Power conversion device and program

Abstract

This power conversion device comprises a conversion unit, a grid forming control unit, a grid following control unit, a modulation unit, a switching unit, and a synchronization adjustment unit. The grid forming control unit generates a first modulation command. The grid following control unit generates a second modulation command. The modulation unit changes the amplitude and phase of an output voltage on the basis of the first modulation command or the second modulation command. The switching unit switches an input to the modulation unit so that either the first modulation command or the second modulation command is input to the modulation unit. Before the input to the modulation unit is switched from the second modulation command to the first modulation command, the synchronization adjustment unit corrects the first modulation command so that the difference between the target amplitude of the first modulation command and the amplitude of a grid voltage becomes less than or equal to a threshold value, the difference between the target frequency of the first modulation command and the frequency of the grid voltage becomes less than or equal to a threshold value, and the difference between the target phase of the first modulation command and the phase of the grid voltage becomes less than or equal to a threshold value.

Description

[Technical field]

[0001] An embodiment of the present invention relates to a power conversion device and a program. [Background technology]

[0002] In recent years, the use of inverter power supplies that convert DC power output from power sources such as generators and storage batteries that use renewable energy into AC power and output it has been increasing. Known control methods for inverter power supplies include the grid forming (GFM) type and grid following (GFL) type. Grid forming control (hereinafter referred to as GFM control) is a control that maintains the amplitude and phase of the output voltage of the inverter power supply at a predetermined set value. Grid following control (hereinafter referred to as GFL control) is a control that makes the amplitude and phase of the output voltage of the inverter power supply follow the amplitude and phase of the voltage of a predetermined power grid. The above-mentioned GFM control and GFL control may be switched depending on the usage status of the inverter power supply, etc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 070493 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional technology, when switching from GFL control to GFM control, the phase and amplitude of the output voltage may fluctuate significantly, which may cause the operation of the inverter power supply to become unstable.

[0005] An object of the present invention is to provide a power conversion device and a program capable of improving stability when switching between control methods. [Means for solving the problem]

[0006] A power conversion device according to an embodiment includes a conversion unit, a system formation control unit, a system tracking control unit, a modulation unit, a switching unit, and a synchronization adjustment unit. The conversion unit converts DC power output from a power source into AC power and outputs the AC power. The system formation control unit generates a first modulation command for changing the amplitude and phase of the output voltage by system formation control that maintains the amplitude and phase of the output voltage from the conversion unit at a predetermined set value. The system tracking control unit generates a second modulation command for changing the amplitude and phase of the output voltage by system tracking control that makes the amplitude and phase of the output voltage follow the amplitude and phase of a system voltage that is a voltage of a predetermined power system. The modulation unit changes the amplitude and phase of the output voltage based on the first modulation command or the second modulation command. The switching unit switches the input to the modulation unit so that either the first modulation command or the second modulation command is input to the modulation unit. The synchronization adjustment unit corrects the first modulation command so that, before the input to the modulation unit is switched from the second modulation command to the first modulation command, a difference between a target amplitude of the first modulation command and the amplitude of the grid voltage is equal to or less than a threshold value, a difference between a target frequency of the first modulation command and the frequency of the grid voltage is equal to or less than a threshold value, and a difference between a target phase of the first modulation command and the phase of the grid voltage is equal to or less than a threshold value. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram illustrating an example of a configuration of a power system according to an embodiment. [Diagram 2] FIG. 2 is a block diagram illustrating an example of a hardware configuration of the power conversion device according to the embodiment. [Diagram 3] FIG. 3 is a block diagram illustrating an example of a functional configuration of a power conversion device according to an embodiment. [Figure 4] FIG. 4 is a control block diagram illustrating an example of processing in the GFM control unit of the embodiment. [Diagram 5] FIG. 5 is a control block diagram illustrating an example of a process in the synchronization adjustment unit according to the embodiment. [Figure 6]FIG. 6 is a flowchart illustrating an example of processing performed when switching from GFL control to GFM control in the power conversion device of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, embodiments will be described with reference to the drawings.

[0009] 1 is a block diagram showing an example of a configuration of a power system 1 according to an embodiment. The power system 1 includes an inverter power supply 11, a transformer 12, and a power grid 13. The power system 1 may be, for example, a so-called microgrid system that configures an independent power grid 13 using distributed power sources including a plurality of power sources such as the inverter power supply 11.

[0010] The inverter power supply 11 includes a power supply 20 and a power conversion device 21. The power supply 20 is a unit that outputs DC power, and may be, for example, a generator that uses renewable energy (for example, solar power, wind power, etc.), a storage battery, etc. The power conversion device 21 is a device that converts DC power output from the power supply 20 into AC power and outputs it. Note that multiple power supplies 20 may be connected to one power conversion device 21.

[0011] The power conversion device 21 of this embodiment has a function of appropriately switching between GFM control (system formation control) for maintaining the amplitude and phase of the output voltage at predetermined set values, and GFL control (system tracking control) for making the amplitude and phase of the output voltage track the amplitude and phase of the voltage of the power system 13.

[0012] The AC power output from the inverter power supply 11 (power conversion device 21) is boosted by the transformer 12 and then output to the power system 13. Depending on the characteristics of the inverter power supply 11 and the power system 13, the transformer 12 may not be necessary.

[0013] 2 is a block diagram showing an example of a hardware configuration of the power conversion device 21 according to the embodiment. The power conversion device 21 illustrated here includes a power conversion circuit 31, a high-frequency filter circuit 32, and a control device 33 (an example of an information processing device).

[0014] The power conversion circuit 31 is a circuit that converts DC power output from the power source 20 into AC power, and may be configured using, for example, a converter circuit, a PWM (Pulse Width Modulation) circuit, etc. The high-frequency filter circuit 32 is a circuit (for example, a reactor) that performs high-frequency filtering (low-pass filtering) processing on the output of the power conversion circuit 31. The control device 33 is an integrated circuit that includes a CPU (Central Processing Unit), a memory, etc., and executes predetermined arithmetic processing and control processing according to a program stored in the memory. The control device 33 may be configured using an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), etc.

[0015] The power conversion circuit 31 changes the amplitude and phase of the output voltage based on a modulation command output from the control device 33. The control device 33 performs GFM control or GFL control based on a feedback signal of the output from the power conversion circuit 31, system voltage information related to the voltage of the power system 13, etc., and controls the output power P out (Output voltage V S In the configuration illustrated here, the control device 33 generates a modulation command to change the amplitude and phase of the reactor current I L , the output current I from the high frequency filter circuit 32 S , the output voltage V from the high frequency filter circuit 32 S The active power and reactive power are calculated based on the above.

[0016] In addition, the control device 33 of this embodiment has a function of switching between GFM control and GFL control depending on predetermined conditions, and a function of correcting a modulation command to improve stability (e.g., suppression of sudden fluctuations in the output voltage) when switching from GFL control to GLM control.

[0017] 3 is a block diagram showing an example of a functional configuration of the power conversion device 21 of the embodiment. The power conversion device 21 of the present embodiment includes a conversion unit 101, a GFM control unit 102 (grid formation control unit), a GFL control unit 103 (grid tracking control unit), a modulation unit 104, and a switching unit 105. These functional components 101 to 105 can be configured, for example, by cooperation between hardware elements such as those illustrated in FIG. 2 and software elements such as a program that controls the control device 33.

[0018] The conversion unit 101 converts the DC power output from the power source 20 into AC power to generate an output power (effective output power) P out At this time, the output voltage V S The amplitude and phase of the signal are adjusted by the modulation section 104 .

[0019] The GFM control unit 102 controls the output voltage V S The GFM control is performed to maintain the amplitude and phase of the output voltage V at a predetermined set value. S The GFL control unit 103 generates a first modulation command for changing the amplitude and phase of the output voltage V S The GFL control is performed to make the amplitude and phase of the output voltage V follow the amplitude and phase of the voltage (system voltage) of a predetermined power system (for example, the power system 13). S A second modulation command is generated to change the amplitude and phase of the

[0020] The switching unit 105 switches the input to the modulation unit 104 in response to a switching signal output from a predetermined control mechanism so that either the first modulation command or the second modulation command is input to the modulation unit 104. The modulation unit 104 controls the output voltage V S The amplitude and phase of the signal are changed.

[0021] The GFM control unit 102 of this embodiment includes a voltage control unit 111, a phase control unit 112, and a synchronization adjustment unit 113.

[0022] The voltage control unit 111 controls the output voltage V S The phase control unit 112 generates an amplitude command indicating a target value of the amplitude of the output voltage V S The first modulation command is generated based on the amplitude command generated by the voltage control section 111 and the phase command generated by the phase control section 112.

[0023] When switching from GFL control to GFM control, the synchronization adjustment unit 113 adjusts the output voltage V S The synchronization adjustment unit 113 of this embodiment corrects the first modulation command so that, before the input to the modulation unit 104 is switched from the second modulation command to the first modulation command, a difference between a target amplitude of the first modulation command and the amplitude of the grid voltage becomes equal to or less than a threshold, a difference between a target frequency of the first modulation command and the frequency of the grid voltage becomes equal to or less than a threshold, and a difference between a target phase of the first modulation command and the phase of the grid voltage becomes equal to or less than a threshold.

[0024] FIG. 4 is a control block diagram showing an example of processing in the GFM control unit 102 of the embodiment. In the voltage control unit 111, the reactive power command value Q ref to reactive power output value Q out The amplitude command offset value V is calculated by QV droop control for the value obtained by subtracting offset Calculate the reference amplitude setting value V set , Amplitude command offset value V offset , and the amplitude command correction value V corr (An example of an amplitude correction signal) is added to calculate the first amplitude setting value V1. sdThe second amplitude setting value V2 is calculated by an automatic voltage regulator (AVR) for the value obtained by subtracting V from V. The first amplitude setting value V1 and the second amplitude setting value V2 are added together to calculate the inverter output d-axis amplitude command value V dref (An example of the target amplitude) is calculated. In addition, the inverter output q-axis amplitude command value V dref is 0 under normal circumstances (for example, when the GFM control is executed in a predetermined stable state).

[0025] In the phase control unit 112, the active power command value P ref to the effective power output value P out The frequency ω1 is calculated by Pf droop control or VSG (Virtual Synchronous Generator) control for the value obtained by subtracting corr (An example of a frequency correction signal) and the deviation Δω between the reference frequency ω0 of the inverter output voltage frequency m Calculate the deviation Δω m The inverter output voltage frequency ω m (An example of a target frequency) is integrated with the transfer function 1 / S of the integral element to obtain the inverter output voltage phase θ GFM (An example of a target phase) is calculated, where s is the Laplace operator.

[0026] Inverter output d-axis amplitude command value V dref , inverter output q-axis amplitude command value V qref , and the inverter output voltage phase θ GFM Based on this, the inverter output voltage command value V ref_GFM The GFL control unit 103 generates an inverter output voltage command value V ref_GFL The switching unit 105 generates an output voltage V S The input to the PWM120 that modulates the inverter output voltage command value V ref_GFMOr inverter output voltage command value V ref_GFL Switch so that one of the two is input.

[0027] The synchronization adjustment unit 113 calculates the system amplitude V grid , the system frequency F grid , the system phase θ indicating the phase of the system voltage grid , and the inverter output voltage command value V ref_GFM Based on this, the amplitude command correction value V corr and frequency command correction value F corr The amplitude command correction value V corr The input to PWM120 is the inverter output voltage command value V ref_GFL to inverter output voltage command value V ref_GFM When switching to the system amplitude V grid and inverter output d-axis amplitude command value V dref The frequency command correction value F corr The input to PWM120 is the inverter output voltage command value V ref_GFL to inverter output voltage command value V ref_GFM When the grid frequency F grid and inverter output voltage frequency ω m The amplitude command correction value V corr The larger the amplitude difference, the greater the inverter output d-axis amplitude command value V dref The frequency command correction value F corr The larger the frequency difference, the greater the inverter output voltage frequency ω m is generated so that the amount of correction for

[0028] In addition, the synchronization adjustment unit 113 adjusts the system amplitude V grid and inverter output d-axis amplitude command value V dref The amplitude difference, which is the difference between the grid and inverter output voltage frequency ω m The frequency difference between thegrid and inverter output voltage phase θ GFM When the phase difference between the inverter output voltage command value V and the inverter output voltage command value V, the inverter output voltage command value V is set to the inverter output voltage command value V. ref_GFL to inverter output voltage command value V ref_GFM Switch to.

[0029] 5 is a control block diagram showing an example of processing in the synchronization adjustment unit 113 of the embodiment. The synchronization adjustment unit 113 of the present embodiment includes a voltage adjustment unit 201 and a frequency adjustment unit 202.

[0030] In the voltage adjustment unit 201, the system amplitude V grid to inverter output d-axis amplitude command value V dref The time constant T corr Here, s in FIG. 5 is a Laplace operator. The value after processing by the transfer function of the first-order lag element is the amplitude command correction value V corr Amplitude command correction value V corr is reset to 0 after the switch from GFL control to GFM control is completed.

[0031] In the frequency adjustment unit 202, the system frequency F grid from inverter output voltage frequency ω m A predetermined constant K is subtracted from the value corr_P The proportional gain process is performed, and the value after the proportional gain process is applied with a predetermined time constant T corr Then, the value after the processing by the transfer function of the first-order lag element and a predetermined bias frequency F bias The sum of these is the frequency command correction value F corr The frequency command correction value F corr is reset to 0 after the switch from GFL control to GFM control is completed. bias By adding the frequency command correction value F before switching from GFL control to GFM control, corrThis prevents the system frequency F grid and the output voltage V S This makes it possible to avoid a problem in which the frequency of the first input signal and the frequency of the second input signal match, causing the phase difference between the two signals (phase difference) to remain unchanged, and the condition that "the phase difference is equal to or smaller than the threshold value" is not satisfied.

[0032] 6 is a flowchart showing an example of processing when switching from GFL control to GFM control in the power conversion device 21 of the embodiment. The synchronization adjustment unit 113 determines whether GFL control is being executed (whether a second modulation command is input to the modulation unit 104) (S101), and ends this routine if GFL control is not being executed (S101: No). If GFL control is being executed (S101: Yes), the synchronization adjustment unit 113 determines whether a switching signal to switch to GFM control has been received (S102), and ends this routine if a switching signal to switch to GFM control has not been received (S103: No).

[0033] When a switching signal to GFM control is received (S102: Yes), the synchronization adjustment unit 113 receives system voltage information (system amplitude V grid , grid frequency F grid , and system phase θ grid ) and the first modulation command (inverter output voltage command value V ref_GFM ) based on the amplitude difference ΔV, the frequency difference ΔF, and the phase difference Δθ (S103). After that, the synchronization adjustment unit 113 calculates the amplitude difference ΔV, the frequency difference ΔF, and the phase difference Δθ based on ... and the synchronization adjustment unit 1 V The frequency difference ΔF is equal to or smaller than the threshold T F The phase difference Δθ is equal to or smaller than the threshold T θ It is determined whether or not it is equal to or less (S104).

[0034] The amplitude difference ΔV is the threshold T V The frequency difference ΔF is equal to or smaller than the threshold T F The phase difference Δθ is equal to or smaller than the threshold T θIf the condition is not met (S104: Yes), the control is switched from the GFL control to the GLM control (S105). Specifically, the synchronization adjustment unit 113 outputs a condition achievement notification signal to the switching unit 115, and upon receiving the condition achievement notification signal, the switching unit 115 changes the input to the PWM 120 to the inverter output voltage command value V ref_GFL to inverter output voltage command value V ref_GFM Switch to.

[0035] On the other hand, the amplitude difference ΔV is the threshold T V The frequency difference ΔF is equal to or smaller than the threshold T F The phase difference Δθ is equal to or smaller than the threshold T θ If the condition that the amplitude command correction value V corr and frequency command correction value F corr (S106), and these amplitude command correction values ​​V corr and frequency command correction value F corr Using the inverter output voltage command value V ref_GFM Then, the corrected inverter output voltage command value V ref_GFM Based on this, step S103 is executed again.

[0036] According to the above embodiment, before switching from GFL control to GFM control, the first modulation command (inverter output voltage command value V ref_GFM This makes it possible to suppress abrupt fluctuations in the output voltage when switching from GFL control to GFM control, improving stability when switching between control methods.

[0037] The program for realizing the functions of the power conversion device 21 in the above-described embodiment is provided mainly by being pre-installed in a storage device provided in the power conversion device 21, but is not limited thereto, and may be provided by being recorded in an installable or executable format on a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, or a DVD (Digital Versatile Disc). In addition, the storage medium is not limited to a medium independent of a computer or an embedded system, but also includes a storage medium in which a program transmitted via a LAN, the Internet, or the like is downloaded and stored or temporarily stored.

[0038] In addition, the above program may be configured to be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network, or may be configured to be provided or distributed via a network such as the Internet.

[0039] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0040] 1...power system, 11...inverter power supply, 12...transformer, 13...power system, 20...power supply, 21...power conversion device, 31...power conversion circuit, 32...high frequency filter circuit, 33...control device, 101...conversion section, 102...GFM control section, 103...GFL control section, 104...modulation section, 105...switching section, 111...voltage control section, 112...phase control section, 113...synchronization adjustment section, 120...PWM, 201...voltage adjustment section, 202...frequency adjustment section

Claims

1. A conversion unit that converts DC power output from a power source into AC power and outputs the AC power; a system configuration control unit that generates a first modulation command for changing the amplitude and phase of the output voltage from the conversion unit through a system configuration control that maintains the amplitude and phase of the output voltage from the conversion unit at predetermined set values; a grid tracking control unit that generates a second modulation command for changing the amplitude and phase of the output voltage by grid tracking control that causes the amplitude and phase of the output voltage to follow the amplitude and phase of a grid voltage that is a voltage of a predetermined power grid; a modulation unit that changes the amplitude and phase of the output voltage based on the first modulation command or the second modulation command; a switching unit that switches an input to the modulation unit so that either the first modulation command or the second modulation command is input to the modulation unit; a synchronization adjustment unit that corrects the first modulation command so that, before an input to the modulation unit is switched from the second modulation command to the first modulation command, a difference between a target amplitude of the first modulation command and an amplitude of the grid voltage becomes equal to or smaller than a threshold value, a difference between a target frequency of the first modulation command and a frequency of the grid voltage becomes equal to or smaller than a threshold value, and a difference between a target phase of the first modulation command and a phase of the grid voltage becomes equal to or smaller than a threshold value; A power conversion device comprising:

2. The synchronization adjustment unit is a voltage adjustment unit that generates an amplitude correction signal having a larger correction amount for the target amplitude as the difference between the target amplitude and the amplitude of the system voltage increases; a frequency adjustment unit that generates a frequency correction signal having a larger correction amount for the target frequency as the difference between the target frequency and the frequency of the system voltage increases; Including, the first modulation command is corrected based on the amplitude correction signal and the frequency correction signal. The power conversion device according to claim 1 .

3. the frequency adjustment unit generates the frequency correction signal so that a correction amount with respect to the target frequency is a value other than 0. The power conversion device according to claim 2 .

4. An information processing device controls a conversion unit that converts DC power output from a power supply into AC power and outputs the AC power, generating a first modulation command for varying the amplitude and phase of the output voltage from the converter by a system formation control for maintaining the amplitude and phase of the output voltage at a predetermined set value; a process of generating a second modulation command for changing the amplitude and phase of the output voltage by a system tracking control for making the amplitude and phase of the output voltage follow the amplitude and phase of a system voltage, which is a voltage of a predetermined power system; changing the amplitude and phase of the output voltage based on the first modulation command or the second modulation command; a process of switching an input to a modulation unit that changes the amplitude and phase of the output voltage so that either the first modulation command or the second modulation command is input to the modulation unit; a process of correcting the first modulation command such that, before an input to the modulation unit is switched from the second modulation command to the first modulation command, a difference between a target amplitude of the first modulation command and an amplitude of the grid voltage becomes equal to or smaller than a threshold value, a difference between a target frequency of the first modulation command and a frequency of the grid voltage becomes equal to or smaller than a threshold value, and a difference between a target phase of the first modulation command and a phase of the grid voltage becomes equal to or smaller than a threshold value; A program that executes the following.

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