JP2019057972A - Solo-operation detection device, solo-operation detection method, and solo-operation detection program - Google Patents

Abstract

To improve the detection accuracy of fluctuated higher harmonic voltages and detect occurrence of a solo operation more accurately.SOLUTION: A reactive power step injection unit 7 of a solo-operation detection device calculate at a harmonic voltage calculation unit 18: a total harmonic voltage distortion based on total harmonic voltages including all of second to seventh harmonic voltages; and a total harmonic voltage distortion A based on harmonic voltages of orders having levels less than a threshold level excluding harmonic voltages of orders having levels equal to or greater than the threshold level in stationary harmonic voltages. In addition, a step injection occurrence-conditions determination unit 19 determines occurrence of harmonic voltages when either the total harmonic voltage distortion or the total harmonic voltage distortion A exceeds a step injection determination criteria.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for detecting an isolated operation that detects whether or not a distributed power supply facility is isolated from an electric power system and is operating independently.

  As is well known, a power conditioner (hereinafter referred to as PCS) converts direct current (DC) power of a distributed power source facility such as a solar cell into alternating current (AC) power, and adapts the frequency and voltage to the power system. Are linked.

  However, when the power system is stopped due to circumstances such as the occurrence of an accident, the distributed power supply facility continues to operate in a single operation that supplies power to the local system load without being disconnected from the power system. If this is the case, a reverse power flow from the distributed power supply facility will flow into the power system that should be in a power outage, and an electric shock may occur due to an isolated operation, which may threaten safety.

  Therefore, the function of reliably detecting the isolated operation state of the distributed power facility and disconnecting the distributed power facility from the power system, that is, the function of preventing the isolated operation of the distributed power facility is indispensable. A detection method has been proposed. Among these, the active islanding detection method detects the islanding by further shifting the frequency shift by injecting reactive power according to the frequency deviation.

  For example, JEM 1498 (Japan Electrical Manufacturers' Association Standard) relates to a standard for an active islanding detection method of a PCS for photovoltaic power generation (hereinafter referred to as a photovoltaic PCS). As shown in FIG. 1, this active islanding detection method includes a control unit of the solar PCS 1, that is, a system frequency measurement unit 5, a frequency feedback unit (reactive power injection unit) 6, a reactive power step injection unit 7, and an isolated operation. This is executed by the detection unit 8.

  Among these, the reactive power step injection unit 7 performs a condition determination for step injection of reactive power, and starts reactive power step injection if a predetermined condition is satisfied. One of the conditions is generation of harmonic voltage fluctuations. That is, as shown in FIG. 2, the transition of second to seventh total harmonic voltage distortion (THD) is monitored, and the occurrence of harmonic voltage fluctuation is determined by comparison with a reference value.

  Here, the harmonic voltage distortion is such that the basic voltage is “V1”, the second harmonic voltage is “V2”, the third harmonic voltage is “V3”, the fourth harmonic voltage is “V4”, 5 The second harmonic voltage is “V5”, the sixth harmonic voltage is “V6”, and the seventh harmonic voltage is “V7”.

  The fundamental voltage “V1” is calculated by the fundamental voltage calculator 17 based on the voltage measured by the voltage measurement circuit 15, and the second to seventh harmonic voltages “V2 to V7” are supplied to the harmonic voltage measurement circuit 16. The harmonic voltage measured in this manner is converted into a frequency spectrum by the harmonic voltage calculator 18 and calculated.

  For example, a method such as Fourier transform (DFT) is used for the frequency spectrum conversion. Patent Document 1 is known as an independent operation detection method for injecting reactive power by detecting occurrence of harmonic voltage fluctuations.

JP2009-44910A

  As described above, although the harmonic voltage increases rapidly with the occurrence of an isolated operation, it also occurs during normal operation in which the power system is normally linked (hereinafter, the normal harmonic voltage is referred to as a steady harmonic voltage). ).

  The steady-state harmonic voltage of each order varies depending on various conditions such as the load of the power system, and also varies depending on the time zone. Here, the order indicating a high level in normal times may not be significantly different from that in normal times even if an isolated operation occurs. In such a case, there is a risk that harmonic voltage fluctuations cannot be detected. If the detection of harmonic generation fluctuations fails, reactive power is not injected and isolated operation cannot be detected.

  “Normal” in Table 1 indicates the steady harmonic voltage, “Independent operation” indicates the harmonic voltage during independent operation, “Fluctuation difference” indicates the difference between both harmonic voltages, and for each order. It is shown. Here, the fifth order is high in “normal” and slightly increased in “single operation”, but the fluctuation difference is small.

  At this time, the fluctuation difference of the total harmonic voltage distortion (THD) stays only as high as “0.91%”, and therefore does not exceed the step injection criterion “1.0%” in FIG. Is not determined.

  In this regard, Patent Document 1 suggests that any order can be measured, not limited to the second to seventh orders. However, it is clarified which order should be measured based on what standard. Not. For this reason, even in Patent Document 1, when the “variation difference” between “normal operation” and “during independent operation” is small, there is a possibility that the harmonic voltage variation cannot be detected.

  The present invention has been made in order to solve such a conventional problem, and it is an object of the present invention to improve the detection accuracy of harmonic voltage fluctuations and more reliably detect the occurrence of isolated operation.

  (1) One aspect of the present invention relates to an isolated operation detection device that detects whether or not a distributed power source is disconnected from an electric power system and is operated independently. The isolated operation detection device includes a reactive power step injection unit that injects reactive power when harmonic voltage fluctuations occur in the power system and detects the isolated operation. The order of the level higher than the threshold is excluded from the harmonic voltage at the time, and the order of the level lower than the threshold is selected to calculate the total harmonic breakdown voltage distortion A. Used to determine whether or not it has occurred.

  (2) Another aspect of the present invention relates to an isolated operation detection method executed by a device that detects whether or not a distributed power source is disconnected from an electric power system and operated independently. In this isolated operation detection method, a calculation step of calculating a total harmonic breakdown voltage distortion A based on the order of a level lower than the threshold by excluding a level higher than the threshold from the normal harmonic voltage, and the total harmonic breakdown, A determination step for determining whether or not a harmonic voltage fluctuation has occurred using the voltage distortion A, and a reactive power injection step for step-injecting reactive power when the harmonic voltage fluctuation has occurred and detecting the isolated operation And having.

  According to the present invention, it is possible to improve the detection accuracy of harmonic voltage fluctuation and more reliably detect the occurrence of an isolated operation.

The whole block diagram of sunlight PCS concerning a standard form active islanding detection method. Explanatory drawing which shows the conditions (harmonic voltage fluctuation | variation) of the same step injection generation. The functional block diagram of the reactive power step injection | pouring part of sunlight PCS which concerns on embodiment of this invention. FIG. 4 is a detailed view of a harmonic voltage calculation unit in FIG. 3. Schematic which shows calculation of a stationary harmonic voltage.

  Hereinafter, an isolated operation detection apparatus according to an embodiment of the present invention will be described. This isolated operation detection device is built in the solar PCS and executes an active isolated operation detection method (frequency feedback method with step injection) of the solar PCS.

  That is, the sunlight PCS 1 shown in FIG. 1 includes a hardware unit and a software unit. This hardware unit includes an inverter unit (such as a switching power supply device) 10 that converts DC power supplied from a distributed power supply facility (such as a solar cell) 3 into AC power, an output side of the inverter unit 10, and a power system 2. A frequency detection circuit 14, a voltage measurement circuit 15, and a harmonic voltage measurement circuit 16 provided between the two.

  On the other hand, the software unit is executed by, for example, a central processing unit (CPU) 4 and includes a current control processing unit 9 that controls the switching operation of the inverter unit 10 and the isolated operation detection device.

  Here, the isolated operation detection device has four control units, that is, a system frequency measurement unit 5, a frequency feedback unit (reactive power injection unit) 6, a reactive power step injection unit 7, and an isolated operation detection unit 8 as in the prior art. doing. The system frequency measuring unit 5 measures the frequency used for calculating the frequency deviation, and the frequency feedback unit 6 has a function of calculating the reactive power to be injected from the system frequency deviation and promoting the frequency shift.

  The reactive power step injection unit 7 injects reactive power in order to promote a frequency shift when the frequency deviation is small, and the reactive power detection unit 8 determines whether or not an isolated operation has occurred based on a change in system frequency.

  However, the isolated operation detecting device is different from the conventional one in the processing contents of the reactive power step injection unit 7. Hereinafter, the isolated operation detection device will be described focusing on the reactive power step injection unit 7.

<Configuration of reactive power step injection unit 7>
The reactive power step injection unit 7 will be described with reference to FIG. The reactive power step injection unit 7 detects the increase when the harmonic distortion of the AC voltage increases due to the independent operation of the distributed power supply facility 3 and performs step injection of reactive power. Thus, if the frequency changes, the frequency feedback unit 6 operates and the isolated operation detection unit 8 detects the isolated operation.

  Specifically, the reactive power step injection unit 7 includes a fundamental voltage measurement circuit 15 and a harmonic breakdown voltage measurement circuit 16 in the hardware unit, a fundamental voltage calculation unit 17 and a harmonic voltage calculation unit 18 in the software unit, and a step injection. The generation condition determination unit 19 and the step injection amount calculation unit 20 are configured.

  The voltage measurement circuit 15 measures the output voltage on the inverter unit 10 side. Based on this measurement result, the fundamental voltage calculator 17 calculates the fundamental voltage V1 and outputs it to the step injection generation condition determination unit 19.

  The harmonic breakdown voltage measuring circuit 16 measures the harmonic voltage from the output voltage on the inverter unit 10 side. Based on the measurement result, the harmonic voltage calculator 18 calculates the second to seventh harmonic voltages “V2 to V7”. Based on the harmonic voltages “V2 to V7”, the total harmonic voltage effective value and the total harmonic voltage effective value A are calculated, and each calculation result is output to the step injection generation condition determining unit 19.

  At this time, the total harmonic voltage effective value is calculated by Equation (2). This formula (2) corresponds to the numerator of formula (1), and the total harmonic voltage effective value is calculated in the same manner as in the prior art. On the other hand, the total harmonic voltage effective value A is determined by excluding the orders of the harmonic voltage “V2 to V7” whose level of the steady harmonic voltage is equal to or higher than the threshold, and selecting only the order of the level lower than the threshold. Calculated in the same manner as the wave voltage effective value.

  Since the steady harmonic voltage varies depending on the time zone, it is preferable to periodically measure and update the steady harmonic voltage. Further, a threshold value may be provided for each order, and a different threshold value may be set for each order.

  The step injection generation condition determination unit 19 calculates the total harmonic voltage distortion and the total harmonic voltage distortion A based on each input information (fundamental voltage, total harmonic voltage effective value, total harmonic voltage effective value A). calculate.

  At this time, the total harmonic voltage distortion is calculated by the equation (1) as in the conventional case. On the other hand, the total harmonic voltage distortion A is calculated by replacing the total harmonic voltage effective value in the equation (1) with the total harmonic voltage effective value A. For example, based on the data in Table 1, the threshold value of “normal” is set to “3.0 V”, and the fifth-order stationary harmonic voltage (4 V) exceeds the threshold value.

  Therefore, as shown in Table 2, the harmonic voltage calculation unit 18 calculates the second, third, fourth, sixth, and seventh steady harmonic voltages excluding the fifth steady harmonic voltage (4 V). Select and calculate the total harmonic voltage RMS value A. The total harmonic voltage effective value A calculated here is replaced with the total harmonic voltage effective value in Equation 1, and the total harmonic voltage distortion A is calculated in the step injection generation condition determining unit 19.

  The step injection generation condition determination unit 19 determines that a harmonic voltage fluctuation has occurred when either one of the total harmonic voltage distortion or the total harmonic voltage distortion A exceeds the step injection determination criterion.

  At this time, according to the data in Table 2, “variation difference during normal operation = 1.13%” and “variation difference during single operation = 1.11%”, which exceeds the step criterion “1.0%” It can be determined that harmonic voltage fluctuation has occurred. The step injection amount calculation unit 20 calculates the step injection amount of reactive power according to the determination result of the step injection generation condition determination unit 19.

<< Processing of Harmonic Voltage Calculation Unit 18 >>
Details of the main part of the reactive power step injection unit 7, that is, the harmonic voltage calculation unit 18, will be described with reference to FIG. Here, the harmonic voltage calculation unit 18 includes a total harmonic voltage effective value calculation unit 18a that calculates the total harmonic voltage effective value, and a total harmonic voltage effective value A calculation unit 18b that calculates the total harmonic voltage effective value A. And is roughly divided.

  (1) First, the processing content of the total harmonic voltage effective value calculation unit 18a will be described. Here, the second to seventh voltages input from the harmonic voltage measuring circuit 16 are converted into a frequency spectrum by discrete Fourier transform (DFT processing).

  A square process is performed on the converted harmonic voltages of the respective orders, a total process is performed to sum all the harmonic voltages after the square process, and a square root process is performed thereafter. Specifically, the arithmetic processing of the above-described equation (2) is executed.

  (2) Next, the processing contents (S01 to S04) of the total harmonic voltage effective value A calculation unit 18b will be described with reference to FIGS. Here, the secondary to seventh-order stationary harmonic voltages input from the harmonic voltage measuring circuit 16 are registered in the buffer 21 of the sunlight PCS1.

  In addition, as the stationary harmonic voltage for calculating the total harmonic voltage effective value A, a moving average value updated at a constant period for each order is used. Furthermore, it is assumed that the total harmonic voltage effective value A calculation unit 18b includes a buffer element number calculation unit 22, a buffer update time determination unit 23, and a moving average calculation unit 24.

  S01: As shown in FIG. 5, the buffer element number calculation unit 22 sets the harmonic voltage for the measurement period to be held by the buffer 21, that is, the buffer element number as “number of buffer elements = measurement period setting value α / measurement interval setting”. The value β ”is calculated (S11). The harmonic voltages for the number of buffer elements calculated here are held in the buffer 21. For example, if “α = 30 minutes” and “β = 1 minute”, the harmonic voltage of “30 minutes / 1 minute = 30” is held.

  S02: The buffer element group held in the buffer 21 is updated at every predetermined measurement interval. Whether or not this update is necessary is determined by the buffer update time determination unit 23. At this time, the buffer update time determination unit 23 calculates a time difference T between the current time t and the previous measurement time t−1, and compares the calculated time difference T with the measurement interval set value β (S21).

  If “time difference T = measurement interval set value β” does not hold as a result of the comparison, it is not necessary to update the buffer element group instead of the update time. On the other hand, if it is established, the update time is reached, so an update command is sent to the moving average calculation unit 24.

S03: moving average calculation section 24 adds the n-th harmonic voltage Z ⁰ measured to date when receiving the update command to the end of the buffer 21. At this time, the harmonic voltage Z ^X at the head of the buffer 21 is discarded, and the total processing of each harmonic voltage is executed (S31).

  At this time, the result of the summation process is “a”, and the number of buffer elements of the buffer 21 calculated in S01 is “b”. Here, the average value “a / b” of the measurement period α, that is, the moving average value is calculated as a stationary harmonic voltage of the order (S32). For example, in the case of “α = 30 minutes” and “β = 1 minute” described above, the second to seventh stationary harmonic voltages are calculated as moving average values for the past 30 minutes (number of buffer elements b = 30) every minute. Calculated.

  S04: The second to seventh stationary harmonic voltages that have undergone the processing of S01 to S03 are compared with a predetermined threshold value, and only the order of the harmonics less than the threshold value is selected.

  That is, it is determined whether or not “steady harmonic voltage <threshold” is satisfied for each of the second to seventh stationary harmonic voltages. As a result of the determination, if not established, the steady harmonic voltage of the order is excluded from the calculation of the total harmonic voltage effective value A, whereas if established, the steady harmonic voltage of the order is equal to the total harmonic voltage effective value A. Selected for calculation.

  The stationary harmonic voltages of each order selected here are squared, summed to sum all the stationary harmonic voltages after the squared processing, and then square root processing is applied to the total harmonic voltage. An execution value A is calculated. Specifically, as described above, if the order of the steady harmonic voltage equal to or higher than the threshold is excluded from the formula (2), and the calculation process of the formula (2) is executed only with the steady harmonic voltage less than the threshold, Good.

  As described above, according to the isolated operation detection device of the present embodiment, the total harmonic breakdown voltage distortion A using only the order of the level lower than the threshold value by excluding the order of the level higher than the threshold value from the stationary harmonic voltage in the normal time. However, even when the step injection criterion is exceeded, it is determined that the harmonic voltage fluctuation has occurred.

  Therefore, the occurrence of harmonic voltage fluctuation can be detected even when the fluctuation difference between the normal harmonic voltage during normal operation and the harmonic voltage during single operation is small. As a result, it is possible to improve the detection accuracy of the harmonic voltage fluctuation and more reliably detect the occurrence of the isolated operation.

  In particular, the steady harmonic voltage of each order is updated at a constant period, so that even if an environmental change such as a load change occurs, the occurrence of the harmonic voltage fluctuation can be continuously detected with high accuracy.

  In addition, this invention is not limited to the said embodiment, It can deform | transform and implement within the range described in each claim. For example, the isolated operation detection device according to the present invention can be configured as a separate device without being incorporated in the solar light PCS.

  The present invention can also be configured as a program that causes a computer to function as the isolated operation detection device according to the present invention. According to this program, the central processing unit 4 of the computer executes the processes of S01 to S04. This program can be distributed through a network, or can be stored in a recording medium for distribution.

1 ... Solar PCS
2 ... Power system 3 ... Distributed power supply equipment (Distributed power supply)
4. Central processing unit (CPU)
5. System frequency measurement unit 6. Frequency feedback unit (reactive power injection unit)
DESCRIPTION OF SYMBOLS 7 ... Reactive power step injection part 8 ... Single operation detection part 9 ... Current control processing part 10 ... Inverter part 11 ... Electric power system line 15 ... Fundamental voltage measurement circuit 16 ... Harmonic voltage measurement circuit 17 ... Fundamental voltage calculation part 18 ... Harmonic voltage calculation unit 18a ... Full length breakdown voltage execution value calculation unit 18b ... Full length breakdown voltage A execution value calculation unit 19 ... Step injection generation condition determination unit 20 ... Step injection amount calculation unit 21 ... Buffer 22 ... Buffer element number calculation unit 23 ... Buffer update time determination unit 24 ... Moving average calculation unit

Claims (7)

An isolated operation detection device that detects whether or not a distributed power source is disconnected from the power system and is operating alone,
Reactive power step injection when stepping in reactive power when a harmonic voltage fluctuation occurs in the power system, and detecting the isolated operation,
The reactive power step injection unit calculates the total harmonic breakdown voltage distortion A by selecting the order of the level lower than the threshold by excluding the order of the level higher than the threshold from the normal harmonic voltage.
The isolated operation detection device, wherein the total harmonic breakdown voltage distortion A is used for determining whether or not a harmonic voltage fluctuation has occurred. The reactive power step injecting unit calculates the total harmonic voltage distortion calculated based on the harmonic voltages of all orders,
The islanding operation detection device according to claim 1, wherein when any one of the total harmonic breakdown voltage distortion A exceeds a step injection criterion, it is determined that a harmonic voltage fluctuation has occurred. While the reactive power step injection unit, the normal harmonic voltage is a constant moving average for each order,
The isolated operation detection apparatus according to claim 1 or 2, wherein the harmonic voltage in the normal state is updated at a constant cycle. An isolated operation detection method executed by an apparatus for detecting whether or not a distributed power source is disconnected from an electric power system and operated independently,
Calculating the total harmonic breakdown voltage distortion A based on the order of the level below the threshold by excluding the order of the level higher than the threshold from the normal harmonic voltage;
A determination step of determining whether or not a harmonic voltage fluctuation has occurred using the total harmonic breakdown voltage distortion A;
Reactive power injection step for injecting reactive power when the harmonic voltage fluctuation occurs and detecting the isolated operation;
An islanding operation detection method comprising: The determination step includes a total harmonic voltage distortion based on harmonic voltages of all orders,
5. The islanding operation detection method according to claim 4, wherein when any one of the total harmonic voltage distortion A exceeds a step injection determination criterion, it is determined that a harmonic voltage is generated. A step of setting the normal harmonic voltage to a constant moving average value for each order;
Updating the normal harmonic voltage at regular intervals;
The islanding operation detection method according to claim 4 or 5, further comprising:   An isolated operation detection program for causing a computer to function as the isolated operation detection device according to claim 1.

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