Power conversion device and control method thereof

Abstract

The present invention provides a power conversion device and a control method thereof. The power conversion device (10) comprises: a converter (12) for converting an AC voltage supplied from an AC power source (14) via a switch (16) into a DC voltage; a smoothing capacitor (18) for smoothing the DC voltage output from the converter; a resistor (20) for suppressing the current flowing into the smoothing capacitor; a switch (22) for short-circuiting both ends of the resistor; a filter (24) including a reactor (46U, 46V, 46W, 48U, 48V, 48W) and a capacitor (54U, 54V, 54W) for removing noise; and a control unit (64) for controlling the opening and closing of the switch and the switch, wherein when the voltage of the smoothing capacitor is less than a voltage threshold, the control unit changes the switch from an open state to a closed state in a state where the switch is open, and when the voltage of the smoothing capacitor is greater than the voltage threshold, the control unit changes the switch from an open state to a closed state in a state where the switch is closed.

Description

Technical Field

[0001] The invention relates to a power conversion device and a control method thereof. Background Art

[0002] Japanese Patent Application Publication No. 2019-013148 discloses a power conversion device that stops switching of a converter when the input voltage of the converter is greater than a set value. Japanese Patent Application Publication No. 2019-013148 can help prevent damage to electrical components. Summary of the invention

[0003] However, the technology described in Japanese Patent Application Publication No. 2019-013148 may not necessarily be able to satisfactorily prevent damage to switching elements and the like included in the converter.

[0004] An object of the present invention is to provide a power conversion device and a control method thereof that can satisfactorily prevent damage to a switching element or the like.

[0005] A power conversion device according to one embodiment of the present invention includes: a converter that converts an AC voltage supplied from an AC power source via a switch into a DC voltage; a smoothing capacitor that smoothes the DC voltage output from the converter; a resistor that is provided between the converter and the smoothing capacitor and suppresses current flowing into the smoothing capacitor; a switch that is connected in parallel with the resistor and can short-circuit both ends of the resistor; a filter that is provided between the switch and the converter and includes a reactor and a capacitor and is used to remove noise; and a control unit that controls the opening and closing of the switch and the switch, wherein when a voltage of the smoothing capacitor is less than a voltage threshold, the control unit changes the switch from an open state to a closed state in a state where the switch is open, and when the voltage of the smoothing capacitor is equal to or greater than the voltage threshold, the control unit changes the switch from the open state to the closed state in a state where the switch is closed.

[0006] In a control method of a power conversion device according to another aspect of the present invention, the power conversion device comprises: a converter that converts an AC voltage supplied from an AC power source via a switch into a DC voltage; a smoothing capacitor that smoothes the DC voltage output from the converter; a resistor that is provided between the converter and the smoothing capacitor and suppresses current flowing into the smoothing capacitor; a switch that is connected in parallel with the resistor and can short-circuit both ends of the resistor; a filter that is provided between the switch and the converter and includes a reactor and a capacitor and is used to remove noise; and a control unit that controls the switch and the switch. The control method of the power conversion device comprises the following steps: a step of determining whether the voltage of the smoothing capacitor is above a voltage threshold; and a step of changing the switch from an open state to a closed state. In the step of changing the switch from the open state to the closed state, when the voltage of the smoothing capacitor is less than the voltage threshold, the switch is changed from the open state to the closed state in an open state, and when the voltage of the smoothing capacitor is above the voltage threshold, the switch is changed from the open state to the closed state in a closed state.

[0007] According to the present invention, it is possible to provide a power conversion device and a control method thereof that can satisfactorily prevent damage to a switching element or the like.

[0008] The above-mentioned objects, features and advantages can be easily understood from the following description of the embodiments explained with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a diagram showing the structure of a power conversion device according to one embodiment.

[0010] Figure 2A and Figure 2B This is a diagram showing an example of changes in voltage of each part when the switch is changed from an open state to a closed state.

[0011] Figure 3 This is a flowchart showing the operation of the power conversion device according to one embodiment.

[0012] Figure 4 It is a diagram showing a configuration of a power conversion device according to a modified example of one embodiment. DETAILED DESCRIPTION

[0013] Hereinafter, a power conversion device and a control method thereof according to the present invention will be described in detail with reference to the accompanying drawings by listing preferred embodiments.

[0014] [One embodiment]

[0015] use Figure 1 to Figure 3 A power conversion device and a control method thereof according to an embodiment will be described. Figure 1 It is a diagram showing the configuration of the power conversion device according to the present embodiment.

[0016] like Figure 1 As shown, the power conversion device 10 of the present embodiment includes a converter 12. The converter 12 converts an AC voltage supplied from an AC power source 14 via a switch 16 into a DC voltage. The converter 12 is, for example, a known pulse width modulation (PWM) converter, but is not limited thereto.

[0017] The AC power source 14 is, for example, a multi-phase AC power source that supplies multi-phase voltages, more specifically, a three-phase AC power source, but is not limited thereto. The AC power source 14 can supply, for example, U-phase, V-phase, and W-phase voltages that are 120 degrees out of phase.

[0018] The switch 16 is used to turn on and off the supply of the AC voltage from the AC power source 14 to the power conversion device 10. As the switch 16, for example, an electromagnetic contactor, a circuit breaker, etc. can be used, but the present invention is not limited thereto.

[0019] The power conversion device 10 further includes a filter 24. The filter 24 is provided between the switch 16 and the converter 12. The filter 24 can remove noise transmitted from the converter 12 side to the AC power source 14 side, and can remove noise transmitted from the AC power source 14 side to the converter 12 side.

[0020] The converter 12 includes a rectifier circuit 30. The rectifier circuit 30 rectifies an AC voltage supplied from the AC power source 14 via the switch 16 into a DC voltage.

[0021] The rectifier circuit 30 includes power element portions 32U, 32V, and 32W corresponding to the respective phases of the AC power source 14 .

[0022] The power element unit 32U corresponding to U includes a diode 36Uu on the upper arm side, a diode 36Ud on the lower arm side, a switching element (semiconductor switching element) 34Uu on the upper arm side, and a switching element 34Ud on the lower arm side.

[0023] The power element unit 32V corresponding to V includes a diode 36Vu on the upper arm side, a diode 36Vd on the lower arm side, a switching element 34Vu on the upper arm side, and a switching element 34Vd on the lower arm side.

[0024] The power element unit 32W corresponding to W includes a diode 36Wu on the upper arm side, a diode 36Wd on the lower arm side, a switching element 34Wu on the upper arm side, and a switching element 34Wd on the lower arm side.

[0025] When describing the diode on the upper arm side in general, the symbol 36u is used, and when describing each diode on the upper arm side, the symbols 36Uu, 36Vu, and 36Wu are used. In addition, when describing the diode on the lower arm side in general, the symbol 36d is used, and when describing each diode on the lower arm side, the symbols 36Ud, 36Vd, and 36Wd are used.

[0026] When describing the switching element in general, the symbol 34 is used, and when describing each switching element, the symbols 34Uu, 34Ud, 34Vu, 34Vd, 34Wu, and 34Wd are used. In addition, when describing the switching element on the upper arm side in general, the symbol 34u is used, and when describing each switching element on the upper arm side, the symbols 34Uu, 34Vu, and 34Wu are used. In addition, when describing the switching element on the lower arm side in general, the symbol 34d is used, and when describing each switching element on the lower arm side, the symbols 34Ud, 34Vd, and 34Wd are used. The switching element 34 may be, for example, an insulated gate bipolar transistor (IGBT), but is not limited to this. A FET (Field Effect Transistor) may also be used as the switching element 34.

[0027] The diode 36u on the upper arm side and the diode 36d on the lower arm side are connected in series. The cathode of the diode 36u on the upper arm side is connected to one output line 42u. The anode of the diode 36u on the upper arm side is connected to the cathode of the diode 36d on the lower arm side. The anode of the diode 36d on the lower arm side is connected to another output line 42d.

[0028] The switching element 34u on the upper arm side and the switching element 34d on the lower arm side are connected in series with each other. The first terminal of the switching element 34u on the upper arm side is connected to the cathode of the diode 36u on the upper arm side. When the switching element 34 is, for example, an IGBT, the first terminal is the collector, and when the switching element 34 is, for example, a FET, the first terminal is one of the source and the drain. The second terminal of the switching element 34u on the upper arm side is connected to the anode of the diode 36u on the upper arm side. When the switching element 34 is, for example, an IGBT, the second terminal is the emitter, and when the switching element 34 is, for example, a FET, the second terminal is the other of the source and the drain. The first terminal of the switching element 34d on the lower arm side is connected to the cathode of the diode 36d on the lower arm side. The second terminal of the switching element 34d on the lower arm side is connected to the anode of the diode 36d on the lower arm side.

[0029] The U-phase voltage, i.e., the U-phase voltage, is supplied to the node 38U, which is connected to the anode of the diode 36Uu on the upper arm side, the second terminal of the switching element 34Uu on the upper arm side, the cathode of the diode 36Ud on the lower arm side, and the first terminal of the switching element 34Ud on the lower arm side.

[0030] The V-phase voltage, i.e., the V-phase voltage, is supplied to the node 38V, which is connected to the anode of the diode 36Vu on the upper arm side, the second terminal of the switching element 34Vu on the upper arm side, the cathode of the diode 36Vd on the lower arm side, and the first terminal of the switching element 34Vd on the lower arm side.

[0031] The W-phase voltage, i.e., the W-phase voltage, is supplied to the node 38W, which is connected to the anode of the diode 36Wu on the upper arm side, the second terminal of the switching element 34Wu on the upper arm side, the cathode of the diode 36Wd on the lower arm side, and the first terminal of the switching element 34Wd on the lower arm side.

[0032] The power conversion device 10 further includes a smoothing capacitor 18. The smoothing capacitor 18 is provided at a subsequent stage of the converter 12. One end of the smoothing capacitor 18 is connected to one output line 42u. The other end of the smoothing capacitor 18 is connected to another output line 42d. The smoothing capacitor 18 smoothes the DC voltage output from the converter 12, that is, the DC voltage rectified by the rectifier circuit 30.

[0033] The power conversion device 10 further includes a resistor 20. The resistor 20 is provided on one output line 42u. The resistor 20 is located between the converter 12 and the smoothing capacitor 18. One end of the resistor 20 is electrically connected to the diode 36u on the upper arm side and the switching element 34u on the upper arm side via one output line 42u. The other end of the resistor 20 is connected to one end of the smoothing capacitor 18 via one output line 42u.

[0034] The power conversion device 10 further includes a switch 22. The switch 22 is connected in parallel with the resistor 20. The switch 22 can short-circuit both ends of the resistor 20. When the switch 22 is closed, both ends of the resistor 20 are in a short-circuited state. When the switch 22 is opened, both ends of the resistor 20 are in a non-short-circuited state.

[0035] When the switch 22 is opened, the converter 12 starts converting the AC voltage to the DC voltage. Therefore, when the converter 12 starts converting the AC voltage to the DC voltage, the resistor 20 can suppress a large inrush current from flowing into the smoothing capacitor 18. After the smoothing capacitor 18 is sufficiently charged, the switch 22 is closed.

[0036] The filter 24 includes reactors 46U, 46V, and 46W. One end of the reactors 46U, 46V, and 46W is connected to input / output terminals 44U, 44V, and 44W at one end of the filter 24, respectively. The AC voltage from the AC power supply 14 is supplied to the input / output terminals 44U, 44V, and 44W at one end of the filter 24 through the switch 16, respectively.

[0037] The filter 24 further includes reactors 48U, 48V, and 48W. The other ends of the reactors 46U, 46V, and 46W are connected to one ends of the reactors 48U, 48V, and 48W, respectively. The other ends of the reactors 48U, 48V, and 48W are connected to input / output terminals 50U, 50V, and 50W at the other end of the filter 24, respectively. The input / output terminals 50U, 50V, and 50W at the other end of the filter 24 are connected to nodes 38U, 38V, and 38W, respectively.

[0038] The filter 24 further includes resistors 52U, 52V, and 52W. The resistors 52U, 52V, and 52W are resistors for suppressing resonance, that is, damping resistors. Nodes 53U, 53V, and 53W connected to the other ends of the reactors 46U, 46V, and 46W and one end of the reactors 48U, 48V, and 48W are connected to one end of the resistors 52U, 52V, and 52W, respectively.

[0039] The filter 24 further includes capacitors 54U, 54V, and 54W. When describing capacitors in general, reference numeral 54 is used, and when describing individual capacitors, reference numerals 54U, 54V, and 54W are used. One end of the capacitors 54U, 54V, and 54W is connected to the other end of the resistors 52U, 52V, and 52W, respectively.

[0040] The filter 24 further includes resistors 56U, 56V, and 56W. When describing the resistors in general, the symbol 56 is used, and when describing the individual resistors, the symbols 56U, 56V, and 56W are used. The resistors 56U, 56V, and 56W are connected in parallel to the capacitors 54U, 54V, and 54W, respectively. The resistors 56U, 56V, and 56W are used to discharge the charges accumulated in the capacitors 54U, 54V, and 54W.

[0041] The other ends of the capacitors 54U, 54V, and 54W are connected to each other.

[0042] The power conversion device 10 further includes a voltage sensor (detection unit) 28. One input terminal of the voltage sensor 28 is connected to one end of the smoothing capacitor 18. The other input terminal of the voltage sensor 28 is connected to the other end of the smoothing capacitor 18. The voltage sensor 28 can detect the voltage of the smoothing capacitor 18, that is, the voltage across the smoothing capacitor 18.

[0043] The power conversion device 10 further includes a PWM control circuit 29. The PWM control circuit 29 is used to perform PWM control on the converter 12. Specifically, the PWM control circuit 29 applies a voltage to the third terminal (gate) of the switching element 34 based on a signal (command) supplied from the control unit 64, thereby switching the switching element 34. The PWM control circuit 29 can adjust the output voltage, that is, adjust the voltage across the smoothing capacitor 18, etc. by appropriately switching the switching element 34.

[0044] The power conversion device 10 further includes a control device 26. The control device 26 is responsible for the overall control of the power conversion device 10. The control device 26 includes a computing unit 58 and a storage unit 60. The computing unit 58 may be composed of, for example, a CPU (Central Processing Unit), etc., but is not limited thereto. The storage unit 60 includes, for example, a volatile memory not shown in the figure and a non-volatile memory not shown in the figure. As a volatile memory, for example, a RAM (Random Access Memory) can be cited. As a non-volatile memory, for example, a ROM (Read Only Memory), a flash memory, etc. can be cited. Programs, data, tables, etc. can be stored in the storage unit 60.

[0045] The calculation unit 58 includes a determination unit 62 and a control unit 64. The determination unit 62 and the control unit 64 can be realized by the calculation unit 58 executing a program stored in the storage unit 60.

[0046] Determining unit 62 determines whether the voltage across smoothing capacitor 18 is equal to or greater than a voltage threshold. Specifically, determining unit 62 determines the voltage across smoothing capacitor 18 based on information supplied from voltage sensor 28. The voltage threshold is a threshold for determining whether the voltage across smoothing capacitor 18 is sufficiently high.

[0047] The control unit 64 can control the opening and closing of the switch 16. When the switch 16 is closed, the AC voltage supplied from the AC power source 14 is supplied to the converter 12 via the switch 16 and the filter 24. When the switch 16 is open, the AC voltage is not supplied to the filter 24 and the converter 12.

[0048] The control unit 64 can control the opening and closing of the switch 22. As described above, when the switch 22 is closed, both ends of the resistor 20 are in a short-circuited state. As described above, when the switch 22 is opened, both ends of the resistor 20 are in a non-short-circuited state.

[0049] The control unit 64 can generate a signal (command) to be supplied to the PWM control circuit 29 based on information obtained from a voltage sensor, a current sensor, etc. (not shown), for example. The control unit 64 can adjust the output voltage, that is, adjust the voltage across the smoothing capacitor 18, etc., by appropriately switching the switching element 34 using the PWM control circuit 29.

[0050] A voltage corresponding to the line voltage of the three-phase AC is applied to both ends of the capacitor 54. Charge corresponding to the applied voltage is accumulated in the capacitor 54. When the switch 16 changes from the closed state to the open state, the charge accumulated in the capacitor 54 at this time starts to discharge via the resistor 56. In a stage where the time from the moment when the switch 16 changes from the closed state to the open state is relatively short, the charge accumulated in the capacitor 54 is not completely discharged, and the voltage across the capacitor 54 is still large. When the switch 16 changes from the open state to the closed state, a resonant voltage may be generated in the filter 24. When the period during which the switch 16 that has changed to the open state returns to the closed state again is relatively short, and when the phase of the line voltage when the switch 16 changes to the open state is opposite to the phase of the line voltage when the switch 16 returns to the closed state, the peak value of the resonant voltage may become significantly larger. When a resonant voltage with a significantly large peak value is applied to the switching element 34, the switching element 34 may be damaged.

[0051] However, when the period during which the switch 16 that has been switched to the open state is returned to the closed state is relatively short, the voltage of the smoothing capacitor 18 is still in a high state. If the resistor 20 is short-circuited by the switch 22, the peak value of the resonant voltage is clamped to the voltage of the smoothing capacitor 18, and thus does not increase significantly. Therefore, in the present embodiment, when the period during which the switch 16 that has been switched to the open state is returned to the closed state is relatively short, that is, when the voltage of the smoothing capacitor 18 is equal to or higher than the voltage threshold, the switch 16 is switched from the open state to the closed state with the switch 22 closed. In addition, even if the switch 16 is switched from the open state to the closed state with the switch 22 closed, since the voltage of the smoothing capacitor 18 is high, a large inrush current does not flow into the smoothing capacitor 18.

[0052] Figure 2A and Figure 2B 1 is a diagram showing an example of changes in voltage of each part when the switch is changed from an open state to a closed state. Figure 2A , a comparative example is shown, that is, an example of a case where the resistor 20 is not short-circuited by the switch 22. Figure 2B FIG. 2 shows an example of the present embodiment, that is, a case where the resistor 20 is short-circuited by the switch 22. Figure 2A and Figure 2BAn example of the voltage on the output side of the switch 16 is shown on the left side. Figure 2A and Figure 2B An example of a resonant voltage is shown on the right side of . In addition, here, for the sake of simplicity of explanation, an example of a case where a DC voltage is applied to the filter 24 via the switch 16 is shown. Figure 2A and Figure 2B 2 shows an example in which the voltage of the smoothing capacitor 18 becomes sufficiently large.

[0053] When the switch 16 is changed from the open state to the closed state in a state where the resistor 20 is not short-circuited by the switch 22, that is, in the case of the comparative example, Figure 2A As shown, the peak value of the resonant voltage becomes significantly larger.

[0054] On the other hand, when the switch 16 is changed from the open state to the closed state in the state where the resistor 20 is short-circuited by the switch 22, that is, in the case of the present embodiment, as shown in FIG. Figure 2B As shown, the peak value of the resonance voltage is clamped to the voltage of the smoothing capacitor 18 .

[0055] Thus, in the present embodiment, when the period for returning the switch 16 that has been switched to the open state to the closed state is relatively short, that is, when the voltage of the smoothing capacitor 18 is sufficiently large, the switch 16 is switched from the open state to the closed state in the state where the switch 22 is closed. Since the resistor 20 is short-circuited by the switch 22, the peak value of the resonant voltage is clamped to the voltage of the smoothing capacitor 18. Since the peak value of the resonant voltage does not increase significantly, according to the present embodiment, it is possible to well prevent the switch element 34 and the like from being damaged.

[0056] On the other hand, when the period during which the switch 16 that has been changed to the open state returns to the closed state again is sufficiently long, the charge accumulated in the capacitor 54 is sufficiently discharged via the resistor 56, so that the voltage across the capacitor 54 becomes sufficiently small. The fact that the voltage across the smoothing capacitor 18 becomes sufficiently small means that the period during which the switch 16 that has been changed to the open state returns to the closed state again is sufficiently long, that is, the voltage across the capacitor 54 becomes sufficiently small. When the voltage across the capacitor 54 becomes sufficiently small, even if the phase of the voltage when the switch 16 is changed to the open state is opposite to the phase of the voltage when the switch 16 is returned to the closed state, the peak value of the resonant voltage does not become significantly large. Therefore, in the present embodiment, when the period during which the switch 16 that has been changed to the open state returns to the closed state again is relatively long, that is, when the voltage of the smoothing capacitor 18 is less than the voltage threshold, the switch 16 is changed from the open state to the closed state in the state where the switch 22 is opened. Since the switch 16 is changed from the open state to the closed state while the switch 22 is in the open state, the resistor 20 can prevent a large inrush current from flowing into the smoothing capacitor 18 .

[0057] use Figure 3 The operation of the power conversion device 10 according to the present embodiment will be described. Figure 3 This is a flowchart showing the operation of the power conversion device according to this embodiment. Figure 3 The operation of the shutter 16 after it changes from the closed state to the open state is shown.

[0058] In step S1, the control unit 64 determines whether to change the switch 16 from the open state to the closed state. When the switch 16 is changed from the open state to the closed state ("Yes" in step S1), the process proceeds to step S2. When the switch 16 is not changed from the open state to the closed state ("No" in step S1), the process ends. Figure 3 Processing shown.

[0059] In step S2, the determination unit 62 determines whether the voltage of the smoothing capacitor 18, that is, the voltage across the smoothing capacitor 18, is greater than or equal to the voltage threshold. If the voltage of the smoothing capacitor 18 is greater than or equal to the voltage threshold ("Yes" in step S2), the process proceeds to step S3. If the voltage of the smoothing capacitor 18 is less than the voltage threshold ("No" in step S2), the process proceeds to step S4.

[0060] In step S3, the control unit 64 closes the switch 22. If the switch 22 is already closed, the control unit 64 maintains the closed state of the switch 22. Thereafter, the process moves to step S5.

[0061] In step S4, the control unit 64 turns on the switch 22. If the switch 22 is already turned on, the control unit 64 maintains the turned-on state of the switch 22. Thereafter, the process proceeds to step S5.

[0062] In step S5, the control unit 64 changes the switch 16 from the open state to the closed state. Figure 3 The indicated processing is completed.

[0063] Thus, according to the present embodiment, when the voltage of the smoothing capacitor 18 is less than the voltage threshold, the switch 16 is changed from the open state to the closed state in the state of the open switch 22, and when the voltage of the smoothing capacitor 18 is equal to or higher than the voltage threshold, the switch 16 is changed from the open state to the closed state in the state of the closed switch 22. According to the present embodiment, when the voltage across the capacitor 54 is large, the resistor 20 is short-circuited by the switch 22, so that the peak value of the resonant voltage is clamped to the voltage of the smoothing capacitor 18. Since the peak value of the resonant voltage does not increase significantly, according to the present embodiment, it is possible to well prevent the switch element 34 and the like from being damaged.

[0064] (Variation Example)

[0065] use Figure 4 A power conversion device 10 according to a modified example of the present embodiment will be described. Figure 4 It is a diagram showing the structure of the power conversion device according to this modification.

[0066] The power conversion device 10 of the present modification example determines whether the voltage of the smoothing capacitor 18 is equal to or higher than the voltage threshold value based on the elapsed time from the time when the switch 16 changes from the closed state to the open state.

[0067] like Figure 4 As shown, in this modified example, the voltage sensor 28 (see Figure 1 In this modification, the calculation unit 58 further includes a timer 66. The timer 66 can be implemented by the calculation unit 58 executing a program stored in the storage unit 60.

[0068] When the switch 16 is changed from the closed state to the open state, the control unit 64 provides information indicating that the switch 16 is changed from the closed state to the open state to the timer 66. The timer 66 counts the elapsed time from the moment when the switch 16 is changed from the closed state to the open state. The elapsed time counted by the timer 66 is provided to the determination unit 62. The determination unit 62 determines whether the voltage of the smoothing capacitor 18 is equal to or higher than the voltage threshold based on the elapsed time counted by the timer 66.

[0069] Operation and Use of the Power Converter 10 of the Modified Example Figure 3The operation of the power conversion device 10 is the same as that of the power conversion device 10, so the description is omitted.

[0070] In this way, it is also possible to determine whether the voltage of the smoothing capacitor 18 is equal to or higher than the voltage threshold value based on the elapsed time from the time when the switch 16 changes from the closed state to the open state.

[0071] The above-described embodiments are summarized as follows.

[0072] The power conversion device (10) comprises: a converter (12) which converts an AC voltage supplied from an AC power source (14) via a switch (16) into a DC voltage; a smoothing capacitor (18) which smoothes the DC voltage output from the converter; a resistor (20) which is provided between the converter and the smoothing capacitor and suppresses current flowing into the smoothing capacitor; a switch (22) which is connected in parallel with the resistor and can short-circuit both ends of the resistor; and a filter (24) which is provided between the switch and the converter and includes a reactor (46 U, 46V, 46W, 48U, 48V, 48W) and capacitors (54U, 54V, 54W) for removing noise; and a control unit (64) for controlling the opening and closing of the switch and the switch, wherein when the voltage of the smoothing capacitor is less than a voltage threshold, the control unit changes the switch from an open state to a closed state in a state where the switch is open, and when the voltage of the smoothing capacitor is greater than or equal to the voltage threshold, the control unit changes the switch from the open state to the closed state in a state where the switch is closed. According to such a structure, when the voltage of the smoothing capacitor is sufficiently large, that is, when the voltage across the capacitor is large, the resistor is short-circuited by the switch, so that the peak value of the resonant voltage is clamped to the voltage of the smoothing capacitor. The peak value of the resonant voltage does not increase significantly, so according to such a structure, it is possible to well prevent the switch element 34 and the like from being damaged.

[0073] The power conversion device further includes a detection unit (28) for detecting the voltage of the smoothing capacitor, and the control unit determines whether the voltage of the smoothing capacitor is equal to or greater than the voltage threshold based on the voltage detected by the detection unit.

[0074] The control unit may also determine whether the voltage of the smoothing capacitor is greater than or equal to the voltage threshold based on the time elapsed from the time when the switch changes from the closed state to the open state. According to such a configuration, a detection unit for detecting the voltage of the smoothing capacitor is not required, which can contribute to cost reduction, etc.

[0075] The converter may be a pulse width modulation converter.

[0076] In a control method for a power conversion device, the power conversion device includes: a converter that converts an AC voltage supplied from an AC power source via a switch into a DC voltage; a smoothing capacitor that smoothes the DC voltage output from the converter; a resistor that is provided between the converter and the smoothing capacitor and suppresses current flowing into the smoothing capacitor; a switch that is connected in parallel with the resistor and can short-circuit both ends of the resistor; a filter that is provided between the switch and the converter and includes a reactor and a capacitor and is used to remove noise; and a control unit that controls the opening and closing of the switch and the switch. The control method for the power conversion device has The method comprises the following steps: a step of determining whether the voltage of the smoothing capacitor is greater than a voltage threshold (S2); and a step of changing the switch from an open state to a closed state (S5), wherein in the step of changing the switch from the open state to the closed state, when the voltage of the smoothing capacitor is less than the voltage threshold, the switch is changed from the open state to the closed state in the state of opening the switch (S4, S5), and when the voltage of the smoothing capacitor is greater than the voltage threshold, the switch is changed from the open state to the closed state in the state of closing the switch (S3, S5).

Claims

1. A power conversion device, characterized in that: have: A converter that converts an AC voltage supplied from an AC power source via a switch into a DC voltage; a smoothing capacitor that smoothes the DC voltage output from the converter; a resistor provided between the converter and the smoothing capacitor to suppress a current flowing into the smoothing capacitor; a switch connected in parallel with the resistor and capable of short-circuiting both ends of the resistor; A filter, which is arranged between the switch and the converter and includes a reactor and a capacitor, and is used to remove noise; as well as a control unit that controls the opening and closing of the switch and the switch, When the voltage of the smoothing capacitor is less than a voltage threshold, the control unit changes the switch from the open state to the closed state with the switch in the open state, and when the voltage of the smoothing capacitor is greater than or equal to the voltage threshold, the control unit changes the switch from the open state to the closed state with the switch in the closed state.

2. The power conversion device according to claim 1, characterized in that: The power conversion device further includes a detection unit for detecting the voltage of the smoothing capacitor. The control unit determines whether the voltage of the smoothing capacitor is equal to or higher than the voltage threshold based on the voltage detected by the detection unit.

3. The power conversion device according to claim 1, characterized in that: The control unit determines whether the voltage of the smoothing capacitor is equal to or higher than the voltage threshold based on an elapsed time from a time when the switch changes from the closed state to the open state.

4. The power conversion device according to any one of claims 1 to 3, characterized in that: The converter is a pulse width modulated converter.

5. A control method for a power conversion device, characterized in that: The power conversion device comprises: A converter that converts an AC voltage supplied from an AC power source via a switch into a DC voltage; a smoothing capacitor that smoothes the DC voltage output from the converter; a resistor provided between the converter and the smoothing capacitor to suppress a current flowing into the smoothing capacitor; a switch connected in parallel with the resistor and capable of short-circuiting both ends of the resistor; a filter, which is provided between the switch and the converter and includes a reactor and a capacitor, and is used to remove noise; and a control unit that controls the opening and closing of the switch and the switch, The control method of the power conversion device comprises the following steps: a step of determining whether the voltage of the smoothing capacitor is above a voltage threshold; and The step of changing the shutter from an open state to a closed state, In the step of changing the switch from the open state to the closed state, when the voltage of the smoothing capacitor is less than the voltage threshold, the switch is changed from the open state to the closed state with the switch in the open state, and when the voltage of the smoothing capacitor is greater than or equal to the voltage threshold, the switch is changed from the open state to the closed state with the switch in the closed state.

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