Power conversion device

Abstract

In the present invention, a temperature sense diode is mounted on each of a plurality of switching elements, and a signal generation unit (3) detects the forward voltage of each temperature sense diode and generates a detection signal for each temperature sense diode. Switching of each switching element is controlled on the basis of each detection signal. A control unit that performs switching control of each switching element stores an upper limit value of the junction temperature of each switching element and a correlation function between a duty ratio of each detection signal and a temperature corresponding to the forward voltage of each temperature sense diode.

Description

Power conversion device

[0001] The present invention relates to a technology applicable to a power conversion device such as an inverter.

[0002] For example, in a power conversion device such as an inverter that outputs multi-phase AC power, desired power conversion is performed by switching control (on / off control) of a plurality of switching elements (e.g., IGBTs) provided in the power conversion device. However, a temperature rise occurs according to the operating conditions of the switching elements.

[0003] When the junction temperature of the switching element exceeds the upper limit value (temperature limit value) due to the temperature rise as described above, there is a risk of damage (thermal breakdown) of the switching element. In such a case, it is desirable to appropriately control the output of the power conversion device (for example, limit it so as to suppress the torque command or output current to a load such as a motor) to prevent the junction temperature of the switching element from exceeding the upper limit value.

[0004] For example, in Patent Document 1, a temperature sensor provided in a switching element group of an inverter (temperature sensor indicated by reference numeral 10 in Patent Document 1), a signal generation unit that detects the voltage output of the temperature sensor (forward voltage of a diode) that changes according to the temperature of the switching element group and generates a detection signal (drive IC indicated by reference numeral 20 in Patent Document 1), and a control unit that estimates and controls the temperature of the inverter based on the detection signal (detection signal having a pulse width corresponding to the forward voltage) (control unit indicated by reference numeral 30 in Patent Document 1) are disclosed.

[0005] Japanese Patent No. 6428547

[0006] In each element of the switching element group as described above, errors may occur due to temperature characteristics. Also, errors due to temperature characteristics may occur in the voltage output of the temperature sensor simply provided in the switching element group as in Patent Document 1, and in the detection signal generated based on the voltage output.

[0007] Therefore, while it was considered to control the output of the power converter to limit it while taking into account the errors due to the temperature characteristics described above, there is a risk that the output of the power converter may be limited more than necessary. In other words, it may become difficult to fully utilize the output capability of the power converter (output capability within the range where the junction temperature of the switching element does not exceed the upper limit).

[0008] The present invention has been made in view of the aforementioned technical problems, and aims to provide a technology that can contribute to making it easier for a power converter to exert its output capability as desired (for example, by using it so that the junction temperature is close to the upper limit) without losing the objective of suppressing the junction temperature of the switching element from exceeding the upper limit.

[0009] One embodiment of the power conversion device according to this invention comprises a plurality of switching elements, each equipped with a temperature sense diode; a plurality of signal generation units provided corresponding to each temperature sense diode of the switching element, which detect the forward voltage of the temperature sense diode and generate a detection signal; and a control unit that controls the switching of each of the plurality of switching elements based on the detection signals generated by each of the signal generation units.

[0010] The detection signal of each signal generation unit is a signal having a pulse width with a duty cycle D corresponding to the forward voltage of the temperature sense diode corresponding to the detection signal, and the control unit stores the upper limit of the junction temperature of each of the plurality of switching elements, the duty cycle D in the detection signal of each signal generation unit, and the coefficients a and b of the following equation (1), which is a correlation function between the two and the forward voltage T of the temperature sense diode corresponding to the detection signal.

[0011] Furthermore, the control unit controls the switching of each switching element so that the temperature T derived by substituting the duty cycle D in the detection signal of each signal generation unit into the following equation (1) does not exceed the upper limit, and a and b in the following equation (1) are coefficients derived in advance by the control unit controlling the switching of each switching element. T (°C) = a × (duty cycle D (%)) + b ……(1).

[0012] Another embodiment comprises a plurality of switching elements, each equipped with a temperature sense diode; a plurality of signal generation units provided corresponding to each temperature sense diode of the switching element, which detect the forward voltage of the temperature sense diode and generate a detection signal; and a control unit that controls the switching of each of the plurality of switching elements based on the detection signals generated by each of the signal generation units.

[0013] The detection signal of each signal generation unit is a signal having a pulse width with a duty cycle D corresponding to the forward voltage of the temperature sense diode corresponding to the detection signal, and the control unit stores the upper limit of the junction temperature of each of the plurality of switching elements, the duty cycle D in the detection signal of each signal generation unit, and the coefficients a and b of the following equation (1), which is a correlation function between the two and the forward voltage T of the temperature sense diode corresponding to the detection signal.

[0014] Furthermore, the control unit controls the switching of each switching element so that the temperature T derived by substituting the duty cycle D in the detection signal of each signal generation unit into the following equation (1) does not exceed the upper limit, and a and b in (1) below are values ​​derived by first heating the temperature sense diode to different temperatures Tα and Tβ, detecting the forward voltage of the temperature sense diode and deriving the duty cycles Dα and Dβ of the detection signal generated, respectively, and substituting those duty cycles Dα and Dβ into the following equations (2) and (3). T (°C) = a × (duty cycle D) + b ……(1) Tα (°C) = a × (duty cycle Dα) + b ……(2) Tβ (°C) = a × (duty cycle Dβ) + b ……(3).

[0015] As described above, the present invention makes it possible to make it easier for the power converter to exert its output capability as desired (for example, by using it so that the junction temperature is close to the upper limit) without losing the objective of suppressing the junction temperature of the switching element from exceeding the upper limit.

[0016] A schematic diagram illustrating the power conversion device 1 according to an embodiment. A schematic diagram illustrating an example of a switching element SW. A diagram showing the characteristics of the temperature sense diode d, signal generation unit 3, and duty cycle D in the power conversion device 1. A flowchart showing an example of how to derive the coefficients a and b in equation (1).

[0017] The power conversion device according to the embodiment of the present invention is completely different from a configuration in which the power conversion device is controlled simply by the voltage output of a temperature sensor provided on a switching element group or a detection signal generated based on said voltage output.

[0018] In other words, this embodiment is configured such that each of the multiple switching elements is equipped with a temperature sense diode, the forward voltage of each temperature sense diode is detected to generate a detection signal (a signal having a pulse width with a duty cycle corresponding to the forward voltage of the temperature sense diode), and each switching element is controlled based on each detection signal.

[0019] In the control unit that controls the switching of each switching element, the upper limit of the junction temperature of each switching element and the correlation function between the duty cycle (D) in each detection signal and the temperature (T) corresponding to the forward voltage of each temperature sense diode (for example, the correlation function shown in equation (1) described later) are stored. Then, the switching control of each switching element is performed so that the temperature (T) derived by substituting the duty cycle (D) in the detection signal of each signal generation unit into the correlation function does not exceed the upper limit of the junction temperature.

[0020] With this configuration, the junction temperature of each switching element is estimated via its respective temperature sense diode, and the switching of each switching element is controlled based on this estimated value. This makes it easier to suppress the effects of errors due to the temperature characteristics of each switching element. Furthermore, it also makes it easier to suppress the effects of errors due to the temperature characteristics of the voltage output of each temperature sense diode and the detection signal generated based on that voltage output.

[0021] This prevents the output of the power converter from being unnecessarily restricted, making it easier to utilize the power converter's output capacity as desired (using the junction temperature up to near its upper limit). In other words, it makes it easier to expand the operating range of the power converter.

[0022] The power conversion device of this embodiment only needs to be configured to estimate the junction temperature of each switching element via its respective temperature sense diode, and to control the switching of each switching element based on the estimated value, allowing for a variety of design modifications. In other words, it is possible to appropriately apply common technical knowledge from various fields (e.g., the power conversion device field, the temperature sensor field, the signal generation field, etc.) and modify the design as needed by referring to prior art documents, etc.

[0023] In the following embodiments, detailed explanations are omitted as appropriate, for example, by referring to the same reference numerals or terms for similar content.

[0024] <Example> <Main Configuration of Power Conversion Device 1> Figures 1 and 2 are schematic diagrams illustrating the power conversion device 1 according to this embodiment. The power conversion device 1 is an inverter or the like capable of outputting multi-phase (three-phase in Figure 1) AC power, and is housed in a casing not shown in the figure.

[0025] In the case of the power converter 1 shown in Figure 1, it mainly comprises a semiconductor module (ASSY) 2 that houses multiple chip-shaped switching elements SW, such as those shown in Figure 2 (six in Figure 1), within a case 20; a gate drive circuit board 21 that is arranged to superimpose on the case 20 and outputs a gate drive signal to each switching element SW; and a control unit (not shown) that controls the current output of the power converter 1 (such as on / off control of the switching elements SW).

[0026] The case 20 is provided with input conductors 22 and output conductors (three conductors corresponding to the three-phase output current in Figure 1) 22 that extend through the case 20 in an inward and outward direction, and each is appropriately connected to the switching element SW inside the case 20.

[0027] Each switching element SW is equipped with a temperature sense diode d (for example, mounted on the surface of a chip-shaped switching element SW as shown in Figure 2). The forward voltage Vf of each temperature sense diode d of each switching element SW changes according to the ambient temperature T (for example, the temperature of the surface of the switching element SW in the case of Figure 2), and this forward voltage Vf can be output to the corresponding signal generation unit 3, which will be described later.

[0028] The forward voltage Vf of such a temperature-sensing diode d has a temperature characteristic as shown in Figure 3(A), for example. As a result, the forward voltage Vf decreases as the temperature T around the temperature-sensing diode d increases.

[0029] Multiple signal generation units 3 (six in Figure 1) are mounted on one end face 21a of the gate drive circuit board 21, corresponding to each switching element SW in the case 20. Each signal generation unit 3 is configured to detect the forward voltage Vf of the temperature sense diode of the corresponding switching element SW in the case 20 and to generate a detection signal based on the detected forward voltage Vf. The detection signals generated as described above are transmitted to the control unit as appropriate.

[0030] An example of a signal generation unit 3 with such a configuration is a configuration similar to the drive IC shown in Patent Document 1 (for example, a configuration in which a comparator, carrier signal generation unit, header pulse generation unit, switch, sequencer, etc. are integrated on an IC chip, as shown by reference numeral 20 in Figure 1 of Patent Document 1).

[0031] The detection signal generated by the signal generation unit 3 has temperature characteristics as shown in Figure 3(B), for example. Specifically, the detection signal has a pulse width with a duty cycle D corresponding to the forward voltage Vf of the temperature sense diode d.

[0032] Focusing on the temperature characteristics in Figures 3(A) and 3(B), the duty cycle D of the detection signal exhibits a linear function with respect to the forward voltage Vf of the temperature sense diode d. That is, both the duty cycle D of the detection signal and the temperature T corresponding to the forward voltage Vf of the temperature sense diode d can be expressed by the correlation function shown in equation (1) below: T (°C) = a × (duty cycle D (%)) + b ……(1).

[0033] Therefore, the temperature T of the temperature sense diode d mounted on each switching element SW can be expressed by the correlation function of equation (1). The coefficients a and b in equation (1) can be derived, for example, by appropriately controlling the switching of each switching element SW through preliminary tests described later.

[0034] The control unit comprises a control circuit board (not shown) on which a CPU, memory, etc., are mounted, and is connected to a semiconductor module 2, a gate drive circuit board 21, etc., via signal cables, connectors, etc.

[0035] This control unit is pre-stored, for example, by conducting a preliminary test of the power converter 1 in an offline state, the upper limit of the junction temperature of each switching element SW and the coefficients a and b of the correlation function of equation (1) corresponding to the temperature T of each temperature sense diode d of each switching element SW are classified according to each switching element SW.

[0036] This control unit, for example, when the power converter 1 is online, controls the switching of each switching element SW based on a desired output command (e.g., output current command or torque command), and appropriately receives detection signals from the signal generation unit 3 corresponding to each switching element SW. The duty cycle D of each received detection signal is then substituted into equation (1) relating to the corresponding switching element SW to derive the temperature T of each temperature sense diode. Each of the temperatures T thus derived is then compared with the upper limit of the junction temperature relating to the corresponding switching element SW.

[0037] For example, if the comparison results indicate that the temperature T is lower than the upper limit (or relatively close to the upper limit), the switching control may be continued or the output may be increased. On the other hand, if the comparison results indicate that the temperature T is likely to exceed the upper limit (or has already exceeded it), the switching control may be suppressed to reduce the temperature T and prevent damage to each switching element SW.

[0038] <An example of how to derive the coefficients a and b in equation (1)> The coefficients a and b in equation (1) can be appropriately derived, for example, in a pre-test of the power converter 1 in an offline state, by heating the temperature sense diode d of each switching element SW to different temperatures Tα and Tβ, and going through steps S1 to S5 of the flow shown in Figure 4. In Figure 4, as examples of temperatures Tα and Tβ, they are set to 30°C (i.e., room temperature) and 80°C (i.e., a temperature several tens of degrees higher than room temperature), respectively.

[0039] In Figure 4, first, in step S1, the temperature sense diode d of the switching element SW is heated to 30°C using a heating device (not shown) (for example, a heating device equipped with a sensor capable of measuring the temperature of the temperature sense diode d). Then, in step S2, the forward voltage Vf of the temperature sense diode d in the heated state (30°C) is detected by the signal generation unit 3, and the detection signal generated by the signal generation unit 3 is received by the control unit to derive the duty cycle Dα of the detection signal.

[0040] Next, in step S3, the temperature sense diode d of the switching element SW is heated to 80°C using the heating device or the like. Then, in step S4, the forward voltage Vf of the temperature sense diode d in the heated state (80°C) is detected by the signal generation unit 3, the detection signal generated by the signal generation unit 3 is received by the control unit, and the duty cycle Dβ of the detection signal is derived.

[0041] In step S5, the coefficients a and b are derived by substituting the temperatures Tα and Tβ (i.e., 30°C and 80°C) obtained in steps S1 and S3, and the duty cycles Dα and Dβ derived in steps S2 and S4, into the following equations (2) and (3): Tα (°C) = a × (duty cycle Dα) + b ……(2) Tβ (°C) = a × (duty cycle Dβ) + b ……(3).

[0042] Although the present invention has been described in detail only with respect to the specific examples described above, it will be obvious to those skilled in the art that a wide variety of modifications are possible within the scope of the technical concept of the present invention, and it is natural that such modifications fall within the scope of the claims.

[0043] For example, in this embodiment, multiple switching elements SW are mounted inside the case 20, but this can also be applied to a power converter in which only one switching element SW is mounted inside the case 20, and multiple such cases 20 are provided.

[0044] 1...Power converter 2...Semiconductor module 3...Signal generation unit SW...Switching element d...Temperature sense diode

Claims

1. The device comprises: a plurality of switching elements, each equipped with a temperature sense diode; a plurality of signal generation units, each corresponding to the temperature sense diode of the switching element, which detect the forward voltage of the temperature sense diode and generate a detection signal; and a control unit that controls the switching of each of the plurality of switching elements based on the detection signals generated by each of the signal generation units, wherein the detection signal of each signal generation unit is a signal having a pulse width with a duty cycle D corresponding to the forward voltage of the temperature sense diode corresponding to the detection signal; the control unit stores: an upper limit value of the junction temperature of each of the plurality of switching elements; and coefficients a and b of the following equation (1), which is a correlation function between the duty cycle D in the detection signal of each signal generation unit and the temperature T corresponding to the forward voltage of the temperature sense diode corresponding to the detection signal; and the control unit controls the switching of each of the switching elements so that the temperature T derived by substituting the duty cycle D in the detection signal of each signal generation unit into the following equation (1) does not exceed the upper limit value. A power conversion device characterized in that a and b in the following equation (1) are coefficients derived in advance by switching control of each switching element by the control unit. T (°C) = a × (duty cycle D (%)) + b ……(1).

2. The device comprises: a plurality of switching elements, each equipped with a temperature sense diode; a plurality of signal generation units, each corresponding to the temperature sense diode of each switching element, which detect the forward voltage of the temperature sense diode and generate a detection signal; and a control unit that controls the switching of each of the plurality of switching elements based on the detection signals generated by each of the signal generation units, wherein the detection signal of each signal generation unit is a signal having a pulse width with a duty cycle D corresponding to the forward voltage of the temperature sense diode corresponding to the detection signal; the control unit stores: an upper limit value of the junction temperature of each of the plurality of switching elements; and coefficients a and b of the following equation (1), which is a correlation function between the duty cycle D in the detection signal of each signal generation unit and the temperature T corresponding to the forward voltage of the temperature sense diode corresponding to the detection signal; and the control unit controls the switching of each of the switching elements so that the temperature T derived by substituting the duty cycle D in the detection signal of each signal generation unit into the following equation (1) does not exceed the upper limit value. A power conversion device characterized in that, a and b in (1) below are values ​​obtained by first heating the temperature sense diode to different temperatures Tα and Tβ, detecting the forward voltage of the temperature sense diode, deriving the duty cycles Dα and Dβ of the detection signal generated, and substituting these duty cycles Dα and Dβ into the following equations (2) and (3). T (°C) = a × (duty cycle D) + b ……(1) Tα (°C) = a × (duty cycle Dα) + b ……(2) Tβ (°C) = a × (duty cycle Dβ) + b ……(3).

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