JP6342354B2 - Isolated operation detection device, isolated operation detection device control method, and grid-connected inverter - Google Patents

Description

  The present invention relates to an isolated operation detection device, an isolated operation detection device control method, and a grid-connected inverter.

  In recent years, a power system in which a distributed power source such as a solar cell or a fuel cell is connected to a power system has been used. In such a power system, a grid-connected inverter that connects a distributed power source and a power system, converts DC power generated by the distributed power source into AC power, and outputs the AC power to the power system is used.

  In the power system as described above, when power transmission in the power system is stopped due to an accident or the like, the grid-connected inverter may continue to operate, and may be in a state of locally supplying power to the power system. Such a state is referred to as an isolated operation state. In the isolated operation state, an accident may occur during work for removing the cause of the accident or the like by charging the power line of the power system by the grid interconnection inverter. Therefore, the grid-connected inverter is required to have a function for detecting and preventing an isolated operation (an isolated operation detecting device) (see Non-Patent Document 1).

  The isolated operation detection device detects a change in the frequency of the voltage (system voltage) of the power system, and causes the grid-connected inverter to output reactive power proportional to the frequency change amount to the power system. And based on the change of the frequency of the system voltage by reactive power, it is detected whether the system interconnection inverter is a single operation state. When the grid interconnection inverter is not in a single operation state, the system voltage does not change even if reactive power is output.

  As described above, the isolated operation detection device detects the isolated operation of the grid-connected inverter by the output of the reactive power to the power system in proportion to the amount of change in the frequency of the system voltage. Here, when the change of the system voltage is difficult to occur, for example, the output of the grid interconnection inverter and the output of the load are balanced, it is difficult to detect the isolated operation. Therefore, Non-Patent Document 1 describes a method of promoting the frequency change of the system voltage by detecting the change of the harmonic voltage generated during the single operation and outputting the reactive power in a stepped manner.

JP 2014-1117016 A

Japan Electric Association, grid connection regulations, JEAC 9701-2012

  FIG. 6 is a block diagram showing the configuration of the isolated operation detection device 1 a corresponding to the method described in Non-Patent Document 1.

  The isolated operation detection device 1a shown in FIG. 6 includes a voltage measurement unit 2, a periodic deviation calculation unit 3, a reactive power command unit 4, an isolated operation detection unit 5, and a harmonic calculation unit 10a.

Voltage measuring unit 2 detects the U-phase voltage of the system voltage V _G (voltage V _GU), and outputs the detection result as the period deviation calculation unit 3 into a harmonic calculation unit 10a.

The period deviation calculating unit 3 calculates a deviation (period deviation) Δt between the period of the voltage V _GU measured by the voltage measuring unit 2 and the period in a steady state, and the calculation result is detected as a single operation with the reactive power command unit 4. To the unit 5.

Harmonic calculation unit 10a, based on the voltage V _GU which is measured by the voltage measuring unit 2, the fundamental wave of the fundamental wave voltage value V _fund and the harmonic voltage value V _harm of the system voltage V _G is calculated (detected) and detected The voltage value V _fund and the harmonic voltage value V _harm are output to the reactive power command unit 4.

The reactive power command unit 4 generates a cyclic deviation Δt based on the cyclic deviation Δt output from the cyclic deviation calculation unit 3 and the fundamental voltage value V _fund and the harmonic voltage value V _harm output from the harmonic calculation unit 10a. A reactive power command (q ′ command) for instructing output of reactive power proportional to is generated.

  The isolated operation detection unit 5 determines whether or not the grid-connected inverter is in an isolated operation state based on the periodic deviation Δt output from the periodic deviation calculation unit 3, and determines that it is in an isolated operation state. An isolated operation detection signal indicating that an isolated operation of the grid interconnection inverter has been detected is output.

  Next, the configuration of the harmonic calculation unit 10a will be described in detail.

  The harmonic calculation unit 10a includes a low-pass filter (LPF) 14, a discrete Fourier transformer (DFT) 15, a total harmonic voltage calculator 16, and a fundamental voltage calculator 17. Have.

The LPF 14 removes an unnecessary high-order harmonic voltage from the voltage V _GU measured by the voltage measuring unit 2 and outputs a combined voltage of the fundamental voltage and a harmonic voltage in a desired frequency band to the DFT 15.

  The DFT 15 performs a discrete Fourier transform on the output of the LPF 14, thereby obtaining a sine wave component (sin (fund)) and a cosine wave component (cos (fund)) of the fundamental voltage, and a sine wave of each harmonic voltage. The components (sin (2nd), sin (3rd),...) And the cosine wave components (cos (2nd), cos (3rd),...) Are calculated. Note that fast Fourier transform may be used instead of discrete Fourier transform.

The total harmonic voltage calculator 16 calculates the effective value of the total harmonic voltage based on the sine wave component and cosine wave component of each harmonic voltage calculated by the DFT 15, and reactive power as the harmonic voltage value V _harm Output to the command unit 4.

The fundamental wave voltage calculator 17 calculates an effective value of the fundamental wave voltage based on the sine wave component and the cosine wave component of the fundamental wave voltage calculated by the DFT 15, and outputs the fundamental wave voltage value V _fund to the reactive power command unit 4. Output.

  In order to detect the isolated operation state with high accuracy, it is necessary to calculate the harmonic voltage with high accuracy and high speed.

  In the isolated operation detection device 1a, discrete Fourier transform or fast Fourier transform is used for the calculation (detection) of the harmonic voltage. When discrete Fourier transform or fast Fourier transform is used, a period corresponding to one cycle of the system voltage is required at the minimum. In addition, when using discrete Fourier transform or fast Fourier transform, a complicated calculation using a large amount of data is required, and the time required for the calculation becomes long. Further, Non-Patent Document 1 stipulates that it is only necessary to obtain up to a predetermined order of harmonics, but when using discrete Fourier transform or fast Fourier transform, it includes even unnecessary harmonic voltages of higher orders. Therefore, the accuracy is poor.

  Patent Document 1 describes a method of obtaining a fundamental voltage and a harmonic voltage by dq conversion of a measured system voltage. However, even in this method, the period necessary for calculating the harmonic voltage is a period corresponding to one cycle of the system voltage. Furthermore, in the dq conversion, it is not possible to detect a multiple third harmonic (3n-order harmonic) in which the phases of the three-phase voltages overlap. In a single operation state, 3n-order harmonics increase, but the method described in Patent Document 1 cannot detect 3n-order harmonics and has poor detection accuracy.

  An object of the present invention is to provide an isolated operation detecting device, an isolated operation detecting device control method, and a grid interconnection inverter capable of solving the above-described problems and reducing the time required for detecting a harmonic voltage and improving accuracy. It is to provide.

  In order to solve the above problems, an isolated operation detection apparatus according to the present invention is mounted on a grid-connected inverter that connects a distributed power source and a power system, and detects an isolated operation of the grid-connected inverter. The voltage measuring unit for measuring the system voltage of the power system, the system voltage measured by the voltage measuring unit is dq0 converted, and in a moving average section of 1/3 times one period of the system voltage, The moving average of the voltage value obtained by the dq0 conversion is calculated, and the fundamental voltage and the harmonic voltage of the system voltage are calculated based on the moving average calculation result and the voltage value obtained by the dq0 conversion. Calculated by a harmonic calculation unit, a deviation calculation unit for calculating a deviation between a cycle of the system voltage in a steady state and a cycle of the system voltage measured by the voltage measurement unit, and the harmonic calculation unit Based on the main wave voltage and the harmonic voltage, the reactive power command unit that causes the grid-connected inverter to output reactive power proportional to the deviation to the power system, and based on the deviation, the grid-connected inverter operates independently. A single operation detection unit that determines whether or not the vehicle is in a state.

  In the isolated operation detection device according to the present invention, the harmonic calculation unit converts the system voltage measured by the voltage measurement unit to dq0, and converts the harmonic voltage into a d-axis voltage, a q-axis voltage AC value, and 0. A voltage component separator that separates the fundamental wave voltage into a q-axis voltage direct current value, and a fundamental that calculates a fundamental wave voltage value based on the q-axis voltage direct current value separated by the voltage component separator. A wave voltage detector, and a total harmonic voltage detector that calculates a total harmonic voltage value based on the d-axis voltage, the q-axis voltage AC value, and the zero-axis voltage separated by the voltage component separator. It is preferable.

  In the isolated operation detection device according to the present invention, the voltage measurement unit measures a U-phase voltage, a V-phase voltage, and a W-phase voltage of the system voltage, and the voltage component separator is measured by the voltage measurement unit. Of the U-phase voltage, V-phase voltage and W-phase voltage, the phase synchronization circuit for detecting the phase of the reference phase voltage, and the voltage measurement using the phase of the reference phase voltage detected by the phase synchronization circuit The d-axis voltage obtained by converting the 3n ± 1st-order (n is an integer) harmonic component into the 3n-order AC component by converting the U-phase voltage, V-phase voltage, and W-phase voltage measured by the unit to 3n ± A q-axis voltage obtained by combining a q-axis voltage AC value obtained by converting a first harmonic component into a 3n-order AC component and a q-axis voltage DC value obtained by converting the fundamental wave voltage into a DC component, and a 3n-order harmonic voltage. Obtain 0-axis voltage converted to 3n order AC component The q-axis voltage is converted to the q-axis by calculating the moving average of the q-axis voltage obtained by the dq0 converter in a dq0 converter and a moving average section of 1/3 times one period of the system voltage. It is preferable to have a moving average calculator that separates the voltage DC value into the q-axis voltage AC value.

  In the isolated operation detection device according to the present invention, the moving average calculator is a moving average of the q-axis voltage obtained by the dq0 converter in a moving average section that is 1/3 times one cycle of the system voltage. By calculating the q-axis voltage DC value, and subtracting the q-axis voltage DC value obtained by the moving average low-pass filter from the q-axis voltage obtained by the dq0 converter. And a subtractor for obtaining the q-axis voltage AC value.

  In order to solve the above problems, the control method of the isolated operation detection device according to the present invention is mounted on a grid-connected inverter that connects a distributed power source and a power system, and detects the isolated operation of the grid-connected inverter. A method for controlling an isolated operation detecting apparatus, comprising: measuring a system voltage of the power system; converting the measured system voltage to dq0; and moving average interval of 1/3 of one period of the system voltage Then, the moving average of the voltage value obtained by the dq0 conversion is calculated, and the fundamental voltage and the harmonic voltage of the system voltage are calculated based on the calculation result of the moving average and the voltage value obtained by the dq0 conversion. A step of calculating a deviation between a cycle of the grid voltage in a steady state and a cycle of the grid voltage to be measured, and based on the calculated fundamental wave voltage and the harmonic voltage. A step of causing the grid-connected inverter to output reactive power proportional to the deviation to the power system, and a step of determining whether the grid-connected inverter is in a single operation state based on the deviation. Including.

  In order to solve the above problem, a grid-connected inverter according to the present invention is provided between a distributed power source and a power system, and converts DC power output from the distributed power source into AC power, A grid-connected inverter that outputs to the power system, and includes any one of the above-described isolated operation detection devices.

  According to the isolated operation detection apparatus, the isolated operation detection apparatus control method, and the grid-connected inverter according to the present invention, it is possible to shorten the time required to detect the harmonic voltage and improve the accuracy.

It is a block diagram which shows the structure of the independent operation detection apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the harmonic calculating part shown in FIG. It is a block diagram which shows the structure of the grid connection inverter which concerns on one Embodiment of this invention. It is a figure which shows the vector locus | trajectory on the alpha beta plane coordinate of 3n +/- 1st harmonic. It is a figure which shows the vector locus | trajectory on the 0 (beta) plane coordinate of a 3n order harmonic. It is a block diagram which shows the structure of the related isolated operation detection apparatus.

  Embodiments of the present invention will be described below.

  FIG. 1 is a block diagram showing a configuration of an isolated operation detection device 1 according to an embodiment of the present invention. The isolated operation detection device 1 according to the present embodiment is mounted on a grid-connected inverter that connects a distributed power source and a power system, converts DC power output from the distributed power source into AC power, and outputs the AC power to the power system. And detecting whether or not the grid-connected inverter is in a single operation state. In FIG. 1, the same components as those in FIG. 6 are denoted by the same reference numerals, and description thereof is omitted.

The islanding operation detection apparatus 1 shown in FIG. 1 differs from the islanding operation detection apparatus 1a shown in FIG. 6 in that the harmonic calculation unit 10a is changed to the harmonic calculation unit 10. In the present embodiment, the voltage measurement unit 2 detects and detects the U-phase voltage (voltage V _GU ), V-phase voltage (voltage V _GV ), and W-phase voltage (voltage V _GW ) of the system voltage V _G. The voltages V _GU , V _GV , and V _GW are output to the harmonic calculation unit 10.

The harmonic calculation unit 10 calculates (detects) the fundamental voltage value V _fund and the harmonic voltage value V _harm of the system voltage V _G based on the voltages V _GU , V _GV , and V _GW measured by the voltage measurement unit 2. Then, the detected fundamental wave voltage value V _fund and harmonic voltage value V _harm are output to the reactive power command unit 4.

  Next, the configuration of the harmonic calculation unit 10 will be described with reference to FIGS. 1 and 2. FIG. 2 is a diagram showing the configuration of the harmonic calculation unit 10 in more detail.

  As shown in FIG. 1, the harmonic calculation unit 10 includes a voltage component separator 11, a total harmonic voltage detector 12, and a fundamental voltage detector 13.

Voltage component separator 11 separates the fundamental wave voltage component of the system voltage V _G and the harmonic voltage component, and outputs a harmonic voltage component in total harmonic voltage detector 12, the fundamental wave voltage fundamental wave voltage component Output to the detector 13.

  The voltage component separator 11 includes a dq0 converter 111 and a moving average calculator 112.

The dq0 conversion unit 111 rotates the voltages V _GU , V _GV , and V _GW measured by the voltage measurement unit 2 by the phase θ about the 0 axis in the αβ0 axis coordinate system, and the d axis voltage V in the dq0 axis coordinate system. _d, the dq0 conversion for converting the q-axis voltage V _q and 0-axis voltage V ₀ performed. The dq0 converter 111 outputs the d-axis voltage V _d and the 0-axis voltage V ₀ obtained by the dq0 conversion to the moving average calculator 112. Further, the dq0 conversion unit 111 outputs the q-axis voltage V _q obtained by the dq0 conversion to the moving average calculator 112.

  The configuration of the dq0 converter 111 will be described in more detail with reference to FIG. 2. The dq0 converter 111 includes a phase locked loop (PLL) 113 and a dq0 converter 114.

The PLL 113 receives the voltage V _GU and obtains the phase θ of the voltage V _GU .

The dq0 converter 114 performs dq0 conversion of the three-phase voltages (voltages V _GU , V _GV , V _GW ) measured by the voltage measuring unit 2 using the phase θ obtained by the PLL 113, and the d-axis voltage V _d Q-axis voltage V _q and 0-axis voltage V ₀ are obtained. The dq0 converter 114 outputs the d-axis voltage V _d and the 0-axis voltage V ₀ obtained by the dq0 conversion to the moving average calculator 112, and the q-axis voltage V _q obtained by the dq0 conversion is the moving average calculator 112. Output to.

Referring back to FIG. 1, the moving average calculator 112 converts the q-axis voltage V _q output from the dq0 converter 111 into a DC component (q-axis voltage DC value) V _qDC and an AC component (q-axis voltage AC value) V. 'is separated into a _q, the DC component V _QDC outputs the fundamental wave voltage detector 13, the AC component V' outputs _q to total harmonic voltage detector 12.

  With reference to FIG. 2, the configuration of the moving average calculator 112 will be described in more detail. The moving average calculator 112 includes a moving average low-pass filter (LPF) 115 and a subtractor 116.

The moving average LPF 115 obtains a moving average of the q-axis voltage V _{q in} a predetermined section. by obtaining the moving average of the q-axis voltage V _q, DC component V _QDC the q-axis voltage V _q is obtained. The moving average LPF 115 outputs the obtained DC component V _qDC of the q-axis voltage V _q to the fundamental voltage detector 13 and the subtractor 116.

The subtractor 116 subtracts the DC component V _qDC from the q-axis voltage V _q output from the dq0 conversion unit 111. By subtracting the DC component V _QDC from the q-axis voltage V _q, the AC component V _'q of the q-axis voltage V _q is obtained. Subtractor 116 outputs an AC component V _'q of the obtained q-axis voltage V _q to total harmonic voltage detector 12.

The total harmonic voltage detector 12 calculates the root mean square (RMS) of the d-axis voltage V _d output from the dq0 converter 111, multiplies the calculated value by 1 / √3, Square the multiplication value. The total harmonic voltage detector 12 performs the same calculation on the AC component V ′ _q of the q-axis voltage V _q output from the moving average calculator 112 and the 0-axis voltage V ₀ output from the dq0 converter 111. I do. The total harmonic voltage detector 12 adds the respective calculated values of the d-axis voltage V _d , the AC component V ′ _q of the q-axis voltage V _q , and the 0-axis voltage V ₀ . Further, the total harmonic voltage detector 12 outputs the square root of the added value as the harmonic voltage V _harm .

The fundamental voltage detector 13 multiplies the DC component V _qDC of the q-axis voltage V _q output from the moving average calculator 112 by 1 / √3 and squares the multiplication value. Further, the fundamental wave voltage detector 13 outputs the square root of the squared value as the fundamental wave voltage V _fund .

  Next, the structure of the grid connection inverter which mounts the independent operation detection apparatus 1 is demonstrated.

  FIG. 3 is a diagram showing a configuration of a power system 60 including a grid interconnection inverter according to an embodiment of the present invention.

  The power system 60 illustrated in FIG. 3 includes a distributed power source 61, a power system 62, and a grid interconnection inverter 63.

  The distributed power source 61 is a power generator that generates AC power using a rotating machine as a generator, such as a wind power generator or a turbine generator, and converts the DC power into DC power using a power converter such as a rectifier. The distributed power supply 61 is a power generator that outputs DC power, such as solar power generation or a fuel cell.

  The power system 62 is a distribution line connected to a local power system or a power company substation.

  The grid interconnection inverter 63 connects the distributed power source 61 and the power system 62. The grid interconnection inverter 63 has, for example, a plurality of semiconductor elements, and controls the switching of the plurality of semiconductor elements, thereby converting the DC power output from the distributed power supply 61 into AC power. Output to system 62.

  The grid interconnection inverter 63 includes the isolated operation detection device 1, a DC / AC converter 64, a linkage switch 65, a stop device 66, and an inverter output control device 67.

Independent operation detecting apparatus 1 detects the change in the frequency of the system voltage V _G, and outputs reactive power command for instructing the output of the reactive power in proportion to the amount of change in frequency (q 'command) to the inverter output control device 67 . In addition, when the isolated operation detecting device 1 detects the isolated operation of the grid interconnection inverter 63, the isolated operation detection device 1 outputs an isolated operation detection signal indicating that the isolated operation of the grid interconnection inverter 63 has been detected to the stop device 66.

  The DC / AC converter 64 converts the DC power generated by the distributed power supply 61 into AC power according to the control of the inverter output control device 67. The DC / AC converter 64 includes, for example, a plurality of semiconductor elements, and converts DC power generated by the distributed power supply 61 into AC power by controlling switching of the plurality of semiconductor elements.

  The interconnection switch 65 is a switch provided between the DC / AC converter 64 and the power system 62. When the interconnection switch 65 is in the closed state, the AC power output from the DC / AC converter 64 is transmitted to the power system 62. When the interconnection switch 65 is in the open state, the DC / AC converter 64 and the power system 62 are disconnected, and power transmission from the DC / AC converter 64 to the power system 62 is not performed.

  When the isolated operation detection signal is output from the isolated operation detection device 1, the stop device 66 outputs a switch / open command indicating that the connected switch 65 is opened to the connected switch 65. Further, when the isolated operation detection signal is output from the isolated operation detection device 1, the stop device 66 outputs a gate block command indicating that the operation of the DC / AC converter 64 is stopped to the inverter output control device 67.

The inverter output control device 67 performs DC / AC conversion based on the AC voltage V _inv and AC power I _G output from the DC / AC converter 64, the system voltage V _G, and the output voltage V _DC of the distributed power source 61. An output command for controlling the output of the converter 64 is generated and output to the DC / AC converter 64. Further, the inverter output control device 67 outputs a switch / open / close command for controlling opening / closing of the interconnection switch 65 to the interconnection switch 65. Further, when the reactive power command (q ′ command) is output from the isolated operation detection device 1, the inverter output control device 67 outputs the reactive power indicated by the reactive power command of the DC / AC converter 64. Control the output. Further, when the gate block signal is output from the stop device 66, the inverter output control device 67 performs the gate block by stopping the switching operation of the semiconductor element included in the DC / AC converter 64.

  Next, the detection operation of the fundamental voltage and the harmonic voltage by the harmonic calculation unit 10 according to the present embodiment will be described.

The PLL 113 detects the phase θ of the voltage V _GU measured by the voltage measuring unit 2. In the present embodiment, the phase of the reference phase voltage is detected using the voltage V _GU with the U phase as the reference phase, but the present invention is not limited to this. The V phase or the W phase may be used as the reference phase, and the method for detecting the phase of the voltage of the reference phase can be appropriately selected.

The dq0 converter 114 converts the three-phase voltages (voltages V _GU , V _GV , and V _GW ) measured by the voltage measuring unit 2 using the phase θ detected by the PLL 113 and performs dq0 conversion in the dq0 axis coordinate system. A d-axis voltage V _d , a q-axis voltage V _q and a zero-axis voltage V ₀ are obtained.

The dq0 conversion can be performed directly using the following equation (1) or indirectly via the αβ0 coordinate system using the following equations (2) and (3).

  The dq0 axis voltage of the rotating coordinate system (dq0 coordinate system) obtained by the dq0 conversion can be regarded as a space vector existing in the αβ0 space. The αβ0 space is obtained by adding a zero axis as a depth to a plane having an α axis and a β axis. Therefore, the dq0 axis voltage can be considered as a vector rotating around the 0 axis of the αβ0 space.

  Since the dq0 axis voltage of the rotating coordinate system obtained by the dq0 conversion is the dq0 conversion using the phase θ of the U-phase voltage that is the reference phase, if it is a sine wave with three-phase balance and no offset The d-axis and the 0-axis are always zero, and the q-axis is a value obtained by multiplying the effective value by √3.

  When a harmonic appears in the UVW phase, the appearance of the dq0 axis voltage varies depending on the order of the harmonic. In the following, the harmonics are 3n-1 order harmonics (n is an integer) such as 2, 5, 8, 11,..., 3n + 1 order harmonics such as 4, 7, 10, 13,. , 9, 12... And 3n-order harmonics.

The 3n-1 order harmonic appears in the d-axis voltage and the q-axis voltage. The 3n-1 first harmonic appears as a vector rotating in the negative direction of the phase θ on the αβ plane at a period 1 / (3n) times the period of the system voltage V _G , that is, at a frequency of 3n times. Therefore, the d-axis voltage and the q-axis voltage appear as 1 / (3n) times the cycle of the system voltage V _G , that is, as a 3n-order sine wave AC.

The 3n + 1 order harmonic appears in the d-axis voltage and the q-axis voltage. The 3n + 1-order harmonic appears as a vector rotating in the positive direction of the phase θ on the αβ plane at a period 1 / (3n) times the period of the system voltage V _G , that is, at a frequency of 3n times. Therefore, the d-axis voltage and the q-axis voltage appear as 1 / (3n) times the cycle of the system voltage V _G , that is, as a 3n-order sine wave AC.

The 3n-order harmonic is a period in which one period corresponds to 120 ° of the fundamental wave, and is equal to the phase difference of the UVW phase, so the 3n-order harmonics of all phases overlap. Therefore, since it is converted as an offset in the dq0 conversion, it appears on the 0 axis as a period 1 / (3n) times the period of the system voltage V _G , that is, as a 3n-order sine wave AC.

  FIG. 4 is a diagram showing vector trajectories of the second, fourth, fifth, and seventh harmonics on the αβ plane coordinates with the α axis as the horizontal axis and the β axis as the vertical axis in the αβ0 space. The perfect circle shows a vector locus of a three-phase balanced sine wave having no offset, and the vector locus makes one round with the fundamental wave period. In FIG. 4, a vector locus obtained by adding m-order harmonics having a magnitude 1 / m times the fundamental wave is superimposed on the vector locus of a three-phase balanced sine wave. Each harmonic has a unique vector locus. In addition, since the 3n-order harmonic appears on the 0 axis in the depth direction, it cannot be observed on the αβ plane coordinates.

  FIG. 5 is a diagram showing vector trajectories of the third and sixth harmonics on the 0β plane coordinates with the 0 axis as the horizontal axis and the β axis as the vertical axis in the αβ0 space. FIG. 5 shows a vector locus obtained by adding m-order harmonics having a magnitude 1 / m times the fundamental wave to a three-phase balanced sine wave. When there is no 3n-order harmonic, it does not have a size in the 0-axis direction on the 0β plane coordinate and moves on the β-axis, that is, a plane vector locus having only the αβ coordinate. In the case of having a wave, as shown in FIG. 5, it becomes a unique vector locus that changes in the 0-axis direction.

In this way, the 3n ± 1st harmonic appears as a sine wave alternating current having a period 1 / (3n) times the period of the system voltage V _{G in} the d-axis voltage and the q-axis voltage. Further, 3n harmonics is 0 in the axial voltage V _0, appears as 1 / (3n) double period sine wave alternating current cycle of the system voltage V _G. On the other hand, in the present embodiment, since the dq0 conversion is performed using the phase θ of the U-phase voltage V _GU that is the reference phase, the fundamental voltage is only the q-axis voltage, and the effective value is multiplied by √3. It appears as a q-axis voltage DC value having a thickness. That is, the q-axis voltage is a combination of an AC voltage (q-axis voltage AC value) caused by 3n ± 1st harmonic voltage and a DC voltage (q-axis voltage DC value) caused by the fundamental voltage. .

In the present embodiment, since dq0 conversion is performed using the phase θ of the U-phase voltage (voltage V _GU ), the DC voltage resulting from the fundamental voltage appears on the q-axis, but is used as a reference. Depending on the phase, a DC voltage resulting from the fundamental voltage may appear on the d-axis.

The moving average calculator 112 (moving average LPF 115) calculates a moving average of the q-axis voltage V _q with a section of 1/3 of the cycle of the system voltage V _G as a moving average section.

As described above, the harmonic voltage, to appear as a composite of the q-axis voltage 3n following sinusoidal alternating, q-axis voltage has a 1 / (3n) times the period of the cycle of the system voltage V _G. Therefore, the moving average section of the moving average calculator 112 (moving average LPF 115), by setting the 1/3 interval of the cycle of the system voltage V _G, cancel the AC component due to harmonic voltage, the fundamental wave voltage The direct current component (q-axis voltage direct current value) resulting from can be obtained. In addition, the moving average LPF 115 is excellent in the attenuation characteristic of an AC component having a period of 1 / n of the moving average section, and is suitable for obtaining a DC component from a q-axis voltage composed of a DC component and a 3n-order AC component. ing.

Since all harmonic voltages have a 1 / (3n) period, the q-axis voltage AC value is obtained by subtracting the q-axis voltage DC value V _qDC obtained by the moving average LPF 115 from the q-axis voltage V _q in the subtractor 116. V ′ _q can be obtained.

The fundamental wave voltage detector 13 _obtains a fundamental wave voltage value V _fund by taking the absolute value of a value obtained by multiplying the q-axis voltage DC value V _qDC obtained by the moving average calculator 112 by 1 / √3.

Further, the harmonic voltage detector 12 obtains effective values of the d-axis voltage V _d , the q-axis voltage AC value V ′ _q, and the 0-axis voltage V ₀ . Harmonic voltage detector 12, for calculating the effective value of the composite of the harmonic voltage converted 3n following sinusoidal AC, and duration of 1/3 of the period of the integration period the system voltage V _G of the effective value operation To do.

Based on the calculated d-axis voltage V _d , q-axis voltage AC value V ′ _q, and effective value of the 0-axis voltage V ₀ , the harmonic voltage detector 12 uses the following formula (4) to calculate the total harmonic voltage: Get the effective value of the value V _harm .

According to this embodiment, the independent operation detecting apparatus 1 includes a voltage measuring unit 2 that measures a system voltage V _G, the fundamental wave voltage and harmonic voltages from the system voltage V _G which is measured by the voltage measurement unit 2 harmonic calculation unit 10 for calculating the bets, the deviation calculating unit 3 for calculating a deviation between the period of the system voltage V _G which is measured by the period and the voltage measuring unit 2 in the steady state of the system voltage V _G, the harmonic Based on the fundamental wave voltage and the harmonic voltage calculated by the calculation unit 10, the reactive power command unit 4 that causes the grid interconnection inverter 63 to output the reactive power proportional to the deviation calculated by the deviation calculation unit 3 to the power system 62. And an isolated operation detecting unit 5 that determines whether or not the grid interconnection inverter 63 is in an isolated operation state based on the deviation calculated by the deviation calculating unit 3. Further, the harmonic calculation unit 10 has been system voltage V _G dq0 convert measured by the voltage measuring unit 2, in one period of 1/3 of the moving average section of the system voltage V _G, obtained by dq0 conversion The moving average of the voltage value is calculated, and the fundamental voltage and the harmonic voltage are calculated based on the moving average calculation result and the voltage value obtained by the dq0 conversion.

By converting the voltage measuring unit dq0 the system voltage V _G which is measured by the 2, 3n ± 1 harmonic voltage of the system voltage V _G is the d-axis voltage and the q-axis voltage, the cycle of the system voltage V _G 1 / (3n) times the cycle, that is, appears as a 3n-order sine wave alternating current. Further, 3n order higher harmonic wave voltage of the system voltage V _G is, 1 / (3n) times the period of the voltage period of the power system 62 to 0 axis, i.e. appears as 3n following sinusoidal alternating.

Then, by calculating a moving average of the q-axis voltage V _{q in} a moving average section that is 1/3 times one cycle of the system voltage V _G , a direct current component due to the fundamental wave voltage of the q-axis voltage V _q ( The q-axis voltage DC value V _qDC ) and the AC component (q-axis voltage AC value V ′ _q ) caused by the harmonic voltage can be separated. Based on the q-axis voltage DC value V _qDC , the fundamental wave voltage can be obtained, and the d-axis voltage V _d and the 0-axis voltage V ₀ obtained by the dq0 conversion and the q-axis voltage AC value V ′ _q Based on the above, the total harmonic voltage can be obtained.

Therefore, it is possible to determine the fundamental wave voltage and harmonic voltage 1/3 times the period of one cycle of the system voltage V _G, it is possible to shorten the time required for detection of the harmonic voltage. Further, since the 3n-order harmonic voltage that increases during the independent operation of the grid interconnection inverter 63 can also be detected, the detection accuracy of the independent operation of the grid interconnection inverter 63 can be improved.

  Although the present invention has been described based on the drawings and embodiments, it should be noted that those skilled in the art can easily make various variations or modifications based on the present disclosure. Therefore, it should be noted that these variations or modifications are included in the scope of the present invention. For example, functions included in each block or the like can be rearranged so as not to be logically contradictory, and a plurality of blocks or the like can be combined into one or divided.

DESCRIPTION OF SYMBOLS 1 Independent operation detection apparatus 2 Voltage measurement part 3 Period deviation calculation part 4 Reactive power command part 5 Independent operation detection part 10 Harmonic calculation part 11 Voltage component separator 12 Total harmonic voltage detector 13 Fundamental voltage detector 60 Electric power system 61 Distributed Type Power Supply 62 Power System 63 Grid-connected Inverter 64 DC / AC Converter 65 Linked Switch 66 Stop Device 67 Inverter Output Controller 111 dq0 Converter 112 Moving Average Calculator 113 Phase Synchronization Circuit (PLL)
114 dq0 converter 115 Moving average low pass filter (LPF)
116 Subtractor

Claims (6)

An independent operation detection device that is mounted on a grid-connected inverter that connects a distributed power source and a power system, and that detects an isolated operation of the grid-connected inverter,
A voltage measuring unit for measuring a system voltage of the power system;
The system voltage measured by the voltage measuring unit is converted to dq0, and the moving average of the voltage value obtained by the dq0 conversion is calculated in a moving average section that is 1/3 times one period of the system voltage, and the moving A harmonic calculation unit that calculates a fundamental voltage and a harmonic voltage of the system voltage based on an average calculation result and a voltage value obtained by the dq0 conversion;
A deviation calculator that calculates a deviation between a cycle of the system voltage in a steady state and a cycle of the system voltage measured by the voltage measurement unit;
Based on the fundamental wave voltage and the harmonic voltage calculated by the harmonic calculation unit, the reactive power command unit that causes the grid-connected inverter to output reactive power proportional to the deviation to the power system,
Based on the deviation, an isolated operation detection unit that determines whether the grid-connected inverter is in an isolated operation state,
An isolated operation detection device comprising: In the isolated operation detection device according to claim 1,
The harmonic calculation unit is
System voltage measured by the voltage measuring unit is converted to dq0, the harmonic voltage is separated into d-axis voltage, q-axis voltage AC value, and 0-axis voltage, and the fundamental voltage is separated into q-axis voltage DC value. A voltage component separator,
A fundamental voltage detector for calculating a fundamental voltage value based on a q-axis voltage DC value separated by the voltage component separator;
A total harmonic voltage detector that calculates a total harmonic voltage value based on the d-axis voltage, the q-axis voltage AC value, and the zero-axis voltage separated by the voltage component separator;
An isolated operation detection device comprising: In the isolated operation detection device according to claim 2,
The voltage measuring unit measures a U-phase voltage, a V-phase voltage, and a W-phase voltage of the system voltage,
The voltage component separator is
A phase synchronization circuit for detecting a phase of a reference phase voltage among the U phase voltage, the V phase voltage, and the W phase voltage measured by the voltage measurement unit;
By converting the U-phase voltage, V-phase voltage, and W-phase voltage measured by the voltage measurement unit using the phase of the reference phase voltage detected by the phase synchronization circuit, the 3n ± 1st order (n Is an integer) d-axis voltage obtained by converting a harmonic component into a 3n-order AC component, q-axis voltage AC value obtained by converting a 3n ± 1st-order harmonic component into a 3n-order AC component, and q obtained by converting a fundamental wave voltage into a DC component. A dq0 converter for obtaining a q-axis voltage obtained by combining the axial voltage DC value and a 0-axis voltage obtained by converting a 3n-order harmonic voltage into a 3n-order AC component;
The q-axis voltage is converted into the q-axis voltage DC value and the q-axis voltage by calculating a moving average of the q-axis voltage obtained by the dq0 converter in a moving average section that is 1/3 times one cycle of the system voltage. a moving average calculator that separates the q-axis voltage AC value;
An isolated operation detection device comprising: In the isolated operation detection device according to claim 3,
The moving average calculator is
A moving average low-pass filter for calculating the q-axis voltage DC value by calculating a moving average of the q-axis voltage obtained by the dq0 converter in a moving average section of 1/3 times one cycle of the system voltage; ,
A subtractor for obtaining the q-axis voltage AC value by subtracting the q-axis voltage DC value obtained by the moving average low-pass filter from the q-axis voltage obtained by the dq0 converter;
An isolated operation detection device comprising: A control method of an isolated operation detection device that is mounted on a grid-connected inverter that connects a distributed power source and a power system, and detects an isolated operation of the grid-connected inverter,
Measuring the system voltage of the power system;
The measured system voltage is dq0 converted, the moving average of the voltage value obtained by the dq0 conversion is calculated in a moving average section of 1/3 of one period of the system voltage, and the moving average calculation result And calculating a fundamental voltage and a harmonic voltage of the system voltage based on the voltage value obtained by the dq0 conversion;
Calculating a deviation between a cycle of the grid voltage in a steady state and a cycle of the grid voltage to be measured;
Based on the calculated fundamental wave voltage and the harmonic voltage, causing the grid-connected inverter to output reactive power proportional to the deviation to the power system;
Determining whether the grid-connected inverter is in a single operation state based on the deviation; and
A control method for an isolated operation detection device comprising: A grid-connected inverter that is provided between the distributed power source and the power system, converts DC power output from the distributed power source into AC power, and outputs the AC power to the power system,
A grid-connected inverter comprising the isolated operation detection device according to any one of claims 1 to 4.

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