JP6612639B2 - Control device for power converter - Google Patents

Description

  Embodiments described herein relate generally to a control device for a power converter that mutually converts power between direct current and alternating current.

  DC power transmission has advantages such as the ability to control power flow quickly and the fact that it is suitable for long-distance power transmission and cable power transmission, and is being introduced worldwide. Conventionally, as a power converter for a DC power transmission system that converts power from DC to AC or from AC to DC, a separately-excited converter using a thyristor applied to a semiconductor switch has been used, but has excellent controllability, In recent years, the introduction of self-excited converters has been progressing because the equipment can be downsized.

  As a self-excited converter for a DC power transmission system, for example, a two-level converter is used. This converter has a DC capacitor, and the DC capacitor is connected to a DC transmission line. Therefore, the capacitor voltage and the DC voltage are equal. For this reason, in controlling the DC side of the two-level converter, the AC side is controlled, that is, by controlling the exchange of power between the AC system and the converter, thereby adjusting the energy of the DC capacitor and controlling the DC voltage.

  Another self-excited converter is a modular multilevel converter (hereinafter also referred to as MMC). The MMC is composed of unit converters including DC capacitors and switching elements connected in series in multiple stages. By shifting the ON / OFF timing of the switching elements, the output voltage waveform can be multi-leveled and converted into a sine wave. You can get closer.

  In the case of MMC, unlike the two-level converter, if the switching element is OFF, the DC capacitor is not connected to the DC side, and if the switching element is ON, the DC capacitor is connected to the DC side. That is, the operating principle of the converter is different from the two-level converter in which the DC capacitor is always connected to the DC side. Therefore, the DC voltage / current control of the two-level converter cannot be applied.

  That is, in the two-level converter, DC voltage / current control is performed by a voltage margin method in which a difference is added to the DC voltage command value in the two-level converter provided at both ends of the DC power transmission system. Depending on the voltage margin, the power transmission end and the power reception end were switched to reverse the power flow. On the other hand, since the operation principle of the converter is different in MMC, this control method cannot be applied. Therefore, a control method using both a voltage margin and a current margin has been proposed.

In the control method using both the voltage margin and the current margin, in a steady state, the voltage margin is V _mag at the transmission end, the current margin is 0, constant current control is performed, the voltage margin is 0 at the reception end, and the voltage margin is I _The DC voltage and current are controlled by performing constant voltage control as _mag .

Yukio Tokiwa, 5 others, “Terminal control and cooperative control in HVDC system using self-excited converter”, IEEJ Transactions B, Vol. 19-26 Toshiaki Kikuma, 4 others, "Control and protection method of self-excited DC power transmission system capable of suppressing DC fault current", IEEJ Transactions B, Vol. 133 No. 5 pp. 449-456

JP 2013-179781 A

  In the control method using both the voltage margin and the current margin, since control is performed with two margins, there is a problem that the control becomes complicated. For example, this control method includes control in which an AC voltage and a DC voltage are multiplied, and AC and DC are mixed to further complicate the control.

  The control device for the power converter according to the embodiment of the present invention is made to solve the above-described problems, and does not depend on the AC side and simplifies DC current control and DC voltage control. It is an object of the present invention to provide a control device for a power converter that can be used.

  In order to achieve the above-described object, the power converter control device according to the present embodiment includes a multi-stage unit converter having a switching element and a capacitor, and controls the power converter that converts power between AC and DC. A DC voltage / current control unit for calculating a converter output voltage for operating the power converter by DC voltage control or DC current control; and causing the power converter to output the converter output voltage. A signal generating unit that generates a signal for turning on and off the switching element, and the DC voltage / current control unit converts the DC current to a DC current command based on a deviation between the DC current and the DC current command value. A tracking unit that calculates a voltage value for tracking the value, an upper limit value and a lower limit value based on a limiter value, and receives an input from the tracking unit based on the upper limit value and the lower limit value A limiter for limiting the force value, a calculation unit for calculating the converter output voltage by adding the output value of the limiter and a DC voltage command value, and a limiter value for setting the limiter value to 0 or a value other than 0 And a setting unit.

  Further, the power converter control device of the present embodiment is a power converter control device in which unit converters having switching elements and capacitors are connected in multiple stages to convert power between alternating current and direct current. A DC voltage / current control unit for calculating a converter output voltage for operating the converter with DC voltage control or DC current control, and the switching element so as to output the converter output voltage to the power converter. A signal generator for generating an on / off signal, wherein the DC voltage / current control unit is a voltage for causing the DC current to follow the DC current command value based on a deviation between the DC current and the DC current command value. A follow-up unit that calculates a value; an arithmetic unit that adds an output value of the follow-up unit and a DC voltage command value; an upper limit value and a lower limit value based on the DC voltage command value and the limiter value; A limiter that limits the output value based on the upper limit value and the lower limit value, and a limiter value setting unit that sets the limiter value to a predetermined value that is 0 or non-zero. The output value is the converter output voltage.

  Further, the power converter control device of the present embodiment is a power converter control device in which unit converters having switching elements and capacitors are connected in multiple stages to convert power between alternating current and direct current. A DC voltage / current control unit for calculating a converter output voltage for operating the converter with DC voltage control or DC current control, and the switching element so as to output the converter output voltage to the power converter. A signal generator for generating an on / off signal, wherein the DC voltage / current control unit is a voltage for causing the DC current to follow the DC current command value based on a deviation between the DC current and the DC current command value. A tracking unit that calculates a value, an upper limit value and a lower limit value based on a DC voltage command value and a limiter value, and receives an input from the tracking unit and outputs based on the upper limit value and the lower limit value A limiter for limiting a limiter value setting unit that sets the limit value to a predetermined non-zero value or 0, with the output value of said limiter to said converter output voltage, characterized by.

It is a figure showing the whole direct-current power transmission system composition to which the control device of the power converter concerning a 1st embodiment is applied. It is a figure which shows the structure of a power converter. It is a functional block diagram of a control device concerning a 1st embodiment. It is a control block diagram of a DC voltage / current control unit. It is a figure which shows a part of control block of a signal generation part. It is a control block diagram of the DC voltage / current control unit of the control device according to the second embodiment. (A) is a control characteristic diagram in a normal state. FIG. 6B is a control characteristic diagram when an accident occurs on the AC side of the current control end. (C) is a control characteristic diagram when an accident occurs on the AC side of the voltage control end. It is a functional block diagram of a control device concerning a 3rd embodiment. It is a control block diagram of a circulating current calculation part. It is a control block diagram of an αβ0 conversion unit. It is a functional block diagram of a control device concerning a 4th embodiment. It is a control block diagram of a direct-current power command value generation unit. It is a control block diagram of a transmission line loss calculating part. It is a control block diagram of a converter loss calculating part. It is a control block diagram of a direct current command value generation unit. It is a figure which shows the direct current power transmission system in the case of carrying out electric power transaction in the alternating current terminal of the current control end of a receiving side. It is a figure which shows the direct current power transmission system in the case of carrying out electric power transaction in the alternating current terminal of the voltage control end at the power transmission side. It is a control block diagram of the DC voltage / current control unit according to another embodiment. It is a control block diagram of the DC voltage / current control unit according to another embodiment. It is a control block diagram of the direct-current power command value generation unit according to another embodiment.

[1. First Embodiment]
[1-1. overall structure]
Below, the control apparatus of the power converter of this embodiment is demonstrated, referring FIGS. FIG. 1 is a diagram illustrating an overall configuration of a DC power transmission system to which a control device according to the present embodiment is applied.

  As shown in FIG. 1, a DC power transmission system (HVDC) is connected to AC systems 1A and 1B, respectively, and is composed of two power converters (hereinafter simply referred to as “converters”) that perform power conversion from AC to DC and from DC to AC. It also has 3A and 3B.

  The converter 3A is connected to the AC system 1A, and the converter 3B is connected to the AC system 1B via a transformer (not shown). Further, the converters 3 </ b> A and 3 </ b> B are connected to each other by a DC power transmission line 5. The DC power transmission line 5 includes a DC overhead line and a DC cable.

  The power converters (converters) 3A and 3B perform power transmission by converting from alternating current to direct current or from direct current to alternating current. Here, the converters 3A and 3B are self-excited converters, and are modular multilevel converters (MMCs: Modular Multilevel Converter). FIG. 2 shows the configuration of the converter 3A. The converters 3A and 3B can be controlled both as a forward converter (REC) for converting from alternating current to direct current and as an inverse converter (INV) for converting from direct current to alternating current. .

  Converters 3 </ b> A and 3 </ b> B include a DC positive terminal and a DC negative terminal connected to DC power transmission line 5. These terminals are direct current terminals, and a higher voltage is defined as a positive side and a lower voltage is defined as a negative side with reference to a neutral point of a leg 31 described later. In this specification, the DC positive terminal side is referred to as “positive side” and the DC negative terminal side is referred to as “negative side” in order to describe the configuration of the converters 3A and 3B.

  As shown in FIG. 2, the converters 3A and 3B each include a leg 31 in which a plurality of chopper cells C are connected between a DC positive terminal and a DC negative terminal in each of the three phases. A voltage is output from the DC positive terminal and the DC negative terminal using C as a unit voltage source.

  In the leg 31, a positive arm 31a in which a plurality of chopper cells C are connected in series and a negative arm 31b in which a plurality of chopper cells C are connected in series are connected in series via two reactors Re on the positive side and the negative side. Being done. The positive arm 31a is also referred to as an upper arm, and the negative arm 31b is also referred to as a lower arm. The positive arm 31a and the negative arm 31b are connected to an AC terminal via a reactor Re, and power is exchanged with the AC systems 1A and 1B via the terminal.

  The chopper cell C is a unit converter. The chopper cell C includes two switching elements C1a and C1b, diodes C2a and C2b, and a capacitor C3. The capacitor C3 is used as a voltage source, and a desired DC voltage is output by an on / off operation of the switching elements C1a and C1b.

  Specifically, the switching elements C1a and C1b are connected in series to each other to form a switching string, and the capacitor C3 is connected in parallel to the switching string. As the switching elements C1a and C1b, self-extinguishing elements such as GTO, IGBT, and IEGT can be used. Feedback diodes C2a and C2b are connected in antiparallel to the switching elements C1a and C1b. The chopper cell C outputs the DC voltage Vc of the capacitor C3 when the switching element C1a is on, and becomes zero voltage when the switching element C1b is on.

  The leg 31 of each phase outputs an arbitrary voltage such as a stepped AC voltage using the chopper cell C as a unit converter. The stepped AC voltage is output by shifting the timing of the switching operation of the switching elements C1a and C1b of each chopper cell C.

  Control devices 4A and 4B are connected to the converters 3A and 3B, respectively. The control devices 4A and 4B control the operations of the converters 3A and 3B. That is, the control devices 4A and 4B operate the converters 3A and 3B by direct current voltage control or direct current control. In the DC power transmission system, one converter 3A, 3B is operated by DC voltage control, and the other converter 3A, 3B is operated by DC current control. In order for the converters 3A and 3B to function as both a forward converter and an inverse converter, the configurations of the control devices 4A and 4B are the same.

[1-2. Detailed configuration]
The control devices 4A and 4B control the operations of the converters 3A and 3B with physical quantities related to direct current. A functional block diagram of the control devices 4A and 4B is shown in FIG. As illustrated in FIG. 3, the control devices 4 </ b> A and 4 </ b> B include a DC detection unit 41, a storage unit 42, a DC voltage / current control unit 43, and a signal generation unit 44.

  The DC detection unit 41 detects a DC current at the DC terminals of the converters 3A and 3B. Specifically, the DC detection unit 41 is a DC current detector. The control devices 4A and 4B only need to receive a direct current in the vicinity of the place where the converters 3A and 3B are connected, and the DC detection unit 41 may not be a constituent requirement of the control devices 4A and 4B. . In other words, the DC detection unit 41 may be provided in the DC power transmission system.

  The storage unit 42 stores various data necessary for processing executed by the DC voltage / current control unit 43. For example, a limiter value provided in a limiter 433 of a DC voltage / current control unit 43 described later is stored.

  The DC voltage / current control unit 43 receives the DC current and the DC current command value and outputs a converter DC output voltage. FIG. 4 is a control block diagram of the DC voltage / current control unit. As shown in FIG. 4, the DC voltage / current control unit 43 includes a calculator 431, a gain 432, a limiter 433, a limiter value setting unit 433 a, and a calculator 434.

The calculator 431 calculates the difference between the DC current command value I _{dc_ref} and the detected DC current I. The gain 432 performs feedback control that follows the difference calculated by the calculator 431 so that the difference becomes zero. The gain 432 can be, for example, P control (proportional control), PI control (proportional integral control), or PID control.

  The calculator 431 and the gain 432 constitute a follow-up unit. The follower performs a calculation for causing the direct current to follow the direct current command value, and outputs the result to the limiter 433.

  The limiter 433 limits the output value of the follower. That is, the limiter 433 is provided with a limiter value that determines whether the converters 3A and 3B are operated by DC voltage control or DC current control, and the output value of the follower is an upper limit value and a lower limit value. Limited by. The limiter value is 0 or a predetermined value that is not 0. The upper limit value is simply referred to as “upper limit value”, and the lower limit value is simply referred to as “lower limit value”.

  In the present embodiment, when the limiter value is L (L ≧ 0), the lower limit value and the upper limit value are based on the limiter value L, the lower limit value is −L, and the upper limit value is + L. The limiter 433 sets the input value as the output value of the limiter 433 if the input value from the follower is within the range of the lower limit value and the upper limit value. Further, if the input value from the tracking unit exceeds the upper limit value, the output value of the limiter 433 is set as the upper limit value. If the input value from the tracking unit is less than the lower limit value, the output value of the limiter 433 is set as the lower limit value. And For example, if the limiter value L is 0, the output value of the limiter 433 is always 0 regardless of the input value from the follower. This is because if L = 0, the upper limit value and the lower limit value are also zero.

  The limiter value setting unit 433a sets the limiter value to 0 or a predetermined value other than 0. The limiter value setting unit 433a may be set with a limiter value stored in advance in the storage unit 42, or may be set by receiving user input via an input unit such as a mouse, a keyboard, or a touch panel. Further, the limiter value setting unit 433a sets the upper limit value and the lower limit value of the limiter 433 based on the limiter value. Here, limiter value setting section 433a sets the lower limit value to −L and the upper limit value to + L.

  In the present embodiment, the upper limit value and the lower limit value of the limiter 433 are the same. However, the upper limit value may be larger than the lower limit value, and the upper limit value may be larger than the lower limit value. It may be small.

  The calculator 434 receives the output value of the limiter 433 and the DC voltage command value as input, and adds them. The value obtained by this addition is the converter DC output voltage to be output by the converters 3A and 3B. The calculator 434 outputs the obtained converter DC output voltage to the signal generator 44.

  The signal generation unit 44 performs on / off control of the switching elements C1a and C1b included in the chopper cells C of the positive side phase arm 31a and the negative side phase arm 31b based on the input converter DC output voltage and converter AC output voltage. Is generated. The converter AC output voltage is an AC voltage output from the converters 3A and 3B.

  Specifically, the signal generation unit 44 first generates a positive arm output voltage command value and a negative arm output voltage command value from the converter DC output voltage and the converter AC output voltage. More specifically, as shown in FIG. 5, the converter AC output voltage is subtracted from 1/2 of the converter DC output voltage to generate a positive arm output voltage command value, and 1 / of the converter DC output voltage is generated. 2 and the converter AC output voltage are added to generate a negative arm output voltage command value.

  Next, the signal generation unit 44 generates a signal for on / off control of the switching elements C1a and C1b of each chopper cell C based on the command values of the positive arm output voltage command value and the negative arm output voltage command value. Then, the signal generation unit 44 outputs the control signal generated to each of the switching elements C1a and C1b, and outputs the converter output voltage obtained by the DC voltage / current control unit 43 so that the converters 3A and 3B Control the behavior.

[1-3. Action]
The operation of the power converter control devices 4A and 4B of the present embodiment will be described. Control devices 4A and 4B determine whether converters 3A and 3B are operated by DC voltage control or DC current control according to a limiter value provided in limiter 433 of DC voltage / current control unit 43.

(1) When the limiter value is 0 The value output from the limiter 433 by the limiter 433 is always 0. Therefore, the DC voltage command value becomes the converter DC output voltage as it is. That is, the converters 3A and 3B controlled by the control devices 4A and 4B in which the limiter value L is set to 0 are voltage control terminals that control the DC voltage to be constant in the DC power transmission system. For example, when the converter 3A is a voltage control end, the limiter value L in the control device 4A is set to zero.

(2) When the limiter value is a predetermined value (a value other than 0) The value output from the limiter 433 is a value that satisfies the range of the limiter value −L to the limiter value + L, and is a control of the follower that controls the direct current. Is reflected in the converter DC output voltage. That is, the converters 3A and 3B controlled by the control devices 4A and 4B in which the limiter value L is set to a predetermined value (a value other than 0) cause the DC current to follow the DC current command value in the DC power transmission system. It becomes the current control end to be controlled. For example, when the converter 3B is used as the current control end, the limiter value L in the control device 4B is set to a non-zero value. Thereby, the limiter 433 has an upper limit value and a lower limit value. The range from the lower limit value to the upper limit value is a voltage fluctuation range for causing the direct current to follow the direct current command value. The current control terminal, for example, controls the converter output voltage to decrease if a direct current is to be drawn, and controls the converter output voltage to be increased if a direct current is to be sent out.

  The limiter value can be determined in consideration of the length of the DC transmission line 5 and the speed at which the power flow is reversed. For example, when the converter 3A is operated as a voltage control terminal on the power transmission side and the converter 3B is operated as a current control terminal on the power reception side, the voltage between the DC terminals at the current control terminal has a voltage drop due to the resistance of the DC power transmission line 5. Therefore, it becomes smaller than the voltage between the DC terminals at the voltage control terminal, that is, the DC voltage command value. Therefore, the limiter value may be set in consideration of at least twice the voltage drop due to the resistance of the DC transmission line 5 so that the DC current can be adjusted even if this voltage drop occurs.

  As described above, the operation of the converters 3A and 3B can be controlled by the limiter value, and the cooperation of the converters 3A and 3B at the end of the DC power transmission system can be achieved by the limiter value. That is, one converter 3A, 3B is operated as a DC voltage control terminal, the other converter 3A, 3B is operated as a DC current control terminal, and the DC voltage command value and DC current command of these converters 3A, 3B are operated. It is possible to obtain a DC power transmission system that keeps the power obtained by multiplying the values constant.

  In particular, the DC voltage / current control unit 43 can control the operation of the converters 3A and 3B only by the physical quantity on the DC side, and does not depend on the physical quantity on the AC side, so that direct current and alternating current are not mixed, Control can be simplified.

[1-4. effect]
In the control devices 4A and 4B of the power converters 3A and 3B according to the present embodiment, the chopper cells C having switching elements C1a and C1b and a capacitor C3 are connected in multiple stages, and the converters 3A and 3B convert power between AC and DC. The control devices 4A and 4B include a DC voltage / current control unit 43 that performs DC current control or DC voltage control on the converters 3A and 3B. The DC voltage / current control unit 43 has a tracking unit that tracks the DC current to the DC current command value, an upper limit value and a lower limit value based on the limiter value, and receives an input from the tracking unit to obtain an upper limit value and a lower limit value. A limiter 433 that limits the output value based on the calculation unit 434 that adds the output of the limiter 433 and the DC voltage command value, and a limiter value setting unit 433a that sets the limiter value to 0 or a predetermined value other than 0. I did it.

  Thereby, it is possible to perform direct current control or direct current voltage control only by direct current side information without depending on alternating current side information, and control of the converters 3A and 3B can be simplified. That is, it is possible to determine whether the DC current control or the DC voltage control is performed by setting the limiter value, and the control configuration can be simplified.

[2. Second Embodiment]
[2-1. Constitution]
A second embodiment will be described with reference to FIGS. 6 and 7. The basic configuration of the second embodiment is the same as that of the first embodiment. Therefore, only a different point from 1st Embodiment is demonstrated, the same code | symbol is attached | subjected about the same part as 1st Embodiment, and detailed description is abbreviate | omitted.

  FIG. 6 is a control block diagram of the DC voltage / current control unit 43 according to the second embodiment. The DC voltage / current control unit 43 according to the second embodiment further includes an AC accident detection unit 45 and a limiter value change unit 46 in addition to the configuration of the first embodiment.

  The AC accident detection unit 45 detects an accident on the AC side of the converters 3A and 3B. Examples of the accident on the AC side include a short circuit and a ground fault in the AC systems 1A and 1B, and a short circuit and a ground fault between the AC systems 1A and 1B and the AC terminals of the converters 3A and 3B.

  The AC accident detection unit 45 includes, for example, an AC voltage detector provided on the AC side of the converters 3A and 3B and a detection unit that detects a decrease in AC voltage based on the AC voltage detected by the detector. Constitute. One of the converters 3A and 3B may be DC current control and the other DC voltage control. The AC voltage detector only needs to be provided in the DC power transmission system, and does not necessarily have to be a component of the control devices 4A and 4B.

  When the AC accident detection unit 45 detects an AC side accident, the AC accident detection unit 45 notifies the limiter value changing unit 46 that an AC accident has occurred. As this notification, for example, a predetermined signal is output to the limiter value changing unit 46.

  The limiter value changing unit 46 changes the limiter value of the limiter 433. Here, the change of the limiter value is triggered by the notification of the occurrence of an AC accident from the AC accident detection unit 45. In other words, when an accident occurs on the AC side of the converter to be controlled, the limiter value on the converter side is changed. Change the limiter value to a value greater than the value before the AC accident. A value larger than the value before the AC accident is an absolute value. In other words, the width formed by the upper limit and the lower limit provided in the limiter 433 is expanded before the AC accident.

Specifically, when DC current control is performed on the power receiving end side converters 3A and 3B of the DC power transmission system, the limiter value changing unit 46 detects the limit value on the power receiving end side by detecting an accident on the AC side of the power receiving end. It is changed to a value V _limit + V _fault that is larger than the _limit value V _limit before the AC accident. Here, V _fault is a positive number. That is, by this change, the width formed by the upper limit and the lower limit of the limiter 433 is increased by 2V _fault . The limiter value V _limit + V _fault to be changed is stored in the storage unit 42 in advance. Similarly, when DC current control is performed on the converters 3A and 3B on the power transmission end side of the DC power transmission system, the limiter value changing unit 46 changes the limiter value on the power transmission end side to the AC accident by detecting the accident on the AC side of the power transmission end. The value is changed to a value V _limit + V _fault which is larger than the previous limiter value V _limit .

On the other hand, when DC voltage control is performed on the converters 3A and 3B on the power transmission end side of the DC power transmission system, the limiter value changing unit 46 changes the limiter value on the power transmission side from 0 to the other end by detecting an accident on the AC side of the power transmission end. To a value V _limit + V _fault that is larger than the _limit value V _limit of the power receiving end that is operating under the direct current control. Here, V _fault is a positive number. The limiter value V _limit + V _fault to be changed is stored in the storage unit 42 in advance. Similarly, when DC voltage control is performed on the converters 3A and 3B on the power receiving end side of the DC power transmission system, the limiter value changing unit 46 changes the limiter value from 0 to the other end by detecting an accident on the AC side of the power receiving end. To a value V _limit + V _fault that is larger than the _limit value V _{limit of the} power transmission end operating in the direct current control.

[2-2. Action]
The operation of the control devices 4A and 4B according to this embodiment will be described with reference to FIG. FIG. 7A is a normal control characteristic diagram. FIG. 7B is a control characteristic diagram when an accident occurs on the AC side of the current control end. FIG. 7C is a control characteristic diagram when an accident occurs on the AC side of the voltage control end.

In the normal state, in the control device 4A that controls the converter 3A that is the voltage control terminal, the limiter value is set at L = 0, so that the DC output voltage of the converter 3A is equal to the voltage of the DC voltage command value V _{dc_ref} . Become. As shown in FIG. 7A, the voltage is constant no matter which current in the predetermined range flows. On the other hand, in the control device 4B that controls the converter 3B that is the current control end, the limiter value is set at L = V _limit , and the converter 3B has the follower unit and the direct current command value I _{dc_ref.} The limiter 433 can change the voltage with a width of ± V _limit with reference to V _{dc_ref} . As shown in FIG. 7A, the intersection of the characteristic line at the voltage control end and the characteristic line at the current control end is the operating point of the converters 3A and 3B.

  Hereinafter, when an AC accident occurs on the AC side of the current control end, and when an AC accident occurs on the AC side of the voltage control end, the operation in each case will be described.

(1) When the current control end is a power receiving end and an AC accident occurs on the AC side, the AC voltage on the power receiving end side decreases. For example, if the converter 3A is operated as a voltage control end with the power transmission end and the converter 3B is operated as a current control end with the power reception end, the AC output from the converter 3B serving as the power reception end with the decrease in the AC voltage. Electric power is also reduced. Here, since the DC voltage remains constant, the DC power flowing into the converter 3B serving as the power receiving end also remains constant, and the balance of power input and output at the power receiving end is lost, resulting in excessive inflow. Therefore, the capacitor voltage of the converter 3B serving as the power receiving end increases and becomes an overvoltage, and the converter 3B may break down.

Therefore, when the AC accident detection unit 45 detects an AC accident on the AC side of the power receiving end, the limit value changing unit 46 detects the _limit value on the power receiving end side by a value V greater than the _limit value V _limit before the AC accident. Change to _limit + _Vfault . As a result, the control characteristic diagram is as shown in FIG. That is, since the voltage at the power receiving end can be made relatively higher than that at the power transmitting end, the direct current flowing from the DC side of the converter 3B serving as the power receiving end can be reduced to zero, and the power supply from the DC side can be reduced. Can be suppressed. Therefore, it is possible to prevent the capacitor voltage from becoming an overvoltage and prevent the converter 3B from being broken.

  The limiter value can be changed more effectively by preventing the inflow of DC power since the voltage at the power transmission end can be increased by making the change width of the upper limit value larger than the change width of the lower limit value. Can do.

(2) When the current control end is a power transmission end and an AC accident occurs on the AC side, the AC voltage on the power transmission end side decreases. For example, if the converter 3A is operated as a current control terminal with the power transmission terminal as the power transmission terminal, and the converter 3B is operated as the voltage control terminal with the power reception terminal, the capacitor voltage of the converter 3A serving as the power transmission terminal is reduced as the AC voltage decreases. descend. This may adversely affect the operation of the converter 3A, such as distortion of the direct current.

Therefore, when the AC accident detection unit 45 detects an AC accident on the AC side of the power transmission end, the limiter value changing unit 46 detects the _limit value on the power transmission end side by a value V greater than the _limit value V _limit before the AC accident. Change to _limit + _Vfault . As a result, the control characteristic diagram is as shown in FIG. That is, since the voltage at the power transmission end can be made relatively lower than that at the power reception end, the direct current can be reduced to 0, and adverse effects on the operation of the converter 3A can be prevented.

  Note that the limiter value can be changed by making the change width of the lower limit value larger than the change width of the upper limit value, whereby the voltage at the power transmission end can be further lowered, and the influence on the AC system can be prevented at an early stage.

(3) When the voltage control terminal is the power transmission terminal and an AC accident occurs on the AC side, the AC voltage on the power transmission terminal side decreases. As the AC voltage decreases, the capacitor voltage at the power transmission end decreases, which may adversely affect the operation of the power transmission end. For example, when the converter 3A is a voltage control end and a power transmission end, and the converter 3B is a current control end and a power reception end, the converter 3A may be adversely affected.

  In this regard, the AC accident detection unit 45 notifies the accident detection to the control device 4B at the current control end (power receiving end) that is the counterpart end via a wired or wireless communication means connecting the control devices 4A and 4B. In response to the notification, the converter 3B is controlled so as to reduce the direct current input to the converter 3B, thereby preventing adverse effects on the converter 3A. That is, an AC accident that occurs on the AC side of the power transmission end from the control device 4A is received by the limiter value changing unit 46 of the control device 4B via the communication means, and the limiter value is changed to a value larger than the limiter value before the AC accident. . As the communication means, known means such as Ethernet (registered trademark) or wireless LAN can be used.

  However, in the DC power transmission system, the converters 3A and 3B are far away, and there may be a case where communication delay cannot be ignored. Therefore, when the AC accident detection unit 45 detects an AC accident on the AC side of the power transmission end, the DC current control is performed at its own end regardless of the DC current control at the other end.

That is, first, when the AC accident detection unit 45 detects an accident on the AC side of the power transmission end, the limiter value changing unit 46 detects the limiter value from 0 at its own end, based on the limiter value at the current control end as the counterpart end. Change to be larger. That is, the limiter value L = 0 is changed to L = V _limit + V _fault . As a result, the control characteristic diagram shown in FIG.

As shown in FIG. 7C, the output voltage at the power receiving end stops at the upper limit value or the lower limit value of the limiter 433. On the other hand, at the power transmission end, by changing the _limit value at the power transmission end to be larger than the limit value at the power reception end, the voltage can be varied with a width of ± (V _limit + V _fault ) with V _{dc_ref} as a reference.

  In other words, the current control is switched to the current control by changing the limiter value at the voltage control end, and the current control at the other end is restricted by the amount that the limiter value is larger than the limiter value at the other end. Therefore, it can be changed to a DC current command value to be controlled at the voltage control terminal instead of a DC current command value to be controlled at the current control terminal. In other words, the voltage control terminal on the power transmission side has a right to control the direct current, and can be changed to a value smaller than the direct current command value to be controlled by the current control terminal, for example, zero.

  As a result, an accident can be dealt with early at the power transmission end without any communication, so that the influence on the converter serving as the power transmission end can be prevented.

(4) When the voltage control terminal is the power receiving terminal and an AC accident occurs on the AC side, the AC voltage on the power receiving terminal side decreases. As the AC voltage decreases, the AC power output from the power receiving end also decreases. Here, since the DC voltage remains constant, the DC power flowing into the power receiving end also remains constant, and the balance of power input and output at the power receiving end is lost, resulting in excessive inflow. Therefore, the capacitor voltage at the power receiving end rises and becomes an overvoltage, and the power receiving end may break down.

  As described above, it is possible to prevent overvoltage by direct current control at the current control end (power transmission end) via the communication means, but there are cases where communication delay cannot be ignored.

  Therefore, when the AC accident detection unit 45 detects an AC accident on the AC side of the power receiving end, the limiter value changing unit 46 detects the limiter value from 0 at its own end, based on the limiter value of the current control end as the counterpart end. Change to be larger. As a result, the control characteristic diagram is as shown in FIG. That is, since the voltage at the power receiving end can be made relatively higher than that at the power transmitting end, the direct current flowing from the DC side of the power receiving end can be reduced to 0, and the power supply from the DC side can be suppressed. . Therefore, it is possible to prevent the capacitor voltage from becoming an overvoltage and to prevent a failure of the power receiving end.

[2-3. effect]
(1) The control devices 4A and 4B of the present embodiment are control devices 4A and 4B that control DC current of the converters 3A and 3B on the power receiving end side in the DC power transmission system, and limiter value changing units that change the limiter values. 46, and the limiter value changing unit 46 changes the limiter value on the power receiving end side to a value larger than the limiter value before the AC accident by detecting the AC accident on the AC side of the converters 3A and 3B on the power receiving end side. I did it.

  Thereby, since the voltage of converter 3A, 3B used as a power receiving end can be made higher than a power transmission end, the electric power supply from the direct current | flow side of a power receiving end can be suppressed. Therefore, an increase in the capacitor voltage at the power receiving end can be suppressed, and destruction of the power receiving end can be prevented.

(2) Control devices 4A and 4B that control DC current of converters 3A and 3B on the power transmission end side in the DC power transmission system, and include a limiter value changing unit 46 that changes a limiter value. The limiter value is changed to a value larger than the limiter value before the AC accident by detecting the AC accident on the AC side of the converters 3A and 3B on the power transmission end side.

  As a result, the voltage of the converters 3A and 3B serving as the power transmission terminals can be made lower than the voltage of the converters 3A and 3B that perform DC voltage control at the power reception terminals, so that the direct current can be brought close to 0, The influence on the converters 3A and 3B at the ends can be prevented.

(3) Control devices 4A and 4B for controlling the converters 3A and 3B on the power transmission end side in the DC power transmission system, where the converters 3A and 3B on the power transmission end side of the DC power transmission system are DC voltage controlled, and the power receiving end side The converters 3A and 3B are controlled by direct current, and include a limiter value changing unit 46 that changes the limiter value. The limiter value changing unit 46 is an AC fault on the AC side of the converters 3A and 3B on the power transmission end side. By detecting this, the limiter value on the power transmission end side is changed to a value larger than the limiter value on the power reception end side.

  Thereby, the converter 3A, 3B at the power transmission end can hold the right to control the direct current. That is, current control can be performed at its own end without depending on the current control at the other end, so that it is possible to quickly respond to an AC accident and to prevent the power transmission end from being affected by the converters 3A and 3B.

(4) Control devices 4A and 4B for controlling the converters 3A and 3B on the power receiving end side in the DC power transmission system, where the converters 3A and 3B on the power receiving end side of the DC power transmission system are DC voltage controlled, The converters 3A and 3B are controlled by direct current, and include a limiter value changing unit 46 that changes the limiter value. The limiter value changing unit 46 is an AC fault on the AC side of the converters 3A and 3B on the power receiving end side. By detecting this, the limit value on the power receiving end side is changed to a value larger than the limit value on the power transmitting end side.

  Thereby, the converter 3A, 3B at the power receiving end can hold the right to control the direct current. That is, current control can be performed at its own end without depending on the current control at the other end, so that it is possible to respond quickly to an AC accident. For example, since the voltage of the converter 3B serving as the power receiving end can be made higher than that of the power transmitting end, power supply from the DC side of the converter 3B serving as the power receiving end can be suppressed. Therefore, an increase in the capacitor voltage of the converter 3B can be suppressed, and the breakdown of the converter 3B can be prevented.

[3. Third Embodiment]
A third embodiment will be described with reference to FIG. The basic configuration of the third embodiment is the same as that of the first embodiment. Therefore, only a different point from 1st Embodiment is demonstrated, the same code | symbol is attached | subjected about the same part as 1st Embodiment, and detailed description is abbreviate | omitted.

  FIG. 8 is a diagram illustrating a configuration of a control device for a power converter according to the third embodiment. The third embodiment is an example of the first embodiment. That is, the control devices 4A and 4B according to the third embodiment are provided with a zero-phase current control unit 50, and the current control unit 50 includes a DC voltage / current control unit 43. In the third embodiment, current detectors (not shown) are respectively provided in the positive side arm 31a and the negative side arm 31b of each phase of the converters 3A and 3B, and the detected current value is a zero-phase current control unit. 50 is output.

  The zero-phase current control unit 50 controls the operations of the converters 3A and 3B so as to follow a predetermined zero-phase current command value based on the detected current of each phase. Specifically, the zero-phase current control unit 50 includes a circulating current calculation unit 51, an αβ0 conversion unit 52, and a DC voltage / current control unit 43.

  As shown in FIG. 9, the circulating current calculator 51 adds the current of the positive arm 31a and the current of the negative arm 31b detected in each phase by the calculator 51a, and the calculated value is added by the calculator 51b. Multiply by 1/2 to calculate the three-phase circulating current of R, S, and T phases.

  As shown in FIG. 10, the αβ0 converter 52 receives the R-phase, S-phase, and T-phase circulating currents calculated by the circulating current calculator 51 and performs αβ0 conversion on these circulating currents to obtain α-phase, β- The circulating current of the phase and zero phase is calculated. This zero-phase circulating current is a direct current flowing in the same phase in each of the three phases, and the capacitor voltage of each leg 31 is made uniform. The zero-phase circulating current is a direct current input to the direct current voltage / current control unit 43.

  The DC voltage / current control unit 43 is the same as that in the first embodiment. However, the DC current command value input to the calculator 431 is a zero phase current command value, and the DC voltage command value input to the calculator 434 is a zero phase voltage command value.

  Instead of the αβ0 converter 52, a dq0 converter may be used. This is because any conversion unit does not change the control of the zero-phase current.

  As described above, since the DC voltage / current control unit 43 is provided in the zero-phase current control unit 50, the following effects can be obtained. That is, the current detectors provided in the positive side phase arm 31a and the negative side phase arm 31b of each phase are normally provided in the modular multilevel converter, and obtain a direct current only with existing equipment. This eliminates the need for a separate current detector only for detecting a direct current. Therefore, the advantage which can simplify control can be enjoyed without the need for existing equipment change.

[4. Fourth Embodiment]
[4-1. Constitution]
A fourth embodiment will be described with reference to FIGS. The basic configuration of the fourth embodiment is the same as that of the first embodiment. Therefore, only a different point from 1st Embodiment is demonstrated, the same code | symbol is attached | subjected about the same part as 1st Embodiment, and detailed description is abbreviate | omitted.

  The fourth embodiment relates to correction of power interchange in a DC power transmission system. The power required at the power regulation point does not necessarily match the power at the power control point that controls the DC power. That is, since the power regulation point and the power control point are different, a power loss is generated by the DC power transmission line 5 and the converters 3A and 3B during power interchange between the two points.

  Here, the power regulation point is a point for determining the power to be traded, and is a point on the AC side of the converter 3A (for example, an AC terminal of the converter 3A) or a point on the AC side of the converter 3B (for example, the converter). 3B AC terminal). The power control point is a point that controls DC power to a DC power command value.

  This embodiment corrects the inconvenience that the difference in power between the power regulation point and the power control point is financially adjusted by the power unit price even in the case of the above mismatch. In the present embodiment, the converters 3A and 3B serving as power transmission terminals are used as voltage control terminals, and the converters 3A and 3B serving as power receiving terminals are used as current control terminals. That is, the limiter value of the control device 4A is set to L = 0 by the limiter value setting unit 433a, the converter 3A serving as the power transmission end is DC voltage controlled, and the limiter value of the control device 4B is set to L ≠ by the limiter value setting unit 433a. The converter 3B serving as the power receiving end is set to 0 and direct current control is performed. The power control point is assumed to be a DC terminal at the voltage control end.

  FIG. 11 is a diagram illustrating a configuration of power converter control devices 4A and 4B according to the fourth embodiment. In addition to the configuration of the first embodiment, the control devices 4A and 4B according to the fourth embodiment include a power regulation point setting unit 61, a DC power command value generation unit 62, a DC current command value generation unit 63, and a switch 64. have.

  The power specified point setting unit 61 sets points used for power transactions. The power regulation point setting unit 61 may set the power regulation point as a power regulation point stored in advance in the storage unit 42 or may accept and set a user input via an input unit such as a mouse, a keyboard, or a touch panel. May be.

  The DC power command value generation unit 62 receives the interchanged power command value as an input, generates a DC power command value, and outputs it. The interchangeable power command value is a power value required at the power regulation point, and is input from, for example, a host control device that controls the DC power transmission system.

  Specifically, as illustrated in FIG. 12, the DC power command value generation unit 62 includes calculators 621 and 622, a transmission line loss calculation unit 623, and a converter loss calculation unit 624. The calculator 621 inputs the interchange power command value and the output value of the transmission line loss calculator 623, adds them, and outputs the result to the calculator 622. The calculator 622 adds the output value of the calculator 621 and the output value of the converter loss calculator 624 as inputs, and outputs the obtained addition value to the DC current command value generator 62. The obtained added value is a DC power command value at the power control point. That is, the DC power command value generation unit 62 can also be said to be a correction unit that generates a DC power command value by correcting the power loss command value for power loss such as transmission line loss and converter loss.

  The power transmission line loss calculation unit 623 calculates the power loss in the DC power transmission line 5 with the interchanged power command value and the DC terminal voltage command value as inputs. The DC terminal voltage command value is a target value of the voltage at the DC terminals of the converters 3A and 3B serving as voltage control terminals. In other words, it is the DC voltage command value at the power control point. The DC terminal voltage command value is input from, for example, an upper control device that controls the DC power transmission system.

  As illustrated in FIG. 13, the transmission line loss calculation unit 623 includes a divider 623a, a transmission line resistance unit 623b, a calculator 623c, a divider 623d, a squarer 623e, a transmission line resistance unit 623f, and a calculator 623g.

  The divider 623a divides the accommodation power command value by the DC terminal voltage command value. The transmission line resistance unit 623b obtains the resistance R of the DC transmission line 5 based on the temperature T of the DC transmission line 5, multiplies the resistance and the value input from the divider 623a, and outputs the result to the computing unit 623c. As a method of obtaining the resistance R, a function R = R (T) depending on the temperature T of the DC transmission line 5 is set in advance, and the temperature T of the DC transmission line 5 is detected by a temperature detection unit (not shown), Substitute into the function to find. Alternatively, a table of the temperature T and the resistance R may be stored in the storage unit 42 in advance, and may be obtained based on the detected temperature T and the table.

  The voltage drop due to the DC power transmission line 5 is calculated by the divider 623a and the power transmission line resistance unit 623b.

  The calculator 623c inputs the output value of the power transmission line resistance unit 623b and the DC terminal voltage command value, and adds them. In other words, the calculator 623c corrects the voltage drop caused by the DC power transmission line 5 with respect to the DC terminal voltage command value. The calculator 623c outputs the obtained addition value to the divider 623dc.

  The divider 623d divides the accommodation power command value by the output value of the calculator 623c and outputs the result to the squarer 623e. The value obtained by the divider 623d is a current value flowing through the DC power transmission line 5 in the case of power interchange taking into account the voltage drop due to the DC power transmission line 5.

  The squarer 623e squares the value input from the divider 623d and outputs the squared value to the power transmission line resistance unit 623f. The transmission line resistance unit 623f has the same configuration as that of the transmission line resistance unit 623b, and multiplies the value (the square of the current) input from the squarer 623e by the resistance value of the DC transmission line 5.

The calculator 623g adds the input value from the transmission line resistance unit 623f and the transmission line no-load loss. The transmission line no-load loss is a power loss that occurs when no current flows through the DC transmission line 5. Since the loss is determined by the length, material, and the like of the DC transmission line 5, for example, the value stored in advance in the storage unit 42 and stored in accordance with the calculation of the transmission line loss is taken out. Sum value obtained by the operation unit 623g is the power loss P _TL that occurs when the power interchange via the DC transmission line 5.

  The converter loss calculation unit 624 calculates the power loss of the converters 3A and 3B using the interchangeable power command value as an input. As shown in FIG. 14, the converter loss calculation unit 624 includes a calculation unit 624a that calculates the absolute value of the accommodation power command value, and a multiplication unit 624b that multiplies the absolute value by the power loss rate of the converters 3A and 3B. Have The power loss rate by the converters 3A and 3B is stored in advance in the storage unit 42, for example, and is taken out when calculating the converter power loss.

  The DC current command value generation unit 63 calculates a DC current command value based on the DC power command value obtained by the DC power command value generation unit 62. This DC current command value is a current command value targeted by the current control end on the power receiving side, and is a value taking into account power loss.

  As shown in FIG. 15, the direct current command value generation unit 63 includes a divider 631 and a limiter 632.

  The divider 631 divides the DC power command value obtained by the DC power command value generation unit 62 and the DC terminal voltage command value. The limiter 632 outputs the obtained value if the current value obtained by the divider 631 is equal to or smaller than the predetermined value, and outputs the predetermined value if the current value exceeds the predetermined value. That is, the limiter 632 is provided with an upper limit value, and the upper limit value is set to the rated current of the converters 3A and 3B.

  As shown in FIG. 12, the switch 64 is provided between the transmission line loss calculation unit 623 and the calculator 621 in the DC power command value generation unit 62. The switch 64 switches whether or not the transmission line loss is added to the calculation of the power loss.

  In other words, the switches 64A and 4B of the control devices 4A and 4B that control the converters 3A and 3B serving as the power receiving ends are configured so that the power specified points set by the power specified point setting unit 61 are the converters 3A and 3B (currents) serving as the power receiving ends. When it is on the AC side of the control end), the power regulation point set by the power regulation point setting unit 61 takes account of the transmission line loss as ON, and the AC of the converters 3A and 3B (voltage control terminals) serving as the transmission terminals When it is the side, it is switched off so that the transmission line loss is not taken into account.

  In other words, the switch 64 is turned on when the power control point provided on the power transmission side and the set power regulation point sandwich the DC transmission line 5, and the switch 64 is turned off when not sandwiched.

  As a specific configuration, for example, the switch 64 is set to the power regulation point set on the alternating current side of the converters 3A and 3B by the power regulation point setting unit 61 and the converters 3A and 3B. From the limiter value L, it has a determination part (not shown) which determines whether the converters 3A and 3B are converters 3A and 3B on the power transmission side or the power reception side, and is turned on / off based on the determination result of the determination part To do.

[4-2. Action]
In the conventional DC power transmission system, the power at the DC terminal of the converter on the power transmission side is controlled to match the power command value. However, the power at the power regulation point at which power is traded does not necessarily match the power at the power control point that matches the power command value. For this reason, the difference power needs to be paid in monetary terms with the unit price of power, which is a burden for users such as power companies.

  Therefore, in the present embodiment, the DC power command value at the power control point, and the power at the power regulation point so as to obtain the accommodation power desired at the power regulation point, that is, the power at the power regulation point coincides with the accommodation power command value, and The direct current command value at the current control end is taken into account the power loss due to the direct current transmission line 5 and the power loss due to the converters 3A and 3B.

  The effect | action of this embodiment is demonstrated using FIG.16 and FIG.17. The tidal current is defined with the direction from the converter 3A to the converter 3B as positive.

(1) When power is traded at the AC terminal of the power receiving side converter FIG. 16 shows a DC power transmission system when power is traded at the AC terminal at the current control end of the power receiving side. As illustrated in FIG. 16, the power regulation point setting unit 61 sets the power regulation point to the AC terminal of the power receiving side converter 3 </ b> B. The power control point is the direct current terminal of the converter 3A on the power transmission side, and the power flow is positive. That is, the limiter value L of the control device 4A is set to 0 to be a voltage control end, the limiter value L of the control device 4B is set to a predetermined value other than 0 to be a current control end, and the direction from the converter 3A to the converter 3B Power interchange.

  Power interchange from the power control point to the power regulation point is performed via the DC transmission line 5 and the converter 3B. Therefore, the power loss due to the DC transmission line 5 and the power loss due to the converter 3B are taken into account. In other words, the switch 64 of the control device 4B is turned on.

Specifically, the DC power command value generation unit 62 converts the transmission line loss P _TL by the DC transmission line 5 calculated by the transmission line loss calculation unit 623 to the interchanged power command value and the conversion calculated by the converter loss calculation unit 624. The converter loss P3B of the converter _3B is added by the calculators 621 and 622, and a DC power command value to be matched at the power control point is calculated. By dividing the DC power command value by the DC current command value generation unit 63 by the DC terminal voltage command value at the power control point, the DC current command value can be obtained. This DC current command value is a current value that should flow into the converter 3B, which is the current control terminal, and is output to the DC voltage / current control unit 43 of the control device 4B. The converter 3B can make the power at the power regulation point coincide with the interchangeable power command value by controlling the current so as to be the DC current command value.

(2) When power is traded at the AC terminal of the converter on the power transmission side FIG. 17 shows a DC power transmission system when power is traded at the AC terminal at the voltage control end on the power transmission side. As illustrated in FIG. 17, the power regulation point setting unit 61 sets the power regulation point to the AC terminal of the converter 3 </ b> B on the power transmission side. The power control point is the DC terminal of the power transmission side converter 3B, and the power flow is negative. That is, the limiter value L of the control device 4B is set to 0 to be a voltage control end, the limiter value L of the control device 4A is set to a predetermined value other than 0 to be a current control end, and the direction from the converter 3B to the converter 3A Power interchange.

  Power interchange from the power regulation point to the power control point is performed via the converter 3B. Therefore, power loss due to the converter 3B is taken into account. In other words, the switch 64 is turned off.

Specifically, the DC power command value generating unit 62, a converter loss P _3B transducers 3B calculated by the converter loss calculation unit 624 to interchange power command value added by the arithmetic unit 622, matching the power control point The DC power command value to be calculated is calculated. By dividing the DC power command value by the DC current command value generation unit 63 by the DC terminal voltage command value at the power control point, the DC current command value can be obtained. This DC current command value is a current value that should flow into the converter 3A, which is the current control terminal, and is output to the DC voltage / current control unit 43 of the control device 4A. The converter 3A can make the power at the power regulation point coincide with the interchanged power command value by controlling the current so as to be the DC current command value.

[4-3. effect]
(1) The control devices 4A and 4B include a DC power command value generation unit 62 that generates a DC power command value at the power control point by correcting the power loss to the interchanged power command value at the power regulation point for performing power transactions. To have. As a result, even if the power regulation point and the power control point are different, the power loss between the two points is taken into account, so that the desired power can be obtained at the power regulation point. Therefore, since the difference between the power at the power regulation point and the power required at the regulation point can be eliminated, it is not necessary to make a monetary payment with the power unit price, and the user burden can be reduced.

(2) The DC power command value generation unit 62 includes a converter loss calculation unit 624 that multiplies the absolute value of the interchangeable power command value by the loss rate of the power converters 3A and 3B. As a result, the DC power command value can be generated taking into account the loss due to the converters 3A and 3B as the power loss.

(3) The DC power command value generation unit 62 includes a transmission line loss calculation unit that calculates the loss of the DC transmission line 5 of the DC transmission system provided with the power converters 3A and 3B. As a result, the DC power command value can be generated taking into account the loss due to the DC power transmission line 5 of the DC power transmission system as the power loss.

(4) In the DC power transmission system, the power converters 3A and 3B serving as power transmission terminals are DC voltage controlled, the power converters 3A and 3B serving as power receiving terminals are DC current controlled, and the power converter 3A serving as the power receiving terminal The DC power command value generation unit 62 turns on the transmission line loss calculation unit 623 when the power regulation point for power trading is the AC side of the power converters 3A and 3B on the power receiving side. In addition, a switch 64 that turns off the power transmission line loss calculation unit 623 when the power transmission side power converters 3A and 3B are on the AC side is provided. Thereby, the power loss can be switched by the power flow, and even if the power regulation point is fixed on the AC side of the specific converters 3A and 3B regardless of the direction of the power flow, the power at the regulation point can be changed. Can be controlled.

(5) The transmission line loss calculation unit 623 calculates the resistance of the DC transmission line 5 based on the temperature of the DC transmission line 5 and calculates the loss of the DC transmission line 5. Thereby, since the loss, that is, the voltage drop of the DC transmission line can be calculated more accurately, the difference between the power at the power regulation point and the power required at the regulation point can be eliminated.

(6) A DC current command value that generates a DC current command value by dividing the DC power command value output from the DC power command value generation unit 62 and the DC voltage command value at the DC terminals of the power converters 3A and 3B. An upper limit value of the generated direct current command value is provided in the direct current command value generation unit 63, and the upper limit value is a rated current of the power converter. Thereby, since direct current command value does not exceed the rated current of converters 3A and 3B, damage to converters 3A and 3B due to overcurrent can be prevented.

(7) In the control device 4A of the converter 3A serving as the power transmission end, the limiter value setting unit 433a sets the limiter value on the power transmission end side to 0 and performs DC voltage control on the converter 3A serving as the power transmission end. That is, the power transmission side is the voltage control end, and the power reception side is the current control end. This facilitates the design of the DC circuit of the DC power transmission system. That is, various facilities and equipment such as a steel tower are arranged on the DC transmission line 5, but it is necessary to design the DC transmission line 5 so as to satisfy the rating of DC transmission.

  In this regard, when the power receiving side is the voltage control terminal, it is necessary to output a voltage larger than that of the power receiving terminal at the current control terminal in consideration of the voltage drop caused by the DC power transmission line 5. For this reason, it is necessary to consider various facilities and equipment such as a steel tower provided on the DC transmission line 5 on the way of power interchange so as to satisfy the rated voltage of DC transmission in consideration of the voltage drop.

  On the other hand, by setting the power transmission side as the voltage control end, the power receiving side only has a voltage drop. Therefore, it is only necessary to design based on the DC voltage command value on the power transmission side, and there is an advantage that it is not necessary to consider the voltage drop. .

[5. Other Embodiments]
In the present specification, a plurality of embodiments according to the present invention have been described. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the invention described in the claims and equivalents thereof as well as included in the scope and gist of the invention.

(1) Although the control devices 4A and 4B of the power converter of this embodiment are applied to the two-terminal DC power transmission system, they may be applied to a multi-terminal DC power transmission system.

(2) As shown in the first to fourth embodiments, the control devices 4A and 4B may be individually provided in the converters 3A and 3B, or may be a higher-level control device that controls the DC power transmission system. It may be provided.

(3) The control devices 4A and 4B can be realized by controlling a computer including a CPU with a predetermined program. The program in this case realizes the processing of each unit as described above by physically utilizing computer hardware. How to set the range to be processed by hardware and the range to be processed by software including a program is not limited to a specific mode.

(4) In the first to fourth embodiments, the unit converter of the converters 3A and 3B is the chopper cell C, but may be a full bridge cell. By making the unit converter a full bridge cell, it is possible to cut off an accident current such as a DC ground fault. The converters 3A and 3B may be a three-winding transformer MMC. Thereby, a total of six buffer reactors for each phase can be eliminated between the positive arm 31a and the negative arm 31b.

(5) Instead of the DC voltage / current control unit 43 of the first to fourth embodiments, the following configuration may be used. That is, as shown in FIG. 18, the DC voltage / current control unit 43 adds the DC voltage command value to the output of the follower unit, and then limits the output value by the upper limit value and the lower limit value based on the DC voltage command value. You may make it do.

  Specifically, the DC voltage / current control unit 43 includes a tracking unit, a calculator 435 that adds the output value of the tracking unit and the DC voltage command value, an upper limit value based on the DC voltage command value and the limiter value, and A limiter 436 that has a lower limit value and receives an input from the arithmetic unit 435 and limits the output value based on the upper limit value and the lower limit value, and a limiter value setting unit 436a that sets the limiter value to 0 or a predetermined value other than 0 And the output value of the limiter 436 may be used as the converter output voltage.

The limiter value setting unit 436a determines the upper limit value and the lower limit value of the limiter 436 based on the sum of the DC voltage command value V _{dc_ref} and the limiter value L. That is, when the limiter value L = 0, the upper limit value and the lower limit value are V _{dc_ref} , and the output (converter output voltage) of the limiter 436 is V _{dc_ref.} Operate with control. On the other hand, when the limiter value L ≠ 0, the upper limit value is V _{dc_ref} + L and the lower limit value is V _{dc_ref} −L. _Therefore , the output (converter output voltage) of the limiter 436 is (V _{dc_ref} −L) to (V _{dc_ref} + L), and the DC voltage / current control unit 43 is operated by DC current control.

  In addition, as shown in FIG. 19, instead of the limiter 436, it has an upper limit value and a lower limit value based on the DC voltage command value and the limiter value, and receives an input from the follower and based on the upper limit value and lower limit value. A limiter 437 for limiting the output value may be used. In any case, the same operational effects as those of the first to fourth embodiments can be obtained, and it is possible to determine whether the direct current voltage control or the direct current control is performed based on the limiter value.

(6) In the fourth embodiment, the DC power command value generation unit 62 may be configured to switch between a calculation formula that considers transmission line loss and converter loss, and a calculation formula that considers only converter loss. Specifically, as shown in FIG. 20, the DC power command value generation unit 62 calculates a power loss by taking into account the transmission line loss and converter loss of the DC power transmission system. 625, a converter loss calculation unit 626 that calculates the converter loss, and a switch 64 that switches to either the transmission line / converter loss calculation unit 625 or the converter loss calculation unit 626 based on the flow direction of the DC power transmission system. You may make it have.

  The function forms of the calculation formulas of the transmission line / converter loss calculation unit 625 and the converter loss calculation unit 626 can be changed as appropriate. Coefficients a to f shown in FIG. 20 are values in consideration of power transmission line and converter losses. The converter loss calculation unit 626 may be the same as the converter loss calculation unit 624 of the fourth embodiment.

  Here, the switch 64 'includes a pair of switches 64a and 64b, and the on / off of these switches 64a and 64b is in an inverted relationship. For example, when the tidal direction is positive, the switch 64a is turned on and the switch 64b is turned off. When the tidal direction is negative, the switch 64a is turned off and the switch 64b is turned on. For example, the power flow direction from the converter 3A to the converter 3B is positive. The DC power command value generation unit 62 may receive an input of the tidal direction from the outside, and may include a determination unit that determines the tidal direction. A known method can be adopted as the configuration of the determination unit.

1A, 1B AC system 3A, 3B Power converter
31 Leg 31a Positive side arm 31b Negative side arm 4A, 4B Control device 41 DC detection unit 42 Storage unit 43 DC voltage / current control unit 431 Calculator 432 Gain 433 Limiter 433a Limiter value setting unit 434 Calculator 435 Calculators 436, 437 Limiter 436a Limiter value setting unit 44 Signal generation unit 45 AC accident detection unit 46 Limiter value change unit 5 DC transmission line 50 Zero-phase current control unit 51 Circulating current calculation units 51a and 51b Calculator 52 αβ0 conversion unit 61 Power reference point setting unit 62 DC power command value generation units 621 and 622 calculator 623 transmission line loss calculation unit 623a divider 623b transmission line resistance unit 623c calculator 623d divider 623e squarer 623f transmission line resistance unit 623g calculator 624 converter loss calculation unit 624a Operation unit 624b Multiplying unit 625 Transmission line / converter loss Calculation unit 626 converter loss calculation unit 63 DC current command value generation section 631 divider 632 limiters 64, 64 'switch C Choppaseru C1a, C1b switching element C2a, C2b diodes C3 capacitor

Claims (18)

A unit converter having a switching element and a capacitor is connected in multiple stages, and is a control device for a power converter that converts power between AC and DC,
A DC voltage / current control unit for calculating a converter output voltage for operating the power converter with DC voltage control or DC current control;
A signal generator for generating a signal for turning on and off the switching element so as to output the converter output voltage to the power converter;
With
The DC voltage / current control unit is:
A follow-up unit that calculates a voltage value for causing the direct current to follow the direct current command value based on the deviation between the direct current and the direct current command value;
A limiter that has an upper limit value and a lower limit value based on a limiter value, receives an input from the follower, and limits an output value based on the upper limit value and the lower limit value;
An arithmetic unit for calculating the converter output voltage by adding the output value of the limiter and a DC voltage command value;
A limiter value setting unit for setting the limiter value to 0 or a non-zero value;
Having
A control device for a power converter characterized by the above. A unit converter having a switching element and a capacitor is connected in multiple stages, and is a control device for a power converter that converts power between AC and DC,
A DC voltage / current control unit for calculating a converter output voltage for operating the power converter with DC voltage control or DC current control;
A signal generator for generating a signal for turning on and off the switching element so as to output the converter output voltage to the power converter;
With
The DC voltage / current control unit is:
A follow-up unit that calculates a voltage value for causing the direct current to follow the direct current command value based on the deviation between the direct current and the direct current command value;
An arithmetic unit for adding the output value of the follower and the DC voltage command value;
A limiter that has an upper limit value and a lower limit value based on a DC voltage command value and a limiter value, and that receives an input from the computing unit and limits an output value based on the upper limit value and the lower limit value;
A limiter value setting unit for setting the limiter value to 0 or a predetermined value other than 0;
Have
The output value of the limiter is the converter output voltage;
A control device for a power converter characterized by the above. A unit converter having a switching element and a capacitor is connected in multiple stages, and is a control device for a power converter that converts power between AC and DC,
A DC voltage / current control unit for calculating a converter output voltage for operating the power converter with DC voltage control or DC current control;
A signal generator for generating a signal for turning on and off the switching element so as to output the converter output voltage to the power converter;
With
The DC voltage / current control unit is:
A follow-up unit that calculates a voltage value for causing the direct current to follow the direct current command value based on the deviation between the direct current and the direct current command value;
A limiter that has an upper limit value and a lower limit value based on a DC voltage command value and a limiter value, and that receives an input from the follower and limits an output value based on the upper limit value and the lower limit value;
A limiter value setting unit for setting the limiter value to 0 or a predetermined value other than 0;
Have
The output value of the limiter is the converter output voltage;
A control device for a power converter characterized by the above. The control device for direct current control of the power converter on the power receiving end side in a direct current power transmission system,
A limiter value changing unit for changing the limiter value;
The limiter value changing unit
By detecting an AC accident on the AC side of the power converter, changing the limiter value to a value greater than the limiter value before the AC accident,
The control apparatus for a power converter according to any one of claims 1 to 3. The limiter value changing unit
A notification of an AC accident on the AC side of the power transmission end is received from the control device of the power converter serving as a power transmission end in the DC power transmission system by a wired or wireless communication unit, and the limiter value is received by the AC accident. Change to a value greater than the previous limiter value,
The power converter control device according to claim 4. The control device for direct current control of the power converter on the power transmission end side in a direct current power transmission system,
A limiter value changing unit for changing the limiter value;
The limiter value changing unit
By detecting an AC accident on the AC side of the power converter, changing the limiter value to a value greater than the limiter value before the AC accident,
The control apparatus for a power converter according to any one of claims 1 to 3. The limiter value changing unit
From the control device of the power converter serving as a power receiving end in the DC power transmission system, a notification of an AC accident on the AC side of the power receiving end is received by a wired or wireless communication means, and the limiter value is received by the AC accident. Change to a value greater than the previous limiter value,
The power converter control device according to claim 6. The control device for controlling the power converter on the power transmission end side in a DC power transmission system,
The power converter on the power transmission end side of the DC power transmission system is DC voltage controlled, and the power converter on the power receiving end side is DC current controlled,
A limiter value changing unit for changing the limiter value;
The limiter value changing unit
By detecting an AC fault on the AC side of the power converter on the power transmission end side, changing the limiter value on the power transmission end side to a value larger than the limiter value on the power receiving end side;
The control apparatus for a power converter according to any one of claims 1 to 3. The control device for controlling the power converter on the power receiving end side in a DC power transmission system,
The power converter on the power receiving end side of the DC power transmission system is DC voltage controlled, and the power converter on the power transmission end side is DC current controlled,
A limiter value changing unit for changing the limiter value;
The limiter value changing unit
By detecting an AC fault on the AC side of the power converter on the power receiving end side, changing the limiter value on the power receiving end side to a value larger than the limiter value on the power transmitting end side,
The control apparatus for a power converter according to any one of claims 1 to 3. The DC voltage / current control unit is provided in a zero-phase current control unit for calculating the DC current;
The control device for a power converter according to claim 1, wherein: Having a DC power command value generation unit for generating a DC power command value at the power control point by correcting the power loss to the interchangeable power command value at the power regulation point for conducting power transactions;
The control device for a power converter according to any one of claims 1 to 10. The DC power command value generation unit is
Having a converter loss calculator for multiplying the absolute value of the interchangeable power command value by the loss rate of the power converter;
The control apparatus for a power converter according to claim 11. The DC power command value generation unit is
Having a transmission line loss calculation unit for calculating the loss of the transmission line of the DC power transmission system provided with the power converter;
The power converter control device according to claim 11 or 12. In the DC power transmission system, a power converter serving as a power transmission end is DC voltage controlled, and a power converter serving as a power receiving end is DC current controlled,
A power converter control device serving as the power receiving end,
The DC power command value generation unit is
When the power regulation point for performing power trading is on the AC side of the power converter serving as the power receiving end, the power line loss calculation unit is turned on, and when the power regulation point is on the AC side of the power converter serving as the power transmitting end, Having a switch to turn off the transmission line loss calculator,
The power converter control device according to claim 13. The transmission line loss calculation unit obtains the resistance of the transmission line based on the temperature of the transmission line, and calculates the loss of the transmission line,
15. The control device for a power converter according to claim 13 or 14. The DC power command value generation unit is
A transmission line / converter loss calculation unit that calculates power loss in consideration of transmission line loss and converter loss of the DC transmission system;
A converter loss calculator for calculating the converter loss of the DC power transmission system;
Based on the flow direction of the DC power transmission system, a switch to switch to either the transmission line / converter loss calculation unit or the converter loss calculation unit,
Having
The control apparatus for a power converter according to claim 11. A DC current command value generating unit that divides a DC power command value output from the DC power command value generating unit and a DC voltage command value at a DC terminal of the power converter to generate a DC current command value,
The DC current command value generation unit is provided with an upper limit value of the generated DC current command value, and the upper limit value is a rated current of the power converter,
The power converter control device according to any one of claims 11 to 16. A control device for a power converter comprising a sending end of the dc power transmission system,
The limiter value setting unit performs direct current voltage control on a power converter serving as the power transmission end by setting the limiter value on the power transmission end side to 0;
The control apparatus for a power converter according to claim 1, wherein:

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