Control device of inverter

Abstract

To solve a problem in which when protecting switching elements of an inverter from overheating, it has been sometimes to unnecessarily limit an output of a motor in a high rotation range.SOLUTION: A control device of an inverter that supplies power to a motor includes a limiting unit that limits the power supply to an inverter when the element temperature of a switching element of the inverter exceeds a predetermined temperature threshold. The limiting unit changes the maximum torque value to a value lower than a predetermined maximum value in response to the element temperature exceeding the temperature threshold.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The technology disclosed in this specification relates to a control device for an inverter.

Background Art

[0002] A configuration is disclosed that includes a semiconductor element included in an inverter, a temperature sensor that detects the temperature of a coolant that cools the semiconductor element, and a control device that restricts the load factor of a motor controlled by a PCU based on the temperature detected by the temperature sensor (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, overheat protection of the switching element of an inverter has been achieved by reducing the load factor limit of the motor according to the switching element temperature with respect to a torque curve showing the torque tolerance value according to the rotational speed of the motor. However, with such a method, there has been a case where unnecessary restrictions are applied to the output of the motor, particularly in the high rotation range.

Means for Solving the Problems

[0005] This specification discloses a control device for an inverter that supplies power to a motor. The control device includes a limiting unit that restricts the power supply of the inverter when the element temperature of a switching element included in the inverter exceeds a predetermined temperature threshold, and the limiting unit changes the maximum value of the torque to a value lower than a predetermined maximum value according to the element temperature exceeding the temperature threshold.

[0006] According to the above configuration, the limiting unit changes the maximum value of the torque to a value lower than a predetermined maximum value according to the element temperature exceeding the temperature threshold value. Therefore, compared with the conventional method, it is possible to avoid unnecessarily limiting the motor output.

Brief Description of Drawings

[0007]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0008] With reference to the drawings, this embodiment will be described. Each figure is merely an example, and this embodiment is not limited to the illustrated content. Also, since each figure is an example, the illustrated shape may not be accurate or a part may be omitted.

[0009] Fig. 1(a) simply shows the configuration of the power conversion device 10. The power conversion device 10 generally includes an inverter 20 and a control device 30 that controls the inverter 20. The power conversion device 10 can adjust the power supplied from the power source 21 to the motor 40. The power source 21 is a DC power source, and the inverter 20 converts the DC supplied from the power source 21 into AC and supplies it to the motor 40. The power conversion device 10 can be adopted, for example, in an electric vehicle, a hybrid vehicle, a fuel cell vehicle, etc. that runs on the motor 40.

[0010] The basic configuration of the inverter 20 will be briefly described. According to the example of FIG. 1(a), the inverter 20 includes a plurality of switching elements 22a, 22b, 22c, 22d, 22e, 22f provided between the power supply 21 and the motor 40, constituting a so-called three-phase (U-phase, V-phase, W-phase) inverter. Hereinafter, without distinguishing the switching elements 22a to 22f, each one will be simply described as the switching element 22. The circuit configuration of the power conversion device 10 is not particularly limited. The power conversion device 10 may have at least one switching element 22 for controlling the power supply to the motor 40.

[0011] Among the switching elements 22a to 22f, the first switching element 22a and the second switching element 22b are connected in series, constituting one leg (i.e., a pair of upper and lower arms) of the three-phase inverter. The first switching element 22a is arranged on the upper arm, and the second switching element 22b is arranged on the lower arm. Similarly, among the switching elements 22a to 22f, the third switching element 22c and the fourth switching element 22d are connected in series, constituting another leg of the three-phase inverter. The third switching element 22c is arranged on the upper arm, and the fourth switching element 22d is arranged on the lower arm.

[0012] Similarly, among the switching elements 22a to 22f, the fifth switching element 22e and the sixth switching element 22f are connected in series, constituting another leg of the three-phase inverter. The fifth switching element 22e is arranged on the upper arm, and the sixth switching element 22f is arranged on the lower arm. The switching element 22 is not particularly limited, and for example, it may be a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor). Also, a freewheeling diode may be connected in anti-parallel to each of the switching elements 22.

[0013] The connection points of the switching elements 22 of the upper and lower arms of each phase are respectively connected to the coils of the corresponding phase of the motor 40. The inverter 20 supplies three-phase AC power to the motor 40 by selectively and intermittently turning on and off these switching elements 22a to 22f under the control of the control device 30. The control device 30 has a plurality of drive ICs and processors for driving the switching elements 22a to 22f respectively. The control device 30 may be regarded as a configuration including an ECU (Electronic Control Unit).

[0014] The control device 30 receives feedback of a signal indicating the rotational speed of the motor 40 from the motor 40. The rotational speed is the number of rotations per unit time. Also, the control device 30 receives a command regarding the target torque of the motor 40 from a higher-level controller (not shown), and based on the command, the feedback rotational speed, and the allowable values of torque, individually outputs drive signals to the switching elements 22a to 22f. The drive signal is not particularly limited, but is, for example, a pulse width modulation (PWM) signal.

[0015] The control device 30 has a temperature detection unit 31 and a restriction unit 32 corresponding to each of the plurality of switching elements 22. However, in Fig. 1(a), only the temperature detection unit 31 and the restriction unit 32 corresponding to one of the plurality of switching elements 22 (for example, the second switching element 22b) are shown. Of course, the temperature detection unit 31 and the restriction unit 32 are only part of the functions of the control device 30. The temperature detection unit 31 is a sensor that detects the element temperature of the corresponding switching element 22, and is, for example, a temperature sensor using a thermistor. The restriction unit 32 restricts the power supply of the inverter 20 when the element temperature of the switching element 22 exceeds a predetermined temperature threshold.

[0016] FIG. 1(b) is a diagram for explaining the output limit of the present embodiment in comparison with the conventional example, and shows a torque curve and the like. The first torque curve 50 represented by the solid line indicates the allowable value of torque corresponding to the rotational speed of the motor 40. The output curve 52 represented by the two-dot chain line indicates the transition of the output of the motor 40, that is, torque × rotational speed. According to the first torque curve 50, in the low rotational speed range where the rotational speed of the motor 40 is low, the allowable value is fixed at a predetermined maximum value Tmax, and then, as the rotational speed increases, the allowable value decreases from the maximum value Tmax. Therefore, in the low rotational speed range, the output increases as the rotational speed increases, and after the rotational speed rises to a certain extent, the output becomes almost stable.

[0017] In the conventional output limit, when the element temperature of the switching element 22 exceeds the temperature threshold, for overheat protection, a load factor limit is applied to the entire first torque curve 50 and changed to a second torque curve 51 as shown by the dashed line, for example. However, in the output limit due to such a change in the torque curve, an unnecessary limit is imposed on the output in the high rotational speed range of the motor 40. That is, in the high rotational speed range, although the current flowing through the switching element 22 decreases compared to the low rotational speed range and the necessity of protecting the element from the overheated state decreases, the output is limited. In the present embodiment, a solution to such a problem is presented.

[0018] FIG. 2(a) shows the output limit process according to the element temperature by a flowchart. The control device 30 continuously executes this flowchart during the period when the motor 40 is driven, that is, in a situation where the rotational speed, torque, and current value supplied to the motor 40 of the motor 40 all exceed 0. In step S100, the limiting unit 32 acquires the element temperature of the switching element 22 from the temperature detection unit 31. In step S110, the limiting unit 32 determines whether or not the element temperature acquired in step S100 exceeds the temperature threshold. If the element temperature exceeds the temperature threshold, the process proceeds from the "Yes" determination to step S130. On the other hand, if the element temperature is below the temperature threshold, the limiting unit 32 proceeds from the "No" determination in step S110 to step S120.

[0019] The limiting unit 32 that has advanced to step S120 continues the standard output and repeats steps S100 and subsequent steps. The standard output mentioned here means the limitation of torque according to the first torque curve 50. That is, the torque is controlled within the range allowed by the first torque curve 50. On the other hand, in step S130, the limiting unit 32 adopts a torque limit according to the element temperature acquired in step S100 and then returns to step S100.

[0020] Figure 2(b) shows a table defining the correspondence between the element temperature and the maximum value of torque, which the limiting unit 32 refers to in step S130. In Figure 2(b), the symbol TH indicates the temperature threshold. In this table, the fixed maximum value of torque corresponding to an element temperature below the temperature threshold TH may be regarded as the above-mentioned maximum value Tmax. The limiting unit 32 refers to this table and acquires a value lower than the maximum value Tmax as the maximum value of torque according to the element temperature exceeding the temperature threshold TH. Then, the limiting unit 32 changes the current maximum value of torque to the maximum value thus acquired and continues torque control.

[0021] Figure 1(b) shows the maximum value of torque after the change, Tmax2. When the element temperature exceeds the temperature threshold TH, the maximum value of torque, for example, is changed from the maximum value Tmax to the maximum value Tmax2 according to the element temperature. In this case, the limiting unit 32 suppresses the current flowing through the switching element 22 so that the torque of the motor 40 does not exceed the maximum value Tmax2, protecting the switching element 22 from overheating. That is, in the rotation range where the first torque curve 50 exceeds the maximum value Tmax2, the limiting unit 32 sets the maximum value Tmax2 as the maximum allowable value of torque, and in the rotation range where the first torque curve 50 is below the maximum value Tmax2, the limiting unit 32 controls the output with the first torque curve 50 as the allowable value of torque, the same as the standard output.

[0022] As a result, compared with the case of changing from the first torque curve 50 to the second torque curve 51, unnecessary output limitation in the high rotation range is eliminated. In particular, assuming the motor performance when the accelerator pedal is depressed and the throttle is fully opened, which is called WOT (Wide Open Throttle) performance, this embodiment can eliminate output loss by making the most of the first torque curve 50 in the high rotation range, so it can be said to be a useful technology.

[0023] As described above, according to this embodiment, a control device 30 for an inverter 20 that supplies power to a motor 40 is disclosed. The control device 30 includes a limiting unit 32 that limits the power supply of the inverter 20 when the element temperature of the switching element 22 included in the inverter 20 exceeds a predetermined temperature threshold. The limiting unit 32 changes the maximum value of the torque to a value lower than a predetermined maximum value Tmax according to the element temperature exceeding the temperature threshold. According to this configuration, the switching element 22 can be protected from the overheated state, and unnecessary output limitation in the high rotation range of the motor 40 can be avoided.

[0024] A modification included in this embodiment will be described. There is a correlation between the temperature of the cooling water (water temperature) for cooling the switching element 22 and the element temperature. Therefore, the temperature detection unit 31 may be a sensor that detects the water temperature. For the module of the inverter 20, a cooler (not shown) is installed adjacent thereto, and the water temperature of the cooling water flowing through the cooler is detected by the temperature detection unit 31. Then, the limiting unit 32 may limit the power supply of the inverter 20 when the water temperature exceeds a predetermined temperature threshold.

[0025] Figure 3(a) shows, in a flowchart, the output limit processing according to the water temperature. Regarding Figure 3(a), the explanations common to Figure 2(a) are omitted. In step S105, the restriction unit 32 acquires the water temperature from the temperature detection unit 31. In step S115, the restriction unit 32 determines whether the water temperature acquired in step S105 exceeds a predetermined temperature threshold. If the water temperature exceeds the temperature threshold, the process proceeds from the "Yes" determination to step S135. On the other hand, if the water temperature does not exceed the temperature threshold, the restriction unit 32 proceeds from the "No" determination in step S115 to step S120. The restriction unit 32 that has proceeded to step S120 continues the standard output and repeats steps S105 and subsequent steps. On the other hand, in step S135, the restriction unit 32 adopts a torque limit according to the water temperature acquired in step S105 and then returns to step S105.

[0026] Figure 3(b) shows a table defining the correspondence between the water temperature and the maximum value of torque, which the restriction unit 32 refers to in step S135. The way of viewing Figure 3(b) is the same as that of Figure 2(b), but the temperature threshold TH in Figure 3(b) may be a value different from the temperature threshold TH shown in Figure 2(b). In a modified example, the restriction unit 32 refers to the table in Figure 3(b) and acquires, as the maximum value of torque, a value lower than the maximum value Tmax according to the water temperature exceeding the temperature threshold TH. Then, the restriction unit 32 changes the current maximum value of torque to the maximum value thus acquired and continues the torque control. Also by such a modified example, the effects according to the above-described present embodiment are achieved.

Explanation of Reference Numerals

[0027] 10: Power conversion device, 20: Inverter, 21: Power supply, 22: Switching element, 30: Control device, 31: Temperature detection unit, 32: Restriction unit, 40: Motor, 50: First torque curve, 51: Second torque curve, 52: Output curve

Claims

【Claim 1】 A control device for an inverter that supplies power to a motor, comprising: a limiting unit that limits the power supply of the inverter when the element temperature of a switching element included in the inverter exceeds a predetermined temperature threshold; the limiting unit changes the maximum value of torque to a value lower than a predetermined maximum value according to the element temperature exceeding the temperature threshold.

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