Power conversion device and power generation system

Abstract

To provide an electric power conversion device and a power generation system, capable of shortening time until it outputs reactive power and improving an output response of the reactive power.SOLUTION: An electric power conversion device according to an embodiment includes: a converter of a power generation system where a direct current side terminal is connected to a direct current linkage unit to which a direct current side terminal of an inverter is connected; and a control device that, when a maximum reactive power command value of the converter is greater than or equal to a reactive power command value of the power generation system, provides the reactive power command value of the power generation system as the reactive power command value of the converter to output reactive power only from the converter.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A typical power conversion device used as a secondary excitation converter for an induction dynamo motor includes an inverter and a converter. Such a power conversion device can adjust the grid voltage by outputting reactive power to the grid. When outputting reactive power to the grid, the inverter supplies excitation current to the induction dynamo motor, causing the rotor of the induction dynamo motor to rotate, and the converter operates to maintain the inverter's DC voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-187156 Summary of the Invention [Problem to be solved by the invention]

[0004] In the power conversion device configured as described above, when reactive power is supplied to the power grid, it takes time to rotate the rotor of the induction generator motor up to a predetermined speed, which may result in a decrease in the output response of the reactive power used to adjust the grid voltage.

[0005] An object of the present invention is to provide a power conversion device and a power generation system that shorten the time required to output reactive power and improve the output response of reactive power. [Means for solving the problem]

[0006] In order to solve the above problem, the power conversion device of the embodiment includes a converter of a power generation system whose DC side terminal is connected to a DC link section to which a DC side terminal of an inverter is connected, and a control device that, when a maximum reactive power command value of the converter is equal to or greater than a reactive power command value of the power generation system, gives the reactive power command value of the power generation system as a reactive power command value of the converter, and causes reactive power to be output only from the converter. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram showing the configuration of a power generation system according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing an outline of reactive power output from the power generation system according to the first embodiment. [Figure 3] FIG. 2 is a diagram showing an outline of reactive power output from a converter of the power generation system according to the first embodiment. [Figure 4] 3 is a flowchart showing a control flow by the control device according to the first embodiment. [Figure 5] 6 is a flowchart showing a control flow by a control device according to a modified example of the first embodiment. [Figure 6] 6 is a flowchart showing a control flow by a control device according to a modified example of the first embodiment. [Figure 7] 6 is a flowchart showing a control flow by a control device according to a modified example of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments for carrying out the invention will be described.

[0009] (First embodiment) 1 is a diagram showing the configuration of a power generation system 1 according to a first embodiment. The power generation system 1 includes a power conversion device 10, a control device 20, an induction generator motor 30, a first transformer 40, a first circuit breaker 50, and a second circuit breaker 60.

[0010] The power conversion device 10 is a secondary excitation conversion device for an induction generator motor 30, and includes a converter 12, an inverter 14, a capacitor 16, and a second transformer 18.

[0011] Converter 12 has an AC side terminal connected to a second transformer 18 (described later) and a DC side terminal connected to a capacitor 16 (described later), and these AC side terminals are connected to the power grid via second transformer 18 and a first transformer 40 (described later). Power is supplied to converter 12 from the power grid via first transformer 40 and second transformer 18. Converter 12 operates to maintain the voltage of capacitor 16 at a predetermined value.

[0012] The inverter 14 has an AC side terminal connected to a secondary excitation winding, which is a rotor winding of the induction generator motor 30 described below, and a DC side terminal connected to a capacitor 16 described below. The inverter 14 supplies power to the secondary excitation winding of the induction generator motor 30 to excite the induction generator motor 30.

[0013] The capacitor 16 is connected to the DC terminal of the inverter 14 and the DC terminal of the converter 12, and is a common DC link between the converter 12 and the inverter 14.

[0014] The second transformer 18 is provided between the converter 12 and a first transformer 40, which will be described later. A current flows between the power system and the converter 12 via the second transformer 18 and the first transformer 40.

[0015] The induction dynamo motor 30 is a three-phase induction dynamo motor, and its rotor is connected to a water turbine 32 for variable-speed pumped-storage power generation. The stator winding of the induction dynamo motor 30 is connected to the power grid via a first transformer 40 (described later), and the secondary excitation winding is connected to an inverter 14. Note that the induction dynamo motor 30 may be connected to, for example, a wind turbine for wind power generation instead of the water turbine 32, as long as it is connected to a rotating body. In the following description, rotating the rotor of the induction dynamo motor 30 will also be simply referred to as rotating the induction dynamo motor 30.

[0016] The control device 20 is realized by a computer device including, for example, a CPU, a storage device, etc. The control device 20 is connected to the power generation system 1 and controls various devices of the power generation system 1 by outputting commands. The control by the control device 20 will be described in detail later.

[0017] The first transformer 40 is provided between the electric power system and the induction generator motor 30 and between the electric power system and the second transformer 18 .

[0018] The first circuit breaker 50 is provided between the power grid and the first transformer 40, and can be opened to stop the current between the power grid and the first transformer 40. The second circuit breaker 60 is provided between the first transformer 40 and the induction generator motor 30, and can be opened to stop the current between the first transformer 40 and the induction generator motor 30.

[0019] Next, a case where the power generation system 1 outputs reactive power Q to the power grid will be described. In this embodiment, as shown in Fig. 2, the converter 12 outputs reactive power Qc to the power grid, the induction generator motor 30 outputs reactive power Qs to the power grid, and the power generation system 1 outputs the total reactive power Q to the power grid. In other words, the following equation (1) holds:

[0020] Q = Qc + Qs …(1)

[0021] Here, we will explain the calculations and control performed by the control device 20. The control device 20 provides a reactive power command value Qcr to the converter 12, thereby causing the converter 12 to output reactive power Qc. Similarly, the control device 20 provides a reactive power command value Qsr to the inverter 14 so that the induction generator motor 30 outputs reactive power Qs.

[0022] The range of power that converter 12 can output is expressed in a rotating coordinate system using the d-axis and q-axis (axes perpendicular to the d-axis). The output current Ic of converter 12 is output within the range of the maximum output current Icm. When the active current Icd required to maintain the DC voltage is expressed by the vector Icd on the d-axis, the reactive current Icq that can be output is expressed by the vector Icq parallel to the q-axis. In this case, the maximum reactive current command value Icqrm of converter 12 is calculated by the following equation (2).

[0023] (Icqrm) 2 =(Icm) 2 -(Icdr) 2 ...Formula (2)

[0024] In addition, the maximum reactive power command value Qcrm of the converter 12 is calculated from the active current command value Icdr of the converter 12, the maximum reactive current command value Icqrm of the converter 12, the active voltage command value Vcdr of the converter 12, and the reactive voltage command value Vcqr of the converter 12 as shown in the following equation (3).

[0025] Qcrm=Vcqr×Icdr−Vcdr×Icqrm…Formula (3)

[0026] The reactive power command value Qcr of the converter 12 must not exceed the reactive power command value Qr of the power generation system 1. Therefore, when the maximum reactive power command value Qcrm of the converter 12 exceeds the reactive power command value Qr, the control device 20 calculates the reactive power command value Qcr of the converter 12 so that it falls within the range of -Qr or more and Qr or less. In this case, the reactive power command value Qcr of the converter 12 may be set equal to the reactive power command value Qr of the power generation system 1, so that the reactive power command value Qr of the power generation system 1 is used as the reactive power command value Qcr of the converter 12.

[0027] Here, the reactive power command value Qsr of the induction generator motor 30 may be set to a value obtained by subtracting the reactive power command value Qcr of the converter 12 from the reactive power command value Qr of the power generation system 1, and the following equation (4) holds.

[0028] Qsr=Qr-Qcr ...Equation (4)

[0029] The control device 20 provides the calculated reactive power command value Qcr of the converter 12 to the converter 12, and provides the calculated reactive power command value Qsr of the induction generator motor 30 to the inverter 14, thereby providing the reactive power command value Qr of the power generation system 1 as the sum of these values. As shown in Fig. 2, the power generation system 1 outputs reactive power Q to the power grid in accordance with the command from the control device 20.

[0030] When the reactive power command value Qr of the power generation system 1 and the reactive power command value Qcr of the converter 12 are equal, the reactive power command value Qsr of the induction generator motor 30 becomes zero by the calculation of equation (4). At this time, the control device 20 provides the reactive power command value Qr of the power generation system 1 as the reactive power command value Qcr of the converter 12. In other words, the power generation system 1 supplies the reactive power Q of the power generation system 1 to the power grid using only the reactive power Qc from the converter 12, as shown in FIG.

[0031] In the calculations of the control device 20, the active voltage command value Vcdr and the reactive voltage command value Vcqr of the converter 12 may be replaced by the active voltage output value Vcd and the reactive voltage output value Vcq of the converter 12.

[0032] Next, with reference to FIG. 4, a control flow by the control device 20 when the power generation system 1 supplies reactive power to the power grid will be described.

[0033] First, the administrator inputs a reactive power command value Qr for outputting reactive power Q from the power generation system 1 to the power grid to the control device 20 (step S100).

[0034] Next, the control device 20 calculates the deviation by subtracting the square of the active current command value Icdr from the square of the maximum output current Icm of the converter 12, and calculates the square root of this deviation as the maximum reactive current command value Icqrm of the converter 12 (step S102). The maximum output current Icm of the converter 12 is an arbitrary value determined by design. The calculation in step S102 corresponds to equation (2).

[0035] Next, the control device 20 calculates, as the maximum reactive power command value Qcrm of the converter 12, the deviation obtained by subtracting the value obtained by multiplying the active current command value Icdr of the converter 12 by the reactive voltage command value Vcqr of the converter 12 from the value obtained by multiplying the reactive current command value Icqrm of the converter 12 by the active voltage command value Vcdr of the converter 12 (step S104). The calculation in step S104 corresponds to equation (3).

[0036] Next, the control device 20 compares the maximum reactive power command value Qcrm of the converter 12 output in step S104 with the reactive power command value Qr of the power generation system 1 (step S106). If the maximum reactive power command value Qcrm of the converter 12 is equal to or greater than the reactive power command value Qr of the power generation system 1 (YES in step S106), the control device 20 calculates the reactive power command value Qr as the reactive power command value Qcr of the converter 12 (step S108).

[0037] After step S108, the control device 20 provides the reactive power command value Qr of the power generation system 1 to the converter 12 as a reactive power command value Qcr of the converter 12, causing the converter 12 to output reactive power Qc (step S110).

[0038] On the other hand, if the maximum reactive power command value Qcrm of the converter 12 is less than the reactive power command value Qr of the power generation system 1 (NO in step S106), this maximum reactive power command value Qcrm is calculated as the reactive power command value Qcr of the converter 12 (step S112).

[0039] After step S112, the control device 20 calculates the deviation obtained by subtracting the reactive power command value Qcr of the converter 12 from the reactive power command value Qr of the power generation system 1 as the reactive power command value Qsr of the induction generator motor 30 (step S114). The calculation in this step corresponds to equation (4).

[0040] After step S114, control device 20 provides a reactive power command value Qcr to converter 12 and a reactive power command value Qsr to inverter 14, thereby providing the reactive power command value Qr for power generation system 1 as the sum of these values. Then, control device 20 causes converter 12 to output reactive power Qc and induction generator motor 30 to output reactive power Qs in accordance with these commands, thereby outputting the sum of these values ​​as reactive power Q from power generation system 1 to the power grid (step S116).

[0041] Next, after step S110 or step S116, control device 20 determines whether or not a reactive power command value Qr has been input from the administrator (step S118). If there is no output command (YES in step S118), control device 20 transmits a command to converter 12 and induction generator motor 30 to stop outputting reactive power, and converter 12 and induction generator motor 30 stop outputting reactive power (step S120). If there is an output command (NO in step S118), the process returns to step S102 and control is performed in accordance with the output command. Here, the output command may be a command to continue outputting reactive power Q input in step S100, or a command to output reactive power of a value different from reactive power Q.

[0042] Note that in step S110, if the control device 20 issues a command to the converter 12 to output the reactive power Q of the power generation system 1 using only the reactive power Qc of the converter 12, then in this step S110, the control device 20 may issue a command to the first circuit breaker 50 to open the second circuit breaker 60, thereby opening the second circuit breaker 60. In other words, in step S110, the reactive power Qc may be supplied from the converter 12 to the power grid with the second circuit breaker 60 open.

[0043] If a command to output reactive power Q that varies with time is input to control device 20 in step S100, the processing from step S102 onward may be performed taking into account the time variation of reactive power Q. For example, there may be a period during which maximum reactive power command value Qcrm of converter 12 is equal to or greater than reactive power command value Qr of power generation system 1 (YES in step S106) and a period during which maximum reactive power command value Qcrm of converter 12 is less than reactive power command value Qr of power generation system 1 (NO in step S106). In this case, during the period during which converter 12 outputs only reactive power Qc (step S110), control device 20 may perform control such as rotating the rotor and water turbine 32 of induction power generation motor 30 to a predetermined speed, closing second circuit breaker 60, or adjusting the amount of water flowing into water turbine 32, in preparation for causing induction power generation motor 30 to output reactive power Qs (step S116). As a result, preparations for outputting reactive power Qs from induction generator motor 30 are completed while converter 12 is outputting reactive power Qc, so that reactive power Q can be quickly started to be output from converter 12. Furthermore, when reactive power Qs is output from induction generator motor 30, the time from receiving reactive power command value Qr to outputting reactive power Qs can be shortened. Therefore, the output response of reactive power Q can be improved.

[0044] If reactive power Q is output using only reactive power Qc of converter 12 (step S110) and preparation for outputting reactive power Qs from induction generator motor 30 is not required, control device 20 may provide a period during which it stops water turbine 32 and induction generator motor 30. This makes it possible to eliminate mechanical loss caused by rotating water turbine 32 and induction generator motor 30.

[0045] As a modification of step S106, when a command to output reactive power Q that changes with time is input to control device 20 in step S100, step S106 may be determined as YES if the period includes only a period in which maximum reactive power command value Qcrm of converter 12 is equal to or greater than reactive power command value Qr of power generation system 1, and step S106 may be determined as NO if the period includes both a period in which maximum reactive power command value Qcrm of converter 12 is equal to or greater than reactive power command value Qr of power generation system 1 and a period in which maximum reactive power command value Qcrm of converter 12 is less than reactive power command value Qr of power generation system 1. This causes induction generator motor 30 to start outputting reactive power Qs during the period in which maximum reactive power command value Qcrm of converter 12 is equal to or greater than reactive power command value Qr of power generation system 1, thereby preventing a situation in which the induction generator motor 30 fails to output reactive power Qs and is unable to output reactive power Q during a period in which maximum reactive power command value Qcrm of converter 12 is less than reactive power command value Qr of power generation system 1. Therefore, the output response of the reactive power Q to the fluctuation of the reactive power command value Qr can be improved.

[0046] Note that step S106 may always proceed to NO regardless of the value of the reactive power command value Qr of the power generation system 1 in step S100.

[0047] According to the present embodiment described above, when reactive power Q is output from power generation system 1 to the power grid, if the reactive power Q of the power system can be output using only reactive power Qc from converter 12, reactive power Qc is output as reactive power Q from only converter 12. At this time, rotation of induction generator motor 30 and water turbine 32 is stopped. This makes it possible to eliminate mechanical loss due to rotation of induction generator motor 30 and water turbine 32. Furthermore, because reactive power Qc is output only from converter 12, there is no need for preparations such as rotating induction generator motor 30 and water turbine 32 up to a predetermined speed in order to output reactive power Q, and the time until reactive power Q is output can be shortened, thereby improving the output response of reactive power Q.

[0048] When reactive power Q is output from converter 12 and induction dynamomotor 30, preparations are made for outputting reactive power Qs from induction dynamomotor 30 during the period when reactive power Q is being output only by converter 12. This allows reactive power Q to be output even during the preparation period of induction dynamomotor 30, shortening the time until reactive power Q is output and improving the output response of reactive power Q.

[0049] Here, a description will be given of a modified example of steps S112 to S114 when the maximum reactive power command value Qcrm of the converter 12 is less than the reactive power command value Qr of the power generation system 1 (NO in step S106). Note that steps S100 to S110 and steps S114 to S120 are similar to those described above, and therefore detailed description thereof will be omitted.

[0050] As a modification of this embodiment, as shown in FIG. 5, the control device 20 may control the reactive power command value Qr of the power generation system 1, which varies over time, so that the reactive power command value Qsr of the induction generator motor 30 is constant and the reactive power command value Qcr of the converter 12 varies over time. In this modification, after step S106, the control device 20 calculates the time-varying component of the reactive power command value Qr as the reactive power command value Qcr of the converter 12 (step S212). The control device 20 calculates the reactive power command value Qcr of the converter 12 within a range not exceeding the maximum reactive power command value Qcrm. Next, based on equation (4), the control device 20 calculates the constant component of the reactive power command value Qr of the power generation system 1, which is output regardless of time, as the reactive power command value Qsr of the induction generator motor 30 (step S214). After step S214, the process proceeds to step S116. Note that steps S212 and S214 do not have to be executed in this order, and step S214 may be executed first, or they may be executed simultaneously. This modification not only provides the same effects as the present embodiment, but also improves the response of reactive power Q because converter 12, which can respond quickly to output fluctuations, responds to time fluctuations in reactive power command value Qr.

[0051] As another modification of this embodiment, as shown in FIG. 6, the control device 20 may assign the reactive power command value Qr of the power generation system to the converter 12 and the induction generator 30 at a predetermined ratio and output the reactive power Q. In this modification, after step S106, the control device 20 calculates, as the reactive current command value Qcr of the converter 12, a value obtained by multiplying the reactive power command value Qr by an arbitrary constant K (0 < K < 1) (step S312). At this time, the control device 20 compares the calculated KQcr with the maximum reactive power command value Qcrm of the converter 12, and determines the coefficient K so that KQr does not exceed the maximum reactive power command value Qcrm. That is, the control device 20 determines K within the range in which the converter 12 can output KQr, and calculates this KQcr as the reactive power command value Qcr of the converter 12, so that Equation (5) holds.

[0052] Qcr = KQr … Equation (5)

[0053] In this case, from Equations (4) and (5), Equation (6) representing the reactive power command value Qsr of the induction generator 30 holds.

[0054] Qsr = (1 - K)Qr … Equation (6)

[0055] Next, the control device 20 calculates the reactive power command value Qsr of the induction generator 30 based on Equation (6) (step S314). After step S314, the process proceeds to step S116. According to this modification, the reactive power command value Qcr of the converter 12 can be determined first from the reactive power command value Qr of the power generation system 1. Therefore, the reactive power Q can be output while arbitrarily adjusting the reactive power Qc of the converter 12, and the same effect as in this embodiment can be obtained.

[0056] As another modification of this embodiment, as shown in FIG. 7, the control device 20 may control based on the frequency component of the reactive power command value Qr so that the converter 12 outputs the high-frequency component of the reactive power Q and the induction generator 30 outputs the low-frequency component. In this modification, after step S106, the control device 20 determines the reactive power force command value Qr of the power generation system 1 force The control device 20 calculates a component of the command value Qr that is higher than a predetermined frequency as the reactive power command value Qcr of the converter 12 (step S412). force The component of the command value Qr that is lower than a predetermined frequency is converted into reactive current of the induction generator motor 30. force After step S414, the power generation system 1 in this modification calculates the reactive power as a command value Qsr. force A low-pass filter (not shown) may be provided to extract and output frequency components lower than a predetermined value from the command value Qr. In steps S412 and S414, the reactive power command value Qcr of the converter 12 and the reactive power command value Qsr of the induction generator motor 30 may be calculated using equations (5) and (6), similar to steps S312 and S314 described above. force The high-frequency components of the command value Qr are components with a fast fluctuation response in the reactive power command value Qr. Since the converter 12 can respond to an output faster than the induction generator motor 30, in addition to the same effects as the present embodiment, the output response of the reactive power Q can be improved.

[0057] In addition to the same effects as the present embodiment, these modifications output reactive power Q of power generation system 1 from converter 12 and induction dynamomotor 30. Therefore, reactive power Qs of induction dynamomotor 30 is lower by reactive power Qc of converter 12 compared to when reactive power Qs is output from induction dynamomotor 30 alone, thereby improving the power factor of induction dynamomotor 30. Furthermore, when reactive power Qs is output from induction dynamomotor 30, reactive power Qs is output from induction dynamomotor 30 via inverter 14. Therefore, by outputting reactive power Q of power generation system 1 as reactive power Qc of converter 12 and reactive power Qs of induction dynamomotor 30, current can be distributed and flowed to converter 12 and inverter 14. As a result, compared to when reactive power Q is output from induction dynamomotor 30 alone, temperature rise in semiconductor elements of inverter 14 due to current can be suppressed, and deterioration and damage to inverter 14 caused by this temperature rise can be prevented.

[0058] The various modifications described above may be combined in any desired manner.

[0059] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied 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 within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0060] 1...power generation system, 10...power conversion device, 12...converter, 14...inverter, 16...capacitor, 18...second transformer, 20...control device, 30...induction generator motor, 32...water turbine, 40...first transformer, 50...first circuit breaker, 60...second circuit breaker.

Claims

1. a converter of a power generation system having a DC side terminal connected to a DC link section to which a DC side terminal of the inverter is connected; a control device that calculates a maximum reactive current command value of the converter based on a maximum output current value of the converter and an active current command value of the converter, calculates a maximum reactive power command value of the converter based on the maximum reactive current command value and an output voltage of the converter, and, when the maximum reactive power command value of the converter is equal to or greater than the input reactive power command value of the power generation system, provides the reactive power command value of the power generation system as a reactive power command value of the converter, thereby causing reactive power to be output only from the converter; A power conversion device comprising:

2. The control device controls an inductive load connected to the inverter during the period when the reactive power is being output.

2. The power conversion device according to claim 1, wherein a period during which the rotor of the induction motor is stopped is provided.

3. the power generation system includes a rotor, an induction generator connected to the inverter, and a circuit breaker that disconnects a transformer from the induction generator; 3. The power conversion device according to claim 1, wherein the control device performs control to perform at least one of rotating the rotor of the induction generator motor and the rotating body at a predetermined speed, closing the circuit breaker, and adjusting the amount of water flowing into the rotating body, in preparation for outputting reactive power from the induction generator motor, during a period in which the reactive power is being output.

4. a converter of a power generation system having a DC side terminal connected to a DC link section to which a DC side terminal of an inverter connected to an induction generator motor is connected; a control device that, when an input reactive power command value of the power generation system fluctuates over time, gives the converter a reactive power command value of the converter that fluctuates over time, and gives the inverter a reactive power command value of the induction generator that does not fluctuate over time, thereby giving the reactive power command value of the power generation system as the sum of the reactive power command value of the converter and the reactive power command value of the induction generator; A power conversion device comprising:

5. a converter of a power generation system having a DC side terminal connected to a DC link section to which a DC side terminal of an inverter connected to an induction generator motor is connected; a control device that allocates the input reactive power command value of the power generation system to a reactive power command value of the converter and a reactive power command value of the induction generator at a predetermined ratio, thereby providing the reactive power command value of the power generation system as the sum of the reactive power command value of the converter and the reactive power command value of the induction generator; A power conversion device comprising:

6. 6. The power conversion device according to claim 5, wherein the control device provides a component of the reactive power command value of the power generation system having a frequency higher than a predetermined frequency as the reactive power command value of the converter, and provides a component of the reactive power command value of the power generation system having a frequency lower than a predetermined frequency as the reactive power command value of the induction generator motor.

7. A power generation system comprising the power conversion device according to claim 1 , 4 or 5 .

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