Motor drive inverter device and control method thereof

Abstract

Provided is an inverter device for driving a motor, including: an inverter circuit having a plurality of switching elements; and a control circuit that controls the inverter circuit, the control circuit changing a temperature estimation logic of the switching elements of the inverter circuit when a rotational speed of the motor is below a predetermined rotational speed threshold and a torque of the motor is above a predetermined torque threshold, thereby accurately performing overheat protection of the switching elements.

Description

TECHNICAL FIELD

[0001] The present application relates to an inverter device for driving a motor and a control method thereof, and more particularly to a technique for overheat protection of switching elements in the inverter device. BACKGROUND

[0002] In a case where a motor is rotated by being supplied with power from an inverter circuit, the switching elements such as IGBTs and FETs used in the inverter circuit perform high-frequency and high-power power conversion, and thus heat is generated in the switching elements due to switching loss. In order to prevent the switching elements from failing due to overheat, overheat protection of the switching elements needs to be considered.

[0003] In the related art, in order to prevent the switching elements or the inverter device from overheating, a temperature detecting element such as a thermistor is provided to directly detect the temperature of the switching elements, and when the detected temperature exceeds a threshold value, the power output from the inverter circuit to the motor is limited or the motor is stopped from rotating, so as to reduce the risk of overheat of the switching elements.

[0004] However, since the temperature detecting element needs to consider not only the insulation but also the delay in measurement of the switching elements operating at high frequency, the temperature detection value sometimes does not accurately reflect the actual temperature of the switching elements. In order to improve the accuracy of temperature measurement, a method of estimating the temperature of the switching elements based on the current flowing through each switching element is generally used. The temperature value thus estimated with high accuracy can accurately grasp the overheat state of the switching elements, and thus overheat protection can be performed.

[0005] On the other hand, when a large torque is applied to the motor but the rotational speed of the motor drastically changes (sudden drop), for example, when a vehicle encounters an obstacle or climbs a slope, the torque applied to the motor is still large, but the rotational speed of the motor can suddenly drop to a very low speed or the motor can be stopped from rotating (so-called "motor lock state"), the temperature value estimated based on the above-described temperature estimation method is smaller than the actual temperature value of the switching elements, and the lower the rotational speed, the greater the difference between the two. At this time, the temperature value cannot accurately perform overheat protection of the switching elements, and the switching elements can fail or even burn out due to overheat. Furthermore, in the above-described motor lock state, the current concentrates in one phase of the multi-phase winding of the motor, and as a result, the switching element corresponding to the phase rapidly heats up, and the switching element can be damaged due to overheat before the switching element is detected to be in an overheat state.

[0006] In the related art, when the motor lock state is determined based on the rotational speed, the torque, and the temperature value of the switching elements, overheat protection of the switching elements is performed by reducing the carrier frequency of the control signal and reducing the frequency of switching operation of the switching elements (for example, Patent Literature 1).

[0007] Further, the temperature of the switching element is detected by a thermistor or the like, and based on the detected temperature and the torque command value at the time when the locked state of the motor is detected, the carrier frequency of the control signal is determined to perform the overheat protection (for example, Patent Document 1).

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Japanese Patent No. 3684871 SUMMARY

[0011] In view of the above, an object of the present application is to provide an inverter device for driving a motor and a control method thereof, which can surely perform overheat protection of a switching element without using a thermistor or the like.

[0012] The inverter device for driving a motor according to the present application includes an inverter circuit having a plurality of switching elements, and a control circuit that controls the inverter circuit, and when the rotational speed of the motor is below a predetermined rotational speed threshold value and the torque of the motor is above a predetermined torque threshold value, the control circuit changes the temperature estimation logic of the switching elements of the inverter circuit.

[0013] In addition, the state where the torque of the motor is high but the rotational speed is low is generally referred to as the locked state of the motor. That is, in the case where the rotational speed of the rotating motor suddenly drops, the locked state described above can sometimes be entered. In the locked state, the temperature of the switching element sharply rises, and thus it is necessary to recognize the locked state as early as possible and perform the corresponding overheat protection. Therefore, it is considered that the rotational speed threshold value is set to be high to recognize the drop in rotational speed as early as possible. For this reason, in the inverter device for driving a motor according to the present application, the rotational speed threshold value is in the range of 100 to 150 rpm, and the torque threshold value is 120 Nm. Thus, in the case of a motor rotating at a rotational speed of, for example, 200 rpm, when the rotational speed thereof drops to 120 rpm and the torque is above the threshold value of 120 Nm, it is recognized that the motor is currently in the locked state. On the other hand, when the rotational speed threshold value is assumed to be 50 rpm, in the case of a motor rotating at a rotational speed of 200 rpm, the locked state is recognized only when the rotational speed thereof drops to 50 rpm and the torque is above the threshold value of 120 Nm. Therefore, compared to the case where the rotational speed threshold value is set to be, for example, 50 rpm, the inverter device for driving a motor according to the present application can recognize the locked state earlier, and as a result, the overheat protection can be performed as early as possible.

[0014] In the motor drive inverter device of the present application, the temperature estimation logic includes normal estimation logic and locked state estimation logic, and the temperature is estimated using the locked state estimation logic when the rotational speed of the motor is below a predetermined rotational speed threshold and the torque of the motor is above a predetermined torque threshold. Thus, the temperature of the switching element can be estimated with high accuracy even in the locked state of the motor.

[0015] In the motor drive inverter device of the present application, the difference between the temperature estimated by the locked state estimation logic and the actual temperature of the switching element is smaller than the difference between the temperature estimated by the normal estimation logic and the actual temperature of the switching element under the same conditions. That is, the temperature estimation logic can be changed to a more appropriate estimation logic in the locked state of the motor. Thus, the temperature of the switching element can be estimated with high accuracy even in the locked state of the motor.

[0016] In the motor drive inverter device of the present application, the control circuit limits the output of the inverter circuit to the motor when the temperature of the switching element estimated by the temperature estimation logic exceeds a predetermined temperature threshold. Thus, the output of the inverter can be limited using the estimated temperature that is as close as possible to the actual temperature, and as a result, high-accuracy overheat protection can be achieved.

[0017] In the motor drive inverter device of the present application, the control circuit limits the output of the inverter circuit to the motor by reducing the carrier frequency of the control signal to be output to the inverter circuit.

[0018] In the motor drive inverter device of the present application, the inverter circuit is a three-phase inverter circuit including six switching elements that constitute three-phase circuits of upper and lower arms, respectively, and the control circuit changes the temperature estimation logic of the switching elements of the inverter circuit when only one phase of the upper arm is turned on and only one phase of the other two phases of the lower arm is turned on. In the locked state of the motor, the current concentrates in one phase of the three phases, and the switching element turned on corresponding to this phase can be overheated and fail. In this case, the temperature can be estimated with high accuracy by using the above-described structure, and as a result, the output limitation to the inverter can be appropriately controlled.

[0019] In addition, at the time of the start of the motor, there is a possibility that the motor enters a locked state. Specifically, after the motor starts rotating from a stationary state, the rotation speed increases and then decreases. In this case, the temperature of the switching element in the inverter sharply increases, and the temperature of the switching element cannot be accurately estimated using the temperature estimation logic at the time of normal operation, i.e., normal estimation logic. Therefore, the motor drive inverter device of the present application includes an inverter circuit having a plurality of switching elements, and a control circuit that controls the inverter circuit. At the time of the start of the motor, the control circuit changes the temperature estimation logic of the switching element of the inverter circuit during a period in which the rotation speed of the motor increases to a first rotation speed value and then temporarily decreases to a second rotation speed value or less.

[0020] In the motor drive inverter device of the present application, the first rotation speed value is 150 rpm, and the second rotation speed value is 10 rpm. Thus, even if the rotation speed temporarily decreases at the time of the start of the motor, the temperature can be accurately estimated with high precision.

[0021] The control method of the motor drive inverter device of the present application includes determining whether the rotation speed of the motor is below a predetermined rotation speed threshold value and whether the torque of the motor is above a predetermined torque threshold value, and changing the temperature estimation logic of the switching element of the inverter circuit of the motor drive inverter device when the rotation speed of the motor is below the rotation speed threshold value and the torque of the motor is above the torque threshold value.

[0022] Thus, the present application can provide a motor drive inverter device and a control method thereof that can accurately perform overheat protection of a switching element, and can accurately estimate the temperature of the switching element even in a locked state of the motor, and effectively perform overheat protection of the switching element using the temperature estimation value. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a block diagram showing the structure of the motor drive inverter device 1 of Embodiment 1 of the present application.

[0024] Figure 2 is a logic diagram showing the temperature estimation logic used in the motor drive inverter device 1 of Embodiment 1 of the present application.

[0025] Figure 3 is a block diagram showing the structure of the control circuit 11 in the motor drive inverter device 1 of Embodiment 1 of the present application.

[0026] Figure 4 is a logic diagram showing another temperature estimation logic used in the motor drive inverter device 1 of Embodiment 1 of the present application.

[0027] Figure 5 is a block diagram showing the structure of the control circuit 11 in the motor drive inverter device 1 of Embodiment 1 of the present application. Figure 4Temperature estimation logic and Figure 2 A schematic diagram comparing temperature estimation logic.

[0028] Figure 6 This is a flowchart illustrating the processing steps of the control circuit 11 in the motor drive inverter device 1 according to Embodiment 1 of the present invention. Detailed Implementation

[0029] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The descriptions and drawings herein are merely illustrative and not intended to limit the scope of the invention.

[0030] <Implementation Method 1>

[0031] <Basic Structure of Inverter Devices>

[0032] Below, refer to Figure 1 The inverter device 1 for driving a motor according to Embodiment 1 of the present invention will be described. Figure 1 This is a block diagram showing the structure of the inverter device for driving the electric motor (hereinafter referred to as the inverter device) 1.

[0033] like Figure 1 As shown, the inverter device 1 consists of an inverter circuit 10 and a control circuit 11. The inverter device 1 is powered by a power supply 12 and drives the motor 13. Here, the power supply 12 is a DC power supply, and the motor 13 is, for example, a three-phase (U, V, W) motor, although four-phase, five-phase, or even more-phase motors can also be used.

[0034] The inverter circuit 11 converts the DC power supplied by the power supply 12 into AC power (three-phase AC power in this embodiment) to supply power to the motor 13. Figure 1 Corresponding to the three-phase coils (U-phase coil, V-phase coil, and W-phase coil) in the motor 13, the inverter circuit 10 is composed of a three-phase (U-phase, V-phase, and W-phase) bridge circuit. Each phase circuit includes two switching elements (a total of six switching elements). The three-phase switching elements located at the upper side of the diagram form the upper arm, and the three-phase switching elements located at the lower side form the lower arm. The connection points of the upper and lower arm switching elements for each phase are respectively connected to the coil of the corresponding phase of the motor 13. Figure 1 The switching elements in the design use MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), but power semiconductor devices such as IGBTs (Insulated Gate Bipolar Transistors) can also be used as the aforementioned switching elements.

[0035] The control circuit 11 can be realized by an ECU (Electronic Control Unit) having a CPU (Central Processing Unit) as a control section. The control circuit 11 outputs a control signal (e.g., a PWM signal) to the inverter circuit 10 based on a temperature signal representing the temperature of the switching element received from the inverter circuit 10, a rotational speed signal representing the rotational speed of the motor received from the motor 13, a throttle signal representing the degree of depression of the accelerator pedal from an external control device such as a vehicle control device, a brake signal representing the degree of depression of the brake pedal, and the like, controls the voltage or current in the inverter circuit 10, and further controls the power output from the inverter circuit 10 to the motor 13, thereby realizing normal operation of the motor 13.

[0036] The above-mentioned "temperature signal" represents the temperature of each switching element in the inverter circuit 10, and is estimated based on the phase current flowing in each phase circuit of the inverter device 10 and the temperature detected by the thermistor provided to the switching element.

[0037] <Basic Principle of Temperature Estimation>

[0038] Figure 2 The basic principle of the above-mentioned temperature estimation method is shown. Here, the temperature of the U-phase switching element in the U-phase circuit in the inverter circuit 10 is estimated as an example. As shown in the figure, first, the magnitude of the U-phase current is detected, and here, the current value can be the instantaneous current value or the average current value. The U-phase current value is input to a multiplier, and the reference resistance parameter A (the reference resistance parameter between the thermistor and the U-phase circuit, which can be determined by the value in a data table stored in advance) is referred to, and the output of the multiplier is input to a subtracter as the temperature difference ΔTt related to the heat dissipation of the switching element after passing through a first filter (since the water temperature in the motor cooling mechanism directly affects the result of the temperature estimation, for example, a water temperature filter can be used as a low-pass filter). In the subtracter, the reference temperature (i.e., the temperature detected by the thermistor) Tt is subtracted to obtain the temperature after subtracting the heat dissipation. At the same time, the U-phase current value is also multiplied in the multiplier by referring to the reference resistance parameter B (the reference resistance parameter between the chip substrate and the U-phase circuit, which can be determined by the value in a data table stored in advance), and the output of the multiplier is input to a second filter (e.g., a proportional integral filter) as the temperature difference ΔTj related to the heat generation of the switching element. Finally, the temperature data related to the heat generation and the heat dissipation, respectively, are added in an adder to obtain the estimated value of the temperature of the U-phase switching element.

[0039] The estimated value of the temperature obtained by the above-mentioned temperature estimation method can appropriately reflect the current overheat condition of the switching element, and thus overheat protection of the switching element can be performed with high accuracy.

[0040] <Basic Structure of Control Circuit>

[0041] Figure 4 is a structural block diagram showing a control circuit 11 in the inverter device 1 of the present application. The control circuit 11 mainly includes a control section 110, a temperature estimation section 111, a torque control section 112, and a rotation speed detection section 113. The control section 110 is constituted by, for example, a CPU, and outputs a control signal (for example, a PWM control signal) to the inverter circuit 10. Among them, a lock state judging section 1101 judges whether or not the vehicle is currently in a motor lock state, that is, a state in which the rotation speed of the motor is reduced due to an external force but the torque applied to the motor is still large. In order to perform overheat protection of the switching elements in the inverter circuit 10, a PWM frequency deciding section 1102 is provided in the control section 110, and when the temperature of the switching elements exceeds a threshold value requiring overheat protection, the PWM frequency deciding section 1102 can lower the carrier frequency of the control signal to be outputted from the control section 110, thereby lowering the switching operation frequency of the switching elements to achieve overheat protection.

[0042] The temperature estimation section 111 estimates the temperature of each phase switching element according to a temperature estimation method shown in Figure 2 . The temperature estimation section 111 is provided with a storage section 1112, a switching section 1114, and an estimation section 1116. The storage section 1112 stores various preset values or parameters (for example, thermal resistance parameters A and B in Figure 2 ) and a plurality of estimation logics to be used when the temperature estimation section 111 performs temperature estimation, one of which is the estimation method shown in Figure 2 . The switching section 1114 switches between the plurality of estimation logics according to the instruction of the control section 110, and selects the logic to be used for temperature estimation (which will be described later in detail). The estimation section 1116 estimates the temperature Tj of the switching element (the junction temperature of the IGBT as the switching element) according to the estimation logic switched by the switching section 1114.

[0043] The torque control section 112 calculates a torque command value to be applied to the motor according to the accelerator signal indicating the degree of depression of the accelerator pedal and the brake signal indicating the degree of depression of the brake pedal sent from an accelerator sensor and a brake sensor (both not shown), and controls the torque Tm of the motor according to the calculated torque command value.

[0044] The rotation speed detection section 113 detects the current rotation speed Vm of the motor using a rotation speed sensor (not shown) or the like.

[0045] The lockout state determination unit 1101 determines, based on the motor torque Tm from the torque control unit 112 and the motor speed Vm from the speed detection unit 113, that when the motor 13 is currently in a locked state, the temperature Tj obtained by the estimation logic currently used by the temperature estimation unit 111 is likely to deviate from the actual temperature of the switching element. Therefore, the control unit 110 issues a command to the switching unit 1114 to switch the temperature estimation logic to an estimation logic suitable for the locked state (details will be explained later). The temperature estimation unit 111 estimates the temperature Tj of the switching element based on the switched estimation logic. The PWM frequency determination unit 1102 determines the carrier frequency of the control signal based on the obtained temperature Tj and outputs it to the inverter circuit 10.

[0046] As described above, by switching the temperature estimation logic while the motor is locked, the temperature of the switching element can be calculated with higher accuracy, and the temperature protection of the switching element can be performed more reliably.

[0047] <Temperature Estimation Logic>

[0048] Figure 2 The temperature estimation logic under normal conditions (including vehicle power driving and regenerative driving) is shown in the figure. Figure 4 The above represents the temperature estimation logic under the motor's locked state. Figure 4 Structure and Figure 2 The structures shown are basically the same, with the main differences being the parameters used for calculation and the settings of the second filter. Therefore, this section will explain the main differences between the two, and will not repeat the similarities.

[0049] Under normal circumstances, such as when the vehicle is powered or regeneratively powered, Figure 2 The temperature of the switching elements is estimated using the phase current of each phase circuit. However, in the motor locked state, Figure 4 In this process, the temperature estimation unit 111 selects the parameter that causes the greatest heat loss to the switching element, such as IGBT, from the input parameters such as motor speed, DC voltage of power supply 12, maximum value of each phase current or three-phase current, carrier frequency of control signal, and modulation rate (equivalent to duty cycle of control signal) to estimate the temperature of the switching element.

[0050] Furthermore, the setting of the second filter differs when the motor is locked. Figure 2 The situation. Figure 5 The diagram illustrates two scenarios with different settings for the second filter. (Example) Figure 5As shown, the temperature difference ΔTj obtained in the locked state of the motor is significantly higher than the temperature difference in the normal case, and the slopes of the two curves are also different. This is a setting to cope with the rapid increase in the temperature of a switching element in a phase in the locked state of the motor. Through simulation experiments, it is known that, in the locked state of the motor, the use of the 2nd filter setting of Figure 5 makes the temperature of the switching element obtained by the estimation logic of Figure 4 closer to the actual temperature, thereby improving the accuracy of temperature estimation and enabling reliable overheat protection of the switching element.

[0051] <Control flow of inverter device>

[0052] Next, with reference to Figure 6 , a specific control flow of the inverter device 1 of the present application for implementing overheat protection of the switching element will be described. Figure 6 is a flowchart showing the processing steps in the control circuit 11 of the inverter device 1.

[0053] First, in step S1, the control circuit 11 obtains the motor speed Vm and the motor torque Tm from the rotation speed detection section 113 and the torque control section 112, respectively.

[0054] In step S2, the locked state judging section 1101 judges whether the motor speed Vm is 150 rpm or less and whether the motor torque Tm is 120 Nm or more, i.e., judges whether the motor is currently in the locked state. In this case, for example, the vehicle encounters an obstacle or the vehicle stalls during climbing, resulting in a large torque (e.g., 140 Nm of rated torque) applied to the motor, but the motor speed suddenly starts to decrease. "150 rpm" here is merely an example and can be any value in the range of 100 to 150 rpm. "120 Nm" is also merely an example and can be a large torque value near the rated torque.

[0055] When the motor speed Vm ≤ 150 rpm and the motor torque Tm ≥ 120 Nm (step S2: Yes), an instruction is issued to the temperature estimation section 111 to cause the switching section 1114 to switch the temperature estimation logic to the locked state estimation logic, so that the temperature estimation section 111 estimates the temperature of the switching element in the locked state estimation logic (step S4).

[0056] When either of the motor speed Vm > 150 rpm or the motor torque Tm < 120 Nm (step S2: No), the temperature estimation section 111 estimates the temperature of the switching element in the normal estimation logic (step S3).

[0057] Then, in step S5, it is determined whether the estimated temperature value Tj obtained in steps S3 and S4 is above the specified temperature threshold Tth. This temperature threshold Tth is the overheating critical value of the switching element, for example, 145°C.

[0058] If the result in step S5 is "yes", that is, the estimated temperature value Tj exceeds the threshold Tth, it indicates that the switching element is in an overheated state. The PWM frequency determination unit 1102 reduces the carrier frequency of the control signal that the control circuit 11 needs to output to the inverter circuit 10 (for example, from 8kHz to 3kHz) to control the switching frequency of the switching element (step S6).

[0059] If the answer in step S5 is "No", it means that the temperature of the switching element has not exceeded the threshold, and the switching element continues to perform switching actions at the original frequency.

[0060] Then, repeat steps S5 and S6 until the overheat protection process of the switching element of control circuit 11 ends.

[0061] According to Embodiment 1 of the present invention, the inverter device 1 for driving a motor and its control method, when the motor enters a locked state and the switching elements may be damaged due to rapid heating, switches the temperature estimation logic to make the estimated temperature more accurately close to the actual temperature, and controls each switching element in the inverter circuit based on the estimated temperature, thereby accurately protecting the switching elements from overheating.

[0062] <Variation Example>

[0063] In the above-described embodiment 1, the output is limited by reducing the carrier frequency of the control signal output from the control circuit 11 to the inverter circuit 10, thereby enabling the switching elements to be protected from overheating. Reducing the carrier frequency here is merely one example of limiting the output; the power consumption of the switching elements can also be reduced by various methods such as reducing the torque command, reducing the current flowing through the switching elements, and reducing the duty cycle (modulation rate) of the control signal, thereby reducing their heat loss.

[0064] In addition, such as Figure 1 As shown, inverter circuit 10 is a three-phase inverter circuit. When only one phase (e.g., phase U) of the upper bridge arm is turned on and only another phase (e.g., phase V) of the lower bridge arm is turned on, a large current flowing through the circuit formed by these two switching elements connected to motor 13 can cause them to overheat rapidly. This could result in the switching elements being damaged due to overheating before it is detected. To address this, by changing the temperature estimation logic of the inverter circuit's switching elements as described in Embodiment 1 above, overheat protection for the switching elements can be provided more accurately.

[0065] In the above-described embodiment 1, the lock state determination section 1101 provided in the control section 110 determines whether the motor is in a locked state based on the rotational speed and the torque of the motor, and determines whether to change the temperature estimation logic based on the determination result. However, the lock state determination section 1101 can not be provided, and the determination of whether to change the temperature estimation logic can be made by monitoring the change in the rotational speed of the motor in real time. For example, at the time of starting the motor, the rotational speed of the motor increases, decreases, and then increases again. That is, in the case where a large torque is applied, the rotational speed of the motor rapidly increases to, for example, 150 to 170 rpm, and then suddenly decreases to 10 rpm or less due to the load connected to the motor, and then the rotational speed normally increases to the rotational speed at the time of power running or regenerative running. In the period in which the rotational speed of the motor increases and then temporarily decreases, the temperature estimation logic can be changed by the inverter device of the present application, so that the switch element is not damaged due to overheating caused by insufficient accuracy of the temperature value.

[0066] The present application can freely combine each embodiment within the scope of the present application, or deform any structural element of each embodiment, or omit any structural element in each embodiment.

[0067] Explanation of Reference Numerals

[0068] 1 Inverter device for motor drive

[0069] 10 Inverter circuit

[0070] 11 Control circuit

[0071] 12 Power supply

[0072] 13 Motor

[0073] 110 Control section

[0074] 1101 Lock state determination section

[0075] 1102 PWM frequency determination section

[0076] 111 Temperature estimation section

[0077] 1112 Storage section

[0078] 1114 Switching section

[0079] 1116 Estimation section

[0080] 112 Torque control section

[0081] 113 Rotational speed detection section

Claims

1. An inverter device for driving an electric motor, characterized in that, including: an inverter circuit having a plurality of switching elements; and a control circuit that controls the inverter circuit, when the rotational speed of a motor is below a preset rotational speed threshold and the torque of the motor is above a preset torque threshold, the control circuit changes the temperature estimation logic of the switching elements of the inverter circuit, and estimates the temperature using a locked state estimation logic, the temperature estimation logic includes normal estimation logic and the locked state estimation logic, the difference between the temperature estimated according to the locked state estimation logic and the actual temperature of the switching elements is smaller than the difference between the temperature estimated by the normal estimation logic and the actual temperature of the switching elements under the same conditions.

2. The inverter device for motor drive according to claim 1, wherein the rotational speed threshold is in the range of 100 to 150 rpm, the torque threshold is 120 Nm.

3. The inverter device for motor drive according to claim 1, wherein when the temperature of the switching elements estimated according to the temperature estimation logic exceeds a preset temperature threshold, the control circuit limits the output of the inverter circuit to the motor.

4. The inverter device for motor drive according to claim 3, wherein the control circuit limits the output of the inverter circuit to the motor by reducing the carrier frequency of the control signal to be output to the inverter circuit.

5. The inverter device for motor drive according to any one of claims 1 to 4, wherein the inverter circuit is a three-phase inverter circuit including six switching elements that respectively constitute three-phase circuits of upper and lower arms, when only any one phase of the upper arm is turned on and only any one phase of the other two phases of the lower arm is turned on, the control circuit changes the temperature estimation logic of the switching elements of the inverter circuit.

6. An inverter device for driving a motor, characterized by comprising: including: an inverter circuit having a plurality of switching elements; and a control circuit that controls the inverter circuit, in a stage where a motor is just started, during a process in which the rotational speed of the motor increases to a first rotational speed value and then temporarily decreases below a second rotational speed value, the control circuit changes the temperature estimation logic of the switching elements of the inverter circuit, and estimates the temperature using a locked state estimation logic, the temperature estimation logic includes normal estimation logic and the locked state estimation logic, the difference between the temperature estimated according to the locked state estimation logic and the actual temperature of the switching elements is smaller than the difference between the temperature estimated by the normal estimation logic and the actual temperature of the switching elements under the same conditions.

7. The inverter device for motor drive according to claim 6, wherein the first rotational speed value is 150 rpm, the second rotational speed value is 10 rpm.

8. A control method that is a control method in an inverter device for driving a motor, characterized by, including: determining whether the rotational speed of a motor is below a preset rotational speed threshold and whether the torque of the motor is above a preset torque threshold, when the rotational speed of the motor is below the rotational speed threshold value and the torque of the motor is above the torque threshold value, changing a temperature estimation logic of a switching element of an inverter circuit of the motor drive inverter device, estimating a temperature using a lock state estimation logic, the temperature estimation logic includes a normal estimation logic and the lock state estimation logic, a difference between the temperature estimated according to the lock state estimation logic and an actual temperature of the switching element is smaller than a difference between a temperature estimated by the normal estimation logic and the actual temperature of the switching element under the same conditions.

Images