Method for protecting regenerative resistor and motor control device

Abstract

To protect a regenerative resistor which consumes regenerative energy during deceleration of a motor without requiring additional hardware resources and without requiring a large operation load.SOLUTION: When a regenerative transistor provided in series with a regenerative resistor is maintained in an on-state in a period in which a main circuit voltage reaches a regenerative threshold voltage and the regenerative transistor is maintained in an off-state when the main circuit voltage is lower than the regenerative threshold voltage, A regeneration constant S representing energy generated in a regenerative resistor per control period is defined (step 102), the regeneration constant S is accumulated in a control period in which a regenerative transistor is turned on (step 105), an accumulated value P of the regeneration constant is reduced according to a time constant in a control period in which the regenerative transistor is turned off, and a state of the regenerative resistor is evaluated based on the accumulated value P to detect an abnormality (step 107,108,111).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to motor control, and more particularly to a protection method for protecting a regenerative resistor from overheating in a device configured to consume power generated by the motor when the motor is decelerated, and a motor control device that implements such a protection method. [Background technology]

[0002] In systems equipped with motors and controlled based on external input commands, for example, a rectifier circuit rectifies commercial power to generate DC power, which is then converted to AC power by an inverter operating based on external commands. This AC power then drives a motor, such as a three-phase synchronous motor or a three-phase induction motor. A pair of power lines, i.e., positive and negative, connects the rectifier circuit to the input side of the inverter. The DC voltage between the positive and negative power lines is called the main circuit voltage. In such systems, when the motor decelerates, it functions as a generator and generates regenerative power, resulting in an increase in the main circuit voltage. An excessive increase in the main circuit voltage can damage smoothing capacitors and other components in the rectifier circuit. Therefore, a regenerative circuit consisting of a regenerative resistor and a regenerative transistor arranged in series is installed between the pair of power lines, and the regenerative power generated by the motor is consumed by the regenerative resistor. The regenerative transistor is used to turn the current flowing through the regenerative resistor on and off. When a regenerative circuit is provided, the regenerative transistor is turned on when the main circuit voltage exceeds a threshold, causing current to flow through the regenerative resistor, which consumes the regenerative power from the motor. This prevents the main circuit voltage from rising excessively. However, if the regenerative resistor continues to consume regenerative power, its temperature rises, causing the regenerative resistor to overheat and, in some cases, burn out. Therefore, in the past, if current was allowed to flow through the regenerative resistor continuously for a certain period of time, the motor would be stopped abnormally and further heat generation in the regenerative resistor would be prevented.

[0003] To prevent overheating in a regenerative resistor, Patent Document 1 discloses variably controlling the proportion of time a regenerative transistor is on in response to a regenerative load factor, which indicates the state of a regenerative circuit equipped with the regenerative resistor, to reduce the load on the regenerative resistor. In Patent Document 1, the regenerative load factor is calculated, for example, from a preset on-voltage and on-duration of the regenerative transistor. Patent Document 2 discloses a control device for a motor that defines the period from the start of a powering mode to the start of the next powering mode as one cycle, and displays the load factor as the proportion of time the regenerative mode is in one cycle. Patent Document 3, which relates to the control of a motor for a hoist used in a crane or the like, discloses a method for providing hysteresis characteristics to a threshold for controlling the on / off of the regenerative transistor based on the main circuit voltage, calculating the cumulative current flow time of the regenerative resistor from the on / off time of the regenerative transistor to estimate the temperature rise of the regenerative resistor, and, when a temperature rise is detected, reducing the output frequency of the inverter circuit to slow down the motor's rotational speed, thereby reducing the regenerative power consumed by the regenerative resistor. Patent Document 4 discloses that a temperature switch is provided in a regenerative resistor, the temperature of the regenerative resistor is estimated based on a signal that controls the on / off of a regenerative transistor, and the supply of DC power is stopped when the temperature switch operates or when the estimated temperature exceeds a predetermined value.

[0004] Patent Document 5 discloses detecting the current flowing through a regenerative resistor to calculate the power consumed by the regenerative resistor, comparing the calculated power with a set value, and outputting an alarm according to the comparison result. Patent Document 6 discloses estimating the load on the regenerative resistor based on the duty ratio of a signal that turns on a regenerative transistor. Patent Document 7 discloses detecting an overcurrent state in a regenerative resistor and cutting off the current to the regenerative resistor when an overcurrent occurs. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-175871 [Patent Document 2] Japanese Utility Model Application Publication No. 5-4790 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-35359 [Patent Document 4] International Publication No. 96 / 34450 [Patent Document 5] Japanese Patent Application Publication No. 10-341582 [Patent Document 6] Japanese Patent Application Laid-Open No. 2003-204687 [Patent Document 7] Japanese Patent Application Laid-Open No. 2002-315352 Summary of the Invention [Problem to be solved by the invention]

[0006] One method for preventing overheating of the regenerative resistor involves determining that an abnormality has occurred if a current flows through the regenerative resistor continuously for a certain period of time. While intermittent regenerative current flow is determined to be normal operation, if such operation continues for a long period of time, the temperature of the regenerative resistor may continue to rise, leading to the regenerative resistor overheating. On the other hand, when the temperature of the regenerative resistor is actually measured or estimated, as described in some of the above patent documents, issues arise, such as the need for hardware such as a temperature sensor and a large computational load.

[0007] An object of the present invention is to provide a protection method that can protect a regenerative resistor without requiring additional hardware resources or a large computational load, and a motor control device that executes such a protection method. [Means for solving the problem]

[0008] A protection method according to one embodiment of the present invention is a protection method for protecting a regenerative resistor in a motor control device that has an inverter that converts DC power to AC power to drive a motor, a pair of power supply lines that supply DC power to the inverter, and a regenerative circuit that includes a regenerative resistor and a switch element connected between the pair of power supply lines and that controls the on / off flow of current to the regenerative resistor, wherein the switch element is maintained on during a period in which a main circuit voltage, which is the voltage between the pair of power supply lines, reaches a regenerative threshold voltage, and the switch element is maintained off when the main circuit voltage is below the regenerative threshold voltage.The protection method defines a regenerative constant that represents the energy generated in the regenerative resistor per control period based on the resistance value of the regenerative resistor and the regenerative threshold voltage, accumulates the regenerative constant during control periods in which the switch element is turned on, decreases the accumulated value of the regenerative constant according to a time constant during control periods in which the switch element is turned off, and evaluates the state of the regenerative resistor based on the accumulated value.

[0009] A motor control device of one embodiment of the present invention is a motor control device that controls a motor in response to an external command, and includes: an inverter that converts DC power to AC power to drive the motor; a regenerative circuit having a pair of power supply lines that supply DC power to the inverter; a regenerative resistor and a switch element connected between the pair of power supply lines and controlling the on / off of current to the regenerative resistor; and control means that controls the inverter in response to an external command and executes control for each control period to keep the switch element on during a period in which a main circuit voltage, which is the voltage between the pair of power supply lines, reaches a regenerative threshold voltage, and to keep the switch element off when the main circuit voltage is below the regenerative threshold voltage.A regenerative constant that represents the energy generated in the regenerative resistor per control period is defined based on the resistance value of the regenerative resistor and the regenerative threshold voltage, and the control means accumulates the regenerative constant during control periods in which the switch element is on, and decreases the accumulated value of the regenerative constant according to a time constant during control periods in which the switch element is off, and determines that an abnormality has occurred when the value obtained by dividing the accumulated value by the allowable energy value of the regenerative resistor in a specified time period exceeds an abnormality detection threshold. [Effects of the Invention]

[0010] According to the present invention, it is possible to protect a regenerative resistor without requiring additional hardware resources or a large calculation load. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a block diagram showing a configuration of a motor control device according to an embodiment; [Figure 2] 10 is a flowchart illustrating a method for protecting a regenerative resistor. [Figure 3] FIG. 10 is a waveform diagram illustrating protection of a regenerative resistor. [Figure 4] FIG. 10 is a diagram illustrating a control error. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows the configuration of a motor control device 10 according to an embodiment.

[0013] A motor control device 10 shown in FIG. 1 receives AC power from an AC power source 11, such as a three-phase AC power source, and drives and controls a motor 12 in response to externally input commands. The motor 12 is, for example, a three-phase synchronous motor or a three-phase induction motor. The motor control device 10 includes a rectifier circuit (converter) 20 that converts the externally supplied AC power into DC power, and an inverter 40 that converts the DC current supplied from the rectifier circuit 20 into AC current. The rectifier circuit 20 includes a diode stack 21 that includes multiple diodes and rectifies the AC power, and a smoothing capacitor 22 provided on the output side of the diode stack 21. The rectifier circuit 20 and the inverter 40 are connected by a pair of positive and negative power lines 23 and 24. A voltage sensor 25 is provided between the power lines 23 and 24 to measure the DC voltage between the power lines 23 and 24, i.e., the main circuit voltage V. The inverter 40 includes a plurality of switching elements 41, such as power MOSFETs (metal oxide semiconductor field effect transistors) or IGBTs (insulated gate bipolar transistors). In the illustrated example, three sets of two switching elements 41 connected in series are connected between the power supply lines 23 and 24. One end of the U-phase, V-phase, and W-phase wiring is connected to the midpoint of the three sets of series connections of the switching elements 41, and the other ends of these wirings are connected to the motor 12.

[0014] A regenerative circuit 30 is provided between the power supply lines 23 and 24 to prevent the main circuit voltage V from excessively increasing due to regenerative power generated when the motor 12 is decelerated, for example. The regenerative circuit 30 includes a regenerative resistor 31 having one end connected to the power supply line 23 and a regenerative transistor 32 having a collector connected to the other end of the regenerative resistor 31, and the emitter of the regenerative transistor 32 being connected to the power supply line 24. The regenerative transistor 32 is a switch element that controls the on / off of the current supply to the regenerative resistor 31.

[0015] The motor control device 10 further includes a control unit 50 that receives external commands, performs calculations necessary to control the motor 12, and controls the entire motor control device 10; an inverter drive unit 51 that generates signals to be applied to the gates of the switching elements 41 of the inverter 40 based on commands from the control unit 50, thereby driving the inverter 40; and a regenerative circuit drive unit 52 that generates signals to be applied to the gates of the regenerative transistor 32 based on commands from the control unit 50, thereby controlling the on / off of the regenerative transistor 32. The control unit 50 also receives a measurement value of the main circuit voltage V from a voltage sensor 25. Although not shown in the figure, when servo control of the motor 12 is performed, a signal from an encoder connected to the motor 12 to detect the position of the motor 12 may also be input to the control unit 50. The control unit 50 is configured, for example, by a microprocessor (MPU) or a microcomputer. Therefore, in this motor control device 10, a control period is determined, and control such as turning the regenerative transistor 32 on and off is performed every control period. This control period is, for example, greater than or equal to 1 millisecond and less than 100 milliseconds.

[0016] In the motor control device 10 shown in FIG. 1, when the motor 12 decelerates and the regenerative power generated at that time increases the main circuit voltage V, the regenerative transistor 32 is turned on, causing a regenerative current to flow through the regenerative resistor 31. Specifically, a regenerative threshold voltage A is defined for the main circuit voltage V to allow a regenerative current to flow through the regenerative resistor 31. When the main circuit voltage V reaches or exceeds the regenerative threshold voltage A, the regenerative transistor 32 is turned on, causing a current to flow through the regenerative resistor 31. When the main circuit voltage V is below the regenerative threshold voltage A, the regenerative transistor 32 is turned off, causing no current to flow through the regenerative resistor 31. When a current flows through the regenerative resistor 31, the regenerative resistor 31 generates heat, and if this heat continues, the regenerative resistor 31 will overheat. Even if a current flows intermittently through the regenerative resistor 31 for a long period of time, the regenerative resistor 31 may overheat. The motor control device 10 of this embodiment has a protection function for implementing a protection method described below to prevent overheating in the regenerative resistor 31. The method for protecting the regenerative resistor 31 in this embodiment will be described below.

[0017] FIG. 2 is a flowchart illustrating a method for protecting a regenerative resistor in this embodiment. First, in step 101, the allowable energy value of the regenerative resistor 31 in a predetermined time is set as W. The allowable energy value W is a value determined by the specifications of the regenerative resistor 31, and is therefore a fixed value. Considering that the on / off control of the regenerative transistor 32 is performed for each control cycle, in step 102, a regenerative constant S, which is the amount of energy generated per control cycle, is calculated based on the regenerative threshold voltage A and the resistance value R of the regenerative resistor 31. If the length of one control cycle is t, the regenerative constant S is calculated using a voltage parameter a determined based on the regenerative threshold voltage A, as follows: S=a 2 ·t / R The voltage parameter a is generally the same as the regeneration threshold voltage A, i.e., a = A, but may be slightly larger than the regeneration threshold voltage A for reasons described below. When current flows through the regeneration resistor 31, the actual main circuit voltage V fluctuates and does not necessarily match the regeneration threshold voltage A. However, the regeneration constant S is a calculated constant that virtually ensures that the main circuit voltage V always matches the voltage parameter a. Both the allowable energy value W and the regeneration constant S are considered to be values ​​specific to the motor control device 10, and can therefore be calculated in advance regardless of whether the motor control device 10 is operating. In other words, steps 101 and 102 are preferably performed in advance as advance preparation. The determined allowable energy value W and regeneration constant S are stored in a memory (not shown) within the control unit 50 before the motor control device 10 actually drives the motor 12.

[0018] If the motor control device 10 is started while the regeneration resistance 31 is in a cold state, in step 103, as an initial setting, the accumulated value P is cleared to 0, and then in step 104, the main circuit voltage V and the regeneration threshold voltage A are compared. If V≥A, that is, if the main circuit voltage V is greater than or equal to the regeneration threshold voltage A, in step 105, the regeneration transistor 32 is controlled to be turned on and the regeneration constant S is added to the accumulated value P. That is, P←P + S. When the regeneration transistor 32 is already on, the on state is continued as it is. On the other hand, if V < A in step 104, that is, if the main circuit voltage V is lower than the regeneration threshold voltage A, in step 106, the regeneration transistor 32 is controlled to be turned off, and the value of the accumulated value P is decreased according to a predetermined time constant. However, the accumulated value P is not allowed to fall below 0. When the regeneration transistor 32 is already off, the off state is continued as it is. Decreasing the value of the accumulated value P according to a predetermined time constant corresponds to modeling the cooling of the regeneration resistance 31. Generally, the temperature decrease in cooling is represented by an exponential decay curve with the time constant as a parameter. Here, in view of the fact that the control is performed discretely for each control cycle, the accumulated value P may be updated for each control cycle as P←α·P using a coefficient α between 0 and less than 1 corresponding to the time constant. Alternatively, under the condition P≥0, with β as a constant, the accumulated value P may be simply updated for each control cycle as P←P - β. The accumulated value P calculated in this way can be used alone to evaluate the state of the regeneration resistance 31.

[0019] After executing either step 105 or 106, the regenerative load factor k is calculated in step 107. The accumulated value P is calculated by subtracting the energy dissipated when regeneration is not occurring from the accumulated regenerative constant S, which represents the energy generated by the regenerative resistor 31 for each control cycle. Therefore, it can be said to be an index of the energy currently stored in the regenerative resistor 31 in the form of thermal energy. Meanwhile, the allowable energy value W represents the energy allowable for the regenerative resistor 31 at a given time. Therefore, by calculating the regenerative load factor k as k = P / W, it is possible to determine the level of the energy currently stored in the regenerative resistor 31 relative to the allowable energy within a given time. Once the regenerative load factor k is calculated, the regenerative load factor k is compared with the abnormality detection threshold B in step 108. If k ≤ B, it is determined that the regenerative resistor 31 is normal and not overheated. The process then proceeds to step 109, where the process waits for the start of the next control cycle. At the start of the next control cycle, the process repeats from step 104. On the other hand, if the regenerative load factor k is greater than the abnormality detection threshold B in step 108, i.e., if k>B, it is determined that there is a possibility that an abnormality such as overheating has occurred in the regenerative resistor 31, and an abnormality stop process is executed in step 111, after which the entire process of controlling the motor 12 is terminated. In the abnormality stop process, for example, the operation of the motor 12 is abnormally terminated by activating a dynamic brake connected to the motor 12, and the current to the regenerative resistor 31 is cut off by controlling the regenerative transistor 32 to be off regardless of the main circuit voltage V, assuming that the processing capacity of the regenerative resistor 31 has reached its limit. The control unit 50 executes steps 103 to 111 of the process described above.

[0020] FIG. 3 shows an example of how the regenerative resistor 31 is protected when the motor 12 is actually driven by the motor control device 10. Assuming that the motor 12 is repeatedly accelerated (i.e., powered) and decelerated, FIG. 3(a) shows the change in the main circuit voltage V, FIG. 3(b) shows the current flow state of the regenerative resistor 31, and FIG. 3(c) shows the change in the regenerative load factor k. When the motor 12 is accelerating, as shown in FIG. 3(a), the main circuit voltage V is low and below the regenerative threshold voltage A. On the other hand, when the motor 12 is decelerating, the main circuit voltage V rises and exceeds the regenerative threshold voltage A. In the figure, the main circuit voltage V fluctuates when the motor 12 is accelerating, i.e., during the period when DC power is supplied from the rectifier circuit 20 to the inverter 40. This is due to voltage fluctuations in the AC power supply 11. In FIG. 3(b), the solid line with arrows at both ends indicates the period when current flows through the regenerative resistor 31. As can be seen from the diagram, when the main circuit voltage V is equal to or greater than the regeneration threshold voltage A, a current flows through the regeneration resistor 31. When the main circuit voltage V is equal to or greater than the regeneration threshold voltage A and a current flows through the regeneration resistor 31, and regenerative energy is consumed in the regeneration resistor 31, the rotation speed of the motor 12 decreases accordingly, and the electromotive force decreases accordingly, so that the main circuit voltage V decreases during the period when a current is flowing through the regeneration resistor 31.

[0021] When a current flows through the regenerative resistor 31 as shown in FIG. 3(b), the regenerative load factor k, expressed as k=P / W as described above, changes as shown in FIG. 3(c). The regenerative load factor k increases while a current is flowing through the regenerative resistor 31 and gradually decreases when the current stops flowing through the regenerative resistor 31. In the example shown in FIG. 3, a current flows intermittently through the regenerative resistor 31, and at the time indicated by X in the figure, the regenerative load factor k exceeds the abnormality detection threshold B. The regenerative load factor k exceeding the abnormality detection threshold B is detected as an abnormality, such as overheating, in the regenerative resistor 31. Then, an abnormality termination process is performed to abnormally stop the motor 12 and stop the power supply to the regenerative resistor 31.

[0022] The protection method of this embodiment evaluates the power consumed by the regenerative resistor 31 without performing real-time calculations based on actual measured values ​​of current and voltage. Specifically, the regenerative constant S is defined in advance assuming that the main circuit voltage V is equal to the regenerative threshold voltage A (or a value slightly greater than the regenerative threshold voltage A), regardless of the actual main circuit voltage V, which fluctuates when current flows through the regenerative resistor 31. The regenerative constant S is then simply added up for each control cycle to calculate the cumulative value of the energy generated when current flows through the regenerative resistor 31. Therefore, this embodiment reduces the amount of calculation required to calculate the cumulative value of the energy in the regenerative resistor 31. Furthermore, the voltage sensor 25 that measures the main circuit voltage V is a standard feature of general motor control devices, and a current sensor or temperature sensor is not required. Therefore, the motor control device 10 of this embodiment can protect the regenerative resistor 31 without requiring additional hardware resources.

[0023] In this embodiment, the energy generated in the regenerative resistor 31 is calculated based on the regenerative threshold voltage A, not on the actual main circuit voltage V, so there is a risk of an error occurring with respect to the energy actually generated in the regenerative resistor 31. Therefore, the results of evaluating this error will be explained using FIG. 4. The regenerative threshold voltage A, which determines whether or not a current flows through the regenerative resistor 31, is often given a hysteresis characteristic as shown in Patent Document 3, etc., so in the following explanation, the threshold for starting to flow current through the regenerative resistor 31 by switching the regenerative transistor 32 from off to on will be referred to as the regenerative start threshold A. H The threshold for turning off the regenerative transistor that is on and cutting off the current to the regenerative resistor 31 is set as the regeneration end threshold A L Furthermore, the maximum value of the main circuit voltage V that is allowed regardless of whether regeneration is performed or not is set to the maximum main circuit voltage C. When the main circuit voltage V exceeds the maximum main circuit voltage C, a separately provided safety device is activated and the entire motor control device 10 is shut down. The voltage value (parameter a) used to calculate the regeneration constant S is the same as in the above case. There is a difference between these voltage values, A L H ​The relationship of C holds. In the examples described below, the regeneration end threshold A L is 390V, the regeneration start threshold A H is 399V, the voltage parameter a used for calculating the regeneration constant S is 400V, and the maximum main circuit voltage C is 417V. The voltage parameter a is determined according to the regeneration end threshold A L and the regeneration start threshold A H and it is necessary that a > A L However, as shown individually, it is preferably set as a value in the vicinity of the regeneration start threshold A H .

[0024] In this embodiment, the main circuit voltage V is captured every control cycle to control the on / off of the regeneration transistor 32. Therefore, even if the motor 12 decelerates and the main circuit voltage V suddenly rises and exceeds the regeneration start threshold A H , the regeneration transistor 32 cannot be controlled to be on at that time, and there may be a slight delay. Considering such a delay, the main circuit voltage V when the regeneration transistor 32 is controlled to be on and current starts to flow through the regeneration resistor 3 is the regeneration start threshold A HThe maximum main circuit voltage C (= 417 V) is considered to be between the maximum main circuit voltage C (= 399 V) and the maximum main circuit voltage C (= 417 V). Figure 4(a) shows the change in main circuit voltage V over time when the regenerative transistor 32 is turned on and current begins to flow through the regenerative resistor 31 when the main circuit voltage V is 417 V. Figure 4(b) shows the change in main circuit voltage V over time when the regenerative transistor 32 is turned on and current begins to flow through the regenerative resistor 31 when the main circuit voltage V is 399 V. In both cases, when current flows through the regenerative resistor 31, the main circuit voltage V decreases at a rate of 2.79 V per millisecond. When the main circuit voltage V decreases to 390 V, the regenerative transistor 32 is turned off and current to the regenerative resistor 31 stops flowing. If the resistance R of the regenerative resistor 31 is 20 Ω, the energy actually generated in the regenerative resistor 31 while the regenerative transistor 32 is on in the case shown in Figure 4(a) is 77.4 J. In contrast, the regeneration constant S calculated with the regeneration threshold voltage A set to 400 V is 8 kJ / sec, so the amount of energy calculated from the regeneration constant S assuming that the regeneration transistor 32 is on for the same time as in the case shown in Figure 4(a) is 76.0 J. Compared to the amount of energy calculated based on the actual main circuit voltage V, the amount of energy calculated by accumulating the regeneration constant S was 98.2%, with an error of about 1.8%.

[0025] Similarly, in the case shown in Figure 4(b), the energy actually generated in the regenerative resistor 31 while the regenerative transistor 32 is on is 24.9 J. On the other hand, the amount of energy calculated from the regenerative constant S is 25.6 J, with an error of about 2.8%.

[0026] In this way, when evaluating the energy generated in the regeneration resistor 31, the regeneration threshold voltage A (or the regeneration end threshold A L and regeneration start threshold A H) and the resistance value R of the regenerative resistor 31, the difference between the actual energy generated in the regenerative resistor 31 is small, and it has been found that the protection method of this embodiment can practically prevent overheating of the regenerative resistor 31. Note that when the on / off control of the regenerative transistor 32 is performed in each control cycle, the regenerative transistor 32 may be turned on after the main circuit voltage V exceeds the regenerative threshold voltage A to a certain extent. If such cases cannot be ignored, it is possible to set the voltage parameter a higher than the regenerative threshold voltage A even in the case described using FIG. 2.

[0027] An example of a configuration for implementing the present invention has been described above, but the above technology can also be configured as follows.

[0028] (1) A protection method for protecting a regenerative resistor in a motor control device, the motor control device comprising: an inverter that converts DC power into AC power to drive a motor; a pair of power lines that supplies the DC power to the inverter; and a regenerative circuit that is connected between the pair of power lines and includes a regenerative resistor and a switch element that controls on / off of current flow to the regenerative resistor, the switch element being maintained on during a period when a main circuit voltage, which is the voltage between the pair of power lines, reaches a regenerative threshold voltage, and the switch element being maintained off when the main circuit voltage is below the regenerative threshold voltage, the method comprising: defining a regeneration constant representing the energy generated in the regeneration resistor per control period based on the resistance value of the regeneration resistor and the regeneration threshold voltage; accumulating the regeneration constant during the control period in which the switch element is turned on, and decreasing the accumulated value of the regeneration constant according to a time constant during the control period in which the switch element is turned off; A protection method comprising: evaluating a state of the regenerative resistor based on the accumulated value.

[0029] (2) A protection method as described in (1), in which an allowable energy value for a predetermined time of the regenerative resistor is set in advance, and an abnormality is determined to have occurred when the value obtained by dividing the accumulated value by the allowable energy value exceeds an abnormality detection threshold.

[0030] (3) The protection method according to (2), further comprising the step of: when it is determined that an abnormality has occurred, executing an abnormal stop process to abnormally stop the motor and to control the switch element to be off.

[0031] (4) The regeneration constant is expressed as follows: R is the resistance value of the regeneration resistor, a is a voltage parameter determined by the regeneration threshold voltage, and a is the power of the energy generated in the regeneration resistor. 2 The protection method according to any one of (1) to (3), wherein the formula is / R.

[0032] (5) The protection method according to (4), wherein the voltage parameter is set to a value equal to or greater than the regeneration threshold voltage.

[0033] (6) The protection method according to (4), wherein the regeneration threshold voltage includes a regeneration start threshold that transitions the switch element in an off state to an on state and a regeneration end threshold that transitions the switch element in an on state to an off state, the regeneration start threshold being greater than the regeneration end threshold, and the voltage parameter being set to a value greater than the regeneration end threshold.

[0034] (7) A motor control device that controls a motor in response to an external command, an inverter that converts DC power into AC power to drive the motor; a pair of power lines for supplying the DC power to the inverter; a regenerative circuit connected between the pair of power supply lines and including a regenerative resistor and a switch element for controlling on / off of current flow to the regenerative resistor; a control means for controlling the inverter in response to the external command, and for executing control for each control cycle to maintain the switch element on during a period in which a main circuit voltage, which is a voltage between the pair of power supply lines, reaches a regeneration threshold voltage, and to maintain the switch element off when the main circuit voltage is below the regeneration threshold voltage; and a regeneration constant representing the energy generated in the regeneration resistor per control cycle is defined based on the resistance value of the regeneration resistor and the regeneration threshold voltage, the control means accumulates the regeneration constant during the control cycle in which the switch element is turned on, decreases the accumulated value of the regeneration constant according to a time constant during the control cycle in which the switch element is turned off, and determines that an abnormality has occurred when a value obtained by dividing the accumulated value by an allowable energy value of the regeneration resistor in a predetermined time period exceeds an abnormality detection threshold.

[0035] (8) The motor control device according to (7), wherein the control means, when determining that the abnormality has occurred, executes an abnormality stop process to abnormally stop the motor and control the switch element to turn off.

[0036] (9) The regeneration constant is expressed as follows: R is the resistance value of the regeneration resistor, a is a voltage parameter determined by the regeneration threshold voltage, and a is the power of the energy generated in the regeneration resistor. 2 The motor control device according to (7) or (8), wherein the motor speed is set to 1 / R.

[0037] (10) The motor control device according to (9), wherein the voltage parameter is set to a value equal to or greater than the regeneration threshold voltage.

[0038] (11) The motor control device according to (9), wherein the regeneration threshold voltage includes a regeneration start threshold that transitions the switch element from an off state to an on state and a regeneration end threshold that transitions the switch element from an on state to an off state, the regeneration start threshold being set to be greater than the regeneration end threshold, and the voltage parameter being set to be greater than the regeneration end threshold.

[0039] According to the configuration described in (1), by accumulating a regeneration constant, which can be set in advance based on the resistance value of the regenerative resistor and the regeneration threshold voltage, for each control period and decreasing the accumulated value according to a time constant, it becomes possible to evaluate the energy generated in the regenerative resistor without relying on the actual main circuit voltage, without requiring additional hardware resources or a large calculation load. Furthermore, by determining that an abnormality has occurred when the value obtained by dividing the accumulated value by the allowable energy value of the regenerative resistor for a predetermined time exceeds the abnormality detection threshold, as in the configuration described in (2), it is possible to accurately detect an abnormality in the regenerative resistor without requiring additional hardware resources or a large calculation load.

[0040] According to the configuration described in (3), when an abnormality is detected, the motor is stopped and power to the regenerative resistor is also stopped, thereby preventing the occurrence of a fault in the regenerative resistor. By adopting the configurations described in (4) and (5), the regenerative constant can be easily determined. Even when the regenerative threshold voltage has a hysteresis characteristic as described in (6), by setting the voltage parameter to a value greater than the regenerative end threshold, it is possible to evaluate the energy generated in the regenerative resistor and detect the occurrence of an abnormality in the regenerative resistor without relying on the actual main circuit voltage, without requiring additional hardware resources or a large calculation load.

[0041] According to the configuration described in (7), the regenerative constant, which can be set in advance based on the resistance value of the regenerative resistor and the regenerative threshold voltage, is accumulated for each control period, the accumulated value is decreased according to the time constant, and an abnormality is determined to have occurred when the value obtained by dividing the accumulated value by the allowable energy value of the regenerative resistor at a specified time exceeds the abnormality detection threshold. This makes it possible for the motor control device to evaluate the energy generated in the regenerative resistor without relying on the actual main circuit voltage, and to accurately detect the occurrence of an abnormality in the regenerative resistor, without requiring additional hardware resources or a large calculation load.

[0042] According to the configuration described in (8), when an abnormality is detected, the motor is stopped and power to the regenerative resistor is also stopped, thereby preventing failure in the regenerative resistor.By adopting the configurations described in (9) and (10), it is possible to easily determine the regenerative constant to be preset in the motor control device.As described in (11), even when the regenerative threshold voltage is given a hysteresis characteristic, by setting the voltage parameter to a value greater than the regenerative end threshold, it becomes possible to evaluate the energy generated in the regenerative resistor regardless of the actual main circuit voltage and detect the occurrence of an abnormality in the regenerative resistor without requiring additional hardware resources or a large calculation load in the motor control device. [Explanation of symbols]

[0043] 10...motor control device; 11...AC power supply; 12...motor; 20...rectifier circuit; 21...diode stack; 22...smoothing capacitor; 23, 24...power line; 25...voltage sensor; 30...regenerative circuit; 31...regenerative resistor; 32...regenerative transistor; 40...inverter; 41...switching element; 50...control unit; 51...inverter drive unit; 52...regenerative circuit drive unit.

Claims

1. A protection method for protecting a regenerative resistor in a motor control device, the motor control device comprising: an inverter that converts DC power into AC power to drive a motor; a pair of power supply lines that supply the DC power to the inverter; and a regenerative circuit that is connected between the pair of power supply lines and includes a regenerative resistor and a switch element that controls on and off of current flow to the regenerative resistor, wherein the switch element is maintained on during a period in which a main circuit voltage, which is the voltage between the pair of power supply lines, reaches a regenerative threshold voltage, and the switch element is maintained off when the main circuit voltage is below the regenerative threshold voltage, defining a regeneration constant representing the energy generated in the regeneration resistor per control period based on the resistance value of the regeneration resistor and the regeneration threshold voltage; accumulating the regeneration constant during the control period in which the switch element is turned on, and decreasing the accumulated value of the regeneration constant according to a time constant during the control period in which the switch element is turned off; A protection method comprising: evaluating a state of the regenerative resistor based on the accumulated value.

2. 2. The protection method according to claim 1, wherein an allowable energy value for the regenerative resistor in a predetermined time is set in advance, and when a value obtained by dividing the accumulated value by the allowable energy value exceeds an abnormality detection threshold, it is determined that an abnormality has occurred.

3. 3. The protection method according to claim 2, further comprising the step of: when it is determined that an abnormality has occurred, executing an abnormal stop process for abnormally stopping the motor and controlling the switch element to be off.

4. The regeneration constant is expressed as follows: R is the resistance value of the regeneration resistor, a is a voltage parameter determined by the regeneration threshold voltage, and a is the power of the energy generated in the regeneration resistor. ２ 4. The method of claim 1, wherein:

5. The protection method of claim 4 , wherein the voltage parameter is set to a value equal to or greater than the regeneration threshold voltage.

6. 5. The protection method according to claim 4, wherein the regeneration threshold voltage includes a regeneration start threshold that transitions the switch element in an off state to an on state and a regeneration end threshold that transitions the switch element in an on state to an off state, the regeneration start threshold being greater than the regeneration end threshold, and the voltage parameter being set to a value greater than the regeneration end threshold.

7. A motor control device that controls a motor in response to an external command, an inverter that converts DC power into AC power to drive the motor; a pair of power lines for supplying the DC power to the inverter; a regenerative circuit connected between the pair of power supply lines and including a regenerative resistor and a switch element for controlling on / off of current flow to the regenerative resistor; a control means for controlling the inverter in response to the external command, and for executing control for each control period to maintain the switch element on during a period in which a main circuit voltage, which is a voltage between the pair of power supply lines, reaches a regeneration threshold voltage, and to maintain the switch element off when the main circuit voltage is below the regeneration threshold voltage; and a regeneration constant representing the energy generated in the regeneration resistor per control cycle is defined based on the resistance value of the regeneration resistor and the regeneration threshold voltage, the control means accumulates the regeneration constant during the control cycle in which the switch element is turned on, decreases the accumulated value of the regeneration constant according to a time constant during the control cycle in which the switch element is turned off, and determines that an abnormality has occurred when a value obtained by dividing the accumulated value by an allowable energy value of the regeneration resistor in a predetermined time period exceeds an abnormality detection threshold.

8. 8. The motor control device according to claim 7, wherein the control means, when determining that the abnormality has occurred, executes an abnormal stop process to abnormally stop the motor and control the switch element to turn off.

9. The regeneration constant is expressed as follows: R is the resistance value of the regeneration resistor, a is a voltage parameter determined by the regeneration threshold voltage, and a is the power of the energy generated in the regeneration resistor. ２ 9. The motor control device according to claim 7, wherein:

10. The motor control device according to claim 9 , wherein the voltage parameter is set to a value equal to or greater than the regeneration threshold voltage.

11. 10. The motor control device according to claim 9, wherein the regeneration threshold voltage includes a regeneration start threshold that transitions the switch element from an off state to an on state and a regeneration end threshold that transitions the switch element from an on state to an off state, the regeneration start threshold being set to be greater than the regeneration end threshold, and the voltage parameter being set to be greater than the regeneration end threshold.

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