Power conversion device

Abstract

This power conversion device comprises: a voltage detector that detects the value of a DC voltage applied to an inverter circuit; a voltage change detector that senses an abnormality in the DC voltage on the basis of a change in the value of the DC voltage detected by the voltage detector, and outputs a predetermined abnormality signal; a driver circuit that has a gate resistor switching circuit that switches the resistor value of a gate resistor connected to the gate of each switching element of the inverter circuit, and that drives each of the switching elements via the gate resistor; and a controller that transmits a drive signal to the driver circuit and also transmits to the driver circuit a gate resistor switching signal for giving an instruction to switch the gate resistor. If the voltage change detector outputs the abnormality signal, the gate resistor switching circuit switches the resistor value of the gate resistor to a second resistor value larger than a first resistor value, regardless of the gate resistor switching signal.

Description

Power Conversion Device

[0001] The present invention relates to a power conversion device that converts DC power into AC power.

[0002] A power conversion device that converts DC power to AC power includes upper and lower arm series circuits for multiple phases, each of which is configured by connecting upper arm switching elements and lower arm switching elements in series. These switching elements are driven by a drive signal input via a gate resistor connected to the gate of each switching element.

[0003] Generally, switching elements provided in power conversion devices generate switching losses when current is applied. By reducing the resistance value of the gate resistor, the switching speed of the switching element can be increased and the loss of the switching element can be reduced. On the other hand, the fluctuation amount of the collector current per unit time when the switching element is turned off increases as the switching speed increases, and a surge voltage occurs in proportion to the fluctuation amount.

[0004] Therefore, a technology has been proposed for switching the resistance value of a gate resistor according to the operating conditions of a switching element, such as the applied voltage and current. For example, Patent Document 1 describes a power conversion device that uses the value of a current sensor that detects AC current and the value of a voltage sensor that detects DC voltage to determine a value equivalent to a peak voltage when a surge voltage is superimposed on a DC voltage applied to a switching element, and compares this value with a predetermined threshold value to switch the gate resistor based on the result. This power conversion device can reduce the switching speed so that the peak voltage of the DC voltage applied to the switching element does not exceed the withstand voltage of the switching element.

[0005] Japanese Patent Application Publication No. 2016-59089

[0006] In the technology described in Patent Document 1, if the internal voltage of the power conversion device suddenly rises due to some abnormality while the resistance value of the gate resistor is low, there is a risk that a surge voltage will cause a breakdown of the switching element, and therefore, the reliability of the power conversion device will decrease if the resistance value of the gate resistor is low.

[0007] The power conversion device according to the present invention includes an inverter circuit having a plurality of phases of series circuits each formed by connecting an upper arm switching element and a lower arm switching element in series between a DC positive terminal and a DC negative terminal, a voltage detector for detecting a value of a DC voltage applied to the inverter circuit, a voltage change detector for detecting an abnormality in the DC voltage based on a change in the value of the DC voltage detected by the voltage detector and outputting a predetermined abnormality signal, an output current detector for detecting an AC current output from a connection point between the upper arm switching element and the lower arm switching element, and a gate resistor for switching the resistance value of a gate resistor connected to the gate of each switching element of the inverter circuit. a driver circuit having a gate resistance switching circuit for switching each of the switching elements via the gate resistance; and a controller for transmitting a drive signal to the driver circuit and a gate resistance switching signal to the driver circuit instructing switching of the gate resistance, wherein the gate resistance switching circuit is capable of switching the resistance value of the gate resistor to one of a plurality of resistance values ​​including at least a first resistance value and a second resistance value greater than the first resistance value, and when the voltage change detector outputs the abnormal signal, the gate resistance switching circuit switches the resistance value of the gate resistor to the second resistance value regardless of the gate resistance switching signal.

[0008] According to the present invention, it is possible to improve the reliability of the power conversion device even when the resistance value of the gate resistor is reduced.

[0009] FIG. 1 is an overall configuration diagram of a power conversion device according to an embodiment of the present invention. FIG. 2 is a detailed configuration diagram of a main part of a power conversion device according to an embodiment of the present invention. FIG. 3 is a graph showing an example of the relationship between the current of a switching element and the collector-emitter voltage. FIG. 4 is a graph showing an example of changing the switching current of the switching speed according to the magnitude of the DC voltage applied to the inverter circuit. FIG. 5 is a diagram explaining the operation of a power conversion device in a load dump state when the present invention is not applied. FIG. 6 is a diagram explaining the operation of a power conversion device in a load dump state when the present invention is applied. FIG. 7 is a circuit block diagram showing an example of the configuration of a voltage change detector.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following description and drawings are examples for explaining the present invention, and some omissions and simplifications have been made as appropriate for clarity of explanation. The present invention can be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.

[0011] FIG. 1 is a diagram showing the overall configuration of a power conversion device 1000 according to one embodiment of the present invention.

[0012] The power conversion device 1000 converts DC power supplied from a DC power supply 2000 such as a battery into AC power to drive a motor 3000. The DC power supply 2000 supplies DC power between a positive terminal P and a negative terminal N of the power conversion device 1000 via a contactor 2001. The motor 3000 is, for example, a three-phase induction motor, and is used as a drive source for a vehicle.

[0013] The power conversion device 1000 includes an inverter circuit 300 connected between a positive terminal P and a negative terminal N and performing power conversion to convert DC power supplied from a DC power supply 2000 into AC power, a voltage detector 100 connected in parallel with the inverter circuit 300 between the positive terminal P and the negative terminal N and detecting a DC voltage applied to the inverter circuit 300, and a capacitor module 200 smoothing the DC current input to the inverter circuit 300. The power conversion device 1000 further includes an overvoltage detector 120, a voltage change detector 150, an output current detector 400, a controller 600, a shutoff circuit 700, a forced switching circuit 710, and a driver circuit 800.

[0014] The inverter circuit 300 includes a power module 310 having an upper and lower arm series circuit formed by connecting in series a switching element 311 and a diode 312 operating as an upper arm, and a switching element 321 and a diode 322 operating as a lower arm. Three power modules 310 are provided for each phase (U phase, V phase, and W phase) of the motor 3000, corresponding to each phase winding. That is, the inverter circuit 300 includes three series circuits formed by connecting in series an upper arm switching element 311 and a lower arm switching element 321 between a DC positive terminal P and a DC negative terminal N. While a three-phase example will be described here, a configuration may also be provided in which multiple power modules 310 are provided to match the number of phases of the motor 3000.

[0015] The output current detector 400 detects, for each phase, the AC current output from the connection point between the upper arm switching element 311 and the lower arm switching element 321, and outputs a detected value Ei of the AC current for each phase to the controller 600. The detected value Ei represents the magnitude of the detected AC current as a voltage value.

[0016] The overvoltage detector 120 detects if the DC voltage applied to the inverter circuit 300 is in an overvoltage state based on the detected value Vdc of the DC voltage output from the voltage detector 100, and outputs an overvoltage signal Eov.

[0017] The voltage change detector 150 detects abnormal fluctuations in the DC voltage applied to the inverter circuit 300 based on changes in the detected value Vdc of the DC voltage output from the voltage detector 100, and outputs an abnormality signal Eld.

[0018] A low-voltage power supply 4000 is connected to the controller 600 from the outside of the power conversion device 1000, and when the ignition key of the vehicle is turned on, a low voltage is supplied from the low-voltage power supply 4000. Then, in accordance with a torque command Ts from a higher-level controller (not shown), a detected value Vdc of DC voltage output from the voltage detector 100, a detected value Ei of AC current output from the output current detector 400, and the like, the controller 600 generates a drive signal Pw for driving the switching elements 311, 321 of each phase, and outputs the drive signal Pw to a driver circuit 800 provided for each of the switching elements 311, 321 of each phase.

[0019] Furthermore, the controller 600 generates a gate resistance switching signal Rs for switching the resistance value of the gate resistor connected to the gate of the switching element 311, 321 of each phase in accordance with the detected values ​​Vdc, Ei of the DC voltage and AC current output from the voltage detector 100 and the output current detector 400, respectively, and transmits the signal to each driver circuit 800. The details of the controller 600 will be described later.

[0020] The shutoff circuits 700 are provided corresponding to the driver circuits 800 provided for the switching elements 311, 321. Each shutoff circuit 700 shuts off the drive signal Pw output from the controller 600 to the driver circuit 800 in response to the overvoltage signal Eov output from the overvoltage detector 120. The shutoff circuits 700 will be described in detail later.

[0021] The forced switching circuits 710 are provided corresponding to the driver circuits 800 provided for the switching elements 311, 321. In response to the abnormality signal Eld output from the voltage change detector 150, each forced switching circuit 710 forcibly switches the resistance value of the gate resistor connected to the gate of the switching element 311, 321 of each phase, regardless of the gate resistance switching signal Rs output from the controller 600. Details of the forced switching circuits 710 will be described later.

[0022] A driver circuit 800 is provided corresponding to each of the switching elements 311, 321 of the inverter circuit 300. Each driver circuit 800 has a gate resistance switching circuit 820 (see FIG. 2) that can switch the resistance value of a gate resistor connected to the gate of the corresponding switching element 311, 321. Each driver circuit 800 drives the corresponding switching element 311, 321 by outputting a gate signal to the gate of the corresponding switching element 311, 321 via the gate resistor in response to a drive signal Pw input from the controller 600. The driver circuit 800 will be described in detail later.

[0023] 2 is a detailed configuration diagram of the main parts of a power conversion device 1000 according to one embodiment of the present invention. This diagram shows, as the main parts of the power conversion device 1000, the configuration of a driver circuit 800 corresponding to the lower arm switching element 321 in one phase of a power module 310, and a shutoff circuit 700 and a forced switching circuit 710 provided between this driver circuit 800 and a controller 600.

[0024] Although not shown in Fig. 2, the driver circuit 800 corresponding to the upper arm switching element 311 of one phase of the power module 310 has the same configuration as the driver circuit 800 corresponding to the lower arm switching element 321. Similar to the lower arm, a shutoff circuit 700 and a forced switching circuit 710 are provided between the driver circuit 800 corresponding to this upper arm and the controller 600. Furthermore, the driver circuits 800 for the upper and lower arms of the other phases also have the same configuration as in Fig. 2, and a shutoff circuit 700 and a forced switching circuit 710 are provided between these driver circuits 800 and the controller 600.

[0025] The AC current detection value Ei from the output current detector 400 and the DC voltage detection value Vdc from the voltage detector 100 are each input to the controller 600. A torque command Ts from a higher-level controller (not shown) is also input to the controller 600. The controller 600 generates a drive signal Pw based on these signals and transmits it to the driver circuit 800 via the shutoff circuit 700. The drive signal Pw is, for example, a PWM signal.

[0026] The controller 600 also determines whether to switch the resistance value of the gate resistor based on the detected AC current value Ei, and transmits a gate resistance switching signal Rs according to the result of the determination to the driver circuit 800 via the forced switching circuit 710. In the driver circuit 800, the resistance value of the gate resistor can be switched between a predetermined first resistance value and a second resistance value greater than the first resistance value. The controller 600 outputs the gate resistance switching signal Rs at either a first voltage level (e.g., H level) that instructs switching to the first resistance value, or a second voltage level (e.g., L level) that instructs switching to the second resistance value.

[0027] The cutoff circuit 700 immediately cuts off the drive signal Pw when the overvoltage signal Eov is input from the overvoltage detector 120. This causes the driver circuit 800 to stop driving the switching element 321.

[0028] When the abnormality signal Eld is input from the voltage change detector 150, the forced switching circuit 710 immediately sets the gate resistance switching signal Rs output to the driver circuit 800 to the second voltage level, regardless of the voltage level of the gate resistance switching signal Rs from the controller 600. As a result, even if the controller 600 is outputting the gate resistance switching signal Rs at the first voltage level, the resistance value of the gate resistor when the driver circuit 800 outputs a gate signal to the switching element 321 is forcibly switched from the first resistance value to the second resistance value in response to the input of the abnormality signal Eld. As a result, the switching speed of the driving of the switching element 321 in response to the gate signal is suppressed.

[0029] The driver circuit 800 includes a drive circuit 810 and a gate resistance switching circuit 820. The drive circuit 810 outputs a gate signal in response to a drive signal Pw input from the controller 600. The gate resistance switching circuit 820 has three types of gate resistors Rn0, Rf1, and Rf2, and outputs the gate signal input from the drive circuit 810 to the gate of the switching element 321 via one of these gate resistors Rn0, Rf1, or Rf2.

[0030] Gate resistor Rn0 is a resistor connected to the gate when the switching element 321 is turned on. Gate resistors Rf1 and Rf2 are resistors connected to the gate when the switching element 321 is turned off, and the resistance value of gate resistor Rf1 is lower than the resistance value of gate resistor Rf2. Here, the resistance value of gate resistor Rf1 corresponds to the above-mentioned first resistance value, and the resistance value of gate resistor Rf2 corresponds to the above-mentioned second resistance value.

[0031] In response to the voltage level of the input gate resistance switching signal Rs, the drive circuit 810 switches the gate resistance through which the gate signal passes when turning off the switching element 321 in the gate resistance switching circuit 820. That is, when the voltage level of the input gate resistance switching signal Rs is a first voltage level, the drive circuit 810 outputs a gate signal to the gate of the switching element 321 via the gate resistance Rf1 of the gate resistance switching circuit 820 when turning off the switching element 321. On the other hand, when the voltage level of the input gate resistance switching signal Rs is a second voltage level, the drive circuit 810 outputs a gate signal to the gate of the switching element 321 via the gate resistance Rf2 of the gate resistance switching circuit 820 when turning off the switching element 321. In this way, the resistance value of the gate resistance connected to the gate of the switching element 321 is switched in accordance with the gate resistance switching signal Rs.

[0032] Generally, switching loss occurs in the switching element 321 when it is driven. This switching loss reduces the efficiency of the inverter circuit 300 and, ultimately, the vehicle's cruising range. Therefore, in the power conversion device 1000 of this embodiment, depending on the operating conditions of the switching element 321, such as voltage and current, if possible, when turning off the switching element 321, the switching speed is increased by switching to a gate resistor Rf1 with a relatively low resistance value, thereby reducing the switching loss of the switching element 321. Specifically, when the DC voltage detection value Vdc by the voltage detector 100 is lower than a predetermined voltage value and the AC current detection value Ei by the output current detector 400 is lower than a predetermined current value, the allowable surge voltage of the switching element 321 becomes high. Therefore, in this case, the gate resistor Rf1 is switched to a gate resistor Rf1 with a relatively low resistance value to increase the switching speed and reduce the switching loss.

[0033] However, if the internal voltage of the power conversion device 1000 suddenly increases due to some abnormality while the resistance value of the gate resistor is set low as described above, a surge voltage generated when the switching element 321 is turned off may cause the switching element 321 to malfunction. Therefore, in the power conversion device 1000 of this embodiment, if an internal voltage increase occurs, the voltage change detector 150 detects this before the controller 600 recognizes it via software. The forced switching circuit 710 then sets the gate resistance switching signal Rs input to the driver circuit 800 to a second voltage level, thereby forcibly switching the resistance value of the gate resistor to a high value at turn-off. This immediately changes the resistance value of the gate resistor, suppressing the switching speed and preventing the switching element 321 from malfunctioning due to a surge voltage, without waiting for the controller 600 to switch the gate resistance switching signal Rs.

[0034] Next, a specific example of switching the resistance value of the gate resistor in accordance with the operating conditions of the switching element 321 will be described below with reference to FIGS.

[0035] 3 is a graph showing an example of the relationship between the current and collector-emitter voltage of the switching element 321. FIG. 3 shows two types of graphs, Vf1 and Vf2, with different slopes. Graph Vf1 shows the relationship between the current and collector-emitter voltage of the switching element 321 when gate resistor Rf1 is connected to the gate, and graph Vf2 shows the relationship between the current and collector-emitter voltage of the switching element 321 when gate resistor Rf2 is connected to the gate. In these graphs Vf1 and Vf2, the horizontal axis represents the effective value Ic of the current flowing through the switching element 321, and the vertical axis represents the peak value Vcep of the voltage applied between the collector and emitter of the switching element 321.

[0036] 3, when switching element 321 is turned off, the voltage applied between the collector and emitter of switching element 321 typically increases as the current flowing through switching element 321 increases. Furthermore, the degree of increase in collector-emitter voltage relative to the current of switching element 321 is greater in graph Vf1 than in graph Vf2. This shows that the smaller the resistance value of the gate resistor and the faster the switching speed, the greater the degree of increase in collector-emitter voltage relative to the current of switching element 321.

[0037] Here, the switching speed of the switching element 321 when it is turned off is inversely proportional to the resistance value of the gate resistor, and tends to be slower as the resistance value increases and faster as the resistance value decreases. Furthermore, the surge voltage generated when the switching element 321 is turned off decreases as the switching speed decreases and increases as the switching speed increases. That is, when the resistance value of the gate resistor is low, the switching loss of the switching element 321 can be reduced, but the surge voltage increases. On the other hand, when the resistance value of the gate resistor is high, the surge voltage applied to the switching element 321 can be reduced, but the switching loss increases.

[0038] Therefore, in the power conversion apparatus 1000 of this embodiment, the resistance value of the gate resistor connected to the switching element 321 is switched based on the AC current detection value Ei detected by the output current detector 400. Specifically, when the current of the switching element 321 is relatively small (Ic≦I0), the controller 600 outputs a gate resistance switching signal Rs at a first voltage level, causing the gate resistance switching circuit 820 to select the gate resistance Rf1. In this case, the current and collector-emitter voltage of the switching element 321 change according to the graph Vf1 in FIG. 3 . On the other hand, when the current of the switching element 321 is relatively large (Ic>I0), the controller 600 outputs a gate resistance switching signal Rs at a second voltage level, causing the gate resistance switching circuit 820 to select the gate resistance Rf2. In this case, the current and collector-emitter voltage of the switching element 321 change according to the graph Vf2 in FIG. 3 . In FIG. 3, Vm represents the allowable value (allowable breakdown voltage) of the collector-emitter voltage of the switching element 321 .

[0039] As described above, by lowering the resistance value of the gate resistor in the low current region to increase the switching speed, and by increasing the resistance value of the gate resistor in the high current region to decrease the switching speed, it is possible to reduce switching loss while keeping the voltage applied between the collector and emitter of the switching element 321 below the allowable value Vm.

[0040] FIG. 4 is a graph showing an example in which the switching current of the switching speed is changed according to the magnitude of the DC voltage applied to the inverter circuit 300. In FIG.

[0041] 4 shows three types of graphs A, B, and C with different switching current values. Graph A shows the relationship between the current and collector-emitter voltage of the switching element 321 at turn-off when the switching current for the switching speed is the lowest current value I0A. Graph B shows the relationship between the current and collector-emitter voltage of the switching element 321 at turn-off when the switching current for the switching speed is the intermediate current value I0B. Graph C shows the relationship between the current and collector-emitter voltage of the switching element 321 at turn-off when the switching current for the switching speed is the highest current value I0C. In these graphs A, B, and C, the horizontal axis represents the effective value Ic of the current flowing through the switching element 321, and the vertical axis represents the peak value Vcep of the voltage applied between the collector and emitter when the switching element 321 is turned off.

[0042] The DC voltage applied to the inverter circuit 300 is detected by the voltage detector 100 as described above, and the detection result is input to the controller 600 as the detection value Vdc. When the detection value Vdc of the input DC voltage is near a predetermined overvoltage detection level Vov (e.g., 500 V), the controller 600 sets the switching speed switching current to a current value I0A. In this case, the voltage applied between the collector and emitter due to the surge voltage when the switching element 321 is turned off changes as shown in graph A depending on the current flowing through the switching element 321, and the resistance value of the gate resistor is switched around the current value I0A. This allows the driver circuit 800 to be controlled so that the voltage applied between the collector and emitter of the switching element 321 does not exceed the allowable value Vm.

[0043] Furthermore, when the detected value Vdc of the input DC voltage is near a predetermined voltage level (e.g., 300 V), the controller 600 sets the switching current for switching the switching speed to current value IOB. In this case, the voltage applied between the collector and emitter in response to the surge voltage when the switching element 321 is turned off changes as shown in graph B in response to the current flowing through the switching element 321, and the resistance value of the gate resistor is switched around current value IOB. As a result, compared to the case of graph A, a state in which the gate resistance value is small and the switching speed is fast can be maintained up to a higher current value IOB, widening the range in which switching loss can be reduced.

[0044] Furthermore, when the detected value Vdc of the input DC voltage is less than a predetermined voltage level (e.g., 300 V), the controller 600 sets the switching current for switching the switching speed to current value IOC. In this case, the voltage applied between the collector and emitter in response to the surge voltage when the switching element 321 is turned off changes as shown in graph C in response to the current flowing through the switching element 321, and the resistance value of the gate resistor is switched around current value IOC. As a result, compared to the case of graph B, the state in which the gate resistance value is small and the switching speed is fast can be maintained up to a higher current value IOC, further widening the range in which switching loss can be reduced.

[0045] The function of varying the switching current of the switching speed in the controller 600 as described above can be realized, for example, by referring to a map showing the relationship between the detected DC voltage value Vdc and the detected AC current value Ei, which is stored in advance in the controller 600. Alternatively, the function of varying the switching current of the switching speed may be realized by calculation using a predetermined calculation formula or the like.

[0046] Next, the operation of the forced switching circuit 710 will be described in detail below with reference to FIGS.

[0047] An abnormality in which the internal voltage increases suddenly due to some factor may occur in the power conversion device 1000. For example, if the contactor 2001 is unintentionally turned off during a regenerative operation of the motor 3000, the power conversion device 1000 enters a load dump state, and the internal voltage increases suddenly.

[0048] Fig. 5 is a diagram illustrating the operation of a power conversion device in a load dump state when the present invention is not applied. Below, as an example of a case when the present invention is not applied, the operation of a conventional power conversion device in a load dump state that does not include the voltage change detector 150 and the forced switching circuit 710 of Fig. 2 will be described with reference to Fig. 5. In the following description, it is assumed that the components of the conventional power conversion device, other than the voltage change detector 150 and the forced switching circuit 710, are the same as those shown in Figs. 1 and 2.

[0049] FIG. 5(a) is a graph showing an example of the relationship between the current and collector-emitter voltage of the switching element 321 when it is turned off. FIG. 5(a) shows two types of graphs, B and Bov, which show different DC voltages applied to the inverter circuit 300. Graph B shows the relationship between the current and collector-emitter voltage of the switching element 321 when it is turned off in a normal state that is not a load dump state, while graph Bov shows the relationship between the current and collector-emitter voltage of the switching element 321 when it is turned off in a load dump state. In these graphs B and Bov, the horizontal axis represents the effective value Ic of the current flowing between the collector and emitter of the switching element 321, and the vertical axis represents the peak value Vcep of the voltage applied between the collector and emitter when the switching element 321 is turned off. Graph B is the same as that shown in FIG. 4.

[0050] Fig. 5(b) is a graph that schematically shows the relationship between the internal voltage of the power conversion device 1000 and the collector-emitter voltage of the switching element 321. In the graph of Fig. 5(b), the horizontal axis represents time, and the vertical axis represents the voltage applied between the collector and emitter of the switching element 321. Note that Fig. 5(b) shows the voltage level on the vertical axis in accordance with Fig. 5(a).

[0051] If the power conversion device 1000 enters a load dump state for some reason, the internal voltage rises, causing an overall increase in the collector-emitter voltage of the switching element 321. Therefore, the relationship between the current and collector-emitter voltage of the switching element 321 at turn-off changes from graph B to graph Bov in FIG. 5( a). If, before the internal voltage rises, the collector-emitter voltage peak value Vcep is, for example, point Vp1 on graph B, after the internal voltage rises, the voltage peak value Vcep changes to point Vp1ov on graph Bov. The voltage indicated by point Vp1ov after this change exceeds the aforementioned allowable value Vm, and therefore, it can be seen that there is a risk of the switching element 321 failing if left unchecked.

[0052] Furthermore, when the power conversion device 1000 enters a load dump state at time t1 in Fig. 5(b), the internal voltage HVDC gradually increases over time as shown in Fig. 5(b). Then, at time t2, which is a time Tov after time t1, the internal voltage HVDC reaches an overvoltage detection level Vov, and the overvoltage detector 120 detects an overvoltage state and outputs an overvoltage signal Eov. In response to the output of this overvoltage signal Eov, the shutoff circuit 700 shuts off the drive signal Pw, thereby stopping the drive of the switching element 321 at time t2.

[0053] However, at time t2, the collector-emitter voltage of the switching element 321 rises to a peak voltage corresponding to point Vp1ov in Fig. 5(a) due to the surge voltage being superimposed on the internal voltage HVDC at turn-off. This peak voltage Vp1ov exceeds the allowable value Vm as shown in Fig. 5(b), and therefore it can be seen that there is a risk of the switching element 321 breaking down if left as is.

[0054] 6 is a diagram illustrating the operation of the power conversion device 1000 in a load dump state when the present invention is applied to solve the above problem. Unlike the case of FIG. 5 described above, FIG. 6 illustrates the operation of the power conversion device 1000 in a load dump state when the voltage change detector 150 and the forced switching circuit 710 are provided in the power conversion device 1000.

[0055] FIG. 6(a) is a graph showing an example of the relationship between the current and collector-emitter voltage of the switching element 321 during turn-off. FIG. 6(a) shows two types of graphs, B and Bov', which represent different DC voltages applied to the inverter circuit 300. Graph B shows the relationship between the current and collector-emitter voltage of the switching element 321 during turn-off in a normal state, not a load dump state, while graph Bov' shows the relationship between the current and collector-emitter voltage of the switching element 321 during turn-off in a normal state during a load dump state. In these graphs B and Bov', the horizontal axis represents the effective value Ic of the current flowing between the collector and emitter of the switching element 321, and the vertical axis represents the peak value Vcep of the voltage applied between the collector and emitter when the switching element 321 is turned off. Graph B is the same as that shown in FIGS. 4 and 5(a).

[0056] Fig. 6(b) is a graph that schematically shows the relationship between the internal voltage of the power conversion device 1000 and the collector-emitter voltage of the switching element 321. In the graph of Fig. 6(b), the horizontal axis represents time, and the vertical axis represents the voltage applied between the collector and emitter of the switching element 321. Note that Fig. 6(b) shows the voltage level on the vertical axis in accordance with Fig. 6(a).

[0057] Fig. 6(c) is a graph showing an internal signal of the voltage change detector 150. In the graph of Fig. 6(c), the horizontal axis represents time, and the vertical axis represents the differential value dV / dt obtained by time-differentiating the DC voltage detection value (voltage detection signal) Vdc detected by the voltage detector 100. Note that the time on the horizontal axis in Fig. 6(c) is shown in accordance with Fig. 6(b).

[0058] When the power conversion device 1000 enters a load dump state, the internal voltage rises, causing an overall increase in the collector-emitter voltage of the switching element 321. Therefore, similar to the case of Fig. 5, the relationship between the current and collector-emitter voltage of the switching element 321 at turn-off changes from graph B to graph Bov' in Fig. 6(a). Furthermore, as shown in Fig. 6(b), when the power conversion device 1000 enters a load dump state at time t1, the internal voltage HVDC rises over time.

[0059] As described above, when the internal voltage HVDC increases over time in the load dump state, the detected value Vdc of the DC voltage indicated by the voltage detection signal output from the voltage detector 100 also increases accordingly. As a result, as shown in FIG. 6(c), the differential value dV / dt of the voltage detection signal increases after time t1.

[0060] The voltage change detector 150 compares the differential value dV / dt of the voltage detection signal with a predetermined threshold value VDth, and when the differential value dV / dt exceeds the threshold value VDth, it outputs the abnormality signal Eld for a certain time interval. As a result, the abnormality signal Eld is output from the voltage change detector 150 for a certain period of time starting from time tld in FIG. 6( c). This abnormality signal Eld is input to the controller 600 and the forced switching circuit 710.

[0061] When the forced switching circuit 710 receives the abnormality signal Eld, as described above, it sets the gate resistance switching signal Rs input to the driver circuit 800 to a second voltage level that instructs the gate resistance switching circuit 820 to select the gate resistance Rf2, regardless of the voltage level of the gate resistance switching signal Rs output from the controller 600. Due to the operation of this forced switching circuit 710, for a certain period from time tld, the gate resistance Rf2 is selected in the gate resistance switching circuit 820 when the switching element 321 is turned off. As a result, as shown in FIG. 6B, the switching speed is slowed down and the surge voltage is reduced compared to the period before time tld.

[0062] When the present invention is applied, by doing as described above, even if the internal voltage HVDC reaches the overvoltage detection level Vov, the peak voltage Vp1ov' generated between the collector and emitter when the switching element 321 is turned off can be suppressed to below the allowable value Vm. Therefore, the switching element 321 can be safely protected.

[0063] Although an example in which the value of the internal voltage HVDC corresponds to graph B has been described in FIG. 6, even if the value of the internal voltage HVDC corresponds to graph C shown in FIG. 4, the function of the forced switching circuit 710 as described above makes it possible to protect the switching element 321 in the same manner.

[0064] As an alternative method for protecting the switching element 321 from surge voltages when it is turned off, it is possible to lower the overvoltage detection level Vov at which the shutoff circuit 700 shuts off the drive signal Pw when the internal voltage HVDC corresponds to the values ​​of graphs B and C. While FIG. 4 illustrates three types of graphs A to C with switching current values ​​I0A to I0C, in practice, it is desirable to provide a multi-stage switching current value or to linearly switch the switching current value according to the internal voltage HVDC. To achieve this, the configuration of the shutoff circuit 700 becomes more complex. Therefore, adopting a method such as this embodiment, in which the voltage change detector 150 detects changes in the internal voltage HVDC over time and, when the changes over time exceed a predetermined value, forcibly switches the resistance value of the gate resistor to reduce the switching speed, provides protection from surge voltages when the switching element 321 is turned off, with a simpler configuration.

[0065] Next, the voltage change detector 150 will be described in detail with reference to FIG.

[0066] 7 is a circuit block diagram showing an example of the configuration of the voltage change detector 150. The voltage change detector 150 includes a differentiating circuit 152, a comparator 154, and a pulse output circuit 156.

[0067] The differential circuit 152 receives a DC voltage detection value (voltage detection signal) Vdc detected by the voltage detector 100. The differential circuit 152 outputs a differential value dV / dt of the input voltage detection signal Vdc to the comparator 154.

[0068] The comparator 154 compares the input differential value dV / dt with a predetermined threshold value VDth and outputs a signal according to the comparison result. Specifically, if the differential value dV / dt is equal to or less than the threshold value VDth, the comparator 154 outputs an L-level signal, and if the differential value dV / dt exceeds the threshold value VDth, the comparator 154 outputs an H-level signal.

[0069] The pulse output circuit 156 outputs a pulse signal of a predetermined width based on the output signal of the comparator 154. Specifically, when the output signal of the comparator 154 changes from L level to H level, the pulse output circuit 156 outputs a pulse signal of a predetermined width as the abnormality signal Eld described above. As a result, the abnormality signal Eld is output from the voltage change detector 150 for a predetermined period after the differential value dV / dt of the voltage detection signal exceeds the threshold value VDth.

[0070] The abnormality signal Eld output from the pulse output circuit 156 as a pulse signal of a predetermined width is input to the gate terminal of the switch element S1 of the forced switching circuit 710. The switch element S1 is connected to the output terminal of the gate resistance switching signal Rs of the controller 600, and when the abnormality signal Eld is input, conducts between this output terminal and ground potential. As a result, regardless of the voltage level of the gate resistance switching signal Rs from the controller 600, the voltage level of the gate resistance switching signal Rs input to the driver circuit 800 becomes L level (second voltage level), and the resistance value of the gate resistor when the gate signal is output from the driver circuit 800 to the switching element 321 at turn-off is forcibly switched to the second resistance value.

[0071] When the internal voltage of the power conversion device 1000 rises due to an abnormality such as a load dump, the voltage detection signal output from the voltage detector 100 rises sharply. This causes the differential value dV / dt of the voltage detection signal output from the differentiating circuit 152 to rise. As a result, when the differential value dV / dt exceeds the threshold value VDth set in the comparator 154, the output of the comparator 154 becomes H level, and the input signal to the pulse output circuit 156 changes from L level to H level. When the input signal to the pulse output circuit 156 changes from L level to H level in this manner, a pulse signal with a constant pulse width is output from the pulse output circuit 156 as the abnormality signal Eld, which is input to the forced switching circuit 710. In response to the input of the abnormality signal Eld from the pulse output circuit 156, the forced switching circuit 710 switches the gate resistance switching signal Rs to the second voltage level.

[0072] The pulse width of the abnormality signal Eld can be set to any value, as long as it is at least longer than the time (e.g., several tens of milliseconds) from when the abnormality signal Eld is output until the internal voltage HVDC of the power conversion device 1000 reaches a predetermined overvoltage detection level Vov and the driving of the switching element 321 is stopped.

[0073] Any values ​​can be set for the circuit constants of the differentiating circuit 152, i.e., the capacitance value of the capacitor C1 and the resistance value of the resistor R1. However, it is preferable to select circuit constants for the differentiating circuit 152 such that even if there is a DC voltage fluctuation due to a ripple voltage generated during normal operation of the power conversion device 1000, the resulting differential value dV / dt of the voltage detection signal will not exceed the threshold value VDth, and the differential value dV / dt of the voltage detection signal will exceed the threshold value VDth only during a load dump.

[0074] 7, the differentiating circuit 152 has two inputs, one of which is the DC voltage detection value (voltage detection signal) Vdc detected by the voltage detector 100 described above. The other is a diagnostic signal Vdc_ck output from the controller 600. This diagnostic signal Vdc_ck is used for initial diagnosis of the voltage change detector 150 as follows.

[0075] The controller 600 can output a predetermined diagnostic signal Vdc_ck to the voltage change detector 150 in a state before the contactor 2001 is turned on and the voltage of the DC power supply 2000 is applied to the power conversion device 1000, i.e., in a state in which the internal voltage HVDC of the power conversion device 1000 is near zero. In the voltage change detector 150, when the diagnostic signal Vdc_ck from the controller 600 is input to the differentiating circuit 152, the output of the differentiating circuit 152 exceeds the threshold value VDth, similar to when the voltage detection signal Vdc from the voltage detector 100 increases. As a result, a pulse signal with a predetermined width is output from the pulse output circuit 156 as the abnormality signal Eld. An initial diagnosis of the voltage change detector 150 is performed by checking the output of this abnormality signal Eld.

[0076] The initial diagnosis of the voltage change detector 150 as described above is performed, for example, every time the power conversion device 1000 is started up. This makes it possible to improve the reliability of the power conversion device 1000.

[0077] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0078] (1) The power conversion device 1000 includes an inverter circuit 300 having a plurality of phases of a series circuit formed by connecting upper arm switching elements 311 and lower arm switching elements 321 in series between a positive terminal P and a negative terminal N of a DC line; a voltage detector 100 that detects the value of a DC voltage applied to the inverter circuit 300; a voltage change detector 150 that detects an abnormality in the DC voltage based on a change in the value Vdc of the DC voltage detected by the voltage detector 100 and outputs a predetermined abnormality signal Eld; The inverter circuit 300 includes an output current detector 400 that detects an AC current output from a connection point between the output current detector 400 and the switching element 321; a driver circuit 800 that has a gate resistance switching circuit 820 that switches the resistance values ​​of gate resistors connected to the gates of each switching element 311, 321 of the inverter circuit 300 and drives each switching element 311, 321 via the gate resistors; and a controller 600 that sends a drive signal Pw to the driver circuit 800 and a gate resistance switching signal Rs to the driver circuit 800 instructing the driver circuit 800 to switch the gate resistances. The gate resistance switching circuit 820 can switch the resistance values ​​of the gate resistors to one of a plurality of resistance values ​​including at least a first resistance value that is the resistance value of the gate resistor Rf1 and a second resistance value that is the resistance value of the gate resistor Rf2 and is greater than the first resistance value. When the voltage change detector 150 outputs an abnormality signal Eld, the gate resistance switching circuit 820 switches the resistance value of the gate resistors to the second resistance value regardless of the gate resistance switching signal Rs. As a result, even if the internal voltage HVDC of the power conversion device 1000 suddenly rises due to some abnormality while the resistance value of the gate resistor is set low, it is possible to avoid failure of the switching elements 311, 321 due to a surge voltage. Therefore, it is possible to improve the reliability of the power conversion device 1000 even when the resistance value of the gate resistor is set low.

[0079] (2) The gate resistance switching circuit 820 switches the resistance value of the gate resistance to the second resistance value when turning off each of the switching elements 311, 321. As a result, even if a surge voltage generated when the switching elements 311, 321 are turned off is superimposed on the internal voltage HVDC when the internal voltage HVDC of the power conversion device 1000 is increased, the voltage applied between the collector and emitter of the switching elements 311, 321 can be suppressed to or below the allowable value Vm.

[0080] (3) The voltage change detector 150 includes a differentiating circuit 152 to which a voltage detection signal Vdc output from the voltage detector 100 in response to the value of the DC voltage is input, a comparator 154 that compares a signal dV / dt output from the differentiating circuit 152 in response to the input of the voltage detection signal Vdc with a predetermined voltage threshold and outputs a signal in response to the comparison result, and a pulse output circuit 156 that outputs a pulse signal of a predetermined width based on the output signal of the comparator 154. This configuration makes it possible to realize a voltage change detector 150 that can reliably detect an abnormality in the DC voltage and output an abnormality signal Eld for a required period of time.

[0081] (4) It is preferable that the circuit constant of the differentiation circuit 152 be determined based on the magnitude of the ripple voltage superimposed on the DC voltage. In this way, it is possible to realize a voltage change detector 150 that does not output an abnormality signal Eld even if there is a DC voltage fluctuation due to a ripple voltage when the power conversion device 1000 is operating normally, but that outputs an abnormality signal Eld only when a load dump occurs.

[0082] (5) The controller 600 can output a predetermined diagnostic signal Vdc_ck to the voltage change detector 150. When the diagnostic signal Vdc_ck is input from the controller 600, the voltage change detector 150 outputs the abnormality signal Eld even when no abnormality in the DC voltage is detected. This configuration allows an initial diagnosis of the voltage change detector 150 to be performed when the power conversion device 1000 is started up, thereby improving the reliability of the power conversion device 1000.

[0083] A variable function may be provided for at least one of the circuit constants of the differentiation circuit 152, i.e., the capacitance value of the capacitor C1 and the resistance value of the resistor R1. For example, by providing a function that makes these values ​​variable in response to an instruction from the controller 600, it becomes possible to set an optimal circuit constant for the differentiation circuit 152 in response to variations in the voltage of the DC power supply 2000 and the capacitance value of the capacitor module 200 of the various power conversion devices 1000.

[0084] Furthermore, in the voltage change detector 150 of this embodiment, the output of the abnormality signal Eld for forcibly switching the resistance value of the gate resistor from the first resistance value to the second resistance value for a certain period is realized by the pulse output circuit 156, but this may be replaced by a circuit other than the pulse output circuit 156, such as a latch circuit. When a latch circuit is used, the desired function can be realized by using a mechanism that latches the output signal of the comparator 154 by the latch circuit until a reset signal is received from the controller 600, for example.

[0085] In addition, in this embodiment, the voltage change detector 150 and the forced switching circuit 710 are realized by hardware circuits having a circuit configuration such as that shown in FIG. 7, but these can also be substituted by software.

[0086] The present invention is not limited to the above-described embodiments, and other embodiments that are conceivable within the scope of the technical concept of the present invention are also included within the scope of the present invention as long as they do not impair the characteristics of the present invention. Furthermore, configurations that combine the above-described embodiments may also be used.

[0087] 100... Voltage detector, 120... Overvoltage detector, 150... Voltage change detector, 152... Differentiation circuit, 154... Comparator, 156... Pulse output circuit, 200... Capacitor module, 300... Inverter circuit, 310... Power module, 311, 321... Switching elements, 312, 322... Diodes, 400... Output current detector, 600... Controller, 700... Shutdown circuit, 710... Forced switching circuit, 800... Driver circuit, 810... drive circuit, 820... gate resistance switching circuit, 1000... power conversion device, 2000... DC power supply, 2001... contactor, 3000... motor, 4000... low voltage power supply, Rn0, Rf1, Rf2... gate resistance, Rs... gate resistance switching signal, Pw... drive signal, Vdc... DC voltage detection value (voltage detection signal), Ei... AC current detection value, Eov... overvoltage signal, Eld... abnormality signal, Vdc_ck... diagnostic signal

Claims

1. An inverter circuit having a plurality of phases, each phase comprising a series circuit formed by connecting a switching element of an upper arm and a switching element of a lower arm in series between a positive terminal and a negative terminal of a direct current; a voltage detector for detecting a value of a direct current voltage applied to the inverter circuit; a voltage change detector for detecting an abnormality of the direct current voltage based on a change in the value of the direct current voltage detected by the voltage detector and outputting a predetermined abnormality signal; an output current detector for detecting an alternating current output from a connection point between the switching element of the upper arm and the switching element of the lower arm; a gate resistor switching circuit for switching a resistance value of a gate resistor connected to a gate of each switching element of the inverter circuit, and a driver circuit for driving each switching element via the gate resistor; and a controller for transmitting a driving signal to the driver circuit and transmitting a gate resistor switching signal for instructing switching of the gate resistor to the driver circuit, wherein the gate resistor switching circuit can switch the resistance value of the gate resistor to any one of a plurality of resistance values including at least a first resistance value and a second resistance value larger than the first resistance value, and when the voltage change detector outputs the abnormality signal, the gate resistor switching circuit switches the resistance value of the gate resistor to the second resistance value regardless of the gate resistor switching signal. A power conversion device.

2. The power conversion device according to claim 1, wherein the gate resistor switching circuit switches the resistance value of the gate resistor to the second resistance value when each switching element is turned off.

3. The power conversion device according to claim 1, wherein the voltage change detector includes a differentiating circuit to which a voltage detection signal output from the voltage detector is input according to the value of the direct current voltage, a comparator for comparing a signal output from the differentiating circuit according to the input of the voltage detection signal with a predetermined voltage threshold value and outputting a signal according to the comparison result, and a pulse output circuit for outputting a pulse signal having a predetermined width based on an output signal of the comparator.

4. The power conversion device according to claim 3, wherein a circuit constant of the differentiating circuit is determined based on a magnitude of a ripple voltage superimposed on the direct current voltage.

5. The power conversion device according to claim 3, wherein a circuit constant of the differentiating circuit is variable according to an instruction from the controller.

6. The power conversion device according to claim 1, wherein the controller is capable of outputting a predetermined diagnostic signal to the voltage change detector, and the voltage change detector outputs the abnormal signal even when the controller inputs the diagnostic signal and the abnormality of the DC voltage is not detected.

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