CONTROL SYSTEM FOR AN INVERTER

Abstract

Control system for an inverter (41) for controlling an electric rotary machine (32) via a three-phase winding of the electric rotary machine (32), wherein the inverter (41) contains six transistors (T11, T12, T13, T14, T15, T16) and six diodes (D11, D12, D13, D14, D15, D16), wherein each of the diodes (D11, D12, D13, D14, D15, D16) is connected antiparallel to a respective transistor from the transistors (T11, T12, T13, T14, T15, T16), wherein the control system comprises: an electronic control unit (50) which, in response to the occurrence of a short-circuit fault in any of the six transistors (T11, T12, T13, T14, T15, T16), performs a three-phase turn-on control such that a first transistor from the transistors (T11, T12, T13, T14, T15, T16) in which the short-circuit fault has occurred, and two other transistors from the transistors (T11, T12, T13, T14, T15, T16) which are connected in parallel to the first transistor are turned on, characterized by the fact that the three-phase turn-on control is started when a recovery loss of a first diode, which is one of the six diodes (D11, D12, D13, D14, D15, D16) in which a recovery current is generated at the start of the three-phase turn-on control, is estimated to be less than a recovery tolerance, wherein The recovery current flows through the first diode when the first diode, through which a forward current flows, receives a voltage in the opposite direction at the start of the three-phase turn-on control. The recovery tolerance is preset to a smaller value than the upper limit of a recovery loss at which the first diode does not break down. The recovery loss is a product of the recovery current generated in the first diode and the reverse voltage applied to the first diode.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The invention relates to a control system for an inverter and in particular a control system for an inverter comprising six transistors and six diodes. 2. Description of the state of the art

[0002] A device that performs three-phase on-control (three-phase turn-on control) when a short-circuit fault occurs in an inverter, such that the switching element in which the short-circuit fault occurred and all switching elements connected in parallel to it are turned on, has been proposed as a conventional control system for an inverter of this type (see, for example, JP 2009-195026A). In this device, if the inverter is short-circuited and the speed of a motor-generator driven by the inverter is equal to or less than a predetermined reference speed, emergency operation control is performed after turning on the switching element in which the short-circuit fault occurred and after turning on any switching element connected in series with it.If the motor-generator speed exceeds the predetermined reference speed, the three-phase ON control is activated. This initiates emergency operation while preventing overcurrent from flowing through the inverter.

[0003] In the inverter control system described above, a diode connected in parallel with the switching element in the opposite direction can break down. When a diode carrying a forward current receives a reverse voltage at the start of the three-phase ON control, a recovery current (a reverse recovery current) flows through the diode. If the reverse voltage is too high or the recovery current is too large at that time, a recovery loss exceeding the recovery tolerance can occur, and as a result, the diode can break down.

[0004] US Patent 2010 / 0263953A1 discloses a control system for an inverter (41) for controlling an electric rotary machine via a three-phase winding of the electric rotary machine, wherein the inverter contains six transistors and six diodes, each of the diodes being connected antiparallel to a respective transistor from the transistors, and wherein the control system includes an electronic control unit which, in response to the occurrence of a short-circuit fault in any of the six transistors, performs a three-phase turn-on control such that a first transistor from the transistors in which the short-circuit fault occurred and two other transistors from the transistors that are connected in parallel to the first transistor are turned on.

[0005] JP 2009-195 026 A discloses a motor control system in which, if a short-circuit fault occurs in an inverter, backup operation is performed by a second motor-generator. If, during backup operation, the rotational speed of a first motor-generator, calculated based on a value detected by a position sensor, exceeds a predetermined reference speed, a motor-generator control unit activates all switching elements connected in parallel to a switching element that failed due to a short circuit with respect to a power supply line. If the rotational speed is equal to or less than the reference speed, the motor-generator control unit activates only the switching elements connected in series with the switching element that failed due to the short circuit. SUMMARY OF THE INVENTION

[0006] It is an object of the invention to provide a control system for an inverter according to which a breakdown of a diode that is part of the inverter is prevented when a switch-on control is performed in response to a short circuit fault in the inverter.

[0007] The problem is solved by a control system having the features of claim 1. The dependent claims are directed to preferred embodiments of the invention.

[0008] As described above, the turn-on control is executed when it is estimated that the recovery loss of the first diode is less than the recovery tolerance. Therefore, breakdown of the diode in which the recovery current is generated can be prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Features, advantages, and the technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, in which the same reference numerals denote the same elements. The drawings show: Fig. 1 a schematic view showing a configuration of an electric vehicle 20 according to an embodiment of the invention; Fig. 2 a flowchart showing an example of single-phase short-circuit fault processing performed by an ECU 50; Fig. 3 a flowchart showing an example of three-phase ON change determination processing performed by the ECU 50; Fig. 4 a flowchart showing a modified example of a three-phase ON changeover determination processing performed by the ECU 50; Fig. 5 a view that represents a condition in which a maximum forward current flows through a U-phase diode D12 when a short-circuit fault occurs in a transistor T14 of an inverter 34; Fig. 6 a view that shows a temporal change of phase currents of a u-phase, a v-phase and a w-phase, and the way in which it is determined whether it is possible to switch to a three-phase ON control; Fig. Figure 7 shows a flowchart illustrating a modified example of the three-phase ON change determination processing performed by the ECU 50. DETAILED DESCRIPTION OF THE EXECUTION FORMS

[0010] The following describes an embodiment of the invention by means of examples.

[0011] Fig. Figure 1 is a schematic view showing a configuration of an electric vehicle 20 according to an embodiment of the invention. As shown in the drawing, the electric vehicle 20 according to this embodiment includes a motor (electric motor) 32, a power control unit (hereinafter referred to as PCU) 33, a battery 36, a relay 42, and an electronic control unit (hereinafter referred to as ECU) 50.

[0012] The motor 32 is designed as a conventional synchronous generator / motor, comprising a rotor in which a permanent magnet is embedded and a stator around which a three-phase winding is wound. The motor 32 is mounted on a drive shaft 26, and the drive shaft 26 is coupled to drive wheels 22a, 22b via a drive shaft (an axle) 23 and a differential gear 24. When the motor 32 rotates, a counter-electromotive voltage (also called induced voltage) Vm is generated.

[0013] The PCU 33 contains an inverter 34, a boost converter / gain converter 35, and a smoothing capacitor 48, all housed in a single package. The inverter 34 contains six transistors T11 to T16, which are configured, for example, as insulated-gate bipolar transistors (IGBTs), and six diodes D11 to D16. The transistors T11 to T16 are arranged in pairs formed by a source-side transistor and a sink-side transistor with respect to a positive electrode bus line 46a and a negative electrode bus line 46b of a high-voltage system power line 46. The six diodes D11 to D16 are connected in parallel (i.e., antiparallel) to the respective transistors T11 to T16 in the opposite direction.Windings (a U-phase winding, a V-phase winding, and a W-phase winding) forming a three-phase winding of the motor 32 are connected at respective junction points between the transistor pairs formed by transistors T11 to T16. Thus, by the ECU 50 setting the on-time ratios of the pairs at transistors T11 to T16 while a voltage is applied to the inverter 34, a rotational magnetic field is generated in the three-phase winding, and as a result, the motor 32 rotates.

[0014] The boost converter 35 is connected to the high-voltage system power line 46, to which inverters 41 and 42 are connected, and to a low-voltage system power line 40, to which battery 36 is connected. The boost converter 35 contains two transistors T21 and T22, two diodes D21 and D22 connected in antiparallel to the respective transistors T21 and T22, and an inductor L. Transistor T21 is connected to the positive electrode bus line 46a of the high-voltage system power line 46. Transistor T22 is connected to transistor T21 and to a negative electrode bus line 40b of the low-voltage system power line 40, which serves as the negative electrode bus line 46b of the high-voltage system power line 46. The inductor L is connected to a junction between transistors T21 and T22 and to the positive electrode bus line 40a of the low-voltage system power line 40.By switching transistors T21 and T22 on and off, the ECU 50 causes the boost converter 35 to amplify the energy or power in the low-voltage system power line 40 and supply the amplified energy or power to the high-voltage system power line 46, as well as to convert the energy or power on the high-voltage system power line 46 down and supply the converted energy or power to the low-voltage system power line 40.

[0015] The battery 36 is configured, for example, as a lithium-ion secondary battery or a nickel-hydrogen secondary battery. A capacitor 44 is connected to the positive electrode bus line 40a and the negative electrode bus line 40b of the low-voltage system power line 40. The relay 42 is located on the battery side 36 of a connection point through which the positive electrode bus line 40a and the negative electrode bus line 40b are connected to the capacitor 44. The relay 42 establishes a connection between the PCU 33 side (the boost converter 35 and the inverter 34) and the battery 36 side, and then breaks the connection.

[0016] Although not shown in the drawing, the ECU 50 is designed as a microcomputer with a CPU and, in addition to the CPU, contains a ROM that stores a processing program, a RAM that temporarily stores data, input / output connectors, and a communication connector. Signals from various sensors are input to the ECU 50 via the input connector. The following can be cited as signals from the various sensors: a rotational position θm from a rotational position sensor 32b, which detects the rotational position of the rotor of motor 32; phase currents Iu, Iv of motor 32, obtained from current sensors 34u, 34v, which are attached to the power lines to which the motor 32 and the inverter 34 are connected; a battery voltage Vb from a voltage sensor attached between the terminals of battery 36;a battery current Ib from a current sensor attached to an output terminal of the battery 36; a battery temperature Tb from a temperature sensor attached to the battery 36; a capacitor voltage (low-voltage system voltage) VB from a voltage sensor 44a attached between terminals of the capacitor 44; a capacitor voltage (high-voltage system voltage) VH from a voltage sensor 48a attached between terminals of the capacitor 48; an ignition signal from an ignition switch 60; a shift position SP from a shift position sensor 62 detecting an operating position of a shift lever 61; an accelerator pedal actuation value Acc from an accelerator pedal position sensor 64 detecting an actuation value of an accelerator pedal 63; a brake pedal position BP from a brake pedal position sensor 66 detecting an actuation value of a brake pedal 65;and a vehicle speed V from a vehicle speed sensor 68. Various control signals are output by the ECU 50 via the output terminal. The following can be cited as different control signals: switching control signals for switching transistors T11 to T16 of inverter 34; switching control signals for switching transistors T21, T22 of boost converter 35;and a control signal that is output to relay 42. Note that the ECU 50 calculates a rotational speed Nm of motor 32 based on the rotational position θm of the rotor of motor 32, which is detected by the rotational position sensor 32b, and calculates a phase current Iw from the phase currents Iu, Iv of motor 32 obtained from the current sensors 34u, 34v. In addition, the ECU 50 calculates a storage ratio SOC (state of charge) of battery 36 based on an integrated value of the battery current Ib, which is detected by the current sensor attached to the output terminal of battery 36.

[0017] The following describes an operation of the electric vehicle 20 according to this embodiment, which is constructed as described above, and in particular an operation that is carried out when a short circuit fault occurs in one of the six transistors T11 to T16 of the inverter 34. Fig. Figure 2 is a flowchart showing an example of single-phase short-circuit fault processing performed by the ECU 50 when a short-circuit fault occurs in any of the six transistors T11 to T16 of inverter 34.

[0018] When single-phase short-circuit fault processing is executed, the ECU 50 first switches off all six transistors T11 to T16 of inverter 34 (step S100). Then, the high-voltage system voltage VH from voltage sensor 48a and the rotational speed Nm of motor 32 are input (step S110). It is assumed here that the input rotational speed Nm of motor 32 is calculated based on the rotational position θm detected by the rotational position sensor 32b. The back EMF voltage Vm is then calculated by multiplying the input rotational speed Nm of motor 32 by a conversion factor km, which is used to calculate the back EMF voltage (the induced voltage) (step S120), after which it is determined whether the high-voltage system voltage VH is equal to or greater than the back EMF voltage Vm (step S130).

[0019] If, in step S130, it is determined that the high-voltage system voltage VH is equal to or greater than the back EMF voltage Vm, a three-phase ON control (three-phase turn-on control) is initiated by turning on the transistor in which the short-circuit fault occurred and the two transistors connected in parallel to it (step S160). The processing then terminates. According to an example of three-phase ON control, if, for instance, a short-circuit fault occurs in transistor T14 of a lower arm, the two lower-arm transistors T15 and T16, which are connected in parallel to transistor T14, are turned on; and if, for instance, a short-circuit fault occurs in transistor T12 of an upper arm, the two upper-arm transistors T11 and T13, which are connected in parallel to transistor T12, are turned on.

[0020] If, in step S130, it is determined that the high-voltage system voltage VH is less than the back EMF voltage Vm, it is determined whether it is possible to switch to three-phase ON control (steps S140, S150). If it is determined that it is possible to switch to three-phase ON control, the three-phase ON control is started by switching on the transistor in which the short-circuit fault occurred and the two transistors connected in parallel to it (step S160), after which the processing is terminated. When determining whether it is possible to switch to three-phase ON control, it is determined that a switch is possible if it is estimated that the recovery loss of any diode among the six diodes D11 to D16 of inverter 34, in which a reverse recovery current is generated when the three-phase ON control is started, is less than a recovery tolerance.If it is not estimated that the recovery loss is less than the recovery tolerance, then a changeover is determined to be impossible. Here, the "recovery loss" is the product of the reverse recovery current generated in a diode through which current flows when a reverse voltage is applied to the diode, and the reverse voltage applied to the diode, and is also referred to as the reverse recovery loss. The "recovery tolerance" is preset to a slightly smaller value than the upper limit of the recovery loss (the reverse recovery loss) at which the diode does not break down.

[0021] In this embodiment, the determination of whether it is possible to switch to three-phase ON control is carried out by executing a three-phase ON changeover determination process (three-phase switch-on changeover determination process), for which an example is given in Fig. Figure 3 shows that in the three-phase ON switching determination process, the rotational speed Nm of motor 32 is input (step S200), and it is determined whether the input speed Nm is less than a predetermined speed threshold Nmref (step S210). If the speed Nm is less than the predetermined speed threshold Nmref, it is determined that it is possible to switch to three-phase ON control (step S220), and if the speed Nm is equal to or greater than the predetermined speed threshold Nmref, it is determined that it is impossible or not possible to switch to three-phase ON control (step S230). Multiplying the speed Nm of motor 32 by the conversion factor km yields the back EMF voltage Vm generated by motor 32, and therefore the speed Nm of motor 32 has a linear relationship to the back EMF voltage Vm. In the single-phase short-circuit fault handling of the Fig. 2. The determination of whether it is possible to switch to three-phase ON control is carried out when the high-voltage system voltage VH is less than the back EMF voltage Vm. Therefore, the reverse voltage applied to the diode in which the reverse recovery current is generated corresponds to the back EMF voltage Vm of motor 32. The recovery loss is the product of the reverse recovery current and the reverse voltage, and therefore the recovery loss is small when the reverse voltage is low. Here, a voltage for which the recovery loss is estimated to reach the recovery tolerance is determined by calculations, experiments, etc., and set as a predetermined voltage. The speed generated by motor 32 when the back EMF voltage equals the predetermined voltage is set as the predetermined speed threshold Nmref.If the rotational speed Nm of motor 32 is less than the predetermined rotational speed threshold Nmref, then the back EMF voltage Vm of motor 32 is consequently less than the predetermined voltage, and therefore it can be estimated that the recovery loss is less than the recovery tolerance. In this embodiment, if the rotational speed Nm of motor 32 is less than the predetermined rotational speed threshold Nmref, it is estimated, based on this reasoning, that the recovery loss is less than the recovery tolerance, and it is thus determined that it is possible to switch to three-phase ON control. On the other hand, if the rotational speed Nm of motor 32 is equal to or greater than the predetermined rotational speed threshold Nmref, it cannot be estimated that the recovery loss is less than the recovery tolerance, and it is therefore determined that it is impossible or not possible to switch to three-phase ON control.It is not possible to switch to three-phase ON control.

[0022] If, during the determination in steps S140 and S150 as to whether it is possible to switch to three-phase ON control, it is determined that it is impossible to switch to three-phase ON control, the routine returns to the processing in step S110, in which the high-voltage system voltage VH and the speed Nm of motor 32 are entered. As long as the high-voltage system voltage VH remains lower than the back EMF voltage Vm, the processing of steps S110 to S150 is repeated until the three-phase ON switching determination process, which is performed in Fig. Figure 3 shows that it is determined whether it is possible to switch to three-phase ON control. If, during this repeated processing in steps S140 and S150, it is determined whether it is possible to switch to three-phase ON control, or if, in step S130, it is determined that the high-voltage system voltage VH is equal to or greater than the back EMF voltage Vm, the repeated processing is terminated and three-phase ON control is initiated (step S160). The processing then ends.

[0023] In the electric vehicle 20 according to this embodiment, as described above, when a short-circuit fault occurs in one of the six transistors T11 to T16 of the inverter 34, it is determined whether the high-voltage system voltage VH is less than the back EMF voltage Vm generated by the motor 32. If it is determined that the high-voltage system voltage VH is less than the back EMF voltage Vm, the three-phase ON control is started after waiting until it is estimated that the recovery loss of the diode in which the reverse recovery current is generated during the start of the three-phase ON control is less than the recovery tolerance. This prevents a situation in which the recovery loss of the diode in which the reverse recovery current is generated during the start of the three-phase ON control exceeds the recovery tolerance, causing the diode to break down.Furthermore, the determination of whether it is possible to switch to three-phase ON control, in other words, the determination of whether it can be estimated that the recovery loss is less than the recovery tolerance, is carried out by determining whether the speed Nm of motor 32 is less than the predetermined speed threshold Nmref, and therefore a breakdown of the diode can be prevented by carrying out a simple determination.

[0024] In the electric vehicle 20 according to this embodiment, the determination of whether it is possible to switch to three-phase ON control is carried out by determining whether the rotational speed Nm of the motor 32 is less than the predetermined rotational speed threshold Nmref. However, the determination of whether it is possible to switch to three-phase ON control can instead be carried out by determining whether the vehicle speed V is less than a predetermined vehicle speed Vref. The vehicle speed V is obtained by multiplying the rotational speed Nm of the motor 32 by a conversion factor kv, and therefore the vehicle speed V can be used in a similar way to the rotational speed Nm of the motor 32. In this case, the predetermined vehicle speed Vref can be calculated by multiplying the conversion factor kv by the predetermined rotational speed threshold Nmref.Alternatively, the determination of whether it is possible to switch to three-phase ON control can be carried out by determining whether the back EMF voltage Vm generated by motor 32 is less than a predetermined voltage Vset. The back EMF voltage Vm generated by motor 32 is obtained by multiplying the rotational speed Nm of motor 32 by the conversion factor km, and therefore the back EMF voltage Vm can be used in a similar way to the rotational speed Nm of motor 32. In this case, the predetermined voltage Vset can be calculated by multiplying the conversion factor km by the predetermined speed threshold Nmref.Furthermore, the determination of whether it is possible to switch to three-phase ON control can be carried out by attaching a voltage sensor to the positive electrode bus line 46a and the negative electrode bus line 46b of the high-voltage system power line 46 and by determining whether a voltage detected by this voltage sensor is less than a predetermined voltage. The voltage detected by the voltage sensor corresponds to the back EMF voltage Vm of the motor 32, and therefore the voltage detected by the voltage sensor can be used in a similar way to the back EMF voltage Vm.

[0025] In the electric vehicle 20 according to this embodiment, the determination of whether it is possible to switch to three-phase ON control is carried out by determining whether the rotational speed Nm of the motor 32 is less than the predetermined rotational speed threshold Nmref. However, the determination of whether it is possible to switch to three-phase ON control can instead be carried out based on the phase currents Iu, Iv, Iw. Fig. Figure 4 is a flowchart showing an example of the three-phase ON switching determination processing performed by the ECU 50 in a case where the determination of whether it is possible to switch to the three-phase ON control is performed on the basis of the phase currents Iu, Iv, Iw.

[0026] If the three-phase ONE change determination processing, which is in Fig. As shown in Figure 4, the ECU 50 first receives the phase currents Iu, Iv of motor 32 from the current sensors 34u, 34v (step S300). The phase current Iw can be easily calculated based on the phase currents Iu, Iv using the equation Iu + Iv + Iw = 0. Then, it is determined whether the transistor in which the short-circuit fault occurred is located in the upper or lower arm (step S310). If the transistor in which the short-circuit fault occurred is located in the lower arm, the smallest of the phase currents lu, Iv, Iw (i.e., the phase current with the largest negative value) is set as a current value Is (step S320), and if the transistor in which the short-circuit fault occurred is located in the upper arm, the largest of the phase currents Iu, Iv, Iw (i.e., the phase current with the largest positive value) is set as a current value Is (step S330).If the transistor where the short-circuit fault occurred is located in the lower arm, the diode in which the reverse recovery current is generated during the start of the three-phase ON control, when transistors T14 to T16 in the lower arm are switched on, is a diode of an upper arm. Therefore, a phase current generated when a forward current flows through the diode of the upper arm takes on a negative value. By setting the smallest of the phase currents Iu, Iv, Iw (i.e., the phase current with the largest negative value) as the current value Is, the current value Is is adjusted to the value of the forward current flowing through the diode in which the largest reverse recovery current is generated.Conversely, if the transistor where the short-circuit fault occurred is located in the upper arm, the diode in which the reverse recovery current is generated when the three-phase ON control is initiated (when transistors T11 to T13 in the upper arm are switched on) is a diode of a lower arm. Therefore, a phase current generated when a forward current flows through the diode of the lower arm takes on a positive value. By setting the largest of the phase currents Iu, Iv, Iw (i.e., the phase current with the largest positive value) as the current value Is, the current value Is is adjusted to the value of the forward current flowing through the diode in which the largest reverse recovery current is generated.

[0027] Then, it is determined whether the absolute value of the set current Is is less than a predetermined current Iref (step S340). If the absolute value of the current Is is less than the predetermined current Iref, it is determined that switching to three-phase ON control is possible (step S350). If the absolute value of the current Is is equal to or greater than the predetermined current Iref, it is determined that switching to three-phase ON control is impossible (step S360). The recovery loss (reverse recovery loss) is the product of the reverse recovery current and the reverse voltage, and therefore the recovery loss is small when the reverse voltage is small.The reverse recovery current can be assumed to increase when the value of the forward current flowing through the diode is large, and therefore, by determining a current value for which it can be estimated that the recovery loss reaches the recovery tolerance, through experiments and the like, and by setting this current value as a predetermined current value Iref, it can be estimated that the recovery loss is less than the recovery tolerance when the absolute value of the current value Is is less than the predetermined current value Iref.

[0028] Fig. 5 is a view that represents a condition in which a maximum forward current flows through the u-phase diode D12 when a short-circuit fault occurs in the transistor T14 of the inverter 34. Fig. Figure 6 presents a view that shows a temporal change in the phase currents of the u-phase, the v-phase, and the w-phase, and the way in which it is determined whether it is possible to switch to three-phase ON control. Note that the condition stated in Fig. 5 is shown, corresponds to a condition that exists at time t1 in Fig. 6 is constructed. As described above, if a short-circuit fault occurs in transistor T14 of a lower arm of inverter 34, transistors T15 and T16, which are connected in parallel to transistor 14, are switched on during three-phase ON control, and therefore a reverse recovery current can be generated in diodes D11 to D13 of the upper arms at the start of three-phase ON control. Among the times at which three-phase ON control is started, the times at which the largest reverse recovery currents are generated in the u-phase, v-phase, and w-phase diodes D11 to D13 are set as times t1, t3, and t2, respectively. The absolute values ​​of the forward currents flowing through the u-phase, v-phase, and w-phase diodes D11 to D13 are in a region B, which is located in an upper part of the Fig. As shown in Figure 6, the absolute value of the current Is is less than the predetermined current Iref. If the three-phase ON control is started at a time within range B, the absolute value of the current Is is less than the predetermined current Iref, and therefore it can be estimated that the recovery loss is less than the recovery tolerance. Conversely, if the three-phase ON control is started at a time within range A, the absolute value of the current Is is equal to or greater than the predetermined current Iref, and therefore it cannot be estimated that the recovery loss is less than the recovery tolerance.

[0029] A similar effect to that of the embodiment above is obtained if the three-phase EIN switching determination processing is carried out according to the modified example shown in Fig. As shown in Figure 4, this is carried out. In other words, it can prevent a situation where the recovery loss of the diode, in which the reverse recovery current is generated when the three-phase ON control starts, exceeds the recovery tolerance and thus causes the diode to break down.

[0030] In the three-phase ON changeover determination processing according to this modified example, the determination of whether it is possible to switch to three-phase ON control is performed using the phase currents Iu, Iv of motor 32, which are obtained from the current sensors 34u, 34v. However, it is sufficient to be able to estimate instantaneous phase currents Iu, Iv, Iw, and therefore the determination of whether it is possible to switch to three-phase ON control can be performed based on a signal from the rotary position sensing sensor 32b (for example, a rotary encoder or resolver), which detects the rotary position of the rotor of motor 32, instead of using the current sensors 34u, 34v.

[0031] The determination of whether it is possible to switch to three-phase ON control can also be carried out on the basis of the phase currents Iu, Iv, Iw and the back electromotive voltage Vm generated by the motor 32. Fig. Figure 7 is a flowchart showing an example of the three-phase ON switching determination processing performed by the ECU 50 in a case where the determination of whether it is possible to switch to the three-phase ON control is carried out on the basis of the phase currents Iu, Iv, Iw and the back electromotive voltage Vm generated by the motor 32.

[0032] If the in Fig. In step 7, the three-phase ON changeover determination processing shown is performed. The ECU 50 first receives the phase currents Iu and Iv of motor 32 from current sensors 34u and 34v, and the back EMF voltage Vm generated by motor 32 (step S400). The phase current Iw can be easily calculated based on the phase currents lu and Iv using the equation lu + Iv + Iw = 0. Then, it is determined whether the transistor in which the short-circuit fault occurred is located in the upper or lower arm (step S410). If the transistor in which the short-circuit fault occurred is in the lower arm, the smallest of the phase currents Iu, Iv, Iw (i.e., the phase current with the largest negative value) is set as the current value Is (step S420), and if the transistor in which the short-circuit fault occurred is in the upper arm, the largest of the phase currents Iu, Iv, Iw (i.e.,The phase current with the largest positive value is set as the current value Is (step S430). The current value Is is defined as described above. Then, it is determined whether the product of the back EMF voltage Vm generated by motor 32 and the absolute value of the current value Is is less than a predetermined value Pref (step S440). If the product of the back EMF voltage Vm and the absolute value of the current value Is is less than the predetermined value Pref, it is determined that it is possible to switch to three-phase ON control (step S450), and if the product of the back EMF voltage Vm and the absolute value of the current value Is is equal to or greater than the predetermined value Pref, it is determined that it is impossible to switch to three-phase ON control (step S460).It can be assumed that the reverse recovery current increases when the value of the forward current flowing through the diode is large, and since the recovery loss (the reverse recovery loss) is the product of the reverse recovery current and the reverse voltage (the back EMF voltage Vm), the recovery loss (the reverse recovery loss) increases steadily when the product of the back EMF voltage Vm and the absolute value of the current Is increases.By determining a product of the blocking voltage and the forward current value, for which it can be estimated that the recovery loss reaches the recovery tolerance, by means of experiments and the like, and by setting this product as a predetermined value Pref, it can be estimated that the recovery loss is less than the recovery tolerance if the product of the back EMF voltage Vm and the absolute value of the current Is is less than the predetermined value Pref. A similar effect to that of the embodiment above is obtained if the three-phase ON-AC determination process is carried out according to the modified example shown in . Fig.Figure 7 is shown. In other words, it can prevent a situation where the recovery loss of the diode, in which the reverse recovery current is generated when the three-phase ON control starts, exceeds the recovery tolerance and thus causes the diode to break down.

[0033] The electric vehicle 20 according to this embodiment includes the boost converter 35, but the boost converter 35 can be omitted. Furthermore, the electric vehicle 20 according to this embodiment includes the drive motor 32, but can also include two or more drive motors. In this embodiment, the invention is used for an electric vehicle, but the invention can also be used for a hybrid vehicle comprising an internal combustion engine and a motor (electric motor).

[0034] In the embodiment, the inverter 34 is an example of an “inverter”, and the ECU 50 is an example of a “control device” in the claims.

[0035] The relationships between the main elements of the invention are specific examples that represent an implementation of the invention as described in the embodiment, and the elements of the invention are not limited to these. In other words, the embodiment is only a specific example of the invention.

[0036] The invention has been described above using its embodiment and its modifications, but the invention is not limited thereto and can of course be implemented in various embodiments within the scope of the invention.

[0037] The invention can be used in the inverter control device manufacturing industry, etc.

[0038] A control system according to the invention for an inverter serves as a control device for an inverter composed of six transistors and six diodes. In this control system, in a case where three-phase ON control is implemented in response to a short-circuit fault in any of the six transistors, such that the transistor in which the short-circuit fault occurred and two transistors connected in parallel to it are switched on, the three-phase ON control is initiated when it is estimated that the recovery loss of any diode among the six diodes in which a reverse recovery current is generated is less than a recovery tolerance.

[0039] In the control system according to the invention for an inverter, in a case where three-phase ON control is implemented in response to a short-circuit fault in one of the six transistors forming the inverter, such that the transistor in which the short-circuit fault occurred and the two transistors connected in parallel to it are switched on, the three-phase ON control is initiated when it is estimated that the recovery loss of the diode among the six diodes in which the reverse recovery current is generated is less than the recovery tolerance. Here, the "recovery loss" is the product of the reverse recovery current generated in a diode through which a forward current flows when a reverse voltage is applied to the diode and the reverse voltage applied to the diode, and is also referred to as the reverse recovery loss.The "recovery tolerance" is preset to a value slightly smaller than the upper limit of the recovery loss (reverse recovery loss) at which the diode does not break down. As described above, the three-phase ON control is initiated when it is estimated that the recovery loss of the diode generating the reverse recovery current is smaller than the recovery tolerance, thus preventing breakdown of the diode generating the reverse recovery current.

[0040] In the control system according to the invention for an inverter, the three-phase ON control can be initiated by estimating that the recovery loss is less than the recovery tolerance when a reverse voltage applied to the diode generating the reverse recovery current is less than a predetermined voltage. Here, the reverse voltage can be detected using a voltage sensor or similar device. As described above, the recovery loss (the reverse recovery loss) is the product of the reverse recovery current and the reverse voltage, and when the reverse voltage is small, the recovery loss (the reverse recovery loss) is also small.By appropriately adjusting the predetermined voltage, it can be estimated that the recovery loss is smaller than the recovery tolerance when the blocking voltage is smaller than the predetermined voltage.

[0041] Furthermore, in the control system according to the invention for an inverter, three-phase ON control can be initiated by estimating that the recovery loss is less than the recovery tolerance when the rotational speed of an electric rotary machine driven by the inverter is less than a predetermined speed. When the electric rotary machine rotates, an induced voltage (a back EMF) is generated, and this voltage corresponds to the rotational speed. Three-phase ON control is typically executed when the back EMF of the electric rotary machine is large, and therefore the reverse voltage applied to the diode is often equal to the back EMF of the electric rotary machine.By using a rotational speed of the electric rotary machine at which the back EMF of the electric rotary machine reaches the aforementioned predetermined voltage at the predetermined speed, the blocking voltage, which serves as the back EMF, can be kept below the predetermined voltage. Therefore, by appropriately adjusting the predetermined speed and the predetermined voltage, it can be estimated that the recovery loss is smaller than the recovery tolerance when the rotational speed of the electric rotary machine is lower than the predetermined speed.Note that in a vehicle where an electric rotary machine controlled by the inverter is installed as a traction motor, the three-phase ON control can be started by estimating that the recovery loss is less than the recovery tolerance when the vehicle speed is less than a predetermined vehicle speed.In this case, the rotational speed of the electric rotary machine is obtained by multiplying the vehicle speed by a conversion factor, and therefore, by setting a vehicle speed at which the rotational speed of the electric rotary machine reaches the predetermined speed, it can be determined that the rotational speed of the electric rotary machine is less than the predetermined speed, and accordingly, as described above, it can be estimated that the recovery loss is less than the recovery tolerance when the vehicle speed is less than the predetermined vehicle speed.

[0042] Furthermore, in the control system according to the invention for an inverter, the three-phase ON control can be initiated by estimating that the recovery loss is less than the recovery tolerance when the forward current flowing through the diode in which the reverse recovery current is generated is less than a predetermined current value. Here, the determination of whether the forward current value is less than the predetermined current can be carried out using a detected value from a current sensor or a signal from a rotary encoder or resolver that detects the rotational speed of the electric rotary machine.As described above, the recovery loss (reverse recovery loss) is the product of the reverse recovery current and the reverse voltage. When the reverse recovery current is small, the recovery loss (reverse recovery loss) is also small. It can be assumed that the reverse recovery current increases when the forward current flowing through the diode is large. Therefore, by appropriately adjusting the predetermined current value, it can be estimated that the recovery loss will be smaller than the recovery tolerance when the forward current is less than the predetermined current value.

[0043] Alternatively, in the control system according to the invention for an inverter, the three-phase ON control can be initiated by estimating that the recovery loss is less than the recovery tolerance when the product of the forward current flowing through the diode generating the reverse recovery current and the reverse voltage applied to the diode is less than a predetermined value. Here, the forward current can be detected using a current sensor. The reverse voltage can also be detected using a voltage sensor or similar device, or it can be estimated from the rotational speed of the electric rotary machine driven by the inverter, the vehicle speed, etc.As described above, the reverse recovery current can be assumed to increase when the forward current flowing through the diode is large, and therefore the recovery loss can be assumed to increase steadily as the product of the forward current flowing through the diode and the reverse voltage increases. Thus, by appropriately adjusting the predetermined value, it can be estimated that the recovery loss will be smaller than the recovery tolerance when the product of the forward current and the reverse voltage is smaller than the predetermined value.

Claims

[1] Control system for an inverter (41) for controlling an electric rotary machine (32) via a three-phase winding of the electric rotary machine (32), wherein the inverter (41) contains six transistors (T11, T12, T13, T14, T15, T16) and six diodes (D11, D12, D13, D14, D15, D16), wherein each of the diodes (D11, D12, D13, D14, D15, D16) is connected antiparallel to a respective transistor from the transistors (T11, T12, T13, T14, T15, T16), wherein the control system comprises: an electronic control unit (50) which, in response to the occurrence of a short-circuit fault in any of the six transistors (T11, T12, T13, T14, T15, T16), performs a three-phase turn-on control such that a first transistor from the transistors (T11, T12, T13, T14, T15, T16) in which the short-circuit fault has occurred, and two other transistors from the transistors (T11, T12, T13, T14, T15, T16) which are connected in parallel to the first transistor are turned on, characterized by , that the three-phase turn-on control is started when a recovery loss of a first diode, which is one of the six diodes (D11, D12, D13, D14, D15, D16) in which a recovery current is generated at the start of the three-phase turn-on control, is estimated to be less than a recovery tolerance, wherein The recovery current flows through the first diode when the first diode, through which a forward current flows, receives a voltage in the opposite direction at the start of the three-phase turn-on control. The recovery tolerance is preset to a smaller value than the upper limit of a recovery loss at which the first diode does not break down. The recovery loss is a product of the recovery current generated in the first diode and the reverse voltage applied to the first diode. [2] Control system according to claim 1, wherein it is estimated that the recovery loss is less than the recovery tolerance when the reverse voltage applied to the first diode is less than a predetermined voltage. [3] Control system according to claim 1, wherein it is estimated that the recovery loss is less than the recovery tolerance when a rotational speed of the electric rotary machine (32) controlled by the inverter (41) is less than a predetermined rotational speed. [4] Control system according to claim 1, wherein it is estimated that the recovery loss is less than the recovery tolerance when a value of a forward current flowing through the first diode is less than a predetermined current value. [5] Control system according to claim 1, wherein the recovery loss is estimated to be less than the recovery tolerance when the product of a forward current flowing through the first diode and the reverse voltage applied to the first diode is less than a predetermined value.

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