JP2017163719A - Power conversion equipment and individual operation detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology that can detect an individual operation appropriately in an active manner without generating a voltage flicker.SOLUTION: An individual operation detection method that detects an individual operation of power conversion equipment 1 which interconnects a distributed power source 2 to a system power supply 3 comprises a first step that superimposes a predetermined order of current harmonic wave into an output of an inverter unit 10 to encourage a change of the predetermined order of voltage harmonic wave appearing at an output side of the inverter unit 10 which converts direct-current power supplied from the distributed power source 2 to alternating-current power to output, a second step that judges about whether to switch the predetermined order of harmonic wave utilized in the first step, and a third step that detects the individual operation according to the predetermined order of switching pattern.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a power converter and an isolated operation detection method.

  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 is provided with the function which detects an independent operation (for example, refer to patent documents 1). When the power conversion device detects an isolated operation, the power conversion device disconnects itself from the system power supply.

  Non-Patent Document 1, which defines a new interconnection regulation for PCS (power conditioning system) for PV (photovoltaic) systems, discloses a frequency feedback method with step injection as a common technique for performing active islanding detection. FIG. 4 is a block diagram showing a configuration of a conventional power conversion device 100 having a frequency feedback type isolated operation detection function with step injection.

  The power converter (PCS) 100 is disposed between the distributed power source 2 and the system power source 3. Although not shown in the figure, between the power converter 100 and the system power supply 3, a pole transformer or a low-voltage distribution that lowers the high-voltage power sent from the high-voltage distribution line to the low-voltage distribution line and supplies the low-voltage distribution line There is a load connected to the electric wire.

  The power conversion apparatus 100 includes an inverter unit 101 that converts DC power supplied from the distributed power supply 2 into AC power. In addition, the power conversion apparatus 100 includes a current control processing unit 102 that performs current control of the inverter unit 101. Furthermore, the power conversion device 100 includes a system frequency measurement unit 103, a frequency feedback unit 104, a reactive power step injection unit 105, and an isolated operation detection unit 106 so that the isolated operation can be detected.

  The system frequency measuring unit 103 measures the system frequency used for calculating the frequency deviation. The frequency feedback unit 104 calculates the reactive power to be injected from the system frequency deviation calculated by the moving average process and prompts the frequency shift. The reactive power step injection unit 105 performs a process of step-injecting reactive power in order to promote a frequency shift under the condition that the frequency deviation is small even when an isolated operation occurs. It should be noted that the frequency deviation becomes minute when the output power of the power converter 100 and the power consumption of the load are balanced during the single operation of the power converter 100.

  The reactive power step injection unit 105 has a frequency deviation within a predetermined minute range (for example, within ± 0.01 Hz), and when the change amount of the fundamental wave voltage or the voltage harmonic distortion satisfies a predetermined condition, Determine that step injection is required. The fundamental wave voltage is a fundamental wave component included in the output voltage from the inverter unit 101. The voltage harmonic distortion is calculated based on harmonic components (secondary to seventh or higher) included in the output voltage from the inverter unit 101. The fundamental voltage and the harmonic voltage can be measured by a measurement circuit included in the reactive power step injection unit 105. The frequency feedback unit 104 adds the reactive power injection amount calculated by the reactive power step injection unit 105 to the reactive power injection amount calculated from the frequency deviation, and transmits the sum to the current control processing unit 102.

  The isolated operation detection unit 106 determines whether or not an isolated operation has occurred based on a change in system frequency. In detail, the isolated operation detection unit 106 includes an active isolated operation determination unit and a passive isolated operation determination unit. The current control processing unit 102 performs current control of the inverter unit 101 so as to inject appropriate reactive power while performing synchronization processing based on the output of the system frequency measurement unit 103.

  Next, the independent operation detection operation of the frequency feedback method with step injection in the power conversion device 100 configured as described above will be described.

  In the power imbalance state between the power converter 100 and the load, the system frequency changes after a power failure of the system power supply 3. Therefore, reactive power is injected by the frequency feedback unit 104, and positive feedback is applied to the frequency change. As a result, the frequency change of the system frequency is increased to reach the isolated operation detection condition (preset), and the isolated operation is detected.

  In a state where the power conversion device 100 and the load are in a power balance, voltage harmonics are generated in the output from the inverter unit 101 due to the influence of the excitation current in the pole transformer after the power failure of the system power supply 3. For this reason, the reactive power step injection unit 105 detects a change in voltage harmonic distortion and injects reactive power so as to reduce the frequency. As a result, the frequency changes and the frequency change is prompted by the frequency feedback unit 104. As a result, isolated operation is detected.

JP2015-220835A JP 2008-259400 A Japanese Patent Laid-Open No. 11-127542

Japan Electrical Manufacturers Association Standard JEM1498 (Established 2012.8.27)

  When the above-described frequency feedback type isolated operation detection function is provided, the frequency feedback unit 104 promotes the frequency change even when a disturbance occurs in the system power supply 3. At this time, if the system impedance is large, flicker (periodic voltage fluctuation) occurs in the system voltage due to injection of reactive power (see, for example, Patent Document 2). When voltage flicker occurs, there is a problem because an adverse effect such as flickering occurs on a device connected to the system power supply 3 such as a fluorescent lamp.

  In order not to cause voltage flicker, it is conceivable to stop the frequency feedback control and adopt the isolated operation detection method described in Patent Document 3, for example. In the islanding operation detection method of Patent Literature 3, the islanding operation is detected by superimposing the harmonic current on the output current of the inverter and detecting the voltage harmonic appearing on the system side. Patent Document 3 also discloses that the harmonic component of the system voltage is separated and positively fed back to the output current of the inverter.

  However, in the configuration disclosed in Patent Document 3, the order of the harmonic current to be superimposed on the output current of the inverter is maintained at a specific order (for example, third order or fifth order). For example, when current harmonics of a specific order are superimposed so as to apply positive feedback due to the occurrence of disturbance, the magnitude of the harmonic voltage distortion generated according to the superimposed harmonic current depends on the value of the system impedance again. There is a case where the same harmonic current is injected and the amount of distortion injection current and the magnitude of the voltage distortion generated are stagnant in that state. That is, there is a case where a specific order voltage harmonic is always superimposed by injection of a specific order current harmonic. In this case, there is a possibility that the isolated operation cannot be detected while achieving the specified value of the current harmonic output of the power converter, which is within 3% of each harmonic distortion and within 5% of the total harmonic distortion. .

  In view of the above, it is an object of the present invention to provide a technique capable of appropriately detecting an isolated operation in an active manner without causing voltage flicker.

  In order to achieve the above object, a power conversion device according to an aspect of the present invention is a power conversion device that links a distributed power source to a system power source, and converts the DC power supplied from the distributed power source into AC power. An inverter unit that converts and outputs, a harmonic detection unit that detects a first harmonic appearing on the output side of the inverter unit, and a first harmonic of a predetermined order according to the detection result of the harmonic detection unit A harmonic feedback unit that performs processing for prompting a change in the frequency of the inverter unit, and the inverter unit so as to superimpose the second harmonic of the predetermined order on the output of the inverter unit according to information from the harmonic feedback unit A control processing unit that performs control processing, a determination unit that determines whether or not to switch the predetermined order based on a detection result of the harmonic detection unit, a change in the first harmonic, and a single operation detection An independent operation detection unit, and when the determination unit determines that the predetermined order is to be switched, the harmonic feedback unit and the control processing unit execute processing by switching the predetermined order (first 1 configuration).

  In the power conversion device having the first configuration, the isolated operation detection unit may be configured to detect the isolated operation according to the switching pattern of the predetermined order (second configuration).

  In the power conversion device having the first or second configuration, the first harmonic may be a voltage harmonic, and the second harmonic may be a current harmonic (third configuration).

  In the power conversion device having any one of the first to third configurations, the predetermined order may be a single order or a combination of a plurality of orders (fourth configuration).

  Further, in order to achieve the above object, an isolated operation detection method according to an aspect of the present invention is an isolated operation detection method for detecting an isolated operation of a power conversion device that links a distributed power supply to a system power supply. In order to promote the change of the first harmonic of the predetermined order that appears on the output side of the inverter unit that converts the DC power supplied from the distributed power source into AC power and outputs the power, the output of the inverter unit has the predetermined order According to a first step of superimposing a second harmonic, a second step of determining whether or not to switch the predetermined order of the harmonic used in the first step, and a switching pattern of the predetermined order And a third step of detecting the isolated operation (fourth configuration).

  According to the present invention, it is possible to provide a technique capable of appropriately detecting an isolated operation in an active manner without causing voltage flicker.

The block diagram which shows the structure of the power converter device which concerns on embodiment of this invention. The block diagram which shows the detailed structure of the harmonic feedback part with which the power converter device which concerns on embodiment of this invention is provided. The flowchart which illustrates the flow of the active type independent operation detection method employ | adopted in the power converter device which concerns on embodiment of this invention. The block diagram which shows the structure of the conventional power converter device provided with the independent operation detection function of the frequency feedback system with step injection

  Hereinafter, a power converter and an isolated operation detection method according to an embodiment of the present invention will be described in detail.

  FIG. 1 is a block diagram showing a configuration of a power conversion device 1 according to an embodiment of the present invention. The power conversion device 1 is disposed between the distributed power source 2 and the system power source 3 and connects the distributed power source 2 to the system power source 3. As in the conventional example shown in FIG. 4, a pole transformer between the power converter 1 and the system power source 3 supplies the low-voltage distribution line with the high-voltage power sent from the high-voltage distribution line. Or a load connected to the low-voltage distribution line.

  In addition, although a solar cell is mentioned as a representative example of the distributed power supply 2, it is not the meaning limited to it. The distributed power source 2 may be, for example, a natural energy power generation means other than a solar cell, a fuel cell, a storage battery, or the like.

  The power conversion device 1 includes an inverter unit 10 that converts DC power supplied from the distributed power source 2 into AC power and outputs the AC power. The inverter unit 10 outputs AC power synchronized with the system power supply 3.

  The power conversion device 1 includes a system frequency measurement unit 11 that measures a system frequency. Specifically, the system frequency measuring unit 11 measures the frequency from the voltage (system voltage) appearing on the output side of the inverter unit 10. In addition, the system frequency measurement unit 11 processes the measured frequency to generate a synchronization signal. For example, the system frequency measurement unit 11 can have the same configuration as the system frequency measurement unit 103 provided in the conventional power conversion device 100 illustrated in FIG. 4.

  The power conversion device 1 includes a harmonic detection unit 12 that detects voltage harmonics (first harmonic of the present invention) appearing on the output side of the inverter unit 10. The harmonic detection unit 12 detects the level of voltage harmonics of a predetermined order by a known method. For example, the harmonic detection unit 12 performs an A / D conversion process and a discrete Fourier transform process after detecting an analog waveform of the output voltage of the inverter unit 10, and sets levels of voltage harmonics of a plurality of orders set in advance. Is detected.

  The power conversion device 1 includes a harmonic feedback unit 13 that performs processing for prompting a change in voltage harmonics of a predetermined order according to the detection result of the harmonic detection unit 12. The predetermined order may be composed of only a single order, or may be composed of a combination of a plurality of orders. FIG. 2 is a block diagram illustrating a detailed configuration of the harmonic feedback unit 13 included in the power conversion device 1 according to the embodiment of the present invention. As shown in FIG. 2, the harmonic feedback unit 13 includes a first moving average calculating unit 131, a second moving average calculating unit 132, a harmonic deviation calculating unit 133, a harmonic current injection amount calculating unit 134, Is provided.

  The first moving average calculation unit 131 and the second moving average calculation unit 132 are based on the voltage harmonics of the predetermined order detected by the harmonic detection unit 12, and the first moving average value of the voltage harmonic level of the predetermined order and A second moving average value is calculated. The voltage harmonic data used for calculating the moving average is updated, for example, every cycle of the system voltage. The moving average value is calculated, for example, in a period shorter than one cycle of the system voltage (for example, 5 ms). The first moving average value is, for example, an average value of voltage harmonic levels in the latest first period. The second moving average value is, for example, an average value of the voltage harmonic level in the second period based on a time point that goes back in the past for a predetermined period. The first period and the second period may be the same period or different.

  The harmonic deviation calculation unit 133 calculates a voltage harmonic level deviation (harmonic deviation) of a predetermined order from the difference between the first moving average value and the second moving average value. The harmonic current injection amount calculation unit 134 calculates a level of a current harmonic of a predetermined order to be injected (superposed) according to the harmonic deviation calculated by the harmonic deviation calculation unit 133.

  The power conversion device 1 controls the inverter unit 10 so as to superimpose a predetermined-order current harmonic (second harmonic of the present invention) on the output of the inverter unit 10 according to the information from the harmonic feedback unit 13. A current control processing unit 14 is provided. The predetermined order may be composed of only a single order, or may be composed of a combination of a plurality of orders. The current control processing unit 14 superimposes a current harmonic of a predetermined order on the output of the inverter unit 10 based on the acquired system frequency.

  The power conversion device 1 determines whether or not to switch the order of the harmonics used in the processing of the harmonic feedback unit 13 and the current control processing unit 14 based on the detection result of the harmonic detection unit 12. 15. The switching determination unit 15 determines whether or not to switch the harmonic order currently used to another harmonic order. The determination timing by the switching determination unit 15 is adjusted in accordance with the timing at which the current control processing unit 14 superimposes the current harmonics. The switching determination unit 15 determines to switch the harmonic order when the level of the voltage harmonic of the predetermined order reaches a predetermined upper limit value. In the present embodiment, the order of switching the harmonic order is determined in advance.

  The power conversion device 1 includes an isolated operation detection unit 16 that detects isolated operation. The isolated operation detection unit 16 includes an active isolated operation determination unit and a passive isolated operation determination unit in detail. The active type isolated operation determination unit monitors the change of the voltage harmonic detected by the harmonic detection unit 12 and detects the isolated operation. More specifically, the active type isolated operation determination unit detects the isolated operation based on the information from the switching determination unit 15 that performs the above-described switching determination based on the detection result of the harmonic detection unit 12. That is, in the present embodiment, the active type isolated operation determination unit indirectly uses the detection result of the harmonic detection unit 12. This is merely an example, and the active type isolated operation determination unit may receive information directly from the harmonic detection unit 12 and detect the isolated operation.

  The passive type isolated operation determination unit detects the isolated operation by a known frequency change rate detection method. In addition, the passive type single operation determination unit may detect the single operation by a known voltage phase jump detection method or the like. In addition, the power converter device 1 of this embodiment has the characteristic which is not in the conventional in the active type isolated operation detection method.

  Next, the active type isolated operation detection method employed in the power conversion device 1 configured as described above will be described. FIG. 3 is a flowchart illustrating the flow of the active isolated operation detection method employed in the power conversion device 1 according to the embodiment of the present invention. In the active type isolated operation detection method of the present embodiment, feedback control is used in which current harmonics are superimposed so that positive feedback is applied to fluctuations in voltage harmonics. Here, as an example, the harmonic feedback unit 13 is set by default to apply positive feedback to fluctuations in voltage harmonics of the second order (an example of the first set value of the predetermined order shown in FIG. 3). It shall be.

  During normal interconnection operation, in principle, no harmonics appear in the system voltage. On the other hand, in the single operation state, harmonics appear in the system voltage due to the influence of the excitation current in the pole transformer. For this purpose, the current control processing unit 14 superimposes the secondary current harmonic on the output of the inverter unit 10 according to the information from the harmonic feedback unit 13 (step S1).

  The switching determination unit 15 checks whether or not the secondary voltage harmonic level detected by the harmonic detection unit 12 has reached the upper limit value after the superposition of the secondary current harmonics (step S2). If the secondary voltage harmonic level has not reached the upper limit (No in step S2), the process returns to step S1. That is, the current control processing unit 14 continues superimposing the second-order current harmonics according to the information from the harmonic feedback unit 13. In the single operation state, the current harmonics are superimposed so as to promote the change of the voltage harmonics, so the secondary voltage harmonics reach the upper limit (Yes in step S2).

  When harmonics appear in the system voltage due to disturbance, the secondary voltage harmonics usually do not reach the upper limit without the effect of superimposing the secondary voltage harmonics on the system voltage. .

  When the secondary voltage harmonic reaches the upper limit value, the switching determination unit 15 determines to switch the order (predetermined order) of the harmonic component used for harmonic feedback (step S3). In this example, the switching determination unit 15 determines to switch from the second harmonic to the fourth harmonic.

  The isolated operation detection unit 16 is provided so as to acquire information from the switching determination unit 15. The islanding operation detection unit 16 confirms whether or not the switching pattern of the harmonic order to be used (predetermined order) is a predetermined switching pattern (step S4). In this example, when the order of the harmonics to be used is switched from the second order to the fourth order to the sixth order, it is determined to be a predetermined switching pattern. For this reason, when the order of the harmonics to be used is switched from the second order to the fourth order, it is determined that the order is not a predetermined switching pattern (No in step S4), and the process returns to step S1. In this example, since the order of the harmonics to be used is switched to the fourth order, the fourth-order current harmonics of a predetermined level are superimposed on the output of the inverter unit 10 in step S1. The fourth-order harmonic is also used after step S2.

  In the single operation state, the current harmonics are superimposed so as to promote the change of the voltage harmonics, so that the fourth-order voltage harmonics also reach the upper limit value. For this reason, the switching determination unit 15 determines to switch from the fourth harmonic to the sixth harmonic. In this stage, the isolated operation detection unit 16 determines that the switching pattern of the harmonic order to be used (predetermined order) has become a predetermined switching pattern (Yes in step S4), and detects that it is in the isolated operation state. (Step S5).

  According to the present embodiment, the above-described voltage flicker can be prevented from occurring because the active type isolated operation detection method uses harmonic feedback instead of frequency feedback. Moreover, in this embodiment, the order of the harmonic used for harmonic feedback is switched to a plurality, and the isolated operation is detected based on the switching pattern. In this method, it is possible to detect the isolated operation while suppressing the level of the current harmonic of each order to be superimposed on the output from the inverter unit 10. For this reason, even when the harmonic feedback is performed due to the occurrence of disturbance in a state where the system impedance is large, the level of the voltage harmonic that is constantly superimposed can be suppressed to a low level. According to the present embodiment, the isolated operation is appropriately detected while achieving the specified value of the current harmonic output of the power converter, which is within 3% of each order harmonic distortion and within 5% of the total harmonic distortion. It is possible.

<First Modification>
In the above description, the default order of the harmonics is set to the second order, and then the predetermined order is switched from the fourth order to the sixth order. However, this is merely an example. Another order may be sufficient as the predetermined order of the harmonic in default, and the predetermined order of the harmonic used for subsequent switching.

<Second Modification>
Moreover, in the above, the predetermined switching pattern which the isolated operation detection part 16 detects that it is an isolated operation is only an illustration. The predetermined switching pattern used for detecting islanding may be changed as appropriate. For example, in the above example, the isolated operation is detected when the predetermined order is switched from secondary to fourth order to sixth order. For example, when the predetermined order is switched from secondary to fourth order to fifth order to sixth order, etc. Alternatively, it may be configured to detect an isolated operation.

<Third Modification>
In the above description, the order of the harmonic current to be superimposed first is determined to be a specific order (for example, second order) in advance, but this is merely an example. You may make it superimpose the current harmonic of the order from which the voltage harmonic was detected first on the output of the inverter part 10 first. As a result, the voltage harmonics of the first order can be brought close to the upper limit at high speed, and the detection of the isolated operation can be accelerated. In this configuration, for example, a change pattern of the order of the daisy chain is set in the order of second order → fourth order → sixth order → eighth order → second order. Then, the single operation is detected at the stage where, for example, four orders are switched. When the sixth-order voltage harmonic is first detected, the sixth-order current harmonic is superimposed on the output of the inverter unit 10. When the level of the sixth-order voltage harmonic reaches the upper limit value, switching is performed so that the eighth-order current harmonic is superimposed on the output of the inverter unit 10. Such switching is repeated, and the isolated operation is detected when the order switching pattern of 6th order → 8th order → secondary → 4th order is detected.

<Fourth Modification>
In the above description, the harmonics to be superimposed on the output of the inverter unit 10 and the orders of harmonics detected for harmonic feedback are single orders. However, this is only an example. The harmonics to be used may be a combination of a plurality of orders. The use of orders that do not normally occur is easier to detect harmonics and can improve the detection accuracy of isolated operation. For example, first, the second order + fourth order + sixth order harmonics are used, and then the third order + fifth order + seventh order → fourth order + seventh order + ninth order, etc. are switched, and the switching pattern of the predetermined order becomes the predetermined pattern. The isolated operation may be detected at this stage.

<Fifth Modification>
In the above description, the detection of the voltage harmonic fluctuation is used as a trigger to promote the voltage harmonic fluctuation. However, this is merely an example. For example, instead of detecting the voltage harmonic fluctuation, or in addition to detecting the voltage harmonic fluctuation, the fluctuation of the voltage harmonic may be promoted by using the detection of the frequency fluctuation as a trigger. For example, when a predetermined frequency fluctuation is detected, a predetermined current harmonic may be injected to promote voltage harmonic fluctuation.

<Sixth Modification>
Moreover, in the above, it was set as the structure which superimposes a current harmonic so that the fluctuation | variation of a voltage harmonic may be promoted. However, this is merely an example, and in some cases, the configuration may be changed so that the voltage harmonics are superimposed so as to promote the fluctuation of the current harmonics.

<Others>
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.

DESCRIPTION OF SYMBOLS 1 Power converter 2 Distributed type power supply 3 System power supply 10 Inverter part 12 Harmonic wave detection part 13 Harmonic feedback part 14 Current control processing part 15 Switching determination part 16 Independent operation detection part

Claims (5)

A power converter for connecting a distributed power source to a system power source,
An inverter unit for converting DC power supplied from the distributed power source into AC power and outputting the AC power;
A harmonic detection unit for detecting a first harmonic appearing on the output side of the inverter unit;
A harmonic feedback unit that performs processing for prompting a change in the first harmonic of a predetermined order according to the detection result of the harmonic detection unit;
A control processing unit that performs control processing of the inverter unit so as to superimpose the second harmonic of the predetermined order on the output of the inverter unit according to information from the harmonic feedback unit;
A determination unit for determining whether to switch the predetermined order based on a detection result of the harmonic detection unit;
An isolated operation detecting unit that detects an isolated operation by monitoring a change in the first harmonic;
With
When it is determined by the determination unit to switch the predetermined order,
The harmonic conversion unit and the control processing unit execute processing by switching the predetermined order.   The said single operation detection part detects the said single operation according to the switching pattern of the said predetermined order, The power converter device of Claim 1 characterized by the above-mentioned. The first harmonic is a voltage harmonic;
The power converter according to claim 1, wherein the second harmonic is a current harmonic.   The power converter according to any one of claims 1 to 3, wherein the predetermined order is a single order or a combination of a plurality of orders. An isolated operation detection method for detecting isolated operation of a power conversion device that links a distributed power supply to a system power supply,
In order to promote the change of the first harmonic of the predetermined order that appears on the output side of the inverter unit that converts the DC power supplied from the distributed power source into AC power and outputs it, the output of the inverter unit has the predetermined order A first step of superimposing a second harmonic of
A second step of determining whether or not to switch the predetermined order of the harmonics used in the first step;
A third step of detecting the single operation according to the switching pattern of the predetermined order;
An islanding operation detection method comprising:

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