Power Conversion Device

Abstract

A power conversion device capable of appropriately implementing overcurrent protection for a system to which the power conversion device is diverted and an inverter is provided. [Solution] The power conversion device includes a first inverter 41 electrically connectable to the armature winding of an induction machine 71, an internal control circuit 60, a case member 44, and an external control circuit 80. The first inverter 41 and the internal control circuit 60 housed in the case member 44, and the case member 44 form a control unit 40. The control unit 40 is diverted from another system. The external control circuit 80 calculates a torque command value Trtgt to be input to the internal control circuit 60. Of the internal control circuit 60 and the external control circuit 80, only the external control circuit 80 has a function to protect the diverted system and the first inverter 41 from overcurrent.

Description

[Technical Field]

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

[0002] Conventionally, as described in Patent Document 1, for example, a power conversion device applied to a system including a rotating electric machine has been known. The power conversion device includes an inverter having upper and lower arm switches, and a control circuit to which a torque command value of the rotating electric machine is input. The control circuit generates a drive signal that controls the torque of the rotating electric machine to the input torque command value and turns the upper and lower arm switches on or off. The control circuit supplies the generated drive signal to the gates of the upper and lower arm switches. As a result, the torque of the rotating electric machine is controlled to the torque command value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-33298 Summary of the Invention [Problem to be solved by the invention]

[0004] The inverter and the control circuit are housed in a case member, and the case member and the inverter and the control circuit housed in the case member constitute a control unit.

[0005] It is conceivable that a control unit installed in one system could be repurposed for another system. For example, the control unit is installed in a mobile object such as an electric vehicle (e.g., HEV or BEV). As mobile objects become more widespread, the number of mobile objects being discarded also tends to increase. From the perspective of a circular economy, it is conceivable to remove used control units from discarded mobile objects and repurpose the removed control units for another system.

[0006] Here, there is a concern that the system and inverter to which the power is diverted may not be able to be properly protected from overcurrent.

[0007] A primary object of the present disclosure is to provide a power conversion device that can protect a system and an inverter to which the power conversion device is diverted from overcurrent. [Means for solving the problem]

[0008] The present disclosure provides a power conversion device applied to a system including a rotating electric machine, an inverter having upper and lower arm switches, the connection points of the upper and lower arm switches being electrically connectable to the armature windings of the rotating electric machine; an internal control circuit to which a torque command value of the rotary electric machine is input; a case member that houses the inverter and the internal control circuit; a separate control circuit separate from the internal control circuit; Equipped with the inverter and the internal control circuit housed in the case member, and the case member constitute a control unit, the control unit is diverted from a system other than the system; The internal control circuit includes: generating a drive signal for controlling the torque of the rotary electric machine to the input torque command value, the drive signal turning on or off the upper and lower arm switches; supplying the generated drive signal to the gates of the upper and lower arm switches; the separate control circuit has a command value calculation unit that calculates the torque command value to be input to the internal control circuit, Of the internal control circuit and the separate control circuit, only the separate control circuit is provided with a protection unit that protects the inverter and the system from an overcurrent.

[0009] The power conversion device of the present disclosure includes a separate control circuit, which has a command value calculation unit that calculates a torque command value to be input to the internal control circuit.

[0010] In the present disclosure, the separate control circuit includes a protection unit that protects the diverted system and the inverter from overcurrent, thereby enabling the diverted system and the inverter to be appropriately protected from overcurrent. [Brief explanation of the drawings]

[0011] [Figure 1] Overall configuration diagram of an in-vehicle system. [Figure 2] FIG. 2 is a diagram showing a control unit and a rotating electric machine mounted on a vehicle. [Figure 3] FIG. [Figure 4] FIG. 1 is a diagram showing a control unit connected to a factory induction machine and a system power supply. [Figure 5] FIG. [Figure 6] 4 is a time chart showing an example of a transition of a rotation speed command value; [Figure 7] 5 is a time chart showing an example of a gradual change process in an external control circuit. [Figure 8] FIG. 4 is a diagram showing torque drooping processing in an external control circuit. [Figure 9] FIG. 10 is a diagram showing a control unit connected to an induction machine and a system power supply in a factory according to another embodiment. [Figure 10] FIG. 10 is a diagram showing a control unit connected to an induction machine and a system power supply in a factory according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a power conversion device according to an embodiment of the present disclosure will be described with reference to the drawings.

[0013] 1 and 2 show various electrical devices mounted on a vehicle 10. FIG.

[0014] The vehicle 10 includes a DC power supply 11, a first rotating electric machine 21, and a second rotating electric machine 22. The DC power supply 11 is a secondary battery that can be charged and discharged, and specifically, for example, a nickel-metal hydride battery or a lithium-ion battery. The DC power supply 11 may also be, for example, a fuel cell.

[0015] The first rotating electric machine 21 and the second rotating electric machine 22 are, for example, synchronous machines. Drive wheels of the vehicle 10 are connected to the rotors of the first rotating electric machine 21 and the second rotating electric machine 22 so as to be capable of transmitting power. The first rotating electric machine 21 functions as an electric motor that rotates the drive wheels to propel the vehicle 10. The second rotating electric machine 22 functions as a generator that generates electricity using the rotational energy of the drive wheels as input.

[0016] The vehicle 10 includes a control unit 40. The control unit 40 includes a first inverter 41, a second inverter 42, and a smoothing capacitor 43. The first inverter 41 and the second inverter 42 are three-phase inverters and include upper and lower arm switches SH and SL. Each of the switches SH and SL is, for example, an N-channel MOSFET or an IGBT.

[0017] In each phase of the first inverter 41, the armature winding of the first rotating electric machine 21 is electrically connected to the connection point of the upper and lower arm switches SH, SL. The first inverter 41 converts DC power supplied from the DC power source 11 into AC power and supplies it to the armature winding.

[0018] In each phase of the second inverter 42, the armature winding of the second rotating electric machine 22 is electrically connected to the connection point of the upper and lower arm switches SH, SL. The second inverter 42 converts the AC power supplied from the armature winding into DC power and supplies it to the DC power source 11.

[0019] The control unit 40 includes a first current sensor 51, a second current sensor 52, and an internal control circuit 60. The first current sensor 51 detects currents for two phases out of the currents (e.g., line currents) of the three-phase armature windings of the first rotating electric machine 21. The second current sensor 52 detects currents for two phases out of the currents (e.g., line currents) of the three-phase armature windings of the second rotating electric machine 22. The detection values ​​of the current sensors 51, 52 are input to the internal control circuit 60. Note that each of the current sensors 51, 52 may detect currents for three phases.

[0020] The vehicle 10 includes a first rotation angle sensor 31, a second rotation angle sensor 32, and a host ECU 33. The first rotation angle sensor 31 detects the rotation angle (electrical angle) of the rotor of the first rotating electric machine 21. The second rotation angle sensor 32 detects the rotation angle (electrical angle) of the rotor of the second rotating electric machine 22. Each of the rotation angle sensors 31, 32 is, for example, a resolver. The detection values ​​of each of the rotation angle sensors 31, 32 are input to an internal control circuit 60.

[0021] The control unit 40 includes a case member 44. The case member 44 houses a first inverter 41, a second inverter 42, a smoothing capacitor 43, a first current sensor 51, a second current sensor 52, and an internal control circuit 60. In other words, the control unit 40 is configured by the inverters 41, 42, the smoothing capacitor 43, the current sensors 51, 52, and the internal control circuit 60 housed in the case member 44, and the case member 44.

[0022] The internal control circuit 60 is primarily composed of a computer (specifically, a microcomputer). The microcomputer includes a CPU (Central Processing Unit). The functions provided by the microcomputer can be provided by software stored in a physical memory device and a computer that executes the software, by software alone, by hardware alone, or by a combination of these. For example, when the microcomputer is provided by hardware electronic circuits, the functions can be provided by digital circuits including multiple logic circuits or analog circuits. For example, the microcomputer executes programs stored in a non-transitory tangible storage medium that serves as its own storage unit. The programs include, for example, processing programs described below. A method corresponding to the program is performed by executing a set of instructions that constitute the program. The storage unit is, for example, a non-volatile memory.

[0023] The internal control circuit 60 is a circuit for controlling the torque of the first rotating electrical machine 21 to the torque command value Trtgt input from the host ECU 33. The internal control circuit 60 will be described below with reference to FIG.

[0024] A torque command value Trtgt transmitted from the host ECU 33 is input to a command value input terminal CT of the internal control circuit 60. The host ECU 33 transmits, for example, a torque command value Trtgt that prevents an overcurrent from flowing through the first inverter 41. A command current setting unit 62 sets d- and q-axis command currents Idtgt and Iqtgt based on the input torque command value Trtgt.

[0025] U- and V-phase currents Iur and Ivr detected by the first current sensor 51 are input to first and second current input terminals CI1 and CI2 of the internal control circuit 60. A first electrical angle θ1 detected by the first rotation angle sensor 31 is input to an angle input terminal CA of the internal control circuit 60. A first coordinate converter 61 converts the U-, V-, and W-phase currents in a three-phase fixed coordinate system into a d-axis current Idr and a q-axis current Iqr in a two-phase rotating coordinate system (dq coordinate system) based on the input U- and V-phase currents Iur and Ivr and the input first electrical angle θ1.

[0026] The d-axis deviation calculation unit 63 calculates the d-axis current deviation ΔId by subtracting the d-axis current Idr from the d-axis command current Idtgt. The q-axis deviation calculation unit 64 calculates the q-axis current deviation ΔIq by subtracting the q-axis current Iqr from the q-axis command current Iqtgt.

[0027] The command voltage calculation unit 65 calculates a d-axis command voltage Vd as a manipulated variable for feedback-controlling the d-axis current Idr to the d-axis command current Idtgt based on the d-axis current deviation ΔId. Also, the command voltage calculation unit 65 calculates a q-axis command voltage Vq as a manipulated variable for feedback-controlling the q-axis current Iqr to the q-axis command current Iqtgt based on the q-axis current deviation ΔIq.

[0028] The second coordinate converter 66 converts the d- and q-axis command voltages Vd, Vq in the two-phase rotating coordinate system into U-, V- and W-phase command voltages VU*, VV*, and VW* in the three-phase fixed coordinate system based on the d- and q-axis command voltages Vd, Vq and the first electrical angle θ1. In this embodiment, the U-, V- and W-phase command voltages VU*, VV*, and VW* have sinusoidal waveforms with a phase difference of 120° in electrical angle.

[0029] The signal generating unit 67 generates drive signals for the upper and lower arm switches SH, SL of the U, V, and W phases of the first inverter 41 based on the U, V, and W phase command voltages VU*, VV*, and VW*. The drive signals are signals that instruct the switches to be on or off. The signal generating unit 67 supplies the generated drive signals to the gates of the upper and lower arm switches SH, SL of each phase of the first inverter 41. As a result, in each phase, the upper arm switch SH and the lower arm switch SL are alternately turned on with dead time therebetween.

[0030] The internal control circuit 60 also has a function of generating drive signals for the upper and lower arm switches SH, SL of each phase of the second inverter 42 in order to perform synchronous rectification in the second inverter 42. More specifically, the detection values ​​of the second current sensor 52 and the second rotation angle sensor 32 are input to the internal control circuit 60. The internal control circuit 60 generates drive signals for the upper and lower arm switches SH, SL of each phase in order to perform synchronous rectification based on the detection values ​​of the second current sensor 52 and the second rotation angle sensor 32. The internal control circuit 60 supplies the generated drive signals to the gates of the upper and lower arm switches SH, SL of each phase of the second inverter 42.

[0031] Incidentally, as vehicles become more widespread, the number of vehicles being discarded also tends to increase. From the perspective of a circular economy, it is conceivable to remove a used control unit 40 from a vehicle 10 to be discarded and reuse the removed control unit 40. In this embodiment, the used control unit 40 is diverted to a factory equipment system. In this case, a situation may arise in which the diverted system and the first inverter 41 are unable to properly implement overcurrent protection. Specifically, because the system before the diverted system is designed specifically for in-vehicle use, there is a concern that the diverted system will be unable to properly implement overcurrent protection.

[0032] Therefore, in this embodiment, overcurrent protection between the facility system of the diverted power source and the first inverter 41 of the control unit 40 can be appropriately implemented.

[0033] Figure 4 shows the equipment system to which the system will be repurposed.

[0034] The system includes an induction machine 71, a system power supply 72, and a noise filter 73, which are arranged outside the control unit 40. The system power supply 72 and the induction machine 71 are electrically connected by a first inverter 41 and a second inverter 42 of the control unit 40. The armature winding of the induction machine 71 is electrically connected to the connection points of the upper and lower arm switches SH, SL of the first inverter 41. The system power supply 72 is electrically connected to the connection points of the upper and lower arm switches SH, SL of the second inverter 42 via a noise filter 73. The induction machine 71 is used, for example, to drive a dust collector, a coolant pump, a ventilation fan, or an air conditioner in a factory.

[0035] The system includes an external current sensor 74, an external voltage sensor 75, and an external control circuit 80 (corresponding to a "separate control circuit"), which are arranged outside the control unit 40. The external current sensor 74 detects currents for two phases out of the currents (e.g., line currents) of the three-phase armature windings of the induction machine 71. The external voltage sensor 75 detects the line voltage of the induction machine 71. The detected values ​​of the external current sensor 74 and the external voltage sensor 75 are input to the external control circuit 80.

[0036] The system includes a host ECU 76 that is disposed outside the control unit 40. The host ECU 76 transmits a rotation speed command value Ntgt of the rotor of the induction machine 71, a reference rotation speed Nst of the rotor of the induction machine 71, and a first current threshold value TH1 to an external control circuit 80.

[0037] The external control circuit 80 is a circuit for calculating a torque command value Trtgt for the induction machine 71 based on the rotation speed command value Ntgt input from the host ECU 76. The external control circuit 80 will be described below with reference to FIG.

[0038] The voltage coordinate conversion unit 81 calculates the d-axis voltage Vdr and the q-axis voltage Vqr in the dq coordinate system based on the input detection values ​​Vuv, Vvw, and Vwu of the external voltage sensor 75 and the phase angle θr calculated by the phase angle conversion unit 84, which will be described later.

[0039] Based on the calculated d-axis voltage Vdr and q-axis voltage Vqr, voltage absolute value calculation unit 82 calculates the magnitude of the voltage vector (hereinafter referred to as voltage amplitude Vr) applied from first inverter 41 to the armature winding of induction machine 71. The d-axis component of voltage amplitude Vr is d-axis voltage Vdr, and the q-axis component of voltage amplitude Vr is q-axis voltage Vqr.

[0040] The normalization unit 83 calculates a normalized rotation speed Nc by normalizing the rotation speed command value Ntgt output from a gradual change unit 93, which will be described later, by the reference rotation speed Nst input from the host ECU 76. Specifically, the normalization unit 83 calculates the normalized rotation speed Nc (=Ntgt / Nst) by dividing the rotation speed command value Ntgt by the reference rotation speed Nst.

[0041] The phase angle conversion unit 84 calculates the phase angle θr based on the normalized rotation speed Nc. The phase angle conversion unit 84 calculates the phase angle θr based on, for example, a time integral value of the normalized rotation speed Nc. The calculated phase angle θr is input to the angle input terminal CA of the internal control circuit 60 shown in FIG. 3. The input phase angle θr is used in the first coordinate conversion unit 61 and the second coordinate conversion unit 66.

[0042] The voltage command value calculation unit 85 calculates a voltage command value Vtgt for V / f control based on the calculated normalized rotation speed Nc. The voltage command value Vtgt is a command value for the voltage amplitude Vr. The voltage command value calculation unit 85 calculates the voltage command value Vtgt so that the ratio of the voltage command value Vtgt to the normalized rotation speed Nc is constant.

[0043] A deviation calculation unit 86 calculates a voltage deviation ΔV by subtracting the calculated voltage amplitude Vr from the calculated voltage command value Vtgt. A command torque calculation unit 87 calculates a torque command value Trq as a manipulated variable for feedback control of the voltage amplitude Vr to the voltage command value Vtgt, based on the calculated voltage deviation ΔV.

[0044] The torque drooping unit 94 performs droop control on the calculated torque command value Trq to calculate a final torque command value Trtgt. The calculated torque command value Trtgt is input to a command value input terminal CT of the internal control circuit 60 shown in FIG. 3. The input torque command value Trtgt is used in the command current setting unit 62. As a result, the torque of the induction machine 71 is controlled to the torque command value Trtgt.

[0045] In this embodiment, the voltage coordinate conversion unit 81, the voltage absolute value calculation unit 82, the normalization unit 83, the phase angle conversion unit 84, the voltage command value calculation unit 85, the deviation calculation unit 86, and the command torque calculation unit 87 correspond to the "command value calculation unit."

[0046] In addition, when the internal control circuit 60 is installed in the vehicle 10, the internal control circuit 60 converts the AC power input from the system power supply 72 to the second inverter 42 via the noise filter 73 into DC power and supplies it to the first inverter 41 using its AC-DC conversion function.

[0047] The current coordinate conversion unit 90 converts the U-, V-, and W-phase currents in the three-phase fixed coordinate system into a d-axis current Idx and a q-axis current Iqx in the dq coordinate system based on the input detection values ​​Iux and Ivx of the external current sensor 74 and the calculated phase angle θr.

[0048] Based on the calculated d-axis current Idx and q-axis current Iqx, the current absolute value calculation unit 91 calculates the magnitude of the current vector (hereinafter referred to as current amplitude Ia) flowing through the armature winding of the induction machine 71. The d-axis component of the current amplitude Ia is the d-axis current Idx, and the q-axis component of the current amplitude Ia is the q-axis current Iqx.

[0049] The determination unit 92 determines whether the calculated current amplitude Ia is greater than the first current threshold TH1 input from the host ECU 76. The determination result of the determination unit 92 is input to the gradual change unit 93.

[0050] The rotation speed command value Ntgt is input to the gradual change unit 93 from the host ECU 76. The gradual change unit 93 performs gradual change control to gradually change the input rotation speed command value Ntgt in accordance with the determination result of the determination unit 92 so that the deviation between the current rotation speed and the rotation speed command value Ntgt becomes a desired value.

[0051] FIG. 6 shows an example of the transition of the rotational speed command value Ntgt set by the host ECU 76.

[0052] At time t1, the host ECU 76 starts to increase the rotation speed command value Ntgt from 0 toward the first rotation speed N1. The host ECU 76 gradually increases the current rotation speed command value Ntgt toward the changed first rotation speed N1, and sets the rotation speed command value Ntgt to the first rotation speed N1 at time t2. The period from time t1 to t2 is, for example, 2 to 5 seconds.

[0053] During the period from time t2 to time t3, the host ECU 76 performs constant speed setting to maintain the rotation speed command value Ntgt at the first rotation speed N1.

[0054] At time t3, the host ECU 76 starts to increase the rotation speed command value Ntgt from the first rotation speed N1 toward the second rotation speed N2. The host ECU 76 gradually increases the current rotation speed command value Ntgt toward the changed second rotation speed N2, and sets the rotation speed command value Ntgt to the second rotation speed N2 at time t4. Note that the period from time t3 to t4 is, for example, the same as the period from time t1 to t2.

[0055] During the period from time t4 to time t5, the host ECU 76 performs constant speed setting to maintain the rotation speed command value Ntgt at the second rotation speed N2.

[0056] At time t5, the host ECU 76 starts to decrease the rotation speed command value Ntgt from the second rotation speed N2 toward 0. The host ECU 76 gradually decreases the current rotation speed command value Ntgt toward the changed value of 0, and at time t5, the rotation speed command value Ntgt becomes 0. Note that the period from time t5 to t6 is the same as, for example, the period from time t1 to t2.

[0057] During the transition periods from time t1 to t2, t3 to t4, and t5 to t6, gradual change control is performed, thereby suppressing an increase in the deviation between the rotational speed command value Ntgt and the rotational speed of the rotor, thereby suppressing the occurrence of a situation in which an overcurrent flows through the armature winding of the induction machine 71 and the first inverter 41.

[0058] In contrast, when the rotation speed command value Ntgt is changed stepwise, the rotation speed of the rotor is slow to follow the rotation speed command value Ntgt during the transition period, which increases the deviation between the rotation speed command value Ntgt and the rotation speed of the rotor, causing an overcurrent to flow through the armature winding of the induction machine 71 and the first inverter 41.

[0059] When the gradual change unit 93 receives a determination result from the determination unit 92 that the current amplitude Ia has exceeded the first current threshold TH1 during execution of the gradual change control, the gradual change unit 93 performs reduction control to reduce the gradual change speed of the rotation speed command value Ntgt to a value lower than that before the determination result was received. Specifically, as shown in FIG. 7, the gradual change unit 93 sets the gradual change speed to 0 at time t1. This makes it possible to suppress an increase in the deviation between the rotation speed command value Ntgt and the rotor rotation speed, which could not be addressed by the gradual change control. As a result, the induction machine 71 and the first inverter 41 can be protected from overcurrent.

[0060] After the gradual change speed is set to 0, the gradual change unit 93 acquires from the determination unit 92 a determination result that the current amplitude Ia has fallen below the first current threshold TH1 at time t2. In this case, the gradual change unit 93 resumes the gradual change control.

[0061] It should be noted that the gradual change unit 93 does not have to set the gradual change rate of the rotation speed command value Ntgt to 0 during the decrease control.

[0062] Returning to the description of FIG. 5 , the torque drooping unit 94 receives the torque command value Trq calculated by the command torque calculation unit 87 and the current amplitude Ia calculated by the current absolute value calculation unit 91. When the torque drooping unit 94 determines that the current amplitude Ia exceeds a second current threshold TH2 that is greater than the first current threshold TH1, the torque drooping unit 94 performs drooping control, in which the torque command value Trtgt obtained by lowering the input torque command value Trq is transmitted to the internal control circuit 60. Specifically, the torque drooping unit 94 multiplies the torque command value Trq by a coefficient K, and transmits the resulting value to the internal control circuit 60 as the torque command value Trtgt (=K×Trq). As shown in FIG. 8 , when the current amplitude Ia is lower than the second current threshold TH2, the torque drooping unit 94 sets the coefficient K to 1. On the other hand, when the current amplitude Ia exceeds the second current threshold TH2, the torque drooping unit 94 sets the coefficient K to a value less than 1, specifically, for example, to 0. This makes it possible to cope with an increase in current amplitude and protect the induction machine 71 and the first inverter 41 from an overcurrent.

[0063] Since TH2 is set to be greater than TH1, drooping control is executed when the overcurrent cannot be suppressed by the gradual change control or the stop control. This allows the induction machine 71 to continue operating as long as possible while protecting the induction machine 71 and the first inverter 41 from overcurrent.

[0064] As described above, in this embodiment, of the internal control circuit 60 and the external control circuit 80, only the external control circuit 80 is provided with the gradual change unit 93 and the torque drooping unit 94 (corresponding to the "protection unit") that protect the diverted system and the first inverter 41 from overcurrent. Therefore, the diverted system and the first inverter 41 can be appropriately protected from overcurrent.

[0065] <Other embodiments> The above embodiment may be modified as follows.

[0066] 9 , the system may include a voltage sensor 77 that detects the voltage of the phase that is the target of detection by the external current sensor 74, and a phase angle calculation circuit 78. The phase angle calculation circuit 78 calculates a phase angle θr based on the phase difference between the phase voltage detected by the voltage sensor 77 and the phase current detected by the external current sensor 74. The calculated phase angle θr is input to an angle input terminal CA of the internal control circuit 60.

[0067] Current detection values ​​for three phases may be input to the current coordinate conversion unit 90 shown in FIG.

[0068] Each detected value input to the external control circuit 80 shown in FIG. 5 may be a filtered value.

[0069] The voltage coordinate conversion unit 81, the voltage absolute value calculation unit 82, the current coordinate conversion unit 90, and the current absolute value calculation unit 91 shown in FIG.

[0070] In the system shown in FIG. 4, a synchronous machine may be provided instead of the induction machine 71.

[0071] The mobile body on which the pre-reuse control unit 40 is installed is not limited to a vehicle, but may be, for example, an aircraft or a ship. Also, the target on which the pre-reuse control unit 40 is installed is not limited to a mobile body, but may be a stationary system.

[0072] The control unit 40 can be used in applications other than factory equipment systems.

[0073] As shown in FIG. 10, the separate control circuit 180 may be provided inside the case member 44 .

[0074] The control unit 40 is not limited to a second-hand product, but may be a new product. [Explanation of symbols]

[0075] 41, 42...first and second inverters, 40...control unit, 44...case member, 60...internal control circuit, 71...induction motor, 80...external control circuit, 93...gradual change section, 94...torque dropping section.

Claims

1. A power conversion device applied to a system including a rotating electric machine (71), an inverter (41) having upper and lower arm switches (SH, SL), the connection points of the upper and lower arm switches being electrically connectable to the armature windings of the rotating electric machine; an internal control circuit (60) to which a torque command value (Trtgt) of the rotating electrical machine is input; a case member (44) that houses the inverter and the internal control circuit; a separate control circuit (80, 180) separate from the internal control circuit; Equipped with The inverter and the internal control circuit housed in the case member, and the case member constitute a control unit (40), the control unit is diverted from a system other than the system; The internal control circuit includes: generating a drive signal for controlling the torque of the rotary electric machine to the input torque command value, the drive signal turning on or off the upper and lower arm switches; supplying the generated drive signals to the gates of the upper and lower arm switches; The separate control circuit has a command value calculation unit (81 to 87) that calculates the torque command value to be input to the internal control circuit, A power conversion device, wherein only the separate control circuit out of the internal control circuit and the separate control circuit is provided with a protection unit (93, 94) that protects the inverter and the system from an overcurrent.

2. A rotational speed command value (Ntgt) of the rotor of the rotating electric machine is input to the separate control circuit, the command value calculation unit calculates the torque command value based on the input rotation speed command value; As the protective part, 2. The power conversion device according to claim 1, further comprising: a gradual change unit that, when the input rotation speed command value changes, gradually changes the current rotation speed command value toward the changed rotation speed command value.

3. The separate control circuit receives an input of a current value flowing through the armature winding, 3. The power conversion device according to claim 2, wherein, when the gradual change unit determines that the input current value has exceeded a current threshold (TH1) while gradually changing the rotation speed command value, the gradual change unit reduces a rate of gradual change of the rotation speed command value to a rate lower than that before it determined that the current value has exceeded the current threshold.

4. The power conversion device according to claim 3 , wherein the gradual change unit reduces the gradual change speed of the rotational speed command value to zero.

5. the current threshold is a first current threshold (TH1); As the protective part, 5. The power conversion device according to claim 3, further comprising a torque drooping unit (94) that reduces the torque command value input to the internal control circuit when it is determined that the input current value exceeds a second current threshold (TH2) that is greater than the first current threshold.

6. The separate control circuit receives an input of a current value flowing through the armature winding, As the protective part, 3. The power conversion device according to claim 1, further comprising a torque drooping unit (94) that reduces the torque command value input to the internal control circuit when it is determined that the input current value exceeds a current threshold (TH2).

7. The power conversion device according to any one of claims 1 to 4, wherein the rotating electric machine is an induction machine.

8. The power conversion device according to any one of claims 1 to 4, wherein the separate control circuit (80) is provided outside the case member.

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