Power conversion device and control device

Abstract

This protects power converters, including power buffer circuits, from momentary power outages. [Solution] The power converter 10 comprises a converter circuit 22, a DC link 20, a power buffer circuit 24, an inverter circuit 25 for driving a load 12, and a control device 27. The power buffer circuit 24 has a discharge circuit 24a including a first capacitor C4 and a first switch S1, and a charging circuit 24b including a first reactor L4 and a second switch S2. The control device 27 performs protection control when the second switch S2 stops switching and the voltage Vc of the first capacitor C4 or the voltage Vdc between the DC links 20 falls below a predetermined first threshold. The protection control includes at least one of a stop control that stops the conversion from DC to AC in the inverter circuit 25, and a cutoff control that cuts off the connection between the AC power supply 11 and the converter circuit 22.

Description

Technical Field

[0001] The present disclosure relates to a power conversion device and a control device.

Background Art

[0002] For example, in a refrigeration device such as an air conditioner, a power conversion device that converts AC power supplied from a commercial power source into AC power for driving an electric motor is used. In a power conversion device, a power buffer circuit may be used to reduce power pulsation.

[0003] Patent Documents 1 and 2 disclose a power conversion device including a converter circuit (diode bridge rectifier circuit) connected to a single-phase AC power source, a power buffer circuit that buffers power by charging and discharging a capacitor, and an inverter circuit that converts the DC voltage input from the power buffer circuit into an AC voltage and outputs it to an electric motor or the like.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the power conversion device as described above, when the voltage supplied from the single-phase AC power source drops due to a power outage or the like, various protections (low voltage protection: LVP) are provided against the inrush current when the power supply resumes later.

[0006] However, in the case of a momentary power outage (instantaneous interruption), the voltage drop occurs in a very short time, so conventional protection circuits cannot adequately detect the voltage drop, and the subsequent inrush current may cause malfunctions in the components included in the power converter.

[0007] Therefore, this disclosure aims to protect a power conversion device including a power buffer circuit from momentary power outages. [Means for solving the problem]

[0008] (1) The power converter of the present disclosure comprises: a converter circuit that converts alternating current (AC) input from an AC power source to direct current (DC); DC links including a first power line and a second power line connected to the output side of the converter circuit, respectively; a power buffer circuit that receives charging power from the DC links and outputs discharge power to the DC links; an inverter circuit that converts the DC input from the DC links to AC and outputs it to a load; and a control device that controls the power buffer circuit and the inverter circuit, wherein the power buffer circuit includes a first capacitor and a first switch connected in series with the first capacitor, and when the first switch conducts between the DC links, a discharge circuit that supplies discharge power to the DC links by discharging the first capacitor and a first reactor The power converter includes a second switch connected in series with the first reactor, and a charging circuit that charges the first capacitor with charging power input from the DC links and stored in the first reactor when the second switch is performing a switching operation that repeatedly switches between a state of conducting and a state of not conducting between the DC links, wherein the control device performs protection control when the second switch stops the switching operation and the voltage of the first capacitor or the voltage between the DC links falls below a predetermined first threshold, and the protection control includes at least one of a stop control that stops the conversion from DC to AC in the inverter circuit, and a cutoff control that cuts off the connection between the AC power supply and the converter circuit.

[0009] When the second switch stops switching, the first capacitor is not charged, which makes it easy for the voltage of the first capacitor to drop during a power outage and for inrush current to increase. In such cases, the control device can protect the power converter, including the power buffer circuit, from momentary power outages by performing protective control.

[0010] (2) Preferably, the method further includes a relay circuit that controls the conduction between the AC power supply and the converter circuit, wherein the interruption control includes control of the relay circuit to interrupt the connection between the AC power supply and the converter circuit.

[0011] By using a relay circuit to interrupt the connection between the AC power supply and the converter circuit, it is possible to prevent inrush current from entering the circuit beyond the converter circuit.

[0012] (3) Preferably, the protection control includes the stop control, the interruption control performed after the stop control, and the restart control performed after the interruption control to initiate the conversion from DC to AC in the inverter circuit.

[0013] Generally, the response speed of a relay circuit is slower than that of an inverter circuit. Therefore, by performing a shutdown control of the inverter circuit first in the protection control, the voltage at the first capacitor can be maintained, and even if an inrush current occurs before the tripping control of the relay circuit, it is possible to suppress the inrush current from becoming large. Furthermore, by performing a restart control after the tripping control, the charge of the first capacitor can be released to the load while preventing the inflow of inrush current. This makes it possible to more reliably protect the power converter, including the power buffer circuit, from momentary power outages.

[0014] (4) Preferably, the control device executes the protective control only while the load is in operation.

[0015] Generally, when the load is not operating, a circuit breaker can protect the power converter from momentary power outages. In contrast, when the load is operating, it is not possible to take measures with a circuit breaker, so protective control by the control unit becomes more important. By executing protective control only when the load is operating, the situations in which protective control is performed can be limited, and the control burden on the control unit can be reduced.

[0016] (5) Preferably, the control device detects the voltage of the first capacitor or the voltage between the DC links at predetermined intervals, and executes the protection control when the voltage of the first capacitor or the voltage between the DC links falls below the first threshold for two or more predetermined consecutive times.

[0017] With this configuration, the control device detects the voltage of the first capacitor or the voltage between the DC links at a predetermined sampling period. If the need for protection control is determined based on only one sampling, there is a risk that protection control may be frequently triggered due to false detections caused by momentary noise, for example, which could hinder power conversion in the power converter. Therefore, by executing protection control when these voltages fall below the first threshold for two or more predetermined consecutive times, malfunctions of the protection control can be reduced.

[0018] (6) Preferably, the predetermined interval is 0.5 milliseconds or less, and the predetermined number of times is 2.

[0019] For example, conventionally, voltage was sampled at 1-millisecond intervals, and normal LVP (Low Voltage Protection) was performed based on the average of 10 samples, making it impossible to respond to very short momentary power outages. In contrast, by shortening the sampling interval to 0.5 milliseconds or less and limiting the number of samples to two, it is possible to reduce malfunctions while enabling protective control even for very short momentary power outages. This makes it possible to protect power converters, including power buffer circuits, from momentary power failures.

[0020] (7) Preferably, the converter circuit, the power buffer circuit, the inverter circuit and the smoothing circuit, which include a second reactor connected in series with the first power line and smooths the DC input to the power buffer circuit, wherein the converter circuit, the power buffer circuit, the inverter circuit and the smoothing circuit are mounted on a printed circuit board, and the DC resistance of the second reactor is 50 mΩ or less.

[0021] Increasing the DC resistance of the second reactor can reduce the inrush current flowing through each component. However, this can lead to problems such as dielectric breakdown of the reactor or deformation of the printed circuit board due to the reactor overheating during operation. In this disclosure, inrush current is prevented by protective control, thus reducing the need to select a second reactor with a large DC resistance, and allowing the use of a smaller reactor with a DC resistance of 50 mΩ or less. This eliminates the aforementioned problems associated with a large DC resistance.

[0022] (8) Preferably, the converter circuit, the power buffer circuit, and the inverter circuit are mounted on a printed circuit board, and the capacitance of the first capacitor is 760uF or more.

[0023] While a larger capacitance of the first capacitor allows for greater power output to the inverter circuit, it also carries the risk of a larger inrush current. In this disclosure, a capacitor with a larger capacitance can be used as the first capacitor with a lower risk because the inrush current is prevented by protective control.

[0024] (9) The control device of the present disclosure is a control device that controls a power converter. The power converter includes a converter circuit that converts alternating current output from an AC power source into direct current, a DC link including a first power line and a second power line respectively connected to the output side of the converter circuit, a power buffer circuit that inputs charging power from the DC link and outputs discharging power to the DC link, and an inverter circuit that converts the DC input from the DC link into AC and outputs it to a load. The power buffer circuit includes a first capacitor and a first switch connected in series to the first capacitor. When the first switch conducts between the DC links, it has a discharge circuit that supplies discharging power to the DC link by discharging the first capacitor, a first reactor, and a second switch connected in series to the first reactor. When the second switch executes a switching operation that repeats a state of conducting and a state of not conducting between the DC links, it has a charging circuit that charges the first capacitor with the charging power input from the DC link and accumulated in the first reactor, and the control device executes protection control when the second switch stops the switching operation and the voltage of the first capacitor or the voltage between the DC links becomes less than or equal to a predetermined first threshold value. The protection control includes stop control for stopping the conversion from DC to AC in the inverter circuit and cutoff control for cutting off between the AC power source and the converter circuit. It is a control device including at least one of the following.

[0025] When the second switch stops the switching operation, the first capacitor is not charged. Therefore, during a power outage, the voltage of the first capacitor tends to drop and the inrush current tends to increase. In such a case, by the control device executing protection control, the power converter including the power buffer circuit can be protected from an instantaneous power outage.

Brief Description of the Drawings

[0026] [Figure 1] It is a block diagram schematically showing the functions of the power conversion device according to the embodiment. [Figure 2]This is a block diagram schematically showing the circuit configuration of the power conversion device according to the embodiment. [Figure 3] This is a flowchart illustrating the control procedure of the control device according to the embodiment. [Figure 4] This is a table showing the scope of protection in comparative examples. [Figure 5] This is a table showing an example of the scope of protection in the embodiment. [Modes for carrying out the invention]

[0027] The embodiments of this disclosure will be described below with reference to the attached drawings.

[0028] [Embodiment] [Overall configuration of power converter 10] Figure 1 is a block diagram schematically showing the functions of the power converter 10 according to this embodiment. Figure 2 is a block diagram schematically showing the circuit configuration of the power converter 10. The power converter 10 is a single-phase to three-phase converter that converts the AC power input from the single-phase AC power source 11 into three-phase AC power corresponding to the loads 12 and 13, and outputs it to the loads 12 and 13 respectively.

[0029] The AC power supply 11 is, for example, a single-phase 200V commercial power supply. The power converter 10 and loads 12 and 13 are components included in the air conditioning system. Loads 12 and 13 are devices having rotating machinery (electric motors), for example, load 12 is a compressor and load 13 is a fan.

[0030] The power conversion device 10 comprises a power converter 10a and a control device 27. The control device 27 controls the power converter 10a.

[0031] The power converter 10a comprises a DC link 20 including a first power line LH and a second power line LL, a relay circuit 21, a converter circuit 22, a smoothing circuit 23, a power buffer circuit 24, and a plurality of inverter circuits 25, 26. Each of these circuits 21 to 26 is connected to the DC link 20 and mounted on a resin-based printed circuit board (not shown).

[0032] The power converter 10 is a power converter with an undervoltage protection (LVP) function. Specifically, the control device 27 monitors the state of the power buffer circuit 24, which includes the first reactor L4 and the first capacitor C4. When the power converter 10 falls into a low-voltage state due to a momentary power outage or the like, the control device 27 performs various protective controls to prevent malfunctions such as damage to circuit components caused by inrush current when recovering from the low-voltage state. The components of the power converter 10 will be described below.

[0033] [Components of the power converter 10] The relay circuit 21 is a circuit that controls the conductivity between the AC power supply 11 and the converter circuit 22. The relay circuit 21 is a mechanical relay that includes, for example, a switch capable of interrupting conductivity between the AC power supply 11 and the converter circuit 22, and a coil that operates the switch, and is also called the main relay. The relay circuit 21 is turned on and off based on the control signal SR output from the control device 27.

[0034] The converter circuit 22 is a rectifier circuit that converts the alternating current (AC) input from the AC power supply 11 into direct current (DC). The converter circuit 22 is a full-wave rectifier circuit employing, for example, a diode bridge, and includes four diodes D21, D22, D23, and D24. The converter circuit 22 converts the single-phase AC voltage Vin input from the AC power supply 11 into a rectified voltage and outputs it between the first power line LH and the second power line LL.

[0035] The smoothing circuit 23 is a filter circuit that smooths the rectified voltage output from the converter circuit 22. The smoothing circuit 23 includes a second reactor L3 and a second capacitor C3. The second reactor L3 is a smoothing reactor connected in series with the first power line LH. The second capacitor C3 is a smoothing capacitor connected between the first power line LH and the second power line LL. The second reactor L3 and the second capacitor C3 temporarily store the power output from the converter circuit 22 and output it with a time delay, thereby removing high-frequency components contained in the rectified voltage and suppressing pulsation. As a result, the filtered rectified voltage Vrec (=|Vin|) is output to the DC link 20.

[0036] The DC resistance of the second reactor L3 is, for example, 50 mΩ (milliohms) or less, and more preferably a reactor with a relatively low resistance of 20 mΩ or less is used. Generally, for the reactor of the smoothing circuit 23, a reactor with a relatively high DC resistance (for example, a reactor with a DC resistance of more than 50 mΩ) is used to suppress inrush current. And, reactors with high DC resistance tend to generate heat and become hot during operation, so reactors are generally large in size to thermally protect the reactor and the printed circuit board.

[0037] In response to this, the power converter 10 suppresses malfunctions caused by inrush current by performing the protection control described later. Thus, because the power converter 10 has a lower risk from inrush current than conventional devices, it can be used even if the second reactor L3 is configured with a low DC resistance value. By setting the DC resistance value of the second reactor L3 to 50 mΩ or less, the need for heat dissipation countermeasures is reduced, the volume required for mounting the second reactor L3 can be made smaller, and the heat loss in the smoothing circuit 23 can be kept low. As a result, the printed circuit board on which these circuits 21 to 26 are mounted can be made smaller, and the need to select a printed circuit board with high heat resistance is reduced, allowing the use of a less expensive printed circuit board.

[0038] The smoothing circuit 23 may be provided upstream of the converter circuit 22 (meaning the "AC power supply 11 side," and the same applies hereinafter), and the single-phase AC voltage Vin may be smoothed before being input to the converter circuit 22 and output to the converter circuit 22. Alternatively, the smoothing circuit 23 may be omitted. In these cases, the rectified voltage output from the converter circuit 22 is treated as the "rectified voltage Vrec."

[0039] The first power line LH and the second power line LL are DC power lines connected to the output side of the converter circuit 22, respectively. A higher potential is applied to the first power line LH than to the second power line LL.

[0040] The power buffer circuit 24 includes a discharge circuit 24a that outputs discharge power to the DC link 20 and a charging circuit 24b that receives charging power from the DC link 20. The power buffer circuit 24 corrects voltage changes when a voltage drop occurs in the DC link 20 due to the charging and discharging of these circuits 24a and 24b, thereby suppressing fluctuations in the voltage of the power flowing through the DC link 20.

[0041] The discharge circuit 24a includes a first capacitor C4 and a first switch S1. The first capacitor C4 is connected between the first power line LH and the second power line LL. The first capacitor C4 is charged by the charging circuit 24b, and this charged power is discharged to the DC link 20 by conducting the first switch S1, thereby exchanging power with the DC link 20. The first capacitor C4 may be realized by a single capacitor element or by a plurality of capacitor elements connected in parallel with each other.

[0042] The capacitance of the first capacitor C4 is, for example, 760uF (microfarads) or more. For example, if the first capacitor C4 includes multiple capacitor elements connected in parallel, the sum of the capacitances of these capacitor elements becomes the capacitance of the first capacitor C4.

[0043] Thus, by using a capacitor with a relatively large capacitance as the first capacitor C4, the output power (inverter output power) output to the loads 12 and 13 can be increased. On the other hand, increasing the capacitance of the first capacitor C4 tends to increase the inrush current when the AC power supply 11 is restored after a power outage. In this regard, the power converter 10 suppresses malfunctions caused by inrush current by performing the protection control described later. Thus, since the power converter 10 has a lower risk from inrush current than conventional devices, it is possible to configure the first capacitor C4 with a large capacitance for practical use.

[0044] The first switch S1 includes a diode D42 and a transistor SC (e.g., an insulated-gate bipolar transistor: IGBT) connected in antiparallel to the diode D42. The first switch S1 is connected in series with the first capacitor C4 on the first power line LH side. The first switch S1 (specifically the transistor SC) is turned on and off based on a control signal SSC output from the control device 27.

[0045] Here, antiparallel connection means that the components are connected in parallel with their forward directions reversed. Specifically, the forward direction of transistor SC is from the second power line LL (low potential) to the first power line LH (high potential), and the forward direction of diode D42 is from the first power line LH to the second power line LL.

[0046] The charging circuit 24b includes a first reactor L4, a second switch S2, and two diodes D40 and D43. The first reactor L4 is connected between the first power line LH and the second power line LL upstream of the first capacitor C4 in the DC link 20. The first reactor L4 temporarily stores the power input to the charging circuit 24b from the DC link 20 as charging power, and then boosts the voltage of this charging power by switching off the second switch S2 and supplies it to the first capacitor C4.

[0047] The second switch S2 includes a diode D41 and a transistor SL (e.g., an IGBT) connected in antiparallel to the diode D41. The second switch S2 is connected in series with the first reactor L4 on the second power line LL side. The second switch S2 (specifically the transistor SL) is controlled on and off based on a control signal SSL output from the control device 27. Here, the forward direction of the transistor SL is from the first power line LH towards the second power line LL.

[0048] Diode D40 has its cathode connected between the first switch S1 and the first capacitor C4, and its anode connected between the first reactor L4 and the second switch S2. This configuration forms a boost chopper.

[0049] Diode D43 is installed between the connection point of the first reactor L4 and the connection point of the first switch S1 in the first power line LH, with its cathode facing downstream and its anode facing upstream. In the power buffer circuit 24, diode D43 has the function of preventing the voltage across the second capacitor C3 from being affected by the voltage across the first capacitor C4 Vc due to the switching of the first switch S1 by suppressing the reverse flow of current through the first power line LH to the upstream side. Note that diode D43 may be omitted.

[0050] The operation of the power buffer circuit 24 will now be explained. First, a rectified voltage Vrec is applied to the power buffer circuit 24. In this state, the control device 27 outputs a control signal SSL, which includes an ON command, to the second switch S2, turning the second switch S2 ON (conducting). As a result, current flows from the first power line LH through the second switch S2 to the second power line LL, and energy is stored in the first reactor L4.

[0051] Next, the control device 27 outputs a control signal SSL, which includes an off command, to the second switch S2, turning the second switch S2 off (to the off state). As a result, the energy stored in the first reactor L4 flows through the diode D40 to the first capacitor C4 and is stored in the first capacitor C4. In this way, the first capacitor C4 is charged by the charging circuit 24b, and a voltage Vc across the first capacitor C4 is generated that is higher than the rectified voltage Vrec (Vc > Vrec).

[0052] As described above, the power buffer circuit 24 functions as a boost circuit by repeatedly turning the second switch S2 on (storing energy in the first reactor L4) and turning the second switch S2 off (charging the first capacitor C4). That is, when the power buffer circuit 24 is operating as a boost circuit, the second switch S2 performs a "switching operation" of repeatedly turning on and off in accordance with the operation command of the control device 27. On the other hand, when the power buffer circuit 24 is not operating as a boost circuit, the second switch S2 stops its switching operation and remains off.

[0053] Then, with the first capacitor C4 charged, the control device 27 outputs a control signal SSC including an ON command to the first switch S1. When the first switch S1 is turned ON, the first capacitor C4 discharges and supplies discharge power to the DC link 20. In this case, the DC voltage Vdc of the DC link 20 at the downstream end of the power buffer circuit 24 is equal to the voltage Vc across the first capacitor C4 (Vdc = Vc).

[0054] On the other hand, when the control device 27 outputs a control signal SSC including an off command to the first switch S1, and the first switch S1 is turned off, no discharge power is supplied from the first capacitor C4 to the DC link 20. In this way, the on / off switching of the first switch S1 switches whether the DC current Idc flowing to the DC link 20 at the downstream end of the power buffer circuit 24 flows from the power buffer circuit 24 or from the converter circuit 22 (and smoothing circuit 23). The control device 27 performs power buffering in the DC link 20 by controlling the on / off switching of the first switch S1 at appropriate timings.

[0055] Multiple inverter circuits 25 and 26 convert the DC input from the DC link 20 into AC and output it to the loads 12 and 13. While this explanation describes an example where the power converter 10 includes two inverter circuits 25 and 26, the number of inverter circuits included in the power converter 10 is not limited; it may be one or three or more. Since the functions of the two inverter circuits 25 and 26 are similar, the inverter circuit 25 will be described below.

[0056] The inverter circuit 25 converts the DC from the DC link 20 to AC and outputs it to the output terminals Pu, Pv, and Pw. As a result, AC currents Iu, Iv, and Iw are output from the output terminals Pu, Pv, and Pw, respectively, and these three-phase AC currents are output to the load 12 (compressor).

[0057] The inverter circuit 25 includes six transistors Sup, Svp, Swp, Sun, Svn, Swn (switching elements) and six diodes Dup, Dvp, Dwp, Dun, Dvn, Dwn, which are connected in antiparallel to these transistors Sup, Svp, Swp, Sun, Svn, Swn, respectively. The transistors Sup, Svp, Swp, Sun, Svn, Swn are, for example, IGBTs.

[0058] Transistors Sup, Svp, and Swp are connected between their output terminals Pu, Pv, and Pw and the first power line LH, respectively, while transistors Sun, Svn, and Swn are connected between their output terminals Pu, Pv, and Pw and the second power line LL, respectively.

[0059] Thus, the inverter circuit 25 constitutes a so-called voltage-type inverter. The control device 27 outputs a control signal Sinv to transistors Sup, Svp, Swp, Sun, Svn, and Swn, and by appropriately switching them on and off using known methods, the inverter circuit 25 converts the DC of the DC link 20 to AC.

[0060] The control device 27 is a computer device that controls each part of the power converter 10. The control device 27 includes a memory and a processor that performs various calculations and controls according to a computer program stored in the memory. The control device 27 may be an integrated circuit such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0061] The control device 27 includes a voltage detector (not shown in Figures 1 and 2) that detects at least one of the voltage Vc across the first capacitor C4 and the DC voltage Vdc across the DC link 20. The voltage detector detects the voltages Vc and Vdc at predetermined intervals X1. The predetermined interval X1 is a time shorter than, for example, 0.5 milliseconds, more specifically 0.162 milliseconds.

[0062] [Problems solved by the power converter 10 and their solutions] Next, the problems that the power converter 10 solves will be explained in detail. For example, if a voltage drop occurs in the AC power supply 11 due to a power outage or the like, there is a risk that an inrush current will flow into the power converter 10 when the AC power supply 11 is restored. The inrush current flows through the first power line LH via the relay circuit 21 and diode D21, and then flows into the first capacitor C4 via the second reactor L3, diode D43 and first switch S1.

[0063] At this time, if the charge capacitance of the first capacitor C4 decreases as the voltage of the AC power supply 11 drops, the voltage Vc across the first capacitor C4 will also be low, making it easy for the inrush current to become large. If the inrush current becomes excessive, there is a risk of malfunctions such as damage to components such as the first capacitor C4.

[0064] For example, in conventional protection circuits, the DC voltage Vdc was sampled at a period of about 1.0 millisecond, and the presence or absence of a voltage drop in the AC power supply 11 was determined based on the average value of multiple (e.g., 10 or more) sampled voltages. In particular, since ripple originating from the power supply cycle of the AC power supply 11 is generated in the voltage Vc across the first capacitor C4, the above averaging process was performed to detect the voltage averaged to include this ripple.

[0065] Because the period for calculating the average value of the DC voltage Vdc is relatively long, in the case of a momentary power outage where the voltage drop in the AC power supply 11 occurs for only a very short time (for example, less than 10 milliseconds), the low-voltage state cannot be determined, and protective control cannot be executed, resulting in the aforementioned component malfunctions.

[0066] To solve this problem, one possible approach is to reduce the number of sampling voltages used to calculate the average value (for example, to less than 5) while keeping the existing protection circuit. While this would allow for the detection of momentary power outages, it would also lead to a new problem: unnecessary protection control would be performed even in situations where excessive inrush current is unlikely to flow through the power converter 10, resulting in a decrease in the operating rate of the power converter 10.

[0067] Therefore, the power converter 10 performs protective control only when a decrease in DC voltage Vdc occurs under conditions where excessive inrush current is likely to flow. Conditions in which excessive inrush current is likely to flow to the power converter 10 include, for example, a situation where the power buffer circuit 24 is "not" functioning as a boost circuit.

[0068] When the power buffer circuit 24 functions as a boost circuit (i.e., when the second switch S2 performs a switching operation and the charging power of the first reactor L4 is boosted and supplied to the first capacitor C4), even if a voltage drop occurs in the AC power supply 11, the voltage Vc across the first capacitor C4 hardly drops and is maintained at a voltage Vc above a predetermined value. Therefore, inrush current is less likely to become large, and malfunctions caused by inrush current are less likely to occur in the first capacitor C4, etc.

[0069] On the other hand, if the power buffer circuit 24 is not functioning as a boost circuit (i.e., if the switching operation of the second switch S2 is stopped), there is no power supplied to charge the first capacitor C4, so the voltage Vc across the first capacitor C4 tends to decrease, and the inrush current tends to increase.

[0070] Therefore, the control device 27 performs protective control when the second switch S2 is conducting between the DC links 20 and the DC voltage Vdc between the DC links 20 (or the voltage Vc across the first capacitor C4, which is equal to the DC voltage Vdc when the first switch S1 is conducting) falls below a predetermined first threshold Th1. This allows protective control to be performed only when a drop in DC voltage Vdc occurs under conditions where excessive inrush current is likely to flow, thereby protecting the power converter 10, including the power buffer circuit 24, from momentary power outages while avoiding unnecessary protective control.

[0071] [Protection control by control device 27] Figure 3 is a flowchart illustrating the control procedure in the control device 27. Furthermore, the control device 27 may perform the protective control described below only when at least one of loads 12 and 13 is in operation. That is, if neither load 12 nor 13 is in operation, the control device 27 does not need to perform the following series of control procedures.

[0072] While loads 12 and 13 are not operating, the power converter 10 can be protected from low-voltage conditions caused by momentary power outages by a circuit breaker (not shown). In contrast, while loads 12 and 13 are operating, it is not possible to take measures using the circuit breaker, so protective control by the control device 27 becomes more important. As described above, by executing protective control only while loads 12 and 13 are operating, the situations in which protective control is executed can be limited, and the control burden on the control device 27 can be reduced.

[0073] Furthermore, "loads 12 and 13 are in operation" means that AC power can be supplied to loads 12 and 13 from inverter circuits 25 and 26. In other words, it means that loads 12 and 13 are powered on. This includes not only the state in which the rotating machinery included in loads 12 and 13 is actually rotating in response to the AC power supply, but also the state in which the rotating machinery has stopped rotating and is in standby mode (idle state).

[0074] [Step S11: Operation of the second switch S2] First, the control device 27 determines whether the second switch S2 (specifically, transistor SL) is performing a switching operation (step S11). For example, if the control device 27 repeatedly outputs a control signal SSL including an ON command and an OFF command to the second switch S2 within a predetermined time, the control device 27 determines that the second switch S2 is performing a switching operation (YES in step S11). On the other hand, if the control device 27 outputs only an OFF command to the second switch S2 and does not output a control signal SSL including an ON command within a predetermined time, the control device 27 determines that the second switch S2 has stopped switching (NO in step S11).

[0075] [Step S12: Instantaneous detection of voltage drop] If the second switch S2 has stopped switching, the control device 27 then determines whether the state in which at least one of the voltage across the first capacitor C4 Vc and the DC voltage between the DC links 20 Vdc is below the first threshold Th1 continues for a predetermined time Y1 or longer (step S12). As described above, the voltage across the first capacitor C4 Vc and the DC voltage between the DC links 20 Vdc are the same when the first switch S1 is conducting, so either value can be used as the basis. The following explanation will use an example of detecting the DC voltage Vdc, but the process is the same when detecting the voltage across the capacitor Vc. The predetermined time Y1 is, for example, 1 millisecond or less, more specifically 0.32 milliseconds.

[0076] For example, the control device 27 detects a DC voltage Vdc at a predetermined interval X1 (for example, 0.5 milliseconds or less, more specifically 0.162 milliseconds), and determines that "the state in which the DC voltage Vdc is below the first threshold Th1 continues for a predetermined time Y1" if the detected value is 2 or more times n1 consecutively. In other words, the predetermined time Y1 is considered to be the product of the predetermined interval X1 and the predetermined number of times n1 (Y1 = X1 × n1 = 0.162 × 2 = 0.32).

[0077] Here, the first threshold Th1 is the voltage value at which the inrush current when the AC power supply 11 is restored is expected to become large enough to cause malfunctions in the components. For example, if the normal DC voltage Vdc is 255V, the inrush current is likely to be excessive when the DC voltage Vdc drops to a voltage lower than 184V before being restored. Therefore, the first threshold Th1 is set to 190V, which is 184V plus a margin, and the control device 27 determines that a state in which the DC voltage Vdc (or the voltage across both ends Vc) is below the first threshold Th1 is a "voltage drop" that carries the risk of excessive inrush current flowing.

[0078] The value of the first threshold Th1 is not limited to 190V as described above, but may be set appropriately based on the voltage value of the AC power supply 11 under normal conditions and the specifications of each component constituting the power converter 10.

[0079] Then, the control device 27 performs protective control (from steps S14 to S16) when at least one of the voltage across the terminals Vc and the DC voltage Vdc falls below the first threshold Th1 (YES in step S12).

[0080] On the other hand, if both the voltage across the terminals Vc and the DC voltage Vdc exceed the first threshold Th1 (NO in step S12), the control device 27 does not perform protective control because the risk of excessive inrush current is low, and returns to step S11.

[0081] [Step S13: Normal determination of voltage drop] Furthermore, if the second switch S2 is performing a switching operation in step S11 (YES in step S11), the power buffer circuit 24 is functioning as a boost circuit, and the risk of excessive inrush current flowing in the event of a momentary power outage is low. Therefore, the control device 27 performs voltage monitoring for a longer predetermined time Y2 rather than for a short period of time Y1 (step S13).

[0082] Here, the predetermined time Y2 is longer than the predetermined time Y1, for example, 10 milliseconds. Indeed, if the second switch S2 performs switching operation and the power buffer circuit 24 functions as a boost circuit, the voltage of the first capacitor C4 can be maintained by the boost operation for a certain period of time. However, if the AC power supply 11 remains in a low voltage state for a longer period of time, the stored energy of the first reactor L4 will be completely transferred to the first capacitor C4, and eventually a voltage drop will occur in the first capacitor C4.

[0083] Therefore, the control device 27 determines whether the state in which at least one of the voltage Vc across the first capacitor C4 and the DC voltage Vdc between the DC links 20 is less than or equal to the first threshold Th1 continues for a predetermined time Y2 or longer (step S13).

[0084] The control device 27 determines that "the state in which the DC voltage Vdc is below the first threshold Th1 continues for a predetermined time Y2" if the detected value of the DC voltage Vdc, which is detected at a predetermined interval X1 (=0.162 milliseconds), is below the first threshold Th1 for, for example, 62 consecutive times. Alternatively, the control device 27 may calculate the average value of the 62 detected values ​​of the DC voltage Vdc and determine that "the state in which the DC voltage Vdc is below the first threshold Th1 continues for a predetermined time Y2" if this average value is below the first threshold Th1.

[0085] Then, the control device 27 executes protective control (from steps S14 to S16) when at least one of the voltage across the terminals Vc and the DC voltage Vdc remains below the first threshold Th1 for a predetermined time Y2 (YES in step S13).

[0086] On the other hand, if neither the voltage across the terminals Vc nor the DC voltage Vdc remains below the first threshold Th1 for a predetermined time Y2 (NO in step S13), the control device 27 does not perform protective control because the risk of excessive inrush current is low, and returns to step S11.

[0087] [Step S14: Stop control] The protective control is performed as a series of controls from step S14 to step S16. First, the control device 27 performs a "stop control" that stops the conversion from DC to AC in inverter circuits 25 and 26 by outputting a control signal Sinv to inverter circuits 25 and 26 (step S14).

[0088] For example, the control device 27 turns off the waveform outputs of inverter circuits 25 and 26 by turning off all transistors Sup, Svp, Swp, Sun, Svn, and Swn.

[0089] This prevents the power stored in the first capacitor C4 from being released to the inverter circuits 25 and 26, and keeps the voltage Vc across the first capacitor C4 at a certain level. As a result, the voltage drop across the first capacitor C4 is suppressed, and even if the AC power supply 11 is immediately restored, an excessive inrush current is prevented from flowing through the first capacitor C4.

[0090] [Step S15: Shutoff control] Next, the control device 27 controls the relay circuit 21 to perform "shutdown control," which interrupts the connection between the AC power supply 11 and the converter circuit 22. Specifically, the control device 27 outputs a control signal SR, which includes a shutdown command, to the relay circuit 21. As a result, the relay circuit 21 turns off (the switch is open), and the conduction between the AC power supply 11 and the converter circuit 22 is interrupted.

[0091] As a result, it is possible to prevent the inrush current that occurs when power is restored after a voltage drop due to a momentary power outage in the AC power supply 11 from entering the circuits 22 to 26 located downstream of the relay circuit 21. Therefore, the power converter 10, including the power buffer circuit 24, can be protected from momentary power outages.

[0092] [Step S16: Restart control] Finally, the control device 27 performs "restart control" by outputting a control signal Sinv to the inverter circuit 25 and inverter circuit 26, thereby initiating the conversion from DC to AC in the inverter circuit 25 and inverter circuit 26 (step S16).

[0093] For example, the control device 27 outputs a control signal Sinv to transistors Sup, Svp, Swp, Sun, Svn, and Swn, and controls them on and off as appropriate using known methods. As a result, inverter circuits 25 and 26 convert the DC of the DC link 20 to AC, thereby discharging the charge stored in the first capacitor C4 to the loads 12 and 13. In other words, this "restart control" also functions as "discharge control" of the first capacitor C4.

[0094] Generally, the reaction speed of the relay circuit 21 is slower than that of the inverter circuits 25 and 26. Therefore, in this embodiment, by first executing the stop control of the inverter circuit 25 (step S14) in the protection control, the charge capacitance of the first capacitor C4 is maintained, and even if an inrush current occurs before the cutoff control of the relay circuit 21 (step S15), it is possible to suppress the inrush current from becoming large.

[0095] Furthermore, by performing restart control (step S16) after the interruption control, the charge of the first capacitor C4 can be released to the loads 12 and 13 while preventing the inrush current from entering the first capacitor C4. This makes it possible to more reliably protect the power converter 10, including the power buffer circuit 24, from momentary power outages. With this, the series of protective controls is completed.

[0096] [Protection range by power converter 10] The protection range provided by the power converter 10 according to this embodiment will be explained with reference to Figures 4 and 5. Figure 4 is a table showing the scope of protection in the comparative example. Figure 5 is a table showing an example of the protection scope in this embodiment.

[0097] Figure 4 shows the protection range when undervoltage protection is performed by the conventional protection circuit, which, in a state where the second switch S2 has stopped switching and the power buffer circuit 24 is not functioning as a boost circuit, does not execute the above protection control (steps S14 to S16), but instead calculates the average value of the DC voltage Vdc every 10 milliseconds with a sampling period of 1.0 millisecond and detects a voltage drop based on the average value.

[0098] Here, time X2 represents "the time [milliseconds] during which the DC voltage flowing through the DC link 20 falls below the voltage Vdc shown on the left of the table when a voltage drop occurs in the AC power supply 11." For example, the column where time X2 is 0.1 and DC voltage Vdc is 255 indicates that "the DC voltage flowing through the DC link 20 fell below 255V for 0.1 milliseconds."

[0099] Let's explain each column. First, "normal" means "a range in which low-voltage protection is not activated, normal operation continues, and the risk of component failure due to inrush current is low." In Figures 4 and 5, the range in which the DC voltage Vdc is 198V or higher is shown as "normal" at all times X2. This is because the voltage drop from the normal DC voltage Vdc of 255V is small, so the inrush current is unlikely to be large in the first place, and the risk of component failure is low.

[0100] Next, "NG" means "a range where low-voltage protection is not performed, normal operation continues, and there is a high risk of component failure due to inrush current." The range that results in NG is a range where low-voltage protection should ideally be performed, but is not performed due to various circumstances such as insufficient time for low-voltage protection.

[0101] In the comparative example shown in Figure 4, the result is "NG" when the DC voltage Vdc is 184V or less and the time X2 is shorter than 10 milliseconds. This is because the voltage drop in DC voltage Vdc from the normal state (255V) is relatively large, increasing the risk of inrush current. However, since this voltage drop occurs only for a short time, the voltage drop cannot be detected, and undervoltage protection is not performed.

[0102] Furthermore, in conventional protection circuits, the threshold for detecting a drop in DC voltage Vdc was set to approximately 160V in order to suppress failures of inverter circuits 25 and 26 caused by a drop in DC voltage Vdc. Therefore, in the range shown in Figure 4 where the DC voltage Vdc is 184V or less and the time X2 is 10 milliseconds or more, the low voltage protection is not performed and the result is NG because the drop in DC voltage Vdc cannot be detected in relation to the above threshold.

[0103] Here, "n-LVP" refers to the range in which undervoltage protection can be provided by the conventional protection circuit. In Figure 4, undervoltage protection can be provided by the conventional protection circuit in the range where the DC voltage Vdc is 156V or less and the time X2 is 10 milliseconds or more.

[0104] In Figure 5, when the DC voltage Vdc is 184V or less and the time X2 is 0.1 milliseconds or less, the voltage drop occurs only for a short time (specifically, less than the predetermined time Y1), so the voltage drop cannot be detected and the protection control is not executed, resulting in an "NG" (Not Safe) result.

[0105] However, in the control device 27, it is possible to perform protective control over this range by shortening the predetermined interval X1 (0.162 milliseconds in the above example) and predetermined time Y1 (0.32 milliseconds in the above example) for sampling the DC voltage Vdc, and by employing circuits with high response speed in the inverter circuits 25, 26, etc. In other words, it is possible to set this range to the range indicated by "i-LVP" described later, rather than "NG". However, considering that setting the predetermined time Y1 to an extremely short value increases the monitoring burden on the control device 27, and that the inrush current is less likely to increase as time X2 is shorter, in this embodiment, 0.32 milliseconds is adopted as a preferred example of the predetermined time Y1.

[0106] Here, "i-LVP" refers to the range in which undervoltage protection can be provided by the protection control of the control device 27 according to this embodiment. In Figure 5, undervoltage protection can be provided by the said protection control in the range in which the DC voltage Vdc is 184V or less and the time X2 is 0.5 milliseconds or more.

[0107] The extended protectionable time range from "10 milliseconds or more" in Figure 4 to "0.5 milliseconds or more" in Figure 5 is due to the shortening of the predetermined interval X1 and predetermined time Y1, as described above. Furthermore, the extended protectionable voltage range from "156V or less" in Figure 4 to "184V or less" in Figure 5 (since protection is not required for voltages above 184V, the entire voltage range is protected) is due to the fact that, while the threshold was set to 160V in the conventional design focusing on the protection of inverter circuits 25 and 26, in this embodiment, the threshold (first threshold Th1) is set to a higher value (for example, 190V) by focusing on the inrush current.

[0108] Thus, while Figure 4 shows "NG" over a wide range, in Figure 5, "NG" is limited to a specific range where the DC voltage Vdc is 184V or less and the time X2 is 0.1 milliseconds or less. Furthermore, even within this range, it is possible to make it possible to perform "i-LVP," that is, undervoltage protection by protective control, by appropriately adjusting the predetermined time Y1.

[0109] Furthermore, even when the protection range is extended in terms of time and voltage as described above, in this embodiment, unnecessary protection operations can be avoided by imposing the restriction that "the power buffer circuit 24 does not operate as a boost circuit (when the second switch S2 has stopped switching)" as a condition for executing the protection operation.

[0110] As described above, the power converter 10 according to this embodiment makes it possible to provide low-voltage protection even in ranges where it was practically difficult to provide low-voltage protection with conventional protection circuits, and the power converter 10 including the power buffer circuit 24 can be protected from momentary power outages.

[0111] [Differentiation] The following describes modified examples of the embodiments. In the modified examples, components identical to those in the above embodiments are denoted by the same reference numerals and their descriptions are omitted.

[0112] [Comparative Examples of Protection Control] In this embodiment, the control device 27 performs the following protective controls in this order: stop control (step S14), interruption control (step S15), and restart control (step S16). However, the protective controls performed by the control device 27 are not limited to these.

[0113] For example, the control device 27 may perform only stop control or only cutoff control as protective control. By performing at least one of stop control and cutoff control in this way, it is possible to suppress excessive inrush current from entering the first capacitor C4, thereby protecting the power converter 10, including the power buffer circuit 24, from momentary power outages.

[0114] [Effects of the Embodiment] (1) The power converter 10 according to this embodiment includes a converter circuit 22 that converts AC input from an AC power source 11 to DC, a DC link 20 including a first power line LH and a second power line LL connected to the output side of the converter circuit 22, a power buffer circuit 24 that receives charging power from the DC link 20 and outputs discharge power to the DC link 20, inverter circuits 25 and 26 that convert DC input from the DC link 20 to AC and output to loads 12 and 13, and a control device 27 that controls the power buffer circuit 24 and the inverter circuits 25 and 26, the power buffer circuit 24 includes a first capacitor C4 and a first switch S1 connected in series with the first capacitor C4, and a discharge circuit 24a that supplies discharge power to the DC link 20 by the discharge of the first capacitor C4 when the first switch S1 conducts between the DC links 20, and The power converter 10 includes a reactor L4 and a second switch S2 connected in series with the first reactor L4, and a charging circuit 24b that charges the first capacitor C4 with the charging power input from the DC link 20 and stored in the first reactor L4 when the second switch S2 is performing a switching operation that repeatedly switches between conducting and not conducting between the DC link 20, and the control device 27 performs protection control when the second switch S2 stops the switching operation and the voltage of the first capacitor C4 or the voltage between the DC link 20 Vdc falls below a predetermined first threshold Th1, and the protection control includes at least one of a stop control S14 that stops the conversion from DC to AC in the inverter circuits 25, 26, and a cutoff control S15 that cuts off the connection between the AC power supply 11 and the converter circuit 22.

[0115] When the second switch S2 stops switching, the first capacitor C4 is not charged, so the voltage Vc of the first capacitor C4 tends to drop during a power outage, and the inrush current tends to increase. In such cases, the control device 27 can protect the power converter 10, including the power buffer circuit 24, from momentary power outages by performing protective control.

[0116] (2) Preferably, the system further includes a relay circuit 21 that controls the conduction between the AC power supply 11 and the converter circuit 22, and the interruption control S15 includes control of the relay circuit 21 to interrupt the connection between the AC power supply 11 and the converter circuit 22.

[0117] By interrupting the connection between the AC power supply 11 and the converter circuit 22 using the relay circuit 21, it is possible to prevent inrush current from entering circuits 22 to 26 after the converter circuit 22.

[0118] (3) Preferably, the protection control includes a stop control S14, a cutoff control S15 performed after the stop control S14, and a restart control S16 performed after the cutoff control S15 to initiate the DC to AC conversion in the inverter circuits 25, 26.

[0119] Generally, the response speed of the relay circuit 21 is slower than that of the inverter circuits 25 and 26. Therefore, by performing the stop control S14 for the inverter circuits 25 and 26 first in the protection control, the voltage in the first capacitor C4 can be maintained, and even if an inrush current occurs before the tripping control S15 for the relay circuit 21, it is possible to suppress the inrush current from becoming large. Furthermore, by performing the restart control S16 after the tripping control S15, the charge in the first capacitor C4 can be released to the loads 12 and 13 while preventing the inflow of inrush current. This makes it possible to more reliably protect the power converter 10, including the power buffer circuit 24, from momentary power outages.

[0120] (4) Preferably, the control device 27 performs protective control only while loads 12 and 13 are in operation.

[0121] Generally, when loads 12 and 13 are not operating, the power converter 10 can be protected from momentary power outages by the circuit breaker. In contrast, when loads 12 and 13 are operating, it is not possible to take measures with the circuit breaker, so protective control by the control device 27 becomes more important. By executing protective control only when loads 12 and 13 are operating, the situations in which protective control is executed can be limited, and the control burden on the control device 27 can be reduced.

[0122] (5) Preferably, the control device 27 detects the voltage Vc of the first capacitor C4 or the voltage Vdc between the DC links 20 at predetermined intervals X1, and executes protection control when the voltage Vc of the first capacitor C4 or the voltage Vdc between the DC links 20 is 2 or more predetermined times n1 consecutively below the first threshold Th1.

[0123] With this configuration, the control device 27 detects the voltage Vc of the first capacitor C4 or the voltage Vdc across the DC link 20 at a predetermined sampling period. If the need for protection control is determined based on only one sampling, protection control may be frequently triggered due to false detections caused by, for example, momentary noise, potentially hindering power conversion in the power converter 10. Therefore, by executing protection control when these voltages Vc and Vdc remain below the first threshold Th1 for a predetermined number of n1 or more consecutive times, malfunctions can be reduced.

[0124] (6) Preferably, the predetermined interval X1 is 0.5 milliseconds or less, and the predetermined number of times n1 is 2.

[0125] For example, conventionally, voltage was sampled at 1-millisecond intervals, and normal LVP (Low Voltage Protection) was performed based on the average value of 10 samples, making it impossible to respond to very short momentary power outages. In contrast, by shortening the sampling interval to 0.5 milliseconds or less, and further limiting the number of samples to two, it is possible to reduce malfunctions while enabling protective control even for very short momentary power outages. This makes it possible to protect the power converter 10, including the power buffer circuit 24, from momentary power outages.

[0126] (7) Preferably, the converter circuit 22, power buffer circuit 24, inverter circuits 25, 26 and smoothing circuit 23 are mounted on a printed circuit board, and the DC resistance of the second reactor L3 is 50 mΩ or less.

[0127] Increasing the DC resistance of the second reactor L3 can reduce the inrush current flowing through each component. However, this can lead to problems such as dielectric breakdown of the reactor or deformation of the printed circuit board due to the reactor overheating during operation. In this disclosure, inrush current is prevented by protective control, thus reducing the need to select a reactor with a large DC resistance value as the second reactor L3, and allowing the use of a smaller reactor with a DC resistance value of 50 mΩ or less. This eliminates the aforementioned problems associated with a large DC resistance value.

[0128] (8) Preferably, the converter circuit 22, the power buffer circuit 24, and the inverter circuits 25 and 26 are mounted on a printed circuit board, and the capacitance of the first capacitor C4 is 760uF or more.

[0129] While a larger capacitance of the first capacitor C4 allows for greater power output to the inverter circuits 25 and 26, it also carries the risk of increased inrush current. In this disclosure, inrush current is prevented by protective control, allowing the use of a capacitor with a larger capacitance as the first capacitor C4 with a lower risk.

[0130] (9) The control device 27 of the present disclosure is a control device 27 that controls the power converter 10a, the power converter 10a comprises a converter circuit 22 that converts AC output from AC power source 11 to DC, a DC link 20 including a first power line LH and a second power line LL connected to the output side of the converter circuit 22, a power buffer circuit 24 that receives charging power from the DC link 20 and outputs discharge power to the DC link 20, and inverter circuits 25 and 26 that convert the DC input from the DC link 20 to AC and output to loads 12 and 13, the power buffer circuit 24 includes a first capacitor C4 and a first switch S1 connected in series with the first capacitor C4, and a discharge circuit 24a that supplies discharge power to the DC link 20 by the discharge of the first capacitor C4 when the first switch S1 conducts between the DC links 20, and first The control device 27 includes a reactor L4 and a second switch S2 connected in series with the first reactor L4, and a charging circuit 24b that charges the first capacitor C4 with the charging power input from the DC link 20 and stored in the first reactor L4 when the second switch S2 is performing a switching operation that repeatedly switches between a state of conducting and a state of not conducting between the DC links 20, and the control device 27 performs protection control when the second switch S2 stops switching operation and the voltage of the first capacitor C4 or the voltage between the DC links 20 Vdc falls below a predetermined first threshold Th1, and the protection control includes at least one of a stop control S14 that stops the conversion from DC to AC in the inverter circuits 25,26, and a cutoff control S15 that cuts off the connection between the AC power supply 11 and the converter circuit 22.

[0131] When the second switch S2 stops switching, the first capacitor C4 is not charged, so the voltage of the first capacitor C4 tends to drop during a power outage, and the inrush current tends to increase. In such cases, the control device 27 can protect the power converter 10a, including the power buffer circuit 24, from momentary power outages by performing protective control.

[0132] [Note] Although embodiments and variations have been described above, it should be understood that a variety of changes in form and details are possible without departing from the spirit and scope of the claims. [Explanation of Symbols]

[0133] 10: Power converter, 10a: Power converter, 11: AC power supply, 12: Load, 13: Load, 20: DC link, 21: Relay circuit, 22: Converter circuit, 23: Smoothing circuit, 24: Power buffer circuit, 24a: Discharge circuit, 24b: Charging circuit, 25: Inverter circuit, 26: Inverter circuit, L4: First reactor, L3: Second reactor, C4: First capacitor, C3: Second capacitor, S1: First switch, S2: Second switch, D2 1: Diode, D22: Diode, D23: Diode, D24: Diode, D40: Diode, D41: Diode, D42: Diode, D43: Diode, SC: Transistor, SL: Transistor, X1: Determined interval, Y1: Determined time, Y2: Determined time, n1: Determined number of times, Th1: First threshold, Vin: Single-phase AC voltage, Vrec: Rectified voltage, Vc: Voltage across both ends, Vdc: DC voltage, LH: First power line, LL: Second power line

Claims

1. A converter circuit (22) that converts AC input from an AC power source (11) to DC, A DC link (20) including a first power line (LH) and a second power line (LL) connected to the output side of the converter circuit (22), A power buffer circuit (24) receives charging power from the DC link (20) and outputs discharge power to the DC link (20), An inverter circuit (25, 26) converts the DC input from the DC link (20) into AC and outputs it to the load (12, 13), A control device (27) that controls the power buffer circuit (24) and the inverter circuits (25, 26), Equipped with, The aforementioned power buffer circuit (24) A discharge circuit (24a) includes a first capacitor (C4) and a first switch (S1) connected in series with the first capacitor (C4), wherein when the first switch (S1) conducts between the DC links (20), discharge power is supplied to the DC links (20) by the discharge of the first capacitor (C4), A charging circuit (24b) includes a first reactor (L4) and a second switch (S2) connected in series with the first reactor (L4), and when the second switch (S2) is performing a switching operation that repeatedly switches between a state of conducting and a state of not conducting between the DC links (20), the charging circuit (24b) charges the first capacitor (C4) with the charging power input from the DC links (20) and stored in the first reactor (L4), It has, The control device (27) executes protection control when the second switch (S2) stops the switching operation and the voltage (Vc) of the first capacitor (C4) or the voltage (Vdc) across the DC link (20) falls below a predetermined first threshold (Th1). The aforementioned protective control is The inverter circuits (25, 26) perform a stop control (S14) to stop the conversion from DC to AC, and A cutoff control (S15) that cuts off the connection between the AC power supply (11) and the converter circuit (22), Including at least one of the following: Power converter (10).

2. A relay circuit (21) controls the conduction between the AC power supply (11) and the converter circuit (22). It further includes, The aforementioned disconnection control (S15) includes control of the relay circuit (21) to disconnect the AC power supply (11) and the converter circuit (22). The power conversion device (10) according to claim 1.

3. The aforementioned protective control is The aforementioned stop control (S14), The shutdown control (S15) is performed after the stop control (S14), The restart control (S16) is performed after the interruption control (S15) and starts the conversion from DC to AC in the inverter circuits (25, 26), including, The power conversion device (10) according to claim 2.

4. The control device (27) executes the protective control only while the loads (12, 13) are in operation. A power conversion device (10) according to any one of claims 1 to 3.

5. The control device (27) detects the voltage (Vc) of the first capacitor (C4) or the voltage (Vdc) between the DC links (20) at predetermined intervals (X1), and executes the protection control when the voltage (Vc) of the first capacitor (C4) or the voltage (Vdc) between the DC links (20) is 2 or more predetermined times (n1) and falls below the first threshold (Th1). A power conversion device (10) according to any one of claims 1 to 3.

6. The predetermined interval (X1) is 0.5 milliseconds or less. The predetermined number of times (n1) is 2. The power conversion device (10) according to claim 5.

7. A smoothing circuit (23) that smooths the DC input to the power buffer circuit (24), including a second reactor (L3) connected in series with the first power line (LH), Furthermore, The converter circuit (22), the power buffer circuit (24), the inverter circuits (25, 26), and the smoothing circuit (23) are each mounted on a printed circuit board. The DC resistance of the second reactor (L3) is 50 mΩ or less. A power conversion device (10) according to any one of claims 1 to 3.

8. The converter circuit (22), the power buffer circuit (24), and the inverter circuits (25, 26) are each mounted on a printed circuit board. The capacitance of the first capacitor (C4) is 760uF or more. A power conversion device (10) according to any one of claims 1 to 3.

9. A control device (27) for controlling a power converter (10a), The power converter (10a) is A converter circuit (22) that converts the AC output from the AC power supply (11) to DC, A DC link (20) including a first power line (LH) and a second power line (LL) connected to the output side of the converter circuit (22), A power buffer circuit (24) receives charging power from the DC link (20) and outputs discharge power to the DC link (20), An inverter circuit (25, 26) converts the DC input from the DC link (20) into AC and outputs it to the load (12, 13), Equipped with, The aforementioned power buffer circuit (24) A discharge circuit (24a) includes a first capacitor (C4) and a first switch (S1) connected in series with the first capacitor (C4), wherein when the first switch (S1) conducts between the DC links (20), discharge power is supplied to the DC links (20) by the discharge of the first capacitor (C4), A charging circuit (24b) includes a first reactor (L4) and a second switch (S2) connected in series with the first reactor (L4), and when the second switch (S2) is performing a switching operation that repeatedly switches between a state of conducting and a state of not conducting between the DC links (20), the charging circuit (24b) charges the first capacitor (C4) with the charging power input from the DC links (20) and stored in the first reactor (L4), It has, The control device (27) executes protection control when the second switch (S2) stops the switching operation and the voltage (Vc) of the first capacitor (C4) or the voltage (Vdc) across the DC link (20) falls below a predetermined first threshold (Th1). The aforementioned protective control is The inverter circuits (25, 26) perform a stop control (S14) to stop the conversion from DC to AC, and A cutoff control (S15) that cuts off the connection between the AC power supply (11) and the converter circuit (22), Including at least one of the following: Control device (27).

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