Power conversion device

Abstract

The power conversion device includes: a power conversion circuit connected to a DC power source and a power system, which performs conversion between DC power and AC power; a phase synchronization circuit that outputs a phase command value based on a system AC voltage phase of the power system; and a control circuit that controls the power conversion circuit based on the phase command value from the phase synchronization circuit. The phase synchronization circuit includes: a phase difference calculation section that calculates a phase difference indicating a deviation of the phase command value with respect to the system AC voltage phase of the power system at a predetermined period; a phase difference correction section; and a phase command value generation section that outputs the phase command value based on an output of the phase difference correction section.

Description

Technical Field

[0001] This invention relates to a power conversion device connected to a power system. Background Technology

[0002] Conventional power conversion devices equipped with a PLL circuit (phase synchronization circuit) are known, as described in, for example, Japanese Patent No. 6392708. According to paragraph 0033 of the aforementioned document, the phase difference Δθ between the input and output signals of the PLL circuit is calculated. The phase difference Δθ is added as a feedforward control quantity to the voltage phase detected by the PLL circuit. This stabilizes the current feedback control system.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent No. 6392708 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] Power conversion circuits can perform AC-DC conversion to convert AC power to DC power and vice versa. AC-DC conversion is also used as a charging operation mode to generate DC power for charging from AC power in the system.

[0008] Due to system disturbances during system operation, the system voltage phase can sometimes change abruptly. If the control cannot keep up with the system disturbance, the aforementioned AC-DC conversion may occur unexpectedly. As a result, problems such as overvoltage may occur, for example, due to the unexpected charging of the DC capacitor located on the DC side of the power conversion circuit.

[0009] Japanese Patent No. 6392708 describes a technique that enables feedforward correction not only when the phase difference is relatively large, but also when the phase difference is relatively small. The correction amount is determined by the phase difference Δθ between the input and output signals of the PLL circuit. On the other hand, abrupt phase changes caused by system disturbances can be so rapid that existing PLL circuits cannot fully capture them. Previous technologies have not adequately addressed this issue, leaving room for improvement.

[0010] The present invention was made to solve the problems mentioned above, and its purpose is to provide a power conversion device that can improve the tracking accuracy of system voltage phase.

[0011] Methods used to solve problems

[0012] The power conversion device of the present invention includes: a power conversion circuit connected to a DC power supply and a power system for converting DC power to AC power; a phase synchronization circuit that outputs a phase command value based on the phase of the AC voltage of the power system; and a control circuit that controls the power conversion circuit based on the phase command value from the phase synchronization circuit.

[0013] The aforementioned phase synchronization circuit includes: a phase difference calculation unit that calculates a phase difference, representing the deviation of a phase command value from the phase of the system AC voltage of the power system, at a preset period; a phase difference correction unit that, when the difference between the current phase difference calculated by the phase difference calculation unit and the previous phase difference calculated by the phase difference calculation unit exceeds a preset reference, adds a first correction amount to the current phase difference and outputs a corrected current phase difference, and when the difference does not exceed the reference, does not add the first correction amount to the current phase difference and outputs an uncorrected current phase difference; and a phase command value generation unit that outputs the phase command value based on the output of the phase difference correction unit.

[0014] Invention Effects

[0015] According to the power conversion device of the present invention, an appropriate correction amount can be added to the phase difference only when there is a certain degree of abrupt change in the phase difference. On the other hand, no correction amount is added when the phase difference does not change so much, so from the viewpoint of use when there is a sudden change in the system voltage phase, an appropriate correction amount can be freely set. As a result, a high degree of tracking of the system voltage phase can be achieved even when system disturbances occur. Attached Figure Description

[0016] Figure 1 This is a structural diagram of the power conversion device according to the implementation method.

[0017] Figure 2 This is a diagram showing the structure of a PLL circuit according to an implementation method. Detailed Implementation

[0018] Figure 1 This is a structural diagram of the power conversion device 10 according to the embodiment. (See diagram below.) Figure 1 As shown, the power conversion device 10 is configured to be sandwiched between the DC power supply device 8 and the power grid 40.

[0019] The power conversion device 10 includes a DC-side relay 12, a DC capacitor 13, a power conversion circuit 14, an AC reactor 15, an AC capacitor 16, and an AC-side relay 17. The power conversion device 10 also includes an instrument current transformer (CT) 51, an instrument voltage transformer (VT) 52, an instrument current transformer (CT) 53, an instrument voltage transformer (VT) 54, and an instrument current transformer (CT) 55.

[0020] The power conversion device 10 also includes an MPPT controller 18, a first subtractor 19, a DC voltage controller 20, a first adder 21, a first coordinate conversion unit 22, a second subtractor 23, a current controller 24, and a PWM drive circuit 25.

[0021] The power conversion device 10 also includes a phase synchronization circuit (PLL circuit) 30 and a power control command value calculation unit 31.

[0022] The DC-side relay 12 is connected to the DC power supply 8. The DC input power from the DC power supply 8 is received by the first terminal of the DC-side relay 12.

[0023] The DC power supply device 8 can be a power source that includes, for example, a solar panel and a battery, or both. The battery can also include various known secondary batteries or fuel cells. A wind turbine and an AC-DC converter can also be used as the DC power supply device 8. The DC power supply device 8 can also be a various renewable energy generation device.

[0024] The power conversion circuit 14 is sandwiched between the DC power supply device 8 and the power grid 40, forming a series circuit together. This power grid is also commonly referred to as the power system. A power system is a system used to supply electricity to power-receiving equipment on the demand side. A power system integrates power generation, transformation, transmission, and distribution.

[0025] The power conversion circuit 14 converts DC power to AC power. The DC terminal of the power conversion circuit 14 is connected to the second terminal of the DC-side relay 12. The power conversion circuit 14 is, for example, a three-phase voltage-source inverter circuit that includes multiple semiconductor switching elements.

[0026] The first terminal of the DC capacitor 13 is connected to the wiring (e.g., busbar) between the DC-side relay 12 and the power conversion circuit 14. The second terminal of the DC capacitor 13 is connected to a reference potential such as ground. The DC capacitor 13 is connected to the DC voltage V presented on the DC side of the power conversion circuit 14. DC And then it was charged.

[0027] AC reactor 15 is connected in series with the AC terminal of power conversion circuit 14. The first terminal of AC-side relay 17 is connected to AC reactor 15. The second terminal of AC-side relay 17 is connected to power grid 40. The first terminal of AC capacitor 16 is connected to the wiring (e.g., busbar) connecting AC reactor 15 and AC-side relay 17. The second terminal of AC capacitor 16 is connected to a reference potential such as ground.

[0028] The instrument current transformer (CT) 51 converts the DC current i DC Converted to a value used by the instrument. DC current i DC This is the current flowing between the DC power supply device 8 and the power conversion circuit 14. The instrument uses a voltage transformer (VT) 52 to convert the DC voltage V... DC Converted to a value used by the instrument. DC voltage V DC It is the voltage between the DC power supply device 8 and the power conversion circuit 14, and it is the voltage of the DC capacitor 13.

[0029] The instrument current transformer (CT) 53 converts the three-phase AC output current i AC Converted to a value used by the instrument. Three-phase AC output current i AC This is the current flowing between the power conversion circuit 14 and the AC reactor 15. The instrument uses a voltage transformer (VT) 54 to convert the system voltage V... Grid Converted to a value used by the instrument. System voltage V Grid This is the three-phase AC voltage between AC capacitor 16 and the power grid 40. The instrument uses a current transformer (CT) 55 to convert the system current i... Grid Converted to a value used by the instrument. System current i Grid It is the three-phase alternating current between AC capacitor 16 and power grid 40.

[0030] The DC current i is input to the MPPT controller 18 DC and DC voltage V DC The first subtractor 19 calculates the instruction value V output by the MPPT controller 18. * DC With DC voltage V DC The difference. The MPPT controller 18 extracts the maximum amount of DC power from the DC power supply unit 8 through MPPT control.

[0031] The DC voltage controller 20 performs DC voltage control based on the subtraction result of the first subtractor 19. The first adder 21 adds the output value of the DC voltage controller 20 to the d-axis current command value i. * d Add. d-axis current command value i * dIt is the instruction value output by the power controller 34, which will be described later.

[0032] The first coordinate transformation unit 22 performs the dq-axis / abc-axis transformation, that is, the coordinate transformation from two-phase to three-phase. The first coordinate transformation unit 22 is based on the addition result of the first adder 21 and the q-axis current command value i. * q Calculate the three-phase AC current command value i * AC q-axis current command value i * q It is the instruction value output by the power controller 34, which will be described later.

[0033] The second subtractor 23 calculates the three-phase AC current command value i. * AC With three-phase AC output current i AC difference.

[0034] The current controller 24 calculates the current command value based on the output of the second subtractor 23. The PWM drive circuit 25 generates a pulse width modulation signal (PWM signal) according to the current command value of the current controller 24. The PWM drive circuit 25 transmits this PWM signal to the power conversion circuit 14 as the drive signal for the semiconductor switching element.

[0035] PLL circuit 30 outputs a phase command value based on the phase of the AC voltage of the power grid 40. PLL circuit 30 is based on the system voltage V. Grid d-axis system voltage V d and q-axis system voltage V q Output phase command value θ * d-axis system voltage V d and q-axis system voltage V q The output is from the second coordinate transformation unit 32, which will be described later. The specific circuit of the PLL circuit 30 is as follows: Figure 2 This will be discussed later.

[0036] The power control command value calculation unit 31 calculates the phase command value θ from the PLL circuit 30. * The power control command value is calculated. This power control command value is used to control the power conversion circuit 14. In this embodiment, the power control command value specifically includes the d-axis current command value i. * d and q-axis current command value i * q The power control command value calculation unit 31 calculates the phase command value θ from the PLL circuit 30. * System voltage V Grid System current i Grid and three-phase AC output current i ACCalculate the d-axis current command value i * d and q-axis current command value i * q .

[0037] The power control command value calculation unit 31 may also have a DC / AC conversion mode and an AC / DC conversion mode. In the DC / AC conversion mode, the power control command value calculation unit 31 calculates the power control command value so that the power conversion circuit 14 converts DC power into AC power. In the AC / DC conversion mode, the power control command value calculation unit 31 calculates the power control command value so that the power conversion circuit 14 converts AC power into DC power.

[0038] The power control command value calculation unit 31 includes a second coordinate transformation unit 32, a third coordinate transformation unit 33, and a power controller 34.

[0039] The second coordinate transformation unit 32 performs abc-axis / dq-axis conversion, i.e., conversion from three-phase to two-phase. Therefore, the second coordinate transformation unit 32 adjusts the coordinates based on the system voltage V. Grid Calculate the d-axis system voltage V d and q-axis system voltage V q .

[0040] The third coordinate transformation unit 33 performs the abc-axis / dq-axis transformation, i.e., the transformation from three-phase to two-phase. Therefore, the third coordinate transformation unit 33 determines the coordinates based on the system current i. Grid Calculate the d-axis system current i d and q-axis system current i q .

[0041] The power controller 34 is based on the above-mentioned calculated value (V) of the second coordinate transformation unit 32. d V q The calculated values ​​(i) of the third coordinate transformation unit 33 and the above-mentioned calculation values ​​(i) d i q ), calculate the d-axis current command value i * d and q-axis current command value i * q .

[0042] In the following explanation, for convenience, the phase difference θ is assigned the subscript k used to represent the time sequence of the control step. Let the phase difference calculated by the PLL circuit 30 in this control step k be the current phase difference θ. k In this case, the phase difference calculated in the previous step k-1 is used as the previous phase difference θ. k－1 This indicates that the phase difference calculated in the next control step k+1 will be used as the next phase difference θ. k+1 express.

[0043] Figure 2 This is a diagram showing the structure of the PLL circuit 30 according to the relevant implementation method. (Example) Figure 2 As shown, the PLL circuit 30 includes a phase difference calculation unit 30a, a phase difference subtractor 30b, a phase difference correction unit 30c, a feedback correction unit 30d, a second adder 30e, and a phase command value generation unit 30f.

[0044] The phase difference calculation unit 30a calculates the phase difference θ using a preset control cycle (k-1, k, k+1…). k Phase difference θ k Indicates the phase command value θ * The system AC voltage phase θ relative to the power grid 40 VGrid The deviation. Phase difference calculation unit 30a is based on the d-axis system voltage V. d and q-axis system voltage V q Calculate the phase difference θ k The phase difference θ in this case k It indicates the extent to which the system voltage phase deviates from a preset reference phase.

[0045] The phase difference subtractor 30b calculates the current phase difference θ. k Compared with the pre-stored previous phase difference θ k－1 The difference between them. In the implementation, the difference obtained by subtracting the value of one phase difference from the value of another phase difference is represented by θ. kd This is also referred to as "the magnitude of the difference θ". kd ".

[0046] The phase difference correction unit 30c is configured to adjust the phase difference according to the magnitude θ. kd The value of the difference θ kd A correction is applied. Specifically, the phase difference correction unit 30c adjusts the magnitude θ of the difference. kd Exceeding the preset baseline value θ th In this case, for the phase difference θ k Add the pre-set first correction amount θ A Therefore, the corrected phase difference (θ) is output. k +θ A ).

[0047] On the other hand, the phase difference correction unit 30c adjusts the magnitude of the difference θ. kd It did not exceed the baseline value θ th In the case of this phase difference θ k Add the first correction θ A As a result, the output shows an uncorrected phase difference θ. k .

[0048] Feedback correction unit 30d based on the magnitude of the difference θ kd Calculate the second correction θ fb The second correction factor θ fb This is the feedback correction amount. The feedback correction unit 30d, as an example, is configured to include a proportional control (P control) block and an integral control (I control) block.

[0049] The second adder 30e adds the output value of the phase difference correction unit 30c to the output value of the feedback correction unit 30d. The phase command value generation unit 30f outputs a phase command value based on the output of the phase difference correction unit 30c. Specifically, the phase command value generation unit 30f generates a phase command value θ based on the output value of the second adder 30e. * .

[0050] As a result, the phase command value generation unit 30f is configured to generate a phase command value based on the current phase difference θ. k and the first correction θ A Second correction θ fb Output phase command value θ * Because of the first correction θ A Second correction θ fb The modifications to both aspects allow for a balance between following and control stability.

[0051] As explained above, the power conversion device 10 according to the relevant embodiment is limited to the magnitude of the difference θ. kd Not large enough to exceed the baseline value θ th In this case, it is possible to determine the phase difference θ in this situation. k Add the first correction θ A .

[0052] On the other hand, the size of the difference θ kd Limited to not exceeding the reference value θ th In the case of this degree, without adding the first correction factor θ A Therefore, from the viewpoint of dealing specifically with rapid changes in the system voltage phase, the first correction amount θ can be... A Set it to an appropriate value as you like.

[0053] Therefore, it is possible to make the system voltage phase θ VGrid The tracking performance is improved. As a result, it is possible to suppress the unexpected rise of DC voltage in DC capacitors during system disturbances.

[0054] The effects of the implementation method will be explained in more detail below. According to the implementation method, the inverter connected to the system provides a function to suppress DC voltage rise during system disturbances. When the inverter is connected, sometimes a sudden change in phase occurs on the side of the power grid 40. At this time, there are problems such as the control failing to follow the change, resulting in charging voltage from the system side to the DC capacitor 13, and overvoltage.

[0055] A typical PLL function is to measure the system voltage V. Grid The phase of the inverter is determined, and the phase command value θ of the inverter is calculated to follow it. In conventional technology, if a system disturbance occurs, the PLL circuit often fails to follow rapid phase changes in the system voltage. If the inverter phase command deviates from the system voltage phase, the dq conversion cannot be calculated correctly. Consequently, the power control command value cannot be calculated correctly. Therefore, it is possible that even when the DC capacitor 13 should be discharged, the phase command value θ may still be used incorrectly. * And a malfunction such as charging the DC capacitor from the 40 side of the power grid.

[0056] Regarding this, the PLL circuit 30 of the implementation method is as follows: Figure 2 As shown, a phase difference correction unit 30c is provided after the phase difference calculation unit 30a. The phase difference correction unit 30c calculates the previous phase difference θ. k－1 Phase difference θ k The phase relationship is compared. When the phase deviation is large, the phase difference θ is compared. k Add the first correction θ A Therefore, an offset can be forcibly applied even with a large phase deviation. As a result, the system's tracking performance under disturbances is improved. Consequently, the aforementioned DC voltage rise can be suppressed.

[0057] Label Explanation

[0058] 8 DC power supply unit; 10 Power conversion device; 12 DC side relay; 13 DC capacitor; 14 Power conversion circuit; 15 AC reactor; 16 AC capacitor; 17 AC side relay; 18 MPPT controller; 19 First subtractor; 20 DC voltage controller; 21 First adder; 22 First coordinate transformation unit; 23 Second subtractor; 24 Current controller; 25 PWM drive circuit; 30 PLL circuit (phase synchronization circuit); 30a Phase difference calculation unit; 30b Phase difference subtractor; 30c Phase difference correction unit; 30d Feedback correction unit; 30e Second adder; 30f Phase command value generation unit; 31 Power control command value calculation unit; 32 Second coordinate transformation unit; 33 Third coordinate transformation unit; 34 Power controller; 40 Power grid; i AC Three-phase AC output current; V DC DC voltage; V Grid System voltage; θ * Phase command value; θ A First correction amount; θ fb Second correction amount; θ k－1 Previous phase difference; θ k Phase difference; θ kdThe magnitude of the difference; θ th Reference phase (reference value); θ VGrid System AC voltage phase; θ VGrid System voltage phase.

Claims

1. A power conversion device, characterized in that, have: A power conversion circuit, connected to a DC power supply and power system, performs the conversion between DC power and AC power; The phase synchronization circuit outputs a phase command value based on the phase of the AC voltage of the power system described above. as well as The control circuit controls the power conversion circuit based on the phase command value from the phase synchronization circuit. The aforementioned phase synchronization circuit includes: The phase difference calculation unit calculates the phase difference, which represents the deviation of the phase command value from the phase of the system AC voltage of the aforementioned power system, using a preset period. The phase difference correction unit, when the difference between the current phase difference calculated by the phase difference calculation unit and the previous phase difference calculated by the phase difference calculation unit exceeds a preset reference, adds a first correction amount to the current phase difference and outputs a corrected current phase difference; and when the difference between the current phase difference calculated by the phase difference calculation unit and the previous phase difference calculated by the phase difference calculation unit does not exceed the reference, does not add the first correction amount to the current phase difference and outputs an uncorrected current phase difference. The phase command value generation unit outputs the phase command value based on the output of the phase difference correction unit.

2. The power conversion device as described in claim 1, characterized in that, The aforementioned phase synchronization circuit includes a feedback correction unit that calculates a second correction amount as a feedback control correction amount. This feedback control correction amount is based on the difference between the current phase difference calculated by the current phase difference calculation unit and the previous phase difference calculated by the previous phase difference calculation unit. The phase command value generation unit is configured to output the phase command value based on the current phase difference, the first correction amount, and the second correction amount.

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