JP2017051072A - Power conversion device, power generation system, control device, and control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device, a power generation system, a control device, and a control method, capable of reducing injection of reactive power at the time of being in isolated operation.SOLUTION: A power conversion device according to an embodiment comprises: a power conversion unit; a frequency variation detection unit; a reactive power injection control unit; and a variation suppression unit. The power conversion unit converts power supplied from a power source to supply the converted power to a power system. The frequency variation detection unit detects a variation in a frequency of the power system. The reactive power injection control unit, on the basis of a result of detection by the frequency variation detection unit, controls injection of reactive power from the power conversion unit to the power system. The variation suppression unit, on the basis of the result of detection by the frequency variation detection unit, executes processing of suppressing a periodic variation in the frequency of the power system.SELECTED DRAWING: Figure 1

Description

  Embodiments disclosed herein relate to a power conversion device, a power generation system, a control device, and a control method.

  2. Description of the Related Art Conventionally, in a power conversion device such as a power conditioner for photovoltaic power generation, an isolated operation detection method for detecting whether or not an isolated operation is performed by disconnecting from a power system is known. As an isolated operation detection method, a technique for detecting a system frequency by detecting a system frequency and injecting reactive power into the power system based on the detection result is known (see, for example, Patent Document 1).

JP-A-8-223809

  However, in the above-described isolated operation detection method, reactive power injection may be repeated, for example, when the isolated operation such as power supply disturbance on the power system side is not performed.

  One aspect of the embodiments has been made in view of the above, and provides a power conversion device, a power generation system, a control device, and a control method that can reduce reactive power injection when not operating alone. For the purpose.

  A power conversion device according to an aspect of an embodiment includes a power conversion unit, a frequency change detection unit, a reactive power injection control unit, and a fluctuation suppression unit. The power conversion unit converts power supplied from a power source and supplies the converted power to the power system. The frequency change detection unit detects a change in frequency of the power system. The reactive power injection control unit controls injection of reactive power from the power conversion unit to the power system based on a detection result of the frequency change detection unit. The fluctuation suppressing unit performs processing for suppressing periodic fluctuations in the frequency of the power system based on the detection result of the frequency change detecting unit.

  According to one aspect of the embodiment, it is possible to provide a power conversion device, a power generation system, a control device, and a control method that can reduce the injection of reactive power when it is not a single operation.

FIG. 1 is a diagram illustrating a configuration example of a power generation system according to an embodiment. FIG. 2 is a diagram illustrating a configuration example of the power conversion unit illustrated in FIG. 1. FIG. 3 is a diagram illustrating a configuration example of the power conversion device illustrated in FIG. 1. FIG. 4 is a diagram illustrating a configuration example of the system frequency deviation calculation unit. FIG. 5 is a diagram illustrating an example of the moving average value and the frequency deviation calculated by the system frequency deviation calculating unit. FIG. 6 is a diagram illustrating an example of a frequency feedback gain in the frequency feedback calculation unit. FIG. 7 is an image diagram showing an example of operations of the frequency change determination unit and the reactive power injection control unit when the system frequency detected by the system frequency determination unit changes. FIG. 8 is a diagram illustrating a state example of the variation mode. FIG. 9 is a diagram illustrating an equivalent circuit of the power system as viewed from the power converter. FIG. 10 is a diagram illustrating the voltage vector and the current vector as vectors in the dq axis coordinate system when the system frequency is constant. FIG. 11 is a diagram showing the voltage vector and the current vector as vectors in the dq axis coordinate system when the fluctuation mode is occurring. FIG. 12 is a diagram illustrating a voltage vector and a current vector as vectors in the dq-axis coordinate system when the variation mode occurs and the q-axis current command adjusted from the q-axis command adjustment unit is output. FIG. 13 is a diagram illustrating another configuration example of the power conversion device. FIG. 14 is a flowchart showing the flow of processing by the control unit.

  Hereinafter, embodiments of a power conversion device, a power generation system, a control device, and a control method disclosed in the present application will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

[1. Power generation system]
FIG. 1 is a diagram illustrating a configuration example of a power generation system according to an embodiment. As shown in FIG. 1, the power generation system 100 according to the embodiment includes a power conversion device 1 and a power generation device 2. The power conversion device 1 is arranged between the power generation device 2 and the power system 3, converts the power generated by the power generation device 2 into three-phase AC power, and outputs it to the power system 3.

  The power conversion device 1 includes a power conversion unit 10, a voltage detection unit 11, a current detection unit 12, and a control unit 20, and converts DC power supplied from the power generation device 2 into three-phase AC power. Output to power system 3. The power generator 2 is a DC power generator such as a solar cell, a DC generator, or a fuel cell. Note that the voltage frequency of the power system 3 may be, for example, 50 Hz or 60 Hz.

  For example, as shown in FIG. 2, the power conversion unit 10 is configured by connecting a plurality of switching elements in a three-phase bridge connection. FIG. 2 is a diagram illustrating a configuration example of the power conversion unit 10. Note that the power conversion unit 10 is not limited to the configuration illustrated in FIG. 2, and may be any configuration that can perform power conversion.

  Although the power converter device 1 shown in FIG. 1 is arrange | positioned between the power generator 2 which is a DC power generator, and the electric power grid | system 3, the power generator 2 may be an AC power generator. In this case, the power conversion device 1 includes a converter that converts AC power supplied from an AC power source into DC power and supplies the DC power to the power conversion unit 10.

  The voltage detector 11 detects an instantaneous value of the three-phase AC voltage Vrst of the power system 3 (hereinafter referred to as the system voltage Vrst). For example, the voltage detection unit 11 can detect the instantaneous values of the line voltages Vrs and Vst of the power system 3 (hereinafter referred to as line voltages Vrs and Vst) as the system voltage Vrst. The line voltage Vrs is a line voltage between the R phase and the S phase of the power system 3, and the line voltage Vst is a line voltage between the S phase and the T phase of the power system 3.

  The current detection unit 12 is provided between the power conversion unit 10 and the power system 3, and an instantaneous value of current flowing between the power conversion unit 10 and each of the R phase, S phase, and T phase of the power system 3 Ir, Is, It (hereinafter referred to as system currents Ir, Is, It) are detected. Note that the current detection unit 12 detects a current by using, for example, a Hall element that is a magnetoelectric conversion element.

  The control unit 20 includes a drive control unit 21, a frequency change detection unit 22, a reactive power injection control unit 23, and a fluctuation suppression unit 24.

  The drive control unit 21 controls the power conversion unit 10 so as to convert DC power supplied from the power generation device 2 into three-phase AC power and output it to the power system 3. For example, the drive control unit 21 controls the power conversion unit 10 so that the system currents Ir, Is, and It become target values.

  The frequency change detection unit 22 detects a change in the frequency of the system voltage Vrst (hereinafter referred to as the system frequency frst). The reactive power injection control unit 23 controls the injection of reactive power from the power conversion unit 10 to the power system 3 based on the detection result of the frequency change detection unit 22.

  For example, the reactive power injection control unit 23 generates a command corresponding to the change in the system frequency frst and notifies the drive control unit 21 when the change in the system frequency frst is detected by the frequency change detection unit 22. Thereby, the drive signal according to the command notified from the reactive power injection control unit 23 is output from the drive control unit 21 to the power conversion unit 10, and the reactive power is injected from the power conversion unit 10 to the power system 3. .

  For example, the reactive power injection control unit 23 generates a command so that reactive power that promotes a change in the system frequency frst is injected into the power system 3 and controls the power conversion unit 10 via the drive control unit 21. The reactive power injection control unit 23 detects an isolated operation of the power conversion apparatus 1 when the system frequency frst changes abruptly due to reactive power injection, for example.

  The reactive power injection control unit 23 disconnects the connection between the power conversion device 1 and the power system 3 when detecting an isolated operation of the power conversion device 1. The disconnection of the connection between the power conversion device 1 and the power system 3 is performed by controlling a disconnection relay (not shown) disposed between the power conversion unit 10 and the power system 3, for example.

  By the way, even when the system frequency frst changes due to factors other than the single operation (for example, the power supply disturbance on the power system 3 side), the reactive power injection control unit 23 supplies the power system 3 based on the change in the system frequency frst. In some cases, the reactive power is injected. In this case, it appears that the system voltage Vrst changes due to the injection of reactive power, and the system frequency frst changes.

  The frequency change detection unit 22 detects the change in the system frequency frst by, for example, comparing the latest detection result of the system frequency frst with the detection result of the past system frequency frst. Therefore, even when the system frequency frst changes due to factors other than the single operation, reactive power may be injected into the power system based on the change in the system frequency frst.

  In this case, the system voltage Vrst changes due to the injection of the reactive power, and the system frequency frst appears to change due to the change. When a change in the system frequency frst is detected by comparing the latest detection result of the system frequency frst with the detection result of the past system frequency frst, the change in the system frequency frst caused by the reactive power injection is the past system frequency frst. Appears as a result of detection. Therefore, it seems that the system frequency frst has changed due to the detection result of the past system frequency frst, the reactive power injection is repeated, and the system voltage Vrst fluctuates periodically (hereinafter sometimes referred to as a fluctuation mode). May occur).

  Therefore, for example, the fluctuation suppressing unit 24 executes processing for controlling the power conversion unit 10 so as to suppress periodic fluctuations in the system frequency frst based on the detection result of the frequency change detecting unit 22. Thereby, when it is not a single operation, when it is not a single operation, injection of reactive power can be reduced. Hereinafter, the configuration of the power conversion device 1 will be described in more detail.

[2. Configuration example of power conversion device 1]
FIG. 3 is a diagram illustrating a configuration example of the power conversion device 1 illustrated in FIG. 1. As illustrated in FIG. 3, the power conversion device 1 includes a power conversion unit 10, voltage detection units 11 and 13, current detection units 12 and 14, and a control unit 20.

  The voltage detection unit 13 detects an instantaneous value of voltage supplied to the power conversion unit 10 from the power generation device 2 (hereinafter referred to as supply voltage Vin). In addition, the current detection unit 14 detects an instantaneous value of current supplied from the power generation device 2 to the power conversion unit 10 (hereinafter referred to as supply current Iin).

  The control unit 20 includes, for example, a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), an input / output port, and various circuits. The CPU of such a microcomputer can realize the control described later by reading and executing a program stored in the ROM.

  The control unit 20 includes a drive control unit 21, a frequency change detection unit 22, a reactive power injection control unit 23, a fluctuation suppression unit 24, and an MPPT (Maximum Power Point Tracking) calculation unit 25. The functions of the drive control unit 21, the frequency change detection unit 22, the reactive power injection control unit 23, the fluctuation suppression unit 24, and the MPPT calculation unit 25 are realized, for example, by the CPU reading and executing the program.

  The drive control unit 21, the frequency change detection unit 22, the reactive power injection control unit 23, the fluctuation suppression unit 24, and the MPPT calculation unit 25 are each partially or entirely, for example, ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable). Gate Array) or the like. Hereinafter, the frequency change detection unit 22, the drive control unit 21, the reactive power injection control unit 23, the fluctuation suppression unit 24, and the MPPT calculation unit 25 will be described in detail in this order.

[2.1. Frequency change detection unit 22]
The frequency change detection unit 22 includes a phase detection unit 31, a system frequency detection unit 32 (an example of a frequency detection unit), and a system frequency deviation calculation unit 33 (an example of a frequency difference calculation unit). The phase detector 31 detects the phase θv of the system voltage Vrst (hereinafter referred to as the system phase θv) based on the line voltages Vrs and Vst.

The phase detector 31 converts the line voltages Vrs and Vst into an α-axis voltage Vα and a β-axis voltage Vβ, which are two αβ components orthogonal to each other on fixed coordinates. For example, the phase detection unit 31 performs an operation of the following formula (1) to convert the line voltages Vrs and Vst into an α-axis voltage Vα and a β-axis voltage Vβ.

  Further, the phase detector 31 detects the system phase θv based on, for example, the α-axis voltage Vα and the β-axis voltage Vβ. The phase detection unit 31 includes, for example, a PLL (Phase Locked Loop) that is executed by the CPU by a program stored in the ROM, but may be configured by hardware such as a logic circuit.

For example, the phase detection unit 31 calculates the following equation (2) to obtain the voltage amplitude E _max . Further, the phase detection unit 31 performs PI (proportional integration) control so that the d-axis voltage Vd becomes zero by, for example, calculations shown in the following formulas (3) and (4) to obtain the system phase θv. In the following formula (4), “T _I ” is an integration time, and “K _P ” is a proportionality constant.

The system frequency detection unit 32 detects the system frequency frst from the system phase θv. The system frequency detection unit 32 obtains the system frequency frst by performing, for example, the calculation shown in the following formula (5).

The system frequency deviation calculation unit 33 has a moving average value f _ave2 of the system frequency frst for the latest first period T1 among the system frequencies frst detected by the system frequency detection unit 32 and a third period from the latest system frequency frst. A difference Δf (hereinafter referred to as a frequency deviation Δf) from the moving average value f _ave1 of the system frequency frst for the second period T2 before T3 is calculated.

  FIG. 4 is a diagram illustrating a configuration example of the system frequency deviation calculation unit 33. As shown in FIG. 4, the system frequency deviation calculation unit 33 includes a first moving average calculation unit 41, a second moving average calculation unit 42, and a subtraction unit 43. For example, the system frequency deviation calculation unit 33 performs calculation every calculation cycle Ts (for example, 5 ms).

For example, the first moving average calculating unit 41 calculates a moving average value of the system frequency frst in the latest second period T2 (for example, 80 ms), and sets the moving average value f _ave1 after the third period T3 (for example, 200 ms). Output. Further, the first moving average calculation unit 41 calculates the moving average value f _ave1 of the system frequency frst for the second period T2 (for example, 80 ms) before the third period T3 (for example, 200 ms) before the latest system frequency frst. It can also be calculated.

For example, the second moving average calculation unit 42 calculates the moving average value f _ave2 of the system frequency frst for the latest first period T1 (for example, 40 ms). The subtracting unit 43 subtracts the moving average value f _ave2 from the moving average value f _ave1 to obtain the frequency deviation Δf.

FIG. 5 is a diagram illustrating an example of the moving average values f _ave1 and f _ave2 and the frequency deviation Δf calculated by the system frequency deviation calculating unit 33. In FIG. 5, the latest calculation cycle Ts is C0, the calculation cycle Ts before n (n is a natural number) cycle is Cn, and the calculation cycle Ts after n cycles is C−n.

In FIG. 5, moving average values f _ave1 and f _ave2 in period C0 are _set as moving average values f _{ave1 (0)} and f _{ave2 (0),} and moving average values f _ave1 and f _ave2 in period C-1 are _set as moving averages. The values f _{ave1 (-1)} and f _{ave2 (-1)} are set, and the moving average values f _ave1 and f _ave2 in the period C-2 are _described as moving average values f _{ave1 (-2)} and f _{ave2 (-2)} .

When acquiring the system frequency frst of the period C0, the first moving average calculation unit 41 outputs the average value of the system frequencies frst of the periods C55 to C40 for 80 ms before 200 ms as the moving average value f _{ave1 (0)} . Further, when the second moving average calculation unit 42 acquires the system frequency frst with the period C0, the second moving average calculator 42 outputs the average value of the latest system frequencies frst with the periods C7 to C0 for 40 ms as the moving average value f _{ave2 (0)} . The subtracting unit 43 subtracts the moving average value f _{ave2 (0)} from the moving average value f _{ave1 (0)} to obtain the frequency deviation Δf.

In the next cycle C-1, when the first moving average calculation unit 41 obtains the system frequency frst of the cycle C-1, the average value of the system frequencies frst of the cycles C54 to C39 for 80 ms before 200 ms is obtained as the moving average value. f Output as _{ave1 (-1)} . Further, when the second moving average calculation unit 42 acquires the system frequency frst of the cycle C-1, the second moving average calculation unit 42 calculates the average value of the system frequencies frst of the latest 40 ms of the cycles C6 to C-1 as the moving average value f _{ave2 (-1 )} Is output. The subtracting unit 43 subtracts the moving average value f _{ave2 (-1)} from the moving average value f _{ave1 (-1)} to obtain the frequency deviation Δf.

Further, in the next cycle C-2, when the first moving average calculation unit 41 acquires the system frequency frst of the cycle C-2, the average value of the system frequencies frst of the cycles C53 to C38 for 80 ms of 200 ms before is calculated as a moving average. Output as the value f _{ave1 (-2)} . Further, when the second moving average calculating unit 42 acquires the system frequency frst of the cycle C-2, the second moving average calculating unit 42 obtains the average value of the system frequencies frst of the latest cycles C5 to C-2 for 40 ms as the moving average value f _{ave2 (−2 )} Is output. The subtracting unit 43 subtracts the moving average value f _{ave2 (−2)} from the moving average value f _{ave1 (−2)} to obtain a frequency deviation Δf.

The system frequency deviation calculation unit 33 thus calculates the moving average values f _ave1 and f _ave2 and the frequency deviation Δf for each calculation cycle Ts.

[2.2. Drive control unit 21]
Next, the drive control unit 21 will be described. As shown in FIG. 3, the drive control unit 21 includes a coordinate conversion unit 51, a current control unit 52, and a PWM control unit 53.

The coordinate conversion unit 51 converts the system currents Ir, Is and It into a d-axis current Id which is a d-axis component of a dq-axis coordinate system rotating at a system frequency frst and a q-axis current Iq which is a q-axis component. The coordinate conversion unit 51 obtains the d-axis current Id and the q-axis current Iq by, for example, calculations of the following formulas (6) and (7).

The current control unit 52 generates a d-axis voltage command Vd ^* and a q-axis voltage command Vq ^* based on the d-axis current command Id ^* , the q-axis current command Iq ^* , the d-axis current Id, and the q-axis current Iq. The current control unit 52 generates the d-axis voltage command Vd ^* by performing PI (proportional integration) control so that the deviation between the d-axis current command Id ^* and the d-axis current Id becomes zero, for example.

The current control unit 52 generates the q-axis voltage command Vq ^* by performing PI (proportional integration) control so that the deviation between the q-axis current command Iq ^* and the q-axis current Iq becomes zero, for example. .

The PWM control unit 53 controls the power conversion unit 10 based on the system phase θv, the d-axis voltage command Vd ^*, and the q-axis voltage command Vq ^* . For example, the PWM control unit 53 obtains R-phase, S-phase, and T-phase voltage commands Vr ^* , Vs ^*, and Vt ^* by calculating the following formulas (8) to (12). For example, the PWM control unit 53 compares the voltage commands Vr ^* , Vs ^*, and Vt ^* with the carrier signal Sc to generate a drive signal for driving the switching element of the power conversion unit 10, and to the power conversion unit 10. Output. The PWM control unit 53 changes the d-axis voltage command Vd ^* and the q-axis voltage command Vq ^* to αβ components, and then converts the αβ components into voltage commands Vr ^* , Vs ^*, and Vt ^* by two-phase three-phase conversion. You can ask for it.

[2.3. Reactive power injection control unit 23]
The reactive power injection control unit 23 includes a frequency feedback calculation unit 61 (hereinafter referred to as a frequency FB calculation unit 61) and an isolated operation determination unit 62.

The frequency FB calculator 61 generates a d-axis current command Id ^* corresponding to the frequency deviation Δf. FIG. 6 is a diagram illustrating an example of the frequency feedback gain in the frequency FB calculation unit 61.

As shown in FIG. 6, for example, when Δf = 0.02 Hz, a d-axis current command Id ^* having a magnitude that outputs reactive power of 2% of the rated power is generated, and when Δf = 0.2 Hz. Then, a d-axis current command Id ^* having a magnitude for outputting reactive power of 10% of the rated power is generated. Further, when −0.01 Hz ≦ Δf ≦ 0.01 Hz, Id ^* = 0.01 × Δf, and in the range of −0.01 Hz to 0.01 Hz, the d-axis current command Id ^* is substantially zero. It is a dead zone region. Note that the frequency feedback gain is not limited to the example shown in FIG. 6, and the range of the dead zone, the magnitude of the gain, and the like can be changed by setting from the outside.

  The isolated operation determination unit 62 detects the isolated operation of the power converter 1 when the system frequency frst changes rapidly due to the reactive power injection by the reactive power injection control unit 23. For example, the isolated operation determination unit 62 determines that the change amount of the system frequency frst exceeds a predetermined amount (for example, a range of + 10% to −10% of the rated frequency) in a predetermined period (for example, 40 ms) based on the frequency deviation Δf. If it is, it is determined that it is a single operation. For example, the single operation determination unit 62 determines that the single operation is performed when the integrated value of the frequency deviation Δf in a predetermined period exceeds a predetermined amount.

  When the isolated operation determination unit 62 detects the isolated operation of the power conversion device 1, the isolated operation determination unit 62 disconnects the connection between the power conversion device 1 and the power system 3. The disconnection of the connection between the power conversion device 1 and the power system 3 is performed by controlling a disconnection relay (not shown) disposed between the power conversion device 1 and the power system 3, for example.

[2.4. Fluctuation suppression unit 24 and MPPT calculation unit 25]
3 is a target value of the effective current to the power system 3 so that the generated power output from the power generator 2 is maximized based on the supply voltage Vin and the supply current Iin. A q-axis current command Iq ^** is generated. For example, the MPPT calculation unit 25 obtains the supply power Pin by multiplying the supply voltage Vin and the supply current Iin, and generates the q-axis current command Iq ^** so that the supply power Pin is maximized.

  The fluctuation suppression unit 24 includes a fluctuation determination unit 71 and a q-axis command adjustment unit 72 (an example of an adjustment unit). Based on the detection result of the frequency change detection unit 22, periodic fluctuations in the frequency of the power system 3 are suppressed. The fluctuation determination unit 71 determines whether or not the fluctuation mode is such that the frequency deviation Δf periodically fluctuates.

  For example, the fluctuation determination unit 71 can determine that the fluctuation mode is such that the frequency deviation Δf periodically fluctuates when the frequency deviation Δf changes after the third period T3 from the timing when the frequency deviation Δf changes. . The fluctuation determination unit 71 can also determine that the fluctuation mode is set when the state in which the frequency deviation Δf is within a predetermined range continues for a predetermined period after the frequency deviation Δf has changed.

If the q-axis command adjustment unit 72 determines that the variation mode is set to the variation mode, the q-axis command adjustment unit 72 suppresses the variation mode instead of the q-axis current command Iq ^** output from the MPPT calculation unit 25. by generating axis current Iq ^*, adjusts the q-axis current command Iq ^*. On the other hand, when the q-axis command adjustment unit 72 determines that the fluctuation determination unit 71 is not in the fluctuation mode, the q-axis current command Iq ^** output from the MPPT calculation unit 25 is used as the q-axis current command Iq ^*. Output.

  Here, the operation of the control unit 20 when a change in the system frequency frst is detected by the frequency change detection unit 22 will be described. FIG. 7 is an image diagram illustrating an example of operations of the frequency change detection unit 22 and the reactive power injection control unit 23 when a change in the system frequency frst is detected by the frequency change detection unit 22.

  As shown in FIG. 7, when the voltage frequency of the power system 3 (hereinafter sometimes referred to as system frequency) changes from time t1 to time t2, the system frequency frst detected by the system frequency detection unit 32 changes. .

When the system frequency frst changes, the moving average value f _ave2 calculated by the second moving average calculator 42 changes. On the other hand, the moving average value f _ave1 output after the third period T3 by the first moving average calculator 41 changes, but at this time, the moving average value f _ave1 does not change by the first moving average calculator 41.

Therefore, since the frequency deviation Δf calculated by the system frequency deviation calculating unit 33 changes, the d-axis current command Id ^* corresponding to the frequency deviation Δf is output from the frequency FB calculating unit 61 to the current control unit 52. As a result, reactive power corresponding to the frequency deviation Δf is injected from the power conversion unit 10 to the power system 3.

After 200 ms from time t4 when the moving average value f _ave2 changes (an example of the third period T3), the moving average value f _ave1 for 80 ms (an example of the second period T2) 200 ms before from the first moving average calculator 41 is obtained. Is output. On the other hand, when the system frequency frst detected by the system frequency detector 32 is constant at time t10 200 ms after time t4 (for example, frst = f1), the moving average value f _ave2 = f1.

Therefore, the frequency deviation Δf calculated by the system frequency deviation calculating unit 33 changes. Therefore, at time t10, the moving average value f _ave1 output from the first moving average calculator 41 changes, and the frequency deviation Δf calculated by the system frequency deviation calculator 33 changes.

When the frequency deviation Δf changes, a d-axis current command Id ^* corresponding to the frequency deviation Δf is output from the frequency FB calculation unit 61 to the current control unit 52. Thereby, the reactive power corresponding to the frequency deviation Δf is injected into the power system 3 from the power conversion unit 10 even though the system frequency frst is not immediately after the change.

  When the voltage frequency of the power system 3 changes due to the injection of reactive power, the system frequency frst detected by the system frequency detection unit 32 changes, and the system shifts to a fluctuation mode in which the above-described processing is periodically repeated by the system frequency frst. There is a case.

  FIG. 8 is a diagram illustrating a state example of the variation mode. As shown in FIG. 8, when the voltage frequency of the power system 3 is changed by the reactive power injected into the power system 3 according to the frequency deviation Δf at time t10, the system frequency frst detected by the system frequency detection unit 32 is changed. Change.

Due to the change in the system frequency frst, the moving average value f _ave1 output from the first moving average calculator 41 after 200 ms changes (see time t10 shown in FIG. 7). The frequency deviation Δf changes due to the change in the moving average value f _ave1 , and reactive power corresponding to the frequency deviation Δf is injected into the power system 3.

  When the voltage frequency of the power system 3 changes due to the injection of reactive power, the system frequency frst detected by the system frequency detection unit 32 changes as shown in FIG. Thereafter, such processing is repeated at a cycle of 200 ms. Therefore, when it is not a single operation, there is a possibility that injection of reactive power may be repeated periodically.

  Therefore, the control unit 20 of the power conversion device 1 according to the embodiment controls the power conversion unit 10 so as to suppress periodic fluctuations in the system frequency frst. Thereby, when it is not a single operation, injection of reactive power can be reduced.

  The periodic variation of the system frequency frst is detected by the variation determination unit 71 shown in FIG. The fluctuation determination unit 71 determines a periodic fluctuation of the frequency deviation Δf. For example, the fluctuation determination unit 71 determines that the frequency deviation Δf is fluctuating when the frequency deviation Δf exceeds a value fth within a predetermined range (for example, the dead band level range of the frequency feedback of the frequency FB calculation unit 61). Can do.

  For example, when the fluctuation determination unit 71 has a fluctuation period of the frequency deviation Δf corresponding to the third period T3, that is, a fluctuation period of the frequency deviation Δf is a period of about 200 ms (for example, a period of 200 ms ± 10 ms), It can be determined that the fluctuation mode has occurred. For example, the fluctuation determination unit 71 can determine that the fluctuation mode has occurred when the frequency deviation Δf changes after the third period T3 from the timing when the frequency deviation Δf changes.

  In the example shown in FIG. 7, a variation in the frequency deviation Δf occurs between times t4 and t6, and further, a variation in the frequency deviation Δf occurs between times t10 and t12. The variation period of the frequency deviation Δf is 200 ms.

  For example, the fluctuation determination unit 71 has a fluctuation period of the frequency deviation Δf corresponding to the third period T3, and the frequency deviation Δf alternates between positive and negative every period corresponding to the third period T3. In the case of a change, it can also be determined that the fluctuation mode has occurred. For example, the fluctuation determination unit 71 determines that the fluctuation mode has occurred when the negative frequency deviation Δf occurs in the next period corresponding to the third period T3 after the positive frequency deviation Δf has occurred. Can do. Thereby, the detection accuracy of the fluctuation mode can be improved.

  The fluctuation determination unit 71 can quickly detect the fluctuation mode by determining that the fluctuation mode has occurred when the fluctuation of the frequency deviation Δf has occurred twice in the interval of the third period T3. it can. The variation determination unit 71 can also determine that the variation mode is occurring when the variation of the frequency deviation Δf occurs three or more times at the interval of the third period T3.

  Further, after the change of the frequency deviation Δf, the fluctuation determination unit 71 determines that the frequency deviation Δf is within a predetermined range of value fth (for example, a value within the dead zone level of the frequency feedback) (for example, the period T4 shown in FIG. 7). Can be determined to be in the variation mode when the operation continues for a predetermined period Tth or more.

Here, an equivalent circuit of the power system 3 viewed from the power converter 1 is considered. FIG. 9 is a diagram illustrating an equivalent circuit of the power system 3 as viewed from the power conversion apparatus 1. “Vo” is a voltage vector output from the power conversion device 1 to the power system 3, and “Io” is a current vector output from the power conversion device 1 to the power system 3. “R _S ” is a resistance component of the line impedance of the power system 3, “L _S ” is a reactance component of the line impedance of the power system 3, and “E” is a vector of the power supply voltage E of the power system 3 (hereinafter, “ , Sometimes referred to as a power supply voltage vector E).

  FIG. 10 is a diagram illustrating the voltage vector Vo and the current vector Io as vectors in the dq axis coordinate system when the system frequency frst is constant. As shown in FIG. 10, the power supply voltage vector E is on the q axis, and the power supply voltage vector E and the voltage vector Vo of the power converter 1 have a phase difference θ.

The relationship between the d-axis voltage command Vd ^* and the q-axis voltage command Vq ^* and the d-axis current command Id ^* and the q-axis current command Iq ^* can be expressed as the following formula (13). In the following formula (13), ω = 2π × f. “F” is the voltage frequency of the power supply of the power system 3.

  FIG. 11 is a diagram showing the voltage vector Vo and the current vector Io as vectors in the dq axis coordinate system when the fluctuation mode is occurring. In FIG. 11, “Vo” is represented as “Vo ′”, “Io” is represented as “Io ′”, and “θ” so as to facilitate comparison with the case where the system frequency frst is constant. Is represented as “θ ′”.

As shown in FIG. 11, when the d-axis current command Id ^* for injecting reactive power is generated, the phase difference θ ′ deviates from the phase difference θ when the system frequency frst is constant. Here, it is assumed that R _S = 0.38Ω, L _S = 0.46 mH, f = 60 Hz, and E = 200V.

In this case, if Iq ^* = 50 A and Id ^* = 0 A, θ = 2.26 °, and if Iq ^* = 50 A and Id ^* = 12.5 A, θ ′ = 3.54 °. Therefore, there is a phase difference Δθ of 1.27 ° between the case where the reactive current of 12.5 A is injected into the power system 3 and the case where the reactive current is not injected into the power system 3, which is detected by the system frequency detection unit 32. The system frequency frst is 60.2 Hz.

Therefore, when the variation mode is detected by the variation determination unit 71, the q-axis command adjustment unit 72 generates and outputs the q-axis current command Iq ^* so that the frequency deviation Δf is within the set range. For example, the fluctuation determination unit 71 generates the q-axis current command Iq ^* so that the frequency deviation Δf is within the dead band level (−0.01 Hz ≦ Δf ≦ 0.01 Hz) of the frequency feedback of the frequency FB calculation unit 61. Can be output.

When the frequency deviation Δf is suppressed within the dead band level of frequency feedback, the following equation (14) can be derived from the above equation (13). Note that R _S = 0.38Ω, L _S = 0.46 mH, f = 60 Hz, E = 200 V, and Id ^* = 12.5 A.

From the above equation (14), the q-axis current command Iq ^* that suppresses the frequency deviation Δf within the dead zone level of the frequency feedback can be expressed by the following equation (15).

Therefore, when R _S = 0.38Ω, L _S = 0.46 mH, f = 60 Hz, E = 200 V, and Id ^* = 12.5 A, the frequency deviation Δf is set to the frequency by setting Iq ^* = 20.83 A. It can be suppressed within the deadband level of feedback. In the calculation of equation (15), the q-axis current command Iq ^* is obtained so that frst = 60.01 Hz, but the q-axis command adjustment unit 72 changes the value of equation (15). Q-axis current command Iq ^* for setting frst = 60.00 Hz can also be obtained.

The q-axis command adjustment unit 72 stores values of the resistance component R _S , the reactance component L _S , the voltage frequency f, and the power supply voltage E in advance, and when the variation mode is detected by the variation determination unit 71, the d-axis Based on the current command Id ^* , the q-axis current command Iq ^* is generated and output by the above-described calculation.

The q-axis command adjustment unit 72 stores, for example, the d-axis current command Id ^* and the q-axis current command Iq ^* for suppressing the variation mode in association with each other, and when the variation mode occurs, the d-axis current command Id ^* is stored. A q-axis current command Iq ^* can also be output based on Id ^* .

FIG. 12 is a diagram showing the voltage vector Vo and the current vector Io as vectors in the dq axis coordinate system when the fluctuation mode occurs and the q axis current command Iq ^* adjusted from the q axis command adjustment unit 72 is output. It is. In FIG. 12, “Vo” is expressed as “Vo”, “Io” is expressed as “Io”, and “θ” is expressed as “θ” so that the comparison with FIGS. "".

As shown in FIG. 12, even when the fluctuation mode occurs, the frequency deviation Δf can be suppressed within the dead zone level of the frequency feedback by the q-axis current command Iq ^* generated by the q-axis command adjustment unit 72. it can.

For example, the q-axis command adjustment unit 72 sets the q-axis current command Iq ^* to suppress the frequency deviation Δf within the dead zone level of the frequency feedback for a predetermined period (for example, a period equal to or longer than the second period T2) after the fluctuation mode is detected. Generate and output to the current control unit 52.

In addition, the q-axis command adjustment unit 72 performs frequency feedback on the frequency deviation Δf in a period in which at least the third frequency deviation Δf occurs after the frequency deviation Δf changes twice at the interval of the third period T3. It is also possible to generate a q-axis current command Iq ^* that is suppressed within the dead zone level.

On the other hand, the q-axis command adjustment unit 72 outputs the q-axis current command Iq ^* generated by the MPPT calculation unit 25 to the current control unit 52 when the variation determination unit 71 determines that the variation mode has not occurred. To do.

3 is an example of a configuration that adjusts the q-axis current command Iq ^*. However, the variation suppression unit 24 does not adjust the q-axis current command Iq ^* , but instead adjusts the q-axis current command Iq ^* . The moving average value of the system frequency frst can be set to zero.

FIG. 13 is a diagram illustrating another configuration example of the power conversion device 1. In addition, about the component similar to the power converter device 1 shown in FIG. 3, the same code | symbol may be attached | subjected and description may be abbreviate | omitted. The q-axis current command Iq ^** generated by the MPPT calculation unit 25 is output to the current control unit 52 of the drive control unit 21 as the q-axis current command Iq ^* .

The fluctuation suppression unit 24 illustrated in FIG. 13 includes a fluctuation determination unit 71 and an adjustment unit 73. The fluctuation determination unit 71 determines whether or not the fluctuation mode is such that the frequency deviation Δf periodically fluctuates. When the adjustment unit 73 determines that the frequency deviation Δf is periodically changing by the change determination unit 71, the adjustment unit 73 replaces the moving average value f _ave1 before the second period T2 with the latest system frequency frst of the second period T2. The first moving average calculator 41 can be controlled such that the moving average value is output from the first moving average calculator 41. In the example shown in FIG. 5, when the latest cycle is the cycle C0, the moving average value of the system frequency frst of the latest second period T2 is the system frequency frst of the cycle C15 to C0 for 80 ms for 200 ms before. Average value.

  For example, the adjustment unit 73 detects that the moving average value of the system frequency frst in the latest second period T2 is the first moving average calculation unit 41 for a predetermined period (for example, a period equal to or longer than the third period T3) after the fluctuation mode is detected. 1st moving average calculating part 41 can be controlled so that it may be output from.

  In addition, when the variation of the frequency deviation Δf occurs twice at the interval of the third period T3, the q-axis command adjustment unit 72 determines that the adjustment unit 73 is, for example, after the second variation of the frequency deviation Δf occurs. The first moving average calculation unit 41 is controlled such that the moving average value of the system frequency frst of the latest second period T2 is output from the first moving average calculation unit 41 for the second period T2 or more after the three periods T3. can do.

[3. Processing of control unit 20]
FIG. 14 is a flowchart showing the flow of processing by the control unit 20. The process shown in FIG. 14 is a process that is repeatedly executed.

  As shown in FIG. 14, the frequency change detection unit 22 of the control unit 20 detects a change in the system frequency frst (step S10). The reactive power injection control unit 23 of the control unit 20 controls the injection of reactive power from the power conversion unit 10 to the power system 3 based on the detection result of the frequency change detection unit 22 (step S11). The fluctuation suppressing unit 24 executes processing for suppressing periodic fluctuations in the system frequency frst based on the detection result of the frequency change detecting unit 22 (step S12).

  As described above, the power conversion device 1 according to the embodiment includes the power conversion unit 10 and the control unit 20 (an example of a control device). The control unit 20 includes a frequency change detection unit 22, a reactive power injection control unit 23, and a fluctuation suppression unit 24. The power conversion unit 10 converts the power supplied from the power generation device 2 (an example of a power source) and supplies the converted power to the power system 3. The frequency change detection unit 22 detects a change in the system frequency frst (an example of the frequency of the power system). The reactive power injection control unit 23 controls the injection of reactive power from the power conversion unit 10 to the power system 3 based on the detection result of the frequency change detection unit 22. Based on the detection result of the frequency change detection unit 22, the fluctuation suppression unit 24 executes processing for suppressing periodic fluctuations in the system frequency frst.

  Thereby, for example, since the periodic fluctuation of the detected system voltage Vrst can be suppressed, the injection of reactive power can be reduced when it is not an independent operation. For this reason, since it is possible to prevent the system voltage Vrst from periodically fluctuating due to the injection of reactive power, it is possible to increase the frequency feedback gain and to increase the speed and accuracy of the isolated operation detection. . The “periodic fluctuation of the system frequency frst” means, for example, as described above, the system frequency frst changes according to the detection result of the past system frequency frst, and the reactive power injection is repeated periodically. In the system frequency frst (hereinafter referred to as periodic frequency fluctuation). For example, the fluctuation suppressing unit 24 suppresses the periodic frequency fluctuation by preventing the occurrence of the periodic frequency fluctuation or reducing the periodic frequency fluctuation. Thereby, the periodic fluctuation of the detected system voltage Vrst can be suppressed, and the injection of reactive power can be reduced.

  Further, the fluctuation suppressing unit 24 includes a q-axis command adjusting unit 72 (an example of an adjusting unit) that adjusts the effective current from the power conversion unit 10 to the power system 3 so as to suppress the periodic fluctuation of the system frequency frst. .

As a result, the q-axis current command Iq ^* is adjusted so as to suppress periodic fluctuations in the frequency of the power system 3, so that, for example, without changing the reactive power injection process by frequency feedback, If not, reactive power injection can be accurately reduced.

The frequency change detection unit 22 includes a system frequency detection unit 32 (an example of a frequency detection unit) and a system frequency deviation calculation unit 33 (an example of a frequency difference calculation unit). The system frequency detection unit 32 detects the system frequency frst. The system frequency deviation calculating unit 33 has a moving average value (for example, moving average value f _ave2 ) of the system frequency frst in the first period T1 among the system frequencies frst detected by the system frequency detecting unit 32 and the first period T1. A frequency deviation Δf that is a difference from the moving average value (for example, moving average value f _ave1 ) of the system frequency frst in the second period T2 that is the previous period is calculated. The reactive power injection control unit 23 controls the injection of reactive power into the power system 3 based on the frequency deviation Δf calculated by the system frequency deviation calculating unit 33 (an example of a difference in moving average value).

  As described above, since the frequency change detection unit 22 detects the change in the system frequency frst by the moving average value of the system frequency frst, the reactive power can be injected with high accuracy.

  In addition, the power conversion device 1 has a change amount of the system frequency frst detected by the frequency change detection unit 22 based on the frequency deviation Δf (an example of a difference in moving average value) calculated by the system frequency deviation calculation unit 33. When it is determined that a predetermined amount has been exceeded during a predetermined period, an isolated operation determination unit 62 is provided that determines that the operation is an isolated operation. Thereby, an isolated operation can be detected with high accuracy.

  The fluctuation suppressing unit 24 includes a fluctuation determining unit 71 that determines a periodic fluctuation of the system frequency frst based on the frequency deviation Δf calculated by the system frequency deviation calculating unit 33.

  As described above, since the fluctuation suppressing unit 24 determines the periodic fluctuation of the system voltage Vrst based on the frequency deviation Δf used for the reactive power injection, it is possible to accurately inject the reactive power when it is not an independent operation. It can be reduced well.

Further, the system frequency deviation calculating unit 33 is the moving average value f _ave2 of the latest frequency in the first period T1 among the system frequency frst detected by the system frequency detecting unit 32 and the third period T3 before the latest frequency. A frequency deviation Δf, which is a difference from the moving average value f _ave1 of the frequency in the second period T2, is calculated. The variation determining unit 71 determines that the system frequency frst varies periodically when the difference calculated by the system frequency deviation calculating unit 33 varies in a cycle corresponding to the third period T3.

  As described above, the fluctuation determination unit 71 detects the periodic fluctuation of the system frequency frst when the frequency deviation Δf used for the reactive power injection fluctuates in a period corresponding to the third period T3. If this is not the case, injection of reactive power can be accurately reduced.

  In addition, the fluctuation determining unit 71 determines that the system frequency frst is periodic when the frequency deviation Δf calculated by the system frequency deviation calculating unit 33 alternately changes between positive and negative every period corresponding to the third period T3. It is determined that it fluctuates.

  As described above, the fluctuation determining unit 71 periodically changes the system frequency frst when the difference in the frequency deviation Δf used for the reactive power injection alternately changes between positive and negative every period corresponding to the third period T3. Since such a change is detected, the reactive power injection can be accurately reduced when it is not a single operation.

  The power conversion device 1 also includes a voltage detection unit 11 that detects the voltage of the power system 3. The control unit 20 includes a phase detection unit 31 and a system frequency detection unit 32. The phase detection unit 31 detects the system phase θv (an example of the voltage phase of the power system 3) from the system voltage Vrst (an example of the power system voltage) detected by the voltage detection unit 11. The system frequency detection unit 32 detects the system frequency frst based on the system phase θv detected by the phase detection unit 31. The system frequency deviation calculator 33 detects a change in the system frequency frst based on the system frequency frst detected by the system frequency detector 32.

  Thereby, compared with the case where the system voltage frst is detected by converting the system voltage Vrst into a square wave by a comparator or the like, the responsiveness when the system frequency frst changes can be improved.

  In addition, the power generation system 100 according to the embodiment includes a power conversion device 1 and a power generation device 2. The power conversion device 1 converts the power generated by the power generation device 2 into AC power corresponding to the power system 3 as power supplied from the power source and outputs the AC power to the power system 3.

  Accordingly, it is possible to provide a power generation system that can reduce injection of reactive power when it is not a single operation.

  The power conversion device 1 described above includes a power conversion unit 10, a frequency change detection unit 22, a reactive power injection control unit 23, and a “means for suppressing periodic fluctuations in the voltage of the power system due to reactive power injection”. Is provided. The fluctuation suppressing unit 24 is an example of “means for suppressing periodic fluctuations in the voltage of the power system due to the injection of reactive power”.

  Further effects and modifications can be easily derived by those skilled in the art. Thus, the broader aspects of the present invention are not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications can be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

DESCRIPTION OF SYMBOLS 1 Power converter 2 Power generator (an example of a power supply)
DESCRIPTION OF SYMBOLS 3 Electric power system 10 Power conversion part 11, 13 Voltage detection part 12, 14 Current detection part 20 Control part 21 Drive control part 22 Frequency change detection part 23 Reactive power injection | pouring control part 24 Fluctuation suppression part 25 MPPT calculating part (MPPT calculating part (command generation part) One case)
31 Phase detector 32 System frequency detector (an example of a frequency detector)
33 System frequency deviation calculation part (an example of a frequency difference calculation part)
41 First Moving Average Calculation Unit 42 Second Moving Average Calculation Unit 43 Subtraction Unit 51 Coordinate Conversion Unit 52 Current Control Unit 53 PWM Control Unit 61 Frequency Feedback Calculation Unit 62 Independent Operation Determination Unit 71 Fluctuation Determination Unit 72 q-axis Command Adjustment Unit ( Example of adjustment unit)
73 Adjustment part

Claims (11)

A power converter that converts the power supplied from the power source and supplies it to the power system;
A frequency change detection unit for detecting a change in frequency of the power system;
Based on the detection result of the frequency change detection unit, a reactive power injection control unit that controls injection of reactive power from the power conversion unit to the power system, and
A power conversion device comprising: a fluctuation suppression unit that executes processing for suppressing periodic fluctuations in the frequency of the power system based on a detection result of the frequency change detection unit. The power conversion device according to claim 1, further comprising: an adjustment unit that adjusts an effective current from the power conversion unit to the power system so as to suppress periodic fluctuations in the frequency of the power system. The frequency change detector is
A frequency detector for detecting the frequency of the power system;
A frequency difference for calculating a difference between a moving average value of a frequency in a first period and a moving average value of a frequency in a second period that is a period before the first period among the frequencies detected by the frequency detection unit. An arithmetic unit,
The reactive power injection control unit
The power converter according to claim 1 or 2, wherein injection of reactive power to the power system is controlled based on the difference calculated by the frequency difference calculator. An isolated operation determination unit that determines that the operation is an isolated operation when it is determined that the amount of change in the frequency of the power system exceeds a predetermined amount during a predetermined period based on the difference calculated by the frequency difference calculation unit. The power conversion device according to claim 3. The fluctuation suppressing unit is
The power converter according to claim 3, further comprising a fluctuation determination unit that determines a periodic fluctuation of the frequency of the power system based on the difference calculated by the frequency difference calculation unit. The frequency difference calculator is
Calculating the difference between the moving average value of the latest frequency of the first period and the moving average value of the frequency of the second period before the latest frequency among the frequencies detected by the frequency detector;
The variation determination unit
6. The frequency of the power system is determined to periodically change when the difference calculated by the frequency difference calculation unit varies in a cycle corresponding to the third period. 6. Power conversion device. The variation determination unit
When the difference calculated by the frequency difference calculation unit alternately changes between positive and negative for each period corresponding to the third period, it is determined that the frequency of the power system varies periodically. The power conversion device according to claim 6. A voltage detector for detecting the voltage of the power system;
A phase detection unit for detecting a voltage phase of the power system from the voltage of the power system detected by the voltage detection unit;
A frequency detection unit that detects a frequency of the power system based on the voltage phase detected by the phase detection unit;
The frequency change detector is
The power conversion device according to claim 1 or 2, wherein a change in the frequency of the power system is detected based on the frequency of the power system detected by the frequency detection unit. The power conversion device according to any one of claims 1 to 8,
A power generation device,
The power converter is
The power generation system, wherein power generated by the power generation device is converted into AC power corresponding to the power system as power supplied from the power source and output to the power system. A frequency change detection unit for detecting a change in the frequency of the power system;
Based on the detection result of the frequency change detection unit, the reactive power injection control unit that controls the injection of reactive power from the power conversion unit to the power system,
And a fluctuation suppression unit that executes a process of suppressing periodic fluctuations in the frequency of the power system based on a detection result of the frequency change detection unit. Detecting power system frequency changes;
Based on the detection result, controlling injection of reactive power from the power converter to the power system;
Executing a process of suppressing periodic fluctuations in the frequency of the power system based on the detection result;
The control method characterized by including.

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