JP4320228B2 - Control device for self-excited converter - Google Patents

Description

  The present invention relates to a control device for a self-excited converter used for a DC power transmission / DC interconnection system or a power supply system in a power system.

  When power is exchanged between different power systems, a DC power transmission / DC interconnection system is used in which voltage-type self-excited converters are installed in each AC system and the DC terminals of these converters are mutually connected. A voltage type self-excited converter is also used in a power supply system that supplies power from a DC power source such as a battery to an AC system. In a power self-excited converter system, a multi-stage system in which a plurality of converters and transformers are connected is often used in order to reduce switching loss and harmonics (see, for example, Patent Document 1).

  FIG. 17 is a block diagram showing the configuration of the control device for this self-excited converter. In the figure, the DC sides of a plurality of self-excited converters 1, 1 ′ are connected in parallel to each other and connected to a DC line, a DC power source, etc. (not shown) via a DC capacitor 2. The AC side of the self-excited converters 1, 1 ′ is connected to the AC system 4 via transformers 3, 3 ′ in which system side windings are connected in series. In FIG. 17, a two-stage system is used for the sake of clarity. However, a four-stage, six-stage, or eight-stage system is adopted, and a relatively small number of times are obtained by shifting the timing of switching pulses for each converter. With this switching, voltage and current with small harmonics can be output.

In the self-excited converter, active power and reactive power can be independently controlled on the AC output side, and orthogonal axis (dq axis) current control is generally performed as the means. As shown in FIG. 17, the current control value Idref of the active power component and the current command value Iqref of the reactive power component are given from the host control system 5 to the AC current control circuit 6. On the other hand, the AC voltage phase θ detected by the phase detection circuit 7 and the detected value of the AC output current from the transformers 3 and 3 ′ are added to the orthogonal axis conversion circuit 8, and the three-phase output currents Ir, Is, It Are converted into orthogonal axis quantities of the active power component Id and the reactive power component Iq by the equations (1) to (4).
Iα = (2 × Ir−Is−It) / 3 (1)
Iβ = (Is−It) / √3 (2)
Then,
Id = Iα × cos θ + Iβ × sin θ (3)
Iq = Iα × sin θ−Iβ × cos θ (4)

  The power components Id and Iq are input to the AC current control circuit 6, and AC output voltage signals Vdc and Vqc that follow the command values Idref and Iqref, respectively, are output. A pulse is generated for each converter based on this signal. A switching pulse is applied to the transducers 1, 1 'by the generator circuits 9, 9'.

FIG. 18 is a block diagram showing a detailed configuration of the alternating current control circuit 6. In the figure, a current command value Idref of active power component and a current command value Iqref of reactive power component are given from the upper control system 5, and an active power component current detection value Id and reactive power component are respectively added by adders 11 and 11 '. The current detection value Iq is matched, and the difference is input to the proportional integration circuits 12 and 12 '. The proportional integration circuits 12 and 12 'output a value corresponding to the input value according to the proportional gain and the integral gain. This signal is reflected in the converter output voltage signals Vdc and Vqc via the adders 14 and 14 ', whereby feedback control is performed so that the detected current value of each axis matches the command value.
On the other hand, for the adders 14 and 14 ′, a value obtained by multiplying the current command values Idref and Iqref by the interconnection impedance value Xc by the multipliers 13 and 13 ′ and an AC primary given from the phase detection circuit 7. The d-axis component Vd and the q-axis component Vq of the side voltage are input and added to the outputs of the proportional integration circuits 12 and 12 'to obtain output voltage signals Vdc and Vqc. It can be said that signals other than the proportional integration circuits 12 and 12 'calculate a voltage to be output by the converter from a given current command value, that is, an active power operating point and a reactive power operating point.

That is, between the interconnection impedance Xc, the dq axis components V1d and V1q of the primary side voltage of the impedance, the dq axis components V2d and V2q of the secondary side voltage, and the dq axis components Id and Iq of the current flowing through the impedance, There is a relationship of the following equations (5) and (6).
V2d−V1d = −Iq × Xc (5)
V2q + V1q = Id × Xc (6)

In the converter system shown in FIG. 17, Xc corresponds to the impedance of the converter transformer, and the secondary voltage corresponds to the converter output voltage. It can be said that the adders 14 and 14 'of the alternating current control circuit in FIG. 18 calculate V2d = Vdc and V2q = Vqc obtained from the equations (5) and (6).
That is, in the AC current control circuit of FIG. 18, a voltage signal to be output by the converter is obtained from an active power current command value, a reactive power current command value, and a system voltage detection value by an open loop calculation, and an error is further detected by current feedback control. Control to eliminate is performed.
JP 2001-258264 A

  In general, the voltage type self-excited converter is designed to stop the protection by an overcurrent when an output current of about 1.5 to 2.0 times the rated current flows. Since voltage-type self-excited converters are more vulnerable to overcurrent than current-type converters, AC current control uses a relatively large gain and combines a feedforward circuit to quickly track system fluctuations and overcurrent. Is preventing.

In the normal operation, the overcurrent protection stop is likely to occur when a transformer is turned on in the vicinity and a large excitation inrush current flows. The magnetizing inrush current causes distortion and positive / negative non-target in the system voltage waveform, and this causes a magnetic bias phenomenon of the transformer for the converter. When magnetism occurs, the excitation circuit is saturated and a large excitation current flows, which flows into the converter, so protection is stopped due to overcurrent.
In order to prevent an overcurrent trip due to a bias, generally a bias suppression control circuit 10, 10 'is provided for each converter as shown in FIG. 17, and a primary side (system side) current I1 of the transformer is provided. And the secondary side (converter side) current I2, that is, a value corresponding to the DC amount of the signal corresponding to the excitation current, is corrected for the AC voltage signal, and control is performed so that the excitation current approaches zero. Is called.
However, the demagnetization suppression control requires a one-cycle integration or the like for detecting the direct current amount, so that the response speed becomes slow. Therefore, there has been a problem that sufficient overcurrent suppression cannot be performed when a large excitation inrush current flows suddenly.

  In addition, AC current control controls the system side current, which is a common value among the converters, whereas the excitation current is different for each of the transformers 3 and 3 '. The current on the instrument side is controlled. For this reason, the operations are contradictory, and there is a case where a sufficient demagnetization suppression effect cannot be obtained by the current control operation. If the gain of the demagnetization suppression control is increased to enhance the suppression effect, there is a problem that the operation becomes unstable due to interference with the current control.

  When the output current in advance is large, for example, at the time of full power operation, the allowable value for the excitation current and the zero-phase current is small, so that the possibility that the converter is stopped due to overcurrent becomes higher.

  Further, when the host control system 5 is controlled to output values corresponding to the load current as the command values Idref and Iqref, for example, when the load current is distorted or fluctuated by turning on a nearby transformer or the like, When the command value itself changes abruptly, the fluctuation of the converter output current increases, and there is a problem that the possibility of occurrence of overcurrent increases.

  An object of the present invention is to provide a control device for a self-excited converter capable of preventing a voltage-type self-excited converter from being stopped by an overcurrent and operating stably.

The invention according to claim 1
A current control circuit that converts a three-phase AC output current into dq axis variables on Cartesian coordinates and controls each axis current to follow a command value, and a difference between currents on the primary side and secondary side of the transformer In the control device of the self-excited converter having the demagnetization suppression control circuit that prevents the magnetism of the transformer by correcting each phase output voltage of the self-excited converter according to
Means is provided for switching the control gain of the current control circuit to a smaller value than usual on condition that the output current exceeds a certain value.

  With this configuration, it is possible to increase the effectiveness of the demagnetization suppression control and prevent the converter overcurrent due to the demagnetization.

The invention according to claim 2
A current control circuit that converts a three-phase AC output current into dq axis variables on Cartesian coordinates and controls each axis current to follow a command value, and a difference between currents on the primary side and secondary side of the transformer In the control device of the self-excited converter having the demagnetization suppression control circuit that prevents the magnetism of the transformer by correcting each phase output voltage of the self-excited converter according to
Control of the current control circuit on condition that the output current exceeds a certain value and the value corresponding to the excitation current that is the input signal of the demagnetization suppression control circuit or the output signal of the demagnetization suppression control circuit exceeds a certain value A means for switching the gain to a value smaller than usual is provided.

  With this configuration, it is possible to increase the effectiveness of the demagnetization suppression control and prevent the converter overcurrent due to the demagnetization.

  As is apparent from the above description, according to the present invention, there is provided a control device for a self-excited converter capable of preventing the voltage-type self-excited converter from being stopped by an overcurrent and operating stably. Can do.

Hereinafter, the present invention will be described in detail based on reference examples and preferred embodiments shown in the drawings. The same components as those of the conventional self-excited converter control device described with reference to FIGS. 17 and 18 are denoted by the same reference numerals, and the description thereof is omitted.

FIG. 1 is a block diagram showing a configuration of a first reference example of a control device for a self-excited converter according to the present invention. In the figure, the main circuit section is configured in the same manner as the conventional apparatus and operates in the same manner, so that the description thereof will be omitted and differences from the conventional apparatus will be described.

The first reference example is different from the conventional apparatus shown in FIG. 17 in that a command value setting circuit 15, a switch circuit 16, and an overcurrent detection circuit 17 are newly provided.

Here, the command value setting circuit 15 is a circuit for setting current command values Idref ′ and Iqref ′ used in the AC current control circuit 6, and its output is input to the switch circuit 16.
On the other hand, current command values Idref and Iqref given from the host control system 5 are also input to the switch circuit 16.
The switch circuit 16 selects one of the current command values Idref and Iqref from the host control system 5 or the current command values Idref ′ and Iqref ′ from the command value setting circuit 15 based on a signal from the overcurrent detection circuit 17. To the AC current control circuit 6.

FIG. 2 is a block diagram showing a detailed configuration of the overcurrent detection circuit 17. Here, the detected value of each phase current on the secondary side (converter side) of each converter transformer 3, 3 ′ is input to absolute value calculation circuits 18, 18 ′, and this absolute value detection circuit 18, 18 ′. Are converted into absolute values and input to the maximum value detection circuit 19.
The maximum value detection circuit 19 selects the phase current of each converter having the largest absolute value and applies it to the level detection circuit 20. The level detection circuit 20 applies a switching signal to the switch circuit 16 when the value added to the level detection circuit 20 exceeds a preset value, for example, a rated current of 100%. Other configurations are the same as the conventional example.

Next, the operation of the first reference example shown in FIG. 1 and FIG. 2 will be described, particularly in that the configuration is different from that of the conventional apparatus. In the control device for the self-excited converter shown in FIG. 1, zero or a constant value close to zero is set in advance as Idref ′ and Iqref ′ in the command value setting circuit 15. The setting method includes manual setting by the user or a fixed value determined by prior analysis.
During the steady operation, the switch circuit 16 selects the command values Idref and Iqref given from the host control system 5. Here, when the converter output current exceeds the rated current due to system disturbance or the like, this is detected by the overcurrent detection circuit 17 and a switching signal is applied to the switch circuit 16. When the current command value is switched to Idref ′, Iqref ′, that is, zero or a small value close to zero, the converter output current on the system side shifts to a small operating point.

Thus, according to the first reference example, when the output current of the converter becomes large, by switching the current command value, the system-side output current can be suppressed to a small value, and the overcurrent level leading to the protection stop. The margin for is increased. For this reason, even if the excitation current and zero-phase current of the transformer for the converter that cannot be controlled by the AC current control circuit increase, overcurrent does not occur and the operation can be continued stably.

FIG. 3 is a block diagram showing the configuration of the second reference example of the control device for the self-excited converter according to the present invention. In the figure, the same elements as those in FIG. 1 showing the first reference example are denoted by the same reference numerals, and the description thereof is omitted. Differences from the first reference example will be described.

This second reference example is the first in that the active power component current command value Idref given from the host control system 5 and the output signal of the overcurrent detection circuit 17 are input to the command value setting circuit 15A. The configuration is different from the reference example .

FIG. 4 is a block diagram showing a detailed configuration of the command value setting circuit 15A. In the figure, the current command value Idref and the reduction gain Kd of the active power component given from the upper control system 5 are input to the multiplier 21, and the result of multiplying each input value is added to the hold circuit 22.
The reduction gain Kd is a value between 0 and 1, for example, the user sets an appropriate value. An output signal of the overcurrent detection circuit 17 is added to the hold circuit 22 as a command signal for holding the input value. The output of the hold circuit 22 is applied to the switch circuit 16 as a current command value Idref ′. On the other hand, as the reactive power component current command value Iqref ′, a preset fixed value is output as it is and applied to the switch circuit 16.

Next, the operation of the second reference example shown in FIGS. 3 and 4 will be described below. In the control device for the self-excited converter shown in FIG. 3, the switch circuit 16 selects the command values Idref and Iqref given from the host control system 5 and applies them to the AC current control circuit 6 during steady operation.
Here, when the output current of the converter exceeds the rated current due to disturbance of the AC system 4 or the like, this is detected by the overcurrent detection circuit 13 and a switching signal is applied to the switch circuit 16. The above operation is the same as that of the first reference example shown in FIG.
On the other hand, in the command value setting circuit 15A, when an overcurrent detection signal is added from the overcurrent detection circuit 17, the output of the hold circuit 22 is given from the input value at that time, that is, from the upper control system 5. The current command value Idref is fixed to a value obtained by multiplying the reduction gain Kd, and the value and the fixed value Iqref ′ are added to the switch circuit 16.
As a result of this operation, the current command value finally applied to the AC current control circuit 6 becomes a value obtained by multiplying the value given from the host control system 5 by the gain Kd as the component current of the active power, and the reactive power Is a preset fixed value Iqref ′.

  As a result, the operating point of the converter shifts to a value where the active power component is close to zero and the reactive power component is a fixed command value Idref ′. If Kd = 0 is set, the command value of the active power component becomes zero.

  If the cause of the overcurrent is the inrush current of the neighboring transformer, the overcurrent can be suppressed if the reactive power operating point outputs a certain value according to the system conditions rather than a point close to zero. There is a case. It is necessary to obtain an appropriate value by analysis such as system simulation in advance. As the fixed value Iqref ′ in FIG. 4, an appropriate reactive power operation point value obtained in this way is set. As the active power component approaches zero, overcurrent tends to be suppressed.

Thus, according to the second reference example , when the converter output current increases, the active power component of the grid-side output current is suppressed to a small value by switching the current command value, and the reactive power component is Move to an operating point where overcurrent is unlikely to occur.
This increases the margin for the overcurrent level leading to protection stop. For this reason, even if the exciting current and zero-phase current of the transformer for the converter that cannot be controlled by the current control circuit increase, overcurrent does not occur and the operation can be continued stably.

FIG. 5 is a block diagram showing the configuration of the third reference example of the control device for the self-excited converter according to the present invention. In the figure, the same elements as those in FIG. 1 showing the first reference example are denoted by the same reference numerals, and the description thereof is omitted. Differences from the first reference example will be described. In the third reference example , the active power component current command value Idref, the reactive power component current command value Iqref, and the output signal of the overcurrent detection circuit 13 given to the command value setting circuit 15B from the host control system 5 are as follows. The added points differ from the first reference example shown in FIG.

FIG. 6 is a block diagram showing a detailed configuration of the command value setting circuit 15B shown in FIG. In the figure, a component current command value Idref and a reduction gain Kd of active power given from the host control system 5 are input to a multiplier 21, and a multiplication result of each input value is applied to a hold circuit 22.
The reduction gain Kd is a value between 0 and 1, for example, the user sets an appropriate value.
On the other hand, the component current command value Iqref of reactive power given from the host control system 5 and the addition value ΔIqref to this current command value are input to the adder 23, each input value is added, and the addition result is input to the hold circuit 24. Is done. The added value ΔIqref is a value of about −0.5 to 0.5, for example, the user sets an appropriate value.
An output signal of the overcurrent detection circuit 17 is added to the hold circuits 22 and 24 as a command signal for holding the input value. A limiter circuit 25 is connected to the output path of the hold circuit 24, and the limiter circuit 25 outputs a result of limiting the value added to the limit circuit 25 so that the value does not exceed the rated current value. The output of the hold circuit 22 is applied to the switch circuit 16 as a current command value Idref ′, and the output of the limiter circuit 25 is applied as a current command value Iqref ′.

Next, the operation of the third reference example shown in FIGS. 5 and 6 will be described. In the third reference example , the switch circuit 16 selects and applies the command values Idref and Iqref given from the upper control system 5 to the alternating current control circuit 6 during steady operation.
Here, when the converter output current exceeds the rated current due to disturbance of the AC system 4 or the like, this overcurrent is detected by the overcurrent detection circuit 17 and a switching signal is applied to the switch circuit 16. The above operation is the same as that of the first reference example shown in FIG.

On the other hand, in the command value setting circuit 15B, when an overcurrent detection signal is added from the overcurrent detection circuit 17, the outputs of the hold circuits 22 and 24 are given from the input values at that time, that is, from the upper control system 5. The value obtained by multiplying the obtained Idref by the reduction gain Kd and the value obtained by adding the addition value ΔIqref to the Iqref given from the upper control system 5 are fixed.
Further, the command value of the reactive power component is limited by the limiter circuit 25 so that the command value does not exceed the rated current, and those results are added to the switch circuit 16 as Idref ′ and Iqref ′.
The current command value finally applied to the alternating current control circuit 6 by this operation becomes a value obtained by reducing the value given from the higher control system 5 by the gain Kd as the component current command value of the active power, and the component of the reactive power The current command value is a value that is deviated by the addition value ΔIqref from the value given by the host control system within the rated current range.

Thus, according to the third reference example, when the output current of the self-excited converter increases, the active power component of the grid-side output current is suppressed to a small value by switching the current command value, and is invalid. The power component shifts to an operating point where overcurrent is unlikely to occur.
This increases the margin for the overcurrent level leading to protection stop. For this reason, even if the exciting current and zero-phase current of the transformer for the converter that cannot be controlled by the current control circuit increase, overcurrent does not occur and the operation can be continued stably.

FIG. 7 shows a modification of the third reference example of the self-excited converter according to the present invention, and is a block diagram showing another configuration example of the command value setting circuit shown in FIG. In the command value setting circuit 15C shown here, the component current command value Idref and the reduction gain Kd of the active power given from the host control system 5 are inputted to the multiplier 21, and the reactive power component current command value Iqref and the reduction gain Kd are inputted. The signal is input to the multiplier 26 and multiplied by each input value.
The reduction gain Kd is a value between 0 and 1, for example, the user sets an appropriate value. The outputs of the multipliers 21 and 26 are input to the hold circuits 22 and 24, respectively. The output signals of the overcurrent detection circuit 17 are added to the hold circuits 22 and 24 as command signals for holding the input values. . The output of each hold circuit is applied to the switch circuit 16 as current command values Idref ′ and Iqref ′.

Hereinafter, the operation of the command value setting circuit 15C shown in FIG. 7 will be described. In the control device of FIG. 5, the switch circuit 16 selects the command values Idref and Iqref given from the upper control system 5 during steady operation.
Here, when the converter output current exceeds the rated current due to disturbance of the AC system 4 or the like, the overcurrent detection circuit 17 detects the overcurrent, and a switching signal is applied to the switch circuit 16. The above operation is the same as that of the first reference example shown in FIG.

On the other hand, in the command value setting circuit 15C shown in FIG. 7, when an overcurrent detection signal is added from the overcurrent detection circuit 17, the outputs of the hold circuits 22 and 24 are the input values at that time, that is, the upper control. The values are fixed to values obtained by multiplying Idref and Iqref given from the system 5 by the reduction gain Kd, respectively.
These results are applied to the switch circuit 16 as current command values Idref ′ and Iqref ′. The current command value finally applied to the alternating current control circuit 6 by this operation is fixed to a value obtained by reducing the value added from the host control system 5 by the gain Kd.

Thus, according to the modification of the third reference example shown in FIG. 7, when the converter output current becomes large, by switching the current command value, the system side output current can be suppressed to a small value, The margin for the overcurrent level leading to protection stop increases. For this reason, even if the exciting current and zero-phase current of the transformer for the converter that cannot be controlled by the current control circuit are increased, the operation can be continued stably without reaching an overcurrent.

  In the case where the host control system 5 is not performing feedback control, the same effect can be obtained even if the hold circuit 22 and the hold circuit 24 in the command value setting circuit of FIG. 7 are removed.

FIG. 8 is a block diagram showing the configuration of the fourth reference example of the control device for the self-excited converter according to the present invention. In the figure, the same elements as those in FIG. 1 showing the first reference example are denoted by the same reference numerals, and the description thereof is omitted. Differences from the first reference example will be described. This reference example differs from FIG. 1 in that signal smoothing circuits 27 and 27 'are provided instead of the command value setting circuit 15 in FIG. 1, and the other configurations are the same as those in FIG. .
Here, the active power component current command value Idref and the reactive power component current command value Iqref given from the host control system 5 are added as inputs to the signal smoothing circuits 27 and 27 ′, respectively, and their outputs are added to the switch circuit 16. It is done.
The signal smoothing circuits 27 and 27 ′ are circuits for smoothing a signal from the upper control system 5 such as a first-order lag circuit that fluctuates. Except for these, the configuration is the same as that of the first reference example shown in FIG.

The operation of the fourth reference example configured as described above will be described below, in particular, with respect to a portion having a configuration different from that in FIG. In this control device, the switch circuit 16 selects the command values Idref and Iqref given from the upper control system 5 during steady operation.
Here, if the output current of the converter exceeds the rated current due to disturbance of the AC system 4 or the like, this is detected by the overcurrent detection circuit 17 and a switching signal is applied to the switch circuit 16, and the switch circuit 16 smoothes the signal. The signals output from the circuits 27 and 27 ′ are selected and added to the alternating current control circuit 6 as a current command value.

Thus, according to the fourth reference example shown in FIG. 8, when the converter output current becomes large, the current command value becomes a value with less fluctuation compared to the case of steady operation. For example, when a control method for calculating a current command value according to the magnitude of the load current is used as the host control system 5, the load current is distorted when a nearby transformer is turned on. The change in the command value itself becomes larger due to the increase in fluctuations, and this tends to cause overcurrent of the converter. However, according to this reference example , the conversion is achieved by smoothing the command value and suppressing fluctuations. Overcurrent of the device can be prevented.

FIG. 9 is a block diagram showing a configuration of a fifth reference example of the self-excited converter according to the present invention. In FIG. 9, the same elements as those in FIG. 1 showing the first reference example are denoted by the same reference numerals. The description is omitted. This reference example is obtained by adding a limit value switching circuit 28 and limiter circuits 29 and 29 'to the first reference example shown in FIG.
Of these, the limit value switching circuit 28 receives an overcurrent detection signal from the overcurrent detection circuit 17 and outputs upper and lower limit values for the current command values Idref and Iqref, and the limiter circuits 29 and 29 ' The current command values Idref and Iqref are respectively limited according to the upper and lower limit values.

  FIG. 10 is a block diagram showing a detailed configuration of the limit value switching circuit 28. In this limit value switching circuit 28, the active power rating Pmax is set as the maximum value of the active power, the reactive power rating Qmax is set as the maximum value of the reactive power, and the fixed value of the capacity MVA is set as the maximum value of the apparent power. When the overcurrent detection circuit 17 detects an overcurrent, the upper and lower limit values Idmax and Idmin for the current command value Idref and the upper and lower limit values Iqmax and Iqmin for the current command value Iqref are output based on these set values. The operation circuits 30 and 30 ', the switch circuit 31, the normalization circuits 32 and 32', and the sign inversion circuits 33 and 33 'are provided.

Among these, the arithmetic circuit 30 inputs the reactive power rating Qmax and the converter capacity MVA and calculates √ (MVA ² −Qmax ² ), and the arithmetic circuit 30 ′ calculates the active power rating Pmax and the converter capacity MVA. This is input to calculate √ (MVA ² −Pmax ² ).
When the overcurrent detection circuit 17 does not detect an overcurrent, the switch circuit 31 adds the active power rating Pmax and the output of the arithmetic circuit 30 'to the standardization circuits 32 and 32', and the overcurrent detection circuit 17 detects the overcurrent. When detected, the output of the arithmetic circuit 30 and the reactive power rating Qmax are switched so as to be applied to the standardization circuits 32 and 32 '.
The normalization circuit 32 normalizes the value added to this via the switch circuit 31 and outputs the upper limit value Idmax of the current command value Idref, and the normalization circuit 32 ′ normalizes the value added to this from the switch circuit 31. Thus, an upper limit value Iqmax of the current command value Iqref is output.
The sign inversion circuit 33 inverts the sign of the upper limit value Idmax of the current command value Idref to a negative value and outputs it as a lower limit value Idmin, and the sign inversion circuit 33 'sets the sign of the upper limit value Idmax of the current command value Iqref to a negative value. And output as a lower limit value Iqmin.

The operation of the fifth reference example configured as described above will be described below, in particular, with respect to the parts different from the first reference example shown in FIG. In this reference example , the switch circuit 16 selects the command values Idref and Iqref given from the upper control system 5 during steady operation.
If the output current of the converter exceeds the rated current due to disturbance of the AC system 4 or the like, this is detected by the overcurrent detection circuit 17 and a switching signal is applied to the switch circuit 16. The signals Idref ′ and Iqref ′ given from 15 are selected and outputted, and given to the alternating current control circuit 6 as current command values.

On the other hand, the output of the overcurrent detection circuit 17 is also applied to the limit value switching circuit 28. When the converter output current exceeds the rated current, the limit value switching circuit 28 switches the signal.
That is, in the limit value switching circuit 28 shown in FIG. 10, in the normal state, the switch circuit 31 selects the active power rating Pmax and the output of the arithmetic circuit 30 'and applies the values to the limiter circuits 29 and 29'.
That is, the active power can be output to the full rating, and the reactive power can be determined in the remaining range obtained by subtracting the active power from the apparent power. Thereby, active power priority control is performed.
Here, when a switching command is given from the overcurrent detection circuit 17, the switch circuit 31 selects the reactive power rating Qmax and the output of the arithmetic circuit 30 and applies the values to the limiter circuits 29 and 29 '. That is, the reactive power can be output to the full rating, and the active power is determined in the remaining range obtained by subtracting the reactive power from the apparent power, and the control is switched to the reactive power priority control.

Thus, according to the fifth reference example shown in FIGS. 9 and 10, when the converter output current increases, the current command value switches from active power priority to reactive power priority. In the case of steady operation, it is generally important that active power such as accommodation power and output power is output from the host control system, and it is necessary to perform active power priority control.
When the converter output current increases, the active power component is narrowed to a value close to zero, and the reactive power can be prevented from being stopped due to overcurrent by outputting an appropriate value. According to this reference example , it is possible to more reliably prevent overcurrent by passing as much active power as necessary during normal operation and switching to reactive power priority when there is a possibility of overcurrent.

FIG. 11 is a block diagram showing the configuration of the sixth reference example of the control device for the self-excited converter according to the present invention. In FIG. 11, the same reference numerals are used for the same elements as in FIG. 9 showing the fifth reference example . The description is omitted.
The sixth reference example is different from the limit value switching circuit 28A shown in FIG. 9 in that each output of the switch circuit 16 is added to the limit value switching circuit 28A. Other than this, the configuration is the same as in FIG.

FIG. 12 is a block diagram showing a detailed configuration of the limit value switching circuit 28A. In the limit value switching circuit 28A, the reactive power command value Iqref and the converter capacity MVA from the switch circuit 16 are added to the arithmetic circuit 30, and the active power command from the switch circuit 16 is added to the arithmetic circuit 30 '. The value Idref and the converter capacitance MVA are added, and the arithmetic circuit 30 calculates √ (MVA ² −Iqref ² ) from MVA and Iqref.
As a result, the obtained value is a value that can output the active power when the reactive power is output in accordance with the command value. Similarly, the arithmetic circuit 30 ′ calculates √ (MVA ² −Idref ² ) from MVA and Idref.
As a result, the obtained value is a value that can output reactive power when active power is output in accordance with the command value. Other configurations are the same as those of the limit value switching circuit 28 shown in FIG.

The operation of the sixth reference example configured as described above will be described in particular with respect to the parts different from the fifth reference example described with reference to FIGS. 9 and 10. In the limit value switching circuit 28A shown in FIG. 12, in the steady state, the switch circuit 31 selects the active power rating Pmax and the output of the arithmetic circuit 30 ', and these values are applied to the limiter circuits 29 and 29'.
That is, the active power can be output to the full rating, and the reactive power can be determined within the remaining range obtained by subtracting the command value of the active power from the apparent power. Thereby, active power priority control is performed.
When a switching command is given from the overcurrent detection circuit 17, the reactive power rating Qmax and the output of the arithmetic circuit 30 are selected in the switch circuit 31, and the values are added to the limiter circuits 29 and 29 '. In other words, the reactive power can be output to the full rating, and the active power is determined in the remaining range obtained by subtracting the reactive power command value from the apparent power, and the control is switched to the reactive power priority control.

Thus, according to the sixth reference example described with reference to FIGS. 11 and 12, when the converter output current becomes large, the current command value is switched from active power priority to reactive power priority.
In the case of steady operation, it is generally important that active power such as accommodation power and output power is output from the host control system, and it is necessary to perform active power priority control. When the converter output current increases, the active power component is narrowed to a value close to zero, and the reactive power can be prevented from being stopped due to overcurrent by outputting an appropriate value.
According to this reference example , it is possible to more surely prevent overcurrent by allowing as much active power as necessary during normal operation and switching to reactive power priority when there is a possibility of overcurrent.

The fifth reference example shown in FIG. 9 and the sixth reference example shown in FIG. 11 are the same as the first reference example shown in FIG. 1 except that the limit value switching circuit 28 or 28A and the limiter circuits 29 and 29 ′, respectively. The limit value switching circuit 28 or the second reference example shown in FIG. 3, the third reference example shown in FIG. 5, and the fourth reference example shown in FIG. By adding 28A and limiter circuits 29 and 29 ', the same effect as the fifth or sixth reference example can be obtained.
Embodiment of the present invention

FIG. 13 is a block diagram showing the configuration of the first embodiment of the control device for the self-excited converter according to the present invention. In FIG. 13, the same elements as those in FIG. Therefore, the description is omitted. In this embodiment, an overcurrent detection circuit 17 is provided for the control device for the self-excited converter shown in FIG. 17, and the output signal is applied to the AC current control circuit 6A. The AC current control circuit 6A is shown in FIG. The configuration is different from that of FIG.

  In FIG. 14, an alternating current control circuit 6A is obtained by newly providing a switch circuit 34 and multipliers 35 and 35 'with respect to the conventional alternating current control circuit 6 shown in FIG. “1” and a reduction gain Kd are given to the input terminal of the switch circuit 34, and either value is selected by the switching signal from the overcurrent detection circuit 17 and applied to the multipliers 35, 35 ′. The reduction gain is an appropriate value of 1 or less, and is set in advance by manual setting or the like. Other configurations are the same as those of the conventional AC current control circuit 6 shown in FIG.

The operation of the first embodiment configured as described above will be described below with a focus on the parts different from the configurations shown in FIGS. In the control device for the self-excited converter shown here, the alternating current control overcurrent is not detected during the normal operation. Therefore, in the alternating current control circuit 6A shown in FIG. Selected and applied to multipliers 35, 35 '. As a result, the converter is controlled as in the conventional case.
Here, when the output current of the converter becomes large due to disturbance of the AC system 4 or the like, a switching command is applied to the switch circuit 34 in the AC current control circuit 6A by the overcurrent detection circuit 17, and the switch circuit 34 has a reduction gain Kd. Is added to the multipliers 35 and 35 '.
As a result, the magnitude of the signal input to the proportional integration circuits 12 and 12 'is reduced to Kd times in the steady state, and the gain of the proportional integration circuit, that is, the feedback control is substantially reduced to Kd times.

Thus, according to the first embodiment shown in FIG. 13 and FIG. 14, when there is a possibility that an overcurrent occurs, the feedback gain of the alternating current control is reduced. The most frequent cause of overcurrent in steady operation is due to biasing due to the introduction of a neighboring transformer, and overcurrent can be achieved by more effective control by the biasing suppression control circuits 10 and 10 '. The probability that it can be prevented is increased.
As described in the conventional apparatus, since the alternating current control and the demagnetization suppression control operate in contradiction, they have sufficient followability, i.e., when a current control circuit with a high gain is adopted, an excess current due to the demagnetization suppression control. Although there is a possibility that the current prevention effect cannot be sufficiently obtained, according to the present embodiment, there is a high-speed current follow-up property during steady operation, and in the case where an overcurrent due to the demagnetization occurs, the demagnetization suppression control is performed. The relative gain can be increased to prevent overcurrent.

In the alternating current control circuit 6A (FIG. 14) constituting the first embodiment, the multipliers 35 and 35 'are inserted in the input parts of the proportional integration circuits 12 and 12'. The same effect can be obtained even if it is inserted into the output portions 12 and 12 '.
Further, the switch circuit 34 and the multipliers 35 and 35 'similar to those shown in FIG. 14 are added to the alternating current control circuit 6A constituting the first to sixth embodiments, respectively, and the same as described in FIG. Effects can be obtained.

FIG. 15 is a block diagram showing the configuration of the second embodiment of the control device for the self-excited converter according to the present invention. In FIG. 15, the same elements as those of the first embodiment shown in FIG. Reference numerals are assigned and explanations thereof are omitted.
In this embodiment, an excitation overcurrent detection circuit 36 is added to the configuration of FIG. 13 showing the first embodiment, and the output of the overcurrent detection circuit 17 is input as one input and the output of the excitation overcurrent detection circuit 36 is output. The difference is that an AND circuit 37 is provided as the other input, and the output signal of the AND circuit 37 is input to the alternating current control circuit 6 instead of the output signal of the overcurrent detection circuit 17.
In this case, for the excitation overcurrent detection circuit 36, a value corresponding to the excitation current of the transformers 3 and 3 'from the demagnetization suppression control circuits 10 and 10', that is, from the secondary current I2 to the primary for each phase. A value obtained by subtracting the current I1 is input. From these values, the excitation overcurrent detection circuit 36 determines whether or not the transformer excitation current exceeds a certain value, and gives the result to the AND circuit 37.

  FIG. 16 is a block diagram showing a detailed configuration of the excitation overcurrent detection circuit 36. This is the same configuration as the overcurrent detection circuit 17 shown in FIG. Become. The internal configuration of the AC current control circuit 6 is the same as that of the first embodiment shown in FIG. 14, and the output of the AND circuit 37 is used as a switching signal of the switch circuit 34.

The operation of the second embodiment configured as described above will be described below with a focus on the parts different from those in FIG. During normal operation, an overcurrent of AC current control is not detected, and “1” is selected by the switch circuit 34 and applied to the multipliers 35 and 35 ′.
As a result, the converter is controlled as in the conventional case. Here, when the output current of the converter increases due to disturbance of the AC system 4 or the like, the output of the overcurrent detection circuit 17 becomes “1”. Further, when the transformer excitation current has a large value, the output of the excitation overcurrent detection circuit 36 becomes “1” and is given to the AND circuit 37, so that a switching command is sent to the switch circuit inside the AC current control circuit 6. The switch circuit 34 selects the reduced gain Kd and supplies it to the multipliers 35 and 35 '.
As a result, the magnitude of the signal input to the proportional integration circuits 12 and 12 'is reduced to Kd times in the steady state, and the gain of the proportional integration circuit, that is, the feedback control is substantially reduced to Kd times.

Thus, according to the second embodiment shown in FIGS. 15 and 16, when there is a possibility that an overcurrent may occur due to the bias of the transformer, that is, an increase in the excitation current, the feedback gain of the AC current control Is reduced.
The most frequent cause of overcurrent in steady operation is due to biasing due to the introduction of a neighboring transformer, and overcurrent can be achieved by more effective control by the biasing suppression control circuits 10 and 10 '. Probability that can be prevented increases.
As described in the conventional apparatus, the alternating current control and the demagnetization suppression control perform opposite operations, and therefore have sufficient followability. That is, when current control with high gain is used, there is a possibility that the overcurrent prevention effect due to the demagnetization suppression control may not be sufficiently obtained, but according to the present embodiment, it has high-speed current followability during steady operation, In addition, when an overcurrent due to the bias is generated, the relative gain of the bias suppression control can be increased to prevent the overcurrent.
Further, when a possibility of overcurrent occurs due to a cause other than the bias, overcurrent can be prevented by operating the alternating current control at high speed as usual.

The block diagram which shows the structure of the 1st reference example of the control apparatus of the self-excited converter which concerns on this invention. The block diagram which shows the detailed structure of the overcurrent detection circuit which comprises the 1st reference example shown in FIG. The block diagram which shows the structure of the 2nd reference example of the control apparatus of the self-excited converter which concerns on this invention. The block diagram which shows the detailed structure of the command value setting circuit which comprises the 2nd reference example shown in FIG. The block diagram which shows the structure of the 3rd reference example of the control apparatus of the self-excited converter which concerns on this invention. The block diagram which shows the detailed structure of the command value setting circuit which comprises the 3rd reference example . FIG. 7 is a block diagram showing another configuration example of the command value setting circuit configuring the third reference example shown in FIG. 6. The block diagram which shows the structure of the 4th reference example of the control apparatus of the self-excited converter which concerns on this invention. The block diagram which shows the structure of the 5th reference example of the self-excited converter which concerns on this invention. The block diagram which shows the detailed structure of the limit value switching circuit which comprises the 5th reference example shown in FIG. The block diagram which shows the structure of the 6th reference example of the control apparatus of the self-excited converter which concerns on this invention. FIG. 12 is a block diagram showing a detailed configuration of a limit value switching circuit constituting the sixth reference example shown in FIG. 11. 1 is a block diagram showing a configuration of a first embodiment of a control device for a self-excited converter. FIG. The block diagram which shows the detailed structure of the alternating current control circuit which comprises 1st Embodiment shown in FIG. The block diagram which shows the structure of 2nd Embodiment of the control apparatus of the self-excited converter based on this invention. The block diagram which shows the detailed structure of the excitation overcurrent detection circuit which comprises 2nd Embodiment shown in FIG. The block diagram which shows the structure of the control apparatus of the conventional self-excited converter. The block diagram which shows the detailed structure of the alternating current control circuit shown in FIG.

DESCRIPTION OF SYMBOLS 1 Self-excited converter 2 DC capacitor 3, 3 'Transformer 4 AC system 5 High-order control system 6, 6A AC current control circuit 7 Phase detection circuit 8 Orthogonal axis conversion circuit 9, 9' Pulse generation circuit 10, 10 ' Bias suppression control circuit 11, 11 'Adder 12, 12' Proportional integration circuit 13, 13 'Multiplier 14, 14' Adder 15, 15A, 15B, 15C Command value setting circuit 16 Switch circuit 17 Overcurrent detection circuit 18 , 18 'absolute value calculation circuit 19 maximum value selection circuit 20 level detector 21 multiplier 22 hold circuit 23 adder 24 hold circuit 25 limiter circuit 26 multiplier 27, 27' smoothing circuit 28, 28A limit value switching circuit 29, 29 'limiter circuit 30, 30' arithmetic circuit 31 switch circuit 32, 32 'normalization circuit 33, 33' sign inversion circuit 34 switch times Path 35, 35 'multiplier 36 excitation overcurrent detection circuit 37 AND circuit 38, 38' absolute value calculation circuit 39 maximum value selection circuit 40 level detector

Claims (2)

A current control circuit that converts a three-phase AC output current into dq axis variables on Cartesian coordinates and controls each axis current to follow a command value, and a difference between currents on the primary side and secondary side of the transformer In the control device of the self-excited converter having the demagnetization suppression control circuit that prevents the magnetism of the transformer by correcting each phase output voltage of the self-excited converter according to
A control device for a self-excited converter, comprising means for switching the control gain of the current control circuit to a smaller value than usual on condition that the output current exceeds a certain value. A current control circuit that converts a three-phase AC output current into dq axis variables on Cartesian coordinates and controls each axis current to follow a command value, and a difference between currents on the primary side and secondary side of the transformer In the control device of the self-excited converter having the demagnetization suppression control circuit that prevents the magnetism of the transformer by correcting each phase output voltage of the self-excited converter according to
On condition that the output current exceeds a certain value and the value corresponding to the excitation current that is the input signal of the demagnetization suppression control circuit or the output signal of the demagnetization suppression control circuit exceeds a certain value, the current control circuit A control device for a self-excited converter, comprising means for switching the control gain to a value smaller than usual.

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