Power conversion device

Abstract

To equalize a heat generation amount per time unit for each of switching elements in a power conversion device having the plurality of switching elements.SOLUTION: A power conversion device 1 is configured by including: series circuits SC1 to SC3 each having two switching elements mutually connected in series, respectively connected to a battery B in parallel; and a control circuit CC for controlling drive of each of switching elements SW1 to SW6 in the series circuits SC1 to SC3, wherein the control circuit CC decreases a duty ratio of a drive signal for driving one switching element if the control circuit determines that current is intensively flowing through the one switching element in one series circuit in the series circuits SC1 to SC3 or a temperature at the one switching element is equal to or higher than a threshold value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power conversion device. [Background technology]

[0002] There is a power conversion device that converts DC power supplied from a power source into three AC powers with different phases by turning on and off six switching elements provided in a bridge circuit, and outputs the AC powers to a motor. Related technology is disclosed in Patent Document 1.

[0003] When the power output from the power conversion device is supplied to a vehicle's driving motor, if a sudden load is placed on the driving motor and the rotation speed of the driving motor becomes zero, such as when the vehicle is stopped on a steep slope or when the vehicle is going over a step, current may flow concentratedly in one of the six switching elements, and the amount of heat generated per unit time by that switching element may be higher than that of the other switching elements.

[0004] In view of this, there are other power conversion devices that, when current flows intensively through one switching element, reduce the switching frequency of that switching element.

[0005] Alternatively, there is another power conversion device in which a current flowing through each switching element is distributed by connecting another switching element in parallel to each switching element.

[0006] Alternatively, there is another power conversion device in which the performance of each switching element is improved by, for example, increasing the size of the terminals of each switching element so that the on-resistance of each switching element is reduced.

[0007] However, when the switching frequency of the switching elements is reduced as in the other power conversion devices described above, there is a risk that sounds generated when the switching elements are switched will change to sounds in the human audible range and become noise.

[0008] Furthermore, when another switching element is connected in parallel to each switching element as in the other power conversion devices described above, there is a concern that the power conversion device may become larger in size due to the increase in the number of other switching elements.

[0009] Furthermore, when the on-resistance of each switching element is reduced as in the other power conversion devices described above, there is a concern that the manufacturing costs will increase due to the need to change the design of the switching elements. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2009-106106 A Summary of the Invention [Problem to be solved by the invention]

[0011] An object according to one aspect of the present invention is to equalize the amount of heat generated per unit time of each switching element in a power conversion device including a plurality of switching elements. [Means for solving the problem]

[0012] One form of the power conversion device according to the present invention is a power conversion device that converts input power into a desired power and outputs it, and is equipped with a plurality of series circuits having two switching elements connected in series with each other and each connected in parallel to a power source, and a control circuit that controls the drive of each switching element of the plurality of series circuits.

[0013] When the control circuit determines that current is flowing concentratedly through one of the switching elements in one of the multiple series circuits, or when the temperature of the one of the switching elements is equal to or higher than a threshold value, the control circuit reduces the duty ratio of the drive signal that drives the one of the switching elements.

[0014] This makes it possible to reduce steady-state losses in switching elements through which current is concentrated or switching elements whose temperature is above a threshold value, so that the heat generation per unit time of the switching elements through which current is concentrated or switching elements whose temperature is above a threshold value can be distributed to the heat generation per unit time of other switching elements, and the heat generation per unit time of each switching element can be equalized.

[0015] The control circuit may be configured to switch the other switching element of one of the series circuits from off to on when a current flows through a diode connected in parallel to the other switching element.

[0016] This reduces the switching loss of the other switching element, and therefore reduces the steady-state loss of the switching element through which current is concentrated or the switching element whose temperature is above a threshold value. Even if the steady-state loss of the other switching element increases, the overall losses between the switching element through which current is concentrated or the switching element whose temperature is above a threshold value and the other switching element can be equalized, and the amount of heat generated per unit time of each switching element can be further equalized.

[0017] The inverter further comprises a U-phase series circuit in which a connection point of a U-phase upper arm switching element and a U-phase lower arm switching element is connected to a U-phase input terminal of a three-phase AC motor, a V-phase series circuit in which a connection point of a V-phase upper arm switching element and a V-phase lower arm switching element is connected to the V-phase input terminal of the three-phase AC motor, and a W-phase series circuit in which a connection point of a W-phase upper arm switching element and a W-phase lower arm switching element is connected to a W-phase input terminal of the three-phase AC motor, and the control circuit, when determining that a current is flowing in a concentrated manner in the U-phase upper arm switching element, reduces a duty ratio of each of drive signals for the U-phase upper arm switching element, the V-phase lower arm switching element, and the W-phase lower arm switching element, and when determining that a current is flowing in a concentrated manner in the U-phase lower arm switching element, reduces a duty ratio of each of drive signals for the U-phase lower arm switching element, the V-phase upper arm switching element, and the W-phase upper arm switching element the duty ratio of each of the drive signals for the V-phase upper arm switching element, the U-phase lower arm switching element and the W-phase lower arm switching element when it is determined that current is flowing in a concentrated manner through the V-phase lower arm switching element; reducing the duty ratio of each of the drive signals for the V-phase lower arm switching element, the U-phase upper arm switching element and the W-phase upper arm switching element when it is determined that current is flowing in a concentrated manner through the V-phase lower arm switching element; reducing the duty ratio of each of the drive signals for the W-phase upper arm switching element, the U-phase lower arm switching element and the V-phase lower arm switching element when it is determined that current is flowing in a concentrated manner through the W-phase upper arm switching element;

[0018] Moreover, the two switching elements may be disposed adjacent to each other.

[0019] For example, if the amount of heat generated per unit time of two switching elements can be equalized by equalizing the overall loss of each of the two switching elements, the two switching elements can be placed adjacent to each other, making it unnecessary to determine the layout of the entire switching elements while taking into account the distribution of the amount of heat generated, and making it easier to design the layout of the entire switching elements. Effect of the Invention

[0020] According to the present invention, in a power conversion device including a plurality of switching elements, the amounts of heat generated per unit time of each switching element can be equalized. [Brief description of the drawings]

[0021] [Figure 1] 1 is a diagram illustrating an example of a power conversion device according to an embodiment; [Diagram 2] 5 is a flowchart illustrating an example of an operation of a calculation unit in the embodiment. [Diagram 3] 4 is a diagram showing an example of a voltage applied to each phase, a U-phase-W-phase line voltage, and a V-phase-W-phase line voltage. FIG. [Figure 4] FIG. 4 is a diagram illustrating an example of a drive signal. [Diagram 5] FIG. 1 is a diagram illustrating a power conversion device according to a first modified example. [Figure 6] 13 is a flowchart showing the operation of a calculation unit in the first modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, the details of the embodiment will be described with reference to the drawings.

[0023] FIG. 1 is a diagram illustrating an example of a power conversion device according to an embodiment.

[0024] The power conversion device 1 shown in Fig. 1 is mounted on a vehicle Ve, such as an industrial vehicle (such as a forklift or a towing tractor) or an electric vehicle, and drives an electric motor M, such as a traction motor. The power conversion device 1 also includes an inverter circuit Inv, current sensors Si1-Si3, and a control circuit CC. The electric motor M is a three-phase AC motor, for example, a synchronous motor such as an embedded magnet synchronous motor or a surface magnet synchronous motor. The electric motor M also includes a position sensor Sr, such as a resolver or an encoder. The position sensor Sr detects a position θ of a rotor (not shown) of the electric motor M, and outputs the detected position θ to the control circuit CC.

[0025] The inverter circuit Inv converts DC power supplied from a battery B as a power source into AC power and outputs it to the motor M, and includes a capacitor C, a series circuit SC1 (U-phase series circuit), a series circuit SC2 (V-phase series circuit), and a series circuit SC3 (W-phase series circuit). The series circuits SC1 to SC3 are each connected in parallel to the battery B.

[0026] The series circuit SC1 includes a switching element SW1 (U-phase upper arm switching element) and a switching element SW2 (U-phase lower arm switching element) connected in series with each other. The series circuit SC2 includes a switching element SW3 (V-phase upper arm switching element) and a switching element SW4 (V-phase lower arm switching element) connected in series with each other. The series circuit SC3 includes a switching element SW5 (W-phase upper arm switching element) and a switching element SW6 (W-phase lower arm switching element) connected in series with each other. Each of the switching elements SW1 to SW6 is an n-channel Metal Oxide Semiconductor Field Effect Transistor (MOSFET), and includes a diode (body diode) connected in parallel with each other.

[0027] The switching elements SW1 to SW6 form a bridge circuit. That is, the drain terminals of the switching elements SW1, SW3, and SW5 are connected to the positive terminal of the battery B via one terminal of the capacitor C, and the source terminals of the switching elements SW2, SW4, and SW6 are connected to the negative terminal of the battery B via the other terminal of the capacitor C. The connection point between the source terminal of the switching element SW1 and the drain terminal of the switching element SW2 is connected to the U-phase input terminal of the motor M via the current sensor Si1. The connection point between the source terminal of the switching element SW3 and the drain terminal of the switching element SW4 is connected to the V-phase input terminal of the motor M via the current sensor Si2. The connection point between the source terminal of the switching element SW5 and the drain terminal of the switching element SW6 is connected to the W-phase input terminal of the motor M via the current sensor Si3.

[0028] Switching element SW1 is turned on or off by drive signal Sd1 output from control circuit CC. Switching element SW2 is turned on or off by drive signal Sd2 output from control circuit CC. Switching element SW3 is turned on or off by drive signal Sd3 output from control circuit CC. Switching element SW4 is turned on or off by drive signal Sd4 output from control circuit CC. Switching element SW5 is turned on or off by drive signal Sd5 output from control circuit CC. Switching element SW6 is turned on or off by drive signal Sd6 output from control circuit CC. By switching elements SW1 to SW6 being turned on or off, respectively, the DC voltage output from battery B is converted into three AC voltages whose phases differ from each other by 120 degrees, and these AC voltages are applied to the U-phase input terminal, V-phase input terminal, and W-phase input terminal of electric motor M, causing the rotor of electric motor M to rotate.

[0029] Each of the current sensors Si1 to Si3 is composed of a Hall element, a shunt resistor, etc. The current sensor Si1 detects a current Iu flowing through a U-phase of the motor M and outputs it to the control circuit CC, the current sensor Si2 detects a current Iv flowing through a V-phase of the motor M and outputs it to the control circuit CC, and the current sensor Si3 detects a current Iw flowing through a W-phase of the motor M and outputs it to the control circuit CC.

[0030] The control circuit CC includes a drive circuit DC, a storage unit 2, and a calculation unit 3.

[0031] The drive circuit DC is composed of an IC (Integrated Circuit) etc., and compares the voltage value of a carrier wave (such as a triangular wave, a sawtooth wave, or an inverse sawtooth wave) with voltage command values ​​Vu*, Vv*, Vw* calculated by a calculation unit 3, and outputs drive signals Sd1 to Sd6 according to the comparison results to the gate terminals of each of the switching elements SW1 to SW6.

[0032] For example, when the voltage command value Vu* is equal to or greater than the voltage value of the carrier wave, the drive circuit DC outputs a high-level drive signal Sd1 and a low-level drive signal Sd1, and when the voltage command value Vu* is smaller than the voltage value of the carrier wave, the drive circuit DC outputs a low-level drive signal Sd1 and a high-level drive signal Sd2. When the voltage command value Vv* is equal to or greater than the voltage value of the carrier wave, the drive circuit DC outputs a high-level drive signal Sd3 and a low-level drive signal Sd4, and when the voltage command value Vv* is smaller than the voltage value of the carrier wave, the drive circuit DC outputs a low-level drive signal Sd3 and a high-level drive signal Sd4. When the voltage command value Vw* is equal to or greater than the voltage value of the carrier wave, the drive circuit DC outputs a high-level drive signal Sd5 and a low-level drive signal Sd6, and when the voltage command value Vw* is smaller than the voltage value of the carrier wave, the drive circuit DC outputs a low-level drive signal Sd5 and a high-level drive signal Sd6.

[0033] The storage unit 2 is configured with a RAM (Random Access Memory) or a ROM (Read Only Memory), etc.

[0034] The calculation unit 3 is configured with a microcomputer or the like, and determines voltage command values ​​Vu*, Vv*, and Vw*.

[0035] Furthermore, when the calculation unit 3 determines that current is flowing intensively through one of the switching elements in one of the series circuits SC1 to SC3, it reduces the duty ratio (the ratio [%] of the high level period of the drive signal to the control period of the drive signal) of the drive signal that drives that one of the switching elements. For example, when the calculation unit 3 determines that current is flowing intensively through one of the switching elements in one of the series circuits SC1 to SC3, it reduces the duty ratio of the drive signal that drives that one of the switching elements by a predetermined duty ratio R. Note that the predetermined duty ratio R is a value found by calculation, experiment, simulation, or the like, and is set to a value that increases as the current flowing through the one of the switching elements increases.

[0036] FIG. 2 is a flowchart showing the operation of the calculation unit 3.

[0037] First, the calculation unit 3 starts drive control of the electric motor M when an instruction to start driving the electric motor M is input by a user operating an input device (not shown) or the like (step Stp1: Yes).

[0038] Next, when the calculation unit 3 determines that current is not flowing in a concentrated manner in any of the switching elements SW1 to SW6 (step Stp2: No), it calculates voltage command values ​​Vu*, Vv*, Vw* as normal control based on the currents Iu to Iw, the position θ, and the rotation speed command value ω* output from outside (for example, a driving control circuit provided in the vehicle Ve) (step Stp3).

[0039] For example, when the currents Iu, Iv, and Iw are constantly changing, the calculation unit 3 determines that the current is not flowing in a concentrated manner in any of the switching elements SW1 to SW6.

[0040] For example, during normal control, the calculation unit 3 determines the voltage command values ​​Vu*, Vv*, and Vw* according to the following 1) to 8).

[0041] 1) The calculation unit 3 obtains the number of rotations ω by dividing the position θ by a predetermined time (such as the clock period of the calculation unit 3).

[0042] 2) The calculation unit 3 calculates the rotation speed difference Δω between the rotation speed command value ω* and the rotation speed ω.

[0043] 3) The calculation unit 3 refers to information (not shown) stored in the memory unit 2 in which the rotation speed of the rotor of the electric motor M and the torque of the electric motor M correspond to each other, and determines the torque corresponding to the rotation speed equivalent to the rotation speed difference Δω as the torque command value T*.

[0044] 4) The calculation unit 3 refers to information (not shown) stored in the memory unit 2 in which the torque of the motor M is associated with the d-axis current command value Id* and the q-axis current command value Iq*, and determines the d-axis current command value Id* and the q-axis current command value Iq* corresponding to the torque command value T*.

[0045] 5) The calculation unit 3 converts the currents Iu to Iw into a d-axis current Id and a q-axis current Iq using a conversion matrix C1 shown in the following equation 1.

[0046]

number

[0047] 6) The calculation unit 3 calculates a difference ΔId between the d-axis current command value Id* and the d-axis current Id, and calculates a difference ΔIq between the q-axis current command value Iq* and the q-axis current Iq.

[0048] 7) The calculation unit 3 obtains the d-axis voltage command value Vd* by calculating the following formula 2, and obtains the q-axis voltage command value Vq* by calculating the following formula 3. Here, Kp is a constant of the proportional term of the PI control, Ki is a constant of the integral term of the PI control, Lq is the q-axis inductance of the motor M, Ld is the d-axis inductance of the motor M, ω is the rotation speed, and Ke is an induced voltage constant.

[0049] d-axis voltage command value Vd* = Kp × difference ΔId + ∫(Ki × difference ΔId)-ωLqIq Equation 2

[0050] q-axis voltage command value Vq* = Kp × difference ΔIq + ∫(Ki × difference ΔIq) + ωLdId + ωKe Equation 3

[0051] 8) The calculation unit 3 converts the d-axis voltage command value Vd* and the q-axis voltage command value Vq* into voltage command values ​​Vu*, Vv*, and Vw* using a conversion matrix C2 shown in the following equation 4.

[0052]

number

[0053] On the other hand, when the calculation unit 3 determines that a current is concentrating in the upper arm switching element of one of the series circuits or that a current is concentrating in the lower arm switching element of one of the series circuits (step Stp2: Yes), as neutral point control, it calculates voltage command values ​​Vu*, Vv*, Vw* based on the currents Iu to Iw, the position θ, and the rotation speed command value ω*, and then corrects the voltage command values ​​Vu*, Vv*, Vw* so that the duty ratio of the drive signal for driving the upper arm switching element of the one series circuit is reduced by a predetermined duty ratio R and the duty ratios of the drive signals for driving each of the lower arm switching elements of the remaining two series circuits are each reduced by a predetermined duty ratio R, or so that the duty ratio of the drive signal for driving the lower arm switching element of the one series circuit is reduced by the predetermined duty ratio R and the duty ratios of the drive signals for driving each of the upper arm switching elements of the remaining two series circuits are each reduced by a predetermined duty ratio R (step Stp4).

[0054] For example, when the currents Iu, Iv, and Iw are each constant for a certain time period longer than the control period of the switching elements, the calculation unit 3 determines that the switching element through which the largest current Iu, Iv, and Iw is flowing is the switching element through which current is flowing in a concentrated manner.

[0055] For example, during neutral point control, the calculation unit 3 calculates the voltage command values ​​Vu*, Vv*, Vw* according to the above 1) to 8), and then corrects the voltage command values ​​Vu*, Vv*, Vw* according to the following 9).

[0056] 9) When calculation unit 3 determines that current is concentrating in switching element SW1, it decreases voltage command value Vu* and increases voltage command values ​​Vv* and Vw* by a voltage amount corresponding to predetermined duty ratio R. This makes it possible to decrease the duty ratio of drive signal Sd1 by the predetermined duty ratio R, and also to decrease the duty ratios of drive signals Sd4 and Sd6 by the predetermined duty ratio R.

[0057] Alternatively, when the calculation unit 3 determines that current is concentrating in the switching element SW2, it increases the voltage command value Vu* and decreases the voltage command values ​​Vv* and Vw* by a voltage corresponding to the predetermined duty ratio R. This makes it possible to reduce the duty ratio of the drive signal Sd2 by the predetermined duty ratio R, and also to reduce the duty ratios of the drive signals Sd3 and Sd5 by the predetermined duty ratio R.

[0058] Alternatively, when the calculation unit 3 determines that current is concentrating in the switching element SW3, it decreases the voltage command value Vv* and increases the voltage command values ​​Vu* and Vw* by a voltage corresponding to the predetermined duty ratio R. This makes it possible to decrease the duty ratio of the drive signal Sd3 by the predetermined duty ratio R, and to decrease the duty ratios of the drive signals Sd2 and Sd6 by the predetermined duty ratio R.

[0059] Alternatively, when the calculation unit 3 determines that current is concentrating in the switching element SW4, it increases the voltage command value Vv* and decreases the voltage command values ​​Vu* and Vw* by a voltage corresponding to the predetermined duty ratio R. This makes it possible to reduce the duty ratio of the drive signal Sd4 by the predetermined duty ratio R, and also to reduce the duty ratios of the drive signals Sd1 and Sd5 by the predetermined duty ratio R.

[0060] Alternatively, when the calculation unit 3 determines that current is concentrating in the switching element SW5, it decreases the voltage command value Vw* and increases the voltage command values ​​Vu* and Vv* by a voltage amount corresponding to the predetermined duty ratio R. This makes it possible to decrease the duty ratio of the drive signal Sd5 by the predetermined duty ratio R, and to decrease the duty ratios of the drive signals Sd2 and Sd4 by the predetermined duty ratio R.

[0061] Alternatively, when the calculation unit 3 determines that current is concentrating in the switching element SW6, it increases the voltage command value Vw* and decreases the voltage command values ​​Vu* and Vv* by a voltage corresponding to the predetermined duty ratio R. This makes it possible to reduce the duty ratio of the drive signal Sd6 by the predetermined duty ratio R, and also to reduce the duty ratios of the drive signals Sd1 and Sd3 by the predetermined duty ratio R.

[0062] Then, if an instruction to end the drive of the electric motor M has not been input by the user operating an input device, etc. (step Stp5: No), the calculation unit 3 repeatedly executes the processing of steps Stp2 to Stp5, and if an instruction to end the drive is input (step Stp5: Yes), it ends the drive control of the electric motor M.

[0063] Here, Fig. 3(a)-(c) are diagrams showing an example of the voltage applied to each phase, the U-phase-W-phase line voltage, and the V-phase-W-phase line voltage when the voltage command values ​​Vu*, Vv*, and Vw* are not corrected. Fig. 3(d)-(f) are diagrams showing an example of the voltage applied to each phase, the U-phase-W-phase line voltage, and the V-phase-W-phase line voltage when the voltage command values ​​Vu*, Vv*, and Vw* are corrected. Note that the horizontal axis of the two-dimensional coordinate system shown in Fig. 3(a)-(f) indicates time, and the vertical axis indicates voltage. The solid lines shown in Fig. 3(a) and Fig. 3(d) indicate the voltage applied to the U-phase or the V-phase. The solid lines shown in Fig. 3(b) and Fig. 3(e) indicate the voltage applied to the W-phase. The solid lines shown in Fig. 3(c) and Fig. 3(f) indicate the U-phase-W-phase line voltage or the V-phase-W-phase line voltage.

[0064] 3(b) and 3(e), when the voltage command values ​​Vu*, Vv*, and Vw* are corrected, the time during which a high-level voltage is applied to the W phase in the control period of the switching elements, i.e., the time during which the switching element SW5 is on, can be reduced compared to when the voltage command values ​​Vu*, Vv*, and Vw* are not corrected. That is, when the voltage command values ​​Vu*, Vv*, and Vw* are corrected, even if a current flows intensively in the switching element SW5, the steady-state loss of the switching element SW5 can be reduced, so that the amount of heat generated per unit time by the switching element SW5 can be distributed to the amount of heat generated per unit time by the other switching elements, and the amount of heat generated per unit time by each switching element can be equalized.

[0065] Also, as shown in Fig. 3(a) and Fig. 3(d), when the voltage command values ​​Vu*, Vv*, and Vw* are corrected, the time during which high-level voltages are applied to the U and V phases in the control period of the switching elements can be reduced by the same amount as the reduction in the time during which high-level voltages are applied to the W phase. This makes it possible to make the effective value (total high-level voltages) of the U-phase-W phase line voltage or the V-phase-W phase line voltage when the voltage command values ​​Vu*, Vv*, and Vw* are corrected equal to the effective value of the U-phase-W phase line voltage or the V-phase-W phase line voltage when the voltage command values ​​Vu*, Vv*, and Vw* are not corrected, as shown in Fig. 3(c) and Fig. 3(f). Therefore, even if current flows in a concentrated manner in one switching element, the heat generated by each switching element can be dispersed while preventing the torque of the motor M from changing.

[0066] In the power conversion device 1 of the embodiment, the switching element connected in series to the switching element whose duty ratio of the drive signal is decreased by the correction of the voltage command values ​​Vu*, Vv*, Vw*, i.e., the switching element whose duty ratio of the drive signal is increased by the correction of the voltage command values ​​Vu*, Vv*, Vw*, is driven by soft switching. Specifically, when a current is concentrated in one switching element, the switching element to be soft switched is switched from off to on when a current is flowing in a diode connected in parallel to the switching element to be soft switched. This allows a configuration in which a current flows in the switching element to be soft switched when a relatively small voltage applied to the diode is applied to the switching element to be soft switched, thereby reducing the switching loss of the switching element to be soft switched.

[0067] Here, Fig. 4 is a diagram showing an example of drive signals Sd1 to Sd6 in the case where current is concentrated in switching element SW5 and voltage command values ​​Vu*, Vv*, and Vw* are corrected. The horizontal axis of the two-dimensional coordinates shown in Fig. 4(a) to Fig. 4(d) indicates time, and the vertical axis indicates voltage. The solid line in Fig. 4(a) indicates drive signals Sd1 and Sd3, the solid line in Fig. 4(b) indicates drive signals Sd2 and Sd4, the solid line in Fig. 4(c) indicates drive signal Sd5, and the solid line in Fig. 4(d) indicates drive signal Sd6. In addition, the times from time t1 to time t2, from time t3 to time t4, from time t5 to time t6, from time t7 to time t8, from time t9 to time t10, from time t11 to time t12, from time t13 to time t14, and from time t15 to time t16 are defined as dead times, which are periods during which the upper arm switching element and the lower arm switching element are not turned off simultaneously.

[0068] In the power conversion device 1 of the embodiment, as shown in FIG. 4(a), when a current flows through the diode connected in parallel to the switching elements SW1 and SW3 during the period from time t5 to time t6 or the period from time t13 to time t14, the switching elements SW1 and SW3 are switched from off to on. This can reduce the switching loss of the switching elements SW1 and SW3. Therefore, even if the duty ratio of the drive signals Sd1 and Sd3 increases due to the correction of the voltage command values ​​Vu*, Vv*, and Vw*, the total loss (the sum of the steady loss and the switching loss) can be equalized between the switching elements SW1 and SW3 and the switching elements SW2 and SW4, and the amount of heat generated per unit time can be equalized between the switching elements SW1 and SW3 and the switching elements SW2 and SW4.

[0069] In the power conversion device 1 of the embodiment, as shown in FIG. 4(d), when a current flows through a diode connected in parallel to the switching element SW6 during the period from time t7 to time t8 or the period from time t15 to time t16, the switching element SW6 is switched from off to on. This reduces the switching loss of the switching element SW6. Therefore, even if the duty ratio of the drive signal Sd6 increases due to the correction of the voltage command values ​​Vu*, Vv*, and Vw*, the overall loss can be equalized between the switching elements SW5 and SW6, and therefore the amount of heat generated per unit time can be equalized between the switching elements SW5 and SW6.

[0070] For example, assume that when current is concentrated in switching element SW5, the steady-state loss of switching element SW5 decreases from 20 [W] to 10 [W] and the steady-state loss of switching element SW6 increases from 10 [W] to 20 [W] by correcting the voltage command values ​​Vu*, Vv*, and Vw*. Note that the switching loss of switching element SW5 is 10 [W] and the switching loss of switching element SW6 is 0 [W].

[0071] In this case, the total loss of switching element SW5 will be 20 [W], and the total loss of switching element SW6 will also be 20 [W]. Since the total loss can be equalized between switching element SW5 and switching element SW6, the amount of heat generated per unit time can be equalized between switching element SW5 and switching element SW6.

[0072] Furthermore, the upper arm switching elements and the lower arm switching elements (switching elements SW1 and SW2, or switching elements SW3 and SW4, or switching elements SW5 and SW6) may be disposed adjacent to each other.

[0073] For example, if the amount of heat generated per unit time by the upper arm switching elements and the lower arm switching elements can be equalized by equalizing the overall losses of the upper arm switching elements and the lower arm switching elements, the upper arm switching elements and the lower arm switching elements can be arranged adjacent to each other, so there is no need to determine the overall layout of switching elements SW1 to SW6 taking into account the distribution of the amount of heat generated, making it easier to design the layout of switching elements SW1 to SW6 as a whole.

[0074] In this manner, the power conversion device 1 of the embodiment is configured to reduce the duty ratio of the drive signal that drives one of the switching elements by a predetermined duty ratio R when it is determined that current is flowing concentratedly through one of the switching elements in one of the series circuits SC1 to SC3.

[0075] This makes it possible to reduce steady-state losses in the switching element through which current is concentrated, and therefore to distribute the amount of heat generated per unit time of the switching element through which current is concentrated to the amount of heat generated per unit time of the other switching elements, thereby equalizing the amount of heat generated per unit time of each switching element.

[0076] The present invention is not limited to the above-described embodiment, and various improvements and modifications are possible without departing from the gist of the present invention.

[0077] <Variation 1> Fig. 5 is a diagram showing the power conversion device 1 in Modification 1. In Fig. 5, the same components as those shown in Fig. 1 are given the same reference numerals, and the description thereof will be omitted.

[0078] The power converter 1 shown in Fig. 5 differs from the power converter 1 shown in Fig. 1 in that it includes temperature sensors St1 to St6. The temperature sensors St1 to St6 are constituted by, for example, thermistors.

[0079] The temperature sensor St1 detects the temperature of the switching element SW1, and outputs the detected temperature to the control circuit CC.

[0080] The temperature sensor St2 detects the temperature of the switching element SW2, and outputs the detected temperature to the control circuit CC.

[0081] The temperature sensor St3 detects the temperature of the switching element SW3, and outputs the detected temperature to the control circuit CC.

[0082] The temperature sensor St4 detects the temperature of the switching element SW4, and outputs the detected temperature to the control circuit CC.

[0083] The temperature sensor St5 detects the temperature of the switching element SW5, and outputs the detected temperature to the control circuit CC.

[0084] The temperature sensor St6 detects the temperature of the switching element SW6, and outputs the detected temperature to the control circuit CC.

[0085] FIG. 6 is a flowchart showing the operation of the calculation unit 3 in the first modification.

[0086] First, the calculation unit 3 starts drive control of the electric motor M when an instruction to start driving the electric motor M is input by a user operating an input device or the like (step Stp1: Yes).

[0087] Next, if the temperatures of all of the switching elements SW1 to SW6 are lower than the threshold value (step Stp2': No), the calculation unit 3 determines the voltage command values ​​Vu*, Vv*, and Vw* based on the currents Iu to Iw, the position θ, and the rotation speed command value ω* as normal control (step Stp3).

[0088] On the other hand, when the temperature of the switching element of the upper arm of one of the series circuits is equal to or higher than the threshold value, or when the temperature of the switching element of the lower arm of one of the series circuits is equal to or higher than the threshold value (step Stp2': Yes), the calculation unit 3 determines the voltage command values ​​Vu*, Vv*, Vw* based on the currents Iu to Iw, the position θ, and the rotation speed command value ω* as neutral point control, and then corrects the voltage command values ​​Vu*, Vv*, Vw* so that the duty ratio of the drive signal for driving the switching element of the upper arm of one of the series circuits is reduced by a predetermined duty ratio R and the duty ratios of the drive signals for driving the switching elements of each of the lower arms of the remaining two series circuits are each reduced by a predetermined duty ratio R, or so that the duty ratio of the drive signal for driving the switching element of the lower arm of one of the series circuits is reduced by the predetermined duty ratio R and the duty ratios of the drive signals for driving the switching elements of each of the upper arms of the remaining two series circuits are each reduced by a predetermined duty ratio R (step Stp4).

[0089] Then, if an instruction to end the driving of the electric motor M has not been input by the user operating the vehicle Ve, etc. (step Stp5: No), the calculation unit 3 repeatedly executes the processing of steps Stp2' to Stp5, and if an instruction to end the driving is input (step Stp5: Yes), it ends the drive control of the electric motor M.

[0090] In this way, the power conversion device 1 of variant example 1 is configured to reduce the duty ratio of the drive signal that drives one of the switching elements in one of the series circuits SC1 to SC3 by a predetermined duty ratio R when the temperature of the one of the switching elements in the series circuits SC1 to SC3 is equal to or higher than a threshold value.

[0091] This makes it possible to reduce steady-state losses in switching elements whose temperatures are above a threshold value, thereby distributing the amount of heat generated per unit time of a switching element whose temperature is above a threshold value to the amount of heat generated per unit time of other switching elements, thereby equalizing the amount of heat generated per unit time of each switching element.

[0092] <Variation 2> The power conversion device 1 shown in Fig. 1 and the power conversion device 1 shown in Fig. 5 are configured to supply AC power to the motor M, but may be configured to supply AC power to the primary coil of a transformer of an isolated DC-DC converter. When configured in this way, the connection point of each switching element of one of two series circuits connected in parallel to each other is connected to one terminal of the primary coil, and the connection point of each switching element of the other series circuit is connected to the other terminal of the primary coil.

[0093] In this way, the power conversion device 1 of variant example 2 is configured to reduce the duty ratio of the drive signal that drives one of the switching elements by a predetermined duty ratio R when it is determined that current is flowing concentratedly in one of the switching elements in one of the two series circuits, or when the temperature of one of the switching elements in one of the two series circuits is equal to or higher than a threshold value.

[0094] This makes it possible to reduce steady-state losses in switching elements through which current is concentrated or switching elements whose temperature is above a threshold value, so that the heat generation per unit time of the switching elements through which current is concentrated or switching elements whose temperature is above a threshold value can be distributed to the heat generation per unit time of other switching elements, and the heat generation per unit time of each switching element can be equalized.

[0095] <Variation 3> In the above-described power conversion device 1, neutral point control is performed when it is determined that current is flowing in a concentrated manner through one of the switching elements of one of the multiple series circuits, regardless of whether the rotation speed ω is zero or not, or when the temperature of one of the switching elements of one of the multiple series circuits is equal to or higher than a threshold value. However, the power conversion device 1 may be configured to perform neutral point control when it is determined that current is flowing in a concentrated manner through one of the switching elements of one of the multiple series circuits and the rotation speed ω is zero or approximately zero, or when the temperature of one of the switching elements of one of the multiple series circuits is equal to or higher than a threshold value and the rotation speed ω is zero or approximately zero.

[0096] With this configuration, the steady-state loss of a switching element through which current flows in a concentrated manner or a switching element whose temperature is equal to or higher than a threshold can be reduced, so that the heat generation per unit time of a switching element through which current flows in a concentrated manner or a switching element whose temperature is equal to or higher than a threshold can be distributed to the heat generation per unit time of other switching elements, and the heat generation per unit time of each switching element can be equalized. [Explanation of symbols]

[0097] 1 Power conversion device 2 Storage section 3 Arithmetic section CC control circuit DC Drive Circuit Inv Inverter circuit C Capacitor SC1~SC3 series circuit SW1~SW6 Switching elements Si1~Si3 Current Sensors Sr Position Sensor St1~St6 Temperature sensors Vehicle M electric motor B Battery

Claims

1. A power conversion device that converts input power into a desired power and outputs the power, A plurality of series circuits each having two switching elements connected in series with each other and each connected in parallel to a power source; A control circuit for controlling the driving of each switching element of the plurality of series circuits; Equipped with When the control circuit determines that a current is flowing intensively through one of the switching elements in one of the plurality of series circuits, or when the temperature of the one of the switching elements is equal to or higher than a threshold value, the control circuit reduces a duty ratio of a drive signal that drives the one of the switching elements. Power conversion equipment.

2. The power conversion device according to claim 1, The control circuit switches the other switching element of one of the series circuits from off to on when a current flows through a diode connected in parallel to the other switching element of the one of the series circuits. Power conversion equipment.

3. The power conversion device according to claim 1, a U-phase series circuit in which a connection point between the U-phase upper arm switching element and the U-phase lower arm switching element is connected to a U-phase input terminal of a three-phase AC motor; a V-phase series circuit in which a connection point between a V-phase upper arm switching element and a V-phase lower arm switching element is connected to a V-phase input terminal of the three-phase AC motor; a W-phase series circuit in which a connection point between the W-phase upper arm switching element and the W-phase lower arm switching element is connected to a W-phase input terminal of the three-phase AC motor; Equipped with The control circuit includes: when it is determined that a current is flowing intensively through the U-phase upper arm switching element, reducing a duty ratio of each of the drive signals of the U-phase upper arm switching element, the V-phase lower arm switching element, and the W-phase lower arm switching element; when it is determined that a current is flowing intensively through the U-phase lower arm switching element, reducing a duty ratio of each of the drive signals of the U-phase lower arm switching element, the V-phase upper arm switching element, and the W-phase upper arm switching element; when it is determined that a current is flowing intensively through the V-phase upper arm switching element, reducing a duty ratio of each of the drive signals of the V-phase upper arm switching element, the U-phase lower arm switching element, and the W-phase lower arm switching element; when it is determined that a current is flowing intensively through the V-phase lower arm switching element, reducing a duty ratio of each of the drive signals of the V-phase lower arm switching element, the U-phase upper arm switching element, and the W-phase upper arm switching element; when it is determined that a current is flowing intensively through the W-phase upper arm switching element, reducing a duty ratio of each of the drive signals of the W-phase upper arm switching element, the U-phase lower arm switching element, and the V-phase lower arm switching element; When it is determined that a current is flowing intensively in the W-phase lower arm switching element, the duty ratio of each of the drive signals of the W-phase lower arm switching element, the U-phase upper arm switching element, and the V-phase upper arm switching element is reduced. A power conversion device that performs at least one of the above.

4. The power conversion device according to claim 1, The two switching elements are disposed adjacent to each other. Power conversion equipment.

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