Control device and control method for elevator

Abstract

Provided are a control device and a control method for an elevator that are not easily trapped in a rescue operation in which a car cannot be driven in a power running direction. In a control device (100), an inverter (8) drives a hoist motor (9) that causes an elevator car to travel. The smoothing capacitor (7) stabilizes the voltage of a DC bus connected to the inverter (8). The regenerative resistor (10) consumes regenerative power generated by the hoist motor (9) during regenerative operation of the elevator. The threshold value setting unit (15) sets the voltage threshold value such that the remaining life of the inverter (8) predicted by the second life prediction unit (17) is longer than the remaining life of the regenerative switching element (11) predicted by the first life prediction unit (16). A switching control unit (13) controls the switching operation of a regenerative switching element (11) that switches whether or not a current flows into a regenerative resistor (10) on the basis of the relationship between the detected value of the DC bus voltage and a set voltage threshold value.

Description

Technical Field

[0001] The present disclosure relates to a control device and a control method for an elevator. Background Art

[0002] Patent Document 1 discloses an example of an elevator. A life estimation circuit for estimating the life of an inverter is provided in a control device of the elevator.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2009-12929 Summary of the invention

[0006] Problems to be solved by the invention

[0007] Even when the life of the inverter is estimated as in the elevator of Patent Document 1, it is sometimes impossible to replace the inverter components before the estimated life is reached due to management reasons. In such a case, the elevator may be stopped in an emergency due to a failure of the inverter. When the elevator stops in an emergency, users riding in the car may be trapped. At this time, if the inverter fails, it is impossible to perform a rescue operation to make the car run in the power running direction and stop at the floor height.

[0008] The present disclosure is made to solve such a problem and to provide a control device and a control method for an elevator that are less likely to be trapped, such that a rescue operation in which the car cannot be run in the power running direction cannot be performed.

[0009] Means for solving problems

[0010] The control device of the elevator disclosed in the present invention comprises: an inverter that drives a traction machine motor that causes a car of the elevator to travel; a smoothing capacitor that stabilizes the voltage of a DC bus connected to the inverter; a regenerative resistor that is connected to the DC bus and consumes regenerative power generated by the traction machine motor during the regenerative operation of the elevator; a regenerative switching element that switches whether or not current flows into the regenerative resistor; a first voltage monitoring unit that detects the voltage of the DC bus; a threshold setting unit that sets a voltage threshold that determines the timing of the switching operation of the regenerative switching element; a switching control unit that controls the switching operation of the regenerative switching element based on the relationship between the voltage value detected by the first voltage monitoring unit and the voltage threshold set by the threshold setting unit; a first life prediction unit that predicts the remaining life of the regenerative switching element; and a second life prediction unit that predicts the remaining life of the inverter, the threshold setting unit setting the voltage threshold in such a way that the remaining life of the inverter predicted by the second life prediction unit is longer than the remaining life of the regenerative switching element predicted by the first life prediction unit.

[0011] The control method of an elevator disclosed in the present invention is a control method of an elevator as follows, the elevator comprising: an inverter that drives a traction machine motor for driving a car; a smoothing capacitor that stabilizes the voltage of a DC bus connected to the inverter; a regenerative resistor that is connected to the DC bus and consumes regenerative power generated by the traction machine motor during regenerative operation; a regenerative switching element that switches whether current flows into the regenerative resistor; a first voltage monitoring unit that detects the voltage of the DC bus; and a switching control unit that controls the switching action of the regenerative switching element based on the relationship between the voltage value detected by the first voltage monitoring unit and a voltage threshold that determines the timing of the switching action of the regenerative switching element, the control method comprising: a first prediction step of predicting the remaining life of the regenerative switching element; a second prediction step of predicting the remaining life of the inverter; and a threshold setting step of setting the voltage threshold in such a way that the remaining life of the inverter predicted in the second prediction step is longer than the remaining life of the regenerative switching element predicted in the first prediction step.

[0012] Effects of the Invention

[0013] According to the control device or control method of the elevator disclosed in the present invention, it is less likely that a car will be trapped in a situation where a rescue operation to move the car in the power running direction cannot be performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a configuration diagram of an elevator control device according to Embodiment 1.

[0015] Figure 2AThis is a diagram for explaining an example of the switching operation of the regenerative switching element during the regenerative operation of the elevator according to the first embodiment.

[0016] Figure 2B This is a diagram for explaining an example of the switching operation of the regenerative switching element during the regenerative operation of the elevator according to the first embodiment.

[0017] Figure 3 It is a diagram for explaining an example of transition of the remaining life of the inverter and the regenerative switching element and setting of the voltage threshold value in the elevator control device according to the first embodiment.

[0018] Figure 4A This is a diagram for explaining an example of prediction of the remaining life of the inverter or the regenerative switching element in the elevator control device according to the first embodiment.

[0019] Figure 4B This is a diagram for explaining an example of prediction of the remaining life of the inverter or the regenerative switching element in the elevator control device according to the first embodiment.

[0020] Figure 5A This is a diagram for explaining an example of determination of an open-circuit failure of a regenerative switching element in the elevator control device according to the first embodiment.

[0021] Figure 5B This is a diagram for explaining an example of determination of an open-circuit failure of a regenerative switching element in the elevator control device according to the first embodiment.

[0022] Figure 6 This is a hardware configuration diagram of the main parts of the control device according to the first embodiment.

[0023] Figure 7 This is a configuration diagram of an elevator control device according to the second embodiment. DETAILED DESCRIPTION

[0024] The embodiments for implementing the object of the present disclosure are described with reference to the accompanying drawings. In each figure, the same or equivalent parts are marked with the same reference numerals, and repeated descriptions are appropriately simplified or omitted. In addition, the object of the present disclosure is not limited to the following embodiments, and any structural element of the embodiment can be deformed or omitted without departing from the scope of the purpose of the present disclosure.

[0025] Implementation method 1.

[0026] Figure 1 This is a configuration diagram of an elevator control device according to Embodiment 1.

[0027] Elevators are used in buildings with multiple floors, etc. In the building, a hoistway (not shown) of the elevator is provided. The hoistway is a space that is long in the vertical direction across multiple floors. The elevator has a car (not shown). The car is arranged in the hoistway. The load of the car is supported by a main rope (not shown). The car is a device that transports elevator users between multiple floors by traveling in the vertical direction in the hoistway. Elevator users get on and off the car when the car stops at the level height of each floor.

[0028] The elevator is controlled by a control device 100. The elevator operates by receiving power from an external AC power supply 1. In this example, the AC power supply 1 is a commercial power supply that supplies three-phase AC power. The output end of each phase of the AC power supply 1 is connected to the input end of the power supply switch 2 of the control device 100.

[0029] Each power-on switch 2 is composed of, for example, a no-fuse breaker. The output end of each power-on switch 2 is connected to the input end of the contactor 3 of the control device 100. The output end of each contactor 3 is connected to each input end of the converter 4 of the control device 100. The converter 4 is composed of, for example, a three-phase diode bridge circuit. The output end of the high-potential side of the converter 4 is connected to the input end of the first DC bus 5. The output end of the low-potential side of the converter 4 is connected to the input end of the second DC bus 6.

[0030] A smoothing capacitor 7 of the control device 100 is connected between the first DC bus 5 and the second DC bus 6. The output end of the first DC bus 5 is connected to the input end of the high potential side of the inverter 8 of the control device 100. The output end of the second DC bus 6 is connected to the input end of the low potential side of the inverter 8 of the control device 100. The inverter 8 is composed of, for example, a two-level three-phase voltage type full bridge circuit. The inverter 8 includes a switching element not shown in the figure. The switching element of the inverter 8 is composed of, for example, an IGBT (Insulated Gate Bipolar Transistor). The output end of the inverter 8 is connected to each input end of the traction machine motor 9. The traction machine motor 9 is a device that generates a driving force for driving the elevator car. The rotating shaft of the traction machine motor 9 is connected to, for example, a driving sheave not shown around which the main rope is hung.

[0031] In the elevator of such a structure, at the time of starting, the contactor 3 is closed. By closing the contactor 3, AC power is supplied from the AC power supply 1 to the converter 4. The converter 4 converts the supplied AC power into DC power. The DC power converted and output by the converter 4 is smoothed by the smoothing capacitor 7. The smoothed DC power is input to the inverter 8. The inverter 8 converts the input DC power into AC power. The AC power converted and output by the inverter 8 is supplied to the traction machine motor 9. The traction machine motor 9 uses the supplied AC power to rotate the rotating shaft and the drive sheave. As the drive sheave rotates, the main rope moves, thereby the car travels in the up and down direction in the hoistway.

[0032] On the other hand, depending on the relationship between the load applied to the car and the direction of travel of the car, the elevator sometimes performs regenerative operation. When the elevator performs regenerative operation, the traction machine motor 9 functions as a generator. That is, the traction machine motor 9 generates regenerative power. The control device 100 is equipped with a function of consuming the regenerative power generated by the traction machine motor 9.

[0033] The control device 100 includes a regenerative resistor 10, a regenerative switch element 11, and a regenerative switch element gate drive circuit 12. The regenerative resistor 10 is, for example, a resistor that consumes electric power as Joule heat. The regenerative switch element 11 is an element that performs a switching operation to switch whether or not current flows in. The regenerative switch element 11 is, for example, composed of an IGBT or the like. The regenerative switch element gate drive circuit 12 is, for example, a gate driver that outputs a signal that drives the switching operation of the regenerative switch element 11. One end of the regenerative resistor 10 is connected to the first DC bus 5. The other end of the regenerative resistor 10 is connected to the collector terminal of the regenerative switch element 11. The emitter terminal of the regenerative switch element 11 is connected to the second DC bus 6. The output end of the regenerative switch element gate drive circuit 12 is connected to the gate terminal of the regenerative switch element 11.

[0034] The control device 100 includes a switching control unit 13 , a first voltage monitoring unit 14 , a threshold setting unit 15 , a first life prediction unit 16 , a second life prediction unit 17 , a first temperature sensor 18 , a second temperature sensor 19 , and a failure determination unit 20 .

[0035] The switching control unit 13 is a part equipped with a function of controlling the switching operation of the regenerative switching element 11. The output of the switching control unit 13 is connected to the input of the regenerative switching element gate drive circuit 12. The switching control unit 13 outputs a control signal for the switching operation to the regenerative switching element 11 via the regenerative switching element gate drive circuit 12.

[0036] The first voltage monitoring unit 14 is a unit equipped with a function of detecting the voltage of the DC bus, that is, the voltage between the first DC bus 5 and the second DC bus 6. The first voltage monitoring unit 14 is connected to the first DC bus 5 and the second DC bus 6. The output of the first voltage monitoring unit 14 is connected to the input of the switching control unit 13.

[0037] The threshold setting unit 15 is a part equipped with a function of setting a voltage threshold of the switching control unit 13. The voltage threshold is used to determine the timing of the switching operation of the regenerative switching element 11 in the switching control unit 13. The output of the threshold setting unit 15 is connected to the input of the switching control unit 13.

[0038] The switching control unit 13 controls the switching action of the regenerative switching element 11 according to the relationship between the voltage value of the DC bus detected by the first voltage monitoring unit 14 and the voltage threshold set by the threshold setting unit 15. In this example, the voltage threshold includes a high potential side voltage threshold and a low potential side voltage threshold. The high potential side voltage threshold is set to a voltage value higher than the low potential side voltage threshold. One or both of the high potential side voltage threshold and the low potential side voltage threshold are set by the threshold setting unit 15. Alternatively, the high potential side voltage threshold or the low potential side voltage threshold may be a preset value. In this example, the high potential side threshold is preset to a specific fixed value that does not become an overvoltage for devices such as the inverter 8 and the smoothing capacitor 7. When the voltage value of the DC bus detected by the first voltage monitoring unit 14 exceeds the high potential side threshold, the switching control unit 13 switches the action of the regenerative switching element 11 to conduction so that the current flows into the regenerative resistor 10. When the voltage value of the DC bus detected by the first voltage monitoring unit 14 is lower than the low potential threshold, the switching control unit 13 switches the operation of the regeneration switching element 11 to off so that current does not flow into the regeneration resistor 10. The switching control unit 13 performs hysteresis control in this way.

[0039] When the elevator is in power running operation, the regenerative switch element 11 is always in the off state where the current does not flow into the regenerative resistor 10. On the other hand, when the converter 4 does not have a function that can regenerate into the AC power supply 1 like a diode converter, when the elevator is in regenerative operation, the regenerative power generated by the traction machine motor 9 is stored in the smoothing capacitor 7. At this time, the DC bus voltage rises. When the DC bus voltage rises and exceeds the high potential side threshold, the switching control unit 13 switches the regenerative switch element 11 to the on state. As a result, a discharge circuit connected to the regenerative resistor 10 is formed between the first DC bus 5 and the second DC bus 6. In the formed discharge circuit, the power stored in the smoothing capacitor 7 and the regenerative power are converted into Joule heat in the regenerative resistor 10 and consumed. At this time, the DC bus voltage drops. In this way, during the regenerative operation of the elevator, the on and off actions of the regenerative switch element 11 are repeated.

[0040] The first life prediction unit 16 is a unit equipped with a function of predicting the remaining life of the regenerative switching element 11. The second life prediction unit 17 is a unit equipped with a function of predicting the remaining life of the inverter 8.

[0041] The first temperature sensor 18 is disposed close to the regenerative switching element 11. The first temperature sensor 18 is mounted near the semiconductor chip of the regenerative switching element 11. The first temperature sensor 18 measures the temperature of the regenerative switching element 11. The measured value of the first temperature sensor 18 is input to the first life prediction unit 16. The measured value of the first temperature sensor 18 is used, for example, to predict the remaining life of the regenerative switching element 11 in the first life prediction unit 16.

[0042] The second temperature sensor 19 is arranged close to the inverter 8. The second temperature sensor 19 is installed near a specific semiconductor chip mounted on the inverter 8. The semiconductor chip is a semiconductor chip selected as having the largest temperature rise during installation among the semiconductor chips mounted on the inverter 8. The semiconductor chip is, for example, a semiconductor chip of a switching element mounted on the inverter 8. The second temperature sensor 19 measures the temperature of the semiconductor chip. The measured value of the second temperature sensor 19 is input to the second life prediction unit 17. The measured value of the second temperature sensor 19 is used, for example, for predicting the remaining life of the inverter 8 in the second life prediction unit 17. The remaining life of the inverter 8 corresponds to, for example, the remaining life of any semiconductor chip mounted on the inverter 8. In addition, a plurality of second temperature sensors 19 may be installed. In this case, each second temperature sensor 19 is installed near each of the plurality of specific semiconductor chips mounted on the inverter 8.

[0043] The threshold setting unit 15 sets the voltage threshold in such a way that the remaining life of the inverter 8 predicted by the second life prediction unit 17 is longer than the remaining life of the regenerative switch element 11 predicted by the first life prediction unit 16. In this example, the threshold setting unit 15 selects a voltage value from a plurality of pre-set voltage values ​​according to the magnitude relationship between the remaining life of the inverter 8 and the remaining life of the regenerative switch element 11, and sets it as the low potential side voltage threshold. Here, the threshold setting unit 15 may also compare the magnitude relationship between the remaining life of the inverter 8 and the remaining life of the regenerative switch element 11 by considering a pre-set life margin. The life margin is set according to the prediction accuracy of the remaining life. This prevents the inverter 8 from reaching the end of its life before the regenerative switch element 11 due to poor prediction accuracy of the remaining life. The threshold setting unit 15 outputs the set voltage threshold to the switching control unit 13, thereby updating the voltage threshold used by the switching control unit 13.

[0044] The fault determination unit 20 is a part equipped with a function of determining the occurrence of an open-circuit fault in the regenerative switching element 11. The input of the fault determination unit 20 is connected to the output of the switching control unit 13. The fault determination unit 20 receives a control signal for the switching operation of the regenerative switching element 11 from the switching control unit 13. The input of the fault determination unit 20 is connected to the output of the first voltage monitoring unit 14. The fault determination unit 20 receives the voltage value of the DC bus detected by the first voltage monitoring unit 14.

[0045] The fault determination unit 20 determines the occurrence of an open circuit fault in the regenerative switching element based on the detected value of the DC bus voltage after a sufficient time has passed since the start of the discharge of the smoothing capacitor 7. The fault determination unit 20 detects the start of the discharge of the smoothing capacitor 7 based on, for example, a control signal of the switching action from the switching control unit 13. The fault determination unit 20 determines the occurrence of a fault, for example, when the smoothing capacitor 7 is charged and the power supply to the smoothing capacitor 7 is disconnected. The fault determination unit 20 determines the occurrence of a fault, for example, when the elevator is stopped and the contactor 3 is in an open state. The fault determination unit 20 may determine the occurrence of a fault in a stop mode in which the elevator stops operating, or may determine the occurrence of a fault when the elevator is stopped in a diagnostic mode such as once a day.

[0046] In addition, sometimes the elevator stops in an emergency due to a failure of the control device 100. In this case, when the car stops at a position between floors, users riding in the car may be trapped. In addition, the position between floors is, for example, a position between the floor heights of adjacent floors. Here, since the elevator is controlled in such a way that the remaining life of the inverter 8 is longer than the remaining life of the regenerative switching element 11, the regenerative switching element 11 will fail before the inverter 8. Therefore, it is expected that when the elevator stops in an emergency due to an open circuit failure of the regenerative switching element 11, the inverter 8 does not fail. Therefore, when being trapped occurs, the control device 100 performs a rescue operation in the power running direction when the fault determination unit 20 determines that the regenerative switching element 11 has an open circuit failure. In the rescue operation in the power running direction, the inverter 8 drives the traction machine motor 9 in such a way that the car runs in the power running direction and stops at the floor height. By performing the rescue operation in the power running direction, remote rescue can be performed, so that early rescue for being trapped can be achieved.

[0047] Next, an example of the switching operation of the regenerative switching element 11 during the regenerative operation of the elevator will be described using FIG. 2 .

[0048] Figure 2A and Figure 2B This is a diagram for explaining an example of the switching operation of the regenerative switching element 11 during the regenerative operation of the elevator according to the first embodiment.

[0049] exist Figure 2A and Figure 2B In each of the graphs shown, the horizontal axis represents the passage of time. In these graphs, the vertical axis represents voltage. In these graphs, the voltage value 21 of the DC bus is represented by a solid line. In these graphs, the voltage threshold 22, the voltage threshold 23, and the voltage threshold 24 are represented by dotted lines.

[0050] Figure 2A An example is shown in which the value obtained by subtracting the life margin from the remaining life of the inverter 8 predicted by the second life prediction unit 17 is longer than the remaining life of the regenerative switching element 11 predicted by the first life prediction unit 16. At this time, the voltage value 21 of the DC bus changes between the high potential side voltage threshold 22 and the first low potential side voltage threshold 23. Here, the high potential side voltage threshold 22 is a preset fixed value. In addition, the first low potential side voltage threshold 23 is a voltage value selected from a plurality of voltage values ​​by the threshold setting unit 15 and set as the low potential side voltage threshold when the remaining life of the inverter 8 obtained by subtracting the life margin 2 is longer than the remaining life of the regenerative switching element 11.

[0051] Figure 2B An example is shown in which a value obtained by subtracting the life margin from the remaining life of the inverter 8 predicted by the second life prediction unit 17 is shorter than the remaining life of the regenerative switching element 11 predicted by the first life prediction unit 16. At this time, the voltage value 21 of the DC bus changes between the high potential side voltage threshold 22 and the second low potential side voltage threshold 24. Here, the second low potential side voltage threshold 24 is a voltage value selected from a plurality of voltage values ​​by the threshold setting unit 15 and set as the low potential side voltage threshold when the remaining life of the inverter 8 obtained by subtracting the life margin is shorter than the remaining life of the regenerative switching element 11.

[0052] The second low potential side voltage threshold 24 is set to a higher potential side than the first low potential side voltage threshold 23. Figure 2B ,exist Figure 2A In the example, the hysteresis width, which is the difference between the voltage value of the high potential side voltage threshold and the low potential side voltage threshold, becomes larger. Figure 2A ,exist Figure 2B In the case of Figure 2B ,exist Figure 2A In the embodiment, the action of the regenerative switching element 11 becomes a lower frequency switching action. Figure 2A ,exist Figure 2BIn the embodiment, the operation of the regenerative switching element 11 becomes a higher frequency switching operation. In the regenerative switching element 11, when a higher frequency switching operation is performed, the switching loss becomes larger and the life becomes shorter. On the other hand, in the regenerative switching element 11, when a lower frequency switching operation is performed, the switching loss becomes smaller and the life becomes longer. Therefore, the relationship between the remaining life of the regenerative switching element 11 and the inverter 8 is adjusted by controlling the hysteresis width.

[0053] Next, use Figure 3 , an example of the transition of the remaining life of the inverter 8 and the regenerative switching element 11 and the setting of the voltage threshold value will be described.

[0054] Figure 3 It is a diagram for explaining an example of transition of the remaining life of the inverter 8 and the regenerative switching element 11 and setting of the voltage threshold value in the elevator control device 100 according to the first embodiment.

[0055] exist Figure 3 In each of the graphs shown, the horizontal axis represents the number of years that have passed since the elevator was newly installed, or since the parts were replaced, etc. When the parts are replaced, the parts of the inverter 8 and the regenerative switching element 11 are replaced at the same time.

[0056] Figure 3 The graph on the upper side of represents the time-dependent change of the voltage threshold value set by the threshold setting unit 15. In this graph, the vertical axis represents the value of the set voltage threshold value. In this graph, a high potential side voltage threshold value 22 and a low potential side voltage threshold value 25 are shown. The low potential side voltage threshold value 25 takes any value of the first low potential side voltage threshold value 23 and the second low potential side voltage threshold value 24.

[0057] Figure 3 The graph below shows the time-dependent changes in the remaining life 26 of the inverter 8 and the remaining life 27 of the regenerative switching element 11. A value obtained by subtracting the life margin 28 from the remaining life 26 of the inverter 8 is indicated by a dotted line 29.

[0058] Immediately after installation or immediately after component replacement, the low potential side voltage threshold 25 is set to the first low potential side voltage threshold 23 of a higher potential. The first low potential side voltage threshold 23 is pre-designed in such a manner that the remaining life 27 of the regenerative switching element 11 is consumed faster than the remaining life 26 of the inverter 8. When the remaining life 27 of the regenerative switching element 11 is consumed over time and becomes lower than a value 29 obtained by subtracting a life margin 28 from the remaining life 26 of the inverter 8, the threshold setting unit 15 sets the low potential side voltage threshold 25 to the second low potential side voltage threshold 24 of a lower potential. The second low potential side voltage threshold 24 is pre-designed in such a manner that the remaining life 27 of the regenerative switching element 11 is consumed slower than the remaining life 26 of the inverter 8. Then, when the remaining life 27 of the regenerative switching element 11 exceeds a value 29 obtained by subtracting the life margin 28 from the remaining life 26 of the inverter 8 , the threshold setting unit 15 sets the low potential side voltage threshold 25 to the first low potential side voltage threshold 23 of a higher potential again.

[0059] Next, an example of prediction of the remaining life of the inverter 8 or the regenerative switching element 11 in the elevator control device 100 will be described using FIG. 4 .

[0060] Figure 4A and Figure 4B This is a diagram for explaining an example of prediction of the remaining life of the inverter 8 or the regenerative switching element 11 in the elevator control device 100 according to the first embodiment.

[0061] The first life prediction unit 16 and the second life prediction unit 17 predict the remaining life according to Miner's rule based on temperature variation, for example, as described below. In addition, as a method for the first life prediction unit 16 and the second life prediction unit 17 to predict the remaining life according to temperature variation, a rainflow method may be used.

[0062] Figure 4A The figure shows the time variation of the measured value of the temperature sensor used to predict the remaining life. Figure 4A In the graph shown in FIG. 1 , the horizontal axis represents the passage of time. In the graph, the vertical axis represents the measured value of temperature. Figure 4A In FIG. 1 , the time variation of the measured value of the first temperature sensor 18 or the second temperature sensor 19 is shown. Figure 4A, the temperature variation of a specific semiconductor chip provided with a temperature sensor of the regenerative switching element 11 or the inverter 8 is shown. With the operation of the elevator, the temperature of the semiconductor chip etc. fluctuates. The first life prediction unit 16 and the second life prediction unit 17 calculate the life consumption corresponding to the temperature difference ΔT from the maximum value of the temperature variation at that time to the next minimum value for each temperature cycle and add them up successively, thereby calculating the cumulative life consumption. Here, the life consumption is a parameter expressed as a percentage, for example. A life consumption of 100% means that the life has been reached. A life consumption of 50% means that half of the life has been consumed.

[0063] The first life prediction unit 16 calculates a predicted value of the remaining life of the regenerative switching element 11 using the accumulated life consumption calculated based on the temperature variation of the first temperature sensor 18. In addition, the second life prediction unit 17 calculates a predicted value of the remaining life of the inverter 8 using the accumulated life consumption calculated based on the temperature variation of the second temperature sensor 19. Here, the second life prediction unit 17 may calculate the remaining life of the semiconductor chip provided with the second temperature sensor 19 as the remaining life of the inverter 8. In addition, when a plurality of second temperature sensors 19 are provided, the second life prediction unit 17 may calculate the remaining life for each of a plurality of specific semiconductor chips provided with the second temperature sensor 19. At this time, the second life prediction unit 17 may use the shortest remaining life among the calculated remaining lives of the specific semiconductor chips as the remaining life of the inverter 8.

[0064] Figure 4B : is a graph showing the relationship between the temperature difference ΔT and the life consumption L corresponding to the temperature difference ΔT. Figure 4B In the graph shown, the horizontal axis represents the temperature difference ΔT. In the graph, the vertical axis represents the life consumption L. The relationship between the temperature difference ΔT and the life consumption L is created in advance, for example, based on a previously performed life acceleration test and calculation. The relationship between the temperature difference ΔT and the life consumption L is created for each specific semiconductor chip, for example.

[0065] Next, an example of determination of an open-circuit failure of the regenerative switching element 11 in the elevator control device 100 will be described using FIG. 5 .

[0066] Figure 5A and Figure 5B This is a diagram for explaining an example of determination of an open-circuit failure of a regenerative switching element in the elevator control device according to the first embodiment.

[0067] exist Figure 5A and Figure 5B In each of the graphs shown, the horizontal axis represents the passage of time. In these graphs, the vertical axis represents the voltage. In these graphs, the DC bus voltage value 21 is represented by a solid line.

[0068] Figure 5A The figure shows the time variation of the DC bus voltage value 21 when the power stored in the smoothing capacitor 7 is discharged in a normal situation where the regenerative switching element 11 does not have an open circuit failure. The power stored in the smoothing capacitor 7 is discharged in the discharge circuit formed by the regenerative switching element 11 and the regenerative resistor 10.

[0069] The fault determination unit 20 detects the switching of the regenerative switching element 11 from the off state to the on state based on the control signal for the switching operation of the regenerative switching element 11 received from the switching control unit 13. The fault determination unit 20 determines whether the DC bus voltage value 21 detected by the first voltage monitoring unit 14 is lower than the discharge voltage threshold 31 after the discharge time 30 has passed since the discharge of the smoothing capacitor 7 started by the switching of the regenerative switching element 11. Here, the discharge time 30 is preset to a time sufficient for the time required for the discharge of the smoothing capacitor 7. The discharge voltage threshold 31 is preset to a voltage sufficient for determining the discharge of the smoothing capacitor 7. When the DC bus voltage value 21 is lower than the discharge voltage threshold 31, the fault determination unit 20 considers that the smoothing capacitor 7 has been discharged normally, and determines that the regenerative switching element 11 has not developed to the point where an open circuit fault occurs.

[0070] Figure 5B When an open circuit failure occurs in the regenerative switching element 11, Figure 5A Similarly, the time change of the DC bus voltage value 21 when the regeneration switching element 11 is switched from the off state to the on state is shown in the case of . In this case, due to the open-circuit fault of the regeneration switching element 11, the discharge circuit cannot be formed, and the discharge of the smoothing capacitor 7 does not start. At this time, even if the discharge time 30 has passed, the DC bus voltage value 21 is higher than the discharge voltage threshold 31. Therefore, the fault determination unit 20 determines that the regeneration switching element 11 has developed an open-circuit fault when the DC bus voltage value 21 is higher than the discharge voltage threshold 31 after the discharge time 30 has passed since the regeneration switching element 11 was switched.

[0071] As described above, the elevator control device 100 of the first embodiment includes the inverter 8, the smoothing capacitor 7, the regenerative resistor 10, the regenerative switching element 11, the first voltage monitoring unit 14, the threshold setting unit 15, the switching control unit 13, the first life prediction unit 16, and the second life prediction unit 17. The inverter 8 drives the traction machine motor 9 for driving the elevator car. The smoothing capacitor 7 stabilizes the voltage of the DC bus connected to the inverter 8. The regenerative resistor 10 is connected to the DC bus. The regenerative resistor 10 consumes the regenerative power generated by the traction machine motor 9 during the regenerative operation of the elevator. The regenerative switching element 11 switches whether the current flows into the regenerative resistor 10. The first voltage monitoring unit 14 detects the voltage of the DC bus. The threshold setting unit 15 sets the voltage threshold that determines the timing of the switching operation of the regenerative switching element 11. The switching control unit 13 controls the switching operation of the regenerative switching element 11 based on the relationship between the voltage value detected by the first voltage monitoring unit 14 and the voltage threshold set by the threshold setting unit 15. The first life prediction unit 16 predicts the remaining life of the regenerative switching element 11. The second life prediction unit 17 predicts the remaining life of the inverter 8. The threshold setting unit 15 sets the voltage threshold so that the remaining life of the inverter 8 predicted by the second life prediction unit 17 is longer than the remaining life of the regenerative switching element 11 predicted by the first life prediction unit 16.

[0072] In addition, the elevator control method of embodiment 1 includes a first prediction step, a second prediction step, and a threshold setting step. The first prediction step is a step of predicting the remaining life of the regenerative switching element 11. The second prediction step is a step of predicting the remaining life of the inverter 8. The threshold setting step is a step of setting a voltage threshold in such a manner that the remaining life of the inverter 8 predicted in the second prediction step is longer than the remaining life of the regenerative switching element 11 predicted in the first prediction step.

[0073] According to such a configuration, since the elevator is controlled in such a manner that the remaining life of the inverter 8 is longer than the remaining life of the regenerative switching element 11, the regenerative switching element 11 will fail before the inverter 8. Therefore, it is expected that the inverter 8 will not fail when the elevator is emergency stopped due to the open circuit failure of the regenerative switching element 11. Since the emergency stop due to the failure of the inverter 8 is unlikely to occur, it is unlikely to be trapped such that the rescue operation of the car cannot be carried out in the power running direction.

[0074] Furthermore, the control device 100 includes a first temperature sensor 18. The first temperature sensor 18 is disposed close to the regeneration switching element 11. The first life prediction unit 16 predicts the remaining life of the regeneration switching element 11 based on the temperature variation measured by the first temperature sensor 18.

[0075] Furthermore, the control device 100 includes a second temperature sensor 19. The second temperature sensor 19 is disposed close to semiconductor chips such as switching elements of the inverter 8. The second life prediction unit 17 predicts the remaining life of the inverter 8 based on the temperature variation measured by the second temperature sensor 19.

[0076] According to such a configuration, the remaining life is predicted based on the measured value of the component temperature change, so the predicted value of the remaining life is more accurate. As a result, it is less likely to cause a car to be trapped, such as being unable to perform a rescue operation to move the car in the power running direction.

[0077] In addition, the control device 100 includes a fault determination unit 20. The fault determination unit 20 determines the occurrence of an open circuit fault in the regenerative switching element 11. When the car stops at a position between floors, the fault determination unit 20 sometimes determines that an open circuit fault has occurred in the regenerative switching element 11. In this case, the inverter 8 drives the traction machine motor 9 in a manner of performing a rescue operation in which the car travels in the power running direction and stops at the level height.

[0078] According to such a structure, even if entrapment occurs when the components of the control device 100 reach the end of their life, rescue operation can be performed in the power running direction. Therefore, compared with entrapment rescue by brake release, remote rescue becomes easier and earlier rescue can be achieved for entrapment.

[0079] Furthermore, the fault determination unit 20 determines the occurrence of an open circuit fault in the regenerative switching element 11 in a condition where the smoothing capacitor 7 is charged and the power supply to the smoothing capacitor 7 is disconnected. In this condition, after the regenerative switching element 11 performs a switching operation so that a current flows into the regenerative resistor 10, the fault determination unit 20 determines the occurrence of an open circuit fault in the regenerative switching element 11 based on the voltage value detected by the first voltage monitoring unit 14.

[0080] According to such a configuration, the fault determination unit 20 determines the occurrence of an open-circuit fault in the regenerative switching element 11 based on the actual detection value of the DC bus voltage, so the occurrence of a fault can be determined more accurately.

[0081] Furthermore, when the voltage value detected by the first voltage monitoring unit 14 exceeds the high potential side voltage threshold, the switching control unit 13 switches the operation of the regenerative switching element 11 so that the current flows into the regenerative resistor 10. When the voltage value detected by the first voltage monitoring unit 14 is lower than the low potential side voltage threshold, the switching control unit 13 switches the operation of the regenerative switching element 11 so that the current does not flow into the regenerative resistor 10. The threshold setting unit 15 sets the voltage threshold when the value obtained by subtracting the predetermined life margin from the remaining life of the inverter 8 predicted by the second life prediction unit 17 is shorter than the remaining life of the regenerative switching element 11 predicted by the first life prediction unit 16. At this time, as the voltage threshold, the threshold setting unit 15 sets at least one of the high potential side voltage threshold and the low potential side voltage threshold in a manner that reduces the difference between the high potential side voltage threshold and the low potential side voltage threshold.

[0082] According to such a configuration, by switching the switching operation between the high-frequency operation and the low-frequency operation, the relationship between the remaining life of the regenerative switching element 11 and the remaining life of the inverter 8 can be adjusted more easily.

[0083] In addition, part or all of the functions related to information processing of the control device 100, such as the threshold setting unit 15, the first life prediction unit 16, the second life prediction unit 17, and the failure determination unit 20, may also be mounted on one or more servers. Part or all of the servers may also be configured at a remote location of the elevator and communicate with each other through a communication network such as the Internet or a telephone line network. Part or all of the information processing functions of the control device 100 may also be implemented by processing or storage resources on a cloud service.

[0084] Furthermore, the remaining life of the regenerative switching element 11 and the remaining life of the inverter 8 may be estimated outside the control device 100. The threshold setting unit 15 may accept manual setting of the voltage threshold by, for example, a maintenance person or the like.

[0085] Next, use Figure 6 An example of the hardware configuration of the control device 100 will be described.

[0086] Figure 6 This is a hardware configuration diagram of the main parts of the control device 100 according to the first embodiment.

[0087] Each function of the control device 100 can be implemented by a processing circuit. The processing circuit has at least one processor 200a and at least one memory 200b. The processing circuit has a processor 200a, a memory 200b, and at least one dedicated hardware 300, or it can be that the processing circuit has at least one dedicated hardware 300 instead of the processor 100a and the memory 100b.

[0088] When the processing circuit includes a processor 200a and a memory 200b, each function of the control device 100 is implemented by software, firmware, or a combination of software and firmware. At least one of the software and firmware is described as a program. The program is stored in the memory 200b. The processor 200a implements each function of the control device 100 by reading and executing the program stored in the memory 200b.

[0089] The processor 200a is also called a CPU (Central Processing Unit), a processing device, an arithmetic device, a microprocessor, a microcomputer, or a DSP. The memory 200b is composed of a nonvolatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Only Memory), or an EEPROM (Electrically Erasable Programmable Read Only Memory).

[0090] When the processing circuit has dedicated hardware 300, the processing circuit is implemented by, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof.

[0091] Each function of the control device 100 can be implemented by a processing circuit separately. Alternatively, each function of the control device 100 can also be implemented collectively by a processing circuit. Regarding each function of the control device 100, a part can be implemented by dedicated hardware 300, and another part can be implemented by software or firmware. In this way, the processing circuit implements each function of the control device 100 through dedicated hardware 300, software, firmware, or a combination thereof.

[0092] Implementation method 2.

[0093] In the second embodiment, the differences from the example disclosed in the first embodiment are described in particular detail. For features not described in the second embodiment, any features of the example disclosed in the first embodiment may be adopted.

[0094] Figure 7This is a configuration diagram of an elevator control device according to the second embodiment.

[0095] The control device 100 includes an inverter gate drive circuit 32 and an inverter control unit 33. The inverter gate drive circuit 32 is, for example, a gate driver that outputs a signal that drives the switching action of each switching element mounted on the inverter 8. Each output end of the inverter gate drive circuit 32 is connected to the gate terminal of the corresponding switching element mounted on the inverter 8. The inverter control unit 33 is a part equipped with a function of controlling the action of the inverter 8, such as the switching action of each switching element mounted on the inverter 8. The output of the inverter control unit 33 is connected to the input of the inverter gate drive circuit 32. The inverter control unit 33 outputs a control signal of the switching action to each switching element mounted on the inverter 8 via the inverter gate drive circuit 32.

[0096] The control device 100 includes a first temperature prediction unit 34 , a second temperature prediction unit 35 , a reference temperature sensor 36 , and a second voltage monitoring unit 37 .

[0097] The first temperature prediction unit 34 is a part equipped with a function of predicting the temperature variation of the regenerative switching element 11. The second temperature prediction unit 35 is a part equipped with a function of predicting the temperature variation of a specific semiconductor chip mounted on the inverter 8. The semiconductor chip is a semiconductor chip selected to have the largest temperature rise during mounting among the semiconductor chips mounted on the inverter 8. The semiconductor chip is, for example, a semiconductor chip of a switching element mounted on the inverter 8. The first temperature prediction unit 34 and the second temperature prediction unit 35 receive control signals for the inverter 8 from the inverter control unit 33, respectively. The first temperature prediction unit 34 receives information on the voltage threshold set by the threshold setting unit 15. The prediction value of the first temperature prediction unit 34 is input to the first life prediction unit 16. The prediction value of the first temperature prediction unit 34 is used for the prediction of the remaining life of the regenerative switching element 11 in the first life prediction unit 16. The first life prediction unit 16 predicts the remaining life of the regenerative switching element 11 based on the temperature variation prediction value of the first temperature prediction unit 34, similarly to the prediction of the remaining life based on the temperature variation measurement value. The predicted value of the second temperature prediction unit 35 is input to the second life prediction unit 17. The predicted value of the second temperature prediction unit 35 is used for prediction of the remaining life of the inverter 8 in the second life prediction unit 17. The second life prediction unit 17 predicts the remaining life of the inverter 8 based on the temperature change predicted value of the second temperature prediction unit 35, similarly to the prediction of the remaining life based on the temperature change measured value.

[0098] The reference temperature sensor 36 is arranged on a heat dissipation path of the regenerative switching element 11 or a specific semiconductor chip mounted on the inverter 8. Alternatively, the reference temperature sensor 36 may be arranged on a heat dissipation path of both the regenerative switching element 11 and the specific semiconductor chip mounted on the inverter 8. The reference temperature sensor 36 is mounted, for example, on a substrate of a heat sink (not shown) to which the inverter 8 and the regenerative switching element 11 are connected. The reference temperature sensor 36 measures a reference temperature. The measured value of the reference temperature sensor 36 is input to each of the first temperature prediction unit 34 and the second temperature prediction unit 35. The reference temperature is used for the prediction of temperature changes by the first temperature prediction unit 34 and the second temperature prediction unit 35. In addition, the reference temperature sensor 36 may be installed independently for the regenerative switching element 11 and the inverter 8, respectively.

[0099] The first temperature prediction unit 34 receives input of the current command value and the voltage command value from the inverter control unit 33. The first temperature prediction unit 34 receives input of information on the voltage threshold value set by the threshold setting unit 15. The first temperature prediction unit 34 predicts temperature variation based on a preset temperature estimation model. The temperature estimation model of the first temperature prediction unit 34 is, for example, a model for calculating the temperature of the regenerative switching element 11 based on a reference temperature, a current command value, a voltage command value, and a low potential side voltage threshold. The temperature estimation model is composed of, for example, a thermal circuit.

[0100] The second temperature prediction unit 35 receives input of the current command value and the voltage command value from the inverter control unit 33. The second temperature prediction unit 35 predicts temperature variation based on a preset temperature estimation model. The temperature estimation model of the second temperature prediction unit 35 is, for example, a model for calculating the temperature of a semiconductor chip such as a switching element mounted on the inverter 8 based on a reference temperature, a current command value, and a voltage command value. The temperature estimation model is, for example, composed of a thermal circuit.

[0101] The second voltage monitoring unit 37 is a part equipped with a function of detecting the secondary side voltage of the regenerative switching element 11. The second voltage monitoring unit 37 is connected to the collector terminal and the emitter terminal of the regenerative switching element 11. The second voltage monitoring unit 37 monitors the collector-emitter voltage of the regenerative switching element 11. The output of the second voltage monitoring unit 37 is connected to the input of the fault determination unit 20.

[0102] The fault determination unit 20 determines the occurrence of an open circuit fault in the regenerative switching element 11 based on the logical matching of the control signal for the switching action of the regenerative switching element 11 received from the switching control unit 13 and the secondary side voltage of the regenerative switching element 11 received from the second voltage monitoring unit 37. For example, when receiving an on command or an off command for the regenerative switching element 11 from the switching control unit 13, the fault determination unit 20 determines whether the measured value of the secondary side voltage of the regenerative switching element 11 has a correct behavior without a logical mismatch. When there is a logical mismatch in the measured value of the secondary side voltage of the regenerative switching element 11, the fault determination unit 20 determines that the regenerative switching element 11 has developed an open circuit fault.

[0103] As described above, the elevator control device 100 of the second embodiment includes the reference temperature sensor 36. The reference temperature sensor 36 is arranged on the heat dissipation path of the semiconductor chip such as the regenerative switching element 11 and the switching element of the inverter 8. The reference temperature sensor 36 measures the reference temperature. The control device 100 includes the first temperature prediction unit 34. The first temperature prediction unit 34 predicts the temperature variation of the regenerative switching element 11 based on the measured value of the reference temperature sensor 36 and the preset temperature estimation model. The first life prediction unit 16 predicts the remaining life of the regenerative switching element 11 based on the temperature variation predicted by the first temperature prediction unit 34.

[0104] In addition, the control device 100 includes a second temperature prediction unit 35. The second temperature prediction unit 35 predicts temperature variations of semiconductor chips such as switching elements of the inverter 8 based on the measured value of the reference temperature sensor 36 and a preset temperature estimation model. The second life prediction unit 17 predicts the remaining life of the inverter 8 based on the temperature variations predicted by the second temperature sensor 35.

[0105] According to such a configuration, the temperature variation of the element is predicted based on the measured value of the reference temperature. Therefore, even when a temperature sensor or the like is not provided near the element, the remaining life can be predicted.

[0106] In addition, the control device 100 includes a second voltage monitoring unit 37. The second voltage monitoring unit 37 detects the secondary side voltage of the regenerative switching element 11. The fault determination unit 20 determines the occurrence of an open circuit fault in the regenerative switching element 11 based on the matching between the control signal output by the switching control unit 13 to the regenerative switching element 11 and the voltage detected by the second voltage monitoring unit 37.

[0107] According to such a configuration, the failure determination unit 20 determines the occurrence of an open-circuit failure in the regenerative switching element 11 based on the actual detection value of the matching between the input and the operation of the regenerative switching element 11 , so that the occurrence of a failure can be determined more accurately.

[0108] Industrial Applicability

[0109] The control device and control method disclosed in the present invention can be applied to elevators.

[0110] Description of symbols

[0111] 1: AC power supply; 2: power supply switch; 3: contactor; 4: converter; 5: first DC bus; 6: second DC bus; 7: smoothing capacitor; 8: inverter; 9: traction machine motor; 10: regeneration resistor; 11: regeneration switch element; 12: regeneration switch element gate drive circuit; 13: switching control unit; 14: first voltage monitoring unit; 15: threshold setting unit; 16: first life prediction unit; 17: second life prediction unit; 18: first temperature sensor; 19: second temperature sensor; 20: fault judgment unit; 21: DC bus voltage value; 22: high potential side voltage threshold; 23: first Low potential side voltage threshold; 24: second low potential side voltage threshold; 25: low potential side voltage threshold; 26: remaining life of the inverter; 27: remaining life of the regenerative switching element; 28: life margin; 29: value obtained by subtracting the life margin from the remaining life of the inverter; 30: discharge time; 31: discharge voltage threshold; 32: inverter gate drive circuit; 33: inverter control unit; 34: first temperature prediction unit; 35: second temperature prediction unit; 36: reference temperature sensor; 37: second voltage monitoring unit; 100: control device; 200a: processor; 200b: memory; 300: dedicated hardware.

Claims

1. A control device, wherein: The control device comprises: an inverter that drives a traction machine motor that moves the elevator car; a smoothing capacitor for stabilizing a voltage of a DC bus connected to the inverter; a regenerative resistor connected to the DC bus to consume regenerative power generated by the traction machine motor during regenerative operation of the elevator; a regeneration switch element for switching whether or not current flows into the regeneration resistor; a first voltage monitoring unit configured to detect a voltage of the DC bus; a threshold setting unit that sets a voltage threshold that determines a timing of a switching operation of the regenerative switching element; a switching control unit that controls a switching operation of the regenerative switching element based on a relationship between a voltage value detected by the first voltage monitoring unit and the voltage threshold value set by the threshold setting unit; a first life prediction unit configured to predict a remaining life of the regenerative switching element; and a second life prediction unit configured to predict the remaining life of the inverter, The threshold setting unit sets the voltage threshold so that the remaining lifetime of the inverter predicted by the second lifetime prediction unit is longer than the remaining lifetime of the regenerative switching element predicted by the first lifetime prediction unit.

2. The control device according to claim 1, wherein: The control device includes a first temperature sensor disposed close to the regenerative switching element. The first lifetime prediction unit predicts a remaining lifetime of the regenerative switching element based on a temperature change measured by the first temperature sensor.

3. The control device according to claim 1, wherein: The control device includes a second temperature sensor disposed close to the switching element of the inverter. The second life prediction unit predicts a remaining life of the inverter based on a temperature change measured by the second temperature sensor.

4. The control device according to claim 1, wherein: The control device comprises: a reference temperature sensor disposed on a heat dissipation path of the regenerative switching element and measuring a reference temperature; as well as a first temperature prediction unit for predicting temperature variation of the regenerative switching element based on a measurement value of the reference temperature sensor and a preset temperature estimation model; The first lifetime prediction unit predicts a remaining lifetime of the regenerative switching element based on the temperature variation predicted by the first temperature prediction unit.

5. The control device according to claim 1, wherein: The control device comprises: a reference temperature sensor disposed on a heat dissipation path of a switching element of the inverter and measuring a reference temperature; and a second temperature prediction unit that predicts temperature variation of a switching element of the inverter based on a measurement value of the reference temperature sensor and a preset temperature estimation model, The second lifetime prediction unit predicts a remaining lifetime of the inverter based on the temperature change predicted by the second temperature prediction unit.

6. The control device according to any one of claims 1 to 5, wherein: The control device includes a failure determination unit configured to determine the occurrence of an open circuit failure in the regenerative switching element. When the fault determination unit determines that an open circuit fault has occurred in the regenerative switch element when the car is parked at a position between floors, the inverter drives the traction machine motor in a rescue operation, wherein the rescue operation causes the car to travel in the power running direction and park at the level height.

7. The control device according to claim 6, wherein: When the regenerative switching element performs a switching action so that current flows into the regenerative resistor while the smoothing capacitor is charged and power supply to the smoothing capacitor is disconnected, the fault determination unit determines the occurrence of an open circuit fault in the regenerative switching element based on a voltage value detected by the first voltage monitoring unit after the switching action.

8. The control device according to claim 6, wherein: The control device includes a second voltage monitoring unit that detects a secondary side voltage of the regenerative switching element. The failure determination unit determines the occurrence of an open-circuit failure in the regenerative switching element based on the matching between a control signal output by the switching control unit to the regenerative switching element and a voltage detected by the second voltage monitoring unit.

9. The control device according to any one of claims 1 to 8, wherein: The switching control unit switches the operation of the regenerative switch element so that current flows into the regenerative resistor when the voltage value detected by the first voltage monitoring unit exceeds the high potential side voltage threshold, and switches the operation of the regenerative switch element so that current does not flow into the regenerative resistor when the voltage value detected by the first voltage monitoring unit is lower than the low potential side voltage threshold, When the value obtained by subtracting a predetermined life margin from the remaining life of the inverter predicted by the second life prediction unit is shorter than the remaining life of the regenerative switching element predicted by the first life prediction unit, the threshold setting unit sets at least one of the high potential side voltage threshold and the low potential side voltage threshold as the voltage threshold in a manner that reduces the difference between the high potential side voltage threshold and the low potential side voltage threshold.

10. A control method, the control method being a control method of an elevator, the elevator comprising: an inverter, which drives the traction machine motor that moves the car; a smoothing capacitor for stabilizing a voltage of a DC bus connected to the inverter; a regenerative resistor connected to the DC bus to consume regenerative power generated by the traction machine motor during regenerative operation; a regeneration switch element for switching whether or not current flows into the regeneration resistor; a first voltage monitoring unit configured to detect a voltage of the DC bus; and a switching control unit that controls the switching operation of the regenerative switching element based on a relationship between the voltage value detected by the first voltage monitoring unit and a voltage threshold that determines a timing of the switching operation of the regenerative switching element, The control method comprises: A first prediction step of predicting the remaining life of the regenerative switching element; A second prediction step, predicting the remaining life of the inverter; and The threshold setting step sets the voltage threshold so that the remaining life of the inverter predicted in the second prediction step is longer than the remaining life of the regenerative switching element predicted in the first prediction step.

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