JP6898719B2 - Power converter and its control method - Google Patents

Description

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

Conventionally, a power conversion device for connecting a distributed power source such as a solar cell to a system power source has been known. If the power converter is not disconnected from the grid power supply and continues to operate independently in the event of a power failure of the grid power supply, problems may occur from the viewpoint of security and ensuring the reliability of the power supply. For this purpose, the conventional power conversion device has a function of detecting the solitary operation, and when the solitary operation is detected, the conventional power conversion device disconnects itself from the system power supply. 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 independent operation.

In the above-mentioned frequency feedback type independent 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 conversion device is large, flicker (periodic voltage fluctuation) occurs in the system voltage due to the injection of reactive power. When flicker occurs, it causes an adverse effect such as flickering on other devices (for example, fluorescent lamps) connected to the system power supply, which causes a problem.

Therefore, in Patent Document 1 by the applicant of the present application, when flicker occurs, the gain of frequency feedback is temporarily lowered, and harmonic current distortion is injected into the power converted by the power conversion device. Then, when a rapid increase in harmonic voltage distortion that occurs when the solitary operation occurs is detected, the gain of the frequency feedback is recovered, and the power conversion device is stopped by the solitary operation detection of the frequency feedback method.

Japanese Patent Application No. 2016-047805

Japan Electrical Manufacturers' Association Standard JEM1498 (established on August 27, 2012)

As a result of further studies by the applicant, the harmonic voltage distortion increases as the line impedance between the system power supply and the power converter increases, but the amount and increase of the harmonic voltage distortion when independent operation occurs. It has been found that the velocity decreases with increasing line impedance. Therefore, in the isolated operation detection using a constant voltage threshold value, the increase amount of the harmonic voltage distortion may not exceed the voltage threshold value depending on the magnitude of the line impedance even if the isolated operation occurs. In this case, since the sudden increase in the harmonic voltage distortion during the independent operation cannot be detected, the gain of the frequency feedback cannot be recovered to detect the independent operation, and the power conversion device cannot be stopped. It was also found that when the line impedance becomes large, a time difference may occur between the time when the independent operation occurs and the time when the harmonic voltage distortion increases rapidly. The current rules stipulate that the power converter should be stopped within 0.2 [sec] from the occurrence of the isolated operation, but if the above time difference occurs, even if the isolated operation occurs, The power converter cannot be stopped immediately and the current rules cannot be observed. Furthermore, if a large harmonic current distortion is constantly injected, the effect is exerted on the voltage of the system power supply. Therefore, it is required that the harmonic current distortion as small as possible is appropriately injected.

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

In order to achieve the above object, the power conversion device according to one aspect of the present invention is independently operated by connecting a distributed power supply to a system power supply and utilizing a frequency feedback function that promotes a frequency change according to a deviation of the system frequency. The harmonic voltage detector that detects the harmonic voltage that appears in the output of the power converter, and the harmonic voltage and system when the gain reduction processing of the frequency feedback function is performed. A current control processing unit that injects an amount of harmonic current corresponding to one of the line impedances between the power supply and the power converter into the power converted by the power converter, and detection with the harmonic current injected. It is configured to include a first determination unit for determining whether or not to end the gain reduction process based on the generated harmonic voltage (first configuration).

The first power converter configuration, further comprising a second determination unit determines whether potential there voltage flicker Luke, current control processing unit, when there is a possibility of voltage flicker first 2 When the determination is made by the determination unit, the gain reduction process is performed (second configuration).

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

In the power conversion device having any of the first to third configurations, the current control processing unit is configured to inject a harmonic current in an amount further corresponding to the output of the power conversion device (fourth configuration). ..

In the power conversion device having any of the first to fourth configurations, the harmonic voltage detection unit has a configuration (fifth configuration) in which the harmonic voltage before the occurrence of voltage flicker is detected in advance.

In the power conversion device having the fifth configuration, the harmonic voltage detection unit has a configuration (sixth configuration) in which the harmonic voltage is detected at the start of operation of the power conversion device.

In the power conversion device having any of the first to sixth configurations, the first determination unit terminates the gain reduction process when the amount of increase in the harmonic voltage that rapidly increases during the gain reduction process exceeds the threshold value ( 7th configuration).

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

The power conversion device having 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 processing is performed, the initial value of the threshold value is the recently injected harmonic. The configuration is set according to the maximum value of the wave current or the harmonic current stored in the storage unit (nineth configuration).

The power conversion device having any of the first to ninth configurations has a configuration in which the harmonic voltage detection unit detects the harmonic voltage at regular intervals (tenth configuration).

In order to achieve the above object, the control method of the power conversion device according to one aspect of the present invention utilizes a frequency feedback function in which a distributed power supply is connected to a system power supply and a frequency change is promoted according to a deviation of the system frequency. It is a control method of the power conversion device that detects the independent operation, and when the step of detecting the harmonic voltage appearing at the output of the power conversion device and the gain reduction processing of the frequency feedback function are performed, the harmonic voltage and , The step of injecting 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, and the detection with the harmonic current injected. The configuration (11th configuration) includes a step of determining whether or not to end the gain reduction process based on the harmonic voltage.

According to the present invention, it is possible to provide a technique capable of more reliably detecting isolated operation using the frequency feedback function.

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

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

<First Embodiment>
FIG. 1 is a block diagram showing a configuration example of a PCS (Power Control System) 1 according to the first embodiment. The PCS 1 is a power conversion device capable of interconnecting the distributed power supply 2 with the system power supply 3, and is arranged between the distributed power supply 2 and the system power supply 3. The distributed power source 2 is not particularly limited, and examples thereof include renewable energy power generation facilities such as solar cells, fuel cells, and storage batteries. The grid power supply 3 is, for example, a power grid provided by an electric power company or the like. Although not shown in FIG. 1, there is a load connected to the pole transformer and the low-voltage distribution line between the PCS 1 and the system power supply 3. The pillar transformer steps down the high-voltage power sent from the high-voltage distribution line to low-voltage power and supplies it to the low-voltage distribution line.

The PCS1 has a frequency feedback type independent operation detection function with step injection. When 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 fails. At this time, the PCS1 detects the independent operation by using the frequency feedback function described later that promotes the frequency change according to the deviation of the system frequency. For example, PCS1 injects ineffective power to give positive feedback to changes in system frequency. As a result, the frequency change of the system frequency becomes large. The PCS1 detects the solitary operation when the preset solitary operation detection condition is satisfied. On the other hand, when the output power Wo and the power consumed by the load are balanced, if the system power supply 3 fails, harmonic voltage distortion occurs in the output of the inverter section 10 due to the influence of the exciting current in the pole transformer, for example. To do. At this time, the PCS1 detects a change in harmonic voltage distortion and detects independent operation by injecting ineffective power to change the system frequency in order to lower the frequency.

Further, the PCS1 has a flicker suppression function that suppresses voltage flicker caused by the independent operation detection function by the frequency feedback method. For example, the PCS1 can suppress the occurrence of voltage flicker by temporarily reducing the gain of the frequency feedback function even when a disturbance occurs in the system. Further, even when the gain of the frequency feedback function is lowered, the PCS1 is provided with a determination unit for determining the possibility of the independent operation, and the gain of the frequency feedback function is returned to the normal state by an appropriate timing, so that the independent operation is performed. It can be detected properly.

As shown in FIG. 1, the PCS1 includes an inverter unit 10, a storage unit 11, a system frequency measurement unit 12, a frequency feedback unit 13, an ineffective power step injection unit 14, an independent 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 DC power to the current-carrying path P between the distributed power source 3 and the system power source 3.

The storage unit 11 is a non-transient storage medium, and stores information, programs, and the like used in each unit of the PCS1. In addition, current distortion information, log information, and the like are also stored in the storage unit 11. 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 power converted by the inverter unit 10 of the PCS1 are associated with each other. Further, in the log information, the amount of harmonic current distortion injected in the past is recorded in chronological order.

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

The frequency feedback unit 13 has a frequency feedback function that promotes a frequency change of the system frequency according to the deviation of the system frequency. The frequency feedback unit 13 calculates the invalid 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 the calculation result (that is, the ineffective power for promoting the shift of the system frequency) to the step injection amount of the ineffective power calculated by the ineffective power step injection unit 14, which will be described later, to perform current control processing. It is transmitted to the unit 16.

The ineffective power step injection unit 14 performs a process for step injecting the ineffective power so as to forcibly cause a deviation of the system frequency under a predetermined condition. The ineffective power step injection unit 14 performs a process of step injecting the ineffective power in order to promote a frequency shift under the condition that the frequency deviation becomes small even when the independent operation occurs, for example. If the output power Wo of the PCS1 and the power consumption of the load are in equilibrium during independent operation, the frequency deviation becomes small. In the ineffective power step injection unit 14, the frequency deviation is within a predetermined minute range (for example, within ± 0.01 [Hz]), and the amount of change in the fundamental wave voltage or the harmonic voltage distortion satisfies the 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 the harmonic components (second to seventh order or higher) included in the output voltage from the inverter unit 10. The fundamental wave 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 independent operation detection unit 15 monitors the system frequency to detect the independent operation. The independent operation detection unit 15 determines whether or not the independent operation has occurred based on the change in the system frequency. In detail, the independent operation detection unit 15 includes an active type independent operation determination unit (not shown) and a passive type independent operation determination unit (not shown).

The current control processing unit 16 controls the current of the inverter unit 10 and injects the reactive power based on the information from the frequency feedback unit 13. The current control processing unit 16 performs synchronous processing based on the output of the system frequency measurement unit 12, and injects an appropriate invalid power by the current control of the inverter unit 10. Further, the current control processing unit 16 injects harmonic current distortion into the power converted by the inverter unit 10 based on the signal output from the 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 power converted by the inverter unit 10 when the gain reduction processing 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 energization 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 harmonic current distortion corresponding to the value of the known line impedance into the power converted by the inverter unit 10. For example, the value of the line impedance may be acquired by a means for detecting the line impedance itself of the current-carrying path P, a 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 may be associated with the line impedance value.

Gain reduction determination unit 17, for example, it determines whether potential there Luke not the voltage flicker in the output of the inverter unit 10 (output power Wo) occurs. As shown in FIG. 1, the gain reduction determination unit 17 includes a current / voltage detection unit 171, an ineffective 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. The current / voltage detection unit 171 includes a current detection circuit and a voltage detection circuit in detail, and can detect the current and the 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 the reactive power. The ineffective power calculation unit 172 always calculates the ineffective power at predetermined predetermined intervals. Further, the negative power calculation unit 172 calculates the average value of the negative power retroactively from the present to the past for a certain period of time. The ineffective power calculation unit 172 outputs the acquired ineffective power value and the average value of the ineffective power to the flicker determination unit 173.

The flicker determination unit 173 determines the possibility of voltage flicker generation based on the change in the ineffective power appearing in the output of the inverter unit 10. Specifically, the flicker determination unit 173 determines that voltage flicker may have occurred when the following first condition or second condition is satisfied. The first condition is a condition assuming a case where the negative power is positive, and the second condition is a condition assuming a case where the negative power is negative. The first condition is that the current disabled power value increases beyond the preset first threshold value with respect to the average value of the disabled power at that time point, and then the current disabled power value turns to decrease. If this is the case. The second condition is that the current disabled power value becomes smaller than the preset second threshold value with respect to the average value of the disabled power at that time, and then the current disabled power value turns to increase. If this 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 disabled power value becomes larger than the added value obtained by adding the preset first threshold value to the average value of the disabled power at that time, and then the current disabled power value is equal to or less than the previous added value. It may be the case that becomes. The second condition is that the current disabled power value is less than the subtracted value obtained by subtracting the preset second threshold value from the average value of the disabled power at that time, and then the current disabled power value is equal to or greater than the previous subtracted value. It may be the case that becomes.

The first condition and the second condition may be configured so that the average value of the ineffective power is not used. In this case, the first condition may be a case where the current ineffective power value becomes larger than the preset first threshold value and then turns in the direction in which the current inactive power value becomes smaller. Further, the second condition may be a case where the current disabled power value becomes smaller than the preset second threshold value, and then the current disabled power value changes to a larger direction. However, in the case of this method, a threshold table is prepared so that the threshold can be changed according to the output, considering that the magnitude of the invalid power in the steady state may differ depending on the output of the power converter 1. It is preferable to do so.

When it is determined that voltage flicker may have 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 voltage flicker may have occurred, the gain of the frequency feedback function of the frequency feedback unit 13 is maintained. That is, the determination of the possibility of voltage flicker generation means determining whether or not the gain of the frequency feedback function is temporarily reduced. The decrease in the gain of the frequency feedback function includes the stop of the frequency feedback function (gain is zero).

The current control processing unit 16 transmitted that the voltage flicker may have occurred so as to superimpose the harmonic current distortion for a predetermined period (for example, one cycle, etc.) at the same time as the gain of the frequency feedback function is lowered, for example. Perform current control. This harmonic current distortion may be, for example, a harmonic of a certain single order, or may be a sum of harmonics of a plurality of orders. Further, in some cases, the harmonics to be superposed may be inter-degree 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 the harmonic voltage distortion that appears at the output of the inverter unit 10 (that is, the output power Wo of the PCS1).

The harmonic distortion calculation unit 182 calculates the amount of change in the harmonic voltage distortion. Total harmonic distortion (THD) is used in the calculation of harmonic voltage distortion. For example, the value obtained by subtracting the average value of the three total harmonic distortions from 3 cycles before to 5 cycles before from the latest total harmonic distortion is regarded as the amount of change in the total harmonic distortion (that is, 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.

In some cases, the harmonic voltage detection unit 181 and the harmonic distortion calculation unit 182 may share the one provided in the ineffective power step injection unit 14. Further, the harmonic distortion calculation unit 182 replaces the total harmonic distortion with, for example, the harmonic distortion of each order, the harmonic distortion between orders, or some harmonic distortion of a plurality of orders. The total value of is calculated, and the amount of change thereof may be calculated.

In the independent operation possibility determination unit 183, the harmonic voltage distortion (more specifically, the amount of change or the rate of change of the 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. ) To determine the possibility of independent operation. It is preferable that the determination period and the harmonic current distortion injection period in the current control processing unit 16 are the same period.

If the gain of the frequency feedback function is lowered when there is a possibility of the solitary operation, the detection of the solitary operation is delayed. Therefore, when it is determined that there is a possibility of the independent operation, the gain reduction processing of the frequency feedback function is terminated, and the normal frequency feedback function is returned to detect the independent operation. 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 independent 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 PCS1 when it is determined that voltage flicker may have occurred. As described above, the possibility of voltage flicker is determined by the gain reduction determination unit 17 monitoring the change in the ineffective power appearing on the system power supply 3 side.

When 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 lowers the gain related to the feedback processing and processes the 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 with the gain set to zero.

The current control processing unit 16 starts injecting a predetermined amount of harmonic current distortion at the same time as the gain related to the feedback processing decreases (step S3). 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 of each hour. Is set to the value of. As a result, the harmonic voltage distortion appears large according to the injection amount of the harmonic current distortion, so that the accuracy in the processing of S6 described later can be improved.

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 independent 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 value. (Step S4).

If the amount of change in the harmonic voltage distortion is equal to or greater than the threshold value (YES in step S4), it is highly possible that the independent operation has occurred during the gain reduction process. Specifically, even in a state where it is difficult for the increase in harmonic voltage distortion that appears when independent operation occurs due to the high line impedance of the energization path P between the PCS 1 and the system power supply 3, the harmonic current Harmonic voltage distortion becomes large according to the amount of distortion injected. Therefore, the amount of change in the harmonic voltage distortion becomes equal to or greater than a predetermined threshold value when the independent operation occurs during the gain reduction process. Then, the process proceeds to S9, which will be described later.

On the other hand, if the amount of change in the harmonic voltage distortion is not equal to or greater than the threshold value (NO in step S4), it is determined that there is no possibility of independent operation. Here, when the harmonic current distortion corresponding to the line impedance has 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 at 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 amount of harmonic current distortion acquired in S6 (step S7). As a result, the harmonic voltage distortion appears large according to the injection amount of the harmonic current distortion, and the amount of change in the harmonic voltage distortion also becomes large when the independent operation occurs. Then, the process proceeds to the next S8.

In S8, if a predetermined time has not elapsed from 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 independent operation is determined again. On the other hand, when a predetermined time has elapsed from 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, for example, about 1 second. After this amount of time, it is highly possible that the voltage flicker has already subsided. In addition, the frequency feedback function can be returned to the normal state in a relatively short time, and independent operation can be appropriately detected.

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 the invalid 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 independent operation can be accurately detected. Further, at the same time that the frequency feedback function is returned to the normal state, the injection of harmonic current distortion is stopped (step S11). Then, the process of FIG. 2 is completed.

The threshold value to be compared with the amount of change in the harmonic voltage distortion in order to determine the possibility of the occurrence of independent operation in S4 of FIG. 2 may be a predetermined constant value, but was acquired in S7. The value may be reset according to the harmonic current distortion. For example, the threshold value in S4 may be set to a predetermined initial value in the initial determination. Then, the threshold value in S4 is a value smaller as the harmonic current distortion acquired in S7 is larger to the extent that a rapid increase in harmonic voltage distortion can be detected when there is a possibility of independent operation occurring in the second and subsequent determinations. The smaller the harmonic current distortion acquired in S7, the larger the value may be set. In this way, when there is a possibility that the independent operation has occurred, the gain reduction process can be completed more reliably and the gain of the frequency feedback function can be recovered.

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

Further, 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, an amount of harmonic current distortion corresponding to the average value of the plurality of harmonic voltage distortions detected in a predetermined period may be injected. In this way, the harmonic current distortion corresponding to the current line impedance can be accurately acquired and injected.

Further, in S6 of FIG. 2, when the line impedance of the energization 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 in S7 of FIG. 2 may be acquired by using the harmonic voltage distortion detected in the state where the harmonic current distortion is not injected, but as shown in FIG. 2, the harmonic current distortion may be acquired. It is preferable to acquire the harmonic voltage distortion detected in the injected state in order to improve the accuracy of the harmonic current distortion. This is because the harmonic voltage distortion that appears at the output of the inverter unit 10 when the independent operation does not occur is relatively small when the harmonic current distortion is not injected, but the harmonic current distortion is injected. This 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 voltage flicker may occur can be made closer to the minimum necessary amount. Therefore, the influence of the injection of harmonic current distortion on the system power supply can be made smaller.

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

Further, the acquisition process of the harmonic current distortion is not limited to the example of FIG. The harmonic current distortion takes into consideration the power Wo output to the current-carrying path P by the inverter unit 10 (that is, the output power Wo of the PCS1), and the output power Wo, the harmonic voltage distortion when the gain is lowered, and the current. It may be detected based on the distortion information. For example, the magnitude of the harmonic voltage distortion that appears corresponding to the same line impedance differs depending on the output power Wo. Therefore, for example, the harmonic voltage distortion, the output power Wo, and the 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, by the value shown in the data table or the interpolation method (interpolation method, interpolation method) using the value, the harmonic current distortion corresponding to the magnitude of the harmonic voltage distortion according to the output power Wo is obtained. It is acquired and injected when reducing the gain of the frequency feedback function. In this way, the harmonic current distortion can be acquired and injected more accurately in consideration of the output power Wo.

<First modification of the first embodiment>
In the present embodiment, when the possibility of voltage flicker is detected, the current control processing unit 16 performs the gain reduction processing of the frequency feedback function. However, this is just an example. As shown in FIG. 3, in the PCS1, the gain decrease determination unit 17 may be configured to transmit the information to the frequency feedback unit 13 when it is determined that the voltage flicker may have occurred. As a result, the frequency feedback unit 13 performs the gain reduction processing of the frequency feedback function.

<Second modification of the first embodiment>
Further, in the present embodiment, the configuration is such that the change in the reactive power is monitored to detect the possibility of voltage flicker. However, this is just an example. FIG. 4 is a schematic diagram showing the frequency deviation-injection ineffective power characteristic of PCS1 according to the second modification of the first embodiment. As shown in FIG. 4, the frequency feedback unit 13 changes the gains (first gain and second gain) of the invalid power calculation when the frequency deviation is ± f [Hz] (for example, f = 0.01 Hz). May be good. When voltage flicker occurs, a phenomenon occurs in which the voltage flicker is injected and then returned to the first gain (or the second gain is in the opposite direction). This phenomenon (gain switching) can be used to determine the possibility of voltage flicker. For example, when the gain once mentioned drops, it is determined that voltage flicker may have occurred.

In addition, the detection of the possibility of voltage flicker may be configured by using a voltage frequency instead of the above-mentioned method using ineffective power. Further, it may be determined that there is a possibility of voltage flicker when an invalid power or a periodic fluctuation of the voltage frequency is detected.

As described above, according to the present embodiment, the power conversion device 1 detects the independent operation by connecting the distributed power supply 2 to the system power supply 3 and using the frequency feedback function that promotes the frequency change according to the deviation of the system frequency. When the harmonic voltage detection 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 power conversion device 1 is used. The harmonic current was injected into the 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 conversion device into the power converted by the power conversion device 1. The configuration includes a first determination unit 18 for determining whether or not to end the gain reduction process based on the harmonic voltage detected in the state.

Further, the control method of the power conversion device 1 is a power conversion device that detects independent operation by connecting the distributed power supply 2 to the system power supply 3 and using a frequency feedback function that promotes a frequency change according to the deviation of the system frequency. In the control method of 1, when the step of detecting the harmonic voltage (THD) appearing in the output of the power converter 1 and the gain reduction processing of the frequency feedback function are performed, the harmonic voltage, the system power supply, and the system power supply are performed. A step of 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 with the harmonic current injected. The configuration includes 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 processing of the frequency feedback function is performed can be increased according to the line impedance between the power conversion device 1 and the system power supply 3. This is because the harmonic voltage appearing at the output of the power converter 1 increases according to the line impedance. Alternatively, when the line impedance itself is known, the above-mentioned 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 is more reliably completed and the frequency feedback occurs when the independent operation occurs without being significantly affected by the magnitude of the line impedance. The function can detect independent operation. Therefore, it is possible to more reliably detect the isolated operation using the frequency feedback function.

Power converter 1 of the above configuration, further comprising a second determination unit 17 determines whether potential there voltage flicker Luke, current control processing unit 16, when there is a possibility of voltage flicker first 2 When the determination is made by the determination unit 17, the gain reduction process is performed .

According to this configuration, the gain reduction processing can be performed when there is a possibility that voltage flicker may occur, so that the occurrence of voltage flicker due to the frequency feedback function can be suppressed.

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 corresponding to the average value of a plurality of harmonic voltages detected in a predetermined period.

According to this configuration, the harmonic current distortion corresponding to the current line impedance can be accurately acquired and injected.

In the power conversion device 1 having the above configuration, the current control processing unit 16 is configured to inject an amount of harmonic current further 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.

In the power conversion device 1 having the above configuration, the first determination unit 18 is configured to end the gain reduction process when the amount of increase in the harmonic voltage that rapidly increases during the gain reduction process exceeds the threshold value.

According to this configuration, when the amount of increase in the harmonic voltage becomes equal to or greater than the threshold value, it is possible to detect that the operation may have become independent. Therefore, by ending the gain reduction process, it is possible to detect the independent operation by using the frequency feedback function.

The power conversion device 1 having the above configuration has a configuration in which the threshold value is set according to the amount of harmonic current injected by the current control processing unit 16. For example, the threshold value is set 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 the independent operation has occurred, the gain reduction process can be completed more reliably and the gain of the frequency feedback function can be recovered.

The power conversion device 1 having the above 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 processing is performed, the initial value of the threshold value is the recently injected harmonic. The configuration is set according to the maximum value of the wave current or the harmonic current stored in the storage unit 11.

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, the second embodiment will be described. In the second embodiment, the harmonic voltage distortion is detected in advance before it is determined that voltage flicker may occur, and the harmonic current distortion to be injected during the gain reduction process is also acquired in advance. Hereinafter, a configuration different from that of the first embodiment will be described. Further, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof may be omitted.

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

According to the process of FIG. 5, the harmonic voltage distortion is detected and the harmonic current distortion is acquired in advance before it is determined that the voltage flicker may occur. Therefore, for example, even if the independent operation occurs immediately after the start of the gain reduction process, the amount of harmonic current distortion acquired in advance is immediately injected, so that a sudden increase in harmonic voltage distortion appearing at the output of the inverter unit 10 is detected. It can be made easy. Therefore, when there is a possibility that the independent operation has occurred, the gain reduction process can be completed more reliably.

The acquisition of the harmonic voltage distortion in S22 is not limited to the example of FIG. 5, and may be performed after the gain reduction processing of the frequency feedback function is performed. That is, when the operation is started in S21, the gain reduction processing of the frequency feedback function may be performed. After that, the harmonic voltage distortion is acquired in S22, the harmonic current distortion is acquired in S23, and then the gain reduction process is completed to recover the gain. In this case, the current distortion information may store the harmonic current distortion corresponding to the harmonic voltage distortion that appears when the gain reduction processing is not performed.

Further, the acquisition of the harmonic current distortion is not limited to the example of FIG. 5, and the acquisition of the harmonic current distortion may be performed by using the harmonic voltage distortion when a predetermined amount of harmonic current distortion is injected in advance. In this way, the harmonic current distortion can be accurately acquired and injected. Therefore, the harmonic current distortion to be injected when it is determined that voltage flicker may occur can be made closer to the minimum necessary amount, and the effect of the injection of harmonic current distortion on the system power supply is smaller. it can.

Further, as shown in FIG. 5, it is considered that voltage flicker may occur by acquiring harmonic current distortion in advance before it is determined that voltage flicker may occur (such as when the operation of PCS1 is started). The initial value of the harmonic current distortion injected in the gain reduction process after the determination can be set in advance.

Further, the timing of acquiring the harmonic current distortion in advance is not limited to the example of FIG. That is, the acquisition timing does not have to be immediately after the start of operation of the PCS1 and may be before it is determined that voltage flicker may occur. Then, when it is determined that voltage flicker may occur, as shown in FIG. 6, detection processing for independent operation using the frequency feedback function is performed while suppressing the occurrence of voltage flicker. In this way, it is not necessary to acquire the harmonic current distortion when it is determined that voltage flicker may occur. Therefore, for example, even if the independent operation occurs immediately after the gain of the frequency feedback function is lowered, the harmonic current distortion of the amount acquired in advance can be immediately injected.

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

According to this configuration, for example, even if the independent operation occurs immediately after the start of the gain reduction processing of the frequency feedback function, the power conversion device 1 can immediately inject the harmonic current corresponding to the harmonic voltage detected in advance. 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 conversion device 1 can more reliably end the gain reduction process of the frequency feedback function when there is a possibility that the independent operation has occurred.

Further, in the power conversion device 1 having the above configuration, the harmonic voltage detection unit 181 is configured to detect the harmonic voltage at the start of operation of the power conversion device 1.

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

<Third Embodiment>
Next, the third embodiment will be described. In the third embodiment, the harmonic voltage distortion is detected at regular intervals and the harmonic current distortion is acquired. Hereinafter, a configuration different from that of the first embodiment will be described. Further, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof may be omitted.

FIG. 7 is a flowchart for explaining the acquisition process of the harmonic current distortion in the third embodiment. The acquisition timing in FIG. 7 is set at a fixed period of time, for example, daily, weekly, monthly, or yearly. Further, the process of FIG. 7 starts, for example, when the operation of the PCS1 starts, and ends when the operation of the PCS1 is stopped. Further, since the processing of S22 and S23 of FIG. 7 is the same as that of FIG. 5 of the second embodiment, the description thereof will be omitted.

First, the PCS1 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), the process returns to S31 after the harmonic current distortion is acquired by the processes of S22 and S23.

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, the harmonic voltage is detected at regular intervals set on a daily, weekly, monthly, or yearly basis, and the harmonic current distortion corresponding to the harmonic voltage is also acquired. Therefore, even if the line impedance changes due to aged deterioration or the like, the power converter 1 suppresses the occurrence of voltage flicker under more suitable conditions (for example, injection of a harmonic current closer to the minimum necessary). , Can detect independent operation.

The embodiment of the present invention has been described above. The configurations of the embodiments and modifications shown above are merely examples of the present invention. The configurations of the embodiments and modifications may be appropriately changed without exceeding the technical idea of the present invention. Moreover, a plurality of embodiments and modifications may be carried out in combination to the extent possible.

1 PCS
10 Inverter unit 11 Storage unit 12 System frequency measurement unit 13 Frequency feedback unit 14 Invalid power step injection unit 15 Independent operation detection unit 16 Current control processing unit 17 Gain drop judgment unit 171 Current / voltage detection unit 172 Invalid power calculation unit 173 Flicker judgment Unit 18 Gain recovery judgment unit 181 Harmonic voltage detection unit 182 Harmonic distortion calculation unit 183 Independent operation possibility judgment unit 2 Distributed power supply 3 System power supply P Current path

Claims (10)

It is a power conversion device that detects independent operation by connecting a distributed power supply to a grid power supply and using a frequency feedback function that promotes a frequency change according to the deviation of the grid frequency.
Comprising a first determination unit, a harmonic voltage detecting unit, and a current control processing unit, a second determination unit, a
The first determination unit determines whether or not voltage flicker may occur, and determines whether or not voltage flicker may occur.
When the first determination unit determines that voltage flicker may occur, the current control processing unit performs gain reduction processing of the frequency feedback function.
The harmonic voltage detection unit detects the harmonic voltage appearing at the output of the power converter, and detects the harmonic voltage.
When the gain reduction processing is performed, the current control processing unit obtains a harmonic current in an amount corresponding to one of the harmonic voltage and the line impedance between the system power supply and the power conversion device. Inject into the power converted by the power converter,
The second determination unit, on the basis of the harmonic the harmonic voltage a current is detected in a state of being injected, the power converter determine whether or not to end the gain reduction processing. The power conversion device according to claim 1 , wherein the current control processing unit injects the harmonic current in an amount corresponding to an average value of a plurality of the harmonic voltages detected in a predetermined period. The power conversion device according to claim 1 or 2 , wherein the current control processing unit injects the harmonic current in an amount further corresponding to the output of the power conversion device. The power conversion device according to any one of claims 1 to 3 , wherein the harmonic voltage detection unit detects the harmonic voltage before the occurrence of voltage flicker in advance. The power conversion device according to claim 4 , wherein the harmonic voltage detection unit detects the harmonic voltage at the start of operation of the power conversion device. The power conversion according to any one of claims 1 to 5 , wherein the second determination unit terminates the gain reduction process when the amount of increase in the harmonic voltage that rapidly increases during the gain reduction process exceeds a threshold value. apparatus. The power conversion device according to claim 6 , wherein the threshold value is set according to the 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 is further provided.
When the gain reduction process is performed, the initial value of the threshold value is set according to the maximum value of the recently injected harmonic current or the harmonic current stored in the storage unit. The power conversion device according to claim 7. The power conversion device according to any one of claims 1 to 8 , wherein the harmonic voltage detection unit detects the harmonic voltage at regular intervals. It is a control method of a power conversion device that detects independent operation by connecting a distributed power supply to a grid power supply and using a frequency feedback function that promotes a frequency change according to the deviation of the grid frequency.
Steps to determine if there is a possibility of voltage flicker,
When it is determined that voltage flicker may occur, the step of performing the gain reduction processing of the frequency feedback function and
The step of detecting the harmonic voltage appearing at the output of the power converter, and
When the gain reduction process is performed, the power converter converts 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. And the step of injecting into the electric power
A step of determining whether or not to end the gain reduction process based on the harmonic voltage detected in the state where the harmonic current is injected, and
A method of controlling a power converter including.

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