JP2017093012A - CONTROL DEVICE AND CONTROL METHOD FOR POWER CONVERSION DEVICE, AND POWER CONVERSION SYSTEM - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a controller of an electric power conversion device and a control method, which can prevent DC magnetization attributed to a residual magnetic flux of an iron core of a transformer even if an iron core of an ACCT is magnetically saturated; and a power conversion system.SOLUTION: A controller 109 of an electric power conversion device which is connected to a power system through a transformer comprises: a first bias magnetization-suppressing controller 111 operable to produce, based on a magnetic excitation current of a transformer 102 detected by an alternating current CT 106, a first correction direction ifor suppressing DC magnetization of the transformer; a second bias magnetization-suppressing controller 112 operable to produce, based on a residual magnetic flux of the transformer estimated based on a system voltage of the power system, a second correction direction ifor reducing the residual magnetic flux of the transformer; a switching device 113 operable to produce a correction direction based on the first and second correction directions; and an operational unit 115 operable to produce a control signal of the electric power conversion device based on a direction value and the correction direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device and a control method for a power conversion device linked to a power system via a transformer, and a power conversion system in which these are used.

  In general, a power converter connected to an AC system is provided with a transformer between the AC system from the viewpoint of stepping up and down the AC voltage and ensuring electrical insulation. A power converter connected to such a transformer controls a DC voltage / DC current not to be output to the iron core of the transformer, so that a DC component is superimposed on the magnetic flux density of the iron core (hereinafter referred to as “DC”). Magnetic saturation due to “polarization” (referred to as DC magnetization) is prevented.

  However, if there is an offset error in the detected value of VT (Voltage transformer) or CT (Current transformer) or in the control means for feedback control of the power conversion device, DC bias is generated. Excessive DC bias can cause magnetic saturation of the transformer core.

  When the transformer iron core is magnetically saturated due to DC bias, the leakage magnetic flux that does not pass through the transformer iron core increases, which increases stray load loss such as the side plates of the transformer tank and the fastening bolts. The stray load loss overheats the tank side plates and tightening bolts, which may weaken the mechanical strength of the transformer.

Further, when the transformer iron core is magnetically saturated due to DC bias, the exciting inductance of the transformer decreases, and the exciting current increases. Since a part of the excitation current also flows through the power conversion device, the allowable current value of the power conversion device may be exceeded and the device may be overcurrent stopped.
Furthermore, when the transformer core is saturated, the noise generated by the transformer also increases.

  As described above, since various problems occur when magnetic saturation occurs in the transformer core, it is necessary to suppress DC bias and magnetic saturation of the transformer core by some means.

  As an example of means for preventing magnetic saturation from occurring, there is a means of using a transformer with an increased resistance to magnetic bias assuming the existence of offset errors such as VT and CT in advance. However, in order to increase the magnetic resistance, it is necessary to increase the core cross-sectional area of the transformer.

  On the other hand, as a technology for detecting DC demagnetization and suppressing it without using a transformer with increased demagnetization tolerance, the transformer primary side (AC system side) and transformer AC side CT (hereinafter referred to as “ACCT”) is installed on each secondary side (power converter side) of the power source, and the DC magnetism state of the transformer core is detected based on signals from these ACCTs. A technique for controlling a conversion device is known (see, for example, Patent Document 1). In this prior art, two currents, the excitation current flowing on the primary side of the transformer and the secondary side of the transformer, and the load current are detected by the ACCT, and the excitation current of the transformer is determined from the difference current between the two detection currents. Is detected, and the DC converter is estimated from the AC component of the excitation current, so that the power converter is controlled to suppress the DC bias.

JP 2014-150598 A

  When the system voltage drops significantly due to a system fault caused by a lightning strike to an overhead power transmission line, or the current flowing through the line changes significantly due to zero, residual magnetic flux may remain in the transformer core depending on the phase of the accident. When an accident recovers from a state in which residual magnetic flux remains in the transformer core and the system voltage is restored, the transformer core is magnetically saturated and an excessive inrush current flows. In this case, a direct current component is superimposed on the magnetic flux density of the transformer core due to the residual magnetic flux. That is, a DC bias is generated in the transformer. On the other hand, the residual magnetic flux of the transformer core is removed by the above-described conventional technology.

  However, in the ACCT, when the current flowing through the line changes suddenly due to an accident, a residual magnetic flux also remains in the iron core of the ACCT depending on the accident occurrence phase. For this reason, when the accident is recovered from the state in which the residual magnetic flux remains, the iron core of the ACCT may be magnetically saturated. When the iron core of the ACCT is magnetically saturated, the current flowing through the line cannot be detected with high accuracy, and as a result, it becomes difficult to suppress the direct current bias by controlling the power converter.

  Therefore, the present invention provides a control device and a control method for a power conversion device, and a power conversion system capable of preventing direct current bias due to residual magnetic flux in the iron core of the transformer even when the iron core of the ACCT causes magnetic saturation. I will provide a.

  In order to solve the above problems, a control device for a power conversion device according to the present invention is a control device for a power conversion device connected to a power system via a transformer, and is an excitation of a transformer detected by AC CT. Based on the first magnetic bias suppression control device that creates the first correction command for suppressing the DC bias of the transformer based on the current, and the residual magnetic flux of the transformer estimated based on the system voltage of the power system A second demagnetization suppression control device that creates a second correction command for reducing the residual magnetic flux of the transformer, and a switch that creates a correction command based on the first correction command and the second correction command And a calculation unit that creates a control signal for the power converter based on the command value and the correction command.

  In order to solve the above problems, a method for controlling a power converter according to the present invention is a method for controlling a power converter connected to a power system via a transformer, and includes an excitation current detected by an AC CT. A first correction command that suppresses the DC bias of the transformer is estimated, the transformer residual magnetic flux is estimated based on the system voltage of the power system, and the estimated residual magnetic flux is reduced. A correction command is created, a correction command is created based on the first correction command and the second correction command, and the power converter is controlled based on the command value and the correction command.

  The power conversion system according to the present invention includes a transformer, a power conversion device connected to the power system via the transformer, and a control device that creates a control signal to be given to the power conversion device. VT (Voltage Transformer) for detecting the system voltage of the power system, and AC CT (Current Transformer) for detecting the excitation current of the transformer, and the control device is a control device for the power conversion device according to the present invention. is there.

  The power conversion system according to the present invention includes a power converter having two transformers and two power conversion main circuits in which the AC side is connected to two power systems via the two transformers and the DC sides are connected to each other. And two control devices for generating control signals to be supplied to the two power conversion main circuits, two VTs for detecting system voltages of the two power systems, and excitation currents of the two transformers Each of the two control devices is a control device for the power conversion device according to the present invention.

  According to the present invention, by appropriately switching the first and second correction commands and controlling the power conversion device, even if the AC CT iron core is magnetically saturated, the DC iron magnetism of the transformer iron core is prevented. can do.

  Problems, configurations, and effects other than those described above will become apparent from the following description of embodiments.

1 shows a power conversion system that is Embodiment 1 of the present invention. Fig. 2 shows changes over time in system voltage, magnetic flux in the iron core of the transformer, and excitation current of the transformer when a system fault occurs. Operation | movement of the present Example 1 at the time of a system fault is shown. The control apparatus of the power converter device in the power converter system which is Example 2 of this invention is shown. Operation | movement of the present Example 2 at the time of a system | strain accident is shown. The control apparatus of the power converter device in the power converter system which is Example 3 of this invention is shown. Operation | movement of the present Example 3 at the time of a system | strain accident is shown. The control apparatus of the power converter device in the power converter system which is Example 4 of this invention is shown. Operation | movement of the present Example 4 at the time of a system | strain accident is shown. 10 shows a power conversion system that is Embodiment 5 of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings. In each figure, the same reference numerals indicate the same constituent elements or constituent elements having similar functions.

  FIG. 1 shows a power conversion system that is Embodiment 1 of the present invention.

  As shown in FIG. 1, a self-excited power conversion device 103 (hereinafter referred to as “power conversion device”) having an IGBT (Insulated Gate Bipolar Transistor) which is a self-extinguishing element includes an alternating current via a transformer 102. It is connected to the system 101 (power system). AC system 101 may be either a single-phase system or a three-phase system. The configuration of the power conversion system as in the first embodiment is applied to, for example, a self-excited reactive power compensator (STATCOM: Static synchronous Compensator).

Power converter 103 includes a power conversion main circuit having an IGBT (Insulated Gate Bipolar Transistor) as the semiconductor switching elements, a DC capacitor connected to the power conversion main circuit, the DC VT for detecting the DC voltage V _C of the DC capacitor Prepare. As the semiconductor switching element, in addition to IGBT, IGCT (Integrated Gate Commutated Thyristor), GTO (Gate Turn Off Thyristor), and the like can be applied.

CT104 and VT105, respectively (current flowing through the power conversion main circuit of the power conversion device 103) power converter detection current _{i conv} and detects a system voltage _{V S.} i _conv and V _S are input to the control device 109 described later, and the power conversion device 103 is feedback-controlled based on the input i _conv and V _S. In the first embodiment, the CT 104 is provided on the power conversion device 103 side (hereinafter referred to as “secondary side”) of the transformer 102, but the AC system 101 side (hereinafter referred to as “primary side”) of the transformer 102. May be provided).

In order to detect the DC bias, an ACCT 106 that is an AC current sensor is provided on the primary side of the transformer 102 and the secondary side of the transformer 102 using a known technique (see, for example, Patent Document 1). A differential current between the primary side ACCT 106 and the secondary side ACCT 106 is passed through the resistor 107, and the differential voltage V _excac generated at both ends of the resistor 107 is detected by the voltage detection means 108. _Vexac is input to the control device 109 and is used for DC bias detection. Note that the inverse ratio of the current ratio of the primary side ACCT and the secondary side ACCT is transformed so that the differential current flowing through the resistor 107 is a conversion ratio conversion multiple of the excitation current of the transformer 102 excluding the DC component. The turn ratio of the primary winding and the secondary winding of the unit 102 is made approximately equal.

The control device 109 outputs an output voltage command V _ref that is a control signal for controlling the output voltage of the power conversion device 103. The PWM circuit 110 outputs a gate pulse g _conv for ON / OFF control of the IGBT in the power conversion main circuit of the power conversion device 103 in accordance with the output voltage command V _ref given from the control device 109. Note that the PWM circuit 110 generates g _conv by a known pulse width modulation (abbreviated as PWM) using the output voltage command V _ref as a modulation wave.

  Next, the configuration of the control device 109 according to the first embodiment will be described.

Polarized磁抑system controller 111 using ACCT106 as input the voltage _{V Exac} occurring resistor 107 by the difference currents of the two _ACCT106, a polarization磁量detector for detecting a DC magnetic deviation of the transformer 102 based on _{V Exac} as input a DC polarization磁量V _mag outputted from the polarization磁量detection unit outputs a magnetic bias correction current command i _{DMP 1} for suppressing the DC polarization磁量V _mag desired value polarized磁抑system controller Is provided.

Using VT105 polarized磁抑system controller 112 receives as input a flux estimator for estimating a residual magnetic flux [Phi _e of the transformer 102 based on the system voltage V _S, the residual magnetic flux [Phi _e outputted from the magnetic flux estimator, the residue It comprises a flux damping control unit for outputting a magnetic flux correction current command i _{DMP 2} to suppress the magnetic flux [Phi _e to a desired value. The signal indicating the system voltage V _S output from the VT105 is also used as an input signal of the system voltage feedforward control in the voltage command value calculator 115. Therefore, in the first embodiment, the VT 105 is used for both the system voltage feedforward control and the residual magnetic flux estimation, thereby suppressing an increase in the number of parts.

Switch 113 receives the magnetic bias correction current command _{i DMP 1} and the magnetic flux correction current command _{i DMP 2,} in accordance with the switching signal _{S w,} either the _{i DMP 1} and _{i DMP 2,} and outputs as the corrected current command _{i COMP} . The correction current command i _COMP is added to the power converter current command value i _ref by the adder 114.

In the first embodiment, the correction current command _{i COMP} are summed in the power converter current command value _{i ref,} but to correct the _{i ref,} DC by polarized磁抑system controller 111 or polarized磁抑system controller 112 magnetic bias Other current values or voltage values may be corrected as long as a suppression effect can be obtained. For example, a current value obtained by adding i _COMP to the power converter detection current i _conv may be input to the voltage command value calculation unit 115. Alternatively, i _COMP may be converted into a corrected voltage command and added to the voltage command V _ref output by the voltage command value calculation unit 115.

The voltage command value calculation unit 115 inputs the DC voltage V _C of the DC capacitor, the system voltage V _S , the power converter detection current i _conv , and the power converter current command value i _ref ′ added with the correction current command i _COMP. Then, based on these V _C , V _S, i _conv, and i _ref ′, an output voltage command V _ref for setting the voltage output from the power converter 103 is created and output.

  In FIG. 1, the configuration of the control device 109 is shown in a functional block diagram. In the first embodiment, an arithmetic processing unit such as a microcomputer operates as each functional unit by executing a predetermined program. Not limited to this, the control device 109 may be configured by other circuits.

  Here, the superposition of the residual magnetic flux of the transformer caused by the system voltage drop at the time of a system failure will be described.

FIG. 2 shows temporal changes of the system voltage V _S of the AC system 101, the magnetic flux Φ in the iron core of the transformer 102, and the exciting current i _ex of the transformer at the time of a system fault. At time t1, for example, by a lightning strike to the overhead lines, and significantly reduced the system voltage Vs, the accident is removed at time t2 that several cycles to several tens of cycles elapse of the AC, the system voltage V _S is the rated voltage Return to value.

At time t1, when the system voltage Vs is remarkably lowered, the residual magnetic flux [Phi _e the flux [Phi in transformer cores 102 remains in the accident phase. Residual magnetic flux [Phi _e, the resistance of the transformer winding and the circuit, although attenuated temporally by loss or the like of the transformer, depending on the capacity and the circuit condition of the transformer, takes more than a few seconds until the residual magnetic flux Φe is attenuated . In such a case, that is, when the accident is removed at the time t2 and the system voltage V _S returns to the rated voltage, and the residual magnetic flux Φe is superimposed on the magnetic flux Φ, the magnetic flux Φ becomes the residual magnetic flux Φe. A sinusoidal waveform is shown as the center.

  Magnetic saturation occurs when the magnetic flux density of the transformer core approaches or exceeds the saturation magnetic flux density determined by the material and shape of the iron core. Since the magnetic flux density is the surface density per unit area of the magnetic flux, the superposition of the residual magnetic flux Φe on the magnetic flux Φ indicates that the direct current component is superposed on the magnetic flux density. Accordingly, the occurrence of the residual magnetic flux Φe in the transformer core indicates that the DC bias is generated.

The DC bias causes magnetic saturation of the iron core of the transformer 102 and greatly distorts the exciting current i _ex of the transformer 102. When magnetic saturation occurs, the excitation current i _ex becomes several times the rated current depending on the circuit conditions. Therefore, the DC bias is suppressed within the tolerance of the transformer by the DC bias suppression function of the control device 109. Is done.

In the first embodiment, the direct-current demagnetization suppression function is provided by the demagnetization suppression control devices 111 and 112. Here, under a situation where the current flowing through the line changes suddenly due to a system fault, a residual magnetic flux may remain in the iron core of the ACCT 106 used by the demagnetization suppression control device 111 depending on the phase at which the accident occurred. When the accident is recovered from the state in which the residual magnetic flux remains, the iron core of the ACCT 106 may be magnetically saturated. When magnetic saturation occurs, the ACCT 106 cannot accurately detect the current flowing through the line, so that the detection accuracy of the excitation current by the voltage _Vexac is lowered. For this reason, the direct-current demagnetization suppression control by the power converter 103 is not necessarily sufficient only by the direct-current demagnetization suppression control by the demagnetization suppression control device 111.

  Therefore, as will be described below, in the first embodiment, the demagnetization suppression control is also performed by the demagnetization suppression control device 112 using the VT 105 in addition to the demagnetization suppression control device 111 using the ACCT 106.

FIG. 3 shows the operation of the first embodiment at the time of a system fault. In FIG. 3, a switching signal S _W for switching the output of the switch 113, an AC voltage V _S of the AC system 101, a power converter detection current i _conv , a correction current command i _COMP output from the switch 113, The magnetic flux Φ in the iron core of the transformer 102 and the exciting current i _ex of the transformer are shown. At the time t1, the system voltage V _S is significantly reduced, and a large accident current flows as the power converter detection current i _conv , and at the time t2, the system voltage Vs returns to the rated voltage value.

As shown in FIG. 3, reference until t1 is the accident occurrence time, t2 after the period is an accident removal time, that is, in the system voltage V _S is normal period, the polarization磁抑system controller 111 using ACCT106 Te, i.e. the output _{i DMP 1} polarized磁抑system controller 111, as corrected current command _{i COMP} to switch 113 outputs, to suppress the direct current magnetic deflection of the transformer 102.

During an accident the period (from time t1 to time t2), the switching signal _{S w} for switching the output of the switch 113 by switching from 0 to 1, the output _{i DMP 1} polarized磁抑system controller 111 using ACCT106 The correction current command i _COMP is changed to the output i _{DMP2 of} the bias magnetism suppression control device 112 using the VT 105.

Flux estimator polarized磁抑system controller 112, a magnetic flux [Phi transformer 102 estimated by integrating the system voltage V _S of the AC system 101 to determine the residual magnetic flux Φe the direct current component included in the magnetic flux [Phi. Then, during the accident period, polarized磁抑system controller 112, by outputting the flux correction current command i _{DMP 2,} such as to reduce the residual magnetic flux .PHI.e, reducing the residual magnetic flux .PHI.e the transformer core.

  According to the first embodiment, by switching the output signal of the switch 113, the DC bias of the iron core of the transformer 102 due to the residual magnetic flux Φe can be suppressed even when the iron core of the ACCT is magnetically saturated. Further, according to the first embodiment, since the residual magnetic flux considered when setting the size of the transformer core can be reduced, it is possible to reduce the size of the transformer by reducing the core cross-sectional area.

Note that the magnetic saturation of the iron core of the ACCT 106 occurs not only when the power converter detection current i _conv becomes excessive when an accident occurs as shown in FIG. 3, but also when the current waveform changes suddenly. Therefore, even in such a case, the first embodiment has the same effect.

In the first embodiment, when the switching signal _S W = 0 for switching the output of the switch 113 outputs the magnetic bias correction current command _{i DMP 1} as the correction current command _{i COMP,} switching signal _S W = 1 when the flux correction current command _{i DMP 2,} but outputs a corrected current command _{i COMP,} not limited thereto, the switching signal _{S W} can be arbitrarily set.

  FIG. 4 shows a control device for a power conversion device in a power conversion system that is Embodiment 2 of the present invention. Hereinafter, differences from the first embodiment will be mainly described.

Controller 401 in the second embodiment, in addition to the configuration of Embodiment 1, further comprising a fault detection means 402 for creating a switching signal S _w.

The accident detection means 402 receives the system voltage V _S , the power converter detection current i _conv , the low voltage threshold ± V _th , and the current threshold ± i _th , and switches based on these voltage and current values. It outputs a switching signal _{S W} vessels 113.

The accident detection means 402 determines that a system fault has occurred when a voltage larger than the absolute value of the low voltage threshold value ± V _th is not output for a certain period, and switches the output value of the switching signal Sw. Alternatively, the accident detection unit 402 determines that a system fault has occurred when a current larger than the absolute value of the current threshold value ± i _th flows, and switches the output value of the switching signal Sw.

  FIG. 5 shows the operation of the second embodiment when a system fault occurs.

Similar to FIG. 3, the system voltage V _S significantly decreases at the time t1, and then an accident current larger than the rated value flows as the power converter detection current i _conv . When the magnitude of the fault current exceeds the absolute value of the current threshold ± i _th (time t1 '), fault detection means 402 determines that a system fault has occurred, the value of the switching signal S _W, It operates to change from 0 to 1 when the system voltage V _S is normal.

Also in the second embodiment, the switch 113, when the switching signal _S W = 0 outputs the magnetic bias correction current command _{i DMP 1} as the correction current command _{i COMP,} when the switching signal _S W = 1 is The magnetic flux correction current command i _DMP2 is output as the correction current command i _COMP .

As shown in FIG. 5, although the magnitude of the _fault current is smaller than the absolute value of the current threshold value ± i _th within one cycle, the grid voltage V _S is still smaller than the absolute value of ± V _th. detecting means 402 determines that a system fault is continued for a period of up to detect a large system voltage than the absolute value of ± V _th fixes the value of the switching signal S _W 1. If the accident detection unit 402 determines that the system voltage V _S has returned to the normal state, the accident detection unit 402 changes the switching signal _SW from 1 to 0.

According to the second embodiment, since the correction current command is switched based on the accident current flowing through the power converter, even if the magnetic saturation of the ACCT iron core caused by the change in the current flowing through the line at the time of the accident occurs, the residual magnetic flux DC magnetic deviation of the transformer according to [Phi _e can be suppressed.

  FIG. 6 shows a control device for a power conversion device in a power conversion system that is Embodiment 3 of the present invention. Hereinafter, differences from the first and second embodiments will be mainly described.

In the third embodiment, switch 602, three output modes, namely an output mode for outputting the magnetic bias correction current command i _{DMP 1,} the output mode to output a magnetic flux correction current command i _{DMP 2,} and a zero value as the correction current command It has an output mode to output. Switch 602 (in this embodiment, -1,1,0) value of the switching signal _{S W} in accordance with, and outputs the corrected current command _{i COMP} in either output mode.

The accident detection means 603 receives the system voltage V _S , the power converter detection current i _conv , the low voltage threshold value ± V _th , and the current threshold value ± i _th , and based on these voltage value and current value , and it outputs a switching signal _{S W} of the switch 602.

Fault detection means 603, a large system voltage than the absolute value of the low voltage threshold ± V _th is, if not detected in a certain period of time, determines that a system fault has occurred, switching the output value of the switching signal S _W . Ayii is fault detection unit 603, when a current larger than the absolute value of the current threshold ± i _th stream, determines that a system fault has occurred, switching the value of the switching signal S _W.

In Embodiment 3, when the switching signal Sw = -1 outputs a magnetic bias correction current command _{i DMP 1} as the correction current command _{i COMP,} when the switching signal _S W = 0 is the zero value as the correction current command When output (i _COMP = 0) and the switching signal S _W = 1, the magnetic flux correction current command i _DMP2 is output as the correction current command i _COMP .

  FIG. 7 shows the operation of the third embodiment at the time of a system fault.

Similar to FIGS. 3 and 5, at time t _{<b> 1} , the system voltage V _S is significantly reduced, and an accident current larger than the rated value of the power converter detection current i _conv flows through the power converter. When the magnitude of the fault current exceeds the absolute value of the current threshold value ± ith (time t1 ′), the fault detection means 603 determines that a system fault has occurred, and at time t1 ′, the switching signal S _W Is changed from −1 to 1 before the occurrence of an accident, that is, when the system voltage is normal.

Further, the accident detection means 603 sets the correction current command to a zero value (i _COMP) during a predetermined period from time t2 to time t2 ′ after the system fault is removed at time t2 and the system voltage returns to the normal state. = 0), a zero output period (switching signal Sw = 0) is provided. The zero output period is a period in which the residual magnetic flux Φe of the ACCT 106 is attenuated in time, and the time t2 ′ is set according to the capacity of the ACCT 106, the magnetic characteristics of the iron core of the ACCT 106, and the like. The accident detection means 106 changes the switching signal _SW from 0 to −1 at time t2 ′.

According to the third embodiment, since the residual magnetic flux Φe attenuation of the core of the ACCT caused by fault current, switch the _{S W} -1, the output _{i DMP 1} polarized磁抑system controller 111 as the corrected current command _{i COMP} Output. Thereby, when the system voltage is normal, the direct-current bias can be reliably suppressed by the bias suppression control device 111 using the ACCT.

  FIG. 8 shows a control device for a power conversion system that is Embodiment 4 of the present invention. Hereinafter, differences from the first to third embodiments will be mainly described.

Fault detection means 802, a system voltage V _S, and outputs the created switching signal S _W of the switch 602 based on the residual magnetic flux [Phi _e of the transformer core to be estimated in the polarized磁抑system controller 112 using a VT105 .

In FIG. 8, the power converter detection current i _conv is not shown as an input signal of the accident detection means 802, but i _conv may be added as an input signal of the accident detection means 802.

In the accident detection means 802, a low voltage threshold value ± V _th and a magnetic flux damping control stop threshold value ± Φ _eth are set in advance, and when a system voltage larger than the absolute value of ± Vth is not detected for a certain period of time, The accident detection means 802 operates to change the value of the switching signal Sw from −1 to 1 or from 0 to 1 (changed from −1 to 1 in FIG. 9 described later).

In addition to the aforementioned operation, fault detection means 802, when the residual magnetic flux [Phi _e are remained within the range of the damping control stop threshold ± .PHI.e _th, to change the value of the switching signal S _W from 1 to 0 To work. At this time, the switcher 602 switches the correction current command i _COMP from the output i _{DMP2 of the} bias suppression control device 112 using the VT 105 to a zero value.

Switch 602, in the same manner as in Example 3, as a correction current command _{i COMP,} and outputs an output mode for outputting the magnetic bias correction current command _{i DMP 1,} the output mode for outputting a magnetic flux correction current command _{i DMP 2,} and a zero value Has an output mode. The switch 602 outputs the correction current command i _COMP in any output mode according to the value of the switching signal Sw.

In the fourth embodiment, when the switching signal _S W = -1 outputs a magnetic bias correction current command _{i DMP 1} as the correction current command _{i COMP,} when the switching signal _S W = 0, the zero value as the correction current command outputs (iCOMP = 0), when the switching signal _S W = 1 is the magnetic flux correction current command _{i DMP 2,} and outputs as the corrected current command _{i COMP.}

Incidentally, by providing the reset circuit for resetting periodically the residual magnetic flux [Phi _e during normal operation the internal fault detection unit 802, switching from the accumulation of integration error generated when estimating the residual magnetic flux by integration of the system voltage V _S 602 May be prevented from malfunctioning.

  FIG. 9 shows the operation of the fourth embodiment when a system fault occurs.

Similar to FIG. 3, 5, 7, at time t1, the system voltage _{V S} is severely degraded.

  During the period after the accident occurrence time t1 and the period after the accident removal time t2, that is, when the system voltage is normal, the demagnetization suppression control device 111 using the ACCT suppresses the DC demagnetization.

From the time t1 to the time ts, by switching the switch signal Sw from -1 to 1, the output _{i DMP 1} polarized磁抑system controller 111 using ACCT106, the output _{i DMP 2} polarization磁抑system controller 112 using a VT105 The correction current command i _COMP is switched. When the correction current command i _COMP is switched to the demagnetization correction current command i _DMP2 , the residual magnetic flux Φ _e of the iron core of the transformer 102 decreases, and from the time ts that falls within the range of the damping control stop threshold value ± Φ _eth. at time t2, the accident detecting means 802 changes the switching signal _{S W} of the switching circuit 602 from 1 to 0, and zero values corrected current command _{i COMP.}

Fault detection means 802 changes at time t2 is the time of the accident elimination time i.e. the system voltage recovery, to operate the polarization磁抑system controller 111 using ACCT106, a switching signal _{S W} of the switch 602 to -1 from 0 To do.

  According to the fourth embodiment, since the operation time of the demagnetization suppression control device 112 during the accident period can be reduced, the transformer 102 and the power conversion device 103 caused by the demagnetization compensation current flowing in the circuit are used. Increase in loss can be prevented. This can prevent the cooling device from becoming large.

  As shown in FIG. 1, the demagnetization suppressing means in the first to fourth embodiments described above is a power in which one power conversion device and one AC system (power system) are interconnected via one transformer. Although applied to the conversion system, the present invention is not limited to this, and the present invention can also be applied to a power conversion system in which a plurality of power conversion devices and a plurality of AC systems are connected via a plurality of transformers. Therefore, such a power conversion system will be described below.

  FIG. 10 shows a power conversion system that is Embodiment 5 of the present invention. The power conversion system has a so-called BTB (back to back) configuration.

  As shown in FIG. 10, the DC sides of the power conversion main circuits 301a and 301b in the power conversion device 300 are connected to each other. The AC side of the power conversion main circuit 301a is connected to the AC system 201a via the transformer 202a, and the AC side of the power conversion main circuit 301b is connected to the AC system 201b via the transformer 202b.

The power conversion main circuit 301a is ON / OFF controlled by the demagnetization suppression control device 302a so as to suppress the DC demagnetization of the transformer 202a. As the demagnetization suppression control device 302a, the control device in any of the first to fourth embodiments described above is used. Therefore, the demagnetization suppression control device 302a receives the power converter detection current i _conv , the system voltage V _S detected by the VT as the detection signal Sa from the primary and secondary sides of the transformer 202a, the primary side of the transformer 202a. And a differential signal _Vexac (see FIG. 1) generated at both ends of a resistor through which a differential current of the secondary side ACCT flows, and a control signal A for controlling the power conversion main circuit 301a based on the input detection signal Sa. (Corresponding to the voltage command value V _ref in FIGS. 1, 4, 6 and 8) is created. Note that the DC detection voltage on the DC side of the power conversion circuit 301a may be added to the input signal. Further, the bias suppression control device 302b receives, as the detection signal Sb from the primary and secondary sides of the transformer 202b, the system voltage V _S detected by the power converter detection current i _conv and VT, the primary side of the transformer 202b. And a differential signal _Vexac (see FIG. 1) generated at both ends of a resistor through which a differential current of the secondary side ACCT flows, and a control signal B for controlling the power conversion main circuit 301b based on the input detection signal Sb. (Corresponding to the voltage command value V _ref in FIGS. 1, 4, 6 and 8) is created. Note that the DC detection voltage on the DC side of the power conversion main circuit 301b may be added to the input signal.

  As a power conversion system having the configuration of the fifth embodiment, for example, there are a self-excited frequency converter and a self-excited high-DC power transmission system that accommodate power between AC power systems having different system frequencies. In the former case, the DC sides of the power conversion main circuits 301a and 301b are connected by a local connection (for example, a bus bar or a cable). In the latter case, the power conversion main circuits 301a and 301b are installed at remote locations, and the DC sides of the power conversion main circuits 301a and 301b are connected by a long-distance transmission line (for example, an overhead transmission line or a submarine cable).

  According to the fifth embodiment, it is possible to reduce the plurality of transformers because the DC bias of the plurality of transformers can be suppressed. For this reason, the size and installation space of the power conversion system can be reduced.

  In addition, this invention is not limited to the Example mentioned above, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 101 ... AC power system 102 ... Transformer 103 ... Power converter 104 ... CT (Current Transformer)
105 ... VT (Voltage Transformer)
106 ... ACCT (AC CT)
DESCRIPTION OF SYMBOLS 107 ... Resistance 108 ... Voltage detection means 109 ... Control apparatus 110 ... PWM circuit 111 ... Demagnetization suppression control apparatus 112 ... Demagnetization suppression control apparatus 113 ... Switch 114 ... Adder 115 ... Voltage command value calculating part 201a, 201b ... AC Power system 202a, 202b ... Transformer 300 ... Power conversion device 301a, 301b ... Power conversion main circuit 302a, 302b ... Demagnetization suppression control device Sa, Sb ... Detection signal A, B ... Control signal 401 ... Control device 402 ... Accident detection Means 601 ... Control device 602 ... Switch 603 ... Accident detection means 801 ... Control device 802 ... Accident detection means

Claims (15)

In the control device for the power conversion device connected to the power system via the transformer,
Based on an excitation current of the transformer detected by AC CT (Current Transformer), a first demagnetization suppression control device that creates a first correction command for suppressing DC demagnetization of the transformer;
A second bias suppression control device for creating a second correction command for reducing the residual magnetic flux of the transformer based on the residual magnetic flux of the transformer estimated based on the system voltage of the power system;
A switch for creating a correction command based on the first correction command and the second correction command;
An arithmetic unit that creates a control signal for the power converter based on a command value and the correction command;
The control apparatus of the power converter device characterized by the above-mentioned. In the control apparatus of the power converter device according to claim 1,
The control device for a power converter according to claim 1, wherein the switch uses the correction command as the second correction command when an accident occurs in the power system. In the control apparatus of the power converter device according to claim 1,
The switching device generates the correction command in response to a switching signal. In the control apparatus of the power converter device according to claim 3,
A control device for a power converter, comprising an accident detection means for creating the switching signal. In the control apparatus of the power converter device according to claim 3,
The control device for a power converter according to claim 1, wherein the switch uses either the first correction command or the second correction command as the correction command in accordance with the switching signal. In the control apparatus of the power converter device according to claim 5,
Accident detection means for creating the switching signal based on the system voltage and the current flowing through the power converter, the accident detection means,
When the system voltage is normal, the switching signal as a first switching signal,
When the magnitude of the current exceeds a predetermined value, the switching signal is changed from the first switching signal to the second switching signal,
When the system voltage is restored, the switching signal is changed from the second switching signal to the first switching signal,
The switch is
In response to the first switching signal, the first correction command is the correction command,
The control apparatus for a power converter, wherein the second correction command is used as the correction command in response to the second switching signal. In the control apparatus of the power converter device according to claim 3,
The control device for a power converter according to claim 1, wherein the switch uses any one of the first correction command, the second correction command, and a zero value as the correction command in accordance with the switching signal. In the control apparatus of the power converter device according to claim 7,
Accident detection means for creating the switching signal based on the system voltage and the current flowing through the power converter, the accident detection means,
When the system voltage is normal, the switching signal as a first switching signal,
When the magnitude of the current exceeds a predetermined value, the switching signal is changed from the first switching signal to the second switching signal,
When the system voltage is restored, the switching signal is changed from the second switching signal to the third switching signal, and the switching signal is the third switching signal for a predetermined period,
After the predetermined period, the switching signal is changed from the third switching signal to the first switching signal,
The switch is
In response to the first switching signal, the first correction command is the correction command,
In response to the second switching signal, the second correction command is the correction command,
A control device for a power converter, wherein the zero value is used as the correction command in response to the third switching signal. In the control apparatus of the power converter device according to claim 7,
Accident detection means for creating the switching signal based on the system voltage and the residual magnetic flux, the accident detection means,
When the system voltage is normal, the switching signal as a first switching signal,
When an accident occurs in the power system, the switching signal is changed from the first switching signal to the second switching signal,
When the magnitude of the residual magnetic flux is smaller than a predetermined value, the switching signal is changed from the second switching signal to a third switching signal,
When the system voltage is restored, the switching signal is changed from the third switching signal to the first switching signal,
The switch is
In response to the first switching signal, the first correction command is the correction command,
In response to the second switching signal, the second correction command is the correction command,
A control device for a power converter, wherein the zero value is used as the correction command in response to the third switching signal. In the control apparatus of the power converter device according to claim 1,
The AC CT has a first AC CT unit provided on the primary side of the transformer, and a second AC CT unit provided on the secondary side of the transformer,
The excitation device is detected based on a differential current between the first AC CT unit and the second AC CT unit. In the control apparatus of the power converter device according to claim 1,
The system voltage is detected by a VT (Voltage Transformer). In the control method of the power conversion device connected to the power system through the transformer,
Based on the excitation current detected by AC CT, create a first correction command to suppress the DC bias of the transformer,
Estimating the residual magnetic flux of the transformer based on the system voltage of the power system, creating a second correction command to reduce the estimated residual magnetic flux,
Creating a correction command based on the first correction command and the second correction command;
A method for controlling a power converter, wherein the power converter is controlled based on a command value and the correction command. In the control method of the power converter device according to claim 12,
A control method for a power converter, wherein the correction command is the second correction command when an accident occurs in the power system. A transformer,
A power converter connected to the power system via the transformer;
A control device for creating a control signal to be given to the power converter;
In a power conversion system comprising:
VT for detecting the system voltage of the power system;
AC CT for detecting the excitation current of the transformer;
With
The said control apparatus is a control apparatus of the power converter device of Claim 1, The power conversion system characterized by the above-mentioned. Two transformers,
A power conversion device having two power conversion main circuits in which the AC side is connected to the two power systems via the two transformers and the DC side is connected to each other,
Two control devices for creating control signals to be given to the two power conversion main circuits;
In a power conversion system comprising:
Two VTs for detecting the system voltage of the two power systems;
Two AC CTs for detecting the excitation currents of the two transformers;
With
Each of said two control apparatuses is a control apparatus of the power converter device of Claim 1, The power converter system characterized by the above-mentioned.

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