JP7007065B2 - Power converter - Google Patents

Description

Embodiments of the present invention relate to a power conversion device.

A power conversion device including a main circuit unit that performs AC / DC conversion between DC power and AC power is known. In such a power conversion device, a capacitor is provided in the main circuit portion for the purpose of suppressing noise. Further, in a power conversion device that handles a relatively large amount of power, a plurality of capacitors are connected in series to suppress the voltage applied to one capacitor.

In such a power conversion device, a failure such as a decrease in capacity or a short circuit may occur in any of the capacitors. Failure of such a capacitor causes failure of other capacitors connected in series and other elements of the main circuit section. Therefore, it has been proposed that the power conversion device detects the failure of each capacitor (for example, Patent Documents 1 and 2). For example, the failure of each capacitor is detected, and the operation of the main circuit unit is stopped according to the detection of any failure of each capacitor. This makes it possible to suppress chain failures of other capacitors and other elements in the main circuit section.

As a method for detecting a failure of each capacitor, for example, it is known that a voltage difference between two capacitors connected in series is calculated, and when this voltage difference exceeds a predetermined threshold value, it is determined as a failure.

However, it may be difficult to appropriately set the threshold value in the failure detection method due to the voltage difference. For example, if there is an initial error in the capacity of each capacitor and the current value flowing through each capacitor changes due to load fluctuation, the threshold value must be set to a value higher than the voltage difference that appears due to the initial error and current motorization. Therefore, it becomes difficult to detect the failure of each capacitor. Therefore, it is desired that the power conversion device can more reliably detect the failure of two capacitors connected in series.

Japanese Patent Application Laid-Open No. 2003-134662 Japanese Unexamined Patent Publication No. 2009-92505

An embodiment of the present invention provides a power conversion device capable of more reliably detecting a failure of two capacitors connected in series.

According to an embodiment of the present invention, a main circuit unit that performs AC / DC conversion between DC power and AC power, a converter provided in the main circuit unit that performs AC / DC conversion, and the main circuit unit said. The first capacitor provided between the converter and the load on the AC side, and the first capacitor provided between the converter and the load on the AC side in the main circuit section and via the load on the AC side . A second capacitor connected in series with the first capacitor, a first voltage detector that detects the voltage of the first capacitor, a second voltage detector that detects the voltage of the second capacitor, and the first capacitor. A failure detection unit for detecting a failure of the first capacitor and the second capacitor based on the voltage ratio of the voltage and the voltage of the second capacitor is provided , and the failure detection unit is provided with respect to the voltage ratio. A threshold value larger than 1 is set, and the voltage ratio is calculated using the larger of the voltage of the first capacitor and the voltage of the second capacitor as a molecule, and the calculated voltage ratio is equal to or higher than the threshold value. In certain cases, a power conversion device for detecting a failure of the first capacitor and the second capacitor is provided.

A power conversion device is provided that can more reliably detect a failure of two capacitors connected in series.

It is a block diagram schematically showing the power conversion apparatus which concerns on embodiment. 2 (a) and 2 (b) are reference graphs illustrating a method of detecting a capacitor failure due to a voltage difference. It is a flowchart which schematically shows an example of the operation of the power conversion apparatus which concerns on embodiment. It is a flowchart which shows the modification of the operation of the power conversion apparatus which concerns on embodiment schematically.

Hereinafter, each embodiment will be described with reference to the drawings.
It should be noted that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of the sizes between the parts, and the like are not necessarily the same as the actual ones. Further, even when the same part is represented, the dimensions and ratios may be different from each other depending on the drawing.
In the specification of the present application and each figure, the same elements as those described above with respect to the above-mentioned figures are designated by the same reference numerals, and detailed description thereof will be omitted as appropriate.

FIG. 1 is a block diagram schematically showing a power conversion device according to an embodiment.
As shown in FIG. 1, the power conversion device 10 includes a main circuit unit 12 and a control unit 14.

The main circuit unit 12 performs AC / DC conversion between DC power and AC power. In this example, the main circuit unit 12 is connected to the DC power source 2 and the load 4. The main circuit unit 12 converts the DC power supplied from the DC power source 2 into AC power, and supplies the converted AC power to the load 4. The main circuit unit 12 is a so-called inverter.

The DC power source 2 is, for example, a converter that converts AC power into DC power. The power conversion device 10 is, for example, a frequency conversion device that converts the supplied DC power into AC power having a frequency different from the frequency of the base AC power and supplies it to the load 4.

However, the power conversion device 10 is not limited to the frequency conversion device. The power conversion device 10 may be any device that performs AC / DC conversion. Contrary to the above, the main circuit unit 12 may be a circuit that converts AC power into DC power and supplies it to the load. Alternatively, the main circuit unit 12 may be a circuit that performs bidirectional conversion of conversion from DC power to AC power and conversion from AC power to DC power. That is, the configuration of the main circuit unit 12 may be any configuration capable of performing at least one of conversion from DC power to AC power and conversion from AC power to DC power.

The control unit 14 is connected to the main circuit unit 12. The control unit 14 controls the AC / DC conversion by the main circuit unit 12. A command value such as a current command or a voltage command is input to the control unit 14. The control unit 14 controls the AC / DC conversion of the main circuit unit 12 based on the input command value. The command value is input to the control unit 14 from, for example, a higher-level controller connected via a network or the like. The command value may be, for example, a preset constant value.

Further, the control unit 14 controls the AC / DC conversion of the main circuit unit 12 so that a substantially constant voltage is supplied to the load 4 based on, for example, a command value. When the AC power is supplied to the load 4, the control unit 14 controls the AC / DC conversion of the main circuit unit 12 so that a voltage having a substantially constant effective value is supplied to the load 4.

The power converter 10 further includes a converter 16, a first capacitor 21, a second capacitor 22, a first voltage detector 31, a second voltage detector 32, and a failure detection unit 40.

The converter 16 is provided in the main circuit unit 12. The converter 16 performs AC / DC conversion. For the converter 16, for example, an inverter circuit in which a plurality of switching elements are bridge-connected is used. The control unit 14 is connected to the converter 16 of the main circuit unit 12, and controls the operation of the converter 16 to control the AC / DC conversion by the main circuit unit 12. More specifically, the control unit 14 is connected to each switching element of the converter 16 and controls the switching of each switching element to control the AC / DC conversion by the main circuit unit 12. However, the configuration of the converter 16 is not limited to the above, and may be any configuration capable of performing AC / DC conversion.

The first capacitor 21 and the second capacitor 22 are provided in the main circuit unit 12. The first capacitor 21 is provided between one of the pair of output terminals (AC terminals) of the converter 16 and one end of the load 4. The second capacitor 22 is provided between the other end of the pair of output terminals of the converter 16 and the other end of the load 4. Therefore, the second capacitor 22 is connected in series with the first capacitor 21 in the main circuit unit 12 via the load 4.

The first capacitor 21 and the second capacitor 22 are, for example, an alternating current filter for resonating at the same frequency as the alternating current output from the converter 16 in order to cancel the inductance component on the circuit including the reactor of the converter 16. be.

However, the arrangement of the first capacitor 21 and the second capacitor 22 is not limited to the above. The first capacitor 21 and the second capacitor 22 may be connected in parallel to the load 4, for example. The first capacitor 21 and the second capacitor 22 may be, for example, a capacitor for DC smoothing provided between a pair of input terminals (DC terminals) of the converter 16. The position where the first capacitor 21 is provided may be any position of the main circuit unit 12. The position where the second capacitor 22 is provided may be any position connected in series with the first capacitor 21 in the main circuit unit 12.

The first capacitor 21 includes, for example, a plurality of capacitors 21c. Each capacitor 21c is connected in series and in parallel. Each capacitor 21c may be connected in series or in parallel. Like the first capacitor 21, the second capacitor 22 includes a plurality of capacitors 22c of at least one of series connection and parallel connection. The first capacitor 21 and the second capacitor 22 are, in other words, a capacitor unit including a plurality of capacitors 21c and 22c. However, if the first capacitor 21 and the second capacitor 22 have the same configuration, there is no problem even if they have 1 parallel-1 series to n parallel-m series. The first capacitor 21 and the second capacitor 22 may be one capacitor.

The first voltage detector 31 detects the voltage V1 of the first capacitor 21. The first voltage detector 31 is connected to the control unit 14. The first voltage detector 31 inputs the detection result of the voltage V1 of the first capacitor 21 to the control unit 14. The configuration of the first voltage detector 31 may be any configuration capable of detecting the voltage V1 of the first capacitor 21.

The second voltage detector 32 detects the voltage V2 of the second capacitor 22. The second voltage detector 32 is connected to the control unit 14. The second voltage detector 32 inputs the detection result of the voltage V2 of the second capacitor 22 to the control unit 14. The configuration of the second voltage detector 32 may be any configuration capable of detecting the voltage V2 of the second capacitor 22.

The failure detection unit 40 detects the failure of the first capacitor 21 and the second capacitor 22. The failure of the first capacitor 21 and the second capacitor 22 detected by the failure detection unit 40 is, for example, a decrease in the capacity of the first capacitor 21 and the second capacitor 22 or a short circuit.

The failure detection unit 40 is provided in the control unit 14. In the failure detection unit 40, the detection result of the voltage V1 of the first capacitor 21 by the first voltage detector 31 and the detection result of the voltage V2 of the second capacitor 22 by the second voltage detector 32 are combined with the control unit 14. Entered via. As a result, the failure detection unit 40 detects the failure of the first capacitor 21 and the second capacitor 22 based on the voltage ratio of the voltage V1 of the first capacitor 21 and the voltage V2 of the second capacitor 22.

More specifically, the failure detection unit 40 detects a state in which either the first capacitor 21 or the second capacitor 22 has failed. That is, the failure detection unit 40 detects a state in which the first capacitor 21 has failed or a state in which the second capacitor 22 has failed. In the state where the first capacitor 21 has failed, the second capacitor 22 may be normal, or a part of the second capacitor 22 may also have failed. In other words, the state in which the first capacitor 21 fails is a state in which the frequency of failure of the first capacitor 21 is higher than the frequency of failure of the second capacitor 22. The same applies to the state in which the second capacitor 22 fails.

When the failure detection unit 40 detects a failure of either the first capacitor 21 or the second capacitor 22, the control unit 14 stops the operation of the AC / DC conversion by the main circuit unit 12 (converter 16). As a result, for example, it is possible to prevent a serious failure of the first capacitor 21 and the second capacitor 22 and a failure of the converter 16 due to the failure of the first capacitor 21 and the second capacitor 22. Can be done.

The configuration of the failure detection unit 40 is not limited to the above. The failure detection unit 40 may be provided separately from the control unit 14, for example. For example, by having the failure detection unit 40 control switching between turning on and off the circuit breaker provided in the input / output unit of the main circuit unit 12, the main circuit unit 12 can be set to the DC power source 2 or a load according to the detection of the failure. It may be separated from 4.

For example, a method of detecting a failure of the first capacitor 21 and the second capacitor 22 by the voltage difference between the voltages V1 and V2 is known. For the voltage difference V_difference, the effective value of the voltage V1 is V1_rms, the effective value of the voltage V2 is V2_rms, the effective value of the current flowing through the first capacitor 21 and the second capacitor 22 is I_rms, the capacity of the first capacitor 21 is C1, and the second. When the capacitance of the capacitor 22 is C2 and the angular frequency is ω, it can be expressed as the following equation (1).

V_difference = V2_rms-V1_rms
= I_rms × (1 / C1-1 / C2) / ω ・ ・ ・ (1)

As described above, it is clear that the voltage difference V_difference depends on the current flowing through the first capacitor 21 and the second capacitor 22.

2 (a) and 2 (b) are reference graphs illustrating a method of detecting a capacitor failure due to a voltage difference.
2 (a) and 2 (b) show the relationship between the voltage difference and the threshold value depending on the presence or absence of the initial error of the capacities of the first capacitor 21 and the second capacitor 22.

FIG. 2A illustrates a case where the capacitances of the first capacitor 21 and the second capacitor 22 have no initial error and the capacitors C1 and C2 match. In this case, the voltage difference V_difference in the normal state becomes 0 from the equation (1). When the first capacitor 21 and the second capacitor 22 fail, the value obtained by multiplying the capacitance difference caused by the failure by the current appears as the voltage difference V_difference. Therefore, even when the current I_rms flowing through the first capacitor 21 and the second capacitor 22 fluctuates due to load fluctuations, for example, it is lower than the voltage difference range obtained by the failure, the capacitance difference to be detected, and the fluctuating current. By setting the threshold value Vth to the value, the failure of the first capacitor 21 or the second capacitor 22 can be detected.

On the other hand, FIG. 2B illustrates a case where there is an initial error in the capacities of the first capacitor 21 and the second capacitor 22, and there is a difference between the capacities C1 and C2. In this case, even in the normal state, a voltage difference occurs due to load fluctuations and the like. Therefore, when there is an initial error in the capacities of the first capacitor 21 and the second capacitor 22, the threshold value Vth is set to a value higher than the range of the voltage difference caused by the load fluctuation during normal operation as shown in FIG. 2 (b). Need to be set. In this way, when there is an initial error, the voltage difference range at normal times expands due to current value fluctuations, so depending on the current value fluctuations, it overlaps with the voltage difference range at the time of failure, making it difficult to set the threshold value Vth. It may become. For example, there is a concern that the failure is not detected even though the failure occurs, and the degree of the failure progresses.

On the other hand, the failure detection unit 40 according to the present embodiment fails in the first capacitor 21 and the second capacitor 22 based on the voltage ratio between the voltage V1 of the first capacitor 21 and the voltage V2 of the second capacitor 22. Is detected. The voltage ratio V_ratio can be expressed by the following equation (2).

V_ratio = V1 / V2
= (I_rms / (ω × C1)) / (I_rms / (ω × C2))
= C2 / C1 ... (2)

As described above, from the equation (2), the voltage ratio V_ratio enables detection without depending on the current. Therefore, by setting a predetermined threshold value Vth for the voltage ratio V_ratio, the failure detection unit 40 more reliably detects the failure of the first capacitor 21 and the second capacitor 22 without being affected by the current value fluctuation. can do.

FIG. 3 is a flowchart schematically showing an example of the operation of the power conversion device according to the embodiment.
As shown in FIG. 3, in the power conversion device 10, when the control unit 14 starts the control of AC / DC conversion by the main circuit unit 12, the first voltage detector 31 detects the voltage V1 of the first capacitor 21 and at the same time, it detects the voltage V1 of the first capacitor 21. , The second voltage detector 32 detects the voltage V2 of the second capacitor 22 (step S101 in FIG. 3). The detected voltages V1 and V2 are input to the failure detection unit 40.

When the failure detection unit 40 inputs the detection results of the voltages V1 and V2, the failure detection unit 40 determines whether or not the voltage V1 of the first capacitor 21 is larger than the voltage V2 of the second capacitor 22 (step S102 in FIG. 3). ).

When the failure detection unit 40 determines that the voltage V1 of the first capacitor 21 is larger than the voltage V2 of the second capacitor 22, the failure detection unit 40 calculates the voltage ratio V_ratio with the voltage V1 as the numerator and the voltage V2 as the denominator (FIG. 3). Step S103).

On the other hand, when the failure detection unit 40 determines that the voltage V1 of the first capacitor 21 is equal to or less than the voltage V2 of the second capacitor 22, the failure detection unit 40 calculates the voltage ratio V_ratio with the voltage V2 as the numerator and the voltage V1 as the denominator (FIG. 3). Step S104).

That is, the failure detection unit 40 calculates the voltage ratio V_ratio with the larger of the voltages V1 and V2 as the numerator. When the voltages V1 and V2 are the same, the voltage ratio V_ratio is "1". Therefore, when the voltage ratio V_ratio is calculated as described above, the voltage ratio V_ratio is larger than "1". When the voltages V1 and V2 are the same, either the voltage V1 or V2 may be set as the numerator.

After calculating the voltage ratio V_ratio, the failure detection unit 40 determines whether or not the voltage ratio V_ratio is equal to or higher than a predetermined threshold value Vth (step S105 in FIG. 3). As described above, in this example, the voltage ratio V_ratio is "1" or more. Therefore, the threshold value Vth is set to an arbitrary value of "1" or more. As a result, when the voltage ratio V_ratio becomes equal to or higher than the threshold value Vth, it can be reliably detected that either the first capacitor 21 or the second capacitor 22 is out of order.

When the failure detection unit 40 determines that the voltage ratio V_ratio is less than the threshold value Vth, the failure detection unit 40 detects the first capacitor 21 and the second capacitor 22 as normal, and returns to the process of step S101 (step S106 in FIG. 3).

On the other hand, when the failure detection unit 40 determines that the voltage ratio V_ratio is equal to or higher than the threshold value Vth, the failure detection unit 40 detects that either the first capacitor 21 or the second capacitor 22 has a failure (step S107 in FIG. 3).

When the failure detection unit 40 detects a failure of either the first capacitor 21 or the second capacitor 22, the control unit 14 stops the control of the AC / DC conversion by the main circuit unit 12. As a result, it is possible to prevent the degree of failure of either the first capacitor 21 or the second capacitor 22 from progressing or the converter 16 from failing in a chain reaction.

As described above, in the power conversion device 10 according to the present embodiment, the failure detection unit 40 is the first based on the voltage ratio V_ratio of the voltage V1 of the first capacitor 21 and the voltage V2 of the second capacitor 22. The failure of the capacitor 21 and the second capacitor 22 is detected. Thereby, as compared with the case where the failure of the first capacitor 21 and the second capacitor 22 is detected by the voltage difference V_difference, for example, the failure of the first capacitor 21 and the second capacitor 22 can be detected more reliably. In this way, it is possible to provide a power conversion device 10 that can more reliably detect a failure of two capacitors 21 and 22 connected in series.

FIG. 4 is a flowchart schematically showing a modified example of the operation of the power conversion device according to the embodiment.
The same reference numerals are given to those having substantially the same functions and configurations as those of the above-described embodiment, and detailed description thereof will be omitted.
As shown in FIG. 4, in this example, after the first voltage detector 31 detects the voltage V1 of the first capacitor 21 and the second voltage detector 32 detects the voltage V2 of the second capacitor 22. , The failure detection unit 40 calculates the voltage ratio V_ratio by V1 / V2 (steps S201 and S202 in FIG. 3).

After calculating the voltage ratio V_ratio, the failure detection unit 40 determines whether or not the calculated voltage ratio V_ratio is equal to or higher than the first threshold value Vth1 and equal to or lower than the second threshold value Vth2 (step S203 in FIG. 3). In other words, the failure detection unit 40 determines whether or not the voltage ratio V_ratio is in the range from the first threshold value Vth1 to the second threshold value Vth2.

When calculating the voltage ratio V_ratio as described above, when the voltage V1 is larger than the voltage V2, the voltage ratio V_ratio is larger than "1", and when the voltage V2 is larger than the voltage V1, the voltage ratio. V_ratio becomes smaller than "1". Therefore, by setting the first threshold value Vth1 to an arbitrary value smaller than "1" and setting the second threshold value Vth2 to an arbitrary value larger than "1", the first capacitor 21 and the second capacitor 22 Any failure can be reliably detected.

When the failure detection unit 40 determines that the voltage ratio V_ratio is equal to or higher than the first threshold value Vth1 and is equal to or lower than the second threshold value Vth2, the failure detection unit 40 detects the first capacitor 21 and the second capacitor 22 as normal, and returns to the process of step S201 (the process of step S201). Step S204 in FIG. 3).

On the other hand, when the failure detection unit 40 determines that the voltage ratio V_ratio is less than the first threshold Vth1, or determines that the voltage ratio V_ratio is larger than the second threshold Vth2, the first capacitor 21 and the second capacitor 22 (Step S205 in FIG. 3).

As described above, in this example, the failure detection unit 40 sets the first threshold Vth1 smaller than 1 and the second threshold Vth2 larger than 1 with respect to the voltage ratio V_ratio, and the voltage ratio V_ratio is the first. When it is less than the threshold value Vth1 or when the voltage ratio V_ratio is larger than the second threshold value Vth2, the failure of either the first capacitor 21 or the second capacitor 22 is detected. Also in this case, as in the above embodiment, the failure of the first capacitor 21 and the second capacitor 22 can be detected more reliably.

When the first threshold value Vth1 and the second threshold value Vth2 are set for the voltage ratio V_ratio, the voltage ratio V_ratio may be calculated by V2 / V1 contrary to the above.

Although some 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 implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and variations thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

2 ... DC power source, 4 ... Load, 10 ... Power converter, 12 ... Main circuit unit, 14 ... Control unit, 16 ... Converter, 21 ... 1st capacitor, 22 ... 2nd capacitor, 31 ... 1st voltage detection Instrument, 32 ... 2nd voltage detector, 40 ... Failure detector

Claims (1)

The main circuit section that performs AC / DC conversion between DC power and AC power,
A converter provided in the main circuit section and performing AC / DC conversion, and
A first capacitor provided between the converter and the load on the AC side in the main circuit section, and
A second capacitor provided between the converter and the load on the AC side in the main circuit unit and connected in series with the first capacitor via the load on the AC side ,
A first voltage detector that detects the voltage of the first capacitor,
A second voltage detector that detects the voltage of the second capacitor,
A failure detection unit that detects a failure of the first capacitor and the second capacitor based on the voltage ratio of the voltage of the first capacitor and the voltage of the second capacitor.
Equipped with
The failure detection unit sets a threshold value larger than 1 with respect to the voltage ratio, and calculates the voltage ratio by using the larger of the voltage of the first capacitor and the voltage of the second capacitor as molecules. A power conversion device that detects a failure of the first capacitor and the second capacitor when the calculated voltage ratio is equal to or higher than the threshold value .

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