Power Conversion Systems

Abstract

To provide a power conversion system capable of reducing an adverse effect of a voltage drop accompanied with suppression of an excessive current.SOLUTION: In a power conversion system, a controller 50 includes: a voltage conversion part for converting a three-phase AC output voltage of a frequency converter 30 into two sets of single-phase AC output voltages with a 90-degree phase difference; a current converter for converting a three-phase AC output current of the frequency converter 30 into two sets of single-phase AC output currents with a 90-degree phase difference; and a voltage command value output part for restricting an AC output current of the frequency converter 30 by reducing a command value of one set of single-phase AC output voltage of two sets of single-phase AC output voltages converted by the voltage converter according to an excess content when one set of single-phase AC output current of two sets of single-phase AC output currents converted by the current converter is in excess of a fixed value between a fixed current and an excessive current protection level, and outputting an output voltage command value of a three-phase AC voltage based on the reduced command value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to a power conversion system. [Background technology]

[0002] Japan's power grid is roughly divided into two different frequencies: 50 Hz in the eastern region and 60 Hz in the western region. Therefore, if the power supply system that supplies power to AC electric railway cars that run through regions with different power grid frequencies is designed to operate exclusively at 60 Hz, a frequency converter (FC) is required to convert the power frequency from 50 Hz to 60 Hz.

[0003] The frequency converter is provided with a control device that suppresses overcurrent that flows when, for example, a short-circuit fault or a ground fault occurs in the power supply system during operation. This control device has the function of suppressing the overcurrent by suddenly reducing the output voltage of the frequency converter in response to the overcurrent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-80132 Summary of the Invention [Problem to be solved by the invention]

[0005] Among the above frequency converters, there is a type that outputs AC power converted to 60 Hz as three-phase AC power to a feeding substation. In order to make effective use of power, this feeding substation converts the three-phase AC power output from the frequency conversion device into two sets of single-phase AC power with a phase difference of 90 degrees, i.e., M-phase and T-phase single-phase AC power, using, for example, a Scott transformer, and supplies each single-phase AC power to a load, such as a train load.

[0006] By the above conversion, the transmission line between the feeding substation and the above load is divided into a transmission line related to single-phase AC power of M phase and a transmission line related to single-phase AC power of T phase. If a short-circuit fault or a ground fault occurs in only one of the transmission lines, for example, the transmission line related to the single-phase AC power at the M-phase, and the control device of the frequency converter suppresses the overcurrent by simply reducing the output voltage of the frequency converter, the voltage of both the transmission line related to the single-phase AC power at the M-phase and the transmission line related to the single-phase AC power at the T-phase where the fault does not occur will be reduced. In other words, the reduction will have an effect on the voltage of the transmission line that does not actually need to be reduced.

[0007] The problem to be solved by the present invention is to provide a power conversion system capable of reducing the effect of a voltage drop caused by suppressing an overcurrent occurring in one of two transmission lines for single-phase AC power between a feeding substation and a load. [Means for solving the problem]

[0008] The power conversion system in an embodiment is a power conversion system that supplies a three-phase AC output of a frequency conversion device to a load connected to a feeding substation, A voltage detected by a voltage sensor between the frequency conversion device and the feeding substation via a transformer, The three-phase AC output voltage of the frequency converter is converted into two sets of single-phase AC output voltages with a phase difference of 90 degrees. The amplitude calculation value of the two sets of single-phase AC output voltages is calculated by a voltage conversion unit; A current detected by a current sensor is output from the frequency conversion device to the feeding substation via the transformer. a current conversion unit that converts the three-phase AC output current of the frequency conversion device into two sets of single-phase AC output currents having a phase difference of 90 degrees; , the above One of two sets of single-phase AC output currents The amplitude calculation value of When the current exceeds a certain value between the rated current and the overcurrent protection level, For a constant value Depending on the excess, a voltage command value of the one set of single-phase AC output voltages from the frequency conversion device; The voltage conversion unit Required was The aforementioned Two sets of single-phase AC output voltages Amplitude calculation value of The single-phase AC output voltage of one of the sets A first voltage of the single-phase AC output voltage of the one set calculated based on the deviation from the amplitude calculation value. Reduce the command value Also, a second voltage command value is calculated as a new command value for the single-phase AC output voltage of the one set, a calculated amplitude value of the other of the two sets of single-phase AC output currents converted by the current conversion unit is obtained, and when this calculated amplitude value exceeds a certain value between a rated current and an overcurrent protection level, a second voltage command value is obtained as a new command value for the single-phase AC output voltage of the other set, by reducing a first voltage command value for the single-phase AC output voltage of the other set, the second voltage command value being obtained based on a deviation between a voltage command value for the single-phase AC output voltage of the other of the two sets of calculated amplitude values ​​for the single-phase AC output voltages obtained by the voltage conversion unit, in accordance with an amount by which this calculated amplitude value exceeds the certain value; , and the second voltage command value of the single-phase AC output voltage of the one set and the second voltage command value of the single-phase AC output voltage of the other set. Based on , by the inverter of the frequency conversion device Three-phase AC voltage An output voltage command value to the inverter of the frequency conversion device The frequency converter outputs an output voltage command value. inverter and a voltage command value output unit that limits the AC output current. [Effects of the Invention]

[0009] According to the present invention, it is possible to reduce the influence of a voltage drop caused by suppressing an overcurrent occurring in one of two transmission lines relating to single-phase AC power between a feeding substation and a load. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating an example of a power conversion system according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of functions of the control device of the power conversion system according to the embodiment. [Figure 3] FIG. 3 is a diagram showing an example of characteristics of the output voltage and the output current when control is performed by the control device of the power conversion system according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the embodiments will be described with reference to the drawings. FIG. 1 is a diagram illustrating an example of a power conversion system according to an embodiment. This power conversion system is, for example, a power conversion system for an electric railway, and includes an AC system 10, a transformer 20, a frequency converter 30 as a power conversion device, a transformer 40, and a control device 50 as a control device for the power conversion device.

[0012] The frequency conversion device 30 includes a converter 31 , a smoothing capacitor (DC link capacitor) 32 , and an inverter 33 . Transformer 20 converts the AC voltage of AC system 10, here a three-phase AC voltage of 50 Hz, into a predetermined voltage. Converter 31 of frequency conversion device 30 converts the voltage from transformer 20 into a DC voltage, for example, using a GTO thyristor. The DC voltage from the DC side terminal of converter 31 is input to the DC side terminal of inverter 33 via smoothing capacitor 32. Inverter 33 converts the voltage input from the DC side terminal into a three-phase AC voltage of a predetermined frequency, here 60 Hz, using, for example, a GTO thyristor. Transformer 40 converts the three-phase AC voltage from inverter 33 into a predetermined voltage and outputs it to a feeding substation (not shown).

[0013] The control device 50 inputs the AC output current flowing in the transmission line between the transformer 40 and the feeding substation, detected by a current sensor 51, and the AC output voltage of the transmission line between the transformer 40 and the feeding substation, detected by a voltage sensor 52, into a control circuit 53, and when the amplitude value of the AC output current of the inverter 33 in the control circuit 53 exceeds a certain value between the rated current and the overcurrent protection level, the voltage command value of the gate pulse of the inverter 33 is reduced according to the excess amount, thereby limiting the AC output current of the inverter 33.

[0014] FIG. 2 is a diagram illustrating an example of functions of the control device of the power conversion system according to the embodiment. As shown in FIG. 2, the control circuit 53 of the control device 50 has a system voltage side MT conversion and amplitude calculation unit 53a, a system voltage (equivalent to M-phase) automatic voltage regulator (AVR) 53b, an M-phase side overcurrent suppression control unit 53c, an M-phase side subtractor 53d, an M-phase side single-phase inverse dq conversion unit 53e, a system current side MT conversion unit 53f, a system voltage (equivalent to T-phase) automatic voltage regulator 53g, a T-phase side overcurrent suppression control unit 53h, a T-phase side subtractor 53i, and a T-phase side single-phase inverse dq conversion unit 53j, and further has an inverse MT conversion unit 53k.

[0015] The overcurrent suppression control unit 53c on the M side includes an amplitude calculation unit 53c1, a filter unit 53c2, a gain unit 53c3, and an excess amount detection unit 53c4. The overcurrent suppression control unit 53h on the T-side includes an amplitude calculation unit 53h1, a filter unit 53h2, a gain unit 53h3, and an excess amount detection unit 53h4.

[0016] The MT conversion and amplitude calculation unit 53a converts the three-phase AC voltage consisting of the R phase, S phase, and T phase of the transmission line between the frequency conversion device 30 and the feeding substation, which is the system voltage detected by the voltage sensor 52, into two sets of single-phase AC voltages, a first set of system voltage (equivalent to M phase) and a second set of system voltage (equivalent to T phase), determines the respective amplitude calculation values, outputs the amplitude calculation value of the system voltage (equivalent to M phase) to the automatic voltage adjustment unit 53b, and outputs the amplitude calculation value of the system voltage (equivalent to T phase) to the automatic voltage adjustment unit 53g.

[0017] The M-side automatic voltage adjustment unit 53b calculates the deviation between the voltage command value of the M-side output voltage from the frequency conversion device 30 and the amplitude calculation value of the system voltage (corresponding to the M-side), and calculates the M-side AC voltage control value based on this deviation.

[0018] The MT conversion unit 53f converts the three-phase AC current consisting of R phase, S phase, and T phase flowing through the transmission line between the transformer 40 and the feeding substation, which is the system current detected by the current sensor 51, into two sets of single-phase AC currents, a first set of system current (equivalent to M phase) and a second set of system current (equivalent to T phase), and outputs the system current (equivalent to M phase) to the overcurrent suppression control unit 53c and the system current (equivalent to T phase) to the overcurrent suppression control unit 53h.

[0019] An amplitude calculation unit 53c1 of the overcurrent suppression control unit 53c on the M-side outputs a calculated amplitude value of the grid current (corresponding to the M-side). This calculated amplitude value is subjected to dead band filtering by a filter unit 53c2 and amplified by a gain unit 53c3. If the amplified value exceeds a certain value, an excess detection unit 53c4 calculates a value proportional to the instantaneous value of the excess. This constant value is a value that is considered to be optimal among values ​​at which the AC output current flowing through the transmission line from the transformer 40 is between the rated current and the overcurrent protection level.

[0020] The AC voltage control value from automatic voltage adjustment unit 53b on the M-phase side is input to the + terminal of subtractor 53d, and the output value from excess amount detection unit 53c4 of overcurrent suppression control unit 53c is input to the - terminal of subtractor 53d. Subtractor 53d outputs the deviation between the AC voltage control value from automatic voltage adjustment unit 53b and the output value from excess amount detection unit 53c4. Single-phase inverse dq transformation unit 53e performs inverse dq transformation on the deviation output from subtractor 53d, and outputs an output voltage command value equivalent to the M-phase by inverter 33 to inverse MT conversion unit 53k.

[0021] In this way, the output from the excess detection unit 53c4 of the overcurrent suppression control unit 53c on the M-phase side is subtracted by the subtractor 53d from the output from the automatic voltage adjustment unit 53b, thereby reducing the output voltage command value equivalent to the M-phase by the inverter 33. This suppresses the overcurrent that flows to the inverter 33 due to a fault in the transmission line on the M-phase side between the feeding substation and the load.

[0022] The automatic voltage adjustment unit 53g on the T-side determines the deviation between the voltage command value of the T-side output voltage from the frequency conversion device 30 and the amplitude calculation value of the system voltage (equivalent to the T-side), and determines the AC voltage control value on the T-side based on this deviation.

[0023] An amplitude calculation unit 53h1 of the overcurrent suppression control unit 53h on the T-side outputs a calculated amplitude value of the grid current (equivalent to the T-side). This calculated amplitude value is filtered by a filter unit 53h2 to remove a dead band, and is amplified by a gain unit 53h3. If the amplified value exceeds a certain value, an excess detection unit 53h4 calculates a value proportional to the instantaneous value of the excess.

[0024] The AC voltage control value from automatic voltage adjustment unit 53g on the T-side is input to the + terminal of subtractor 53i, and the output value from excess detection unit 53h4 of overcurrent suppression control unit 53h is input to the - terminal of subtractor 53i. The subtractor 53i outputs the deviation between the AC voltage control value from automatic voltage adjustment unit 53g and the output value from excess detection unit 53h4. Single-phase inverse dq conversion unit 53j performs inverse dq conversion on the deviation output from subtractor 53i, and outputs an output voltage command value equivalent to T-side by inverter 33 to inverse MT conversion unit 53k.

[0025] In this way, the output from the excess detection unit 53h4 of the overcurrent suppression control unit 53h on the T-side is subtracted by the subtractor 53i from the output from the automatic voltage adjustment unit 53g, thereby reducing the output voltage command value equivalent to the T-side output by the inverter 33. This suppresses the overcurrent that flows to the inverter 33 due to a fault in the transmission line on the T-side between the feeding substation and the load.

[0026] The inverse MT conversion unit 53k receives as input the output voltage command value corresponding to the M phase from the single-phase inverse dq conversion unit 53e and the output voltage command value corresponding to the T phase from the single-phase inverse dq conversion unit 53J, performs inverse MT conversion on these values, and outputs an output voltage command value for a three-phase AC voltage consisting of the R phase, S phase, and T phase from the inverter 33 as a gate pulse for the inverter 33.

[0027] The output from the excess detection unit 53c4 of the overcurrent suppression control unit 53c on the M-side from the output from the automatic voltage adjustment unit 53b is subtracted by the subtractor 53d, thereby reducing the output voltage command value equivalent to the M-side by the inverter 33. Alternatively, the output from the excess detection unit 53h4 of the overcurrent suppression control unit 53h on the T-side from the output from the automatic voltage adjustment unit 53g is subtracted by the subtractor 53i, thereby reducing the output voltage command value equivalent to the T-side by the inverter 33. These results are reflected in the output voltage command value of the three-phase AC voltage output from the inverse MT conversion unit 53k.

[0028] The voltage of the transmission line related to the single-phase AC power of the M-phase in the transmission line between the feeding substation and the above-mentioned load is affected by the R-phase and T-phase output voltages from the frequency converter 30. In addition, the voltage of the transmission line related to the single-phase AC power of the T-phase in the transmission line between the feeding substation and the above-mentioned load is affected by the R-phase, S-phase, and T-phase output voltages from the frequency converter 30.

[0029] FIG. 3 is a diagram showing an example of characteristics of the output voltage and the output current when control is performed by the control device of the power conversion system according to the embodiment. Figure 3 shows that when an overcurrent occurs in the system current in the transmission line to the feeding substation (symbol a) due to a short-circuit fault or a ground fault occurring in the transmission line to the feeding substation, the system voltage is suddenly reduced during the fault circuit isolation time (symbol b), thereby controlling the system current to be below the overcurrent protection level (symbol c).

[0030] FIG. 3 also shows that after the above-described control of the system current, when power is restored (symbol e) after the momentary power outage time (symbol d), which is the reclosing time, the control circuit 53 returns the system voltage to the voltage before the occurrence of the short-circuit fault or ground fault.

[0031] In this embodiment, when a short-circuit fault or a ground fault occurs in only one of the transmission lines between the feeding substation and the above-mentioned load, for example, the transmission line related to the single-phase AC power of the M-phase, either the transmission line related to the single-phase AC power of the T-phase, the control device 50 of the frequency conversion device 30 does not simply reduce the output voltage of the frequency conversion device 30 in response to the overcurrent, but reduces the output voltage command value corresponding to the M-phase by suppressing the overcurrent on the M-phase side.

[0032] Then, since the output voltage of the frequency conversion device 30 is reduced in accordance with the result of reducing only the output voltage command value corresponding to the M-phase, the reduction does not affect the voltage corresponding to the T-phase of the transmission line, which does not actually need to have its voltage reduced. The same applies when a short-circuit fault or a ground fault occurs in the transmission line related to the single-phase AC power of the T-phase. Therefore, it is possible to reduce the impact of a voltage drop caused by suppressing an overcurrent that occurs in one of the transmission lines related to the two pairs of single-phase AC power between the feeding substation and the load.

[0033] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0034] 30...frequency conversion device, 31...converter, 33...inverter, 50...control device, 51...current sensor, 52...voltage sensor, 53...control circuit, 53a...MT conversion and amplitude calculation unit, 53b, 53g...automatic voltage adjustment unit, 53c, 53h...overcurrent suppression control unit, 53e, 53j...single-phase inverse dq conversion unit, 53f...MT conversion unit, 53k...inverse MT conversion unit.

Claims

1. A power conversion system that supplies a three-phase AC output of a frequency conversion device to a load connected to a feeding substation, a voltage conversion unit that converts a three-phase AC output voltage of the frequency conversion device between the frequency conversion device and the feeding substation via a transformer, the voltage being detected by a voltage sensor, into two sets of single-phase AC output voltages having a phase difference of 90 degrees, and calculates amplitude calculation values ​​of the two sets of single-phase AC output voltages; a current conversion unit that converts a three-phase AC output current of the frequency conversion device, which is detected by a current sensor and output from the frequency conversion device to the feeding substation via the transformer, into two sets of single-phase AC output currents having a phase difference of 90 degrees; a calculated amplitude value of one of the two sets of single-phase AC output currents converted by the current conversion unit is obtained, and when this calculated amplitude value exceeds a certain value between a rated current and an overcurrent protection level, a first voltage command value of the one set of single-phase AC output voltage obtained based on a deviation between a voltage command value of the one set of single-phase AC output voltage from the frequency conversion device and the calculated amplitude value of the one set of single-phase AC output voltage among the two sets of calculated amplitude values ​​of the single-phase AC output voltage obtained by the voltage conversion unit is reduced in accordance with the amount of excess over the certain value to obtain a second voltage command value which is a new command value of the one set of single-phase AC output voltage; determining a calculated amplitude value of the other of the two sets of single-phase AC output currents converted by the current conversion unit, and when this calculated amplitude value exceeds a certain value between a rated current and an overcurrent protection level, determining a second voltage command value that is a new command value for the other of the single-phase AC output voltages by reducing a first voltage command value for the other of the single-phase AC output voltages obtained based on a deviation between a voltage command value for the other of the two sets of calculated amplitude values ​​of the single-phase AC output voltages obtained by the voltage conversion unit, in accordance with an amount by which this calculated amplitude value exceeds the certain value; a voltage command value output unit that outputs an output voltage command value of a three-phase AC voltage by an inverter of the frequency conversion device, the output voltage command value being based on the second voltage command value of the single-phase AC output voltage of the one set and the second voltage command value of the single-phase AC output voltage of the other set, to the inverter of the frequency conversion device, thereby limiting the AC output current of the inverter of the frequency conversion device; A power conversion system comprising a control device having the following:

2. The voltage command value output unit of the control device When the single-phase AC output current of one of the sets exceeds the predetermined value, a voltage proportional to an instantaneous value of the excess over the predetermined value is applied. determining the second voltage command value for the single-phase AC output voltage of the one set by reducing the first voltage command value for the single-phase AC output voltage of the one set, the first voltage command value being determined based on a deviation between a voltage command value for the single-phase AC output voltage of the one set from the frequency conversion device and a calculated amplitude value for the single-phase AC output voltage of the one set determined by the voltage conversion unit; When the single-phase AC output current of the other set exceeds the predetermined value, the output voltage is increased in accordance with a value proportional to an instantaneous value of the excess over the predetermined value. determining the second voltage command value for the single-phase AC output voltage of the other set by reducing the first voltage command value for the single-phase AC output voltage of the other set, the first voltage command value being determined based on a deviation between a voltage command value for the single-phase AC output voltage of the other set from the frequency conversion device and a calculated amplitude value for the single-phase AC output voltage of the other set determined by the voltage conversion unit; A gate pulse command value of the frequency conversion device based on the second voltage command value of the single-phase AC output voltage of one set and the second voltage command value of the single-phase AC output voltage of the other set is calculated as an output voltage command value of a three-phase AC voltage by an inverter of the frequency conversion device, and is output to the inverter of the frequency conversion device, thereby limiting the AC output current of the inverter of the frequency conversion device. The power conversion system of claim 1 .

3. The voltage command value output unit of the control device a first voltage adjustment unit that outputs the first voltage command value of the one set of single-phase AC output voltages, the first voltage command value being calculated based on a deviation between a voltage command value of the one set of single-phase AC output voltages from the frequency conversion device and a calculated amplitude value of the one set of single-phase AC output voltages calculated by the voltage conversion unit; a first voltage command value output unit that, when the single-phase AC output current of the one set converted by the current conversion unit exceeds the certain value, outputs the second voltage command value of the single-phase AC output voltage of the one set by subtracting a value proportional to an instantaneous value of the excess from the first voltage command value of the single-phase AC output voltage of the one set output from the first voltage adjustment unit; a second voltage adjustment unit that outputs the first voltage command value for the single-phase AC output voltage of the other set, the first voltage command value being calculated based on a deviation between a voltage command value for the single-phase AC output voltage of the other set from the frequency conversion device and a calculated amplitude value for the single-phase AC output voltage of the other set calculated by the voltage conversion unit; a second voltage command value output unit that, when the single-phase AC output current of the other set converted by the current conversion unit exceeds the certain value, subtracts a value proportional to an instantaneous value of the excess from the first voltage command value of the single-phase AC output voltage of the other set output from the second voltage adjustment unit, thereby outputting the second voltage command value of the single-phase AC output voltage of the other set, The voltage command value output unit of the control device an output voltage command value for the three-phase AC voltage by an inverter of the frequency conversion device, based on the second voltage command value for the single-phase AC output voltage of one of the sets output from the first voltage command value output unit and the second voltage command value for the single-phase AC output voltage of the other set output from the second voltage command value output unit, by outputting to the frequency conversion device an output voltage command value for the inverter of the frequency conversion device; The power conversion system of claim 1 .

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