Motor drive device having overvoltage protection circuit

Abstract

This motor drive device comprises: a motor drive circuit that drives a synchronous motor by supplying AC power to the synchronous motor via power lines; an overvoltage protection circuit that short-circuits between the phases of the power lines by turning on a semiconductor switch when driving of the synchronous motor by the motor drive circuit is stopped and prevents the occurrence of overvoltage due to a back electromotive force between the terminals of the synchronous motor; and a temperature estimation unit that calculates a temperature estimation value of the semiconductor switch by using a motor constant and a semiconductor switch constant, said motor constant including at least one of the inertia and back electromotive force constants of the synchronous motor, said semiconductor switch constant including the on-resistance, thermal resistance, and thermal time constant of the semiconductor switch.

Description

[Technical field]

[0001] The present invention relates to a motor drive device having an overvoltage protection circuit. [Background technology]

[0002] In a motor drive device that drives a synchronous motor, when the drive of the synchronous motor stops due to factors such as the inability to control the motor drive device or an emergency stop by the motor drive device, the synchronous motor generates energy based on a back electromotive force (back electromotive voltage). The energy generated in the synchronous motor is regenerated to an AC power source or to a regenerative load (regenerative resistor) provided in a DC link. However, if the synchronous motor is large or rotates at high speed, the energy based on the back electromotive force generated when the drive of the synchronous motor stops becomes very large, and an overvoltage occurs in the motor drive device. For this reason, an overvoltage protection circuit (back electromotive voltage protection circuit) is provided to protect the motor drive device from the back electromotive force generated when the synchronous motor decelerates.

[0003] For example, an overvoltage protection device for suppressing overvoltage in a power conversion device having a regenerative energy release means, a capacitor discharge means, a voltage detection means, and an overvoltage control means, the power converter being connected to a capacitor connected to a DC power source and converting the power of the DC power source into AC power and supplying it to an armature winding of a synchronous motor to drive the synchronous motor, the voltage detection means detecting the voltage of the armature winding of the synchronous motor when the power converter is stopped, the overvoltage control means detecting the regenerative energy release means when the voltage of the armature winding exceeds a first predetermined value, An overvoltage protection device is known in which the voltage of the armature winding is reduced by controlling regenerative energy release means to short-circuit the armature windings and release the rotational energy of the synchronous motor, the short-circuit between the armature windings caused by the regenerative energy release means is released when the voltage of the armature winding has fallen to a second predetermined value smaller than the first predetermined value, and the capacitor discharge means is controlled to discharge the charge of the capacitor when the voltage of the armature winding has fallen to a third predetermined value smaller than the first predetermined value (see, for example, Patent Document 1).

[0004] For example, a drive device for a permanent magnet synchronous motor is known which includes an inverter that receives a DC voltage from a DC power supply as an input and outputs a voltage to a permanent magnet synchronous motor, DC voltage detection means that detects a DC regenerative voltage appearing on the input side of the inverter, and inverter control means that controls the voltage output by the inverter, wherein the inverter control means includes: shorting means that controls the inverter so as to short-circuit the lines of the inverter and the permanent magnet synchronous motor based on an increasing regenerative voltage detected by the DC voltage detection means during regenerative operation, opening means that controls the inverter so as to open the lines of the inverter and the permanent magnet synchronous motor based on a decreasing regenerative voltage detected by the DC voltage detection means, and intermittent short-circuiting means that controls the inverter so as to alternately open and short-circuit the lines of the inverter and the permanent magnet synchronous motor based on the increasing regenerative voltage detected by the DC voltage detection means (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-200490 A [Patent Document 2] JP 2012-050332 A Summary of the Invention [Problem to be solved by the invention]

[0006] When the drive of the synchronous motor is stopped and a back electromotive force is generated, the overvoltage protection device prevents the application of an overvoltage to the motor drive device by short-circuiting the phases of the power lines between the motor drive device and the synchronous motor. For the short circuit in the overvoltage protection device, a semiconductor switch such as a thyristor is often used because of its high operating speed. When the semiconductor switch is turned on and a short-circuit current flows, the temperature of the semiconductor switch rises, so that it is necessary to wait for the temperature of the semiconductor switch to drop before driving the synchronous motor again with the motor drive device. For this reason, a temperature sensor for monitoring the semiconductor switch must be provided in the overvoltage protection device, which is costly. In addition, if the temperature sensor breaks down, it is not possible to monitor the temperature of the semiconductor switch, so it is not possible to grasp the appropriate timing for re-driving the motor drive device, which may hinder the efficient operation of the motor drive device and even lead to a breakdown of the overvoltage protection circuit. Therefore, there is a need for a technology that can accurately grasp the temperature of a semiconductor switch provided in an overvoltage protection circuit for protecting the motor drive device from the back electromotive force generated when the drive of the synchronous motor is stopped, at low cost. [Means for solving the problem]

[0007] The motor drive device includes a motor drive circuit that drives the synchronous motor by supplying AC power to the synchronous motor via a power line; an overvoltage protection circuit that is provided between the synchronous motor and the motor drive circuit and shorts the phases of the power lines by turning on a semiconductor switch when driving of the synchronous motor by the motor drive circuit stops, thereby preventing the occurrence of overvoltage due to back electromotive force between the terminals of the synchronous motor; and a temperature estimator that calculates an estimated temperature of the semiconductor switch, which rises when the semiconductor switch is turned on and then falls, using a motor constant including at least one of an inertia and a back electromotive force constant associated with the synchronous motor, and a semiconductor switch constant including an on-resistance, a thermal resistance, and a thermal time constant associated with the semiconductor switch. Effect of the Invention

[0008] According to one aspect of the present disclosure, it is possible to accurately grasp the temperature of a semiconductor switch provided in an overvoltage protection circuit for protecting a motor drive device from a back electromotive force generated when drive of a synchronous motor is stopped at low cost. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 illustrates a motor drive device according to an embodiment of the present disclosure. [Diagram 2] 5 is a flowchart showing an operation flow of the motor drive device according to an embodiment of the present disclosure. [Diagram 3] 10 is a diagram illustrating an example of a transition of an estimated temperature of a semiconductor switch calculated by a temperature estimator in the motor drive device according to an embodiment of the present disclosure. [Figure 4] FIG. 11 is a diagram illustrating a first modified example of a motor drive device according to an embodiment of the present disclosure. [Diagram 5] 13 is a flowchart showing an operation flow of a fifth modified example of a motor drive device according to an embodiment of the present disclosure. [Figure 6] FIG. 13 is a diagram illustrating a sixth modified example of a motor driving device according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A motor drive device having an overvoltage protection circuit will be described below with reference to the drawings. In each drawing, the same components are given the same reference symbols. In addition, the scale of these drawings is appropriately changed to facilitate understanding. The illustrated embodiment is one example for carrying out the present invention, and the present invention is not limited to these embodiments.

[0011] FIG. 1 is a diagram illustrating a motor drive device according to one embodiment of the present disclosure.

[0012] As an example, a case where a synchronous motor 2 is driven by a motor drive device 1 is shown. In this embodiment, the number of phases of the synchronous motor 2 is not particularly limited to this embodiment, and may be, for example, three phases or single phase. Machines in which the synchronous motor 2 is provided include, for example, machine tools, robots, forging machines, injection molding machines, industrial machines, and the like.

[0013] A motor driving device 1 according to one embodiment of the present disclosure includes a motor control unit 10, a motor driving circuit 11, an overvoltage protection circuit 12, a temperature estimation unit 13, an permission signal output unit 14, a current sensor 21, a rotational speed calculation unit 22, and a speed sensor 23.

[0014] The motor drive circuit 11 and the synchronous motor 2 are connected via a power line. The motor drive circuit 11 drives the synchronous motor 2 by supplying AC power to the synchronous motor 2 via the power line. For this reason, the motor drive circuit 11 has, for example, an inverter 101. The inverter 101 is made up of a bridge circuit of switching elements and diodes connected in inverse parallel to the switching elements. The inverter 101 is made up of a three-phase bridge circuit when the synchronous motor 2 is a three-phase motor, and is made up of a single-phase bridge circuit when the synchronous motor 2 is a single-phase motor. In the illustrated example, the synchronous motor 2 is a three-phase synchronous motor, so the inverter 101 is configured as a three-phase inverter. In the inverter 101, a positive side switching element SU U The lower arm of the U phase is provided with a negative switching element SU LThe V-phase upper arm is provided with a positive switching element SV U The V-phase lower arm is provided with a negative switching element SV L The W-phase upper arm is provided with a positive switching element SW U The W-phase lower arm is provided with a negative switching element SW L In the inverter 101, each switching element is controlled to be turned on and off according to, for example, a PWM switching control method. Examples of the switching elements include unipolar transistors such as FETs, bipolar transistors, IGBTs, thyristors, and GTOs, but the type of the switching elements themselves does not limit this embodiment, and other switching elements may be used.

[0015] The DC side of the inverter 101 is provided with a smoothing capacitor 3 and a DC power supply V dc The inverter 101 is provided with a DC power supply V dc The DC power input from the DC power source V is converted to AC power and supplied to the synchronous motor 2 via the power line. dc The inverter is composed of, for example, a rectifier circuit connected to an AC power source, or a battery that stores DC power.

[0016] The motor control unit 10 controls the on / off of each switching element of the inverter 101 in the motor drive circuit 11. The motor control unit 10 controls the power conversion operation of the inverter 101 based on the rotation speed (speed feedback) of the synchronous motor 2 detected by the speed sensor 23, the current (current feedback) flowing through the power line detected by the current sensor 21, a predetermined torque command, and an operation program for the synchronous motor 2. The speed, torque, or rotor position of the synchronous motor 2 is controlled based on the AC power supplied from the inverter 101. Note that the configuration of the motor control unit 10 described here is merely an example, and the configuration of the motor control unit 10 may be specified by including terms such as a position command generating unit, a position control unit, a speed control unit, a current control unit, and a torque command creating unit.

[0017] An overvoltage protection circuit 12 is connected to a power line connecting the synchronous motor 2 and the motor drive circuit 11. The overvoltage protection circuit 12 includes a semiconductor switch 103 and a diode rectifier circuit 102 having an AC terminal to which the power line is connected and a DC terminal to which the semiconductor switch 103 is connected.

[0018] The diode rectifier circuit 102 in the overvoltage protection circuit 12 is a rectifier that rectifies AC power based on the back electromotive force of the synchronous motor 2 to output DC power. In the illustrated example, the synchronous motor 2 is a three-phase motor, so the diode rectifier circuit 102 is configured as a three-phase full-bridge circuit, but if the synchronous motor 2 is a single-phase motor, the diode rectifier circuit 102 is configured as a single-phase full-bridge circuit.

[0019] The semiconductor switch 103 in the overvoltage protection circuit 12 has a short-circuit switching function of short-circuiting the terminals on the DC output side of the diode rectifier circuit 102 by turning it on, and not short-circuiting the terminals on the DC output side of the diode rectifier circuit 102 by turning it off. Examples of the semiconductor switch 103 include a thyristor, an IGBT, an FET, a GTO, or a transistor. The on-off operation of the semiconductor switch 103 in the overvoltage protection circuit 12 may be controlled by, for example, the motor control unit 10, or a control unit (not shown) separate from the motor control unit 10 may be provided. When the drive of the synchronous motor 2 stops due to factors such as failure to control the motor drive device 1 or an emergency stop by the motor drive device 1, the synchronous motor 2 decelerates and generates a counter electromotive force, and a large overvoltage is applied to the motor drive circuit 11. For example, when a voltage exceeding the withstand voltage is applied to the smoothing capacitor 3 in the motor drive circuit 11, the smoothing capacitor 3 is damaged, and in the worst case, a fire may occur. Therefore, when the drive of the synchronous motor 2 is stopped, the semiconductor switch 103 in the overvoltage protection circuit 12 is turned on to short-circuit the terminals on the DC output side of the diode rectifier circuit 102. For example, when the motor control unit 10 receives an alarm indicating that the motor drive device 1 has become uncontrollable, the motor control unit 10 commands the semiconductor switch 103 to turn on. For example, when an emergency stop signal is input to the motor drive device 1, the motor control unit 10 commands the semiconductor switch 103 to turn on. For example, when the line voltage of the power line connecting the motor drive circuit 11 and the synchronous motor 2 exceeds a predetermined voltage, the motor control unit 10 detects this and commands the semiconductor switch 103 to turn on.

[0020] When the semiconductor switch 103 is off, it does not short-circuit the terminals on the DC output side of the diode rectifier circuit 102, i.e., nothing is connected between the terminals on the DC output side of the diode rectifier circuit 102. When the semiconductor switch 103 is on, it short-circuits the terminals on the DC output side of the diode rectifier circuit 102. The diode rectifier circuit 102 rectifies AC power based on the "counter electromotive force of the synchronous motor 2" and outputs DC power only when the semiconductor switch 103 is on and the terminals on the DC output side of the diode rectifier circuit 102 are short-circuited. Since all of the energy based on the counter electromotive force is consumed via the diode rectifier circuit 102 and the semiconductor switch 103 in the overvoltage protection circuit 12, it is possible to protect the motor drive device 1 from the counter electromotive force. When the semiconductor switch 103 is on, the synchronous motor 2 gradually decelerates, and a short-circuit current continues to flow through the semiconductor switch 103 until it completely stops (i.e., until the rotational energy of the synchronous motor 2 becomes zero), and the temperature of the semiconductor switch 103 rises. Thereafter, after the synchronous motor 2 stops, the temperature of the semiconductor switch 103 in the ON state gradually drops because no current flows through it. If the motor drive device 1 starts driving the synchronous motor 2 before the temperature of the semiconductor switch 103 has sufficiently dropped, and then the motor drive device 1 stops driving the synchronous motor 2 again and the semiconductor switch 103 of the overvoltage protection circuit 12 is turned ON, heat may accumulate in the semiconductor switch 103, resulting in destruction. In order to avoid such destruction of the semiconductor switch 103, the motor drive device 1 according to an embodiment of the present disclosure estimates the temperature of the semiconductor switch 103 after it is turned ON by calculation without using a temperature sensor, does not permit the synchronous motor 2 to start driving until the estimated temperature value falls below a predetermined temperature threshold, and permits the synchronous motor 2 to start driving when the estimated temperature value falls below the predetermined temperature threshold.

[0021] The temperature estimation unit 13 calculates an estimated temperature value of the semiconductor switch 103 using a motor constant including an inertia and a back electromotive force constant related to the synchronous motor 2, and a semiconductor switch constant including an on-resistance, a thermal resistance, and a thermal time constant related to the semiconductor switch 103. Details of the calculation process by the temperature estimation unit 13 will be described later. When the semiconductor switch 103 is turned on, the synchronous motor 2 gradually decelerates, and until it completely stops (i.e., until the rotational energy of the synchronous motor 2 becomes zero), a short-circuit current continues to flow through the semiconductor switch 103, and the temperature of the semiconductor switch 103 increases. After the temperature of the semiconductor switch 103 increases and reaches a maximum temperature, the temperature of the semiconductor switch 103 decreases. In one embodiment of the present disclosure, information on the temperature of the semiconductor switch 103, which increases when the semiconductor switch is turned on and then decreases, is not obtained by a temperature sensor, but is obtained as an estimated value calculated by the temperature estimation unit 13.

[0022] When the estimated temperature value of the semiconductor switch 103, which is decreasing after reaching a maximum temperature, falls below a first temperature threshold, the permission signal output unit 14 outputs a signal to the motor control unit 10 to permit the motor drive circuit 11 to start driving the synchronous motor 2.

[0023] FIG. 2 is a flowchart showing an operation flow of the motor drive device according to one embodiment of the present disclosure.

[0024] In a state where the synchronous motor 2 is driven at a certain rotation speed by the motor drive device 1, in step S101, the motor control unit 10 judges whether or not the drive of the synchronous motor 2 has stopped. When the drive of the synchronous motor 2 is stopped due to factors such as the inability to control the motor drive device 1 or an emergency stop by the motor drive device 1, the synchronous motor 2 decelerates and generates a back electromotive force. For example, the motor control unit 10 judges that the drive of the synchronous motor 2 has stopped when it receives an alarm indicating that the motor drive device 1 has become out of control or an emergency stop signal for the motor drive device 1. Alternatively, the motor control unit 10 may judge that the drive of the synchronous motor 2 has stopped when the line voltage of the power line connecting the motor drive circuit 11 and the synchronous motor 2 exceeds a predetermined voltage. If it is judged that the drive of the synchronous motor 2 has stopped in step S101, the motor control unit 10 commands the semiconductor switch 103 in the overvoltage protection circuit 12 to turn on, thereby shorting the terminals on the DC output side of the diode rectifier circuit 102, and proceeds to step S102.

[0025] In step S102, the temperature estimator 13 calculates a temperature estimate of the semiconductor switch 103 by using a motor constant including an inertia and a back electromotive force constant associated with the synchronous motor 2, and a semiconductor switch constant including an on-resistance, a thermal resistance, and a thermal time constant associated with the semiconductor switch 103. When the semiconductor switch 103 is turned on, the synchronous motor 2 gradually decelerates, and a short-circuit current continues to flow through the semiconductor switch 103 until the synchronous motor 2 is completely stopped (i.e., until the rotational energy of the synchronous motor 2 becomes zero), and the temperature estimate of the semiconductor switch 103 calculated by the temperature estimator 13 increases. After the temperature estimate of the semiconductor switch 103 reaches the maximum temperature, the temperature estimate of the semiconductor switch 103 calculated by the temperature estimator 13 decreases.

[0026] In step S103, the permission signal output unit 14 judges whether the estimated temperature value of the semiconductor switch 103 during the temperature drop calculated by the temperature estimator 13 has fallen below the first temperature threshold. Until the estimated temperature value rises and reaches the maximum temperature, the processes of steps S102 and S103 are repeatedly executed, and the calculation of the estimated temperature value by the temperature estimator 13 continues. After the estimated temperature value reaches the maximum temperature, the estimated temperature value gradually falls over time, and at a certain point in time, the estimated temperature value falls below the first temperature threshold. When the permission signal output unit 14 judges that the estimated temperature value of the semiconductor switch 103 during the temperature drop calculated by the temperature estimator 13 has fallen below the first temperature threshold, the process proceeds to step S104. Note that after the estimated temperature value reaches the maximum temperature, the temperature drops with a certain time constant, so that it is possible to predict and calculate the time required for the estimated temperature value to fall below the first temperature threshold after reaching the maximum temperature. Therefore, the temperature estimation unit 13 continuously calculates the temperature estimation value from when the semiconductor switch 103 is turned on until the estimated temperature value rises and reaches the maximum temperature, and after the estimated temperature reaches the maximum temperature, predicts and calculates the "drive standby time" as the time starting from the time when the estimated temperature value reaches the maximum temperature and ending from the time when the estimated temperature value falls below the first temperature threshold, and when the drive standby time has elapsed since the estimated temperature value reached the maximum temperature, the permission signal output unit 14 determines that this is the time when the estimated temperature value of semiconductor switch 103, which is decreasing and calculated by the temperature estimation unit 13, has fallen below the first temperature threshold.

[0027] In this way, the temperature estimation unit 13 sequentially calculates the temperature estimation value from when the semiconductor switch is turned on with the driving stop of the synchronous motor 2 (step S101) until the temperature estimation value reaches the maximum temperature, and after the temperature estimation value reaches the maximum temperature, the temperature estimation value decreases exponentially, so predicts and calculates a "driving standby time" starting from the time when the temperature estimation value reaches the maximum temperature and ending from the time when the temperature estimation value falls below the first temperature threshold.

[0028] The first temperature threshold may be set to, for example, about a value obtained by subtracting the maximum temperature that increases with one operation of the overvoltage protection circuit 12 from the heat resistance temperature of the semiconductor switch 103, and may be set by referring to the heat resistance temperature specified in a specification table or instruction manual of the semiconductor switch 103. Preferably, the first temperature threshold may be set to a temperature lower than the heat resistance temperature of the semiconductor switch 103 so that the semiconductor switch 103 is not destroyed even if the semiconductor switch 103 is turned on multiple times in a short period of time, causing a short circuit current to flow and heat to accumulate. The first temperature threshold may be stored in a rewritable storage unit (not shown) and may be rewritable by an external device, and may be changed to an appropriate value as necessary even after the first temperature threshold has been set.

[0029] In step S104, the permission signal output unit 14 outputs a signal to the motor control unit 10 to permit the motor drive circuit 11 to start driving the synchronous motor 2. As a result, the motor control unit 10 enters a standby state so that the motor control unit 10 can resume drive control of the synchronous motor 2 at any time. It is preferable that the operator performs preparation work for restarting the drive of the synchronous motor 2, such as removing the cause of the uncontrollable state if the cause of the drive stop of the synchronous motor 2 in step S101 is, for example, an inability to control the motor drive device 1, and removing the cause of the emergency stop if, for example, an emergency stop by the motor drive device 1 is caused. After the overvoltage protection circuit 12 is started and the semiconductor switch 103 is turned on, the motor control unit 10 cannot control the drive of the synchronous motor 2 unless the permission signal output unit 14 permits the motor drive circuit 11 to start driving the synchronous motor 2 in step S104, so that the safety of the motor drive device 1 can be ensured. After the permission signal output unit 14 permits the motor drive circuit 11 to start driving the synchronous motor 2 in step S104, the worker removes the cause of the stop of the drive of the synchronous motor 2, and then the synchronous motor 2 is actually driven.

[0030] Next, the calculation process performed by the temperature estimation unit 13 will be described in detail.

[0031] FIG. 3 is a diagram illustrating an example of a transition of the estimated temperature of the semiconductor switch calculated by a temperature estimator in the motor drive device according to an embodiment of the present disclosure.

[0032] The temperature estimation unit 13 calculates an estimated temperature value of the semiconductor switch 103 using motor constants including the inertia and back electromotive force constants associated with the synchronous motor 2, and semiconductor switch constants including the on-resistance, thermal resistance, and thermal time constant associated with the semiconductor switch 103.

[0033] Among the motor constants used to calculate the temperature estimate, the inertia (moment of inertia) of synchronous motor 2 is A [kgm 2 ]. Inertia A [kgm 2 ] includes the inertia of the synchronous motor 2 itself and the inertia of the object connected to the rotating shaft of the synchronous motor 2. In addition, the back electromotive force coefficient of the synchronous motor 2 is V k [V / (rad / sec)] and the number of poles of synchronous motor 2 is N.

[0034] Among the semiconductor switch constants used in the calculation of the temperature estimate, the on-resistance of the semiconductor switch 103 is R t [Ω], thermal resistance is B [℃ / W], the thermal time constant when the temperature rises is τ1 [sec], and the thermal time constant when the temperature drops is τ2 [sec].

[0035] In addition, since the loss in the motor windings and the loss in the diode rectifier circuit 102 are sufficiently small compared to the loss in the semiconductor switch 103, the loss in the motor windings and the loss in the diode rectifier circuit 102 are ignored in the following explanation, but the temperature estimate may be calculated including these losses.

[0036] With the synchronous motor 2 being driven at a certain rotational speed by the motor drive device 1, if the semiconductor switch 103 in the overvoltage protection circuit 12 is turned on to short the power line immediately after the motor drive circuit 11 stops driving the synchronous motor 2 and the synchronous motor 2 enters a free-running state, a current flows through the semiconductor switch 103, and the temperature continues to rise until it reaches the maximum temperature. The temperature estimator 13 calculates the estimated temperature rise of the semiconductor switch 103 for each minute time Δt [sec] as follows: That is, time t0 is the time immediately after the semiconductor switch 103 is turned on, and time t i-1 From time t i (where i is a natural number greater than or equal to 1) is an infinitesimal time Δt [sec].

[0037] Here, the parameters used in the following calculations are defined as shown in Table 1.

[0038] [Table 1]

[0039] Loss P of the semiconductor switch 103 during the short time Δt [sec] from time t0 to time t1 immediately after the semiconductor switch 103 is turned on t_1 [W] and consumed energy ΔE1 can be calculated as follows:

[0040] The rotation speed ω1 [rad / sec] of the synchronous motor 2 at time t0 immediately after the semiconductor switch 103 is turned on is determined by the electrical angular frequency F I1 [rad / sec] and the number of poles N of the synchronous motor 2 according to Equation 1. Since the current sensor 21 does not detect the current after the semiconductor switch 103 is turned on, the current sensor 21 always detects the current during normal operation of the motor drive device 1 so that the current immediately before the semiconductor switch 103 is turned on can be reliably detected.

[0041]

number

[0042] The rotation speed calculation unit 22 calculates the rotation speed ω1 [rad / sec] of the synchronous motor 2 at time t0 immediately after the semiconductor switch 103 is turned on, in accordance with Equation 1, based on the value of the current detected by the current sensor 21.

[0043] The rotational energy E1 [J] at time t0 immediately after the semiconductor switch 103 is turned on is expressed as inertia A [kgm 2 ] and the rotational speed ω1 [rad / sec] of the synchronous motor 2 at time t0, according to Equation 2.

[0044]

number

[0045] The back electromotive force V at time t0 immediately after the semiconductor switch 103 is turned on bemf_1 [V] is the back electromotive force coefficient V k It can be calculated using [V / (rad / sec)] according to Equation 3.

[0046]

number

[0047] Here, the effective value V [V] and the angular frequency ω [rad / sec] of the three-phase AC voltage v a [V], v b [V] and v c [V] is expressed as in Equation 4.

[0048]

number

[0049] The three-phase AC voltage v expressed by Equation 4 a [V], v b [V] and v cThe average value E of the DC voltage output from the diode rectifier circuit 102 with [V] as input d [V] is expressed as in Equation 5.

[0050]

number

[0051] By rearranging equation 5, we obtain equation 6.

[0052]

number

[0053] The back electromotive force V at time t0 immediately after the semiconductor switch 103 is turned on bemf_1 The average value V1 [V] of the DC voltage applied across the semiconductor switch 103 when [V] is generated is expressed as in Equation 7 using Equation 6.

[0054]

number

[0055] The loss P of the semiconductor switch 103 at time t0 immediately after the semiconductor switch 103 is turned on t_1 [W] is expressed as in Equation 8 using the average value V1 [V] of the DC voltage expressed in Equation 7.

[0056]

number

[0057] The energy consumption ΔE1 [J] in the semiconductor switch 103 during a short time Δt [sec] from time t0 immediately after the semiconductor switch 103 is turned on is expressed as the loss P t_1 Using [W], it is expressed as Equation 9.

[0058]

number

[0059] The rotational energy E2 [J] of the synchronous motor 2 during the next infinitesimal time Δt [sec] starting at time t1, which is the infinitesimal time Δt [sec] after time t0, is expressed as in Equation 10.

[0060]

number

[0061] The relational expression shown in Equation 11 holds between the rotational speed ω2 [rad / sec] of the synchronous motor 2 at time t1 and the rotational energy E2 [J] of the synchronous motor 2.

[0062]

number

[0063] When the rotation speed ω2 [rad / sec] of the synchronous motor 2 at time t1 is calculated from Equation 10 and Equation 11, it is expressed as Equation 12.

[0064]

number

[0065] After time t2, the same process as above is executed.

[0066] Based on Equations 1 to 12, at each time t i The parameters in are calculated as follows:

[0067] After the semiconductor switch 103 is turned on, at time t i The rotation speed ω of synchronous motor 2 at i+1 [rad / sec] is expressed as in Equation 13.

[0068]

number

[0069] time t i The back electromotive force V bemf_i+1 [V] is expressed as in Equation 14.

[0070]

number

[0071] time t i The back electromotive force V bemf_i+1 The average value of the DC voltage applied across the semiconductor switch 103 when [V] occurs is V i+1 [V] is expressed as in Equation 15.

[0072]

number

[0073] time t i Loss P of the semiconductor switch 103 in t_i+1 [W] is expressed as in Equation 16.

[0074]

number

[0075] time t i Energy consumption ΔE during a short time Δt [sec] from i+1 [J] can be calculated using Equation 17.

[0076]

number

[0077] time t i+1 The rotational energy E of synchronous motor 2 during the short time Δt [sec] from i+2 [J] can be calculated using Equation 18.

[0078]

number

[0079] time t i Temperature rise ΔT of the semiconductor switch 103 during a short time Δt [sec] from i+1 [℃] is the loss P of the semiconductor switch 103 t_i+1 It is expressed as Equation 19 using the thermal resistance B [℃ / W] and the thermal load [W].

[0080]

number

[0081] When the synchronous motor 2 stops, the semiconductor switch 103 is at the maximum temperature T peak [℃] until the synchronous motor 2 stops (i.e., the rotation speed ω i [rad / sec] becomes 0, or the rotation speed ω i The time P [sec] required for the time t [rad / sec] to become equal to or smaller than a certain infinitesimal threshold can be calculated by solving each of the above recurrence equations. n If the synchronous motor 2 stops at time t n The maximum temperature T of the semiconductor switch 103 that peak [℃] is expressed by Equation 20. Here, the ambient temperature of the motor drive device 1 or the overvoltage protection circuit 12 is T a [℃]. Ambient temperature T a [°C] may be a predetermined constant value assuming that the temperature around the motor driving device 1 or the overvoltage protection circuit 12 is constant, or may be a temperature measured by a temperature sensor installed near the motor driving device 1 or the overvoltage protection circuit 12.

[0082]

number

[0083] When the synchronous motor 2 stops, the temperature of the semiconductor switch 103 reaches the maximum temperature T peak After reaching the first temperature threshold T th When the synchronous motor 2 stops, the temperature of the semiconductor switch 103 falls below the maximum temperature T peak Time t when [℃] is reached n When the temperature of the semiconductor switch 103 reaches the first temperature threshold T th The drive waiting time t Q [sec] can be found by solving equation 21.

[0084]

number

[0085] Note that the above time t i-1 Energy consumption ΔE during a short time Δt [sec] from i [J] and temperature rise ΔT i In calculating the temperature [℃], the rotation speed ω of the synchronous motor 2 during the short time Δt [sec] is i [rad / sec], Rotational energy E of synchronous motor 2 i [J], back emf V bemf_i [V], the average value of the DC voltage across the semiconductor switch 103, V i [V] and loss P of semiconductor switch t_i [W] is considered to be constant. The infinitesimal time Δ[sec] is set to, for example, 1 millisecond, but may be set to another value. Since it generally takes several to several tens of seconds for the synchronous motor 2 to stop, the rotation speed ω of the synchronous motor 2 is set to, for example, 1 millisecond during the infinitesimal time Δt[sec]. i [rad / sec], Rotational energy E of synchronous motor 2 i [J], back emf V bemf_i [V], the average value of the DC voltage across the semiconductor switch 103, V i [V] and loss P of semiconductor switch t_iEven if [W] is considered constant, the calculated energy consumption ΔE during the short time Δt [sec] i [J] and temperature rise ΔT i The error in [℃] is negligible.

[0086] The temperature estimation unit 13 calculates the inertia A [kgm 2 ] and the motor constants V, including the back EMF constant k [V / (rad / sec)] and the on-resistance R t [Ω], thermal resistance B [℃ / W], thermal time constant τ1 [sec] during temperature rise, and thermal time constant τ2 [sec] during temperature fall, and the rotation speed ω of the synchronous motor 2 detected by the rotation speed calculation unit 22 i [rad / sec] to calculate the estimated temperature of the semiconductor switch 103. peak [°C], the temperature estimation unit 13 calculates the estimated temperature value of the semiconductor switch 103 according to the formulas 13 to 20, and the estimated temperature value is the maximum temperature T peak After reaching the maximum temperature T peak Time t when [℃] is reached n When the temperature of the semiconductor switch 103 reaches the first temperature threshold T th The time t required for the time Q to fall below Q The temperature estimation unit 13 calculates the maximum temperature T peak After calculating the maximum temperature T peak Time t reached [℃] n When the temperature of the semiconductor switch 103 reaches the first temperature threshold T th The drive standby time t required until the time Q falls below Q The enable signal output unit 14 calculates the maximum temperature T peak Time t reached [℃] n From drive standby time t QThe time when the estimated temperature value of the semiconductor switch 103 has fallen below the first temperature threshold is determined as the time when [sec] has elapsed, and a signal to permit the motor drive circuit 11 to start driving the synchronous motor 2 is output to the motor control unit 10.

[0087] Next, some modified examples according to an embodiment of the present disclosure will be listed.

[0088] In a first modified example according to an embodiment of the present disclosure, the rotation speed of the synchronous motor 2 in the infinitesimal time Δt [sec] used in the calculation of the temperature estimation value by the temperature estimator 13 is not a value calculated based on the value of the current detected by the current sensor 21, but a value detected by a speed sensor 23 attached to the synchronous motor 2. FIG. 4 is a diagram showing a first modified example of a motor drive device according to an embodiment of the present disclosure. In the first modified example, the rotation speed ω i [rad / sec] is detected by the speed sensor 23 attached to the synchronous motor 2. This makes it possible to omit the calculation based on the formula 1 by the rotation speed calculation unit 22 shown in Fig. 1 and the calculation based on the formulas 12 and 13 by the temperature estimation unit 13, thereby reducing the calculation load.

[0089] In the second modified example according to the embodiment of the present disclosure, the rotation speed of the synchronous motor 2 at the time t0 immediately after the semiconductor switch 103 is turned on, which is used for calculating the temperature estimation value by the temperature estimator 13, is calculated by dividing the rotation speed by the rated rotation speed ω rate In the second modification, the synchronous motor 2 is rotated at a rated speed ω rate According to the second modification, the rotation speed of the synchronous motor 2 at time t0 immediately after the semiconductor switch 103 is turned on is set to the rated rotation speed ω rate [rad / sec], the calculation based on Equation 1 by the rotation speed calculation unit 22 shown in FIG. 1 and the calculation based on Equations 12 and 13 by the temperature estimation unit 13 can be omitted, thereby reducing the calculation load.

[0090] In a third modified example according to an embodiment of the present disclosure, a table is created in advance to show the relationship between the rotation speed of the synchronous motor 2 at time t0 immediately after the semiconductor switch 103 is turned on and the time from when the semiconductor switch 103 is turned on until the temperature of the semiconductor switch 103 becomes equal to or lower than the first temperature threshold. Since there is a one-to-one correspondence between the rotation speed of the synchronous motor 2 at time t0 immediately after the semiconductor switch 103 is turned on and the maximum temperature that the synchronous motor 2 can reach, there is a one-to-one correspondence between the rotation speed of the synchronous motor 2 at time t0 immediately after the semiconductor switch 103 is turned on and the time from when the semiconductor switch 103 is turned on until the temperature of the semiconductor switch 103 becomes equal to or lower than the first temperature threshold. Therefore, the rotation speed of the synchronous motor 2 at time t0 immediately after the semiconductor switch 103 is turned on is obtained by calculation by the rotation speed calculation unit 22 or measurement by the speed sensor 23, and the "time from when the semiconductor switch 103 is turned on until the temperature of the semiconductor switch 103 becomes equal to or lower than the first temperature threshold" corresponding to the obtained rotation speed of the synchronous motor 2 is read from the table. According to the third modified example, there is no need to execute complex calculations every time the overvoltage protection circuit 12 operates, and therefore the calculation load is reduced.

[0091] In the fourth modification according to the embodiment of the present disclosure, the loss P of the semiconductor switch 103 at time t0 immediately after the semiconductor switch 103 is turned on, which is expressed by Equation 8, t_1 [W] is assumed to be constant until the synchronous motor 2 stops, thereby reducing the calculation load. Since the rotation speed of the synchronous motor 2 is highest at time t0 immediately after the semiconductor switch 103 is turned on, the short-circuit current flowing through the semiconductor switch 103 is the largest, and therefore the loss in the semiconductor switch 103 is also the largest. Therefore, the loss P t_1 If [W] is used in the calculation relating to the subsequent very short time Δt [sec], the estimated temperature value of the semiconductor switch 103 may become higher than the actual temperature, but this has the advantage of reducing the calculation load.

[0092] The fifth modification according to an embodiment of the present disclosure provides an additional return route for the short-circuit current in case the short-circuit current that occurs when the overvoltage protection circuit 12 is operating continues to flow for an unexpectedly long period of time.

[0093] FIG. 5 is a flowchart showing an operation flow of the fifth modified example of the motor drive device according to an embodiment of the present disclosure.

[0094] If the synchronous motor 2 has an unexpectedly large inertia, and the drive of the synchronous motor 2 stops and a counter electromotive force is generated, the time during which a short-circuit current flows through the semiconductor switch 103 becomes unexpectedly long, and heat continues to accumulate in the semiconductor switch 103, causing the temperature rise of the semiconductor switch 103 to exceed the tolerance of the semiconductor switch 103, which may result in damage to the semiconductor switch 103. Therefore, in the fifth modified example, when the estimated temperature value of the semiconductor switch that is rising calculated by the temperature estimator 13 exceeds the second temperature threshold value, a positive-side switching element SU U , S.V. U , and S.W. U Negative side switching element SU L , S.V. L , and S.W. L By turning on all of these, the short-circuit current flows not only through the overvoltage protection circuit 12 but also through the switching elements of the inverter 101 in the motor drive circuit 11 that are turned on. As a result, the energy based on the back electromotive force is consumed in the inverter 101 in the motor drive circuit 11 via the diode rectifier circuit 102 and the semiconductor switch 103 in the overvoltage protection circuit 12, so that the time during which the short-circuit current flows in the semiconductor switch 103 can be shortened and the temperature rise of the semiconductor switch 103 can be suppressed.

[0095] The second temperature threshold may be set to a temperature lower than the heat resistance temperature of semiconductor switch 103, and may be set by referring to the heat resistance temperature specified in a specification table or instruction manual of semiconductor switch 103. The second temperature threshold may be stored in a rewritable storage unit (not shown) and may be rewritable by an external device, and may be changed to an appropriate value as necessary even after the second temperature threshold has been set.

[0096] In a state where the synchronous motor 2 is driven at a certain rotation speed by the motor drive device 1, in step S201 shown in Fig. 5, the motor control unit 10 determines whether or not the drive of the synchronous motor 2 has stopped. When the drive of the synchronous motor 2 is stopped due to factors such as an inability to control the motor drive device 1 or an emergency stop by the motor drive device 1, the synchronous motor 2 decelerates and generates a back electromotive force. For example, the motor control unit 10 determines that the drive of the synchronous motor 2 has stopped when an alarm indicating that the motor drive device 1 has become out of control or an emergency stop signal for the motor drive device 1 is received. Alternatively, the motor control unit 10 may determine that the drive of the synchronous motor 2 has stopped when the line voltage of the power line connecting the motor drive circuit 11 and the synchronous motor 2 exceeds a predetermined voltage. If it is determined in step S201 that the drive of the synchronous motor 2 has stopped, the motor control unit 10 commands the semiconductor switch 103 in the overvoltage protection circuit 12 to turn on, thereby shorting the terminals on the DC output side of the diode rectifier circuit 102, and the process proceeds to step S202.

[0097] In step S202, the temperature estimator 13 calculates a temperature estimate of the semiconductor switch 103 using a motor constant including at least one of the inertia and back electromotive force constants of the synchronous motor 2 and a semiconductor switch constant including the on-resistance, thermal resistance, and thermal time constant of the semiconductor switch 103. When the temperature estimate of the semiconductor switch 103 is calculated using a value detected by the speed sensor 23, the inertia value is not required for the calculation of the temperature estimate by the temperature estimator 13 in step S202. When the semiconductor switch 103 is turned on, the synchronous motor 2 gradually decelerates, and a short-circuit current continues to flow through the semiconductor switch 103 until the synchronous motor 2 is completely stopped (i.e., until the rotational energy of the synchronous motor 2 becomes zero), and the temperature estimate of the semiconductor switch 103 calculated by the temperature estimator 13 increases. After the temperature estimate of the semiconductor switch 103 reaches the maximum temperature, the temperature estimate of the semiconductor switch 103 calculated by the temperature estimator 13 decreases. Until the estimated temperature value increases and reaches the maximum temperature, the processes of steps S202 and S203 are repeatedly executed, and the temperature estimator 13 continues to calculate the estimated temperature value.

[0098] In step S203, motor control unit 10 determines whether the temperature estimate calculated by temperature estimator 13 is rising. Since the temperature estimate continues to rise from when semiconductor switch 103 is turned on until the temperature estimate of semiconductor switch 103 reaches the maximum temperature, it is determined in step S203 that the temperature estimate is rising from when semiconductor switch 103 is turned on until the temperature estimate of semiconductor switch 103 reaches the maximum temperature, and the process proceeds to step S204. After the temperature estimate of semiconductor switch 103 reaches the maximum temperature, the temperature estimate decreases, so it is determined in step S203 that the temperature estimate is not rising, and the process proceeds to step S206.

[0099] In step S204, the motor control unit 10 determines whether or not the rising estimated temperature value of the semiconductor switch calculated by the temperature estimator 13 has exceeded the second temperature threshold. If it is determined that the estimated temperature value has exceeded the second temperature threshold, the process proceeds to step S205, and if it is not determined that the estimated temperature value has exceeded the second temperature threshold, the process returns to step S202.

[0100] In step S205, the motor control unit 10 turns on the negative side switching element SU L , S.V. L , and S.W. L In step 205, the motor control unit 10 controls the inverter 101 in the motor drive circuit 11 to turn on all of the switching elements of the inverter 101 in the motor drive circuit 11 that are turned on, in addition to the overvoltage protection circuit 12. U , S.V. U , and S.W. U may be controlled so as to turn on all of the above. When step S205 is executed, a current flows through both the overvoltage protection circuit 12 and the motor drive circuit 11, and therefore the estimated temperature value of the semiconductor switch 103 cannot be calculated accurately. Therefore, an abnormality process such as an alarm output is executed and the process ends.

[0101] In step S206, the permission signal output unit 14 determines whether the estimated temperature value of the semiconductor switch 103 during the temperature drop calculated by the temperature estimator 13 has fallen below the first temperature threshold. After the estimated temperature value reaches the maximum temperature, the estimated temperature value gradually drops over time, and at a certain point in time, the estimated temperature value falls below the first temperature threshold. When the permission signal output unit 14 determines that the estimated temperature value of the semiconductor switch 103 during the temperature drop calculated by the temperature estimator 13 has fallen below the first temperature threshold, the process proceeds to step S207. Note that after the estimated temperature value reaches the maximum temperature, the temperature drops with a certain time constant, so that it is possible to predict and calculate the time required for the estimated temperature value to fall below the first temperature threshold after reaching the maximum temperature. Therefore, the temperature estimation unit 13 continuously calculates the temperature estimation value from when the semiconductor switch 103 is turned on until the estimated temperature value rises and reaches the maximum temperature, and after the estimated temperature reaches the maximum temperature, predicts and calculates the "drive standby time" as the time starting from the time when the estimated temperature value reaches the maximum temperature and ending from the time when the estimated temperature value falls below the first temperature threshold, and when the drive standby time has elapsed since the estimated temperature value reached the maximum temperature, the permission signal output unit 14 determines that this is the time when the estimated temperature value of semiconductor switch 103, which is decreasing and calculated by the temperature estimation unit 13, has fallen below the first temperature threshold.

[0102] In step S207, the permission signal output unit 14 outputs a signal to the motor control unit 10 to permit the motor drive circuit 11 to start driving the synchronous motor 2. As a result, the motor control unit 10 enters a standby state so that the motor control unit 10 can resume drive control of the synchronous motor 2 at any time. It is preferable that the operator performs preparation work for restarting the drive of the synchronous motor 2, such as removing the cause of the uncontrollable state if the cause of the drive stop of the synchronous motor 2 in step S201 is, for example, an inability to control the motor drive device 1, and removing the cause of the emergency stop if, for example, an emergency stop by the motor drive device 1 is caused. After the overvoltage protection circuit 12 is started and the semiconductor switch 103 is turned on, the motor control unit 10 cannot control the drive of the synchronous motor 2 unless the permission signal output unit 14 permits the motor drive circuit 11 to start driving the synchronous motor 2 in step S206, so that the safety of the motor drive device 1 can be ensured. After the permission signal output unit 14 permits the motor drive circuit 11 to start driving the synchronous motor 2 in step S207, the worker removes the cause of the stop of the drive of the synchronous motor 2, and then the synchronous motor 2 is actually driven.

[0103] A sixth modified example according to an embodiment of the present disclosure counts the number of temperature changes, consisting of increases and decreases in the temperature of semiconductor switch 103, that place a particular strain on semiconductor switch 103, and if the counted number exceeds a predetermined number threshold, an alarm is output indicating that semiconductor switch 103 is at risk of damage, thereby making the present invention useful for preventive maintenance.

[0104] FIG. 6 is a diagram illustrating a sixth modified example of a motor driving device according to an embodiment of the present disclosure.

[0105] In general, when the semiconductor switch 103 is subjected to repeated large temperature changes, stress is applied between members having different thermal contraction rates within the semiconductor switch 103, shortening the lifespan. As described above, when the semiconductor switch 103 is turned on, the temperature estimate of the semiconductor switch 103 gradually increases and gradually decreases after reaching the maximum temperature. For example, if the rotation speed of the synchronous motor 2 is low when the semiconductor switch 103 is turned on, the maximum temperature of the temperature estimate of the semiconductor switch 103 is low, so no load is placed on the semiconductor switch 103, but if the rotation speed of the synchronous motor 2 is high when the semiconductor switch 103 is turned on, the maximum temperature of the temperature estimate of the semiconductor switch 103 is high, so that a load is placed on the semiconductor switch 103. Therefore, in the sixth modified example, among the temperature changes consisting of an increase and decrease in the temperature of the semiconductor switch 103, temperature changes that place a particular burden on the semiconductor switch 103 are extracted and counted by comparing the temperature estimation value calculated by the temperature estimation unit 13 with a third temperature threshold, and if the number of counts exceeds a predetermined number threshold, an alarm is outputted indicating that there is a risk of damage to the semiconductor switch 103.

[0106] The third temperature threshold may be set to a temperature lower than the heat resistance temperature of semiconductor switch 103, and may be set by referring to the heat resistance temperature specified in a specification table or instruction manual of semiconductor switch 103. The third temperature threshold may be stored in a rewritable storage unit (not shown) and may be rewritable by an external device, and may be changed to an appropriate value as necessary even after the third temperature threshold has been set.

[0107] Moreover, assuming that an extremely large short-circuit current flows through semiconductor switch 103, the number of times threshold may be set to a value smaller than the durable number of operations of semiconductor switch 103 specified in, for example, a specification table or instruction manual for semiconductor switch 103. Note that the number of times threshold may be stored in a rewritable storage unit (not shown) and rewritable by an external device, and even after the number of times threshold has been set, it may be changed to an appropriate value as necessary.

[0108] As shown in FIG. 6, the motor driving device 1 further includes a counting unit 24 and an alarm output unit 25 in addition to the configuration of the motor driving device 1 described with reference to FIG.

[0109] The counting unit 24 counts the number of times that the rising estimated temperature value of the semiconductor switch 103 calculated by the temperature estimating unit 13 exceeds the third temperature threshold. Since the temperature of the semiconductor switch 103 rises and falls once in one operation of the overvoltage protection circuit 12, the number of times that the estimated temperature value of the semiconductor switch 103 exceeds the third temperature threshold does not exceed once in one operation of the overvoltage protection circuit 12. In other words, the number of times that the estimated temperature value of the semiconductor switch 103 exceeds the third temperature threshold is always equal to or less than the number of operations of the overvoltage protection circuit 12.

[0110] The alarm output unit 25 outputs an alarm when the number of times counted by the count unit 24 exceeds a predetermined number of times threshold. The alarm output from the alarm output unit 25 is sent to a display unit (not shown), and the display unit displays a message encouraging the replacement of the semiconductor switch 103. Examples of the display unit include a standalone display device, a display device attached to the motor drive device 1, a display device attached to a higher-level control device (not shown), a display device attached to a personal computer and a mobile terminal, and a light-emitting device such as an LED or a lamp. For example, if the display unit is composed of a light-emitting device such as an LED or a lamp, the light-emitting device will emit light when receiving an alarm to encourage the worker to replace the semiconductor switch 103. In addition, for example, the alarm output from the alarm output unit is sent to, for example, an audio device (not shown), and the audio device will emit a sound such as a voice, a speaker, a buzzer, or a chime when receiving an alarm to encourage the worker to replace the semiconductor switch 103. This allows the worker to easily and reliably grasp the deterioration of the semiconductor switch 103, and can easily take measures such as replacing the semiconductor switch 103.

[0111] In the embodiment and each modified example of the present disclosure described above, the temperature estimation value calculated by the temperature estimation unit 13 may be appropriately calibrated by, for example, installing a temperature sensor near the semiconductor switch 103 to measure the actual temperature of the semiconductor switch 103 and performing calculation processing by the temperature estimation unit 13. If the temperature estimation value calculated by the temperature estimation unit 13 differs significantly from the actual temperature of the semiconductor switch 103 measured by the temperature sensor, it may be determined that the arithmetic processing device including the temperature estimation unit 13 has a failure, and in that case, measures such as replacing the arithmetic processing device can be taken.

[0112] The motor control unit 10, the temperature estimation unit 13, the enable signal output unit 14, the count unit 24, and the alarm output unit 25 may be constructed, for example, in the form of a software program, or may be constructed in combination with various electronic circuits and a software program, or may be composed only of various electronic circuits. For example, when these are constructed in the form of a software program, the functions of each of the above-mentioned units can be realized by operating a calculation processing device such as a DSP or an FPGA according to the software program. Alternatively, the motor control unit 10, the temperature estimation unit 13, the enable signal output unit 14, the count unit 24, and the alarm output unit 25 may be realized as a semiconductor integrated circuit in which a software program that realizes the functions of each unit is written. Alternatively, the motor control unit 10, the temperature estimation unit 13, the enable signal output unit 14, the count unit 24, and the alarm output unit 25 may be realized as a recording medium in which a software program that realizes the functions of each unit is written. Also, the motor control unit 10, the temperature estimation unit 13, the enable signal output unit 14, the count unit 24, and the alarm output unit 25 may be provided, for example, in a numerical control device of a machine tool, or in a robot controller that controls a robot.

[0113] Moreover, the motor control unit 10, the temperature estimation unit 13, the permission signal output unit 14, the count unit 24, and the alarm output unit 25 may be configured by a combination of analog circuits and digital circuits, or may be realized by a processing device constructed in the form of a software program, or may be configured only by analog circuits. Note that the current sensor 21 and the speed sensor 23 may be sensors that are generally provided in the motor drive device 1.

[0114] In addition, the memory unit that stores the first temperature threshold, the second temperature threshold, the third temperature threshold, and the number threshold may be composed of an electrically erasable and recordable non-volatile memory such as an EEPROM (registered trademark), or a random access memory that can be read and written at high speed such as a DRAM, an SRAM, etc. [Explanation of symbols]

[0115] 1 Motor drive unit 2 Synchronous motor 3. Smoothing capacitor 10 Motor control unit 11 Motor drive circuit 12 Overvoltage protection circuit 13 Temperature estimation section 14 Enabling signal output section 21 Current Sensor 22 Rotational speed calculation section 23 Speed ​​Sensor 24 Counting section 25 Alarm output section 101 Inverter 102 Diode rectifier circuit 103 Semiconductor Switch

Claims

1. a motor drive circuit that drives a synchronous motor by supplying AC power to the synchronous motor via a power line; an overvoltage protection circuit provided between the synchronous motor and the motor drive circuit, which turns on a semiconductor switch when the drive of the synchronous motor by the motor drive circuit stops, thereby shorting the phases of the power lines and preventing the generation of an overvoltage due to a back electromotive force between the terminals of the synchronous motor; a temperature estimator that calculates an estimated temperature value of the semiconductor switch, which rises when the semiconductor switch is turned on and then falls, by using a motor constant including at least one of an inertia constant and a back electromotive force constant related to the synchronous motor and a semiconductor switch constant including an on-resistance, a thermal resistance, and a thermal time constant related to the semiconductor switch; A motor drive device comprising:

2. 2. The motor drive device according to claim 1, further comprising an enable signal output unit that outputs a signal to enable the motor drive circuit to start driving the synchronous motor when the decreasing estimated temperature value of the semiconductor switch calculated by the temperature estimator falls below a first temperature threshold.

3. a current sensor for detecting a value of a current flowing through the power line; a rotation speed calculation unit that calculates a rotation speed of the synchronous motor based on a value of the current detected by the current sensor; Further equipped with 3. The motor drive device according to claim 1, wherein the temperature estimator calculates the estimated temperature value of the semiconductor switch by using the motor constant, the semiconductor switch constant, and the rotation speed of the synchronous motor calculated by the rotation speed calculator.

4. A speed sensor is further provided to detect a rotation speed of the synchronous motor.

3. The motor drive device according to claim 1, wherein the temperature estimator calculates the estimated temperature of the semiconductor switch by using the motor constant, the semiconductor switch constant, and a rotation speed of the synchronous motor detected by the speed sensor.

5. 5. The motor drive device according to claim 1, wherein when the rising estimated temperature value of the semiconductor switch calculated by the temperature estimator exceeds a second temperature threshold, all of the positive side switching elements provided in an upper arm or all of the negative side switching elements provided in a lower arm in a bridge circuit of an inverter in the motor drive circuit are turned on.

6. a counting unit that counts the number of times that the estimated temperature value of the semiconductor switch during the rise calculated by the temperature estimating unit exceeds a third temperature threshold; an alarm output unit that outputs an alarm when the number of times counted by the count unit exceeds a predetermined number of times threshold; The motor drive device according to any one of claims 1 to 5, further comprising:

7. 7. The motor drive device according to claim 1, wherein the overvoltage protection circuit comprises a diode rectifier circuit having an AC terminal to which the power line is connected and a DC terminal to which the semiconductor switch is connected.

Images