JP2018064328A - Power conversion apparatus and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of further reliably detecting independent operation using a frequency feedback function.SOLUTION: The power conversion apparatus interconnects a distributed power supply to a system power supply and detects the independent operation by using a frequency feedback function that urges the frequency change according to the deviation of the system frequency. The power conversion apparatus includes a harmonic voltage detection unit, a current control processing unit, and a first determination unit. The harmonic voltage detection unit detects a harmonic voltage appearing at the output of the power conversion device. The current control processing unit, when the gain reduction processing of the frequency feedback function is performed, injects a harmonic current of the amount corresponding to one of the harmonic voltage and the line impedance between the system power supply and the power conversion apparatus into the power converted by the power conversion apparatus. The first determination unit determines whether or not to terminate the gain reduction processing on the basis of the harmonic voltage detected in a state in which the harmonic current is injected.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power conversion device and a control method thereof.

  2. Description of the Related Art Conventionally, a power conversion device that links a distributed power source such as a solar cell to a system power source is known. If the power conversion device continues to operate independently without being disconnected from the system power supply at the time of a power failure of the system power supply, there is a possibility that a problem may arise from the viewpoint of ensuring safety and ensuring the reliability of power supply. For this reason, the conventional power converter device has a function of detecting an isolated operation, and disconnects itself from the system power supply when the isolated operation is detected. For example, Non-Patent Document 1, which defines a new interconnection rule for a PCS (power conditioning system) for a PV (photovoltaic) system, presents a frequency feedback method with step injection that actively detects islanding.

  In the above-described frequency feedback type isolated operation detection, the frequency feedback operates even when a disturbance occurs in the system power supply. At this time, if the line impedance of the energization path between the system power supply and the power converter is large, flicker (periodic voltage fluctuation) occurs in the system voltage due to injection of reactive power. When flicker occurs, there is a problem because other devices (for example, fluorescent lamps) connected to the system power supply have an adverse effect such as flickering.

  For this reason, in Patent Document 1 by the applicant of the present application, when flicker occurs, the gain of frequency feedback is temporarily reduced, and harmonic current distortion is injected into the power converted by the power converter. And if the rapid increase of the harmonic voltage distortion which generate | occur | produces when a single operation generate | occur | produces is detected, the gain of a frequency feedback will be recovered | restored and the power converter device will be stopped by the single operation detection of a frequency feedback system.

JP2015-220835A

Japan Electrical Manufacturers Association Standard JEM1498 (Established 2012.8.27)

  As a result of further examination by the applicant, the harmonic voltage distortion increases with the increase of the line impedance between the system power supply and the power converter, but the amount of increase and increase of the harmonic voltage distortion when an isolated operation occurs It has been found that the speed decreases with increasing line impedance. Therefore, in the isolated operation detection using a constant voltage threshold, even if the isolated operation occurs, the increase amount of the harmonic voltage distortion may not exceed the voltage threshold depending on the magnitude of the line impedance. In this case, since a rapid increase in the harmonic voltage distortion during the single operation cannot be detected, the frequency feedback gain cannot be recovered to detect the single operation, and the power converter cannot be stopped. It has also been found that when the line impedance increases, there may be a time difference between the time when the isolated operation occurs and the time when the harmonic voltage distortion rapidly increases. In the current rules, it is stipulated that the power conversion device is stopped within 0.2 [sec] from the occurrence of the isolated operation, but when the time difference as described above occurs, The power converter cannot be shut down immediately and the current rules cannot be observed. Furthermore, if a large harmonic current distortion is always injected, the influence is given to the voltage of the system power supply. Therefore, it is required that a harmonic current distortion as small as possible is appropriately injected.

  In view of the above situation, an object of the present invention is to provide a technique that can more reliably detect an isolated operation using a frequency feedback function.

  In order to achieve the above object, a power converter according to an aspect of the present invention is an independent operation using a frequency feedback function that links a distributed power supply to a system power supply and promotes a frequency change according to a system frequency deviation. A harmonic voltage detection unit that detects a harmonic voltage appearing in the output of the power conversion device, and when the gain reduction processing of the frequency feedback function is performed, the harmonic voltage and the system A current control processing unit that injects a harmonic current in an amount corresponding to one of the line impedances between the power supply and the power converter into the power converted by the power converter, and detected in a state where the harmonic current is injected And a first determination unit that determines whether or not to end the gain reduction process based on the harmonic voltage that has been made (first configuration).

  The power conversion device having the first configuration is configured to further include a second determination unit (second configuration) that determines whether to perform gain reduction processing when there is a possibility of occurrence of voltage flicker. .

  In the power conversion device having the first or second configuration, the current control processing unit injects an amount of harmonic current corresponding to an average value of a plurality of harmonic voltages detected in a predetermined period (third Composition).

  The power conversion device having any one of the first to third configurations has a configuration (fourth configuration) in which the current control processing unit injects an amount of higher harmonic current corresponding to the output of the power conversion device. .

  In the power conversion device having any one of the first to fourth configurations, the harmonic voltage detection unit is configured to previously detect the harmonic voltage before voltage flicker occurs (fifth configuration).

  In the power converter of the fifth configuration, the harmonic voltage detector is configured to detect the harmonic voltage at the start of operation of the power converter (sixth configuration).

  In the power conversion device having any one of the first to sixth configurations, the first determination unit terminates the gain reduction process when the increase amount of the harmonic voltage that rapidly increases during the gain reduction process is equal to or greater than a threshold value ( (7th structure).

  In the power conversion device of the seventh configuration, the threshold is set according to the amount of harmonic current injected by the current control processing unit (eighth configuration).

  The power conversion device of the eighth configuration further includes a storage unit that stores the harmonic current injected by the current control processing unit, and when the gain reduction process is performed, the initial value of the threshold is the harmonic value that has been recently injected. It is set as the structure (9th structure) set according to the maximum value of the wave current or the harmonic current memorize | stored in the memory | storage part.

  In the power conversion device having any one of the first to ninth configurations, the harmonic voltage detection unit is configured to detect the harmonic voltage every tenth period (tenth configuration).

  In order to achieve the above object, a method for controlling a power conversion device according to an aspect of the present invention uses a frequency feedback function that links a distributed power source to a system power source and promotes a frequency change according to a system frequency deviation. A method for controlling a power converter that detects a single operation, wherein a step of detecting a harmonic voltage that appears in the output of the power converter and a gain reduction process of a frequency feedback function are performed. , A step of injecting a harmonic current in an amount corresponding to one of the line impedances between the system power supply and the power converter into the power converted by the power converter, and the harmonic current being detected. And a step of determining whether or not to end the gain reduction process based on the higher harmonic voltage (the eleventh configuration).

  ADVANTAGE OF THE INVENTION According to this invention, the technique which can detect the isolated operation using a frequency feedback function more reliably can be provided.

It is a block diagram which shows the structural example of PCS which concerns on 1st Embodiment. 10 is a flowchart for explaining an example of PCS operation when it is determined that there is a possibility that voltage flicker has occurred. It is a block diagram which shows the structural example of PCS which concerns on the 1st modification of 1st Embodiment. It is a schematic diagram which shows the frequency deviation-injection reactive power characteristic of PCS which concerns on the 2nd modification of 1st Embodiment. It is a flowchart for demonstrating the acquisition process of the harmonic current distortion in 2nd Embodiment. 10 is a flowchart for explaining another example of the operation of the PCS when it is determined that there is a possibility that voltage flicker has occurred. It is a flowchart for demonstrating the acquisition process of the harmonic current distortion in 3rd Embodiment.

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

<First Embodiment>
FIG. 1 is a block diagram illustrating a configuration example of a PCS (Power Control System) 1 according to the first embodiment. The PCS 1 is a power conversion device that allows the distributed power source 2 to be connected to the system power source 3, and is disposed between the distributed power source 2 and the system power source 3. The distributed power source 2 is not particularly limited, and examples thereof include natural energy power generation facilities such as solar cells, fuel cells, and storage batteries. The system power supply 3 is a power network provided by, for example, an electric power company. In addition, although illustration in FIG. 1 is abbreviate | omitted between PCS1 and the system power supply 3, the load etc. which were connected to the pole transformer and the low voltage distribution line exist. The pole transformer reduces the high-voltage power sent from the high-voltage distribution line to the low-voltage power and supplies it to the low-voltage distribution line.

  The PCS 1 has a frequency feedback type isolated operation detection function with step injection. If the output power Wo of the PCS 1 and the power consumed by the load are not balanced, the system frequency changes when the system power supply 3 is powered off. At this time, the PCS 1 detects an isolated operation using a frequency feedback function to be described later that promotes a frequency change according to the deviation of the system frequency. For example, the PCS 1 injects reactive power and applies positive feedback to changes in the system frequency. As a result, the frequency change of the system frequency increases. The PCS 1 detects an isolated operation when a preset isolated operation detection condition is met. On the other hand, when the output power Wo is balanced with the power consumed by the load, if the system power supply 3 fails, for example, the harmonic voltage distortion occurs in the output of the inverter unit 10 due to the influence of the excitation current in the pole transformer. To do. At this time, the PCS 1 detects a single operation by detecting a change in the harmonic voltage distortion and injecting reactive power to change the system frequency in order to lower the frequency.

  The PCS 1 also has a flicker suppression function that suppresses voltage flicker caused by the isolated operation detection function using the frequency feedback method. For example, even when a disturbance occurs in the system, the PCS 1 can suppress the occurrence of voltage flicker by temporarily reducing the gain of the frequency feedback function. In addition, even when the gain of the frequency feedback function is lowered, the PCS 1 includes a determination unit that determines the possibility of isolated operation and returns the gain of the frequency feedback function to the normal state at an appropriate timing. It can be detected properly.

  As shown in FIG. 1, the PCS 1 includes an inverter unit 10, a storage unit 11, a system frequency measurement unit 12, a frequency feedback unit 13, a reactive power step injection unit 14, an isolated operation detection unit 15, and a current control. A processing unit 16, a gain reduction determination unit 17, and a gain recovery determination unit 18 are provided.

  The inverter unit 10 converts the DC power supplied from the distributed power source 2 into AC power Wo, and outputs the AC power Wo to the energization path P between the inverter unit 10 and the system power source 3.

  The storage unit 11 is a non-transitory storage medium, and stores information and programs used in each unit of the PCS 1. The storage unit 11 also stores current distortion information, log information, and the like. The current distortion information is, for example, a data table in which the harmonic voltage distortion appearing at the output of the inverter unit 10 and the harmonic current distortion injected into the electric power converted by the inverter unit 10 of the PCS 1 are associated with each other. In the log information, the amount of harmonic current distortion injected in the past is recorded in time series.

  The system frequency measuring unit 12 measures the system frequency and calculates a frequency deviation by, for example, moving average processing of the system frequency.

  The frequency feedback unit 13 has a frequency feedback function that promotes the frequency change of the system frequency according to the deviation of the system frequency. The frequency feedback unit 13 calculates reactive power to be injected into the power converted by the inverter unit 10 in order to promote the shift of the system frequency. The frequency feedback unit 13 adds a later-described step injection amount of the reactive power calculated by the reactive power step injection unit 14 to the calculation result (that is, the reactive power for promoting the shift of the system frequency), thereby performing current control processing. Transmit to unit 16.

  The reactive power step injection unit 14 performs a process for step-injecting reactive power so as to force a system frequency deviation under a predetermined condition. For example, the reactive power step injection unit 14 performs a process of step-injecting reactive power in order to promote a frequency shift under a condition in which the frequency deviation is small even when an isolated operation occurs. When the output power Wo of the PCS 1 and the power consumption of the load are balanced during the single operation, the frequency deviation is small. The reactive power step injection unit 14 has a frequency deviation within a predetermined minute range (for example, within ± 0.01 [Hz]), and a variation amount of the fundamental voltage or the harmonic voltage distortion satisfies a predetermined condition. In some cases, it is determined that step injection is necessary. The fundamental wave voltage is a fundamental wave component included in the output voltage from the inverter unit 10. The harmonic voltage distortion is calculated based on harmonic components (secondary to seventh or higher) included in the output voltage from the inverter unit 10. The fundamental voltage and the harmonic voltage distortion can be measured by a measurement circuit (not shown) included in the reactive power step injection unit 14.

  The isolated operation detection unit 15 monitors the system frequency and detects isolated operation. The isolated operation detection unit 15 determines whether or not an isolated operation has occurred based on a change in the system frequency. The isolated operation detection unit 15 includes an active isolated operation determination unit (not shown) and a passive isolated operation determination unit (not shown) in detail.

  The current control processing unit 16 performs current control of the inverter unit 10 and injects reactive power based on information from the frequency feedback unit 13. The current control processing unit 16 injects appropriate reactive power through current control of the inverter unit 10 while performing synchronization processing based on the output of the system frequency measuring unit 12. Further, the current control processing unit 16 injects harmonic current distortion into the electric power converted by the inverter unit 10 based on a signal output from a gain recovery determination unit 18 described later. For example, the current control processing unit 16 injects an amount of harmonic current distortion corresponding to the harmonic voltage distortion into the electric power converted by the inverter unit 10 when a gain reduction process described later of the frequency feedback function is performed. .

  The harmonic voltage appearing at the output of the power conversion device 1 increases according to the line impedance of the current path P between the PCS 1 and the system power supply 3. Therefore, when the line impedance itself is known, the current control processing unit 16 may inject a harmonic current distortion corresponding to the known line impedance value into the electric power converted by the inverter unit 10. For example, the value of the line impedance may be acquired by means for detecting the line impedance itself of the energization path P, means for receiving an operation input of the line impedance, or the like. In this case, in the current distortion information, the harmonic voltage distortion appearing at the output of the inverter unit 10 only needs to be associated with the line impedance value.

  For example, when there is a possibility that voltage flicker occurs in the output (output power Wo) of the inverter unit 10, the gain reduction determination unit 17 determines whether or not the gain of the frequency feedback function is temporarily reduced. As shown in FIG. 1, the gain decrease determination unit 17 includes a current / voltage detection unit 171, a reactive power calculation unit 172, and a flicker determination unit 173.

  The current / voltage detection unit 171 is provided between the output side of the inverter unit 10 and the system power supply 3. Specifically, the current / voltage detection unit 171 includes a current detection circuit and a voltage detection circuit, and can detect a current and a voltage appearing in the output of the inverter unit 10.

  The reactive power calculation unit 172 acquires the current and voltage detected by the current / voltage detection unit 171 and calculates reactive power. The reactive power calculation unit 172 always calculates reactive power at predetermined intervals. The reactive power calculation unit 172 calculates the average value of reactive power retroactively from the present to a certain period in the past. The reactive power calculation unit 172 outputs the acquired reactive power value and the average value of the reactive power to the flicker determination unit 173.

  The flicker determination unit 173 determines the possibility of occurrence of voltage flicker based on the change in reactive power appearing at the output of the inverter unit 10. Specifically, the flicker determination unit 173 determines that there is a possibility that voltage flicker has occurred when the following first condition or second condition is satisfied. The first condition is a condition assuming a case where the reactive power is positive, and the second condition is a condition assuming a case where the reactive power is negative. The first condition is that the current reactive power value becomes larger than the first threshold value set in advance with respect to the average value of reactive power at the time point, and then the current reactive power value is reduced. Is the case. The second condition is such that the current reactive power value becomes smaller than a preset second threshold with respect to the average value of reactive power at that time, and then the current reactive power value increases. Is the case. The first threshold value and the second threshold value may be the same value or different values.

  The first condition is that the current reactive power value is larger than an added value obtained by adding a preset first threshold value to the average value of reactive power at the time, and then the current reactive power value is equal to or lower than the previous added value. It may be the case. The second condition is that the current reactive power value is smaller than a subtraction value obtained by subtracting a preset second threshold value from the average value of reactive power at the time, and then the current reactive power value is equal to or greater than the previous subtraction value. It may be the case.

  The first condition and the second condition may be configured such that the average value of reactive power is not used. In this case, the first condition may be a case where the current reactive power value becomes larger than a preset first threshold value, and then the current reactive power value becomes smaller. In addition, the second condition may be a case where the current reactive power value becomes smaller than a preset second threshold value and then the current reactive power value becomes larger. However, in the case of this method, a threshold table is prepared so that the threshold can be changed according to the output in consideration that the magnitude of the reactive power in the steady state may vary depending on the output of the power conversion device 1. It is preferable to do this.

  When it is determined that there is a possibility that voltage flicker has occurred, the information is transmitted to the current control processing unit 16, and gain reduction processing is performed in which the gain of the frequency feedback function of the frequency feedback unit 13 is temporarily reduced. . If the flicker determination unit 173 does not determine that there is a possibility that voltage flicker has occurred, the gain of the frequency feedback function of the frequency feedback unit 13 is maintained. That is, the determination of the possibility of occurrence of voltage flicker means determining whether or not to temporarily reduce the gain of the frequency feedback function. Note that the decrease in the gain of the frequency feedback function includes stopping the frequency feedback function (gain is zero).

  The current control processing unit 16 that has been notified that the voltage flicker may have occurred, for example, simultaneously superimposes the harmonic current distortion for a predetermined period (for example, one period) at the same time as the gain of the frequency feedback function is reduced. Perform current control. The harmonic current distortion may be, for example, a single order harmonic or a combination of a plurality of orders of harmonics. In some cases, the harmonics to be superimposed may be inter-order harmonics. The magnitude of the harmonic current distortion to be injected will be described later.

  The gain recovery determination unit 18 determines whether or not to end the gain reduction process when the gain of the frequency feedback function is reduced. As shown in FIG. 1, the gain recovery determination unit 18 includes a harmonic voltage detection unit 181, a harmonic distortion calculation unit 182, and an independent operation possibility determination unit 183.

  The harmonic voltage detection unit 181 is connected between the output side of the inverter unit 10 and the system power supply 3 and detects harmonic voltage distortion appearing in the output of the inverter unit 10 (that is, the output power Wo of the PCS 1).

  The harmonic distortion calculation unit 182 calculates the amount of change in harmonic voltage distortion. For the calculation of the harmonic voltage distortion, total harmonic distortion (THD) is used. For example, a value obtained by subtracting the average value of three total harmonic distortions from three cycles before to five cycles before the latest total harmonic distortion is the amount of change in total harmonic distortion (ie, harmonic voltage distortion). .

  Further, the harmonic distortion calculation unit 182 acquires and acquires the harmonic current distortion corresponding to the harmonic voltage distortion detected by the harmonic voltage detection unit 181 based on the current distortion information stored in the storage unit 11. A signal indicating the harmonic current distortion is output to the current control processing unit 16.

  Note that the harmonic voltage detection unit 181 and the harmonic distortion calculation unit 182 may share those provided in the reactive power step injection unit 14 in some cases. Further, the harmonic distortion calculation unit 182 replaces the total harmonic distortion with, for example, harmonic distortion of each order, harmonic distortion between orders, or some harmonic distortion of a plurality of orders. It is also possible to calculate the amount of change by calculating the total value.

  The isolated operation possibility determination unit 183 is a harmonic voltage distortion that appears at the output of the inverter unit 10 after the harmonic current distortion is injected by the current control processing unit 16 (more specifically, the amount or rate of change of the harmonic voltage distortion). ) To determine the possibility of isolated operation. It is preferable that the determination period and the harmonic current distortion injection period in the current control processing unit 16 be the same period.

  If the gain of the frequency feedback function is lowered when there is a possibility of an isolated operation, the detection of the isolated operation is delayed. For this reason, when it is determined that there is a possibility of isolated operation, the gain reduction processing of the frequency feedback function is terminated, and the normal operation is detected by returning to the normal frequency feedback function. On the other hand, when there is no possibility of independent operation, the gain of the frequency feedback function is reduced for a predetermined period. That is, the determination of the possibility of isolated operation means determining whether or not to end the gain reduction process of the frequency feedback function.

  Next, FIG. 2 is a flowchart for explaining an operation example of the PCS 1 when it is determined that there is a possibility that voltage flicker has occurred. The possibility of occurrence of voltage flicker is determined by monitoring the change in reactive power that appears on the system power supply 3 side by the gain reduction determination unit 17 as described above.

  If it is determined that voltage flicker may have occurred, the flicker possibility flag is turned on (step S1). When the flicker possibility flag is turned on, the current control processing unit 16 reduces the gain related to the feedback processing and processes information input from the frequency feedback unit 13. That is, the gain of the frequency feedback function by the frequency feedback unit 13 is reduced (step S2). At this time, the frequency feedback function may be stopped by setting the gain to zero.

  The current control processing unit 16 starts injecting a predetermined amount of harmonic current distortion simultaneously with the decrease in the gain related to the feedback processing (step S3). Note that the amount of harmonic current distortion (that is, the initial value) at this time is preferably a relatively large value, for example, 5% or less of the total harmonic distortion and 3% or less of the harmonic distortion at each hour. Is set to the value of Thereby, the harmonic voltage distortion appears greatly according to the injection amount of the harmonic current distortion, so that it is possible to improve the accuracy in the process of S6 described later.

  Next, the gain recovery determination unit 18 determines whether or not to end the gain reduction process of the frequency feedback function based on the harmonic voltage distortion when the harmonic current distortion is injected. First, the gain recovery determination unit 18 (more specifically, the isolated operation possibility determination unit 183) determines whether or not the amount of change in the harmonic voltage distortion (that is, the total harmonic distortion THD) is equal to or greater than a predetermined threshold. (Step S4).

  If the amount of change in harmonic voltage distortion is equal to or greater than the threshold (YES in step S4), there is a high possibility that an isolated operation has occurred during the gain reduction process. Specifically, even if the increase amount of the harmonic voltage distortion that appears when the isolated operation occurs due to the high line impedance of the current path P between the PCS 1 and the system power supply 3 is high, Higher harmonic voltage distortion appears depending on the amount of distortion injection. Therefore, the amount of change in the harmonic voltage distortion becomes equal to or greater than a predetermined threshold when an isolated operation occurs during the gain reduction process. And a process progresses to S9 mentioned later.

  On the other hand, if the amount of change in harmonic voltage distortion is not greater than or equal to the threshold value (NO in step S4), it is determined that there is no possibility of independent operation. If the harmonic current distortion corresponding to the line impedance has already been acquired (YES in step S5), the process proceeds to S8 described later. On the other hand, when the harmonic current distortion corresponding to the line impedance is not acquired (NO in step S5), the harmonic voltage distortion appearing in the output of the inverter unit 10 is detected and associated with the harmonic voltage distortion. Harmonic current distortion is acquired (step S6). The current control processing unit 16 starts injection of the harmonic current distortion in the amount acquired in S6 (step S7). Thereby, the harmonic voltage distortion appears greatly according to the injection amount of the harmonic current distortion, and the amount of change in the harmonic voltage distortion also increases when the single operation occurs. Then, the process proceeds to the next S8.

  In S8, when the predetermined time has not elapsed since the start of the gain reduction process of the frequency feedback function (NO in step S8), the process returns to step S4, and the possibility of the independent operation is determined again. On the other hand, if a predetermined time has elapsed since the start of the gain reduction process of the frequency feedback function (YES in step S8), the process proceeds to S9. The “predetermined time” in step S8 is not particularly limited, but is set to about 1 second, for example. If this time has passed, there is a high possibility that the voltage flicker has already been settled. Further, the frequency feedback function can be returned to the normal state in a relatively short time, and the isolated operation can be detected appropriately.

  Next, in step S9, the gain recovery determination unit 18 determines that there is a possibility of independent operation, and the flicker possibility flag is turned off. When the flicker possibility flag is turned off, the current control processing unit 16 finishes the gain reduction processing to recover the gain (step S10), and injects reactive power according to the information input from the frequency feedback unit 13. . That is, the frequency feedback function by the frequency feedback unit 13 is returned to the normal state, and the detection of the isolated operation can be accurately detected. Further, at the same time as the frequency feedback function is returned to the normal state, injection of harmonic current distortion is stopped (step S11). Then, the process of FIG. 2 ends.

  Note that the threshold value to be compared with the change amount of the harmonic voltage distortion in order to determine the possibility of isolated operation in S4 in FIG. 2 may be a predetermined constant value, but was acquired in S7. It may be reset to a value corresponding to the harmonic current distortion. For example, a predetermined initial value may be set as the threshold value in S4 in the first determination. The threshold value in S4 is smaller as the harmonic current distortion acquired in S7 is larger in the second and subsequent determinations so that a sudden increase in harmonic voltage distortion can be detected when there is a possibility of isolated operation. May be set to a larger value as the harmonic current distortion obtained in S7 is smaller. In this way, when there is a possibility that an isolated operation has occurred, the gain reduction processing can be more reliably completed and the gain of the frequency feedback function can be recovered.

  In addition, the threshold value (that is, initial value) used for the first determination in S4 is set according to the harmonic current distortion acquired recently (for example, the harmonic current distortion acquired last during the previous operation of PCS1). Also good. Alternatively, since the line impedance does not normally decrease, based on the log information stored in the storage unit 11, according to the maximum value of the harmonic current distortion injected by the current control processing unit 16 in the past. It may be set. In this way, a threshold value corresponding to the harmonic current distortion corresponding to the current line impedance can be set as an initial value.

  Moreover, in S5 of FIG. 2, it may be determined whether or not the harmonic current distortion corresponding to the line impedance has been acquired a plurality of times. And / or in S6, harmonic current distortion in an amount corresponding to the average value of a plurality of harmonic voltage distortions detected in a predetermined period may be injected. In this way, harmonic current distortion corresponding to the current line impedance can be obtained and injected with high accuracy.

  Moreover, in S6 of FIG. 2, when the line impedance of the current path P between the PCS 1 and the system power supply 3 is known, the harmonic current distortion associated with the value of the line impedance may be acquired.

  Further, the harmonic current distortion may be obtained using the harmonic voltage distortion detected in the state where the harmonic current distortion is not injected in S7 of FIG. 2, but as shown in FIG. In order to improve the accuracy of the harmonic current distortion, it is preferable to obtain the harmonic current distortion by using the harmonic voltage distortion detected in the state where is injected. This is because the harmonic voltage distortion appearing at the output of the inverter unit 10 when no isolated operation occurs is relatively small when the harmonic current distortion is not injected, but the harmonic current distortion is injected. It is because it appears larger than the case. Further, since the harmonic current distortion can be acquired with higher accuracy, the harmonic current distortion to be injected when it is determined that there is a possibility of occurrence of voltage flicker can be made closer to the necessary minimum amount. Therefore, the influence of the harmonic current distortion injection on the system power supply can be further reduced.

  Further, S8 in FIG. 2 may be omitted. That is, when flicker is detected in S1, the gain reduction process of the frequency feedback function is continued until the amount of change in harmonic voltage distortion (that is, total harmonic distortion THD) exceeds a predetermined threshold value in S4. Also good. When S8 is omitted in FIG. 2, the process after YES in S5 and the process after S7 return to S4.

  Moreover, the acquisition process of harmonic current distortion is not limited to the illustration of FIG. The harmonic current distortion takes into account the electric power Wo that the inverter unit 10 outputs to the energization path P (that is, the output electric power Wo of the PCS 1), and this output electric power Wo, the harmonic voltage distortion when the gain is reduced, and the current It may be detected based on distortion information. For example, the magnitude of the harmonic voltage distortion that appears corresponding to the same line impedance varies depending on the output power Wo. Therefore, for example, harmonic voltage distortion, output power Wo, and harmonic current distortion corresponding to the harmonic voltage distortion for each output power Wo may be associated with the current distortion information. In this case, for example, the harmonic current distortion corresponding to the magnitude of the harmonic voltage distortion corresponding to the output power Wo is obtained by a value indicated by the data table or an interpolation method (interpolation method, extrapolation method) using the value. Acquired and injected when lowering the gain of the frequency feedback function. In this way, it is possible to acquire and inject harmonic current distortion with higher accuracy in consideration of the output power Wo.

<First Modification of First Embodiment>
In this embodiment, when the possibility of occurrence of voltage flicker is detected, the current control processing unit 16 performs a gain reduction process of the frequency feedback function. However, this is only an example. As illustrated in FIG. 3, in the PCS 1, the gain reduction determination unit 17 may transmit the information to the frequency feedback unit 13 when determining that there is a possibility that voltage flicker has occurred. Thereby, the frequency feedback part 13 performs the gain reduction process of a frequency feedback function.

<Second Modification of First Embodiment>
In the present embodiment, the configuration is such that the possibility of voltage flicker is detected by monitoring the change in reactive power. However, this is only an example. FIG. 4 is a schematic diagram illustrating frequency deviation-injection reactive power characteristics of the PCS 1 according to the second modification of the first embodiment. As shown in FIG. 4, the frequency feedback unit 13 changes the reactive power calculation gain (first gain and second gain) with a frequency deviation of ± f [Hz] (for example, f = 0.01 Hz) as a boundary. Also good. When voltage flicker occurs, a phenomenon occurs in which the reactive power that becomes the second gain is injected and then the first gain is returned (or the second gain in the reverse direction). By using this phenomenon (gain switching), the possibility of occurrence of voltage flicker can be determined. For example, when the gain once decreased, it is determined that there is a possibility that voltage flicker has occurred.

  In addition, the detection of the possibility of voltage flicker may be configured using a voltage frequency instead of the method using reactive power described above. Alternatively, it may be determined that there is a possibility of voltage flicker when a periodic variation in reactive power or voltage frequency is detected.

  As described above, according to the present embodiment, the power conversion device 1 detects the isolated operation using the frequency feedback function that links the distributed power source 2 to the system power source 3 and promotes the frequency change according to the system frequency deviation. When the power voltage reduction unit 181 that detects the harmonic voltage appearing at the output of the power conversion device 1 and the gain reduction processing of the frequency feedback function are performed, the harmonic voltage, and A current control processing unit 16 that injects an amount of harmonic current corresponding to one of the line impedances between the system power supply and the power converter into the power converted by the power converter 1, and the harmonic current was injected. And a first determination unit 18 that determines whether or not to end the gain reduction process based on the harmonic voltage detected in the state.

  In addition, the control method of the power conversion apparatus 1 is a power conversion apparatus that detects a single operation using a frequency feedback function that links a distributed power supply 2 to a system power supply 3 and promotes a frequency change according to a system frequency deviation. 1, when the harmonic voltage (THD) appearing in the output of the power converter 1 is detected and the gain reduction processing of the frequency feedback function is performed, the harmonic voltage, the system power supply, Injecting a harmonic current in an amount corresponding to one of the line impedances between the power converters into the power converted by the power converter 1, and a harmonic detected in a state where the harmonic current is injected And a step of determining whether or not to end the gain reduction process based on the voltage.

  According to these configurations, the harmonic current injected when the gain reduction process of the frequency feedback function is performed can be increased according to the line impedance between the power converter 1 and the system power supply 3. This is because the harmonic voltage appearing at the output of the power converter 1 increases in accordance with the line impedance. Alternatively, when the line impedance itself is known, the above harmonic current can be increased according to the known line impedance. Therefore, by increasing the harmonic voltage by injecting the harmonic current, the gain reduction process can be completed more reliably and the frequency feedback when the isolated operation occurs without being greatly affected by the magnitude of the line impedance. Isolated operation can be detected by the function. Therefore, it is possible to more reliably detect an isolated operation using the frequency feedback function.

  The power conversion apparatus 1 having the above configuration is configured to further include a second determination unit 17 that determines whether or not to perform gain reduction processing when there is a possibility of occurrence of voltage flicker.

  According to this configuration, since it is possible to perform the gain reduction process when there is a possibility of occurrence of voltage flicker, it is possible to suppress the occurrence of voltage flicker due to the frequency feedback function.

  The power conversion device 1 having the above configuration is configured such that the current control processing unit 16 injects an amount of harmonic current according to the average value of a plurality of harmonic voltages detected in a predetermined period.

  According to this configuration, harmonic current distortion corresponding to the current line impedance can be obtained and injected with high accuracy.

  The power conversion device 1 having the above-described configuration is configured such that the current control processing unit 16 injects an amount of higher harmonic current corresponding to the output Wo of the power conversion device 1.

  According to this configuration, the harmonic current distortion can be accurately acquired and injected in consideration of the output Wo of the power conversion device 1.

  The power conversion device 1 having the above configuration is configured such that the first determination unit 18 ends the gain reduction process when the increase amount of the harmonic voltage that rapidly increases during the gain reduction process is equal to or greater than a threshold value.

  According to this configuration, when the increase amount of the harmonic voltage is equal to or greater than the threshold value, it is possible to detect that there is a possibility that the operation is independent. Therefore, by completing the gain reduction process, it is possible to detect an isolated operation by using the frequency feedback function.

  The power converter 1 having the above configuration is configured such that the threshold is set according to the amount of harmonic current injected by the current control processing unit 16. For example, the threshold is set to be smaller as the amount of harmonic current is larger and larger as the amount of harmonic current is smaller.

  According to this configuration, when there is a possibility that an isolated operation has occurred, the gain reduction process can be more reliably completed and the gain of the frequency feedback function can be recovered.

  The power conversion device 1 having the above-described configuration further includes a storage unit 11 that stores the harmonic current injected by the current control processing unit 16, and when the gain reduction process is performed, the initial value of the threshold is the harmonic value that was recently injected. The wave current or the harmonic current stored in the storage unit 11 is set according to the maximum value.

  According to this configuration, a threshold value corresponding to the harmonic current corresponding to the current line impedance can be set as an initial value.

Second Embodiment
Next, a second embodiment will be described. In the second embodiment, before it is determined that there is a possibility of occurrence of voltage flicker, the harmonic voltage distortion is detected in advance, and the harmonic current distortion injected during the gain reduction process is also acquired in advance. Hereinafter, a configuration different from the first embodiment will be described. Moreover, the same code | symbol is attached | subjected to the structure part similar to 1st Embodiment, and the description may be abbreviate | omitted.

  FIG. 5 is a flowchart for explaining the harmonic current distortion acquisition process in the second embodiment. When the operation of the PCS 1 is started (step 21), harmonic voltage distortion appearing in the output of the inverter unit 10 is detected (step S22). And the harmonic current distortion corresponding to the detected harmonic voltage distortion is acquired based on the current distortion information stored in the memory | storage part 11 (step S23).

  According to the process of FIG. 5, before it is determined that there is a possibility of occurrence of voltage flicker, the harmonic voltage distortion is detected and the harmonic current distortion is acquired in advance. Therefore, for example, even if an isolated operation occurs immediately after the start of the gain reduction process, a pre-acquired amount of harmonic current distortion is immediately injected, so a rapid increase in harmonic voltage distortion appearing at the output of the inverter unit 10 is detected. Easy to do. Therefore, when there is a possibility that an isolated operation has occurred, the gain reduction process can be completed more reliably.

  In addition, it is not limited to the illustration of FIG. 5, Acquisition of the harmonic voltage distortion in S22 may be implemented after the gain reduction process of a frequency feedback function is performed. That is, when the operation is started in S21, a gain reduction process for the frequency feedback function may be performed. After this, the harmonic voltage distortion is acquired in S22, and after the harmonic current distortion is acquired in S23, the gain reduction process is terminated and the gain is recovered. In this case, the current distortion information only needs to store the harmonic current distortion corresponding to the harmonic voltage distortion that appears when the gain reduction process is not performed.

  Further, the present invention is not limited to the example of FIG. 5, and the acquisition of the harmonic current distortion may be performed using the harmonic voltage distortion when a predetermined amount of the harmonic current distortion is injected in advance. In this way, harmonic current distortion can be acquired and injected with high accuracy. Therefore, the harmonic current distortion injected when it is determined that voltage flicker may occur can be brought closer to the necessary minimum amount, and the influence of the harmonic current distortion injection on the system power supply can be reduced. it can.

  Further, as shown in FIG. 5, it is possible to generate voltage flicker by acquiring the harmonic current distortion in advance before it is determined that there is a possibility of occurrence of voltage flicker (such as when the operation of the PCS 1 is started). The initial value of the harmonic current distortion injected in the gain reduction process after the determination can be set in advance.

  Moreover, the timing which acquires a harmonic current distortion beforehand is not limited to the illustration of FIG. That is, the acquisition timing does not have to be immediately after the start of the operation of the PCS 1 and may be before it is determined that there is a possibility of occurrence of voltage flicker. If it is determined that there is a possibility of occurrence of voltage flicker, as shown in FIG. 6, the isolated operation detection process using the frequency feedback function is performed while suppressing the occurrence of voltage flicker. In this way, it is not necessary to acquire harmonic current distortion when it is determined that voltage flicker may occur. For this reason, for example, even if an isolated operation occurs immediately after the gain of the frequency feedback function is reduced, a previously acquired amount of harmonic current distortion can be injected immediately.

  As described above, according to the present embodiment, the harmonic voltage detection unit 181 is configured to detect in advance the harmonic voltage before voltage flicker occurs.

  According to this configuration, for example, even if the single operation occurs immediately after the start of the gain reduction process of the frequency feedback function, the power conversion device 1 can immediately inject the harmonic current corresponding to the previously detected harmonic voltage. Therefore, it is possible to easily detect a sudden increase in the harmonic voltage appearing at the output of the inverter unit 10. Therefore, the power converter device 1 can more reliably end the gain reduction process of the frequency feedback function when there is a possibility that an isolated operation has occurred.

  Furthermore, the power converter device 1 having the above configuration is configured such that the harmonic voltage detection unit 181 detects the harmonic voltage when the power converter device 1 starts operation.

  According to this configuration, the initial value of the harmonic current injected when the gain reduction process is performed can be set in advance by detecting the harmonic voltage in advance at the start of operation.

<Third Embodiment>
Next, a third embodiment will be described. In the third embodiment, the harmonic voltage distortion is detected every certain period, and the harmonic current distortion is acquired. Hereinafter, a configuration different from the first embodiment will be described. Moreover, the same code | symbol is attached | subjected to the structure part similar to 1st Embodiment, and the description may be abbreviate | omitted.

  FIG. 7 is a flowchart for explaining the harmonic current distortion acquisition process in the third embodiment. Note that the acquisition timing in FIG. 7 is set to a point in time of a certain period, for example, daily, weekly, monthly, or yearly. Further, for example, the process of FIG. 7 is started when the operation of PCS1 is started, and is ended when the operation of PCS1 is stopped. Moreover, since the process of S22 and S23 of FIG. 7 is the same as that of FIG. 5 of 2nd Embodiment, these description is abbreviate | omitted.

  First, the PCS 1 determines whether or not the current time is the timing for acquiring the harmonic current distortion (step S31). If it is not the timing (NO in step S31), the process returns to S31. If it is the timing (YES in step S31), after the harmonic current distortion is acquired by the processes of S22 and S23, the process returns to S31.

  As described above, according to the present embodiment, the power conversion device 1 is configured such that the harmonic voltage detection unit 181 detects the harmonic voltage at regular intervals.

  According to this configuration, for example, the harmonic voltage is detected at regular intervals set in units of days, weeks, months, or years, and harmonic current distortion corresponding to the harmonic voltage is also acquired. Therefore, even if the line impedance changes due to aging degradation or the like, the power conversion device 1 suppresses the occurrence of voltage flicker under more suitable conditions (for example, injection of harmonic current closer to the necessary minimum). Independent operation can be detected.

  The embodiment of the present invention has been described above. The configurations of the embodiment and the modification described above are merely examples of the present invention. The configuration of the embodiment and the modification may be changed as appropriate without departing from the technical idea of the present invention. In addition, a plurality of embodiments and modifications may be implemented in combination within a possible range.

1 PCS
DESCRIPTION OF SYMBOLS 10 Inverter part 11 Memory | storage part 12 System frequency measurement part 13 Frequency feedback part 14 Reactive power step injection part 15 Independent operation detection part 16 Current control processing part 17 Gain fall determination part 171 Current / voltage detection part 172 Reactive power calculation part 173 Flicker determination Unit 18 Gain recovery determination unit 181 Harmonic voltage detection unit 182 Harmonic distortion calculation unit 183 Independent operation possibility determination unit 2 Distributed power source 3 System power source P Power supply path

Claims (11)

A power conversion device that detects a single operation using a frequency feedback function that links a distributed power source to a system power source and promotes a frequency change according to a deviation in the system frequency,
A harmonic voltage detector for detecting a harmonic voltage appearing in the output of the power converter;
When the gain reduction processing of the frequency feedback function is performed, an amount of harmonic current corresponding to one of the harmonic voltage and the line impedance between the system power supply and the power converter is converted to the power converter. A current control processing unit for injecting power to be converted at
A first determination unit that determines whether or not to end the gain reduction process based on the harmonic voltage detected in a state where the harmonic current is injected;
A power conversion device comprising:   The power converter according to claim 1, further comprising a second determination unit that determines whether or not to perform the gain reduction process when there is a possibility of occurrence of voltage flicker.   The power converter according to claim 1 or 2, wherein the current control processing unit injects the harmonic current in an amount corresponding to an average value of the plurality of harmonic voltages detected in a predetermined period.   The power converter according to any one of claims 1 to 3, wherein the current control processing unit injects an amount of the harmonic current that further corresponds to the output of the power converter.   The power converter according to any one of claims 1 to 4, wherein the harmonic voltage detection unit detects the harmonic voltage before voltage flicker is generated.   The power converter according to claim 5, wherein the harmonic voltage detector detects the harmonic voltage at the start of operation of the power converter.   The power conversion according to any one of claims 1 to 6, wherein the first determination unit terminates the gain reduction process when an increase amount of the harmonic voltage that rapidly increases during the gain reduction process exceeds a threshold value. apparatus.   The power converter according to claim 7, wherein the threshold is set according to an amount of the harmonic current injected by the current control processing unit. A storage unit for storing the harmonic current injected by the current control processing unit;
When the gain reduction process is performed, the initial value of the threshold is set according to the most recently injected harmonic current or the maximum value of the harmonic current stored in the storage unit. The power conversion device according to claim 8.   The said harmonic voltage detection part is a power converter device in any one of Claims 1-9 which detect the said harmonic voltage for every fixed period. A control method for a power converter that detects a single operation using a frequency feedback function that links a distributed power source to a system power source and promotes a frequency change according to a deviation in the system frequency,
Detecting a harmonic voltage appearing at the output of the power converter;
When the gain reduction processing of the frequency feedback function is performed, an amount of harmonic current corresponding to one of the harmonic voltage and the line impedance between the system power supply and the power converter is converted to the power converter. Injecting into power to be converted at
Determining whether to end the gain reduction process based on the harmonic voltage detected in a state where the harmonic current is injected;
The control method of a power converter device provided with.

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