JP2020072566A - Control arrangement of power converter - Google Patents

Abstract

To provide a control arrangement of power converter capable of continuing operation stably even when the current direction is inverted.SOLUTION: A control arrangement of power converter includes a first constant voltage control circuit creating a first phase control angle, on the basis of a set DC voltage command value, and a DC voltage outputted from the power converter, a constant current control circuit creating a second phase control angle, on the basis of a set DC current command value and a DC current flowing through a DC transmission line, a minimum value selection circuit for selecting the smaller one of the first phase control angle and the second phase control angle and outputting, and a first limiter setting circuit for setting the upper limit of output from the minimum value selection circuit. When the power converter changes operation state from forward converter to inverse converter by a tide direction command, the first limiter setting circuit limits the output so that the DC voltage does not exceed the phase control angle when tracking the DC voltage command value.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to a control device for a power converter.

  The DC power transmission system has been attracting attention as a means for highly efficiently realizing long-distance power transmission including offshore wind power generation. Further, the DC power transmission system is also a useful means for accommodating electric power between different electric power systems at the time of a peak of electric power demand or a disaster.

  The power conversion device used in such a backbone power system needs to maintain a stable operating state according to various natural conditions and load conditions.

  When a separately excited power converter is used in a DC power transmission system, stable operation is required even in a transient state such as startup or reversal of the flow direction.

JP, 2016-5374, A

  The embodiment provides a control device for a power converter that can stably continue operation even when the flow direction is reversed.

  A power converter control device according to an embodiment controls a power converter provided between an AC power system and a DC power transmission line. The control device includes a first constant voltage control circuit that generates a first phase control angle based on a set DC voltage command value and a DC voltage output from the power converter, a set DC current command value, and A constant current control circuit that generates a second phase control angle based on a direct current flowing through the DC transmission line, and a minimum that selects and outputs the smaller one of the first phase control angle and the second phase control angle. A value selection circuit and a first limiter setting circuit that sets an upper limit of the output of the minimum value selection circuit. When the power converter changes the operation state from the forward converter to the inverse converter according to the instruction to change the state in the power flow direction, the first limiter setting circuit causes the DC voltage to change after the instruction is input. The output is limited so as not to exceed the phase control angle when following the DC voltage command value.

  In the present embodiment, a control device for a power converter that can stably continue operation even when the power flow direction is reversed is realized.

It is a block diagram which illustrates the control device of the power converter concerning a 1st embodiment. It is a block diagram which illustrates a direct-current power transmission system. FIG. 3A and FIG. 3B are schematic graphs illustrating output characteristics of the power converter for explaining the operation at the time of power flow reversal. FIG. 4A is a schematic graph explaining the operation of the control device of the first embodiment. FIG. 4B is a schematic timing chart explaining the operation of the control device of the comparative example. It is a block diagram which illustrates the control device of the power converter concerning a 2nd embodiment. 7 is a schematic timing chart illustrating the operation of the control device of the second embodiment. It is a block diagram which illustrates the control device of the power converter concerning a 3rd embodiment. It is a typical timing chart explaining operation | movement of the control apparatus of 3rd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
It should be noted that the drawings are schematic or conceptual, and the relationship between the thickness and width of each portion, the size ratio between the portions, and the like are not always the same as the actual ones. Even when the same portion is shown, the dimensions and ratios may be different depending on the drawings.
In the specification and the drawings of the application, components similar to those described in regard to a drawing thereinabove are marked with like reference numerals, and a detailed description is omitted as appropriate.

(First embodiment)
FIG. 1 is a block diagram illustrating a control device for a power converter according to this embodiment.
As shown in FIG. 1, the control device 10 of the embodiment generates the phase control angle α based on the DC voltage and DC current of the power converter or the command values thereof, and supplies the phase control angle α to the power converter.

  The control device 10 includes a constant current control circuit (ACR) 11, a constant voltage control circuit (AVR) 12, a minimum value selection circuit (LVG) 14, an output limiter circuit 15, and a limiter control circuit 20 according to the flow direction. Equipped with. The control device 10 further includes a startup limiter setting circuit 30. The control device 10 includes a margin angle control circuit (AγR) 13.

  The LVG 14 selects the minimum value from the phase control angle αACR generated by the ACR 11, the phase control angle αAVR generated by the AVR 12, and the phase control angle αAγR generated by AγR 13 and outputs it as the phase control angle α. An output limiter circuit 15 is provided at the output of the LVG 14.

  The power converter controlled by the control device 10 mutually converts the AC voltage and the DC voltage into electric power. The power converter may operate as a forward converter that converts an AC voltage into a DC voltage, and may operate as an inverse converter that converts a DC voltage into an AC voltage. In the case of a two-terminal power grid in which the power converter is connected to both terminals of the DC transmission line, when one terminal operates as a forward converter, the other terminal operates as an inverse converter. In this way, the exchange of the forward converter and the inverse converter at both terminals is called power flow inversion. In the following, a terminal that operates as a forward converter will also be referred to as a REC terminal, and a terminal that operates as an inverse converter will be referred to as an INV terminal.

  When the power converter operates as the REC end, the ACR 11 generates the phase control angle αACR so that the DC current output by the power converter follows the set DC current command value Idp. At this time, the AVR 12 generates the phase control angle αAVR larger than the phase control angle αACR. Therefore, the power converter at the REC end is operated by constant current control according to the phase control angle αACR.

  When the power converter operates as the INV end, the ACR 11 is set with a current value obtained by subtracting the current margin ΔIdp from the DC current command value Idp. At this time, the DC voltage command value Vdp is set in the AVR 12. In this case, the phase control angle αAVR is smaller than the phase control angle αACR, so the power converter at the INV end is operated by constant voltage control according to the phase control angle αAVR.

  The power flow direction limiter control circuit 20 acts on the output limiter circuit 15 to set upper and lower limiter values of the output limiter circuit 15. More specifically, the power flow direction limiter control circuit (hereinafter, simply referred to as a limiter control circuit) 20 outputs different limit values according to the power flow direction state, and sets upper and lower limiter values, respectively. The limiter control circuit 20 outputs upper and lower limit values α0UL and α0LL at the REC end. The limiter control circuit 20 outputs upper and lower limit values α1UL and α1LL at the INV end. The limiter control circuit 20 shifts between the limiter values α0UL and α0LL and the upper and lower limit limits α1UL and α1LL, respectively, after a predetermined shift period according to a command for changing the power flow direction.

  The magnitude relationships between the upper and lower limit values α0UL and α0LL during REC end operation and the upper and lower limit values α1UL and α1LL during INV end operation are α1UL> α0UL and α1LL> α0LL. Further, each limit value of the transition period from α0UL, α0LL to α1UL, α1LL is represented by a function of time, and each function can be set arbitrarily. For example, the limit value function can be a linear function, an exponential function, including first order lag, or any other suitable function.

  The limiter control circuit 20 is preset with limit values α0UL, α0LL and limit values α1UL, α1LL. Limit value functions αUL (t) and αLL (t) are preset in the limiter control circuit 20.

  The upper limit value α0UL at the REC end is set to about 120 ° so that the phase control angle α can be controlled in an appropriate range during the protection operation.

  The upper limit value α1UL at the INV end is set based on the phase control angle αAVR generated by the AVR12. For example, when the αAVR is operated at about 140 °, the α1UL is set to about 160 °.

  The limit value functions αUL (t) and αLL (t) may be appropriately adjusted and set according to the DC power transmission system in which the control device 10 is used. For example, when the functions αUL (t) and αLL (t) are linear functions, the rate of increase of the limit value can be adjusted by changing the linear coefficient according to the DC power transmission system.

  Further, the values of the limit values α0UL, α0LL, α1UL, α1LL may be adjusted together with the functions αUL (t) and αLL (t) according to the DC power transmission system.

  The limiter control circuit 20 controls the phase control angle when the phase control angle α output by the LVG 14 becomes the DC voltage command value (rated value) set in the AVR 12 when the power flow direction is reversed from the REC end to the INV end. The upper limit value is limited so as not to exceed. Therefore, the control device 10 can supply the power converter with the phase control angle α that does not exceed the phase control angle when outputting the DC voltage command value (rated voltage) at the time of power flow reversal. Therefore, the power converter can stably reverse the power flow and continue the operation wp without causing overshoot or undershoot. Further, since the phase control angle α at the time of power flow reversal is smaller than the phase control angle at the time of outputting the rated voltage, the size of the phase control angle α is limited and the possibility of commutation failure is reduced. It should be noted that the upper limit value limited by the limiter control circuit 20 may be about the setting range of the DC voltage command value (rated value), and an appropriate value is set according to the specifications in the actual DC power transmission system, the power converter, or the like. ..

  Note that the lower limit value may be a constant α0LL in the operation at the time of power flow reversal. Further, since the lower limit value is not directly related to the above-mentioned problem, detailed description thereof will be omitted below.

  The startup limiter setting circuit 30 is connected between the limiter control circuit 20 and the output limiter circuit 15. The startup limiter setting circuit 30 acts on the output limiter circuit 15 in response to the startup command, and limits the value of the phase control angle α output by the LVG 14.

  More specifically, the startup limiter setting circuit 30 includes a limiter setting unit 31, a timer 32, and a switch circuit 33. The limiter setting unit 31 has an initial value α0 of the limiter at startup. When the starter command is input, the limiter setting unit 31 shifts the limiter value from α0 to α0UL, and similarly shifts from α0 to α0LL.

  The transition periods from α0 to α0UL and α0LL are the same in this example, but may be different. The time change rate of the limiter value during the transition period is arbitrarily selected such as linear or exponential.

  The value of α0 is set in advance to a phase control angle such that an overcurrent can be suppressed while supplying a sufficient current to the DC transmission line or the power system when the power converter is started. When starting as the REC end, the value of α0 is, for example, about 85 °.

  The two outputs of the limiter setting unit 31 output the upper and lower limit values, respectively. One of the inputs of the switch circuit 33 is connected to these outputs. Two outputs of the limiter control circuit 20 are connected to the other input of the switch circuit 33, respectively. The output of the switch circuit 33 is connected so as to act on the output limiter circuit 15.

  The switch circuit 33 is switched according to the output of the timer 32. In the initial state, the switch circuit 33 connects the output of the limiter setting unit 31 to the output limiter circuit 15. When a startup command is input to the startup limiter setting circuit 30, the output of the limiter setting unit 31 starts shifting toward the limit values α0UL and α0LL, and the connection of the switch circuit 33 is maintained until the shifting period elapses. It

  When the transition period elapses, the output of the timer 32 is inverted and the input of the switch circuit 33 is switched to the output of the limiter control circuit 20. The timing at which the output of the timer 32 is inverted may be immediately after the transition period has elapsed, or after a predetermined period has elapsed after the transition period has elapsed. The value may be adjusted and set to an appropriate value according to the DC power transmission system in which the control device 10 is used.

  The AγR 13 inputs a predetermined margin angle and outputs the maximum phase control angle αAγR so that the power converter does not fail in commutation. Even if the phase control angle is the largest, an appropriate value is set so that the power converter can reliably commutate. In the operation in each of the embodiments described below, the phase control angle αAγR generated by AγR13 is sufficiently larger than the other phase control angles αACR and αAVR and is not selected by the LVG 14 unless otherwise specified.

The operation of the control device 10 for a power converter according to this embodiment will be described.
FIG. 2 is a block diagram illustrating a DC power transmission system.
As shown in FIG. 2, the DC power transmission system 100 includes AC power systems 1 and 1a, a DC power transmission line 3, control devices 10 and 10a, and power converters 40 and 40a. The control device 10 is connected to the power converter 40. The control device 10a is connected to the power converter 40a. The control devices 10 and 10a can receive data of the DC current command value Idp, a power flow reversal command, and the like from, for example, a host control system. The control devices 10 and 10a take in the detected values of the DC voltage from the DC current command value Idp and the power converters 40 and 40a, respectively, generate the phase control angle α on the basis of these, and generate the phase control angle α in the power converters 40 and 40a. Supply each.

  The control device 10a and the power converter 40a have the same configuration as, for example, the control device 10 and the power converter 40 of the above-described embodiment, but they do not necessarily have to have the same configuration, and DC power transmission is mutually performed. You can do it.

  The power converter 40 is connected between the power system 1 and the DC power transmission line 3. The power converter 40 is connected to another power converter 40 a via the DC power transmission line 3. The power converter 40a is connected between the DC power transmission line 3 and the power system 1a.

  When the power converter 40 is at the REC end, the power converter 40 converts the AC voltage of the power system 1 into a DC voltage and transmits the DC voltage to the power converter 40 a via the DC transmission line 3.

  When the power converter 40 is at the INV end, the power converter 40 converts the DC voltage transmitted through the DC power transmission line 3 by the power converter 40a into an AC voltage and supplies the AC voltage to the power system 1. ..

  In the following, when the power converter 40 is at the REC end, the control device 10 receives an instruction to change the power flow direction from the host control system to the INV end and switches to the INV end.

FIG. 3A and FIG. 3B are schematic graphs illustrating output characteristics of the power converter for explaining the operation at the time of power flow reversal.
In the output characteristic graphs of FIGS. 3A and 3B, the horizontal axis represents the DC current Id flowing through the DC transmission line 3, and the vertical axis represents the DC voltage Vd at each terminal. In both graphs of FIG. 3A and FIG. 3B, the solid line shows the output characteristic of the power converter 40, and the broken line shows the output characteristic of the power converter 40a.

  As shown in FIG. 3A, the power converter 40 operating as the REC terminal outputs the DC current Id so as to follow the set DC current command value Idp by the constant current control. In the output characteristics of the power converter 40, when the direct current Id is smaller than the direct current command value Idp, the voltage that the power converter 40 can output is limited by the lower limiter value of the phase control angle. When DC current Id is larger than DC current command value Idp, power converter 40 operates by constant voltage control, and its output voltage is controlled so as to follow the DC voltage command value.

  In the power converter 40a at the INV end of this example, the command value for constant current control is set by subtracting the current margin ΔIdp from the DC current command value Idp. When the direct current Id is smaller than (Idp-ΔIdp), the voltage that the power converter 40a can output is limited by the lower limiter value of the phase control angle. When the DC current Id is larger than (Idp-ΔIdp), the voltage output from the power converter 40a is subjected to constant voltage control at the DC voltage set by the DC voltage command value Vdp.

  When both the power converters 40 and 40a operate as the INV terminal, when the direct current Id becomes large, the voltage that can be output is limited by the AγR13.

  As described above, in the power converter 40 at the REC end, constant current control is performed by the ACR 11 that follows the DC current command value Idp, and in the power converter 40a at the INV end, constant voltage control by the AVR that follows the DC voltage command value Vdp. Becomes The two characteristic graphs intersect at one point, and the intersecting point is the operating point OP1 of the DC power transmission system 100. That is, in the DC power transmission system 100, the REC terminal transmits power at the DC current command value Idp, and the INV terminal receives power by the constant voltage control of the DC voltage Vd1.

  When the control device 10 at the REC end receives the command for changing the power flow direction, the DC current command value Idp is applied after subtracting the current margin ΔIdp. Then, the control device 10a at the INV end cancels the subtraction of the current margin ΔIdp from the direct current command value Idp. Therefore, the control device 10 at the REC end increases the phase control angle αACR to reduce the output DC current.

  As a result, as shown in FIG. 3B, the solid line characteristic graph is shifted leftward by the current margin ΔIdp, and the broken line characteristic graph is shifted rightward by the current margin ΔIdp. As a result, the operating point OP2 becomes the DC voltage (-Vd1) that follows the DC voltage command value (-Vdp) set in the control device 10. The control device 10 increases the phase control angle αAVR to invert the DC voltage.

FIG. 4A is a schematic timing chart explaining the operation of the control device of the present embodiment.
FIG. 4A shows time changes of the phase control angles αACR and αAVR generated by the ACR 11 and AVR 12, respectively, and time changes of the phase control angle α output from the LVG 14. FIG. 4A shows functions αUL (t) and αLL (t) that represent the time changes of the upper and lower limiter values applied to the AVR 12 together with the time changes of these phase control angles. In the figure, the curves of the time functions αUL (t) and αLL (t) are shown by broken lines. Further, in the figure, αAVR is shown by a one-dot chain line, αACR is shown by a two-dot chain line, and α is shown by a solid line.

  It should be noted that, in the figure, it is difficult to see the change due to the overlapping of the curves, so even if the values are the same at the same time, they are displayed vertically shifted. Specifically, before the power flow reversal and in the first half of the power flow reversal, α has a value equal to αACR, but αACR is displayed slightly larger than α. Further, in the latter half of the power flow reversal and after the power flow reversal, α has a value equal to αAVR, but αAVR is displayed slightly larger than α. The same applies to similar drawings (FIGS. 6 and 8) of other embodiments described later.

  As shown in FIG. 4A, when the power flow inversion command is input and the power flow inversion is started (time t1), the upper and lower limiter functions αUL (t) and αLL (t) are changed from α0UL and α0LL. It changes so as to increase toward α1UL and α1LL, respectively.

  Since the voltage output by power converter 40 changes toward DC voltage command value −Vdp controlled by AVR 12, phase control angle αAVR output by AVR 12 increases.

  The current output by the power converter 40 is set by subtracting the current margin ΔIdp from the DC current command value Idp controlled by the ACR 11, so that the phase control angle αACR output by the ACR 11 also increases.

  The size of the function αUL (t) is set so as to increase more slowly than αAVR. In this example, the function αUL (t) is a first-order lag function that has a slower coefficient than the response of αAVR. At time t2, αAVR is limited by αUL (t2). αUL (t) limits the rise of αAVR until αAVR equals αACR. After time t3, αAVR becomes smaller than αACR, and the operation of the power converter 40 switches from constant current control to constant voltage control.

  As described above, the control device 10 of the present embodiment limits αAVR from time t1 to time t3 so as not to be larger than the magnitude of the phase control angle α at a time sufficiently later than time t3. Here, the period from time t1 to time t3 is a period from when the power flow inversion is started by the power flow inversion command to when the power converter is switched to the constant voltage control operation. Further, the phase control angle α at a time sufficiently later than the time t3 is the phase control angle when outputting the DC voltage command value (rated value). Therefore, the absolute value of the DC voltage output by the power converter does not become larger than the absolute value of the DC voltage command value (rated value), and overshoot and undershoot are prevented from occurring. Further, in the control device 10, the phase control angle α can make it difficult for commutation failure to occur at the time of power flow reversal.

FIG. 4B is a schematic graph explaining the operation of the control device of the comparative example.
For comparison with the case of the present embodiment, FIG. 4B shows a change in the phase control angle generated by the control device when the limiter control circuit 20 does not operate.
The control device of the comparative example has the same configuration as the control device 10 of the above-described embodiment, except that the limiter value of the upper limit of AVR is constant at α1UL. The value of the lower limiter is constant at α0LL.

  As shown in FIG. 4B, αAVR increases as in the case of the embodiment, but since the upper limit is not limited by the function αUL (t) at time t2, αAVR (t2) becomes αUL (t2). It also increases after reaching the corresponding value.

  The phase control angle α when αAVR becomes the DC voltage command value (rated value) rises, and at time t4, αAVR becomes equal to αACR. After that, αAVR decreases until reaching time t5. The value αAVR (t5) of αAVR at time t5 is substantially equal to the phase control angle α when the DC voltage command value (rated value) is reached.

  Here, αAVR (t4) is larger than αAVR (t5). Then, αAVR (t4) and αAVR (t5) are less than or equal to αACR. In other words, between time t4 and time t5, αAVR is equal to or greater than the phase control angle when the DC voltage command value (rated value) set by AVR12 is reached, and LVG14 is such a phase control angle. The α is supplied to the power converter 40. Therefore, the power converter tries to output a DC voltage whose absolute value is larger than the DC voltage command value (rated value), so that the output voltage overshoots or undershoots. Then, during the period in which the phase control angle is controlled to be large, the margin angle becomes small, and there is a possibility that commutation failure will occur.

  Next, the operation of the limiter setting circuit 30 at startup of the control device 10 of this embodiment will be described. As already shown in FIG. 1, since the switch circuit 33 connects the output of the limiter setting unit 31 to the limiter circuit of the AVR 12, the limiter setting unit 31 keeps the limiter circuit of the AVR 12 until a start command is input. Is set to the initial value α0 of the limiter.

  When the activation command is input, the limiter setting unit 31 changes the upper and lower limit values of the limiter at a predetermined time change rate and outputs the values during the period set by the timer 32. The upper and lower limiter values α0UL and α0LL are reached.

  After that, the startup limiter setting circuit 30 inverts the output of the timer 32 and switches the input of the switch circuit 33. The switch circuit 33 supplies the value of the limiter output from the limiter control circuit 20 to the AVR 12.

The effect of the control device for the power converter according to the present embodiment will be described.
The control device 10 of the present embodiment includes a limiter control circuit 20, and the limiter control circuit 20 acts on the output limiter circuit in response to a command to change the power flow direction. The limiter control circuit 20 changes the value of the upper limiter from the limiter value at the REC end to the limiter value at the INV end.

  In the AVR 12, the phase control angle αAVR is increased and the output voltage of the power converter 40 is inverted in response to the command to change the power flow direction. On the other hand, the limiter control circuit 20 sets the magnitude of the phase control angle α to the DC voltage command value (rated value) set in the AVR 12 regardless of the response of the AVR 12 after the power flow inversion starts. The upper limit of α is limited so as not to exceed. Therefore, the phase control angle α does not exceed the phase control angle when the DC voltage becomes the DC voltage command value, so that the output voltage is prevented from overshooting (undershooting) or commutation failure. You can

  Power converters are often provided with overvoltage protection against excessive DC voltage in order to prevent damage to the device itself or the system. If the operation of the power converter is stopped due to the overvoltage protection functioning due to the overshoot or the undershoot, the DC power transmission system may be shut off and it may take time to restart. When a commutation failure occurs, the DC voltage and the tidal current may fluctuate significantly, and a large disturbance may occur in the AC system to which the power converter is connected. In the control device 10 for a power converter of the present embodiment, such an unexpected operation stop can be prevented, and the operation of the DC power transmission system can be stably continued.

  In the control device 10 of the present embodiment, the upper limit limiter value α0UL at the REC end operation and the upper limiter value α1UL at the INV end operation are set in advance, and the function αUL (t) in the transition period of the limiter value is set. It can be set appropriately and arbitrarily. Therefore, since the appropriate function αUL (t) can be set according to the DC power transmission system, the increase in αAVR at the time of power flow reversal can be limited, and overshoot, undershoot, and commutation failure can be reliably performed. Can be prevented.

  Furthermore, since α0UL and α1UL can be appropriately and arbitrarily adjusted and set together with the function αUL (t), it is possible to more reliably prevent overshoot, undershoot, and commutation failure depending on the DC power transmission system. it can.

  In the present embodiment, the startup limiter setting circuit 30 is further provided, and the limiter control circuit 20 is switched and operated after the startup limiter setting circuit 30 completes its operation. Therefore, the limiter control circuit 20 can stably realize the power flow reversing operation without interfering with the operation of the startup limiter setting circuit 30.

(Second embodiment)
FIG. 5: is a block diagram which illustrates the control apparatus of the power converter which concerns on this embodiment.
In the present embodiment, the control device 210 includes a limiter control circuit 220 according to the power flow direction. The power flow direction limiter control circuit (hereinafter, simply referred to as a limiter control circuit) 220 acts on the limiter circuit of the AVR 12 to set the upper limiter value of the AVR 12. In the case of this embodiment, the upper limiter value of the limiter circuit of the AVR 12 is determined by comparing the value of the actual DC voltage output by the power converter with a preset determination value.

  When the absolute value of the DC voltage output from the power converter reaches the absolute value of the return determination value of the DC voltage, the limiter control circuit 220 outputs the phase control angle α at which the LVG 14 outputs the upper and lower limiter values. Set to match. The upper and lower limit values of the output limiter circuit 15 are preset values αUL and αLL.

  In this example, the limiter control circuit 220 includes absolute value circuits 221, 222, a comparator 223, a one-shot circuit 224, and a switch circuit 225. The detected value Vd of the DC voltage and the return determination value Vd (det) are input to the absolute value circuits 221 and 222, respectively. The outputs of the absolute value circuits 221 and 222 are input to the comparator 223. The output of the comparator 223 is input to the one-shot circuit 224. The output of the one-shot circuit 224 is input to the control input of the switch circuit 225.

  The switch circuit 225 includes two switches 225a and 225b. A preset upper limiter value αUL is set to one input of the switch 225a. The output of the LVG 14 is connected to the other input of the switch 225a. The output of switch 225a is connected to the limiter circuit of AVR12 and provides the upper limiter value. A preset lower limiter value αLL is set to one input of the switch 225b. The output of the LVG 14 is connected to the other input of the switch 225b. The output of switch 225b is connected to the limiter circuit of AVR12 to provide a lower limiter value. The control inputs of the switches 225a and 225b are connected to the output of the one-shot circuit 224.

  While the output of the one-shot circuit 224 is at the low level, the switches 225a and 225b set αUL and αLL as the limit values of the AVR12. While the output of the one-shot circuit 224 is at the high level, the switches 225a and 225b set the output of the LVG 14 as the limit value of the AVR 12.

The operation of the control device of this embodiment will be described.
FIG. 6 is a schematic graph illustrating the operation of the control device of this embodiment.
The upper diagram of FIG. 6 shows the time changes of the phase control angles αACR and αAVR generated by the ACR 11 and AVR 12 and the time changes of the phase control angle α output by the LVG 14. αACR is shown by a two-dot chain line, αAVR is shown by a one-dot chain line, and α is shown by a solid line. αUL is a limiter value of the upper limit of AVR and is constant with respect to time. The figure also shows the lower limit limiter value αLL.
The lower diagram of FIG. 6 shows the time change of the DC voltage Vd output by the power converter controlled by the control device with a thick solid line.
In the upper and lower diagrams of FIG. 6, the time axes are the same.

  As shown in FIG. 6, when the power flow inversion is started by the power flow inversion command at time t1, the phase control angles αACR and αAVR start to increase, and the DC voltage Vd output from the power converter starts to invert and decreases. To do.

  When the DC voltage Vd further decreases and reaches the return determination value −Vd (det) at time t11, the output of the comparator 223 of the limiter control circuit 220 is inverted to high level. The one-shot circuit 224 to which the high level signal is input supplies a one-shot pulse signal having a preset pulse width to the control input of the switch circuit 225.

  The high-level one-shot pulse signal causes the switch 225a to switch the upper limiter value of the AVR 12 from one input supplied with αUL to the other input supplied with the output of the LVG 14. At the same time, the switch 225b switches the lower limit value of the AVR 12 from one input to which αLL is supplied to the other input to which the output of the LVG 14 is supplied.

  Since the upper and lower limiter values are set to the same value of α, the AVR 12 has the same magnitude as the phase control angle α output by the LVG 14 during the high level period of the one-shot pulse signal. Output α.

  In the period until time t11, the value of αACR is smaller than the value of αAVR, and therefore the value of α is equal to αACR. On the other hand, the value of αAVR is forcibly set to the value of α by the one-shot circuit 224 at time t11. When the period of the pulse width output by the one-shot circuit 224 elapses, αAVR changes according to the response performance of AVR12, but since t11 does not exceed αACR, the DC voltage determined by αAVR is , DC voltage command value (rated value) will not be exceeded.

The effects of the control device of the present embodiment will be described.
In the present embodiment, the control device 210 includes a limiter control circuit 220. In the case of the present embodiment, the limiter control circuit 220 switches the limiter value depending on whether or not the DC voltage Vd output from the power converter has reached a predetermined return determination value, so that αAVR can be reliably increased. Can be suppressed.

  In the present embodiment, αAVR changes stepwise at the moment when the DC voltage return determination value Vd (det) is detected, but the value of the phase control angle α output by the LVG 14 is equal to the magnitude of αACR and αAVR. Since it is determined by selecting the smaller one, the output phase control angle α does not change suddenly, and therefore the current or DC voltage output by the power converter does not change suddenly.

  An appropriate value can be arbitrarily set as the value of the return determination value Vd (det) of the DC voltage. If α when the return determination value Vd (det) is detected is smaller than the phase control angle α when the DC voltage command value (rated value) set in the AVR 12 is reached, αAVR after the time t11 is also a DC voltage command. It is possible to prevent the phase control angle from reaching a value (rated value) from being exceeded. The return determination value Vd (det) can be set to, for example, about 90% of the DC voltage command value (rated value), and the output voltage can be adjusted by adjusting the DC voltage transmission system according to the DC transmission system. It is possible to prevent overshoot, undershoot and commutation failure.

(Third Embodiment)
FIG. 7: is a block diagram which illustrates the control apparatus of the power converter which concerns on this embodiment.
In the present embodiment, the control device 310 includes a limiter control circuit 320 depending on the power flow direction. The limiter control circuit (hereinafter, simply referred to as a limiter control circuit) 320 according to the power flow direction includes an AVR 321. The AVR 321 executes constant voltage control by feedback control, whereas the AVR 321 executes constant voltage control by open loop control. The DC voltage command value Vdp, the DC current Id, the AC voltage Vac, and the commutation impedance Zc are input to the AVR 321, and the estimated value αAVR0 of the phase control angle is calculated based on these.

  The limiter control circuit 320 further includes an adder 322. A preset bias value αm is added to the estimated value αAVR0 by the adder 322 to the upper limit value of the limiter. As the upper limit value of AVR12, αAVR0 'obtained by adding αm to αAVR0 is supplied.

  The bias value αm is set to such a small value that the phase control angle αAVR0 generated by the limiter control circuit 320 in normal operation does not limit the output of the AVR12. The bias value αm is several degrees, for example, about 3 degrees.

The operation of the control device 310 of this embodiment will be described.
FIG. 8 is a schematic graph illustrating the operation of the control device of this embodiment.
The line type in FIG. 8 is the same as that described in FIG. However, the broken line curve indicates the estimated value αAVR0 ′ of the phase control angle output by the limiter control circuit 320.

  As shown in FIG. 8, at time t1, when the power flow inversion is started by the power flow inversion command, αACR and αAVR increase, and α also increases.

  The limiter control circuit 320 inputs the DC voltage command value Vdp, the DC current Id, the AC voltage Vac, and the commutation impedance Zc, and calculates the estimated value αAVR0 of the phase control angle using a well-known relational expression. Here, the well-known relational expression is for obtaining a phase control angle such that the DC voltage Vd output by the power converter under constant voltage control is controlled to a DC voltage command value (rated value). Since the DC current Id and the AC voltage Vac are measured values, the AVR 321 executes open loop control.

  Since the estimated value αAVR0 is the measured value of the DC voltage Vd, it changes according to the change in the absolute value of the DC voltage Vd after the start of the power flow inversion. Therefore, the curve of the broken line has a substantially constant value over the entire period, although it slightly increases or decreases during the period when the DC current Id is changing. Note that the upper limiter value αUL of the AVR12 is set to a value larger than the output of the AVR12 that is normally operating and the estimated value αAVR0 '.

  At time t21, the phase control angle αAVR generated by the AVR12 reaches αAVR0 ', so that the phase control angle αAVR is prevented from becoming larger.

  After that, at time t22, αAVR becomes smaller than αACR, the phase control angle α output by control device 310 becomes equal to αAVR, and the power converter performs constant voltage control operation at the DC voltage command value (rated value). can do.

The effects of the control device of the present embodiment will be described.
In this embodiment, the control device 310 includes an AVR 321. The AVR 321 inputs the DC voltage command value Vdp, the DC current Id, the AC voltage Vac, and the commutation impedance Zc so that the DC voltage Vd output from the power converter is controlled to the DC voltage command value (rated value). The phase control angle αAVR0 is calculated. As described above, the AVR 321 executes the open loop control, and the estimated value αAVR0 output by the calculation is substantially equal to the phase control angle α when the DC voltage command value (rated value) is output. Therefore, it is possible to prevent the magnitude of αAVR from exceeding the phase control angle when outputting the DC voltage command value (rated value). Therefore, the output voltage can prevent overshoot, undershoot, and commutation failure.

  The bias value αm is added to the estimated value αAVR0 of the phase control angle output by the AVR 321, and the upper limit value is set. Since the bias value αm is preset to a value that is sufficiently smaller than the estimated value αAVR0, by adding the bias value αm, not only the upper limit of the phase control angle at the time of power flow reversal but also during normal operation, It is possible to prevent the value of the phase control angle αAVR generated by the AVR 12 from being influenced.

  In the case of any of the above-described embodiments, when the power flow is reversed from the REC end to the INV end, it has been described that the voltage changes from + Vdp to −Vdp, but since the control device controls by the absolute value of the DC voltage, The same applies to changing from −Vdp to + Vdp.

  According to the embodiments described above, it is possible to realize a control device for a power converter that can stably continue operation even when the power flow direction is reversed.

  Although some 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, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent thereof. Further, the above-described respective embodiments can be implemented in combination with each other.

  1, 1a power system, 3 DC transmission line, 10, 10a, 210, 310 control device, 11 constant current control circuit, 12 constant voltage control circuit, 13 margin angle control circuit, 14 minimum value selection circuit, 15 output limiter circuit, 20, 220, 320 Limiter control circuit, 30 Start-up limiter setting circuit, 31 Limiter setting unit, 32 Timer, 33 switch circuit, 40, 40a Power converter, 100 DC power transmission system, 221, 222 Absolute value circuit, 223 Comparator , 224 one-shot circuit, 225 switch circuit, 321 constant voltage control circuit, 322 adder

Claims (6)

A control device for a power converter provided between an AC power system and a DC transmission line,
A first constant voltage control circuit that generates a first phase control angle based on the set DC voltage command value and the DC voltage output by the power converter;
A constant current control circuit for generating a second phase control angle based on the set direct current command value and the direct current flowing through the direct current transmission line;
A minimum value selection circuit that selects and outputs the smaller one of the first phase control angle and the second phase control angle;
A first limiter setting circuit for setting an upper limit of the output of the minimum value selection circuit,
Equipped with
When the power converter changes the operation state from the forward converter to the inverse converter by the command to change the state in the flow direction,
The first limiter setting circuit limits the output so that the DC voltage does not exceed a phase control angle when the DC voltage follows the DC voltage command value after the command is input. The first limiter setting circuit,
A first upper limit value set when the power converter operates as a forward converter;
A second upper limit value having a value larger than the first upper limit value and set when the command is input;
A first function relating to a time for making a transition from the first upper limit value to the second upper limit value;
The control device for the power converter according to claim 1, further comprising: A third upper limit value having a value smaller than the first upper limit value;
A second function relating to a time for making a transition from the third upper limit value to the first upper limit value;
Further comprising a second limiter setting circuit including
The second limiter setting circuit,
When starting the power converter by a start command,
The control device for a power converter according to claim 2, wherein the command is input after the third upper limit value is transited to the first upper limit value via the second function according to the start command.   After the input of the command, when the DC voltage output from the power converter reaches a preset threshold value, the first limiter setting circuit sets the upper limit of the first constant voltage control circuit and The control device for the power converter according to claim 1, wherein the first phase control angle is set to the second phase control angle at that time by limiting a lower limit. The first limiter setting circuit,
A phase at which the DC voltage output by the power converter is equal to the DC voltage command value based on the DC voltage command value, the DC current output by the power converter, the AC voltage of the power system, and the commutation impedance. A second constant voltage control circuit for calculating an estimated value of the control angle,
The control device for a power converter according to claim 1, wherein the upper limit of the output of the first constant voltage control circuit is set by the output of the second constant voltage control circuit. The first limiter setting circuit,
The control device for the power converter according to claim 5, further comprising an adder provided at an output of the second constant voltage control circuit.

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