Power conversion device

Abstract

The power conversion device of the present invention includes: a voltage detector that detects a DC voltage value applied to an inverter circuit; a voltage change detector that detects an anomaly in the DC voltage based on a change in the DC voltage value detected by the voltage detector and outputs a predetermined anomaly signal; a drive circuit having a gate resistor switching circuit that switches the resistance value of a gate resistor connected to the gate of each switching element of the inverter circuit, and drives each switching element via the gate resistor; and a controller that sends a drive signal to the drive circuit and sends a gate resistor switching signal to the drive circuit instructing the switching of the gate resistor. When the voltage change detector outputs the anomaly signal, the gate resistor switching circuit switches the resistance value of the gate resistor to a second resistance value greater than the first resistance value, independent of the gate resistor switching signal.

Description

Technical Field

[0001] This invention relates to a power conversion device that converts DC power to AC power. Background Technology

[0002] A power conversion device that converts DC power to AC power includes an upper and lower arm series circuit, equivalent to a multiphase circuit, which connects the switching elements of the upper arm and the lower arm in series. Furthermore, these switching elements are driven by a drive signal input via a gate resistor connected to the gate of each switching element.

[0003] Typically, switching losses occur when power is applied to the switching elements of a power conversion device. Reducing the gate resistor value can increase the switching speed of the switching element, thereby reducing these losses. On the other hand, the variation in collector current per unit time when the switching element is turned off increases with increasing switching speed, and surge voltage is generated proportionally to its magnitude.

[0004] Therefore, a technique has been proposed to switch the gate resistor value based on the operating conditions of the switching element, such as the applied voltage and current. For example, Patent Document 1 describes a power conversion device that uses the values ​​of a current sensor that detects alternating current and a voltage sensor that detects DC voltage to calculate the equivalent peak voltage value when a surge voltage is superimposed on the DC voltage applied to the switching element, and switches the gate resistor based on the result obtained by comparing this value with a predetermined threshold. This power conversion device can reduce the switching speed, thereby ensuring that the peak voltage of the DC voltage applied to the switching element does not exceed the withstand voltage of the switching element.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2016-59089 Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] In the technology described in Patent Document 1, when the gate resistor value is set to a low value, a surge voltage may cause the switching element to malfunction if the internal voltage of the power conversion device rises sharply due to some anomaly. Therefore, the reliability of the power conversion device decreases when the gate resistor value is set to a low value.

[0010] Technical solutions to solve technical problems

[0011] The power conversion device according to the present invention includes: an inverter circuit having a series circuit equivalent to a multiphase quantity between a positive and a negative DC terminal, the series circuit connecting the upper arm switching element and the lower arm switching element in series; a voltage detector that detects the DC voltage value applied to the inverter circuit; a voltage change detector that detects an abnormality in the DC voltage based on the change in the DC voltage value detected by the voltage detector and outputs a predetermined abnormality signal; an output current detector that detects the alternating current output from the connection point of the upper arm switching element and the lower arm switching element; and a drive circuit having a function to control the inverter circuit. A gate resistor switching circuit that switches the resistance value of the gate resistor connected to the gate of each switching element of the inverter circuit, and drives the switching elements via the gate resistor; and a controller that sends a drive signal to the drive circuit and sends a gate resistor switching signal to the drive circuit indicating to switch the gate resistor, the gate resistor switching circuit being able to 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 greater than the first resistance value, and, when the voltage change detector outputs the abnormal 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.

[0012] Invention Effects

[0013] According to the present invention, the reliability of the power conversion device can be improved even when the resistance value of the gate resistor is set to a low value. Attached Figure Description

[0014] Figure 1 This is an overall structural diagram of the power conversion device according to one embodiment of the present invention.

[0015] Figure 2 This is a detailed structural diagram of the main parts of the power conversion device according to an embodiment of the present invention.

[0016] Figure 3 This is an example graph showing the relationship between the current of a switching element and the collector-emitter voltage.

[0017] Figure 4 This is a graph illustrating an example of how the switching current changes the switching speed depending on the magnitude of the DC voltage applied to the inverter circuit.

[0018] Figure 5 This is a diagram illustrating the operation of the power conversion device under load drop conditions when the present invention is not applied.

[0019] Figure 6 This is a diagram illustrating the operation of the power conversion device under load drop conditions when applying the present invention.

[0020] Figure 7 This is a circuit block diagram illustrating an example of a voltage change detector. Detailed Implementation

[0021] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The following description and drawings are examples for illustrating the present invention, and appropriate omissions and simplifications have been made to clarify the description. The present invention can also be implemented in various other ways. Unless otherwise specified, each structural element can be either a single element or a plurality of elements.

[0022] Figure 1 This is an overall structural diagram of the power conversion device 1000 according to an embodiment of the present invention.

[0023] The power conversion device 1000 converts the DC power supplied from the DC power source 2000, such as a battery, into AC power to drive the motor 3000. The DC power source 2000 supplies DC power between the positive terminal P and the negative terminal N of the power conversion device 1000 via a contactor 2001. The motor 3000 is, for example, a three-phase induction motor, used as the drive source for the vehicle.

[0024] The power conversion device 1000 includes: an inverter circuit 300 connected between a positive terminal P and a negative terminal N, performing power conversion to convert DC power supplied from a DC power source 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, detecting the DC voltage applied to the inverter circuit 300; and a capacitor module 200 filtering the DC current input to the inverter circuit 300. The power conversion device 1000 also includes: an overvoltage detector 120, a voltage change detector 150, an output current detector 400, a controller 600, a cutoff circuit 700, a forced switching circuit 710, and a drive circuit 800.

[0025] The inverter circuit 300 includes a power module 310, which has an upper and lower arm series circuit formed by connecting a switching element 311 and a diode 312 operating as the upper arm and a switching element 321 and a diode 322 operating as the lower arm in series. Furthermore, the power module 310 is configured to have a three-phase (U-phase, V-phase, W-phase) quantity corresponding to each phase winding of the motor 3000. That is, the inverter circuit 300 has a three-phase series circuit between the positive DC terminal P and the negative DC terminal N, which connects the upper arm switching element 311 and the lower arm switching element 321 in series. Here, a three-phase example is used, but for example, a multi-phase power module 310 structure could be configured to match the number of phases of the motor 3000.

[0026] The output current detector 400 detects the AC current output from the connection point of the upper arm switching element 311 and the lower arm switching element 321 for each phase, and outputs the AC current detection value Ei of each phase to the controller 600. The detection value Ei is represented by a voltage value to indicate the magnitude of the detected AC current.

[0027] The overvoltage detector 120 detects an overvoltage condition when the DC voltage applied to the inverter circuit 300 is in an overvoltage state, based on the DC voltage detection value Vdc output from the voltage detector 100, and outputs an overvoltage signal Eov.

[0028] The voltage change detector 150 detects abnormal fluctuations in the DC voltage applied to the inverter circuit 300 based on the change in the DC voltage detection value Vdc output from the voltage detector 100, and outputs an abnormal signal Eld.

[0029] With the low-voltage power supply 4000 connected externally to the power conversion device 1000, a low voltage is supplied to the controller 600 when the vehicle's ignition key is in the on state. Furthermore, based on the torque command Ts from the upper-level controller (not shown), the DC voltage detection value Vdc output from the voltage detector 100, and the AC current detection value Ei output from the output current detector 400, drive signals Pw for driving the phase switching elements 311 and 321 are generated and output to the drive circuit 800 provided for each phase's switching element 311 and 321, respectively.

[0030] Furthermore, the controller 600 generates a gate resistance switching signal Rs based on the DC voltage detection value Vdc and AC current detection value Ei output from the voltage detector 100 and the output current detector 400, respectively. This signal is used to switch the resistance value of the gate resistor connected to the gate of the switching elements 311 and 321 of each phase, and is sent to each drive circuit 800. Details of the controller 600 will be described later.

[0031] Each cutoff circuit 700 is provided corresponding to the drive circuit 800 provided for each switching element 311, 321. Each cutoff circuit 700 cuts off the drive signal Pw output from the controller 600 to the drive circuit 800 in response to the overvoltage signal Eov output from the overvoltage detector 120. Details of the cutoff circuit 700 will be described later.

[0032] The forced switching circuit 710 is provided for each drive circuit 800 provided for each switching element 311, 321. Each forced switching circuit 710, in response to an abnormal signal Eld output from the voltage change detector 150, 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 resistor switching signal Rs output from the controller 600. Details of the forced switching circuit 710 will be described later.

[0033] The drive circuit 800 is provided corresponding to each switching element 311, 321 of the inverter circuit 300. Each drive circuit 800 has a gate resistance switching circuit 820 (see reference) capable of switching the resistance value of the gate resistor connected to the gate of the corresponding switching element 311, 321. Figure 2 Each drive circuit 800 outputs a gate signal to the gate of the corresponding switching element 311, 321 via a gate resistor based on the drive signal Pw input from the controller 600, thereby driving the switching element. Details of the drive circuit 800 will be described later.

[0034] Figure 2 This is a detailed structural diagram of the main parts of the power conversion device 1000 according to an embodiment of the present invention. In this figure, as the main parts of the power conversion device 1000, the structure of the drive circuit 800 corresponding to the lower arm switching element 321 in the power module 310 which corresponds to a phase quantity is shown, as well as the cut-off circuit 700 and the forced switching circuit 710 provided between the drive circuit 800 and the controller 600 are shown.

[0035] In addition, although Figure 2 The diagram is omitted, but the structure of the drive circuit 800 corresponding to the upper arm switching element 311 in the power module 310, which corresponds to one phase, is the same as the structure of the drive circuit 800 corresponding to the lower arm switching element 321. Furthermore, a cut-off circuit 700 and a forced switching circuit 710 are provided between the drive circuit 800 corresponding to the upper arm and the controller 600, just as they are for the lower arm. Furthermore, the drive circuits 800 for the upper and lower arms of other phases also have the same structure as... Figure 2 With the same structure, a cut-off circuit 700 and a forced switching circuit 710 are also provided between these drive circuits 800 and controller 600.

[0036] 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 respectively input to the controller 600. Additionally, the 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 sends it to the drive circuit 800 via the cutoff circuit 700. The drive signal Pw is, for example, a PWM signal.

[0037] Furthermore, the controller 600 determines whether to switch the gate resistor value based on the AC current detection value Ei, and sends the gate resistor switching signal Rs corresponding to the determination result to the drive circuit 800 via the forced switching circuit 710. In the drive circuit 800, the gate resistor value can be switched to either a predetermined first resistance value or a second resistance value greater than the first resistance value. The controller 600 outputs the gate resistor switching signal Rs at either a first voltage level (e.g., H level) indicating switching to the first resistance value or a second voltage level (e.g., L level) indicating switching to the second resistance value.

[0038] When an overvoltage signal Eov is input from the overvoltage detector 120, the cutoff circuit 700 immediately cuts off the drive signal Pw. This stops the drive circuit 800 from driving the switching element 321.

[0039] When an abnormal 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 drive circuit 800 to the second voltage level, regardless of the voltage level of the gate resistance switching signal Rs from the controller 600. Therefore, even when the controller 600 outputs the gate resistance switching signal Rs at the first voltage level, the resistance value of the gate resistor when the drive circuit 800 outputs the gate signal to the switching element 321 will be forcibly switched from the first resistance value to the second resistance value upon the input of the abnormal signal Eld. As a result, the driving switching speed of the switching element 321 corresponding to the gate signal is suppressed.

[0040] The drive circuit 800 includes a drive circuit 810 and a gate resistor switching circuit 820. The drive circuit 810 outputs a gate signal according to the drive signal Pw input from the controller 600. The gate resistor switching circuit 820 has three 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 any one of these gate resistors Rn0, Rf1, and Rf2.

[0041] The gate resistor Rn0 is the resistor connected to the gate when the switching element 321 is turned on. Gate resistors Rf1 and Rf2 are the resistors connected to the gate when the switching element 321 is turned off, with the resistance value of gate resistor Rf1 being lower than that of gate resistor Rf2. Here, the resistance value of gate resistor Rf1 is equivalent to the first resistance value described above, and the resistance value of gate resistor Rf2 is equivalent to the second resistance value described above.

[0042] The drive circuit 810 responds to the voltage level of the input gate resistance switching signal Rs, and switches the gate resistance through which the gate signal passes when the switching element 321 is turned off 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 gate signal is output to the gate of the switching element 321 via the gate resistance Rf1 of the gate resistance switching circuit 820 when the switching element 321 is turned off. On the other hand, when the voltage level of the input gate resistance switching signal Rs is a second voltage level, the gate signal is output to the gate of the switching element 321 via the gate resistance Rf2 of the gate resistance switching circuit 820 when the switching element 321 is turned off. Thus, the resistance value of the gate resistance connected to the gate of the switching element 321 is switched according to the gate resistance switching signal Rs.

[0043] Typically, switching element 321 generates switching losses during operation. These switching losses are a major cause of reduced efficiency in inverter circuit 300, and consequently, reduced vehicle range. Therefore, in the power conversion device 1000 of this embodiment, based on the operating conditions of switching element 321 such as voltage and current, the switching speed is increased and the switching losses of switching element 321 are reduced when possible by switching to a gate resistor Rf1 with a relatively low resistance value when switching element 321 is turned off. Specifically, when the DC voltage detection value Vdc based on voltage detector 100 is lower than a specified voltage value, and the AC current detection value Ei based on output current detector 400 is lower than a specified current value, the allowable surge voltage of switching element 321 becomes high. Therefore, in this case, switching to a gate resistor Rf1 with a relatively low resistance value increases the switching speed and reduces switching losses.

[0044] However, when the gate resistor value is set to a low value as described above, if the internal voltage of the power conversion device 1000 increases sharply due to some anomaly, the 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, when an internal voltage rise occurs, the voltage change detector 150 detects the situation earlier than the controller 600 identifies the situation through software. Then, the gate resistor switching signal Rs input to the drive circuit 800 is set to the second voltage level by the forced switching circuit 710, thereby forcibly switching the gate resistor value to a higher value when turned off. As a result, without waiting for the gate resistor switching signal Rs based on the controller 600 to switch, the resistance value of the gate resistor can be changed immediately to suppress the switching speed, thereby preventing the switching element 321 from malfunctioning due to surge voltage.

[0045] Next, refer to Figure 3 and Figure 4 A specific example of switching the resistance value of the gate resistor according to the operating conditions of the switching element 321 will be explained.

[0046] Figure 3 This is an example graph showing the relationship between the current of the switching element 321 and the collector-emitter voltage. Figure 3 The diagram shows two curves, Vf1 and Vf2, with different slopes. Curve Vf1 represents the relationship between the current in switching element 321 and the collector-emitter voltage when gate resistor Rf1 is connected to the gate, while curve Vf2 represents the relationship between the current in switching element 321 and the collector-emitter voltage when gate resistor Rf2 is connected to the gate. In these curves Vf1 and Vf2, the horizontal axis represents the effective value Ic of the current flowing through switching element 321, and the vertical axis represents the peak value Vcep of the collector-emitter voltage applied to switching element 321.

[0047] like Figure 3 As shown by curves Vf1 and Vf2, typically, when switching element 321 is turned off, the collector-emitter voltage applied to switching element 321 increases with the increase of the current flowing through switching element 321. Furthermore, for the degree of increase in collector-emitter voltage relative to the current of switching element 321, curve Vf1 becomes greater than curve Vf2. Therefore, it can be concluded that the smaller the gate resistor value and the faster the switching speed, the greater the increase in collector-emitter voltage relative to the current of switching element 321.

[0048] 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, tending to be slower when the resistance value is higher and faster when the resistance value is lower. 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 gate resistor value is low, although the switching losses of the switching element 321 can be reduced, the surge voltage increases. On the other hand, when the gate resistor value is high, although the surge voltage applied to the switching element 321 can be reduced, the switching losses increase.

[0049] Therefore, in the power conversion device 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 based on the output current detector 400. Specifically, when the current of the switching element 321 is relatively small (Ic≤I0), a gate resistor switching signal Rs is output from the controller 600 at a first voltage level, thereby selecting the gate resistor Rf1 in the gate resistor switching circuit 820. In this case, the current of the switching element 321 is related to the collector-emitter voltage according to... Figure 3 The current of the switching element 321 varies with the curve Vf1. On the other hand, when the current of the switching element 321 is relatively large (Ic > I0), a gate resistor switching signal Rs is output from the controller 600 at a second voltage level, thereby selecting the gate resistor Rf2 in the gate resistor switching circuit 820. In this case, the current of the switching element 321 varies with the collector-emitter voltage according to... Figure 3 The curve Vf2 changes accordingly. Figure 3 In this context, Vm represents the allowable value (allowable withstand voltage) of the collector-emitter voltage of the switching element 321.

[0050] As described above, the gate resistance value is reduced in the low current region to increase the switching speed, while the gate resistance value is increased in the high current region to reduce the switching speed. This allows the collector-emitter voltage applied to the switching element 321 to be suppressed to below the allowable value Vm, while reducing switching losses.

[0051] Figure 4 It is a graph showing an example of how the switching current changes the switching speed depending on the magnitude of the DC voltage applied to the inverter circuit 300.

[0052] Figure 4The diagram shows three curves, A, B, and C, with different switching current values. Curve A represents the relationship between the current when the switching element 321 is turned off and the collector-emitter voltage when the switching current is at its lowest value (I0A). Curve B represents the relationship between the current when the switching current is at its middle value (I0) and the collector-emitter voltage when the switching current is at its highest value (I0C). In these curves 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 to the collector-emitter when the switching element 321 is turned off.

[0053] 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 a detection value Vdc. When the input DC voltage detection value Vdc is near a specified overvoltage detection level Vov (e.g., 500V), the controller 600 sets the switching current for the switching speed to a current value I0A. In this case, the voltage applied between the collector and emitter corresponding to the surge voltage when the switching element 321 is turned off varies according to the current flowing through the switching element 321 as shown in curve A, and the resistance value of the gate resistor is switched around the current value I0A. Thus, the drive circuit 800 can be controlled so that the voltage applied between the collector and emitter of the switching element 321 does not exceed the allowable value Vm.

[0054] Furthermore, when the input DC voltage detection value Vdc is near a specified voltage level (e.g., 300V), the controller 600 sets the switching current for the switching speed to a current value I0B. In this case, the voltage applied between the collector and emitter corresponding to the surge voltage when the switching element 321 is turned off varies according to the current flowing through the switching element 321, as shown in curve B, and the gate resistance value switches around the current value I0B. Therefore, compared to the case of curve A, a state with a smaller gate resistance and faster switching speed can be maintained up to a higher current value I0B, thereby expanding the range for reducing switching losses.

[0055] Furthermore, when the input DC voltage detection value Vdc is near a specified voltage level (e.g., 300V), the controller 600 sets the switching current for the switching speed to a current value I0C. In this case, the voltage applied between the collector and emitter corresponding to the surge voltage when the switching element 321 is turned off varies according to the current flowing through the switching element 321, as shown in curve C, and the gate resistance value switches around the current value I0C. Therefore, compared to the case of curve B, a state with a smaller gate resistance and faster switching speed can be maintained up to a higher current value I0C, thereby further expanding the range for reducing switching losses.

[0056] Furthermore, the variable switching current function of the switching speed in the controller 600, as described above, can be implemented, for example, by pre-storing a mapping representing the relationship between the DC voltage detection value Vdc and the AC current detection value Ei in the controller 600 and referring to that mapping. Alternatively, the variable switching current function can also be implemented by using calculations of a prescribed formula.

[0057] Next, refer to Figure 5 and Figure 6 The following is a detailed explanation of the operation of the forced switching circuit 710.

[0058] In the power conversion device 1000, an abnormality of a sharp increase in internal voltage sometimes occurs due to certain main reasons. For example, during the regenerative operation of the motor 3000, if the contactor 2001 unexpectedly turns off, the power conversion device 1000 enters a load drop state, and the internal voltage increases sharply.

[0059] Figure 5 This diagram illustrates the operation of a power conversion device under load sag conditions without the application of this invention. Hereinafter, as an example of a situation where this invention is not applied, [the following is an example using...]. Figure 5 For those not set Figure 2 The operation of a conventional power conversion device with voltage change detector 150 and forced switching circuit 710 under load drop conditions will be described. Furthermore, in the following description, in the conventional power conversion device, all structures except for voltage change detector 150 and forced switching circuit 710 are described as... Figure 1 , Figure 2 The structure shown is general.

[0060] Figure 5 (a) is an example graph showing the relationship between the current when the switching element 321 is turned off and the collector-emitter voltage. Figure 5In (a), two curves, B and Bov, are shown when the DC voltage applied to the inverter circuit 300 is different. Curve B represents the relationship between the current when the switching element 321 is turned off and the collector-emitter voltage under normal conditions without a load drop, while curve Bov represents the relationship between the current when the switching element 321 is turned off and the collector-emitter voltage under load drop conditions. In these curves B and Bov, the horizontal axis represents the effective value Ic of the current flowing through the collector-emitter of the switching element 321, and the vertical axis represents the peak value Vcep of the voltage applied to the collector-emitter when the switching element 321 is turned off. Furthermore, curves B and... Figure 4 The same as shown.

[0061] Figure 5 (b) is a graph schematically showing the relationship between the internal voltage of the power conversion device 1000 and the collector-emitter voltage of the switching element 321. Figure 5 In the graph in (b), the horizontal axis represents time, and the vertical axis represents the voltage applied between the collector and emitter of the switching element 321. Additionally, in Figure 5 In (b), the voltage level on the vertical axis is aligned with... Figure 5 (a) Matching map shown.

[0062] If, for some reason, the power conversion device 1000 enters a load drop state, the internal voltage rises, causing an overall increase in the collector-emitter voltage of the switching element 321. Therefore, the relationship between the current of the switching element 321 during turn-off and the collector-emitter voltage changes. Figure 5 (a) shows a change from curve B to curve Bov. If, before the internal voltage rises, the peak collector-emitter voltage Vcep is, for example, point Vp1 on curve B, then after the internal voltage rises, the peak voltage Vcep changes to point Vp1ov on curve Bov. It can be seen that since the voltage shown at point Vp1ov after this change exceeds the aforementioned allowable value Vm, this could potentially cause the switching element 321 to malfunction.

[0063] Furthermore, if the power conversion device 1000 is in Figure 5 (b) At time t1, the load suddenly drops, then the following... Figure 5 As shown in (b), the internal voltage HVDC gradually increases over time. Furthermore, at time t2, after time Tov from time t1, if the internal voltage HVDC reaches the overvoltage detection level Vov, the overvoltage detector 120 detects the overvoltage state and outputs an overvoltage signal Eov. Based on the output of this overvoltage signal Eov, the cutoff circuit 700 cuts off the drive signal Pw, thereby stopping the drive of the switching element 321 at time t2.

[0064] However, at time t2, the collector-emitter voltage of the switching element 321 will rise to a level equivalent to the surge voltage superimposed on the internal voltage HVDC during turn-off. Figure 5 (a) The peak voltage at point Vp1ov. It can be seen that because this peak voltage Vp1ov is as... Figure 5 As shown in (b), the value exceeds the allowable value Vm, and if this continues, it may cause the switching element 321 to malfunction.

[0065] Figure 6 This diagram illustrates the operation of the power conversion device 1000 under a load drop condition when the present invention is applied, addressing the aforementioned technical problems. Figure 6 In the middle, with the above Figure 5 The following describes the operation of the power conversion device 1000 under a load drop condition, where a voltage change detector 150 and a forced switching circuit 710 are provided in the power conversion device 1000.

[0066] Figure 6 (a) is a graph showing an example of the relationship between the current when the switching element 321 is turned off and the collector-emitter voltage. Figure 6 In (a), two curves, B and Bov', are shown with different DC voltages applied to the inverter circuit 300. Curve B represents the relationship between the current when the switching element 321 is turned off and the collector-emitter voltage under normal conditions of no load drop, while curve Bov' represents the relationship between the current when the switching element 321 is turned off and the collector-emitter voltage under normal conditions of load drop. In these curves B and Bov', the horizontal axis represents the effective value Ic of the current flowing through the collector-emitter of the switching element 321, and the vertical axis represents the peak value Vcep of the voltage applied to the collector-emitter when the switching element 321 is turned off. Furthermore, curves B and... Figure 4 and Figure 5 Same as shown in (a).

[0067] Figure 6 (b) is a graph schematically showing the relationship between the internal voltage of the power conversion device 1000 and the collector-emitter voltage of the switching element 321. Figure 6 In the graph in (b), the horizontal axis represents time, and the vertical axis represents the voltage applied between the collector and emitter of the switching element 321. Additionally, in Figure 6 In (b), the voltage level on the vertical axis is aligned with... Figure 6 (a) Matching map shown.

[0068] Figure 6 (c) is a graph representing the internal signal of the voltage change detector 150. In Figure 6In the graph (c), the horizontal axis represents time, and the vertical axis represents the derivative value dV / dt obtained by differentiating the DC voltage detection value (voltage detection signal) Vdc based on the voltage detector 100 over time. Additionally, in Figure 6 In (c), the time on the horizontal axis is aligned with... Figure 6 (b) Matching map shown.

[0069] If the power conversion device 1000 enters a load drop state, the internal voltage rises, causing an overall increase in the collector-emitter voltage of the switching element 321. Therefore, with Figure 5 Similarly, the relationship between the current when the switching element 321 is turned off and the collector-emitter voltage is as follows: Figure 6 (a) shows a change from curve B to curve Bov'. Additionally, as... Figure 6 As shown in (b), if the power conversion device 1000 becomes a load drop state at time t1, the internal voltage HVDC will rise over time.

[0070] As described above, under load sag conditions, if the internal voltage HVDC rises over time, the corresponding DC voltage detection value Vdc represented by the voltage detection signal output from the voltage detector 100 also rises. As a result, as... Figure 6 As shown in (c), after time t1, the differential value dV / dt of the voltage detection signal increases.

[0071] Inside the voltage change detector 150, the differential value dV / dt of the voltage detection signal is compared with a predetermined threshold VDth. If the differential value dV / dt exceeds the threshold VDth, the aforementioned abnormal signal Eld is output over a certain time width. Thus, from... Figure 6 During a certain period starting from time tld in (c), an abnormal signal Eld is output from the voltage change detector 150. This abnormal signal Eld is input to the controller 600 and the forced switching circuit 710.

[0072] If the forced switching circuit 710 receives an abnormal signal Eld, then, as previously described, regardless of the voltage level of the gate resistance switching signal Rs output from the controller 600, it sets the gate resistance switching signal Rs input to the drive circuit 800 to the second voltage level instructing the gate resistance switching circuit 820 to select the gate resistance Rf2. Through the operation of this forced switching circuit 710, during a certain period starting from time tld, the gate resistance switching circuit 820 selects the gate resistance Rf2 when the switching element 321 is turned off. The result is as follows: Figure 6 As shown in (b), the surge voltage is reduced due to the decrease in switching speed compared to the period before time tld.

[0073] When the present invention is applied, by setting it 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.

[0074] In addition, Figure 6 The example given is the case where the value of the internal voltage HVDC is equivalent to curve B. However, even when the value of the internal voltage HVDC is equivalent to curve B... Figure 4 In the case of curve C shown, the switching element 321 can also be protected by the function of the forced switching circuit 710 as described above.

[0075] Here, as another method of protecting against surge voltage when the switching element 321 is turned off, it is possible to consider changing the overvoltage detection level Vov of the cut-off drive signal Pw by the cut-off circuit 700 to a lower value when the value of the internal voltage HVDC is equivalent to curves B and C. However, although Figure 4 The example illustrates three curves A to C for switching current values ​​from I0A to I0C. However, in practice, it is desirable to further segment or linearly switch the switching current value according to the internal voltage HVDC. To achieve this, the structure of the cut-off circuit 700 becomes complex. Therefore, by using a method as in this embodiment, detecting the time change of the internal voltage HVDC in the voltage change detector 150, and forcibly switching the resistance value of the gate resistor to reduce the switching speed when the time change exceeds a predetermined value, protection against surge voltage when the switching element 321 is turned off can be achieved with a simpler structure.

[0076] Next, use Figure 7 The details of the voltage change detector 150 are explained below.

[0077] Figure 7 This is a circuit block diagram illustrating an example of the structure of a voltage change detector. The voltage change detector 150 includes a differentiating circuit 152, a comparator 154, and a pulse output circuit 156.

[0078] The differential circuit 152 inputs the detected value (voltage detection signal) Vdc of the DC voltage based on the voltage detector 100. The differential circuit 152 outputs the derivative value dV / dt of the input voltage detection signal Vdc to the comparator 154.

[0079] Comparator 154 compares the input differential value dV / dt with a predetermined threshold VDth and outputs a signal corresponding to the comparison result. Specifically, when the differential value dV / dt is less than or equal to the threshold VDth, it outputs an L-level signal; when the differential value dV / dt exceeds the threshold VDth, it outputs an H-level signal.

[0080] The pulse output circuit 156 outputs a pulse signal of a specified 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, it outputs a pulse signal of a specified width as the aforementioned abnormal signal Eld. Thus, during a specified period after the differential value dV / dt of the voltage detection signal exceeds the threshold VDth, the voltage change detector 150 outputs the abnormal signal Eld.

[0081] An abnormal signal Eld, output as a pulse signal of a specified width from the pulse output circuit 156, is input to the gate terminal of the switching element S1 in the forced switching circuit 710. The switching element S1 is connected to the output terminal of the gate resistance switching signal Rs of the controller 600, and when the abnormal signal Eld is input, it makes the output terminal conduct to the 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 drive circuit 800 becomes L level (second voltage level), thereby forcibly switching the resistance value of the gate resistor when the drive circuit 800 outputs the gate signal to the switching element 321 during turn-off to the second resistance value.

[0082] When the internal voltage of the power conversion device 1000 rises due to an anomaly such as a sudden load drop, the voltage detection signal output from the voltage detector 100 rises sharply. Consequently, the differential value dV / dt of the voltage detection signal output from the differentiating circuit 152 increases. As a result, when the differential value dV / dt exceeds the threshold VDth set in the comparator 154, the output of the comparator 154 becomes H level, and the input signal of the pulse output circuit 156 changes from L level to H level. Therefore, when the input signal of the pulse output circuit 156 changes from L level to H level, a pulse signal with a certain pulse width is output from the pulse output circuit 156 as an abnormal signal Eld, and input to the forced switching circuit 710. Based on the abnormal signal Eld input from the pulse output circuit 156, the forced switching circuit 710 switches the gate resistor switching signal Rs to the second voltage level.

[0083] Here, the pulse width of the aforementioned abnormal signal Eld can be set to any value. As long as it is at least greater than the time from the output abnormal signal Eld until the internal voltage HVDC of the power conversion device 1000 reaches the specified overvoltage detection level Vov, thereby stopping the drive of the switching element 321 (for example, about tens of ms), there is no problem even if the pulse width of the abnormal signal Eld is set to any time.

[0084] Furthermore, the circuit constants of the differentiating circuit 152, namely the capacitance value of capacitor C1 and the resistance value of resistor R1, can be set to arbitrary values. Preferably, a circuit constant is chosen such that even if there are DC voltage fluctuations caused by pulsating voltages generated during normal operation of the power conversion device 1000, the differential value dV / dt of the resulting voltage detection signal will not exceed the threshold VDth, and will only exceed the threshold VDth during a sudden load drop.

[0085] like Figure 7 As shown, the input to the differentiating circuit 152 has two systems: one is the DC voltage detection value (voltage detection signal) Vdc based on the voltage detector 100, as described above; the other is the diagnostic signal Vdc_ck output from the controller 600. This diagnostic signal Vdc_ck is used for the initial diagnosis of the voltage change detector 150, as described below.

[0086] 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., when the internal voltage HVDC of the power conversion device 1000 is close to zero), the controller 600 can output a predetermined diagnostic signal Vdc_ck to the voltage change detector 150. In the voltage change detector 150, if the diagnostic signal Vdc_ck from the controller 600 is input to the differentiating circuit 152, similar to the case where the voltage detection signal Vdc from the voltage detector 100 rises, the output of the differentiating circuit 152 exceeds the threshold VDth. As a result, a pulse signal of a predetermined width is output from the pulse output circuit 156 as an abnormal signal Eld. Initial diagnosis of the voltage change detector 150 is performed by confirming the output of this abnormal signal Eld.

[0087] The initial diagnostics of the voltage change detector 150 described above are performed, for example, each time the power conversion device 1000 is started. This improves the reliability of the power conversion device 1000.

[0088] According to one embodiment of the present invention described above, the following effects are achieved.

[0089] (1) The power conversion device 1000 includes: an inverter circuit 300, which has a series circuit equivalent to a multiphase quantity between the positive terminal P and the negative terminal N of the DC circuit, the series circuit connecting the upper arm switching element 311 and the lower arm switching element 321 in series; a voltage detector 100, which detects the DC voltage value applied to the inverter circuit 300; a voltage change detector 150, which detects the abnormality of the DC voltage based on the change of the DC voltage value Vdc detected by the voltage detector 100, and outputs a predetermined abnormality signal Eld; and an output power supply. The system includes: a current detector 400 that detects the alternating current output from the connection point of the upper arm switching element 311 and the lower arm switching element 321; a drive circuit 800 having a gate resistor switching circuit 820 that switches the resistance value of the gate resistor connected to the gate of each switching element 311, 321 of the inverter circuit 300, and drives each switching element 311, 321 via the gate resistor; and a controller 600 that sends a drive signal Pw to the drive circuit 800 and a gate resistor switching signal Rs indicating the switching of the gate resistor. The gate resistor switching circuit 820 is capable of switching the resistance value of the gate resistor to any one of a plurality of resistance values, including at least a first resistance value as the resistance value of the gate circuit Rf1 and a second resistance value as the resistance value of the gate circuit Rf2 that is greater than the first resistance value. When the voltage change detector 150 outputs an abnormal signal Eld, the gate resistor switching circuit 820 switches the gate resistor value to a second resistance value, independent of the gate resistor switching signal Rs. In this way, even if the internal voltage HVDC of the power conversion device 1000 rises sharply due to some abnormality when the gate resistor value is set low, failure of the switching elements 311 and 321 due to surge voltage can be avoided. Therefore, the reliability of the power conversion device 1000 can be improved even when the gate resistor value is set low.

[0090] (2) When each of the switching elements 311 and 321 is turned off, the gate resistor switching circuit 820 switches the resistance value of the gate resistor to the second resistance value. In this way, even when the internal voltage HVDC of the power conversion device 1000 rises, the surge voltage generated when the switching elements 311 and 321 are turned off is superimposed on the internal voltage HVDC, and the voltage between the collector and emitter of the switching elements 311 and 321 can be suppressed to below the allowable value Vm.

[0091] (3) The voltage change detector 150 includes: a differentiating circuit 152, which receives a voltage detection signal Vdc output from the voltage detector 100 based on a DC voltage value; a comparator 154, which compares the signal dV / dt output from the differentiating circuit 152 with a predetermined voltage threshold based on the input voltage detection signal Vdc, and outputs a signal corresponding to the comparison result; and a pulse output circuit 156, which outputs a pulse signal of a predetermined width based on the output signal of the comparator 154. In this way, a voltage change detector 150 can be realized that reliably detects an abnormality when a DC voltage abnormality occurs and can output an abnormality signal Eld within a necessary period.

[0092] (4) The circuit constant of the preferred differential circuit 152 is determined based on the magnitude of the pulsating voltage superimposed on the DC voltage. In this way, a voltage change detector 150 can be realized that, under the normal operation of the power conversion device 1000, even if there is a change in the DC voltage caused by the pulsating voltage, the voltage change detector 150 will not output an abnormal signal Eld, but will only output an abnormal signal Eld when the load suddenly drops.

[0093] (5) The controller 600 can output a specified diagnostic signal Vdc_ck to the voltage change detector 150. If the diagnostic signal Vdc_ck is input from the controller 600, the voltage change detector 150 will output an abnormal signal Eld even if no abnormality in the DC voltage is detected. In this way, the initial diagnosis of the voltage change detector 150 can be performed when the power conversion device 1000 is started, thereby improving the reliability of the power conversion device 1000.

[0094] Furthermore, a variable function can be set for at least one of the circuit constants of the differentiating circuit 152, namely the capacitance value of capacitor C1 and the resistance value of resistor R1. For example, by setting a function to make these values ​​variable according to instructions from the controller 600, it is possible to adapt to the diversity of various power conversion devices 1000 with different voltages of the DC power supply 2000 and different capacitance values ​​of the capacitor module 200, and to set the optimal circuit constants of the differentiating circuit 152.

[0095] Furthermore, in the voltage change detector 150 of this embodiment, an abnormal signal Eld is output to forcibly switch the resistance value of the gate resistor from a first resistance value to a second resistance value within a certain period of time via a pulse output circuit 156. However, it can also be replaced by a circuit other than the pulse output circuit 156, such as a latch circuit. When using a latch circuit, for example, it can be configured to latch the output signal of the comparator 154 until a reset signal from the controller 600 is input, thereby achieving the desired function.

[0096] Furthermore, in this embodiment, the voltage change detector 150 and the forced switching circuit 710 are, for example, through... Figure 7 The circuit structure shown can be implemented using hardware circuits, but it can also be replaced by software.

[0097] This invention is not limited to the embodiments described above. Other embodiments that can be considered within the scope of the technical concept of this invention, as long as they do not impair the characteristics of this invention, are also included within the scope of this invention. Additionally, a structure combining the above embodiments may also be used.

[0098] Label Explanation

[0099] 100 Voltage Detector

[0100] 120 Overvoltage Detector

[0101] 150 Voltage Change Detector

[0102] 152 Differentiating Circuit

[0103] 154 comparators

[0104] 156 Pulse Output Circuit

[0105] 200 Capacitor Module

[0106] 300 inverter circuit

[0107] 310 Power Module

[0108] 311, 321 Switching elements

[0109] 312 / 322 diodes

[0110] 400 Output Current Detector

[0111] 600 controller

[0112] 700 Cut-off circuit

[0113] 710 Forced Switching Circuit

[0114] 800 drive circuit

[0115] 810 drive circuit

[0116] 820 Gate Resistor Switching Circuit

[0117] 1000 power conversion device

[0118] 2000 DC power supply

[0119] 2001 Contactor

[0120] 3000 electric motor

[0121] 4000 Low Voltage Power Supply

[0122] Gate resistors Rn0, Rf1, Rf2

[0123] Rs gate resistance switching signal

[0124] Pw drive signal

[0125] Vdc DC voltage detection value (voltage detection signal)

[0126] Ei AC current detection value

[0127] Eov overvoltage signal

[0128] Eld Abnormal Signal

[0129] Vdc_ck diagnostic signal.

Claims

1. A power conversion device, characterized by, include: An inverter circuit having a series circuit equivalent to a multiphase quantity between the positive and negative terminals of DC, the series circuit connecting the switching elements of the upper arm and the switching elements of the lower arm in series. A voltage detector that detects the value of the DC voltage applied to the inverter circuit; A voltage change detector detects anomalies in the DC voltage based on changes in the value of the DC voltage detected by the voltage detector, and outputs a specified abnormality signal; An output current detector that detects the alternating current output from the connection point between the switching elements of the upper arm and the switching elements of the lower arm; The drive circuit has a gate resistor switching circuit that switches the resistance value of a gate resistor connected to the gate of each switching element of the inverter circuit, and drives each switching element via the gate resistor. as well as The controller sends a drive signal to the drive circuit and a gate resistance switching signal to the drive circuit, indicating the switching of the gate resistance. 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 greater than the first resistance value. When the voltage change detector outputs the abnormal 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.

2. The power conversion device as described in claim 1, characterized in that, When each switching element is turned off, the gate resistor switching circuit switches the resistance value of the gate resistor to the second resistance value.

3. The power conversion device as described in claim 1, characterized in that, The voltage change detector includes: A differentiating circuit, which receives a voltage detection signal from the voltage detector based on the value of the DC voltage; A comparator that, based on the input voltage detection signal, compares the signal output from the differentiating circuit with a predetermined voltage threshold and outputs a signal corresponding to the comparison result; and A pulse output circuit that outputs a pulse signal of a specified width based on the output signal of the comparator.

4. The power conversion device as described in claim 3, characterized in that, The circuit constants of the differentiating circuit are determined based on the magnitude of the pulsating voltage superimposed on the DC voltage.

5. The power conversion device as described in claim 3, characterized in that, The circuit constants of the differentiating circuit can be varied according to instructions from the controller.

6. The power conversion device as described in claim 1, characterized in that, The controller is capable of outputting a specified diagnostic signal to the voltage change detector. If the diagnostic signal is input from the controller, the voltage change detector will output the abnormal signal even if it does not detect the abnormality of the DC voltage.

Images