JP7199469B2 - power converter - Google Patents

Description

The present application relates to a power converter.

2. Description of the Related Art A power conversion device is mounted on a vehicle such as a device having an electric motor as a load, a hybrid vehicle equipped with an electric motor and an engine, an electric vehicle, or the like. In the case of a vehicle, when the vehicle runs over a curb and the tires are locked, the accelerator pedal is not sufficiently depressed, and when the vehicle is on a steep slope, the vehicle stops and the motor locks. Further, in a vehicle, when climbing a slope at extremely low speed, the rotor may not be able to follow the rotation, and the electric motor may stall. When the electric motor is locked or stalled, a specific power conversion element among a plurality of power conversion elements, that is, a switching element and a freewheeling diode, which constitutes the power conversion device, is supplied with a large current for a long period of time. It is necessary to take measures to prevent thermal destruction of the element.

The power conversion device of Patent Document 1 includes a calorific value measuring means for measuring each loss of a plurality of power conversion elements constituting the power conversion device, and the thermal resistance value of each power conversion device is stored in advance. The power conversion device of Patent Document 1 calculates the temperature rise in each power conversion element based on the heat resistance value and the amount of loss measured by the heat generation measuring means, and flows to the power conversion element with the maximum calculated temperature rise. It is disclosed to change the on/off timing of the drive signal for each power conversion element generated by the control arithmetic means so as to distribute the current to other elements.

Japanese Patent No. 3638265 (Figs. 1 and 12)

In a power conversion device mounted on a vehicle or the like, the energization rate of the switching element is higher than that of the freewheeling diode during steady operation. One of the factors that determine the size of the power conversion device is the size of the power conversion element. Therefore, from the viewpoint of the duty ratio during steady operation, it is common to design the freewheeling diodes smaller than the switching elements in terms of the size of the power conversion elements that constitute the power converter. Therefore, if the freewheeling diode is designed to be smaller than the switching element in the power conversion device of Patent Document 1, the temperature rise will dramatically increase when a large current flows through the freewheeling diode when the motor is locked or stalled. Therefore, the current distribution may reach a limit. In order to avoid a rapid temperature rise, there is a problem that the free wheel diode is enlarged.

An object of the technology disclosed in the specification of the present application is to realize a power converter that is small and that can prevent a rapid temperature rise.

An example power conversion device disclosed in the present specification supplies AC power converted from DC power to drive a motor. A power conversion device includes a plurality of switching elements and a freewheeling diode, and a plurality of temperature monitors that output first temperature information that is temperature information of each switching element, a power conversion circuit that supplies AC power to drive a motor, It includes a control calculation unit that determines switching timings of a plurality of switching elements in the power conversion circuit and generates a first drive signal, and a rotation detector that detects the rotor position of the electric motor. The power conversion device further includes an element temperature estimating unit that estimates second temperature information, which is temperature information of the freewheeling diode, based on the first temperature information, and a stall determination unit that determines a stall state of the motor based on the rotor position of the motor. a loss reduction unit that reduces the amount of heat generated by the switching element when the stall determination unit determines a stall state; and a first drive signal that is output as a second drive signal without being changed, or the first drive signal. and a gate drive circuit that outputs a third drive signal that switches the switching elements according to the second drive signal to the power conversion circuit. and have. When the stall state is determined by the stall determining unit and the first temperature information of the switching element connected in series with the freewheeling diode in which the second temperature information is maximized by the operation of the loss reducing unit is lowered Only the second drive in which the ON time of the switching element in the first drive signal is changed so as to distribute the current flowing through the freewheeling diode with the maximum second temperature information to the switching element connected in series with the freewheeling diode. Output the signal to the gate drive circuit.

In one example of the power conversion device disclosed in the specification of the present application, the first temperature information of the switching element connected in series with the freewheeling diode in which the stall state is determined and the second temperature information is maximum is the loss reduction unit. Since the current flowing through the freewheeling diode is distributed to the switching elements connected in series only when it is lowered by the operation, it is possible to reduce the size and prevent a rapid temperature rise.

1 is a diagram showing a configuration of a power converter according to Embodiment 1; FIG. 2 is a diagram showing the configuration of the power conversion circuit of FIG. 1; FIG. FIG. 2 is a diagram showing the configuration of a control calculation unit in FIG. 1; 5 is a diagram showing an example of loss calculation of the power conversion device according to Embodiment 1; FIG. It is a figure which shows the energization time distribution example of the power converter device before loss reduction operation|movement. FIG. 4 is a diagram showing an example of energization time distribution of the power conversion device according to Embodiment 1; It is a figure which shows the example of the maximum loss of the power converter device before loss reduction operation|movement. 4 is a diagram showing a maximum loss example of the power conversion device according to Embodiment 1; FIG. 2 is a diagram showing a hardware configuration that implements functions of the power converter according to Embodiment 1; FIG. FIG. 7 is a diagram showing the configuration of a first power conversion device according to Embodiment 2; FIG. 7 is a diagram showing the configuration of a second power conversion device according to Embodiment 2; FIG. 10 is a diagram showing the configuration of a first power conversion device according to Embodiment 3; FIG. 10 is a diagram showing the configuration of a second power conversion device according to Embodiment 3; FIG. 13 is a diagram showing the configuration of a power conversion device according to Embodiment 4; FIG. 13 is a diagram showing a configuration of a power conversion device according to Embodiment 5; FIG. 13 is a diagram showing a configuration of a power conversion device according to Embodiment 6;

Embodiment 1.
FIG. 1 is a diagram showing the configuration of a power converter according to Embodiment 1. FIG. 2 is a diagram showing the configuration of the power conversion circuit in FIG. 1, and FIG. 3 is a diagram showing the configuration of the control calculation section in FIG. FIG. 4 is a diagram showing an example of loss calculation of the power converter according to Embodiment 1. FIG. FIG. 5 is a diagram showing an example of energization time distribution of the power converter before the loss reduction operation, and FIG. 6 is a diagram showing an example of energization time distribution of the power converter according to the first embodiment. FIG. 7 is a diagram showing an example of the maximum loss of the power converter before the loss reduction operation, and FIG. 8 is a diagram showing an example of the maximum loss of the power converter according to the first embodiment. FIG. 9 is a diagram showing a hardware configuration that realizes the functions of the power converter according to Embodiment 1. FIG. The power conversion device 1 includes a power conversion circuit 4, a current detector 7, a rotation detector 9 for detecting the rotor position θ, a gate drive circuit 8, a duty control section 23, a control calculation section 3, a loss reduction section 26, and a stall determination. A unit 27 and an element temperature estimating unit 25 are provided. The power converter 1 drives, for example, a three-phase AC electric motor 2 that is a load. 1 and 2 show an example in which the load of the power converter 1 is a three-phase alternating current electric motor 2 . In this case, the power conversion circuit 4 converts DC power into AC power, and supplies the AC power converted from the DC power to the electric motor 2 . The current detector 7 detects the value of the output current output from the power conversion circuit 4 to the electric motor 2, that is, the output current values iu, iv, and iw.

The power conversion circuit 4 includes two power conversion elements, a switching element 5a such as an IGBT (Insulated Gate Bipolar Transistor) and a freewheeling diode 6a connected in anti-parallel to the switching element 5a. It consists of two arms. The power conversion circuit 4 shown in FIG. 2 has six arms. A leg configured by connecting in series a first arm having a switching element 5a and a freewheeling diode 6a and a second arm having a switching element 5b and a freewheeling diode 6b is connected to a load between the two arms. It has an output terminal 51u to be connected. A leg configured by serially connecting a third arm having a switching element 5c and a freewheeling diode 6c and a fourth arm having a switching element 5d and a freewheeling diode 6d is connected to a load between the two arms. It has an output terminal 51v to be connected. A leg configured by serially connecting a fifth arm having a switching element 5e and a freewheeling diode 6e and a sixth arm having a switching element 5f and a freewheeling diode 6f is connected to a load between the two arms. It has an output terminal 51w to be connected. As appropriate, the reference numerals for the switching elements are 5 in general, and 5a to 5f when distinguishing them. 6 is used as the symbol for the freewheeling diode in general, and 6a to 6f are used when distinguishing between them.

One end of the three legs is connected to the high potential side wiring 52p, and the other end of the three legs is connected to the low potential side wiring 52n. A DC power supply 10 and a smoothing capacitor 11 are connected between an input terminal 50p connected to a high-potential wiring 52p and an input terminal 50n connected to a low-potential wiring 52n. A DC power supply 10 supplies power to the power converter 1 via a smoothing capacitor 11 .

As shown in FIGS. 1 and 2, when the load is a three-phase AC electric motor 2, the power conversion circuit 4 has three legs, and the output terminals 51u, 51v, and 51w of each leg are the U phase of the electric motor 2, It is connected to the V phase and W phase. As appropriate, the leg connected to the U phase is the U phase leg, the leg connected to the P side of the DC power supply 10, that is, the high potential side of the U phase leg is the UP phase power conversion element, and the N side of the DC power supply 10, that is, the Those connected to the low potential side are expressed as UN-phase power conversion elements. The V-phase and W-phase legs and arms are expressed in the same manner as the U-phase leg and U-phase arms. The switching element 5a and the freewheeling diode 6a are UP-phase power conversion elements, and the switching element 5b and the freewheeling diode 6b are UN-phase power conversion elements. The switching element 5c and the freewheeling diode 6c are VP-phase power conversion elements, and the switching element 5d and the freewheeling diode 6d are VN-phase power conversion elements. The switching element 5e and the freewheeling diode 6e are WP-phase power conversion elements, and the switching element 5f and the freewheeling diode 6f are WN-phase power conversion elements.

The power conversion circuit 4 includes gate terminals 53a to 53f to which the gate drive signal sg4 output from the gate drive circuit 8 is input. The gate terminal 53a is connected to the gate of the switching element 5a, and the gate terminal 53b is connected to the gate of the switching element 5b. Similarly, gate terminals 53c and 53d are connected to gates of switching elements 5c and 5d, respectively, and gate terminals 53e and 53f are connected to gates of switching elements 5e and 5f, respectively. The power conversion circuit 4 also includes temperature monitors 24a to 24f that detect a temperature rise ΔTsw, which is temperature information of the switching elements 5a to 5f. A temperature rise ΔTswa of the switching element 5a detected by the temperature monitor 24a is output from the monitor terminal 54a, and a temperature rise ΔTswb of the switching element 5b detected by the temperature monitor 24b is output from the monitor terminal 54b. Similarly, the temperature rise ΔTswc of the switching element 5c detected by the temperature monitor 24c is output from the monitor terminal 54c, and the temperature rise ΔTswd of the switching element 5d detected by the temperature monitor 24d is output from the monitor terminal 54d. A temperature rise ΔTswe of the switching element 5e detected by the temperature monitor 24e is output from the monitor terminal 54e, and a temperature rise ΔTswf of the switching element 5f detected by the temperature monitor 24f is output from the monitor terminal 54f. The temperature rise ΔTsw is a generic term for the six temperature rises ΔTswa to ΔTswf. As appropriate, the six temperature rises ΔTswa to ΔTswf are expressed as a temperature rise ΔTsw when they are not distinguished.

The element temperature estimator 25 estimates the temperature rise ΔTdi, which is the temperature information of each of the freewheeling diodes 6a to 6f. More specifically, the element temperature estimator 25 estimates the temperature rises ΔTdia to ΔTdif of the free wheel diodes 6a to 6f based on the temperature rises ΔTswa to ΔTswf output from the temperature monitors 24a to 24f of the switching elements 5a to 5f. presume. As appropriate, the temperature rise ΔTsw of the switching element 5 is expressed as first temperature information, and the temperature rise ΔTdi of the freewheeling diode 6 is expressed as second temperature information. The temperature rise ΔTdia of the freewheeling diode 6a is estimated from the temperature rise ΔTswa of the switching element 5a, and the temperature rise ΔTdib of the freewheeling diode 6b is estimated from the temperature rise ΔTswb of the switching element 5b. The temperature rise ΔTdic of the freewheeling diode 6c is estimated from the temperature rise ΔTswc of the switching element 5c, and the temperature rise ΔTdid of the freewheeling diode 6d is estimated from the temperature rise ΔTswd of the switching element 5d. The temperature rise ΔTdie of the freewheeling diode 6e is estimated from the temperature rise ΔTswe of the switching element 5e, and the temperature rise ΔTdif of the freewheeling diode 6f is estimated from the temperature rise ΔTswf of the switching element 5f. The temperature rise ΔTdi is a general term for six temperature rises ΔTdia to ΔTdif. The six temperature rises ΔTdia to ΔTdif are appropriately expressed as temperature rise ΔTdi when they are not discriminated.

A current detector 7 exists for each of the U-phase, V-phase, and W-phase. The U-phase current detector 7a, the V-phase current detector 7b, and the W-phase current detector 7c detect the value of the output current of each phase output from the output terminals 51u, 51v, and 51w to the electric motor 2, that is, the output current Find the values iu, iv, iw. Current detector 7 is a general term for three current detectors 7a, 7b, and 7c. As appropriate, the three current detectors 7a, 7b, and 7c are expressed as the current detector 7 when they are not distinguished from each other.

The control calculation unit 3 determines the switching timings of the switching elements 5a to 5f so that the electric motor 2 performs desired operations, and controls the output power output from the power conversion circuit 4 to the electric motor 2. FIG. The control calculation unit 3 outputs the gate drive signal sg2 and normal voltage command values vu0*, vv0*, vw0* to the duty control unit 23 . A gate drive signal sg3 whose duty is adjusted by the duty controller 23 is generated based on the gate drive signal sg2, and the gate drive circuit 8 drives the switching elements 5a to 5f based on the gate drive signal sg3. sg4 is generated. The gate drive signal sg2 has six gate drive signals up0, un0, vp0, vn0, wp0 and wn0 corresponding to the six switching elements 5a, 5b, 5c, 5d, 5e and 5f. The gate drive signal sg3 has six gate drive signals up1, un1, vp1, vn1, wp1 and wn1 corresponding to the six switching elements 5a, 5b, 5c, 5d, 5e and 5f. The gate drive signal sg4 has six gate drive signals up, un, vp, vn, wp, and wn corresponding to the six switching elements 5a, 5b, 5c, 5d, 5e, and 5f.

The stall determination unit 27 calculates the rotation speed Nm of the electric motor 2 based on the rotor position θ output from the rotation detector 9, and determines whether the electric motor 2 is in a stalled state. The stall state is a state in which the electric motor 2 is in an extremely low rotation state, and the rotor cannot follow the rotating magnetic field on the stator side of the electric motor 2 . The stall determination unit 27 determines that the engine is in a stalled state when the number of rotations Nm is extremely low, such as 10 rpm. When the stall determination unit 27 determines that the electric motor 2 is in the stall state, the stall determination unit 27 outputs a stall determination signal sig1 indicating the stall state. For example, when the stall determination signal sig1 indicates a stalled state, it is at H level, and when the stall determination signal sig1 indicates a non-stalled state, it is at L level. Here, since the method of converting the rotor position θ into the rotation speed Nm of the electric motor 2 is well known, the description thereof will be omitted.

The stall determination unit 27 outputs a stall determination signal sig<b>1 to the duty control unit 23 and the loss reduction unit 26 . The duty control unit 23 receives the stall determination signal sig1 indicating the stall state, and starts an operation to increase the distribution amount of the current flowing through the free wheel diode to the switching elements. A stall determination signal sig1 indicating a stall state is a command to change the current distribution to the duty control section 23 . The loss reduction unit 26 receives the stall determination signal sig1 indicating the stall state, and starts the operation of reducing the loss of the switching element 5. FIG. The stall determination signal sig1 indicating the stall state is a command to the loss reduction unit 26 to reduce the loss of the switching element 5 .

Loss reduction unit 26 receives stall determination signal sig1 indicating a stall state and outputs frequency change signal sig2 indicating a change to control operation unit 3 . For example, when frequency change signal sig2 indicates change, it is at H level, and when frequency change signal sig2 indicates no change, it is at L level. The control calculation unit 3 receives the frequency change signal sig2 indicating the change and generates a gate drive signal sg2 having a frequency lower than that before the stall state determination, that is, lower than normal. Loss of the switching element 5 is reduced by lowering the frequency of the gate drive signal sg2. Since the loss of the switching element 5 is reduced, the amount of heat generated by the switching element 5 is reduced. The loss reduction unit 26 is a functional block that instructs the start of an operation for reducing the loss of the switching element 5 or an operation for reducing the amount of heat generated by the switching element 5. It is an example of a reduced signal.

The duty control unit 23 receives the stall determination signal sig1 indicating the stall state, and the normal voltage command values vu0*, vv0*, vw0 output from the control calculation unit 3 when the loss of the switching element 5 is reduced. The voltage command values vua*, vva*, vwa* with * changed, and the voltage command change signal sig3 for generating the gate drive signal sg2 based on the voltage command values vua*, vva*, vwa*, i.e., the change to the control calculation unit 3. The duty control unit 23 controls the temperature rise ΔTsw, which is the first temperature information, of the switching element 5 connected in series to the freewheeling diode 6 in which the temperature rise ΔTdi, which is the second temperature information, is maximized by the operation of the loss reduction unit 26. When the voltage drops, the voltage command values vua*, vva*, vwa* and the voltage command change signal sig3 indicating the change are output to the control calculation unit 3 . For example, when voltage command change signal sig3 indicates change, it is at H level, and when voltage command change signal sig3 indicates no change, it is at L level.

The gate drive circuit 8 outputs a gate drive signal sg4 for controlling ON/OFF operations of the switching elements 5a to 5f according to the gate drive signal sg3 generated from the duty control section 23. FIG. The gate drive signal sg4 changes at the same timing as the gate drive signal sg3, but the voltage value is different from that of the gate drive signal sg3.

The control calculation unit 3 will be explained. The control calculation unit 3 includes a vector control unit 12 that generates voltage command values vu0*, vv0*, and vw0* for the U-phase, V-phase, and W-phase; A selector 41 that selects any of the voltage command values vua*, vva*, and vwa* generated in and outputs the voltage command values vu*, vv*, and vw*, the voltage command values vu*, vv*, A PWM control unit 18 is provided for generating a gate drive signal sg2 for PWM (Pulse Width Modulation) control of the power conversion circuit 4 based on vw*. There are various methods for generating the gate drive signal sg2. Here, the voltage command values vu0*, vv0*, vw0* for each phase are calculated by known vector control, V/F (Voltage/Frequency) control, etc., and the voltage command values vu0*, vv0*, vw0* for each phase are calculated. A method of generating the gate drive signal sg2 by a known triangular wave comparison sine wave PWM method based on vw0* will be described.

As shown in FIG. 3 , the vector control section 12 includes a torque control section 13 , a current control section 14 , a voltage coordinate conversion section 15 , a coordinate conversion section 16 and an angular velocity conversion section 17 . The PWM control section 18 includes a triangular wave oscillator 19 , comparators 20 a , 20 b and 20 c , inverters 21 a , 21 b and 21 c and a dead time circuit 22 . The comparator 20a and inverter 21a are U-phase comparators and inverters, the comparator 20b and inverter 21b are V-phase comparators and inverters, and the comparator 20c and inverter 21c are W-phase comparators. and an inverter.

First, the operation of the vector control section 12 will be described. The angular velocity converter 17 converts the rotor position θ detected by the rotation detector 9 into an angular velocity ω. The torque controller 13 calculates a d-axis current target value id* and a q-axis current target value iq* from the angular velocity ω of the electric motor 2 converted by the angular velocity converter 17 and the torque command value T*. The torque command value T* is output from, for example, a higher control device. A coordinate transformation unit 16 generates a d-axis current value id and a q-axis current value iq from the output current values iu, iv, and iw detected by the current detector 7 . The current control unit 14 controls the d-axis current value id and the q-axis current value iq corresponding to the angular velocity ω of the electric motor 2 to follow the d-axis current target value id* and the q-axis current target value iq*. A voltage target value vd* and a q-axis voltage target value vq* are output. The voltage coordinate conversion unit 15 converts the d-axis voltage target value vd* and the q-axis voltage target value vq* into voltage command values vu0*, vv0*, vw0* for each phase.

The selector 41 has selectors 41a, 41b, and 41c for each of the U phase, V phase, and W phase. The selector 41 is a general term for the three selectors 41a, 41b and 41c. The three selectors 41a, 41b, and 41c are appropriately expressed as selector 41 when they are not distinguished from each other. The voltage command values vu0*, vv0*, vw0* generated by the vector control unit 12 are the voltage command values when the stall determination unit 27 does not perform stall determination, that is, normal voltage command values. When the voltage command change signal sig3 output from the duty control unit 23 indicates no change (for example, L level), the selector 41 selects the voltage command values vu0*, vv0*, vw0* output from the duty control unit 23. are output as voltage command values vu*, vv*, vw*. When voltage command change signal sig3 output from duty control unit 23 indicates a change (for example, H level), selector 41 selects voltage command values vua*, vva*, vwa* output from duty control unit 23 as Output as voltage command values vu*, vv*, vw*.

Selector 41a outputs voltage command value vu0* as voltage command value vu* when voltage command change signal sig3 indicates no change, and outputs voltage command value vua* as voltage command value vu* when voltage command change signal sig3 indicates change. Output as command value vu*. Similarly, selector 41b outputs voltage command value vv0* as voltage command value vv* when voltage command change signal sig3 indicates no change, and outputs voltage command value vv* when voltage command change signal sig3 indicates change. * is output as the voltage command value vv*. Selector 41c outputs voltage command value vw0* as voltage command value vw* when voltage command change signal sig3 indicates no change, and outputs voltage command value vwa* as voltage command value vw* when voltage command change signal sig3 indicates change. Output as command value vw*.

The operation of the PWM control section 18 will be explained. The PWM control unit 18 includes a triangular wave oscillator 19 that outputs a carrier wave vc, comparators 20a, 20b, 20c, inverters 21a, 21b, 21c, and a dead time circuit 22. Carrier wave vc is used to generate gate drive signal sg1. The PWM control unit 18 generates a gate drive signal sg1 based on the voltage command values vu*, vv*, vw* of each phase, and generates a gate drive signal sg2 in which the dead time of the gate drive signal sg1 is adjusted. The gate drive signal sg1 has six gate drive signals up*, un*, vp*, vn*, wp*, wn* corresponding to the six switching elements 5a, 5b, 5c, 5d, 5e, 5f. doing. The comparator 20a compares the voltage command value vu* with the carrier wave vc, which is the output of the triangular wave oscillator 19, and generates a gate drive signal up* for the switching element 5a on the P side. The inverter 21a generates a gate drive signal un* by inverting the gate drive signal up* for the switching element 5b on the N side. The comparators 20b, 20c and the inverters 21b, 21c operate similarly. Comparator 20b compares voltage command value vv* with carrier wave vc that is the output of triangular wave oscillator 19, and generates gate drive signal vp* for switching element 5c on the P side. The inverter 21b generates a gate drive signal vn* by inverting the gate drive signal vp* for the N-side switching element 5d. The comparator 20c compares the voltage command value vw* with the carrier wave vc that is the output of the triangular wave oscillator 19, and generates a gate drive signal wp* for the switching element 5e on the P side. The inverter 21c generates a gate drive signal wn* by inverting the gate drive signal wp* for the N-side switching element 5f.

The dead time circuit 22 is provided to prevent a power supply short-circuit due to simultaneous ON of the P-side switching elements 5a, 5c, and 5e and the N-side switching elements 5b, 5d, and 5f when there is a delay in the OFF operation of the switching element 5. , a dead time tdd is added to delay the ON period of the gate drive signal sg1 by a predetermined time. The dead time circuit 22 outputs a gate drive signal sg2 obtained by adding a dead time tdd to the gate drive signal sg1. The dead time circuit 22 generates a gate drive signal up0 by adding a dead time tdd to the gate drive signal up*, and generates a gate drive signal un0 by adding a dead time tdd to the gate drive signal un*. Similarly, the dead time circuit 22 generates the gate drive signal vp0 by adding the dead time tdd to the gate drive signal vp*, generates the gate drive signal vn0 by adding the dead time tdd to the gate drive signal vn*, and A gate drive signal wp0 is generated by adding a dead time tdd to the drive signal wp*, and a gate drive signal wn0 is generated by adding a dead time tdd to the gate drive signal wn*.

The PWM control unit 18 compares the voltage command values vu*, vv*, vw* for each of the three phases output from the selector 41 with the carrier wave vc output from the triangular wave oscillator 19 . As a result, when the amplitude of the voltage command values vu*, vv*, vw* of each phase is larger than the amplitude of the carrier wave vc, the gate drive signal is output so as to turn on the P-side switching element of that phase. On the other hand, when the amplitude of the voltage command values vu*, vv*, vw* of each phase is smaller than the amplitude of the carrier wave vc, a gate drive signal is output to turn off the P-side switching element of that phase.

The PWM control unit 18 generates gate drive signals up*, vp*, wp* for the P-side switching elements 5a, 5c, 5e of each phase. The gate drive signals un*, vn*, and wn* of the switching elements 5b, 5d, and 5f on the N side are the gate drive signals up*, vp*, and wp* of the switching elements 5a, 5c, and 5e on the P side. 21a, 21b and 21c are used. The gate drive signals sg1 and sg2 are pulse signals.

The gate drive signal sg2 generated by the control calculation unit 3 becomes the gate drive signal sg4 through the duty control unit 23 and the gate drive circuit 8 as described above, and the gate drive signal sg4 is output to the power conversion circuit 4. . The duty control section 23 includes a target voltage changing section 29 and a pattern generating section 30 . The target voltage changing unit 29 changes the normal voltage command values vu0*, vv0*, vw0* of each phase to the voltage command values vua*, vva*, vwa* by a method described later, and furthermore, changes the voltage command values vua* , vva*, and vwa* to generate a voltage command change signal sig3 for generating a gate drive signal sg2. The pattern generating section 30 generates a pattern, that is, a pulse-shaped gate drive signal sg3, taking into consideration the device characteristics, generation of harmonics, and the like. The gate drive signals sg3 and sg4 are also pulse signals like the gate drive signals sg1 and sg2. A method of generating the gate drive signal sg3 by the duty control unit 23 and the gate drive signal sg4 by the gate drive circuit 8 will be described.

The power conversion circuit 4 turns on or off the six switching elements 5 by the pulse-like gate drive signal sg4, and gives the electric motor 2 a sinusoidal line voltage. At this time, losses occur in the power conversion elements forming the six arms of the power conversion circuit 4, that is, the six switching elements 5 and the six free wheel diodes 6. FIG. The arm loss Pla, which is the loss per arm, can be expressed by adding the switching element loss Pls, which is the loss of the switching element 5, and the diode loss Pld, which is the loss of the freewheeling diode 6. FIG. The switching element loss Pls can be expressed by adding the steady loss Psat of the switching element 5 and the switching loss Psw of the switching element 5 . The diode loss Pld can be expressed by adding the stationary loss Pf of the freewheeling diode 6 and the recovery loss Pr of the freewheeling diode 6 . Therefore, the arm loss Pla can be expressed as in Equation (1).

Pla=Psat+Psw+Pf+Pr (1)

Let Vsat be the saturation voltage of the switching element 5, Imot be the switching element current that flows through the switching element 5, and Dt be the duty ratio of the gate drive signal of the switching elements 5a, 5c, and 5e on the P side. Loss Psat can be expressed as in Equation (2).
Psat=Vsat×Imot×Dt (2)

Assuming that the time during which the switching element 5 is ON is the ON time and the time during which the switching element 5 is OFF is the OFF time, the duty ratio Dt can be expressed as ON time/(ON time+OFF time).

Pon is the loss when the switching element 5 is turned on, Poff is the loss when the switching element 5 is turned off, fc is the frequency of the carrier wave vc, Eon is the energy in the switch-on state per pulse, and Eoff is the energy in the switch-off state per pulse. Then, the switching loss Psw of the switching element 5 can be expressed as in Equation (3).
Psw=Pon+Poff=fc×(Eon+Eoff) (3)

Assuming that the saturation voltage of the freewheeling diode 6 is Vfsat, and the duty factor Dt and the switching element current Imot are used, the steady-state loss Pf of the freewheeling diode 6 can be expressed as in Equation (4). Assuming that the voltage of the DC power supply 10 is Vdc, the recovery current of the freewheeling diode 6 is Irr, and the recovery time is trr, the recovery loss Pr of the freewheeling diode 6 can be expressed as in Equation (5).
Pf=(1−Dt)×Vfsat×Imot (4)
Pr=Vdc×Irr×trr/4 (5)

A switching element current Imot flowing through the switching element 5 is expressed by Equation (6) using an amplitude I0 and a phase ωt. Assuming that the modulation factor and the power factor angle in the triangular wave comparison sine wave PWM are MR and θp, respectively, the duty factor Dt can be expressed by Equation (7).
Imot=I0 sinωt (6)
Dt=1/2+MR×sin(ωt+θp)/2 (7)

Using these equations (1) to (7), the loss shown in FIG. 4 is obtained by calculating the loss of the six switching elements 5 and the six freewheeling diodes 6 in the stalled state. The loss of the power conversion element of each phase has periodicity as shown in FIG. The horizontal axis is the electrical angle [rad] of the electric motor 2, and the vertical axis of the switching element current Imot is current. The vertical axis of the P-side switching element loss Plsp, P-side diode loss Pldp, N-side switching element loss Plsn, and N-side diode loss Pldn is loss. The U phase will be described as an example. When the switching element current Imot in the U phase is positive, that is, when the electrical angle of the electric motor 2 is 0 to π, current flows only through the switching element 5a on the P side of the U phase and the freewheel diode 6b on the N side of the U phase. Since no current flows through the switching element 5b on the N side and the freewheeling diode 6a on the U-phase P side, a loss occurs in these two power conversion elements, that is, the switching element 5a and the freewheeling diode 6b, and no current flows in the U-phase. No loss occurs in the N-side switching element 5b and the U-phase P-side freewheeling diode 6a.

When the U-phase switching element current Imot is negative, that is, when the electrical angle of the motor 2 is π to 2π, current flows only through the U-phase N-side switching element 5b and the U-phase P-side freewheeling diode 6a. Since no current flows through the P-side switching element 5a and the U-phase N-side freewheeling diode 6b, a loss occurs in these two power conversion elements, that is, the switching element 5b and the freewheeling diode 6a. No loss occurs in the P-side switching element 5a and the U-phase N-side freewheeling diode 6b.

Further, between the U-phase P-side switching element 5a and the U-phase N-side freewheeling diode 6b, there is a large difference in the generated loss due to the difference in element characteristics due to the difference in element size and the difference in current flow time. Similarly, between the U-phase N-side switching element 5b and the U-phase P-side freewheeling diode 6a, there is a large difference in the generated loss due to the difference in element characteristics due to the difference in element size and the difference in current flow time. This difference in generated loss is caused by the difference in element characteristics and also by the difference in the energization time of each element as shown in FIG. FIG. 5 is a diagram showing an example of the energization time distribution of a normal power conversion device. It is a figure which shows the example of time allocation. In FIG. 5, a carrier wave waveform 61 that is the waveform of the carrier wave vc, a voltage command waveform 62 that is the waveforms of the target voltage command values vu*, vv*, and vw*, and an energization pattern of the P-side power conversion element on the P-side An energization pattern 63a, an N-side energization pattern 63b that is the energization pattern of the N-side power conversion element, a P-side switching element loss characteristic 68a that is the characteristic of the P-side switching element loss Plsp, and a P-side that is the characteristic of the P-side diode loss Pldp A diode loss characteristic 68c, an N-side switching element loss characteristic 68b that is the characteristic of the N-side switching element loss Plsn, and an N-side diode loss characteristic 68d that is the characteristic of the N-side diode loss Pldn are shown. The horizontal axis is the electrical angle [rad] of the electric motor 2 . The vertical axis of the carrier waveform 61, the voltage command waveform 62, the P-side energization pattern 63a, and the N-side energization pattern 63b is voltage. The vertical axis of the P-side switching element loss characteristic 68a, the P-side diode loss characteristic 68c, the N-side switching element loss characteristic 68b, and the N-side diode loss characteristic 68d is the loss. FIG. 5 also shows the conduction time Tsp of the P-side switching element, the conduction time Tsn of the N-side switching element, the conduction time Tdp of the P-side freewheeling diode, and the conduction time Tdn of the N-side freewheeling diode.

FIG. 7 shows the maximum loss when the permissible loss of this power conversion element, that is, the permissible loss of the switching element 5 and the freewheeling diode 6 is 200 W and 100 W, respectively. FIG. 7 shows the maximum loss in a bar graph. SW is a switching element and D is a freewheeling diode. The vertical axis is the loss [W]. A switching element maximum loss 71a, which is the maximum loss of the switching element 5, is 185W. The switching element maximum loss 71a has a margin Pm1 of only 7.5% with respect to the allowable loss of 200 W, and there is no margin. A freewheeling diode maximum loss 71b, which is the maximum loss of the freewheeling diode 6, is 95W. The freewheeling diode maximum loss 71b has a margin Pm2 of only 5% with respect to the permissible loss of 100 W, which is less than the margin of the switching element 5.

In the power conversion device of Patent Document 1, the energization time of the power conversion element is distributed, and the generated loss is distributed between the P-side power conversion element and the N-side power conversion element. Both the free wheel diode 6 has no margin. Therefore, even if the loss of the freewheeling diode 6 is distributed to the switching element 5, the loss of the freewheeling diode 6 can only be reduced from 95W to 90W, for example. Although the margin is improved from 5% to 10% with respect to the allowable loss of 100 W, the improvement effect is small.

In order to further reduce the loss of the freewheeling diode 6, it is necessary to reduce the steady-state loss Pf, since the steady-state loss Pf accounts for the majority of the loss generated in the stall state. However, since the saturation voltage Vfsat in equation (4) is inversely proportional to the size of the freewheeling diode 6, the size of the freewheeling diode 6 increases when the saturation voltage Vfsat is lowered. An increase in the size of the freewheeling diode 6 increases the size of the power conversion device, leading to an increase in the price of the power conversion device.

Therefore, in order to realize a compact power conversion device 1 that can prevent a rapid temperature rise, attention was paid to the switching element 5 that is easier to control the generated loss than the freewheeling diode 6 . As for the ratio of the loss generated by the switching element 5, the stationary loss Psat and the switching loss Psw are approximately equal. In the first embodiment, the carrier frequency for switching the switching element 5 using the loss reduction unit 26, that is, the frequency fc of the carrier wave vc of the triangular wave oscillator 19 is made lower than usual, thereby reducing the loss of the switching element 5. explain. As appropriate, the code for the carrier frequency is fc.

The stall determination unit 27 outputs to the loss reduction unit 26 a trigger signal for starting loss reduction after determination of the stall state, that is, the stall determination signal sig1 indicating the aforementioned stall state. The loss reduction unit 26 receives this trigger signal and outputs a frequency change signal sig2 indicating a change to the triangular wave oscillator 19 of the PWM control unit. Triangular wave oscillator 19 receives frequency change signal sig2 indicating a change and outputs carrier wave vc of frequency fc lower than usual to comparators 20a-20c. By doing so, the frequency fc in equation (3) is lowered, that is, the switching loss Psw is lowered, and the maximum loss of the switching element 5 is reduced from 185W to 160W, for example. Due to the decrease in temperature rise ΔTsw, which is input first temperature information, duty control unit 23 controls switching element 5 connected in series to freewheeling diode 6 in which temperature rise ΔTdi, which is second temperature information, is maximized. Determine that the loss has decreased.

After that, the duty control section 23 determines the energization rate Dt of the power conversion element, that is, the switching element 5 and the freewheeling diode 6 based on the temperature rise ΔTdi of each freewheeling diode 6 output from the element temperature estimating section 25 . That is, the duty control unit 23 distributes the current flowing through the freewheeling diode 6 with the maximum second temperature information to the switching element 5 connected in series with the freewheeling diode 6. The gate drive signal sg3 with the ON time of 5 changed is output to the gate drive circuit 8. As described above, the element temperature estimator 25 estimates the temperature rise ΔTdi of the free wheel diode 6 based on the temperature rise ΔTsw of each switching element 5 output from the temperature monitors 24a to 24f of each of the switching elements 5a to 5f. , and the estimated temperature rise ΔTdi is sent to the duty control section 23 .

FIG. 6 shows an example of energization time distribution of the power conversion device 1 when the loss of the freewheeling diode 6 is reduced. Target voltage command values vua*, vva*, vwa* are generated by the target voltage changing unit 29, and the voltage command waveform 62 shown in FIG. The horizontal and vertical axes in FIG. 6 are the same as the horizontal and vertical axes in FIG. FIG. 6 shows a P-side conduction pattern 64a that is the conduction pattern of the P-side power conversion element, an N-side conduction pattern 64b that is the conduction pattern of the N-side power conversion element, and a characteristic of the P-side switching element loss Plsp. A switching element loss characteristic 69a, a P-side diode loss characteristic 69c that is the characteristic of the P-side diode loss Pldp, an N-side switching element loss characteristic 69b that is the characteristic of the N-side switching element loss Plsn, and N that is the characteristic of the N-side diode loss Pldn side diode loss characteristic 69d.

The voltage command waveform 67 shown in FIG. 6 is obtained by adding a voltage that is 0.4 times the voltage amplitude of the voltage command waveform 62 to the voltage amplitude of the voltage command waveform 62 in the electrical angle range of 0 to π. This is an example in which a voltage of 0.4 times the voltage amplitude of the voltage command waveform 62 is subtracted in the interval of 2π. The target voltage changing unit 29 generates the U-phase voltage command value vua* as follows. The target voltage changing unit 29 adds 0.4 times the normal voltage command value vu0* to the voltage command value vu0* in the electrical angle 0 to π interval, and increases the normal voltage command value in the electrical angle π to 2π interval. A new target voltage command value vua* is generated by subtracting 0.4 times the voltage command value vu0* from vu0*. The target voltage changing unit 29 similarly generates V-phase and W-phase voltage command values vva* and vwa*. The target voltage changing unit 29 adds a voltage command value vv0* that is 0.4 times the normal voltage command value vv0* in the interval between 0 and π in electrical angle, and increases the normal voltage command value in the interval between π and 2π in electrical angle. A new target voltage command value vva* is generated by subtracting 0.4 times the voltage command value vv0* from vv0*. The target voltage changing unit 29 adds a voltage command value vw0* that is 0.4 times the normal voltage command value vw0* in the electrical angle 0 to π interval, and increases the normal voltage command value in the electrical angle π to 2π interval. A new target voltage command value vwa* is generated by subtracting 0.4 times the voltage command value vw0* from vw0*.

FIG. 8 shows the maximum loss when the energization pattern of the power conversion element is changed as shown in FIG. 6 after the loss of the switching element 5 is reduced by the loss reduction unit 26 . The horizontal and vertical axes in FIG. 8 are the same as the horizontal and vertical axes in FIG. The maximum loss of the switching element 5 is a switching element maximum loss 72a, and the maximum loss of the freewheeling diode 6 is a freewheeling diode maximum loss 72b. In FIG. 8, the switching element maximum loss 71a and the freewheeling diode maximum loss 71b before loss allocation shown in FIG. 7 are indicated by dashed lines. As described above, the operation of the loss reduction unit 26 reduces the maximum loss of the switching element 5 from 185 W to 160 W, resulting in the switching element maximum loss 73 . After that, by changing the energization pattern of the power conversion element as shown in FIG. 6, the maximum loss of the freewheeling diode 6 could be reduced from 95W to 65W. However, the maximum loss of the switching element 5 becomes a switching element maximum loss 72a of 190W when an increased loss 74 of 30W is added to the switching element maximum loss 73.

Since the total loss of the switching element maximum loss 72a and the freewheeling diode maximum loss 72b is only the loss of the freewheeling diode 6 distributed to the switching element 5 in the same phase, the loss generated by the entire power conversion element of the phase is before distribution and distribution. No change afterwards. However, the loss of the free wheel diode 6 is greatly reduced, and the margin Pm4 when the allowable loss is 100 W is greatly improved from the margin Pm2 of 5% to 35%. On the other hand, the loss of the switching element 5 increases by 30 W, and the margin Pm3 when the allowable loss is 200 W becomes 5% from the margin Pm1 of 7.5%.

FIG. 8 will be described using the U phase as an example. The maximum loss of the U-phase switching elements 5a and 5b is reduced from 185 W to 160 W by the operation of the loss reduction unit 26, and the switching element maximum loss 73 is reached. After that, by changing the energization pattern of the U-phase power conversion element as shown in FIG. 6, the maximum loss of the freewheeling diodes 6a and 6b can be reduced from 95W to 65W. However, the maximum loss of the switching elements 5a and 5b becomes a switching element maximum loss 72a of 190W when an additional loss 74 of 30W is added to the switching element maximum loss 73. The total loss of the switching element maximum loss 72a and the freewheeling diode maximum loss 72b at an electrical angle of 0 to π is only the loss of the U-phase N-side freewheeling diode 6b distributed to the U-phase P-side switching element 5a. There is no change in the generated loss of the entire phase power conversion element before and after distribution. Also, the total loss of the switching element maximum loss 72a and the freewheeling diode maximum loss 72b at an electrical angle of π to 2π is just the loss of the freewheeling diode 6a on the U-phase P side distributed to the switching element 5b on the U-phase N side. , there is no change in the overall loss generated by the U-phase power conversion elements before and after distribution. However, the loss of the free wheel diodes 6a and 6b is greatly reduced, and the margin Pm4 when the allowable loss is 100 W is greatly improved from the margin Pm2 of 5% to 35%. On the other hand, the loss of the switching elements 5a and 5b increases by 30 W, and the margin Pm3 when the allowable loss is 200 W becomes 5% from the margin Pm1 of 7.5%.

When the loss of the entire power conversion element is distributed in the U phase as shown in Fig. 6, the phase voltage of the U phase breaks down from the sinusoidal waveform significantly. is the voltage between Therefore, in the pattern generating section 30 that generates the conduction rate distribution pattern, that is, the P-side conduction pattern 64a and the N-side conduction pattern 64b, the other phases (V phase, W phase) are similarly loss-divided, and the line voltage becomes sinusoidal. Then, control is performed so that there is no difference between the line voltages before and after loss distribution. Making the U phase, V phase, and W phase have the same loss distribution is the same as the control of Patent Document 1. The duty control unit 23 generates the gate drive signal sg3 in consideration of element characteristics, generation of harmonics, etc., in addition to maintaining the line voltage.

When it is determined that the electric motor 2 is in the stall state, the power conversion device 1 of Embodiment 1 reduces the loss of the switching element 5 using the loss reduction unit 26, and then uses the duty control unit 23 to reduce the loss of each phase. The power conversion element, that is, the energization time of the switching element 5 and the freewheeling diode 6 was changed to distribute the loss between the P-side power conversion element and the N-side power conversion element. Therefore, in the power converter 1 of Embodiment 1, the loss of the freewheeling diode 6, which is smaller than the switching element 5 and has no temperature margin, is borne by the switching element 5, which is larger than the freewheeling diode 6 and has a temperature margin. As a result, it is possible to avoid an increase in the size of the free wheel diode 6 without causing a rapid temperature rise. Therefore, the power conversion device 1 of Embodiment 1 is small and can prevent a rapid temperature rise. Since the power conversion device 1 of Embodiment 1 can be made small, a low-cost power conversion device can be realized.

1 may be realized by the processor 120 and the memory 121 shown in FIG. 9 . In this case, the control calculation unit 3 , the duty control unit 23 , the element temperature estimation unit 25 , the loss reduction unit 26 , and the stall determination unit 27 are implemented by the processor 120 executing a program stored in the memory 121 . Also, the plurality of processors 120 and the plurality of memories 121 may cooperate to execute each function.

As described above, the power converter 1 of Embodiment 1 supplies AC power converted from DC power to drive the electric motor 2 . The power conversion device 1 includes a plurality of switching elements 5 and a freewheeling diode 6, and a plurality of temperature monitors 24a, 24b, 24c, 24d, 24e that output first temperature information (ΔTsw) that is temperature information of each switching element 5, 24f for supplying AC power for driving the electric motor 2; and control for determining switching timings of the plurality of switching elements 5 in the power conversion circuit 4 and generating a first drive signal (gate drive signal sg2). A calculation unit 3 and a rotation detector 9 for detecting the rotor position θ of the electric motor 2 are provided. The power conversion device 1 further includes an element temperature estimating unit 25 that estimates second temperature information (ΔTdi), which is temperature information of the freewheeling diode 6, based on the first temperature information (ΔTsw), and a rotor position θ of the electric motor 2. a stall determination unit 27 that determines the stall state of the electric motor 2 based on the stall determination unit 27; a loss reduction unit 26 that reduces the amount of heat generated by the switching element 5 when the stall determination unit 27 determines the stall state; The second drive signal (gate drive signal sg2) is output as the second drive signal (gate drive signal sg3) without changing the drive signal (sg2), or the second drive signal (gate drive A duty control unit 23 that outputs a signal sg3) and a third drive signal (gate drive signal sg4) that switches the plurality of switching elements 5 according to a second drive signal (gate drive signal sg3) to the power conversion circuit 4. and a gate drive circuit 8 for outputting. The duty control unit 23 determines the stall state by the stall determination unit 27, and the switching element 5 connected in series with the freewheeling diode 6 in which the second temperature information (ΔTdi) is maximized by the operation of the loss reduction unit 26. When the first temperature information (ΔTsw) decreases, the current flowing through the freewheeling diode 6 with the maximum second temperature information (ΔTdi) is distributed to the switching element 5 connected in series with the freewheeling diode 6. , outputs to the gate drive circuit 8 a second drive signal (gate drive signal sg3) obtained by changing the ON time of the switching element 5 in the first drive signal (gate drive signal sg2). With this configuration, the power conversion device 1 of Embodiment 1 is determined to be in a stalled state, and the first temperature When the information (ΔTsw) decreases due to the operation of the loss reduction unit 26, the current flowing through the freewheeling diode 6 is distributed to the switching element 5 connected in series.

Embodiment 2.
FIG. 10 is a diagram showing the configuration of a first power converter according to the second embodiment, and FIG. 11 is a diagram showing the configuration of a second power converter according to the second embodiment. It has been explained that the power conversion device 1 of Embodiment 1 can reduce the loss of the switching element 5 by reducing the carrier frequency fc. However, depending on the value of the carrier frequency fc, current pulsation and noise may increase due to the decrease in the carrier frequency fc. Since it is preferable that the electric power converter 1 mounted on the vehicle has small current pulsation and noise, in the second embodiment, the loss reduction unit 26 speeds up the change speed of the gate drive signal sg4 of the gate drive circuit 8, that is, the switching speed. explain.

As a method for increasing the switching speed, there is a method such as reducing the resistance value of the gate resistance of the gate drive circuit 8. However, since this is a known technique, detailed description thereof will be omitted here. The loss sharing method is the same as in the first embodiment. The first power converter 1 according to Embodiment 2 shown in FIG. 10 differs from the power converter 1 shown in FIG. 1 in that the loss reduction unit 26 generates the switching speed change signal sig4 instead of the frequency change signal sig2. different in that The parts different from the power converter 1 of Embodiment 1 will be mainly described. In the first power converter 1 according to Embodiment 2, the frequency change signal sig2 is not input to the triangular wave oscillator 19 shown in FIG. The loss reduction unit 26 receives the stall determination signal sig1 indicating the stall state, and outputs to the gate drive circuit 8 a switching speed change signal sig4 indicating a high-speed command to increase the switching speed from before the stall state determination. For example, when switching speed change signal sig4 indicates a high speed command, it is at H level, and when switching speed change signal sig4 indicates a low speed command, it is at L level. Gate drive circuit 8 receives switching speed change signal sig4 indicating a high speed command and speeds up the switching speed of gate drive signal sg4. By increasing the switching speed of the gate drive signal sg4, the energy Eon in the switch-on state and the energy Eoff in the switch-off state in equation (3) are reduced, that is, the loss of the switching element 5 can be reduced. Since the loss of the switching element 5 is reduced, the amount of heat generated by the switching element 5 is reduced. The switching speed change signal sig4 is an example of a loss reduction signal that reduces the loss of the switching element 5. FIG.

The first power conversion device 1 of the second embodiment is small in size and can prevent a rapid temperature rise, like the power conversion device 1 of the first embodiment. Since the first power conversion device 1 of Embodiment 2 can be made small, a low-cost power conversion device can be realized. By speeding up the switching speed of the gate drive signal sg4, the first power converter 1 of Embodiment 2 can avoid current pulsation and increase in noise, and can realize a power converter suitable for vehicles.

A method of increasing the switching speed of the gate drive signal sg4 of the gate drive circuit 8 may be added to the power converter 1 of the first embodiment. The second power converter 1 according to Embodiment 2 shown in FIG. 11 differs from the power converter 1 shown in FIG. 1 in that the loss reduction unit 26 generates the frequency change signal sig2 and the switching speed change signal sig4. different in The parts different from the power converter 1 of Embodiment 1 will be mainly described. The loss reduction unit 26 receives the stall determination signal sig1 indicating the stall state, outputs a frequency change signal sig2 indicating a change to the control calculation unit 3, and outputs a switching speed change signal sig4 indicating a high speed command to the gate drive circuit 8. Output. The operations of the loss reduction unit 26 and the gate drive circuit 8 related to the added switching speed change signal sig4 are the same as those of the first power converter 1 of the second embodiment.

The second power conversion device 1 of the second embodiment is small in size and can prevent a rapid temperature rise, like the power conversion device 1 of the first embodiment. Since the second power conversion device 1 of Embodiment 2 can be made small, a low-cost power conversion device can be realized. The second power converter 1 of Embodiment 2 can avoid current pulsation and increase in noise by increasing the switching speed of the gate drive signal sg4, and can realize a power converter suitable for vehicles.

Needless to say, the loss reduction unit 26 in the power conversion device 1 of Embodiment 2 can be applied to all of the embodiments described later. Also in this case, the same effect as in the second embodiment can be obtained.

Embodiment 3.
FIG. 12 is a diagram showing the configuration of a first power converter according to Embodiment 3, and FIG. 13 is a diagram showing the configuration of a second power converter according to Embodiment 3. As shown in FIG. Embodiment 3 describes an example in which the loss reduction unit 26 increases the voltage value of the gate drive signal sg4 of the gate drive circuit 8. FIG. The first power converter 1 according to Embodiment 3 shown in FIG. 13 is different from the power converter 1 shown in FIG. The difference is that the gate voltage change signal sig5 is generated instead of the signal sig2. The parts different from the power converter 1 of Embodiment 1 will be mainly described.

In the first power converter 1 according to Embodiment 3, the frequency change signal sig2 is not input to the triangular wave oscillator 19 shown in FIG. The loss reduction unit 26 receives the stall determination signal sig1 indicating the stall state, and outputs to the gate drive circuit 8 a gate voltage change signal sig5 indicating a change to increase the voltage value of the gate drive signal sg4 from before the stall state determination. For example, it is H level when the gate voltage change signal sig5 indicates change, and is L level when the gate voltage change signal sig5 indicates no change. Gate drive circuit 8 receives gate voltage change signal sig5 indicating a change and increases the voltage value of gate drive signal sg4. As the voltage value of the gate drive signal sg4 increases, the saturation voltage Vsat in Equation (2) decreases, and the steady-state loss Psat of the switching element 5 can be reduced. By reducing the steady-state loss Psat of the switching element 5, the loss of the switching element 5 can be reduced. Since the loss of the switching element 5 is reduced, the amount of heat generated by the switching element 5 is reduced. Gate voltage change signal sig5 is an example of a loss reduction signal that reduces the loss of switching element 5 .

The first power conversion device 1 of the third embodiment is small in size and can prevent a rapid temperature rise, like the power conversion device 1 of the first embodiment. Since the first power conversion device 1 of Embodiment 3 can reduce the steady-state loss Psat, even in a power conversion device of a motor control system in which the carrier frequency fc of PWM control is small, the temperature rise of the switching element 5 can be reduced, Since the loss of the freewheeling diode 6, which has no temperature margin, can be borne by the switching element 5, which has a temperature margin, it is possible to prevent the size of the freewheeling diode 6 from increasing. Since the first power conversion device 1 of Embodiment 3 can be made small, a low-cost power conversion device can be realized.

A method of increasing the voltage value of the gate drive signal sg4 of the gate drive circuit 8 may be added to the power converter 1 of the first embodiment. The second power converter 1 according to Embodiment 3 shown in FIG. 13 differs from the power converter 1 shown in FIG. 1 in that the loss reduction unit 26 generates the frequency change signal sig2 and the gate voltage change signal sig5 different in The parts different from the power converter 1 of Embodiment 1 will be mainly described. The loss reduction unit 26 receives the stall determination signal sig1 indicating the stall state, outputs the frequency change signal sig2 indicating the change to the control calculation unit 3, and outputs the gate voltage change signal sig5 indicating the change to the gate drive circuit 8. do. The operations of the loss reduction unit 26 and the gate drive circuit 8 related to the added gate voltage change signal sig5 are the same as those of the first power converter 1 of the third embodiment.

The second power conversion device 1 of the third embodiment is small in size and can prevent a rapid temperature rise, like the power conversion device 1 of the first embodiment. The second power converter 1 of the third embodiment has the same effects as the first power converter 1 of the third embodiment.

As a method for increasing the voltage value of the gate drive signal sg4, an example using the booster 31 has been described, but the method is not limited to this example. As means for increasing the voltage value of the gate drive signal sg4, means such as switching to a power supply with a different voltage may be used. Further, when the method of increasing the switching speed of the gate drive signal sg4 described in Embodiment 2 and the method of increasing the voltage value of the gate drive signal sg4 are performed at the same time, the loss reduction output from the loss reduction unit 26 One signal is sufficient. In this case, the switching speed change signal sig4 may also serve as the gate voltage change signal sig5, and the gate voltage change signal sig5 may also serve as the switching speed change signal sig4.

Embodiment 4.
The power converter 1 of the fourth embodiment accurately estimates the temperature rise ΔTdi of the free wheel diode 6 in the power converters 1 of the first to third embodiments. That is, the power converter 1 of Embodiment 4 is an example including the element temperature estimator 25 that outputs the temperature rise ΔTdi with high accuracy. FIG. 14 is a diagram showing a configuration of a power converter according to Embodiment 4. FIG. In the power conversion device 1 shown in FIG. 14, the temperature rise ΔTsw of the switching element 5 is not input to the element temperature estimation unit 25 of the power conversion device 1 in FIG. A voltage detector 28 for detecting the value of the input voltage, that is, the input voltage value Vi is added, the element temperature estimation unit 25 reads the diode loss Pld, the loss map 42, and the thermal resistance storage unit reads the thermal resistance value Rth of the freewheeling diode 6 An example with 43 is shown. The parts different from the power converter 1 of Embodiment 1 will be mainly described.

In estimating the temperature rise ΔTdi of the freewheeling diode 6, the loss of the freewheeling diode 6 will be described. The loss of the freewheeling diode 6 is the diode loss Pld, which is the loss of the freewheeling diode per arm, and is part of the equation (1) in the first embodiment. Diode loss Pld can be expressed by Equation (8).
Pld=Pf+Pr (8)

The loss map 42 stores data on the diode loss Pld associated with the rotational speed Nm of the electric motor 2, the output current values iu, iv, and iw of the power conversion circuit 4, and the input voltage value Vi of the power conversion circuit 4. there is The element temperature estimator 25 calculates the rotation speed Nm of the electric motor 2 calculated based on the rotor position θ output from the rotation detector 9, and the output current values iu, iv, and iw output from the current detector 7. , and the input voltage value Vi output from the voltage detector 28 are used to read out the diode loss Pld.

Next, the thermal resistance value will be explained. The thermal resistance value Rth of the freewheeling diode 6 varies depending on the structure of the cooling system, but is a known value in terms of design. The thermal resistance storage unit 43 stores data of the thermal resistance value Rth of each free wheel diode 6 mounted in the power conversion circuit 4 . In the case of the power conversion circuit 4 shown in FIG. 2, the thermal resistance storage unit 43 stores six thermal resistance values Rth for each of the six freewheeling diodes 6a to 6f. The thermal resistance storage unit 43 stores a constant thermal resistance value regardless of the rotation speed Nm of the electric motor 2, the output current values iu, iv, and iw of the power conversion circuit 4, and the input voltage value Vi of the power conversion circuit 4. A resistance value Rth is stored.

When calculating the temperature rise ΔTdi of each free wheel diode 6, the element temperature estimator 25 uses the loss map 42 to calculate the rotation speed Nm of the electric motor 2 based on the rotor position θ output from the rotation detector 9, Based on the output current values iu, iv, iw and the input voltage value Vi, the diode loss Pld is read. Then, the element temperature estimating section 25 reads the thermal resistance value Rth from the thermal resistance storage section 43 with the reading of the diode loss Pld as a trigger. After that, the element temperature estimator 25 calculates the temperature rise ΔTdi of the freewheeling diode 6 according to the equation (9).
ΔTdi=Pld×Rth (9)

Since the power converter 1 of Embodiment 4 can accurately calculate the temperature rise ΔTdi of the freewheeling diode 6, it is possible to prevent excessive loss distribution that occurs when the accuracy of the temperature rise ΔTdi of the freewheeling diode 6 is poor. . If excessive loss sharing occurs, it is conceivable that the switching element 5 will be destroyed. Since the power conversion device 1 of Embodiment 4 can prevent excessive loss sharing, the size of the freewheeling diode 6 can be made smaller than when the temperature rise ΔTdi of the freewheeling diode 6 has poor accuracy. .

Similarly to the power converter 1 of the first embodiment, the power converter 1 of the fourth embodiment reduces the loss of the switching element 5 using the loss reduction unit 26 when it is determined that the electric motor 2 is in the stall state. After that, the duty control unit 23 is used to change the energization time of the power conversion element of each phase, that is, the switching element 5 and the freewheeling diode 6, and distribute the loss between the P-side power conversion element and the N-side power conversion element. Therefore, it is possible to reduce the size and prevent a rapid temperature rise. Furthermore, since the power conversion device 1 of Embodiment 4 can calculate the temperature rise ΔTdi of the freewheeling diode 6 with high accuracy, it is possible to realize a smaller power conversion device than when the temperature rise ΔTdi of the freewheeling diode 6 has poor accuracy. .

The element temperature estimator 25 including the voltage detector 28, the loss map 42, and the thermal resistance memory 43 described in the fourth embodiment can also be applied to the power converters 1 of the second and third embodiments.

Embodiment 5.
The power converter 1 of Embodiment 5 is an example including an element temperature estimator 25 that outputs a temperature rise ΔTdi with high accuracy, like the power converter 1 of Embodiment 4. FIG. FIG. 15 is a diagram showing a configuration of a power converter according to Embodiment 5. FIG. The power converter 1 shown in FIG. 15 shows an example in which the element temperature estimator 25 of the power converter 1 in FIG. 1 is provided with the proportional calculator 44 for calculating the temperature rise ΔTdi. The parts different from the power converter 1 of Embodiment 1 will be mainly described.

In the fourth embodiment, an example of calculating temperature rise ΔTdi of freewheeling diode 6 using thermal resistance value Rth having a constant thermal resistance value has been described. However, since the constant thermal resistance value includes manufacturing variations, the calculated temperature rise ΔTdi of the freewheeling diode 6 may become higher than the actual temperature rise. Therefore, if the loss is excessively distributed from the freewheeling diode 6 to the switching element 5, the switching element 5 may be destroyed. The power conversion device 1 of the fifth embodiment is an example that can calculate the temperature rise ΔTdi of the freewheeling diode 6 more accurately than the power conversion device 1 of the fourth embodiment.

In the fifth embodiment, it is noted that the freewheeling diode 6 is connected in anti-parallel to the switching element 5 in each arm. The temperature rises of the freewheeling diode 6 and the switching element 5 forming the same arm are known in design, and the relationship between the temperature rise ΔTdi of the freewheeling diode 6 and the temperature rise ΔTsw of the switching element 5 forming the same arm is known in design. be. Therefore, the temperature rise ΔTdi of each free wheel diode 6 can be calculated as shown in Equation (10) using the temperature rise ΔTsw of the switching element 5 forming the same arm and the coefficient α.
ΔTdi=α×ΔTsw (10)

The proportional calculation unit 44 executes the calculation of Equation (10) from the temperature rise ΔTswa of the switching element 5a output from the temperature monitor 24a, and outputs α×ΔTswa as ΔTdia. Similarly, the proportional calculation unit 44 performs the calculation of Equation (10) from the temperature rise ΔTswb of the switching element 5b output from the temperature monitor 24b, and outputs α×ΔTswb as ΔTdib. Proportional calculation unit 44 executes calculation of equation (10) from temperature rises ΔTswc to ΔTswf of switching elements 5c to 5f output from temperature monitors 24c to 24f, respectively, and outputs ΔTdic to ΔTdif.

The power conversion device 1 of Embodiment 5 performs the calculation shown in the equation (10) by the proportional calculation unit 44, that is, the calculation of multiplying ΔTsw, which is the first temperature information, by the coefficient α, so that the heat The temperature rise ΔTdi of the freewheeling diode 6 can be calculated more accurately than the power converter 1 of the fourth embodiment without using the resistance value.

As with the power converter 1 of the first embodiment, the power converter 1 of the fifth embodiment reduces the loss of the switching element 5 using the loss reduction unit 26 when it is determined that the electric motor 2 is in the stall state. After that, the duty control unit 23 is used to change the energization time of the power conversion element of each phase, that is, the switching element 5 and the freewheeling diode 6, and distribute the loss between the P-side power conversion element and the N-side power conversion element. Therefore, it is possible to reduce the size and prevent a rapid temperature rise. Furthermore, since the power conversion device 1 of the fifth embodiment can calculate the temperature rise ΔTdi of the freewheeling diode 6 more accurately than the power conversion device 1 of the fourth embodiment, a smaller power conversion device can be realized.

The element temperature estimator 25 including the proportional calculator 44 described in the fifth embodiment can also be applied to the power converters 1 of the second and third embodiments.

Embodiment 6.
The power conversion device 1 of the sixth embodiment is an example including an element temperature estimator 25 that outputs a highly accurate temperature rise ΔTdi, like the power conversion device 1 of the fourth embodiment. FIG. 16 is a diagram showing a configuration of a power converter according to Embodiment 6. FIG. In the power conversion device 1 of Embodiment 5, an example in which the proportional calculation unit 44 uses the fixed-value coefficient α to perform calculation as in Equation (10) is shown. There are many stall states, but in the case of a stall that climbs a hill at a very low speed, the temperature rise of the power conversion element changes with time. It may not be calculated accurately. In the power converter 1 of the sixth embodiment, the coefficient α is related to the rotation speed Nm of the electric motor 2, the output current values iu, iv, and iw, and the input voltage value Vi. The power conversion device 1 is an example in which the temperature rise ΔTdi of the freewheeling diode 6 is calculated by the equation (10) using the coefficient α that changes according to the state of the electric motor 2 . The power conversion device 1 of Embodiment 6 is added with a voltage detector 28 that outputs the input voltage value Vi of the power conversion circuit 4, and the element temperature estimator 25 and the proportional calculation unit 44 form a coefficient model that outputs the coefficient α. 45 is provided, which is different from the power converter 1 of the fifth embodiment. The parts different from the power converter 1 of Embodiment 5 will be mainly described.

The coefficient model 45 includes the rotation speed Nm of the electric motor 2 calculated based on the rotor position θ output from the rotation detector 9, the output current values iu, iv, and iw output from the current detector 7, and the voltage The input voltage value Vi output from the detector 28 is used to output the coefficient α. Since the input information input to the coefficient model 45, that is, the rotation speed Nm, the output current values iu, iv, iw, and the input voltage value Vi are parameters that change with time, the coefficient α can be changed from a fixed value to a variable value. By using the coefficient model 45, the coefficient α that changes according to the state of the electric motor 2 can be obtained.

The power conversion device 1 of Embodiment 6 uses the rotation speed Nm of the electric motor 2, the output current values iu, iv, and iw output from the current detector 7, and the input voltage value Vi output from the voltage detector 28. , and the coefficient α that changes according to changes in the input information is used to calculate the temperature rise ΔTdi of the freewheeling diode 6 as shown in Equation (10). It is possible to calculate the temperature rise ΔTdi of the free wheel diode 6 with high accuracy even when the vehicle is stalling up a slope.

Similarly to the power converter 1 of the first embodiment, the power converter 1 of the sixth embodiment reduces the loss of the switching element 5 using the loss reduction unit 26 when it is determined that the electric motor 2 is in the stall state. After that, the duty control unit 23 is used to change the energization time of the power conversion element of each phase, that is, the switching element 5 and the freewheeling diode 6, and distribute the loss between the P-side power conversion element and the N-side power conversion element. Therefore, it is possible to reduce the size and prevent a rapid temperature rise. Furthermore, the power conversion device 1 of Embodiment 6 can calculate the temperature rise ΔTdi of the free wheel diode 6 with high accuracy even when stalling up a slope at extremely low rotation. A power conversion device that is even smaller than the device 1 can be realized.

The element temperature estimator 25 including the proportional calculator 44 and the coefficient model 45 described in the sixth embodiment can also be applied to the power converters 1 of the second and third embodiments.

It should be noted that while this application describes various exemplary embodiments and examples, various features, aspects, and functions described in one or more of the embodiments may lie in particular embodiments. The embodiments can be applied singly or in various combinations. Accordingly, numerous variations not illustrated are envisioned within the scope of the technology disclosed herein. For example, modification, addition or omission of at least one component, extraction of at least one component, and combination with components of other embodiments shall be included.

DESCRIPTION OF SYMBOLS 1... Power converter device 2... Electric motor 3... Control calculating part 4... Power converter circuit 5, 5a, 5b, 5c, 5d, 5e, 5f... Switching element 6, 6a, 6b, 6c, 6d, 6e , 6f... Free wheel diode, 7, 7a, 7b, 7c... Current detector, 8... Gate drive circuit, 9... Rotation detector, 19... Triangular wave oscillator (oscillator), 23... Duty control section, 24a, 24b, 24c, 24d, 24e, 24f temperature monitor 25 element temperature estimator 26 loss reduction unit 27 stall determination unit 28 voltage detector 43 thermal resistance storage unit 44 proportional operation unit 45 coefficient model, α... coefficient, θ... rotor position, fc... frequency, iu, iv, iw... output current value, Nm... rotation speed, Pld... diode loss, Pldp... P-side diode loss, Pldn... N-side diode loss, Rth... thermal resistance value, sig2... frequency change signal (loss reduction signal), sig4... switching speed change signal (loss reduction signal), sig5... gate voltage change signal (loss reduction signal), vc... carrier wave, ΔTdi, ΔTdia, ΔTdib , ΔTdic, ΔTdid, ΔTdie, ΔTdif ... temperature rise (second temperature information), ΔTsw, ΔTswa, ΔTswb, ΔTswc, ΔTswd, ΔTswe, ΔTswf ... temperature rise (first temperature information), sg2 ... gate drive signal (first drive signal), sg3... gate drive signal (second drive signal), sg4... gate drive signal (third drive signal), Vi... input voltage value

Claims (11)

A power conversion device that supplies AC power converted from DC power to drive a motor,
a power conversion circuit including a plurality of switching elements and a free wheel diode, and a plurality of temperature monitors that output first temperature information that is temperature information of each of the switching elements, and supplying the AC power for driving the electric motor;
a control calculation unit that determines switching timings of the plurality of switching elements in the power conversion circuit and generates a first drive signal;
a rotation detector that detects a rotor position of the electric motor;
an element temperature estimating unit that estimates second temperature information, which is temperature information of the freewheeling diode, based on the first temperature information;
a stall determination unit that determines a stall state of the electric motor based on the rotor position of the electric motor;
a loss reduction unit that reduces the amount of heat generated by the switching element when the stall determination unit determines a stalled state;
a duty control unit that outputs the first drive signal as a second drive signal without changing it, or that outputs a second drive signal in which the ON time of the switching element in the first drive signal is changed;
a gate drive circuit that outputs to the power conversion circuit a third drive signal that switches the plurality of switching elements according to the second drive signal,
The duty control unit
The first temperature information of the switching element connected in series to the freewheeling diode in which the stall condition is determined by the stall determination unit and the second temperature information is maximized by the operation of the loss reduction unit has decreased. ON time of the switching element in the first drive signal so as to distribute the current flowing through the freewheeling diode with the maximum second temperature information to the switching elements connected in series with the freewheeling diode only when to the gate drive circuit. The control calculation unit includes an oscillator that generates a carrier wave used to generate the first drive signal,
2. The power converter according to claim 1, wherein said loss reduction unit outputs a loss reduction signal for lowering the frequency of said carrier wave to a frequency before the determination, when said stall determination unit determines a stall state. 2. The loss reduction unit according to claim 1, wherein when the stall state is determined by the stall determination unit, the loss reduction unit outputs to the gate drive circuit a loss reduction signal that makes the switching speed of the third drive signal faster than before the determination. power converter. 2. The loss reduction unit outputs a loss reduction signal for increasing the voltage value of the third drive signal to the gate drive circuit when the stall state is determined by the stall determination unit. A power converter as described. When the stall determination unit determines a stall state, the loss reduction unit causes the gate drive circuit to make the switching speed of the third drive signal faster than before the determination, and determines the voltage value of the third drive signal. 2. The power converter of claim 1, outputting a loss reduction signal that is greater than before. The control calculation unit includes an oscillator that generates a carrier wave used to generate the first drive signal,
The loss reduction unit is
outputting to the oscillator a first loss reduction signal that lowers the frequency of the carrier wave than before the determination when the stall determination unit determines a stall state, and switching the third drive signal to the gate drive circuit; 2. The power converter according to claim 1, which outputs a second loss reduction signal that makes the speed faster than before the determination. The control calculation unit includes an oscillator that generates a carrier wave used to generate the first drive signal,
The loss reduction unit is
outputting to the oscillator a first loss reduction signal that lowers the frequency of the carrier wave than before the determination when the stall determination unit determines the stall state, and outputs the voltage of the third drive signal to the gate drive circuit; 2. The power converter according to claim 1, which outputs a second loss reduction signal that makes the value larger than before the determination. The control calculation unit includes an oscillator that generates a carrier wave used to generate the first drive signal,
The loss reduction unit is
outputting to the oscillator a first loss reduction signal that lowers the frequency of the carrier wave than before the determination when the stall determination unit determines a stall state, and switching the third drive signal to the gate drive circuit; 2. The power converter according to claim 1, which outputs a second loss reduction signal that makes the speed higher than before the determination and the voltage value higher than before the determination. A power conversion device that supplies AC power converted from DC power to drive a motor,
a power conversion circuit including a plurality of switching elements and a free wheel diode, and a plurality of temperature monitors that output first temperature information that is temperature information of each of the switching elements, and supplying the AC power for driving the electric motor;
a control calculation unit that determines switching timings of the plurality of switching elements in the power conversion circuit and generates a first drive signal;
a rotation detector that detects a rotor position of the electric motor;
an element temperature estimating unit that estimates second temperature information that is temperature information of the freewheeling diode;
a stall determination unit that determines a stall state of the electric motor based on the rotor position of the electric motor;
a loss reduction unit that reduces the amount of heat generated by the switching element when the stall determination unit determines a stalled state;
a duty control unit that outputs the first drive signal as a second drive signal without changing it, or that outputs a second drive signal in which the ON time of the switching element in the first drive signal is changed;
a gate drive circuit that outputs to the power conversion circuit a third drive signal that switches the plurality of switching elements according to the second drive signal;
a voltage detector that detects the value of the input voltage input to the power conversion circuit;
a current detector that detects the value of the output current output from the power conversion circuit to the electric motor,
The element temperature estimator,
a thermal resistance storage unit storing a thermal resistance value of the freewheeling diode;
a loss map storing a diode loss of the free wheel diode associated with the rotation speed of the electric motor calculated based on the rotor position, the value of the output current of the power conversion circuit, and the value of the input voltage; , and
estimating the second temperature information based on the thermal resistance value and the diode loss;
The duty control unit
The first temperature information of the switching element connected in series to the freewheeling diode in which the stall condition is determined by the stall determination unit and the second temperature information is maximized by the operation of the loss reduction unit has decreased. the ON time of the switching element in the first drive signal so as to distribute the current flowing through the freewheeling diode with the maximum second temperature information to the switching element connected in series with the freewheeling diode. to the gate drive circuit. The power conversion device according to any one of claims 1 to 8, wherein the element temperature estimating unit includes a proportional calculation unit that calculates the second temperature information by multiplying the first temperature information by a coefficient. . a voltage detector that detects the value of the input voltage that is input to the power conversion circuit; and a current detector that detects the value of the output current that is output from the power conversion circuit to the electric motor,
The element temperature estimator,
11. A coefficient model for outputting the coefficient based on the number of rotations of the electric motor calculated based on the rotor position, the value of the output current of the power conversion circuit, and the value of the input voltage according to claim 10. A power converter as described.

Images