JPH10171543A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a power converter capable of accurately detecting a DC component included in output voltage and preventing or suppressing the magnetic deflection of a voltage transformer even at the time of an accident causing a loss in the voltage of an AC power system or non-steady operation allowing a self-excited converter to repeat gate block and gate deblock. SOLUTION: This power converter is provided with the self-excited converter 2 connected to the AC power system 1 through a voltage transformer 3 and a gate timing computing circuit 16 for calculating timing from gate block up to gate deblock. Gate deblock is executed based on a GDB command to be an output from the circuit 16 and voltage is outputted based on an output voltage command.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter having a self-extinguishing element and having a power converter connected to an AC power system or a load via a transformer. The present invention relates to a technique for preventing direct current magnetic bias.

[0002]

2. Description of the Related Art FIG.
FIG. 1 is a circuit diagram showing a configuration for preventing a DC bias of a transformer in a conventional power conversion device provided with a power transformer connected to an AC power system via a transformer, which is disclosed in Japanese Patent Application Laid-Open Publication No. H10-209,026.

In FIG. 10, 1 is an AC power system, 2 is a self-excited converter that generates an AC voltage based on a gate drive signal, 3 is a transformer that connects the AC power system 1 and the self-excited converter 2, Is a DC voltage source for supplying a DC voltage to the self-excited converter 2, 5A and 5B are current detectors for detecting a current flowing through the windings of the transformer 3, and 6 is a subtractor for calculating the difference between the current detectors 5A and 5B. , 7 is a DC component detector for detecting a DC component from the output of the subtractor 6, 8 is an instrument transformer for detecting the voltage of the AC power system 1, 9 is a voltage reference for providing a set voltage of the AC power system 1, 10 Is the voltage reference 9 and the instrument transformer 8
A voltage command value generating circuit for generating a voltage command for the self-excited converter 2 in accordance with the signal of (1), an adder 11 for adding the output of the DC component detector 7 and the output of the voltage command value generating circuit 10,
Is a pulse width modulation control circuit that determines the firing timing of the self-extinguishing element of the self-excited converter 2 according to the output of the adder 11 and creates a gate pulse signal. 13 amplifies the output of the pulse width modulation control circuit 13. This is a gate pulse amplifier circuit that supplies a gate drive signal to the self-excited converter 2.

Next, the operation of the conventional power converter shown in FIG. 10 will be described. In the power converter shown in FIG. 10, when a DC component is contained in the voltage of the AC power system 1 or the output voltage of the self-excited converter 2, the transformer 3
An exciting current including a DC component flows through the transformer 3, and the DC component of the exciting current causes the transformer 3 to be demagnetized and the iron core of the transformer 3 to be saturated.

[0005] Among the winding currents of the transformer 3, the current flowing through the winding connected to the AC power system 1 is defined as the primary winding current, and the current flowing through the winding connected to the self-excited converter 2 is defined as two. Assuming that the secondary winding current is the secondary winding current of the transformer 3 detected by the current detector 5A and the secondary winding current of the primary winding of the transformer 3 detected by the current detector 5B, As an input, an excitation current of the transformer 3 is obtained by obtaining a difference by the subtractor 6. Therefore, a DC component included in an excitation current for demagnetizing the iron core of the transformer 3 is detected from an output of the subtractor 6. Is detected by the DC component detector 7.

The DC component included in the exciting current of the transformer 3 detected in this manner is converted into a self-excited converter generated by the voltage command value generating circuit 10 according to the output of the instrument transformer 8 and the voltage reference 9. 2 is added by the adder 11 and acts as a voltage command correction value of the self-excited converter 2.

The pulse width modulation control circuit 12 creates a gate pulse signal in accordance with the output of the adder 11, and further creates a gate drive signal from the gate pulse signal by a gate pulse amplifier circuit 13. The gate drive signal is converted into a self-excited signal. When applied to the device 2, the self-excited converter 2 switches the self-extinguishing element according to the voltage of the DC voltage source 4 to generate a voltage corresponding to the output of the adder 11.

As described above, in the conventional power converter shown in FIG. 10, since the self-excited converter 2 outputs a voltage corresponding to the output of the adder 11, the voltage of the AC power system 1 or the self-excited converter is output. When a DC component is included in the output voltage of the converter 2, the DC component included in the exciting current of the transformer 3 is detected and supplied to the adder 11, so that the voltage of the AC power system 1 or the voltage of the self-excited converter 2 is output. The self-excited converter 2 generates a voltage for canceling the DC component included in the output voltage, and operates so as to avoid DC bias of the transformer 3.

[0009]

Since the conventional power converter is configured as described above, the self-excited converter 2 operates so as to cancel the DC component included in the output voltage during normal operation. .

[0010] On the other hand, when an accident such as complete loss of voltage occurs in the AC power system 1 and gate blocking is performed at the same time, when gate deblocking is performed again, residual magnetic flux remains in the transformer 3. If gate deblocking is not performed in the same phase as the phase of the output voltage when the gate is blocked, the DC component is superimposed on the magnetic flux of the transformer 3, the core of the transformer 3 is demagnetized, the exciting current increases, and the Self-excited converter 2
Stops protection. In the worst case, the elements constituting the converter may be damaged.

When an accident occurs in the AC power system 1 such that one-phase or two-phase voltage remains, when the transformer 3 is a neutral point grounding system, the zero-phase voltage is several tens times the rated current. The current flows, the current detector 5A and the current detector 5B are saturated, and an accurate current cannot be detected, and the demagnetization suppression control is performed with an erroneous current measurement value. In some cases, a voltage correction value is output.

If an accident occurs in the AC power system 1 such that one-phase or two-phase voltage remains, when the transformer 3 has a star-delta connection and a neutral grounding system, the normal current detector Since 5B is installed at a position for detecting a phase current connected to the transformer, a zero-phase current flows through the current detector 5A, but a zero-phase current does not flow through the current detector 5B, and only the difference between the two is taken. The DC current cannot be accurately detected because the zero-phase current remains only by the above. For this reason, the demagnetization suppression control is performed using an erroneous current measurement value, and an erroneous voltage correction value that promotes demagnetization may be output.

The present invention has been made in order to solve the above-described problems. In the event of an accident in which the voltage of the AC power system 1 is lost, or when the self-excited converter 2 uses a gate block and a gate deblock, It is an object of the present invention to provide a power converter capable of accurately detecting a DC component included in an output voltage even in a repetitive non-stationary state and preventing or suppressing DC bias of a transformer.

[0014]

A power converter according to a first aspect of the present invention includes a gate timing calculation circuit for calculating a timing from gate blocking to gate deblocking, and a gate deblocking command (hereinafter referred to as GDB). Command, and outputs a voltage based on the output voltage command.

According to such a configuration, the gate is blocked by calculating the timing from the gate blocking to the gate deblocking by the converter, and then the gate is deblocked at the most appropriate timing, and the transformer is biased. Magnetization can be prevented.

Further, the power converter according to the second invention is characterized in that:
In the first aspect, the gate timing calculation circuit calculates a magnetic flux density of the transformer by integrating a voltage applied to the transformer, and stores a position of the magnetic flux density when the gate is blocked. GD at the same position
It is composed of an arithmetic circuit that outputs the B command.

According to such a configuration, the gate timing calculation circuit calculates the magnetic flux density of the transformer from the output voltage, degates the gate at the same magnetic flux density position as when the gate is blocked, and the transformer is demagnetized. Can be prevented.

Further, a power converter according to a third invention is characterized in that:
In the above-mentioned first invention, the gate timing calculation circuit stores a time of one cycle of the voltage of the AC line in advance, and calculates a timing for outputting a GDB command by a timer after gate blocking. It is composed.

According to such a configuration, in the gate timing calculation circuit, the gate is deblocked at a point where an integer multiple of the output voltage period has elapsed since the gate was blocked by the timer counter, and the transformer is demagnetized. Can be prevented.

Further, a power converter according to a fourth invention is characterized in that:
In the first aspect, the gate timing calculation circuit includes a phase detection circuit that calculates a phase of the voltage of the AC line, and stores a phase when the gate is blocked.
It is composed of an arithmetic circuit that outputs a GDB command at the same phase as the phase.

According to such a configuration, in the gate timing calculation circuit, the phase is calculated by the phase detection circuit that calculates the phase of the voltage of the AC line, and the gate is deblocked in the same phase as the phase when the gate is blocked. It is possible to prevent the device from being demagnetized.

Further, a power converter according to a fifth invention is characterized in that:
A voltage detector for detecting the voltage of the AC line, a first current detector for detecting each winding current of the transformer, and a current detector for detecting the same current as the first current detector, but having a large saturation current value, and thus having high accuracy. Current detector, an input selection circuit for selecting an appropriate one of the inputs from the first and second current detectors, and a first or second signal selected by the input selection circuit. A DC component calculation circuit for calculating a DC component included in the output voltage of the converter from the output of the current detector,
A voltage command correction value calculation circuit for calculating a voltage command correction value from the DC component calculation circuit is provided, and a voltage is output based on the output voltage command value and the voltage command correction value.

With this configuration, in the event of an AC accident, the output of the current detector is included in the output voltage without being saturated by switching from the current detector having a small saturation current to the current detector having a large saturation current. DC components can be accurately detected.

Further, a power converter according to a sixth invention is characterized in that:
In the fifth invention, the input selection circuit detects that the AC line is grounded or short-circuited from the output of the voltage detector, and switches the input from the first and second current detectors. It is composed of circuits.

According to such a configuration, the input from the two current detectors is switched using the detected value of the AC voltage in the input switching circuit, whereby the DC component included in the output voltage can be accurately detected. it can.

The power converter according to a seventh aspect of the present invention
In the fifth aspect of the invention, the input selection circuit includes an arithmetic circuit that compares inputs from the current detector and selects a larger one.

According to this configuration, the input switching circuit is a circuit that selects the maximum value of the inputs from the two current detectors, so that the DC component included in the output voltage can be accurately detected. it can.

Further, the power converter according to the eighth invention is characterized in that:
A voltage detector for detecting the voltage of the AC line, a current detector for detecting each phase current connected to the transformer, and a second detector which detects the same current as the first current detector but has a low saturation current value and therefore has a low accuracy. A current detector, an input selection circuit for selecting an appropriate one of the inputs from the first and second current detectors, and a zero on the star side from the output of the current detector selected by the input selection circuit. A zero-phase operation circuit for calculating a phase current, a DC component operation circuit for calculating a DC component included in the output voltage of the converter based on the output of the current detector selected by the input selection circuit and the zero-phase current A voltage command correction value calculation circuit that calculates a voltage command correction value from the DC component calculation circuit, and outputs a voltage based on the output voltage command value and the voltage command correction value.

According to such a configuration, by calculating the zero-phase component flowing on the star side of the transformer from the output of the current detector, the zero-phase component that does not appear on the delta side is removed to accurately output the output voltage. The included DC component can be detected.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. Hereinafter, Embodiment 1 of the present invention will be described with reference to FIG. In the figure, elements having the same functions as those of the conventional power converter shown in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted.

14 is a GB / GDB command circuit for performing gate block and gate deblock, 15 is a GB / GDB status signal (gate block / gate deblock status signal) of the self-excited converter 2, and 16 is a GB / GDB command circuit. A gate timing calculation circuit for calculating gate deblocking timing from the output of 14, the GB / GDB state signal 15 and the output of the instrument transformer 8, and 17 is a GB / GDB command.

FIG. 2 shows the relationship between the voltage applied to the transformer 3 and the magnetic flux density. Reference numeral 18 denotes a voltage applied to the transformer 3, where a dotted line indicates a portion where the voltage has been lost. 19A is the magnetic flux density of the transformer 3 when the gate is deblocked at the timing of 22A, 19B is the magnetic flux density of the transformer 3 that is gate-deblocked at the timing of 22B, 20
Is the residual magnetic flux of the transformer 3 when the gate is blocked at the timing of 21.

Next, the operation will be described. The voltage of the AC power system 1 is completely lost for some reason, and GB / GDB
When the GB command is output from the command circuit 14, the self-excited converter 2 blocks the gate. The gate timing arithmetic circuit recognizes the position where the self-excited converter 2 has gate-blocked by the GB / GDB state signal 15. Next, GB / GDB
When the GDB command is output from the command circuit 14, the gate timing calculation circuit 14 outputs the GDB command to the gate pulse amplifier circuit 13 at the optimum position and restarts the self-excited converter 2.

The GB / GDB command is output directly to the self-excited converter 2 without being output to the gate pulse amplifier circuit, or is output to the voltage command value creation circuit 10 or the like to operate the self-excited converter 2. Is also good.

Here, the optimum position for gate deblocking will be described with reference to FIG. When the self-excited converter 2 gate-blocks at the timing of 21, the voltage 18 applied to the transformer 3 is lost. Here, the residual magnetic flux of the transformer 3 is held at the position of 20. Next, the timing of gate deblocking is now performed at 22A.
Has a magnetic flux density of 19A, which is three times higher than the rated magnetic flux.
The core of the transformer 3 is demagnetized, the exciting current increases, an overcurrent occurs, and the protection of the self-excited converter 2 stops. In the worst case, the elements constituting the converter may be damaged.
Therefore, by performing gate deblocking at a timing of 22B from the output of the gate timing calculation circuit, the iron core of the transformer 3 can stably operate without being demagnetized. In other words, the gate deblocking is performed at an optimum position where the gate of the self-excited converter 2 is deblocked at the same magnetic flux position as the magnetic flux of the iron core of the transformer 3 when the self-excited converter 2 is gate-blocked. In addition, it can be said that this optimal gate deblocking position is a position where a time that is an integral multiple of the voltage cycle of the AC voltage system has elapsed since the gate blocking. It can also be said that the phase is the same as that of the AC voltage system when the gate is blocked.

As described above, the conventional power converter shown in FIG. 10 does not have the gate timing operation circuit 16 when the self-excited converter 2 performs gate deblocking after gate blocking, and therefore performs gate deblocking. The timing was not always constant, and as shown in FIG. 2 and the paragraph number [0035], it was impossible to suppress the magnetization of the core of the transformer 3 when the gate was deblocked, but as shown in FIG. The power conversion device according to the first embodiment calculates the gate deblocking timing using the gate timing calculation circuit 16, thereby preventing the core of the transformer 3 from being demagnetized when the gate is deblocked. .

Embodiment 2 Hereinafter, a second embodiment of the present invention will be described with reference to FIG. In the figure, elements having the same functions as those of the conventional power converter shown in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted.

14 is a GB / GDB command circuit, 15 is a GB / GDB status signal of the self-excited converter 2, and 16 is GB / GD.
A gate timing calculation circuit that calculates the GDB timing from the output of the B command circuit 14, the GB / GDB status signal 15, and the output of the instrument transformer 8, and 17 is a GB / GDB command,
Numeral 3 denotes a magnetic flux calculating circuit for calculating the magnetic flux density from the voltage applied to the transformer 3, 24 stores the position of the magnetic flux density of the gate block from the GB / GDB state signal 15 and the output of the magnetic flux calculating circuit 23, and This is a storage operation circuit for calculating and outputting an optimal gate deblock timing from the output of the GDB instruction circuit 14.

Next, the operation will be described. First, the magnetic flux density of the transformer 3 is calculated in the magnetic flux calculation circuit 23 according to the equation (1) from the voltage applied to the transformer 3 which is always the output of the instrument transformer.

Magnetic flux density = {(applied voltage) dt} / {(number of windings of transformer) / (cross-sectional area of iron core)} (1)

The magnetic flux density calculated by the magnetic flux calculation circuit 23 is always traced by the storage calculation circuit 24, and the magnetic flux density at the moment when the self-excited converter 2 is gate-blocked is stored. Next, when the GDB command is output from the GB / GDB command circuit 14 to the storage operation circuit 24, the GDB is performed at the same magnetic flux position as the magnetic flux of the iron core of the transformer 3 when the gate is blocked as described in paragraph [0035]. Output command.

As described above, the conventional power converter shown in FIG. 10 does not have the gate timing operation circuit 16 when the self-excited converter 2 performs the gate deblocking after the gate blocking, so that the gate deblocking is performed. The timing is not always constant, and as shown in FIG. 2 and the paragraph number [0035], it was impossible to suppress the magnetization of the core of the transformer 3 when the gate was deblocked, but as shown in FIG. The power conversion device according to the second embodiment uses the gate timing operation circuit 16 to output a GDB command at the position of the same magnetic flux as the magnetic flux of the iron core of the transformer 3 when the gate is blocked. It is possible to prevent the core of the transformer 3 from being demagnetized.

Embodiment 3 Hereinafter, a third embodiment of the present invention will be described with reference to FIG. In the figure, elements having the same functions as those of the conventional power converter shown in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted.

14 is a GB / GDB command circuit, 15 is a GB / GDB status signal of the self-excited converter 2, and 16 is GB / GD.
A gate timing calculation circuit for calculating the GDB timing from the output of the B command circuit 14 and the GB / GDB status signal 15; 17 a GB / GDB command; 25 a timer counter;
24 is a GB / GDB status signal 15 and a timer counter 25
The time of the gate block is stored from the output of
This is a storage operation circuit for calculating and outputting the optimal gate deblock timing from the output of the B command circuit 14.

Next, the operation will be described. The storage operation circuit 24 calculates and stores the voltage cycle of the AC power system in advance. The counting is started by the output of the timer counter 25 from the moment when the self-excited converter 2 blocks the gate. When the GDB command is output from the GB / GDB command circuit 14 to the storage operation circuit 24, the paragraph number [0035] will be described. As described above, the GDB command is output at the timing of an integral multiple of the stored voltage cycle.

As described above, the conventional power converter shown in FIG. 10 does not have the gate timing operation circuit 16 when the self-excited converter 2 performs gate deblocking after gate blocking, so that gate deblocking is performed. The timing is not always constant, and as shown in FIG. 2 and the paragraph number [0035], it was impossible to suppress the magnetization of the core of the transformer 3 when the gate was deblocked, but as shown in FIG. The power conversion device according to the second embodiment uses the gate timing calculation circuit 16 to always output the GDB command after an integer multiple of the voltage cycle after gate blocking,
It is possible to prevent the magnetism of the iron core of the transformer 3 when the gate is deblocked.

Embodiment 4 Hereinafter, a fourth embodiment of the present invention will be described with reference to FIG. In the figure, elements having the same functions as those of the conventional power converter shown in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted.

14 is a GB / GDB command circuit, 15 is a GB / GDB status signal of the self-excited converter 2, and 16 is GB / GD.
A gate timing calculation circuit for calculating the GDB timing from the output of the B command circuit 14 and the GB / GDB state signal 15, 17 is a GB / GDB command, and 26 is a phase detection for obtaining a voltage phase from a voltage applied to the transformer 3. Circuit, 2
4 stores the phase of the voltage of the AC power system when the gate is blocked from the GB / GDB state signal 15 and the output of the phase detection circuit 26, and calculates the optimal gate deblock timing from the output of the GB / GDB command circuit 14. This is a storage operation circuit for outputting.

Next, the operation will be described. First, the phase of the voltage applied to the transformer 3, which is always the output of the instrument transformer, is calculated by the phase detection circuit 26. The voltage phase calculated by the phase detection circuit 26 is always traced by the storage calculation circuit 24, and the voltage phase at the moment when the self-excited converter 2 is gate-blocked is stored. Next, GB / GDB command circuit 1
When the GDB command is output from 4 to the storage operation circuit 24, the GDB command is output in the same phase as the voltage phase of the AC power system when the gate is blocked as described in paragraph [0035].

As described above, the conventional power converter shown in FIG. 10 does not have the gate timing operation circuit 16 when performing the gate deblocking after the self-excited converter 2 performs the gate blocking, so that the gate deblocking is performed. The timing is not always constant, and as shown in FIG. 2 and the paragraph number [0035], it was impossible to suppress the magnetization of the core of the transformer 3 when the gate was deblocked, but as shown in FIG. The power converter according to the first embodiment outputs the GDB command at the same phase as the voltage phase of the AC power system when the gate is blocked by using the gate timing calculation circuit 16, and thereby the transformer 3 when the gate is deblocked is output. It is possible to prevent the magnetic core from being demagnetized.

Embodiment 5 FIG. Hereinafter, a fifth embodiment of the present invention will be described with reference to FIG. In the figure, elements having the same functions as those of the conventional power converter shown in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 6, 5C and 5D are current detectors having a larger saturation current than 5A and 5B, and 27 is a current detector 5
This is an input switching circuit for switching between inputs A and 5C or inputs from current detectors 5B and 5D.

Next, the operation will be described. When an accident occurs in which one or two phases of the voltage of the AC power system 1 is grounded, an excessive zero-phase current flows through the AC power system 1 if the neutral point of the transformer 3 is grounded. . At this time, since the current detectors 5A and 5B used for normal control have a small saturation current due to high accuracy, they are saturated and it is difficult to detect an accurate current. Therefore, the input switching circuit 27 switches the current detectors 5C and 5D so as to be used for control, thereby performing control with more accurate current measurement values.

As described above, the conventional power converter shown in FIG. 10 does not have the two current detectors having different saturation characteristics and the input switching circuit for switching the input from the two current detectors. Or, in the event of an accident where two phases are grounded, an accurate current cannot be detected, and it is difficult to obtain an accurate voltage correction value to suppress the magnetic demagnetization of the core of the transformer 3, but as shown in FIG. The power conversion device according to the second embodiment
By switching the current detectors with three different saturation characteristics and the inputs from them in a timely manner, accurate current can be detected even in the event of a single-phase or two-phase ground fault in the power system.
It is possible to calculate a more accurate voltage correction value and to suppress the magnetism of the iron core of the transformer 3.

Embodiment 6 FIG. Hereinafter, a sixth embodiment of the present invention will be described with reference to FIG. In the figure, elements having the same functions as those of the conventional power converter shown in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 7, 5D is a current detector having a larger saturation current than 5B, 27 and 27A are input switching circuits for switching inputs from current detectors 5B and 5D and current detectors 5C and 5A, respectively, and 28 and 28A. Is a voltage drop detection circuit for detecting a drop in the voltage of the AC power system 1 from the output of the instrument transformer 8, 29 and 29A are voltage drop detection circuits 28
Output from the current detectors 5B and 5D and the current detector 5
This is an input switch for switching the input from A and 5C.

Next, the operation will be described. First, it is confirmed in advance by simulation or calculation how much the voltage will drop before an overcurrent occurs, and the value is set in the voltage drop detection circuit 28. If an accident occurs in the AC power system 1, a drop in the voltage of the AC power system 1 is detected from the output of the instrument transformer 8, and if it is equal to or less than the set value, the switch that selects the normal current detector 5B Is switched to select the current detector 5D, and the value is output.

As described above, the conventional power converter shown in FIG. 10 does not have two current detectors having different saturation characteristics and an input switching circuit for switching the input between them, so that a single-phase AC power system can be used. Alternatively, in the event of an accident where two phases are grounded, an accurate current cannot be detected, and it has been difficult to obtain an accurate voltage correction value to suppress the magnetic demagnetization of the iron core of the transformer 3, as shown in FIG. The power conversion device according to Embodiment 6
It has two different current detectors with different saturation characteristics, and switches the input from them when the voltage drops to detect the correct current even in the event of a single-phase or two-phase ground fault in the power system. By calculating an appropriate voltage correction value, it is possible to suppress the magnetic demagnetization of the iron core of the transformer 3.

Embodiment 7 FIG. Hereinafter, a seventh embodiment of the present invention will be described with reference to FIG. In the figure, elements having the same functions as those of the conventional power converter shown in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 8, 5D is a current detector having a larger saturation current than 5B, 27 is an input switching circuit for switching the input between 5B and 5D, and 30 is a maximum value for selecting the maximum value of the current detectors 5B and 5D. It is a detection circuit.

Next, the operation will be described. The maximum value detection circuit 30 compares the inputs from the current detection circuits 5B and 5D and selects the maximum value. This is because the output of the current detector 5B is selected at the time of normal current measurement by slightly lowering the transformation ratio of the current detector 5D, but the current detector 5B is saturated at the time of overcurrent detection. Since the output of the detector 5B reaches a plateau, as a result, the output of the current detector 5D is selected in the event of an accident in the AC power system 1.

As described above, the conventional power converter shown in FIG. 10 does not have the two current detectors having different saturation characteristics and the input switching circuit for switching the input between them. Alternatively, it was difficult to detect an accurate current at the time of an accident in which two phases were ground-faulted, and it was difficult to obtain an accurate voltage correction value to suppress the magnetism of the core of the transformer 3, as shown in FIG. The power conversion device according to the seventh embodiment
By having two different current detectors with different saturation characteristics, comparing them and selecting the maximum value, it detects the correct current even in the event of a single-phase or two-phase ground fault in the power system, and provides more accurate By calculating an appropriate voltage correction value, it is possible to suppress the magnetic demagnetization of the iron core of the transformer 3.

Embodiment 8 FIG. Hereinafter, an eighth embodiment of the present invention will be described with reference to FIG. In the figure, elements having the same functions as those of the conventional power converter shown in FIG. 10 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 9, 5E is a current detector for measuring a phase current flowing between each terminal of the transformer 3 and each terminal of the self-excited converter 2 instead of the winding current of the transformer 3, and 31 is an input switch. A zero-phase operation circuit that calculates the zero-phase component of the current of the AC power system 1 from the output of the circuit, and 32 is a winding current operation circuit that calculates the winding current of the transformer 3 from the phase current from the output of the current detector 5E. is there. The input switching circuit 27 is equivalent to the circuit shown in FIG. 6, FIG. 7, or FIG.

Next, the operation will be described. When an accident occurs in which one or two phases of the voltage of the AC power system 1 is grounded, an excessive zero-phase current flows through the AC power system 1 if the neutral point of the transformer 3 is grounded. . At this time, the operation of the input switching circuit 27 is the same as that described in the above-mentioned item 47, 51 or 55, and therefore the description is omitted. From the output of the input switching circuit 27, 3
The phase sum is calculated to calculate the zero-phase current. By subtracting the difference between the output from the input switching circuit and the zero-phase current by the subtractor 6A, a three-phase current not including the zero-phase current is obtained. On the other hand, when the transformer 3 has a star-delta connection as shown in FIG. 9, the zero-phase current circulates in the delta winding and is not measured by the current measuring device 5E. Accordingly, the three-phase current obtained by the subtracter 6A, in which the winding current of the transformer 3 that does not include the zero-phase component is calculated from the phase current from the output of the current detector 5E by the winding current calculation circuit 32, By subtracting the difference from the winding current force by the subtractor 6 and inputting the difference to the DC component detector 7, an accurate DC component included in the output voltage can be obtained.

As described above, the conventional power converter shown in FIG. 10 does not have the zero-phase operation circuit 31 for detecting the zero-phase current flowing on the star connection side of the transformer. If a single-phase or two-phase ground fault occurs in the AC power system 1 in a simple circuit, it is difficult to detect the DC component accurately by the DC component detector 7 and obtain an accurate voltage correction value at the time of the fault to obtain the transformer. Although it was difficult to suppress the magnetization of the iron core of the third embodiment, the power converter of the third embodiment shown in FIG. Since a three-phase current not including a zero-phase current can be obtained by subtraction, a more accurate DC component is detected from the output current of the current detector 5E, a more accurate voltage correction value is calculated, and the core of the transformer 3 is calculated. Can be suppressed.

[0067]

As described above, the power converter according to the first aspect of the present invention includes the gate timing operation circuit for calculating the timing from gate blocking to gate deblocking. The gate is deblocked based on the output GDB command, and the voltage is output based on the output voltage command. Therefore, the gate is deblocked at an erroneous timing and the transformer is continuously operated without demagnetizing the transformer. it can.

The gate timing calculation circuit of the power converter according to the second invention calculates the magnetic flux density of the transformer by integrating the voltage applied to the transformer, and calculates the magnetic flux when the gate is blocked. Since the position of the density is stored and the GDB command is output at the same position, the GDB timing can be calculated from the actual magnetic flux density of the iron core, and the optimum timing can be obtained.

Further, the gate timing operation circuit of the power converter according to the third invention stores the time of one cycle of the voltage of the AC line in advance, outputs the GDB command by the timer after gate blocking. Since the timing is calculated, the optimal timing for outputting the GDB command within one cycle can be reliably obtained when the voltage of the AC power system is restored.

Further, the gate timing calculation circuit of the power converter according to the fourth invention comprises a phase detection circuit for calculating the phase of the voltage of the AC line, stores the phase when the gate is blocked, and stores the phase and The GDB command is output in the same phase. Usually, since the self-excited converter includes the above-described phase detector, it is possible to obtain an optimal timing for outputting the GDB command without newly adding a magnetic flux calculation circuit or a timer counter.

Further, in the power converter according to the fifth invention, the voltage detector for detecting the voltage of the AC line, the current detector A for detecting each winding current of the transformer, and the current detector A A current detector B that detects the same current but has a low saturation current value and therefore has a low accuracy, an input selection circuit that selects the input from these current detectors whichever is more appropriate, and a current detection selected by these input selection circuits A DC component calculation circuit for calculating a DC component included in the output voltage of the converter from an output of the converter, a voltage command correction value calculation circuit for calculating a voltage command correction value from these DC component calculation circuits, In order to output a voltage based on the voltage command correction value and the voltage command correction value, even in the event of a system fault in which a zero-phase current flows such that the current measuring device used for steady-state control saturates, the transformer It is possible to reliably suppress the DC magnetic deviation.

Further, the input switching device of the power converter according to the sixth aspect of the present invention detects that the AC line is grounded or short-circuited from the output of the voltage detector, and switches the input from the current detector. Because of the circuit configuration, switching of the current detector when the voltage of the AC power system is lost can be easily and reliably realized.

Further, since the input selection circuit of the power converter according to the seventh aspect of the present invention is constituted by an arithmetic circuit for comparing the inputs from the current detectors and selecting the larger one, the switching can be performed rapidly. It can be performed without any accompanying problems, and can also cope with overcurrents other than when the system voltage is lost.

Further, in the power converter according to the eighth aspect, the same as the voltage detector for detecting the voltage of the AC line, the current detector for detecting each phase current connected to the transformer, and the current detector A A current detector B for detecting a current but having a low saturation current value because of a large saturation current value; an input selection circuit for selecting an input from these current detectors whichever is more appropriate; a current detector selected by these input selection circuits A zero-phase operation circuit for calculating a star-side zero-phase current from the output of the DC-DC converter included in the output voltage of the converter based on the output of the current detector selected by these input selection circuits and the zero-phase current And a voltage command correction value calculation circuit for calculating a voltage command correction value from these DC component calculation circuits, based on the output voltage command value and the voltage command correction value. Since so as to output the voltage, without detecting a winding current of the transformer directly, without being affected by the zero-phase current can be reliably suppressed DC magnetic deviation of the transformer.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a power conversion device according to Embodiment 1 of the present invention.

FIG. 2 is a diagram showing a relationship between a voltage applied to a transformer and a magnetic flux of the transformer.

FIG. 3 is a circuit diagram showing a power converter according to Embodiment 2 of the present invention.

FIG. 4 is a circuit diagram showing a power converter according to Embodiment 3 of the present invention.

FIG. 5 is a circuit diagram showing a power converter according to Embodiment 4 of the present invention.

FIG. 6 is a circuit diagram showing a power converter according to a fifth embodiment of the present invention.

FIG. 7 is a circuit diagram showing a power converter according to Embodiment 6 of the present invention.

FIG. 8 is a circuit diagram showing a power converter according to Embodiment 7 of the present invention.

FIG. 9 is a circuit diagram showing a power conversion device according to Embodiment 8 of the present invention.

FIG. 10 is a circuit diagram showing a conventional power converter.

[Explanation of symbols]

1 AC power system, 2 self-excited converter, 3 transformer,
4 DC voltage source, 5A, 5B, 5C, 5D, 5E Current detector, 6, 6A Subtractor, 7 DC component detector, 8
Instrument transformer, 9 voltage reference, 10 voltage command value creation circuit, 11 adder, 12 pulse width modulation control circuit, 13
Gate pulse amplifier circuit, 14 GB / GDB command circuit, 15 GB / GDB status signal, 16 Gate timing operation circuit, 17 GB / GDB command, 18 Transformer applied voltage, 19A, 19B Transformer magnetic flux, 20 Transformer residual magnetic flux, 21 GB timing, 22A, 22B G
DB timing, 23 magnetic flux calculation circuit, 24 storage calculation circuit, 25 timer counter, 26 phase detection circuit, 27, 27A input switching circuit, 28, 28A voltage drop detection circuit, 29, 29A input selection switch, 30
Maximum value selection circuit, 31 zero-phase operation circuit, 32 winding current operation circuit.

Claims (8)

[Claims] 1. A power converter connected to an AC system via a transformer, and a power converter capable of freely performing a gate block or a gate deblocking based on a command, and outputting a voltage based on an output voltage command. A power conversion device for outputting, comprising a gate timing calculation circuit for calculating timing from gate blocking to gate deblocking,
A power converter, wherein gate deblocking is performed based on a gate deblocking command output from the gate timing calculation circuit, and a voltage is output based on the output voltage command. 2. The gate timing calculation circuit calculates a magnetic flux density of the transformer by integrating a voltage applied to the transformer, and stores a position of the magnetic flux density when the gate is blocked and stores the same. 2. The power converter according to claim 1, further comprising an arithmetic circuit that outputs a gate deblocking command at a position. 3. The gate timing calculation circuit includes a circuit for storing in advance the time of one cycle of the voltage of the AC line, calculating the timing of outputting a gate deblocking command by a timer after gate blocking. The power conversion device according to claim 1, wherein the power conversion is performed. 4. The gate timing calculation circuit includes a phase detection circuit that calculates a phase of a voltage of the AC line,
2. The power conversion device according to claim 1, further comprising an arithmetic circuit that stores a phase at the time of gate blocking and outputs a gate deblocking command at the same phase as the phase. 5. A power converter, comprising: a power converter connected to an AC line via a transformer having a neutral point grounded, and outputting a voltage based on an output voltage command. A voltage detector for detecting, a first current detector for detecting each winding current of the transformer, a second current for detecting the same current as the first current detector but having a low saturation current value and a low accuracy. A detector, an input selection circuit for selecting an appropriate one of the inputs from the first and second current detectors, and an output from the first or second current detector selected by the input selection circuit. A DC component calculation circuit for calculating a DC component included in the output voltage of the converter,
A voltage command correction value calculation circuit that calculates a voltage command correction value based on a calculation result of the DC component calculation circuit, and outputs a voltage based on the output voltage command value and the voltage command correction value. Power converter. 6. The input selection circuit includes an arithmetic circuit that detects that an AC line is grounded or short-circuited from an output of the voltage detector, and switches an input from the first and second current detectors. The power conversion device according to claim 5, wherein: 7. The power conversion device according to claim 5, wherein the input selection circuit comprises an arithmetic circuit for comparing inputs from the current detector and selecting a larger value. 8. A power converter, comprising: a power converter connected to an AC line via a star-delta connection transformer having a neutral point grounded, and outputting a voltage based on an output voltage command. A voltage detector for detecting the voltage of the AC line, a first current detector for detecting each phase current connected to the transformer, and a current for detecting the same current as the first current detector. Current detector, an input selection circuit that selects an appropriate one of the inputs from the first and second current detectors, and the first and second signals selected by the input selection circuit. A zero-phase operation circuit for calculating a star-side zero-phase current from an output of the current detector, based on an output of the first or second current detector selected by the input selection circuit and the zero-phase current; Included in the output voltage of the above converter A DC component calculating circuit for calculating a DC component, a voltage command correction value calculating circuit for calculating a voltage command correction value from the DC component calculating circuit, and a voltage based on the output voltage command value and the voltage command correction value. A power conversion device characterized by outputting.