JP2006204069A - Individual operation detecting method and individual operation detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a system characteristic change that is due to shift to individual operation, and to suppress misdetections due to phenomena other than the shifting to the individual operations, in an interlinked system. <P>SOLUTION: A voltage detector 6 and a current detector 7 continuously measure voltages and currents, at the linked point of a commercial power supply system 1 and a distributed power supply 3. Harmonic analyzers 8a, 8b perform wavelet transform from the measured voltage and current values, to calculate the predetermined component of each order of harmonic waves. An admittance value calculating portion 9 calculates the admittance value of each order of harmonic waves, based on the voltage and the current value of the harmonic component of each order. An index-determining portion 10 determines that the distribution power supply has shifted to the state of the individual operation, when a state where the change of the admittance value, to at least a single next-order harmonic wave exceeds a predetermined threshold, continues for a prescribed period of time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an isolated operation detection method and an isolated operation detection device for detecting that a distributed power supply has shifted to an isolated operation state in a grid interconnection system in which a distributed power supply is connected to a commercial power system.

  Various grid interconnection systems have been proposed in order to link private power generation facilities such as demand cogeneration facilities to the power grid.

  In this type of grid-connected system, if the power system's substation breaker is opened due to an accident in the power system, etc., and the power supply from the commercial power system is stopped (shut off), the distributed power equipment is connected to the system. If the system is operated while being connected, a reverse power flow flows from the distributed power source to the power system that is normally in a power failure state, which may cause an electric shock accident or the like due to an independent operation and threaten safety. For this reason, the function of reliably detecting the isolated operation state of the distributed power supply facility and disconnecting (disconnecting) the distributed power supply facility from the commercial power system, that is, the function of preventing the isolated operation of the distributed power supply is indispensable.

  Therefore, various isolated operation detection methods for detecting that the distributed power supply has been in an isolated operation state due to a system power failure or the like have been proposed. For example, as an active islanding detection method, a frequency shift method, an active power fluctuation method, a reactive power fluctuation method, a load fluctuation method, a third harmonic detection method, and the like are known. The detection principle is, for example, that the AC output of the inverter is subjected to voltage and frequency fluctuations that have almost no effect on the commercial power system. At the time of transition, the islanding operation is detected from periodic fluctuations caused by fluctuations in voltage and frequency.

  However, when an islanding detection device based on the active islanding detection method is used, the islanding detection sensitivity is high when a plurality of islanding detection devices, particularly islanding detection devices of different types are mixed in the commercial power system. It has been confirmed that it decreases. For example, in a reactive power fluctuation type isolated operation detection device in which a private power generation device is a fuel cell, the frequency is such that the first wave is −5% and the next one wave is + 5% every 0.5 seconds (25 waves). However, when an isolated operation actually occurs, interference due to output fluctuations of other different types of isolated operation detection devices may occur, and variations in frequency and reactive power may be canceled out. .

On the other hand, as a passive detection method, a voltage phase jump detection method for detecting a sudden change in the voltage phase at the connection point at the time of transition from parallel operation to single operation, and a rapid change in frequency are detected. There are a frequency change rate detection method, a third-order harmonic voltage distortion rapid increase detection method that detects a rapid increase in the third-order harmonic component due to the excitation characteristics of the pole transformer, and the like. For example, in Patent Document 1, a voltage at an interconnection point is detected, and based on the detected value, a frequency, an average value, or a harmonic content rate of the voltage is calculated, and any of these calculated values is predetermined. It is described that when the threshold value is exceeded, it is determined to be an isolated operation. Since such a passive detection method has no influence on the system, even if a plurality of islanding detection devices exist in the commercial power system, the sensitivity of islanding detection is reduced due to mutual interference. You can avoid that.
JP 2002-291158 A

  However, in the conventional passive detection method, there is a possibility that erroneous detection may occur when a state change similar to that at the time of shifting to the single operation occurs due to a load change or the like during the parallel operation. For example, in the third harmonic voltage distortion rapid increase detection method used in a system including a current control type inverter, erroneous detection is likely to occur when starting a capacitor input type device represented by an air conditioner. Alternatively, in the method of detecting isolated operation from changes in the voltage, phase, and frequency of the fundamental wave component, if the load and power generation amount match at the location where the distributed power source is installed, the change is small and the change is accurate. It is difficult to detect.

  The present invention has been made in view of such a problem, and in the passive method of the single operation, the shift to the single operation can be clearly detected, and erroneous detection due to an event other than the shift to the single operation An object of the present invention is to provide an isolated operation detection method that can avoid the above.

  An isolated operation detection method according to the present invention is an isolated operation detection method for detecting that a distributed power source linked to a commercial power system has shifted to an isolated operation state, and is connected to the commercial power system and the distributed power source. Continuously measuring voltage and current at a point, calculating system characteristics for a predetermined harmonic based on the measured values of the voltage and current, and detecting an isolated operation state based on the calculated change in system characteristics It is characterized by.

  The isolated operation detection device of the present invention is applied to a grid interconnection system that can supply power from a distributed power source by a private power generator to a consumer load connected to a commercial power system, and the distributed power source is in an isolated operation state. Detect that it has moved to. A voltage measurement unit that continuously measures a voltage at the connection point of the distributed power supply; a current measurement unit that continuously measures a current at the connection point of the distributed power supply; the voltage measurement unit and the current measurement A harmonic analysis unit that calculates at least one harmonic component of a predetermined order from each measurement output of the unit, and a voltage value and a current value of a harmonic for each order calculated by the harmonic analysis unit An admittance value calculation unit for calculating an admittance value for each of the harmonic components, and a change in the admittance value for the harmonic of at least one order calculated by the admittance value calculation unit exceeds a predetermined threshold value. And an index determination unit that outputs a determination result indicating that the distributed power source has shifted to the single operation state when the state has continued for a predetermined time. .

  According to the present invention, since the system characteristic for a predetermined harmonic is calculated based on the measured values of the voltage and current at the interconnection point, it is possible to clearly detect a change in the system characteristic due to the shift to the single operation. Moreover, the occurrence of erroneous detection due to an event other than the shift to the single operation is suppressed. Furthermore, since it is a passive method, there is no influence on the system, and the detection sensitivity does not decrease.

  In the isolated operation detection method of the present invention, preferably, harmonic components of at least one of the third, fifth, seventh, ninth, eleventh, and thirteenth orders are selected, and the selected order harmonics are selected. The admittance value obtained for each wave component is used as the system characteristic. Preferably, a plurality of order harmonic components are selected, and an admittance value obtained for each of the selected order harmonic components is used as the system characteristic.

  The harmonic components can be obtained by wavelet transforming the measured values of voltage and current.

  Preferably, regarding a change in the admittance value with respect to the harmonic component of at least one order, it is determined that the single operation is performed when a state exceeding a predetermined threshold is continued for a predetermined time. In addition, preferably, with respect to a change in the admittance value for each of the harmonic components of a predetermined plurality of orders, it is determined that the single operation is performed when a state exceeding a predetermined threshold has continued for a predetermined time.

  In the isolated operation detection device of the present invention, preferably, at least one of the third, fifth, seventh, ninth, eleventh, and thirteenth harmonic components is used as the harmonic component. Preferably, a plurality of order harmonic components are used as the harmonic components.

  The harmonic components can be obtained by wavelet transforming the measured values of voltage and current.

  Preferably, regarding a change in the admittance value for the harmonic component of at least one order in a predetermined time interval, it is determined that the single operation is performed when a state exceeding a predetermined threshold is continued for a predetermined time. Further, preferably, regarding a change in a predetermined time interval of each admittance value with respect to the harmonic components of a predetermined plurality of orders, it is determined that the single operation is performed when a state exceeding a predetermined threshold continues for a predetermined time.

  Embodiments of the present invention will be specifically described below with reference to the drawings.

  FIG. 1 is a block diagram showing a grid interconnection system in which an isolated operation detection device according to an embodiment of the present invention is installed. Reference numeral 1 denotes a commercial power system, to which a customer load 2 is connected. The customer load 2 can be supplied with electric power from the distributed power source 3 by the private power generator via the cutoff unit 4 to configure a grid interconnection system. When the private power generation device is a direct current power supply device such as a solar cell or a fuel cell, the output of the power generation device is controlled and supplied to the same voltage and the same frequency as the commercial power system 1 by an inverter.

  The isolated operation detection device 5 connected to detect that the distributed power supply 3 has shifted to the isolated operation state includes a voltage measuring unit 6 that continuously measures the voltage at the interconnection point of the distributed power supply 3, and the distributed power supply 3. The current measuring unit 7 continuously measures the current at the connection point. The measurement outputs of the voltage measurement unit 6 and the current measurement unit 7 are respectively supplied to the harmonic analysis units 8a and 8b. Each of the harmonic analysis units 8 a and 8 b calculates a predetermined harmonic component and supplies it to the admittance value calculation unit 9. The admittance value calculation unit 9 calculates an admittance value for each predetermined harmonic from the voltage value and current value of the harmonic for each predetermined order.

  The admittance value for each predetermined harmonic calculated by the admittance value calculation unit 9 is supplied to the index determination unit 10. The index determination unit 10 indicates that the distributed power source 3 has shifted to the single operation state when a change in a predetermined time interval exceeds a predetermined threshold for a predetermined time for any one of the admittance values for each predetermined higher harmonic. Output the judgment result. The determination result of the index determination unit 10 is supplied to the cutoff unit 4, and when the determination result indicating the isolated operation state of the distributed power source 3 is output, the cutoff unit 4 disconnects the distributed power source 3 from the commercial power system 1.

  For the analysis of the harmonic component in the harmonic analysis units 8a and 8b, a method of calculating the harmonic component by wavelet transforming the measured values of voltage and current can be applied. Further, the harmonic analysis units 8a and 8b and the admittance value calculation unit 9 calculate the admittance value, and the index determination unit 10 determines the order of the harmonic component to be determined as the third, fifth, seventh, At least one order can be selected and used from the 9th, 11th, and 13th harmonic components. For example, a method using only the 7th harmonic component or a method using a combination of the 3rd, 5th and 7th harmonic components can be appropriately selected according to application conditions. Which harmonic component is appropriate to use depends on the conditions related to the detection of the isolated operation, and therefore needs to be selected as appropriate after consideration of the conditions.

  The isolated operation detection method in the present embodiment will be described with reference to the flowchart of FIG. 2 showing the operation of the isolated operation detection device 5 having the above configuration.

  First, the voltage and current at the interconnection point between the commercial power system 1 and the distributed power source 3 are continuously measured by the voltage measuring unit 6 and the current measuring unit 7 (step S1). Next, the harmonic analysis units 8a and 8b perform, for example, harmonic analysis by wavelet transform on the measured voltage value and current value to calculate predetermined respective harmonic components (step S2). Next, the admittance value calculation unit 9 calculates an admittance value for each predetermined harmonic from the voltage value and current value of each predetermined harmonic component (step S3). That is, the admittance value for each order is calculated by calculating (current value for each order) / (voltage value for each order).

  Next, the index determination unit 10 determines whether or not the distributed power source 3 has shifted to the single operation state based on a change in the admittance value with respect to each predetermined harmonic (step S4). That is, for at least one of the admittance values for each predetermined harmonic, when the change from the admittance value before a predetermined time exceeds a predetermined threshold for a predetermined time, the distributed power source 3 has shifted to the single operation state. Determine (step S5). If none of the changes in the admittance value for each predetermined harmonic has exceeded the predetermined threshold value, or if the state in which the change in the admittance value has exceeded the predetermined threshold value has not continued for a predetermined period of time, it is determined as an isolated operation state. Without repeating, steps S1 to S4 are repeated. For detecting the change in the admittance value, it is preferable to use a change rate (Y1 / Y0) of the admittance value as described later.

  As described above, distributed power sources are installed by calculating the system characteristics for a predetermined harmonic based on the measured values of voltage and current at the interconnection point, and detecting the isolated operation state based on the calculated changes in system characteristics. Even when the load and the power generation amount match at the place, the change in the admittance value at the time of shifting to the single operation is sufficiently large, and the change can be detected with high accuracy. Moreover, even when a state change similar to that at the time of shifting to the single operation occurs due to a load change or the like during the parallel operation, the occurrence of erroneous detection can be suppressed. This is because even in such a case, the system characteristic, for example, the admittance value, with respect to a predetermined harmonic calculated based on the measured values of voltage and current is such that the change is negligible. In particular, by monitoring a plurality of harmonic orders, it is possible to reliably detect an isolated operation even when the load and the distributed power generation amount are balanced.

  Below, the result of having simulated the admittance value change and the voltage change at the time of the load change during the independent operation and the parallel operation will be described. The simulation was performed using a simulated power system (analog simulator) shown in FIG. In the figure, reference numeral 11 denotes a power generator on the system side, and Tr1 and Tr2 denote transformers installed in the substation. G1 and G2 are first and second distributed power sources, respectively. Reference numerals 12 and 13 denote transformers, and SC denotes a capacitor. CB1 to CB9 indicate circuit breakers.

  The simulation of the accuracy of the isolated operation detection at the connection point of the first distributed power supply G1 of this simulated power system is performed, and the output of the isolated operation detection at the time of the following events including the state of the isolated operation of the first distributed power supply G1 Investigated about.

(A) Capacitor SC in parallel (B) Capacitor SC disconnected (C) Transformer Tr2 in parallel (with circuit breaker CB1 turned on with the primary side of Tr2 connected)
(D) Disconnection of transformer Tr2 (opening of circuit breaker CB1 with the primary side of Tr2 connected)
(E) Line disconnection between circuit breakers CB6 and CB7 (F) Line parallel between circuit breakers CB6 and CB7 (G) Single operation of first distributed power supply G1 (opening of circuit breaker CB5)
(H) Disconnection of second distributed power supply G2 (opening of circuit breaker CB9)
(I) Paralleling of the second distributed power supply G2 (turning on the circuit breaker CB9)
(J) Single operation of second distributed power supply G2 (opening of circuit breaker CB7)
(K) Disconnection of transformer Tr2 (breaker CB2 is opened with the primary side of Tr2 disconnected)
(L) Charging the transformer Tr2 (with the breaker CB2 turned on with the primary side of Tr2 disconnected)
In order to evaluate the output of the isolated operation detection, the admittance value change rate (Y1 / Y0) was calculated as shown in FIG. That is, an event is generated 0.4 seconds after the start of the test, and the admittance value for each harmonic is an average value (Y0) between 0.2 seconds and 0.3 seconds from the start of the test, and 0 from the start of the test. The average value (Y1) between 6 seconds and 0.7 seconds was determined. From these values, the rate of change of admittance value (Y1 / Y0) was calculated. In the case of the conventional method as a comparative example, the rate of change of each harmonic voltage was calculated instead of the admittance value.

  The simulation results for the embodiment of the present invention are shown in FIG. This result is an admittance value change rate with respect to the seventh harmonic. The horizontal axis corresponds to each event described above. Each symbol plotted in the figure corresponds to the admittance value change rate under each of the following conditions. The harmonic content means the ratio of the harmonic voltage to the fundamental voltage. The expression that the harmonic content is large or small means that the harmonic content on the large side is set to 2-3% and the small side is set to 1%.

  □: When the adjacent generator (second distributed power supply G2) is in a disconnected state and the harmonic content on the system side is larger than the harmonic content on the load side.

  X: When the adjacent generator (second distributed power supply G2) is in a disconnected state and the harmonic content on the system side is smaller than the harmonic content on the load side.

  ◇: When the adjacent generator (second distributed power supply G2) is connected and the harmonic content on the system side is larger than the harmonic content on the load side.

  +: When the adjacent generator (second distributed power supply G2) is connected and the harmonic content on the system side is smaller than the harmonic content on the load side.

  As is clear from FIG. 5, in the case of the single operation (G) of the first distributed power supply G1, changes in the admittance value are markedly exhibited under all conditions. On the other hand, in other events (A) to (F) and (H) to (L), almost no change in the admittance value is observed. If the threshold is set to 1.4, it is possible to discriminate only the single operation event. Therefore, according to the embodiment of the present invention, it is possible to reliably determine the transition to the single operation without being affected by other events.

  As a comparative example, FIG. 6 shows the result of simulation for the rate of change (V1 / V0) of the seventh harmonic voltage. The calculation conditions for the rate of change (V1 / V0) are the same as those shown in FIG. As is apparent from FIG. 6, the seventh harmonic voltage is also applied to other events (A) to (F) and (H) to (L) other than the single operation (G) of the first distributed power supply G1. The change is large. Therefore, even if it is attempted to detect an isolated operation based on the rate of change of the seventh harmonic voltage, it is difficult to determine the transition to the isolated operation due to the influence of other events.

  According to the islanding operation detection method of the present invention, the transition to the islanding operation can be clearly detected, and the occurrence of erroneous detection due to an event other than the transition to the islanding operation is suppressed. It is extremely useful to apply.

The block diagram which shows the grid connection system in which the isolated operation detection apparatus in embodiment of this invention was installed Flow chart showing the operation of the islanding detection device The figure which shows the simulation electric power system for simulation for evaluating the detection accuracy by the islanding detection device The figure which shows the calculation method of the admittance value change rate for evaluating the precision of islanding detection The figure which shows the test result of the precision of the independent operation detection by embodiment of this invention The figure which shows the test result of the accuracy of islanding detection by comparison example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Commercial power system 2 Load 3 Distributed power supply 4 Shut-off part 5 Isolated operation detection device 6 Voltage measurement part 7 Current measurement part 8a, 8b Harmonic analysis part 9 Admittance value calculation part 10 Index determination part 11 Generator 12, 13 Transformer CB1 CB9 Breaker G1 First distributed power supply G2 Second distributed power supply SC Capacitor Tr1, Tr2 Transformer

Claims (12)

In the isolated operation detection method for detecting that the distributed power source connected to the commercial power system has shifted to the isolated operation state,
Continuously measure the voltage and current at the interconnection point of the commercial power system and the distributed power source, calculate the system characteristics for a predetermined harmonic based on the measured values of the voltage and current, the calculated system characteristics An isolated operation detection method that detects an isolated operation state based on a change.   Select at least one harmonic component of the third, fifth, seventh, ninth, eleventh, and thirteenth orders, and determine the admittance value obtained for each of the selected harmonic components. The islanding operation detection method according to claim 1, which is used as the system characteristic.   The islanding operation detection method according to claim 2, wherein a plurality of order harmonic components are selected, and an admittance value obtained for each of the selected order harmonic components is used as the system characteristic.   The islanding operation detection method according to any one of claims 1 to 3, wherein the harmonic component is obtained by wavelet transforming measured values of voltage and current.   The islanding operation detection according to any one of claims 2 to 4, wherein the islanding operation is determined when a state exceeding a predetermined threshold is continued for a predetermined time with respect to a change in admittance value with respect to the harmonic component of at least one order. Method.   The isolated operation detection method according to claim 5, wherein the isolated operation is determined when a state exceeding a predetermined threshold is continued for a predetermined time with respect to a change in admittance value for each of the harmonic components of a plurality of orders. Applicable to a grid-connected system that can supply power from a distributed power source by a private power generator to a consumer load connected to a commercial power system, and to detect that the distributed power source has shifted to a single operation state In the detection device,
A voltage measuring unit for continuously measuring the voltage at the interconnection point of the distributed power source;
A current measurement unit that continuously measures the current at the interconnection point of the distributed power source;
From each measurement output of the voltage measurement unit and the current measurement unit, a harmonic analysis unit that calculates at least one harmonic component of a predetermined order;
An admittance value calculation unit for calculating an admittance value for each of the harmonic components of each of the harmonics from a voltage value and a current value of the harmonics of the respective orders calculated by the harmonic analysis unit;
Regarding the change in the admittance value for the harmonics of at least one order calculated by the admittance value calculation unit, when the state exceeding a predetermined threshold has continued for a predetermined time, the distributed power source has shifted to the single operation state. An isolated operation detection device comprising: an index determination unit that outputs a determination result to be displayed.   The isolated operation detection apparatus according to claim 7, wherein at least one of third-order, fifth-order, seventh-order, ninth-order, eleventh-order, and thirteenth-order harmonic components is used as the harmonic component.   The isolated operation detection apparatus according to claim 8, wherein a harmonic component having a plurality of orders is used as the harmonic component.   The isolated operation detection device according to any one of claims 7 to 9, wherein the harmonic component is obtained by performing wavelet transform on a measured value of voltage and current.   The change in the predetermined time interval of the admittance value with respect to the harmonic component of at least one order is determined to be a single operation when a state exceeding a predetermined threshold continues for a predetermined time. Single operation detection device. The single-unit operation according to claim 9 or 10, wherein the single operation is determined when a state exceeding a predetermined threshold is continued for a predetermined time with respect to a change in a predetermined time interval of each admittance value for the harmonic components of a predetermined plurality of orders. Driving detection device.

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