WO2015059771A1

WO2015059771A1 - Power conversion device and power conversion method for power conversion device

Info

Publication number: WO2015059771A1
Application number: PCT/JP2013/078600
Authority: WO
Inventors: 大輔松元; 修治加藤
Original assignee: 株式会社日立製作所
Priority date: 2013-10-22
Filing date: 2013-10-22
Publication date: 2015-04-30

Abstract

The present invention addresses the problem of reducing the size of an initial charging resistor and suppressing ripple voltage in a power conversion device. A power conversion device (1) comprises: a converter (3) for, during a steady operation, outputting a DC voltage that is more than or equal to a first voltage (V1) and less than or equal to a second voltage; a smoothing capacitor (Cn) having nonlinear characteristics and smoothing the DC voltage output from the converter (3) during the steady operation, said nonlinear characteristics being such that a capacitance obtained when a voltage of the first voltage (V1) to the second voltage, inclusive, is applied to the smoothing capacitor (Cn) is larger than a capacitance obtained when a voltage of zero volts or more to less than the first voltage (V1) is applied to the smoothing capacitor (Cn); an initial charging resistor (Ri) for limiting the current flowing through the smoothing capacitor (Cn) during initial charging; a switch (4) for switching whether to perform initial charging to the smoothing capacitor (Cn) or to perform smoothing on the output of the converter (3) by the smoothing capacitor (Cn) during the steady operation; and a control circuit unit (5) for controlling the switch (4).

Description

Power conversion device and power conversion method for power conversion device

The present invention relates to a power conversion device using a smoothing capacitor and a power conversion method of the power conversion device.

The power conversion device includes a converter and a smoothing capacitor connected to the DC output terminal of the converter. Due to the operation of the switching element of the converter, the DC voltage output from the power conversion device has a waveform disturbance called a ripple voltage. By connecting a smoothing capacitor to the converter, electric energy is stored in the smoothing capacitor. Thereby, a ripple voltage can be suppressed, a DC voltage can be smoothed, and the load connected to a power converter device can function normally. Thus, the smoothing capacitor is an indispensable part of the power converter.

Patent Document 1 discloses a power conversion device using a nonlinear composite film capacitor composed of an antiferroelectric polymer particle composite as an energy storage component.

When the power converter is started, the smoothing capacitor is discharged, which is equivalent to a resistor having a resistance value of 0 [Ω]. Therefore, since a large current called an inrush current flows into the smoothing capacitor, each element constituting the power conversion device may be damaged. Therefore, a predetermined amount of charge must be charged to the smoothing capacitor when starting up the power converter. This operation is called initial charge. If the initial charging is completed, the power conversion device switches to steady operation.
The power conversion device connects a resistor having a predetermined resistance value between the smoothing capacitor and the power source, and suppresses an inrush current flowing into the smoothing capacitor during the initial charge. This resistor is called the initial charge resistor.

US Patent Application Publication No. 2011/0074361

The resistance value of the initial charging resistor needs to be determined according to the desired inrush current. At this time, the magnitude of the inrush current and the resistance value and dimension of the initial charging resistance are in a proportional relationship. By increasing the resistance value of the initial charging resistance, a larger inrush current can be suppressed, but there is a possibility that the component size becomes large, the power converter becomes large, and the component cost increases.

By reducing the smoothing capacitor capacity, the inrush current is reduced, and the resistance value of the initial charging resistor and its component dimensions can be reduced. However, if the smoothing capacitor capacity is reduced, the ripple voltage may increase during steady operation.

Therefore, an object of the present invention is to provide a power conversion device and a power conversion method for the power conversion device that have a small resistance value of the initial charging resistance and can suppress a ripple voltage during steady operation.

In order to solve the above-described problem, in the invention of the power conversion device of the present invention, during steady operation, the converter that outputs a DC voltage that is equal to or higher than the first voltage and equal to or lower than the second voltage; The capacitance is larger when the applied voltage is greater than or equal to the first voltage and less than or equal to the second voltage than the capacitance when the voltage is less than the first voltage, and the converter outputs during steady operation. A non-linear capacitor for smoothing the DC voltage, an initial charging resistor for limiting a current flowing through the non-linear capacitor at the time of initial charging, and an output during steady operation of the converter by the non-linear capacitor And a control circuit unit for controlling the switch.

In the invention of the power conversion method of the power conversion device of the present invention, the power conversion device includes a converter that outputs a direct current voltage that is equal to or higher than the first voltage and equal to or lower than the second voltage during steady operation, The electrostatic capacity when the applied voltage is higher than the first voltage and lower than the second voltage is larger than the electrostatic capacity when the voltage is lower than the first voltage, and the converter outputs during steady operation. A non-linear capacitor for smoothing the direct current voltage, an initial charging resistor for limiting a current flowing in the non-linear capacitor at the time of initial charging, a switch, and a control circuit unit. The control circuit unit controls the switch so as to perform initial charging to the nonlinear capacitor during initial charging, and to smooth the output of the converter by the nonlinear capacitor during steady operation, and during initial charging. Furthermore, control is performed so that the voltage applied to the nonlinear capacitor is a DC voltage lower than the first voltage.
Other means will be described in the embodiment for carrying out the invention.

According to the present invention, it is possible to provide a power conversion device and a power conversion method for the power conversion device that have a low initial charge resistance and can suppress a ripple voltage during steady operation.

It is a schematic block diagram which shows the initial charging circuit of the power converter device in 1st Embodiment. It is a flowchart which shows the initial charging process in 1st Embodiment. It is a graph which shows the characteristic of the accumulation charge amount with respect to the applied voltage of a linear capacitor and each nonlinear capacitor. It is a graph which shows the characteristic of the electrostatic capacitance with respect to the applied voltage of a linear capacitor and a nonlinear capacitor. It is a schematic block diagram which shows the initial charging circuit of the power converter device in 2nd Embodiment. It is a flowchart which shows the initial charging process in 2nd Embodiment. It is a schematic block diagram which shows the power converter device in 3rd Embodiment. It is a flowchart which shows the initial charging process in 3rd Embodiment.

Hereinafter, modes for carrying out the present invention (hereinafter referred to as “embodiments”) will be described in detail with reference to the drawings. In order to describe the embodiments, the same or related reference numerals are given to the same elements in the respective drawings. In each embodiment, the description of the same element is omitted without being repeated in principle.

(First embodiment)
FIG. 1 is a configuration diagram illustrating an outline of a power conversion device 1 according to the first embodiment.
As shown in FIG. 1, the power conversion device 1 includes a converter 3, a smoothing capacitor Cn, and an initial charging circuit 2. The output side of the converter 3 is connected to the initial charging circuit 2. The power conversion device 1 converts input power and supplies it to a connected load (not shown).
The converter 3 converts AC power into DC power and outputs it, and is connected to the smoothing capacitor Cn via the initial charging circuit 2.
The smoothing capacitor Cn smoothes the DC voltage output by the converter 3 during steady operation. The smoothing capacitor Cn is a capacitor having nonlinear characteristics (hereinafter referred to as “nonlinear capacitor”). The characteristics of this nonlinear capacitor will be described in detail with reference to FIGS.
The initial charging circuit 2 includes a charging power source Vd, an initial charging resistor Ri, a switch 4, and a control circuit unit 5, and is connected to the converter 3 and the smoothing capacitor Cn. The smoothing capacitor Cn, the charging power supply Vd, and the initial charging resistor Ri are electrically connected via a metal plate called a bus bar or a metal cable to form a series circuit. The initial charging circuit 2 performs an initial charging process for charging the smoothing capacitor Cn. This initial charging process will be described in detail with reference to FIG.
The charging power source Vd is a power source that supplies DC power, and applies a voltage V1 (first voltage) between a positive electrode and a negative electrode.
The switch 4 includes terminals 41 to 43, and switches between conduction between the

terminals

41 and 42 or conduction between the

terminals

41 and 43 according to a control signal. The switch 4 is controlled by the control circuit unit 5.

The control circuit unit 5 controls the initial charging circuit 2. The control circuit unit 5 outputs a control signal to the switch 4.
The positive side of the charging power source Vd is electrically connected to the terminal 42 of the switch 4 via the initial charging resistor Ri. A terminal 41 of the switch 4 is electrically connected to one end of the smoothing capacitor Cn. A terminal 43 of the switch 4 is electrically connected to the positive electrode side of the converter 3. The negative electrode side of charging power supply Vd is electrically connected to the other end of smoothing capacitor Cn and the negative electrode side of converter 3.

FIG. 2 is a flowchart showing the initial charging process in the first embodiment. Here, description will be made with reference to each part of FIG.
The control circuit unit 5 of the initial charging circuit 2 starts the initial charging process, for example, immediately after the power is supplied to the initial charging circuit 2. At this time, the smoothing capacitor Cn is in a discharged state.
In step S10, the control circuit unit 5 switches the switch 4 to the initial charge resistance Ri side. That is, the control circuit unit 5 controls the switch 4 so that the

terminals

41 and 42 are electrically connected. As a result, the charging power source Vd can be charged by passing a current through the smoothing capacitor Cn via the initial charging resistor Ri.

In step S11, the control circuit unit 5 waits for a predetermined time. The predetermined time is a time sufficiently longer than the time constants of the initial charging resistor Ri and the smoothing capacitor Cn of the initial charging circuit 2. Thereby, the control circuit unit 5 can charge the smoothing capacitor Cn with the voltage V1.
In step S12, the control circuit unit 5 switches the switch 4 to the converter 3 side. That is, the control circuit unit 5 controls the switch 4 so that the

terminals

41 and 43 are electrically connected. When the process of step S12 ends, converter 3 ends the initial charging process and performs steady operation.
As a result, the smoothing capacitor Cn can smooth the output voltage between the positive electrode side and the negative electrode side during the steady operation of the converter 3 and remove the ripple voltage of the converter 3.

FIG. 3 is a graph showing characteristics of the accumulated charge amount with respect to the applied voltage Vc of the linear capacitor and the first to third nonlinear capacitors. The vertical axis in FIG. 3 indicates the amount of charge [C] accumulated on the dielectric surface of each capacitor. The horizontal axis in FIG. 3 indicates the applied voltage Vc [V] of each capacitor.
A solid line La indicates a characteristic of a capacitor having a conventional linear characteristic (hereinafter referred to as “linear capacitor”). A solid line N1a indicates the characteristics of the first nonlinear capacitor used for the smoothing capacitor Cn of FIG. 1, for example. A broken line N2a indicates the characteristic of the second nonlinear capacitor. An alternate long and short dash line N3a indicates the characteristics of the third nonlinear capacitor. The linear capacitor and the first to third nonlinear capacitors are configured with the same volume. The first to third nonlinear capacitors have different characteristics. The correspondence between each line and each capacitor is common in FIGS. 3 and 4.
In the case of the linear capacitor indicated by the solid line La, the increase amount of the accumulated charge amount with respect to the increase of the applied voltage Vc maintains a predetermined value regardless of the applied voltage Vc.
In the case of the first nonlinear capacitor indicated by the solid line N1a, when the applied voltage Vc increases and exceeds the voltage V1, the increase in the amount of accumulated charge with respect to the increase in the applied voltage Vc increases rapidly. When the applied voltage Vc further increases and exceeds the voltage V2 (second voltage), the increase amount of the accumulated charge with respect to the increase of the applied voltage Vc decreases rapidly. The amount of increase in the accumulated charge amount with respect to the increase in the applied voltage Vc of the first nonlinear capacitor becomes the largest when the applied voltage Vc is between the voltage V1 and the voltage V2.
The characteristic curve of the accumulated charge amount of the second nonlinear capacitor indicated by the broken line N2a exists slightly on the lower voltage side than the characteristic curve of the accumulated charge amount of the first nonlinear capacitor. The characteristic curve of the accumulated charge amount of the third nonlinear capacitor indicated by the one-dot chain line N3a is further on the constant voltage side than the characteristic curve of the accumulated charge amount of the second nonlinear capacitor indicated by the broken line N2a. Other than that, the characteristics of the stored charge amount of the second and third nonlinear capacitors are the same as those of the first nonlinear capacitor.

The characteristics of the first to third nonlinear capacitors will be described in comparison with a linear capacitor.
The capacitor includes a dielectric and two electrodes separated by the dielectric. As shown in FIG. 3, the dielectric used for the linear capacitor has a characteristic that the amount of charge accumulated on the surface thereof increases linearly with respect to the change of the applied voltage Vc.
On the other hand, the first to third nonlinear capacitors use an antiferroelectric material between the electrodes. As shown in FIG. 3, the antiferroelectric material has a characteristic that the amount of charge accumulated on its surface changes nonlinearly with respect to the change of the applied voltage Vc. Here, the voltage V1 is set to be approximately equal to or lower than the coercive electric field of the dielectric of the first nonlinear capacitor. Thereby, in the first nonlinear capacitor, when the absolute value of the applied voltage Vc is less than the voltage V1, the increase amount of the accumulated charge amount with respect to the increase of the applied voltage Vc is smaller than the increase amount of the charge amount of the linear capacitor. On the other hand, in the first nonlinear capacitor, when the absolute value of the applied voltage Vc is not less than the voltage V1 and not more than the voltage V2, the increase in the accumulated charge amount with respect to the increase in the applied voltage Vc is an increase in the charge amount of the linear capacitor. Greater than the amount.

FIG. 4 is a graph showing the characteristics of the capacitance with respect to the applied voltage Vc of the linear capacitor and the first to third nonlinear capacitors. The vertical axis in FIG. 4 indicates the capacitance [μF] of each capacitor. The horizontal axis in FIG. 4 indicates the applied voltage Vc [V] of each capacitor.
A solid line Lb indicates the characteristics of the linear capacitor. A solid line N1b indicates the characteristic of the first nonlinear capacitor. A broken line N2b indicates the characteristic of the second nonlinear capacitor. An alternate long and short dash line N3b indicates the characteristics of the third nonlinear capacitor.

The capacitance is proportional to the quotient of the accumulated charge amount by the applied voltage Vc. Therefore, the slope of the accumulated charge amount shown in FIG. 3 is proportional to the capacitance shown in FIG. The applied voltage Vc at which the electrostatic capacitances of the first to third nonlinear capacitors shown in FIG. 4 reach the peak is the same as the applied voltage Vc that maximizes the slope of the accumulated charge amount shown in FIG.
Regardless of the applied voltage Vc, the linear capacitors have substantially the same capacitance. On the other hand, the capacitances of the first to third nonlinear capacitors vary depending on the applied voltage Vc.

When the applied voltage Vc is 0 [V] to the voltage V1, the capacitance of the first nonlinear capacitor is less than the capacitance of the linear capacitor.
When the applied voltage Vc increases and exceeds the voltage V1, the capacitance of the first nonlinear capacitor exceeds the capacitance of the linear capacitor.
When the applied voltage Vc is between the voltage V1 and the voltage V2, the capacitance of the first nonlinear capacitor is larger than the capacitance of the linear capacitor.
The capacitance of the first nonlinear capacitor is larger when the applied voltage Vc is between the voltage V1 and the voltage V2 than when the applied voltage Vc is from 0 [V] to the voltage V1.

(Difference between linear capacitor and nonlinear capacitor)
The initial charging circuit 2 (see FIG. 1) performs an initial charging process when the applied voltage Vc is lower than the voltage V1, and charges the smoothing capacitor Cn. When the first nonlinear capacitor is used as the smoothing capacitor Cn, the capacitance of the first nonlinear capacitor at the initial charge is smaller than the capacitance of the linear capacitor having the same volume. Therefore, since the inrush current at the start of the initial charge can be suppressed, the resistance value of the initial charge resistance Ri can be reduced. Therefore, it is possible to suppress the component size and the component cost related to the initial charging resistance Ri.

Furthermore, the converter 3 (see FIG. 1) smoothes the DC voltage output during the steady operation with the smoothing capacitor Cn. When the first nonlinear capacitor is used as the smoothing capacitor Cn, the capacitance of the first nonlinear capacitor during steady operation is larger than the capacitance of the linear capacitor having the same volume as this. Therefore, the smoothing capacitor Cn can effectively suppress the ripple voltage of the converter 3.

(Difference between the capacitance of the non-linear capacitor during the initial charge and the capacitance during steady operation)
Further, when the first nonlinear capacitor is used as the smoothing capacitor Cn, the electrostatic capacity at the initial charge is smaller than the electrostatic capacity at the steady operation and the impedance is large. During the initial charge, a large current called an inrush current flows through the smoothing capacitor Cn. The magnitude of the inrush current is inversely proportional to the sum of the impedance of the initial charging resistor Ri and the impedance of the smoothing capacitor Cn. The initial charging circuit 2 of the first embodiment outputs a DC voltage V1 from the charging power supply Vd, and controls so that the impedance of the smoothing capacitor Cn at the initial charging is larger than that at the steady operation. Therefore, the resistance value of the initial charging resistor Ri can be reduced, and the component size and component cost related to the initial charging resistor Ri can be suppressed.
During steady operation, converter 3 outputs a DC voltage not lower than voltage V1 and not higher than voltage V2. When this DC voltage is smoothed by the smoothing capacitor Cn, the capacitance of the smoothing capacitor Cn is larger than the capacitance at the time of initial charge. Therefore, the smoothing capacitor Cn can effectively suppress the ripple voltage of the converter 3.

In the case of a power converter having an output voltage characteristic different from that of the first embodiment, the second and third nonlinear capacitors having different characteristics are used as the smoothing capacitor Cn, and the charging power supply Vd is output in conjunction therewith. Adjust the DC voltage. As a result, the resistance value of the initial charging resistor Ri can be reduced, and the component dimensions and component costs associated with the initial charging resistor Ri can be suppressed.

(Second Embodiment)
The first charging circuit 2 of the first embodiment is limited to the one in which the charging power supply Vd outputs the voltage V1, and there is a problem that a circuit having an arbitrary power supply voltage cannot be used. The second embodiment solves this.
FIG. 5 is a configuration diagram illustrating an outline of a power conversion device 1A according to the second embodiment. The same code | symbol is provided to the element same as the power converter device 1 of 1st Embodiment shown in FIG.
As shown in FIG. 5, the initial charging circuit 2 </ b> A of the second embodiment includes a charging power source Vd <b> 2 that is different from the initial charging circuit 2 of the first embodiment, and further includes a voltage sensor 9.
The charging power source Vd2 is a power source that supplies DC power, and applies a voltage Vx between the positive electrode and the negative electrode. The voltage Vx is a voltage not lower than the voltage V1 and not higher than the voltage V2.
The voltage sensor 9 is connected between both terminals of the smoothing capacitor Cn, and the output side is connected to the control circuit unit 5. The voltage sensor 9 measures the applied voltage Vc to the smoothing capacitor Cn and notifies the control circuit unit 5 of applied voltage information.

FIG. 6 is a flowchart showing the initial charging process in the second embodiment. Here, description will be made with reference to each part of FIG.
The control circuit unit 5 of the initial charging circuit 2A starts the initial charging process, for example, immediately after the power is turned on to the initial charging circuit 2A. At this time, the smoothing capacitor Cn is in a discharged state.
In step S20, the control circuit unit 5 switches the switch 4 to the initial charge resistance Ri side. That is, the control circuit unit 5 controls the switch 4 so that the

terminals

41 and 42 are electrically connected. As a result, the charging power source Vd2 can be charged by passing a current through the smoothing capacitor Cn via the initial charging resistor Ri.

In step S21, the control circuit unit 5 measures the applied voltage Vc with the voltage sensor 9, and determines whether or not the applied voltage Vc is equal to or higher than the voltage V1. If the determination condition is not satisfied (No), the control circuit unit 5 repeats the process of step S21. If the determination condition is satisfied (Yes), the control circuit unit 5 performs the process of step S22. As described above, the initial charging circuit 2A initially charges the smoothing capacitor Cn with the voltage Vx exceeding the voltage V1, and determines whether or not the applied voltage Vc exceeds the voltage V1, and thus the initial charging process is terminated. The first charge can be completed quickly.
In step S22, the control circuit unit 5 switches the switch 4 to the converter 3 side. That is, the control circuit unit 5 controls the switch 4 so that the

terminals

41 and 43 are electrically connected. When the process of step S22 ends, converter 3 ends the initial charging process and performs steady operation.
As a result, the smoothing capacitor Cn can smooth the output voltage between the positive electrode side and the negative electrode side during the steady operation of the converter 3 and remove the ripple voltage of the converter 3.

(Third embodiment)
The power conversion device 1B of the third embodiment does not include the charging power source Vd of the first embodiment. In the third embodiment, the control of the converter is switched between the initial charging and the steady operation instead.
FIG. 7 is a schematic configuration diagram illustrating a power conversion device 1B according to the third embodiment.
The power conversion device 1B includes an initial charging resistor array Ri2, a switch array 4B, a converter 3B, a smoothing capacitor Cn, and an inverter 7, and is connected to a power supply unit 6 and a load 8.

The power supply unit 6 is a commercial power supply, for example, and is a three-phase AC power supply. The voltage of the power supply unit 6 is, for example, in the range of 10 to 1000 [V]. The AC frequency of the power supply unit 6 is, for example, in the range of 10 to 100 [Hz].
The initial charging resistor array Ri2 is composed of three resistors. The switch array 4B is composed of three switches. The three resistors of the initial charging resistor array Ri2 and the three switches of the switch array 4B are respectively connected in parallel between the three-phase AC terminal of the power supply unit 6 and the three-phase AC terminal of the converter 3B. It is connected.
The initial charging resistor array Ri2 is a resistor that limits the inrush current that flows through the smoothing capacitor Cn during the initial charging.

Switch array 4B is a switch that electrically connects the three-phase AC terminal of power supply unit 6 and the three-phase AC terminal of converter 3B during the steady operation of converter 3B.
The converter 3B is a two-level, three-phase PWM (Pulse Width Modulation) converter that converts AC power into DC power. Converter 3B includes an R-phase leg, an S-phase leg, and a T-phase leg, and the output side is connected to smoothing capacitor Cn.
In the R-phase leg, an R-phase upper arm in which the switching element QR1 and the rectifying element DR1 are connected in antiparallel and an R-phase lower arm in which the switching element QR2 and the rectifying element DR2 are connected in antiparallel are connected in series. . The R phase of the three-phase alternating current of the power supply unit 6 is connected to a node R that connects the R phase upper arm and the R phase lower arm.

In the S-phase leg, an S-phase upper arm in which the switching element QS1 and the rectifying element DS1 are connected in antiparallel and an S phase lower arm in which the switching element QS2 and the rectifying element DS2 are connected in antiparallel are connected in series. . The S phase of the three-phase alternating current of the power supply unit 6 is connected to a node S that connects the S phase upper arm and the S phase lower arm.
In the T-phase leg, a T-phase upper arm in which the switching element QT1 and the rectifying element DT1 are connected in anti-parallel and a T-phase lower arm in which the switching element QT2 and the rectifying element DT2 are connected in anti-parallel are connected in series. . The T phase of the three-phase alternating current of the power supply unit 6 is connected to a node T that connects the T-phase upper arm and the T-phase lower arm.

The smoothing capacitor Cn smoothes the DC voltage output by the converter 3B during steady operation. The characteristic of the smoothing capacitor Cn is the first nonlinear capacitor indicated by the solid line in FIGS. The DC voltage output from the converter 3B includes a ripple voltage. The smoothing capacitor Cn is for smoothing the DC voltage by suppressing the ripple voltage.

Inverter 7 is connected to the output side of converter 3 </ b> B, and its own AC output side is connected to load 8. The inverter 7 includes a U-phase leg, a V-phase leg, and a W-phase leg.
In the U-phase leg, a U-phase upper arm in which switching element QU1 and rectifying element DU1 are connected in antiparallel and a U-phase lower arm in which switching element QU2 and rectifying element DU2 are connected in antiparallel are connected in series. . A node U that connects the U-phase upper arm and the U-phase lower arm is connected to the U-phase among the three phases that drive the load 8.

In the V-phase leg, a V-phase upper arm in which the switching element QV1 and the rectifying element DV1 are connected in antiparallel and a V-phase lower arm in which the switching element QV2 and the rectifying element DV2 are connected in antiparallel are connected in series. . A node V that connects the V-phase upper arm and the V-phase lower arm is connected to the V phase of the three phases that drive the load 8.
In the W-phase leg, a W-phase upper arm in which switching element QW1 and rectifying element DW1 are connected in antiparallel and a W-phase lower arm in which switching element QW2 and rectifying element DW2 are connected in antiparallel are connected in series. . A node W that connects the W-phase upper arm and the W-phase lower arm is connected to the W-phase of the three phases that drive the load 8.

The control circuit unit 5B outputs a control signal to the gates of the respective switching elements QR1, QR2,... Of the converter 3B to switch between a conductive state (on state) and a non-conductive state (off state). Converts AC power to DC power. During steady operation, the DC power output from the converter 3B is smoothed by the smoothing capacitor Cn and input to the inverter 7 on the right side of FIG.
The control circuit unit 5B outputs a control signal to the gates of the switching elements QU1, QU2,... Of the inverter 7, switches between the conductive state and the non-conductive state, and converts the DC power supplied by the converter 3B into AC power. , Supplied to the load 8. The control circuit unit 5B further outputs a control signal to the switch array 4B to switch between steady operation and initial charge.

Here, each switching element QR1, QR2,..., Each switching element QU1, QU2,... Is, for example, GTO (Gate Turn-Off), IGBT manufactured using silicon, silicon carbide, gallium nitride, diamond or the like as a main material. (Insulated Gate Bipolar Transistor), MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), JFET (Junction Field Effect Transistor) and other single-element structures, or two or more of these semiconductor elements connected in series or in parallel It is.
For each rectifying element DR1, DR2,... And each rectifying element DU1, DU2,..., For example, a pn diode or Schottky barrier diode manufactured using the same material as the switching elements QR1, QR2,. Or a single structure of a semiconductor element such as a Schottky barrier diode in which these are mixed, or a structure in which two or more of these semiconductor elements are connected in series or in parallel.

The power converter 1B of the third embodiment is configured to output the output voltage of the converter 3B, which is a PWM converter connected to a three-phase AC power source such as a commercial power source, instead of the initial charging with the charging power source Vd of the first embodiment. Thus, the smoothing capacitor Cn is charged for the first time.
At the time of initial charging, the control circuit unit 5B controls the converter 3B so that the capacitance of the smoothing capacitor Cn is smaller than the capacitance of the linear capacitor having the same volume. That is, the control circuit unit 5B controls the converter 3B to output the voltage V1 from the voltage 0 [V].
During steady operation, the control circuit unit 5B controls the converter 3B so that the capacitance of the smoothing capacitor Cn is larger than the capacitance of the linear capacitor having the same volume. That is, the control circuit unit 5B performs control so that the converter 3B outputs the voltage V1 [V] or higher and the voltage V2 or lower.
According to the power conversion device 1B of the third embodiment, since the smoothing capacitor Cn is initially charged by the PWM converter, the applied voltage Vc of the smoothing capacitor Cn can be adjusted appropriately. Therefore, the initial charge resistance array Ri2 can be further reduced in size. Furthermore, the power conversion device 1B can smooth the ripple voltage more than the comparative example during steady operation.

FIG. 8 is a flowchart showing the initial charging process in the third embodiment. Here, description will be given with reference to each part of FIG.
The control circuit unit 5B starts the initial charging process, for example, immediately after the power conversion device 1B is turned on. At this time, the smoothing capacitor Cn is in a discharged state.

In step S30, control circuit unit 5B sets the DC voltage output from converter 3B to voltage V1.
In step S31, the control circuit unit 5B turns off all the switch arrays 4B. Thus, the converter 3B can be charged by passing a current through the smoothing capacitor Cn via the initial charging resistor array Ri2.

In step S32, the control circuit unit 5B waits for a predetermined time. This predetermined time is sufficiently longer than the time constants of the initial charging resistor array Ri2 and the smoothing capacitor Cn. Thereby, the control circuit unit 5B can charge the smoothing capacitor Cn with the voltage V1.
In step S33, the control circuit unit 5B turns on all the switch arrays 4B.
In step S34, control circuit unit 5B sets the DC voltage output from converter 3B to an arbitrary value not lower than voltage V1 and not higher than voltage V2, ends the initial charging process, and starts steady operation.
Thereby, the smoothing capacitor Cn can smooth the output voltage between the positive electrode side and the negative electrode side during the steady operation of the converter 3B, and can remove the ripple voltage of the converter 3B.

During steady operation, the converter 3B outputs a DC voltage not lower than the voltage V1 and not higher than the voltage V2, and applies it to the smoothing capacitor Cn which is a non-linear capacitor. Thereby, in 3rd Embodiment, compared with the case where a linear capacitor is used as the smoothing capacitor Cn, an electrostatic capacitance becomes large and it can suppress a ripple voltage.

(Modification)
The present invention is not limited to the embodiments described above, and includes various modifications. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. A part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.
In the above-described embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), particularly when clearly indicated and when clearly limited to a specific number in principle. Except, it is not limited to the specific number, and may be more or less than the specific number.

Furthermore, in the above-described embodiment, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and clearly considered essential in principle. This also applies to the above numbers (including the number, numerical value, quantity, range, etc.). Inductors, capacitances, resistance components, etc. that are parasitic on the circuit of the embodiment described above, and inductors, resistance components, capacitors, etc. that are arbitrarily arranged in circuit design, or a combination of inductors, resistors, capacitors, etc. The description of a general-purpose accessory device for providing an additional function such as a snubber circuit and a fuse is omitted.

The above-described configurations, functions, processing units, processing means, etc. may be partially or entirely realized by hardware such as an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by a processor interpreting and executing a program that realizes each function. Information such as programs, tables, and files for realizing each function may be stored in a recording device such as a memory, a hard disk, an SSD (Solid State Drive), or a recording medium such as a flash memory card or a DVD (Digital Versatile Disk). it can.

In each embodiment, the control lines and information lines indicate what is considered necessary for the explanation, and not all control lines and information lines on the product are necessarily shown. In practice, it may be considered that almost all the components are connected to each other.
Examples of modifications of the present invention include the following (a) to (e).

(A) In 1st Embodiment, the voltage which the power supply part 6 outputs may be arbitrary voltages which are more than voltage V1 and less than voltage V2. As a result, the power conversion device 1 charges the smoothing capacitor Cn to a sufficient voltage, and further reduces the inrush current to the smoothing capacitor Cn when switching from the initial charging state to the steady operation state. Can do.

(B) The minimum configuration in the third embodiment is only required to include the power supply unit 6, the initial charge resistor array Ri2, the converter 3B, and the smoothing capacitor Cn, and the inverter 7 is not an essential component.

(C) The power conversion device 1B of the third embodiment may further include a charging power source for charging the smoothing capacitor Cn, an initial charging resistor Ri, and the switch 4.

(D) In the power conversion device 1A of the second embodiment, the charging power supply Vd2 for charging the smoothing capacitor Cn may be configured to be able to output an arbitrary voltage by external control. As a result, the smoothing capacitor Cn can be initially charged more rapidly.

(E) The nonlinear capacitor and the initial charging method of the above embodiment can be applied to a power conversion device equipped with an MMC (ModularModMultilevel Converter). Particularly, it is suitable for a ZC (Zero-Sequence Canceling) type MMC-mounted power conversion device that transfers power to and from a load device connected to an output terminal or a power source by controlling a common mode (zero phase) component. .

1, 1A,

1B Power converter

2, 2A

Initial charging circuit

3, 3B Converter 4 Switch 4B Switch array Ri Initial charging resistor Ri2 Initial

charging resistor array

5, 5B Control circuit unit 6 Power supply unit 7 Inverter 8 Load 9 Voltage sensor Cn Smoothing Capacitor Vc Applied voltage V1 Voltage (first voltage)
V2 voltage (second voltage)
Vd, Vd2 Charging power supply

Claims

A converter that outputs a DC voltage not less than the first voltage and not more than the second voltage during steady operation;
Capacitance when the applied voltage is greater than or equal to the first voltage and less than or equal to the second voltage is greater than the capacitance when the applied voltage is greater than or equal to 0 volts and less than the first voltage, And a non-linear capacitor for smoothing the DC voltage output by the converter during steady operation;
An initial charging resistor that limits the current flowing through the nonlinear capacitor during initial charging; and
A switch for switching whether to perform initial charge to the nonlinear capacitor or to smooth the output during steady operation of the converter by the nonlinear capacitor;
A control circuit unit for controlling the switch;
A power conversion device comprising:
The control circuit unit further includes
At the time of initial charge, control is performed so that the voltage applied to the nonlinear capacitor is at least a DC voltage less than the first voltage.
The power conversion apparatus according to claim 1.
The control circuit unit further includes
If it is detected during initial charging that the voltage applied to the nonlinear capacitor is equal to or higher than the first voltage, the switch is controlled so as to smooth the output during steady operation of the converter by the nonlinear capacitor. ,
The power conversion apparatus according to claim 1.
The first voltage is lower than the coercive field of the dielectric of the nonlinear capacitor;
The power conversion apparatus according to claim 1.
It is further equipped with a direct current power supply for initial charging,
The switch switches whether the non-linear capacitor is connected to the initial charging resistor connected to the DC power source or to the converter.
The power conversion apparatus according to claim 1.
The DC power supply outputs a DC voltage less than the first voltage;
The power conversion device according to claim 5.
The initial charging resistor and the switch are connected in parallel to the AC side of the converter,
The power conversion apparatus according to claim 1.
At the time of initial charge, the capacitance of the nonlinear capacitor is smaller than the capacitance of a linear capacitor of the same volume,
The power conversion device according to claim 1, wherein the power conversion device is a power conversion device.
At the time of initial charge, the converter outputs a DC voltage less than the first voltage.
The power conversion device according to claim 7.
A converter that outputs a DC voltage not less than the first voltage and not more than the second voltage during steady operation;
Capacitance when the applied voltage is greater than or equal to the first voltage and less than or equal to the second voltage is greater than the capacitance when the applied voltage is greater than or equal to 0 volts and less than the first voltage, And a non-linear capacitor for smoothing the DC voltage output by the converter during steady operation;
An initial charging resistor that limits the current flowing through the nonlinear capacitor during initial charging; and
A switch,
A control circuit unit;
With
The control circuit unit is
At the time of initial charge, the first charge to the nonlinear capacitor is performed, and at the time of steady operation, the switch is controlled so as to smooth the output of the converter by the nonlinear capacitor,
Further, at the time of initial charge, control is performed so that the voltage applied to the non-linear capacitor becomes a DC voltage less than the first voltage.
A power conversion method of the power conversion device according to claim.