Braking device, power conversion system, and braking control method

Abstract

To make it possible to further enhance operation continuity of a power converter provided with a braking device.SOLUTION: A braking device in a power conversion system in which an AC motor is driven by a regenerative AC / DC converter includes: a first series circuit, a second series circuit, and a braking control unit. The first series circuit is provided so as to be connected in parallel to a DC side of the AC / DC converter and includes a first braking resistor and a first semiconductor switch. The second series circuit is connected in parallel to the first series circuit, and includes a second braking resistor and a second semiconductor switch. When temperature of one of the first braking resistor and the second braking resistor is in a first state exceeding first threshold temperature, the braking control unit sets a drive method of the first semiconductor switch or the second semiconductor switch to a drive method different from the drive method in a case where temperature of the braking resistor does not exceed the first threshold temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a braking device, a power conversion system, and a braking control method. [Background technology]

[0002] When an electric motor driven by a power converter is braked, regenerative energy is generated on the DC side of the power converter. A braking device converts this regenerative energy into heat and consumes it using a braking resistor installed on the DC side of the power converter. While there are power conversion systems that suspend operation of the power converter when a malfunction related to temperature rise occurs in the braking device, there has been a demand for improved operational continuity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-027114 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a braking device, a power conversion system, and a braking control method that can further improve the operational continuity of a power converter equipped with a braking device. [Means for solving the problem]

[0005] A braking device according to one aspect of the embodiment is a braking device in a power conversion system that drives an AC motor using a regenerative AC / DC converter. The braking device includes a first series circuit, a second series circuit, and a braking control unit. The first series circuit is connected in parallel to the DC side of the AC / DC converter and includes a first braking resistor and a first semiconductor switch. The second series circuit is connected in parallel to the first series circuit and includes a second braking resistor and a second semiconductor switch. The braking control unit controls the first semiconductor switch or the second semiconductor switch when in a first state or a second state. Control Temperature of the moving resistor is the The first state is a state in which the temperature of either the first braking resistor or the second braking resistor exceeds a threshold temperature. The aforementioned The second condition includes a condition in which the temperatures of both the first braking resistor and the second braking resistor exceed a first threshold temperature. The aforementioned The braking resistor temperature may exceed a first threshold temperature, or the temperature of either the first braking resistor or the second braking resistor may exceed a second threshold temperature. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a configuration diagram of a power conversion system including a braking device according to an embodiment. [Figure 2] FIG. 3 is a diagram for explaining a control rule for braking control according to the embodiment. [Figure 3] FIG. 3 is a schematic block diagram of the braking device shown in FIG. 2. [Figure 4] FIG. 4 is a block diagram showing an example of a comparator shown in FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, a braking device, a power conversion system, and a braking method according to embodiments will be described with reference to the drawings. In the following description, components having the same or similar functions will be assigned the same reference numerals. Duplicate descriptions of these components may be omitted. Electrical connection may simply be referred to as "connected." In the following description, "orthogonal" includes cases where the components are approximately orthogonal. In addition, "equal in size" includes cases where the components are approximately equal.

[0008] FIG. 1 is a configuration diagram of a power conversion system 1 including a braking device 20 according to an embodiment.

[0009] The power conversion system 1 includes, for example, a diode converter 2 (REC), an inverter 3 (INV), a smoothing capacitor 4, a power conversion control device 10, and a braking device 20.

[0010] First, the configuration of the main circuit will be described in order. The DC output of the diode converter 2 and the DC input of the inverter 3 are electrically connected via a DC link, with their positive poles (P) electrically connected to each other and their negative poles (N) electrically connected to each other. A smoothing capacitor 4 is provided in the DC link, and each terminal of the smoothing capacitor 4 is electrically connected to the positive pole and the negative pole of the DC link, respectively.

[0011] Diode converter 2 is, for example, a three-phase AC input rectifier, and its input section is electrically connected to the secondary winding of input transformer T. Diode converter 2 rectifies AC to convert AC power input from input transformer T into DC power. Smoothing capacitor 4 smoothes the converted DC voltage.

[0012] The inverter 3 has an AC side connected to the windings of the AC motor M. The inverter 3, for example, converts DC power to AC power and outputs the converted AC power to each phase of the AC motor M. An output transformer (not shown) may be provided between the inverter 3 and the AC motor M. The inverter 3 includes, for example, a switching element that converts the DC power on the DC side into AC power, and a reverse-connected diode connected in anti-parallel to the switching element. The switching element is an example of a semiconductor switching element. The inverter 3 is a three-phase AC output type inverter.

[0013] Next, the power conversion control device 10 will be described. The power conversion control device 10 includes a speed controller 11, a current controller 13, a PWM control unit 14 (PWM), and a first gate signal control unit 15 (GB1).

[0014] The speed controller 11 generates a torque command such that the speed detection value detected by the speed detector SS of the AC motor M coincides with a speed command SREF supplied from, for example, a higher-level device. The current controller 13 generates a control variable such that a desired current based on the torque command flows through the windings of the AC motor M. The PWM control unit 14 PWM-modulates the control variable from the previous stage to generate gate pulses for controlling the switches of the inverter 3.

[0015] The first gate signal control unit 15 (GB1) supplies the gate pulse output generated by the PWM control unit 14 to the inverter 3. The first gate signal control unit 15 limits the output of the gate pulse in accordance with the control signal GB. For example, when the control signal GB is 1, the first gate signal control unit 15 limits the output of the gate pulse, and when the control signal GB is 0, the first gate signal control unit 15 outputs the gate pulse.

[0016] Next, the braking device 20 will be described. The braking device 20 includes braking resistors 5A and 5B, switches 6A and 6B, temperature sensors 7A and 7B, cooling fans 8A and 8B, a state estimation unit 21, a modulation unit 22 (MOD), and a second gate signal control unit 23 (GB2).

[0017] Braking resistors 5A and 5B are an example of a braking resistor that converts regenerative energy into heat by the flow of discharge current from smoothing capacitor 4. Freewheeling diodes (not shown) may be provided in parallel with braking resistors 5A and 5B.

[0018] The switches 6A and 6B each include a switching element and a reverse-connected diode connected in antiparallel to the switching element. The switching element is an example of a semiconductor switching element.

[0019] Braking resistor 5A and switch 6A are connected in series with each other and connected via a DC link so that both ends of the series connection are in parallel with smoothing capacitor 4. When switch 6A is closed, a discharge current flows through braking resistor 5A to discharge the charge accumulated in smoothing capacitor 4. Braking resistor 5B and switch 6B are connected in series with each other and connected via a DC link so that both ends of the series connection are in parallel with smoothing capacitor 4. When switch 6B is closed, a discharge current flows through braking resistor 5A to discharge the charge accumulated in smoothing capacitor 4.

[0020] The temperature sensor 7A is disposed near the braking resistor 5A and is configured to be able to detect the temperature of the braking resistor 5A. The temperature sensor 7B is disposed near the braking resistor 5B and is configured to be able to detect the temperature of each of the braking resistors 5B.

[0021] The cooling fan 8A is arranged near the braking resistor 5A and provides ventilation around the braking resistor 5A and its heat sink, thereby improving the cooling efficiency of the braking resistor 5A. The cooling fan 8B is arranged near the braking resistor 5B and provides ventilation around the braking resistor 5B and its heat sink, thereby improving the cooling efficiency of the braking resistor 5B. The cooling fan 8A detects when it has stopped due to a malfunction or the like, and upon detection, outputs a fan stop signal FAA. The cooling fan 8B detects when it has stopped due to a malfunction or the like, and upon detection, outputs a fan stop signal FAB.

[0022] The state estimation unit 21 estimates the state of the braking device 20 based on the temperatures of the braking resistors 5A and 5B and the operating states of the cooling fans 8A and 8B. For example, the state estimation unit 21 estimates the temperatures of the braking resistors 5A and 5B from the detection results of the temperature sensors 7A and 7B. The state estimation unit 21 estimates the operating states of the cooling fans 8A and 8B using the fan stop signals FAA and FAB. Based on the estimated state of the braking device 20, the state estimation unit 21 generates an alarm signal ALM, braking torque limit value control signals TL1 and TL2, and gate control signals GCA and GCB. The braking torque limit value control signals TL1 and TL2 are simply referred to as signals TL1 and TL2.

[0023] The modulation unit 22 determines the braking torque in response to a braking request from, for example, a host device, and PWM-modulates a signal corresponding to the braking torque to generate gate pulses GPA0 and GPB0 for controlling the switches 6A and 6B. The braking torque in response to the braking request may be determined, for example, using a conversion table. The modulation unit 22 may limit the upper limit of the braking torque based on the estimated state of the braking device 20. The upper limit is the limit here, and no limit is imposed if the level does not reach the upper limit. For example, the modulation unit 22 may limit the upper limit of the braking torque based on the estimated state of the braking device 20.

[0024] The second gate signal control unit 23 (GB2) receives a gate pulse GPA0 from the modulation unit 22 and controls the output of the gate pulse GPA to the switch 6A based on the gate control signal GCA from the state estimation unit 21. When the gate control signal GCA from the state estimation unit 21 is significant, the output of the gate pulse GPA is limited. The second gate signal control unit 23 receives a gate pulse GPB0 from the modulation unit 22 and controls the output of the gate pulse GPB to the switch 6B based on the gate control signal GCB from the state estimation unit 21. When the gate control signal GCB from the state estimation unit 21 is significant, the output of the gate pulse GPB is limited.

[0025] Referring to FIG. 2, the control rules for braking control by the braking device 20 of the embodiment will be described. 2 is a diagram for explaining the control rules for braking control in the embodiment. An example of the control rules for braking control by the braking device 20 is summarized in a table. The table of control rules has the items of "detection condition," "processing," and "determination." The conditions for the braking device 20 to detect a state are shown in the "detection condition," and the "processing" performed by the braking device 20 in accordance with these conditions and the results of the "determination" of the braking device 20 are shown, respectively.

[0026] First detection condition: When "the cooling fan 8A or 8B stops" or "the temperature of the braking resistor 5A or 5B reaches a first high temperature state," the braking device 20 "issues an alarm" and outputs a control signal TCONT that "limits the regenerative torque to 50%." In this case, the braking device 20 determines that a "minor malfunction" has occurred. The first high temperature state is a state in which the temperature exceeds a first threshold temperature TH1, which will be described later.

[0027] Second detection condition: When "both cooling fans 8A and 8B have stopped" or "when the temperatures of both braking resistors 5A and 5B have reached the first high temperature state," the braking device 20 "issues an alarm" and outputs a control signal TCONT that "limits the regenerative torque to 0.5%." In this case, the braking device 20 determines that a "minor malfunction" has occurred.

[0028] Third detection condition: When the temperatures of both braking resistors 5A and 5B reach the second high temperature state, the braking device 20 stops the power conversion device. In this case, the braking device 20 determines that a serious malfunction has occurred. The second high temperature state is a state in which the temperature exceeds a second threshold temperature TH2, which will be described later.

[0029] The operation of the braking device 20 that utilizes the detection conditions shown in FIG. 2 will now be described.

[0030] By including braking resistors 5A and 5B, braking device 20 is configured so that the allowable limit of braking force (referred to as the regenerative torque limit) is higher than when a single braking resistor with the same specifications as braking resistors 5A and 5B is used. When braking device 20 is in a normal state, braking control device 9 continues operation of the power conversion system and applies braking using switches 6A and 6B to obtain the desired braking force (regenerative torque). The regenerative torque limit at this time is set to 100%. Note that this regenerative torque limit is double that of a configuration using a single braking resistor. In other words, by providing braking resistors 5A and 5B, the braking force under normal conditions is higher than that of a configuration using a single braking resistor.

[0031] If the temperature of one of the braking resistors 5A and 5B exceeds the first threshold temperature TH1, or if a malfunction occurs in one of the cooling fans 8A and 8B, the braking device 20 temporarily restricts the use of the braking resistor in which the high temperature or cooling fan malfunction is detected, thereby lowering the braking resistor temperature to a desired range. If the temperature of the braking resistor exceeds the first threshold temperature TH1, the other braking resistor is used to continue operating the power conversion system. In this case, the regenerative torque limit is 50% of the normal limit, but the braking force (regenerative torque) equivalent to that obtained with a single braking resistor can be obtained. By temporarily restricting the use of the braking resistor in this way, the braking device 20 limits further temperature rise.

[0032] If the temperatures of both braking resistors 5A and 5B are higher than the first threshold temperature, or if a malfunction occurs in both cooling fans 8A and 8B, the braking device 20 temporarily limits the use of both braking resistors 5A and 5B to control the braking resistor temperatures to fall to a desired range. During this time, the braking device 20 controls the switches 6A and 6B so that the temperatures of the braking resistors 5A and 5B fall to the desired range. More specifically, during this time, the braking device 20 turns off the switches 6A and 6B. The braking device 20 temporarily reduces the regenerative torque limit to temporarily reduce the braking force (regenerative torque), thereby limiting the regenerative torque. Even in this state, the power conversion system 1 continues to operate.

[0033] The braking device 20 continues the above control even if the temperature of either the braking resistor 5A or 5B becomes higher than the first threshold temperature TH1 or the second threshold temperature TH2, thereby continuing operation of the power conversion system 1. The second threshold temperature TH2 is set higher than the first threshold temperature TH1.

[0034] When the temperatures of both braking resistors 5A and 5B are higher than the second threshold temperature, there is a possibility that a factor preventing the temperature from being restored has occurred. When the temperatures of both braking resistors 5A and 5B are higher than the second threshold temperature, braking device 20 suspends operation of power conversion system 1.

[0035] The braking device 20 continues to monitor the state of the braking device 20 during the period from when the power conversion system 1 is in operation until the operation is interrupted (stopped), and continues the operation of the power conversion system 1 accordingly.

[0036] Figure 3 shows a schematic block diagram of the braking device 20 shown in Figure 2. Unless otherwise specified, the input and output logic of each calculation block is positive logic. The range shown in Figure 3 includes the range related to the state estimation unit 21, modulation unit 22, and second gate signal control unit 23 of the braking device 20.

[0037] The state estimation unit 21 includes, for example, calculation blocks 211 to 218.

[0038] The calculation block 211 is a signal level determiner. The operation block 211 includes a comparator that compares the magnitude of the signals input to the input terminals. A first input of the calculation block 211 is connected to the terminal TB7A. The terminal TB7A is a terminal connected to the output of the temperature sensor 7A. A signal TRA indicating the temperature of the braking resistor 5A detected by the temperature sensor 7A is supplied to the first input of the calculation block 211.

[0039] A second input of the calculation block 211 is connected to a terminal TB7B. The terminal TB7B is a terminal connected to the output of the temperature sensor 7B. A signal TRB indicating the temperature of the braking resistor 5B detected by the temperature sensor 7B is supplied to the second input of the calculation block 211.

[0040] FIG. 4 is a block diagram showing an example of the comparator (arithmetic block 211) shown in FIG. The calculation block 211 includes, for example, four comparators, calculation blocks 211a to 211d. The calculation block 211a identifies the temperature indicated by the signal TRA using the second threshold temperature TH2 and outputs a signal HTRA indicating the identification result from a first output of the calculation block 211. The calculation block 211b identifies the temperature indicated by the signal TRB using the second threshold temperature TH2 and outputs a signal HTRB indicating the identification result from a second output of the calculation block 211. The calculation block 211c identifies the temperature indicated by the signal TRA using the first threshold temperature TH1 and outputs a signal LTRA indicating the identification result from a third output of the calculation block 211. The calculation block 211d identifies the temperature indicated by the signal TRB using the first threshold temperature TH1 and outputs a signal LTRB indicating the identification result from a fourth output of the calculation block 211. For example, the calculation block 211a outputs 1 as the signal HTRA when the temperature indicated by the signal TRA exceeds the second threshold temperature TH2, and outputs 0 when the temperature does not exceed the second threshold temperature TH2. The same applies to the other calculation blocks.

[0041] Returning to FIG. 3, the explanation will continue. A first input of operation block 212 is connected to a first output of operation block 211. A second input of operation block 212 is connected to a second output of operation block 211. A first input of operation block 213 and a first input of operation block 216 are connected to a third output of operation block 211. A second input of operation block 213 and a second input of operation block 216 are connected to a fourth output of operation block 211.

[0042] A first input of the calculation block 214 and a first input of the calculation block 217 are connected to the terminal TB8A. A fan alarm signal FAA detected by the cooling fan 8A is supplied via the terminal TB8A to the first input of the calculation block 214 and the first input of the calculation block 217. For example, when the cooling fan 8A stops, the fan alarm signal FAA becomes 1.

[0043] A second input of the calculation block 214 and a first input of the calculation block 217 are connected to the terminal TB8B. A fan alarm signal FAB detected by the cooling fan 8B is supplied via the terminal TB8B to the second input of the calculation block 214 and the first input of the calculation block 217. For example, when the cooling fan 8B stops, the fan alarm signal FAB becomes 1.

[0044] Operation block 213 and operation block 214 are OR gates that perform a logical OR operation on two inputs. Operation block 213 outputs the operation result as signal GCA. Operation block 214 outputs the operation result as signal GCB. The output of operation block 213 is connected to a first input of operation block 215 and a first input of second gate signal control unit 23. The output of operation block 214 is connected to a second input of operation block 215.

[0045] Operation block 216 and operation block 217 are AND gates that perform a logical AND operation on two inputs. Operation block 216 and operation block 217 output the operation results as signals S216 and S217. The output of operation block 216 is connected to a first input of operation block 218. The output of operation block 217 is connected to a second input of operation block 218.

[0046] Operation block 215 and operation block 218 are OR gates that perform a logical OR operation on two inputs. Operation block 215 outputs the operation result as signal TL1. Operation block 218 outputs the operation result as signal TL2. A first input of modulation unit 22 is connected to the output of operation block 215. A second input of modulation unit 22 is connected to the output of operation block 218.

[0047] When the detection condition 1 in FIG. 2 is satisfied, the signal TL1 becomes 1. When the detection condition 2 in FIG. 2 is satisfied, the signal TL2 becomes 1.

[0048] The second gate signal control unit 23 includes operation blocks 231 and 232. The operation blocks 231 and 232 are two-input AND gates with a first input being negative logic. A gate control signal GCA from the previous stage is supplied to a first input of the operation block 231 and a first input of the operation block 232. A gate signal GPA0 is supplied to a second input of the operation block 231. A gate signal GPB0 is supplied to a second input of the operation block 232.

[0049] When the braking device 20 is in a normal state, the signals TL1, TL2 and gate control signal GCA are all 0, and the gate control signals GCA and GCB are 0. When signals TL1 and TL2 are both 0, modulation unit 22 sets the regenerative torque limit to the value (100%) when braking device 20 is in a normal state, and generates gate signals GPA0 and GPB0 according to the magnitude of the required torque. Because gate control signal GCA is 0, second gate signal control unit 23 transparently outputs gate signals GPA0 and GPB0 supplied from modulation unit 22 as gate signals GPA and GPB.

[0050] When the state of the braking device 20 is determined to be a minor failure, either the signal TL1 or the signal TL2 is 1 and the gate control signal GCA is 0 according to the configuration shown in FIG. The modulation unit 22 sets the regenerative torque limit to a value (for example, 50% or 0.5%) that is lower than the value when the braking device 20 is in a normal state, based on the values ​​of the signals TL1 and TL2, and limits the maximum value accordingly to generate gate signals GPA0 and GPB0 according to the magnitude of the required torque. In the case of a minor fault, the gate control signal GCA is 0, so the second gate signal control unit 23 transparently outputs the gate signals GPA0 and GPB0 supplied from the modulation unit 22 as gate signals GPA and GPB.

[0051] When the state of the braking device 20 is determined to be a serious failure, both the signals TL1 and TL2 are 1 and the gate control signal GCA is 1 according to the configuration shown in FIG. The modulation unit 22 sets the regenerative torque limit to a value (for example, 0.5%) that is lower than the value when the braking device 20 is in a normal state, based on the values ​​of the signals TL1 and TL2, and generates gate signals GPA0 and GPB0 according to the magnitude of the required torque by restricting the maximum value. In the case of a major fault, the gate control signal GCA is 1, so the second gate signal control unit 23 masks the gate signals GPA0 and GPB0 supplied from the modulation unit 22 and restricts the output of the gate signals GPA and GPB.

[0052] According to the embodiment, the braking device 20 is a braking device in a power conversion system 1 that drives an AC electric motor M using a regenerative inverter 3 (AC / DC converter). The first series circuit of the braking device 20 is connected in parallel to the DC side of the inverter 3 and includes a braking resistor 5A (first braking resistor) and a switch 6A (first semiconductor switch). The second series circuit is connected in parallel to the first series circuit and includes a braking resistor 5B (second braking resistor) and a switch 6B (second semiconductor switch). When the braking resistors (5A, 5B) are in a first state where their temperatures exceed a first threshold temperature TH1, the braking control units (21, 22, 23) change the drive method of the switch 6A or 6B to a drive method different from the drive method used when the temperature of the braking resistors does not exceed the first threshold temperature TH1. This enables the braking device 20 to further improve the operational continuity of the inverter 3 in which the braking device 20 is provided.

[0053] The braking control unit may perform one or more protective operations to reduce the power consumption of the braking resistors (5A, 5B) when the braking device 20 is in the first state. The braking control unit may perform control for the protective operation to reduce the conduction time of the switch 6A or 6B, for example. The protective operation may include control to lower a limit value (regenerative torque limit) that restricts the upper limit of the regenerative torque related to braking of the AC motor M. This protection operation may include controlling the switch 6A or 6B to be continuously in the OFF state.

[0054] For example, when a first state occurs due to a temperature rise in braking resistor 5A, the braking control unit may turn switch 6A off and control switch 6B on and off to suppress heat generation in braking resistor 5A. Furthermore, when both a first state caused by a temperature rise in braking resistor 5A and another first state caused by a temperature rise in braking resistor 5B occur, the braking control unit may keep both switches 6A and 6B in the off state.

[0055] The braking device 20 includes a cooling fan 8A (first cooling fan) that promotes heat dissipation from the braking resistor 5A, and a cooling fan 8B (second cooling fan) that promotes heat dissipation from the braking resistor 5B. The braking control unit may be configured so that a malfunction of the cooling fan 8A or a malfunction of the cooling fan 8B is not included in the causes of stopping the power conversion system 1.

[0056] As described above, braking resistors 5A and 5B convert regenerative energy into heat. Cooling fans 8A and 8B increase the cooling efficiency of braking resistors 5A and 5B by blowing air. The braking control unit controls the conversion rate of braking resistors 5A and 5B, detects the state of braking device 20, and stops power conversion system 1 in the event of a major fault. This further improves the operational continuity of power conversion system 1 equipped with braking device 20.

[0057] According to at least one embodiment described above, the braking device is a braking device in a power conversion system that drives an AC electric motor using a regenerative AC / DC converter. The braking device includes a first series circuit, a second series circuit, and a braking control unit. The first series circuit is connected in parallel to the DC side of the AC / DC converter and includes a first braking resistor and a first semiconductor switch. The second series circuit is connected in parallel to the first series circuit and includes a second braking resistor and a second semiconductor switch. When the temperature of either the first braking resistor or the second braking resistor is in a first state where the temperature of the braking resistor exceeds a first threshold temperature, the braking control unit changes the driving method of the first semiconductor switch or the second semiconductor switch to a driving method different from the driving method used when the temperature of the braking resistor does not exceed the first threshold temperature, thereby further improving the operational continuity of the power converter provided with the braking device.

[0058] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

[0059] For example, the main circuit including the diode converter 2 and the inverter 3 and the braking device 20 may be configured in a redundant manner. [Explanation of symbols]

[0060] 1 power conversion system, 2 diode converter, 3 inverter, 4 smoothing capacitor, 5A, 5B braking resistor, 6A, 6B switch, 7A, 7B temperature sensor, 8A, 8B cooling fan, 10 power conversion control device, 11 speed controller, 13 current controller, 14 PWM control unit, 20 braking device, 21 state estimation unit (braking control unit), 22 modulation unit (braking control unit), 23 second gate signal control unit (braking control unit), M AC motor

Claims

1. A braking device in a power conversion system in which an AC motor is driven by a regenerative AC / DC converter, a first series circuit provided on a DC side of the AC / DC converter so as to be connected in parallel, the first series circuit including a first braking resistor and a first semiconductor switch; a second series circuit connected in parallel with the first series circuit and including a second braking resistor and a second semiconductor switch; a braking control unit that, when in the first state or the second state, changes a driving method of the first semiconductor switch or the second semiconductor switch to a driving method different from a driving method when the temperature of the braking resistor does not exceed a first threshold temperature; Equipped with the first state includes a state in which the temperature of either the first braking resistor or the second braking resistor exceeds the first threshold temperature; the second state includes a state in which the temperature of both the first braking resistor and the second braking resistor exceeds the first threshold temperature, or a state in which the temperature of either the first braking resistor or the second braking resistor exceeds a second threshold temperature. Braking device.

2. The braking control unit When the braking resistor is in the first state or the second state, one or more protective actions are performed to reduce power consumption of the first braking resistor or the second braking resistor.

2. The braking device of claim 1.

3. The braking control unit Control for the protection operation is performed to reduce the conduction time of the first semiconductor switch or the second semiconductor switch.

3. The braking device according to claim 2.

4. The protection operation includes controlling the AC motor to lower a limit value that limits an upper limit value of a regenerative torque related to braking the AC motor. The braking device according to claim 2 or 3.

5. The protection operation includes controlling the first semiconductor switch or the second semiconductor switch to a continuous off state. A braking device according to any one of claims 2 to 4.

6. The braking control unit When the first state occurs due to a rise in temperature of the first braking resistor, the first semiconductor switch is turned off and the second semiconductor switch is controlled to be turned on and off.

2. The braking device of claim 1.

7. The braking control unit When the temperatures of both the first braking resistor and the second braking resistor exceed a second threshold temperature, both the first semiconductor switch and the second semiconductor switch are kept in an off state.

2. The braking device of claim 1.

8. a first cooling fan for promoting heat dissipation from the first braking resistor; a second cooling fan for promoting heat dissipation from the second braking resistor; Equipped with The braking control unit A malfunction of the first cooling fan and a malfunction of the second cooling fan are not included in the causes of stopping the power conversion system.

2. The braking device of claim 1.

9. A power conversion system that drives an AC motor using a regenerative AC / DC converter, a first series circuit provided on a DC side of the AC / DC converter so as to be connected in parallel, the first series circuit including a first braking resistor and a first semiconductor switch; a second series circuit connected in parallel with the first series circuit and including a second braking resistor and a second semiconductor switch; a braking control unit that, when in the first state or the second state, changes a driving method of the first semiconductor switch or the second semiconductor switch to a driving method different from a driving method when the temperature of the braking resistor does not exceed a first threshold temperature; Equipped with the first state includes a state in which the temperature of either the first braking resistor or the second braking resistor exceeds the first threshold temperature; the second state includes a state in which the temperature of both the first braking resistor and the second braking resistor exceeds the first threshold temperature, or a state in which the temperature of either the first braking resistor or the second braking resistor exceeds a second threshold temperature. Power conversion systems.

10. A braking method using a braking device in a power conversion system in which an AC motor is driven by a regenerative AC / DC converter, comprising: The braking device is a first series circuit provided on a DC side of the AC / DC converter so as to be connected in parallel, the first series circuit including a first braking resistor and a first semiconductor switch; a second series circuit connected in parallel with the first series circuit and including a second braking resistor and a second semiconductor switch; Equipped with When in the first state or the second state, a driving method of the first semiconductor switch or the second semiconductor switch is set to a driving method different from a driving method when the temperature of the braking resistor does not exceed a first threshold temperature. Including, the first state includes a state in which the temperature of either the first braking resistor or the second braking resistor exceeds the first threshold temperature; the second state includes a state in which the temperature of both the first braking resistor and the second braking resistor exceeds the first threshold temperature, or a state in which the temperature of either the first braking resistor or the second braking resistor exceeds a second threshold temperature. Braking control method.

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