage generation means), 15 ... Frequency measurement circuit (frequency measurement means), 16... Arithmetic processing unit.

Claims (7)

An isolated operation detection device for detecting an isolated operation state of a distributed power source connected to an electric power system from a sudden change in the voltage phase of the electric power system,
Sampling voltage generating means for sampling the measurement voltage obtained by measuring the voltage of the power system at a predetermined period and A / D converting to generate a sampling voltage;
An extracting means for extracting a system fundamental wave voltage component from the sampling voltage;
Frequency measuring means for measuring the frequency of the fundamental wave of the system from the measurement voltage;
The phase difference between the phase of the system fundamental wave voltage component in the current cycle of the system fundamental wave and the phase of the system fundamental wave voltage component in the reference cycle, which is one cycle before the current cycle, is greater than or equal to a set value. Voltage phase jump detection means for detecting whether there is,
Based on the frequency, a sudden frequency change detecting means for detecting whether or not a sudden frequency change having a larger amount of fluctuation than a sudden frequency change due to a step increase defined in the accident continuation requirement is generated;
An isolated operation detecting means for detecting that the phase difference is equal to or larger than the set value and detecting that the large frequency sudden change has occurred.
An isolated operation detection device comprising: In the isolated operation detection device according to claim 1,
Further comprising a voltage drop detection means for detecting whether or not all of the three-phase line voltages of the power system are 80% or more of the rated voltage based on the system fundamental wave voltage component;
The isolated operation detecting means detects that all of the three-phase line voltages are 80% or more of the rated voltage, detects that the phase difference is equal to or more than the set value, and detects the large An isolated operation detection device that detects an isolated operation state of the distributed power supply when it is detected that a sudden frequency change has occurred. An isolated operation detection method of a voltage phase jump detection method for detecting an isolated operation state of a distributed power source that is interconnected to an electric power system from a sudden change in the voltage phase of the electric power system,
Sampling a measurement voltage obtained by measuring the voltage of the power system at a predetermined period and A / D converting to generate a sampling voltage;
Extracting a system fundamental voltage component from the sampling voltage;
Measuring the frequency of the system fundamental wave from the measured voltage;
The phase difference between the phase of the system fundamental wave voltage component in the current cycle of the system fundamental wave and the phase of the system fundamental wave voltage component in the reference cycle, which is one cycle before the current cycle, is greater than or equal to a set value. Detecting whether or not there is,
Based on the frequency, detecting whether or not a sudden frequency change with a larger amount of fluctuation than a sudden frequency change due to a step increase specified in the accident continuation requirement has occurred,
Detecting that the phase difference is equal to or greater than the set value, and detecting that the large frequency sudden change has occurred, detecting a single operation state of the distributed power source; and
An islanding operation detection method comprising: In the isolated operation detection method according to claim 3,
Further comprising detecting whether all of the three-phase line voltages of the power system are 80% or more of the rated voltage based on the system fundamental voltage component,
In the step of detecting the single operation state, it is detected that all of the three-phase line voltages are 80% or more of the rated voltage, and the phase difference is detected to be equal to or more than the set value, An isolated operation detection method, comprising: detecting an isolated operation state of the distributed power source when detecting that the large frequency sudden change has occurred. In the isolated operation detection method according to claim 4,
In the step of detecting the isolated operation state, all of the three-phase line voltages in the current cycle are 80% or more of the rated voltage, and all of the three-phase line voltages in the reference cycle are the rated voltage. When it is detected that the voltage is 80% or more, the phase difference is equal to or more than the set value, and the occurrence of the large frequency sudden change is detected, An isolated operation detection method characterized by detecting the above. In the isolated operation detection method according to any one of claims 3 to 5,
In the step of detecting the sudden frequency change, it is detected whether or not a frequency fluctuation equal to or greater than a predetermined frequency fluctuation amount has occurred in a first period shorter than the n cycles,
The predetermined frequency fluctuation amount is set to be larger than the frequency fluctuation amount due to the step increase and smaller than the frequency fluctuation amount when a sudden change in the voltage phase of the settling value occurs. Detection method. In the isolated operation detection method according to claim 6,
Further comprising calculating an average frequency by averaging the latest predetermined number of the frequencies,
The step of detecting the sudden frequency change includes:
The occurrence of a sudden change in the frequency is detected by detecting a frequency fluctuation that changes at a larger fluctuation rate than the lamp fluctuation specified in the operation continuation requirement at the time of the accident in a second period shorter than the first period. Process,
The difference between the latest frequency and the average frequency calculated immediately before the occurrence detection of the sudden frequency change during the third period shorter than the first period from the occurrence detection of the sudden frequency change is the predetermined frequency. Detecting whether the amount of variation is greater than or equal to,
An islanding operation detection method comprising: