Inverter control device, motor drive device and electric power steering device

Abstract

Inverter control device comprising: at least a first and second inverter (20, 120); a current detector that detects a current flowing through a main circuit of the first inverter (20); a current controller (320) that generates a voltage command value of the first inverter (20) based on a detected current and a current command; and a voltage command predictor (340) that generates a voltage command value of the second inverter (120) based on a variation of the voltage command value of the first inverter (20), wherein the current detector sequentially detects a current flowing through the main circuit of the first inverter (20) and a current flowing through the main circuit of the second inverter (120).The current controller (320) generates the voltage command value of the first inverter (20) based on the detected current and a predetermined current command during a current detection period of the first inverter (20), and the voltage command predictor (340) generates the voltage command value of the second inverter (120) during the current detection period of the first inverter (20) by adding a variation of the voltage command value of the first inverter (20) to the previous voltage command value of the second inverter (120).

Description

Technical FieldThe present invention relates to an inverter control device mounted in a vehicle, and more particularly to a method for reducing a calculation load of a control device for controlling inverters and motors of a plurality of channels.Prior ArtIn recent years, the development of autonomous vehicles has been rapidly advanced, and functional safety standards required for electric parts are increasing. For example, in an inverter control device used in an electric power steering device for an autonomous vehicle, a technique for securing safety by duplicating the system is known in the art.JP 2012-76644 A (PTL 1) discloses a technique of adding a current detection value of a first inverter and a current detection value of a second inverter, and generating a voltage command on the basis of the added current detection value and a current command value.PTL 2 relates to a current detection device including sensor portions that detect motor currents flowing in the windings for the phases of the winding groups, a control device that calculates voltage commands relating to each winding group based on the motor current detected by each sensor portion, a voltage application device that applies the voltage based on the voltage commands to each winding group, and a failure detection device that detects whether or not a sensor portion has failed. When the failure detection device has detected a failure of one sensor section, the control device calculates a voltage instruction with respect to the winding group corresponding to the failure of the sensor section based on a motor current of another winding group.PTL 3 relates to a rotational position detection means that detects a rotational position of a rotating machine; failure determination means that determines the failure of the rotational position detection means; control means that calculates a voltage command for each winding group of the rotating machine based on the rotational position detected by the rotational position detection means; and voltage application means that applies a voltage to each winding group based on the voltage command. According to the failure determination by the failure determination means, the control means outputs a voltage command for rotational position estimation to the voltage application means, and estimates the rotational position based on the voltage and / or the current determined from the winding group from the voltage command.PTL 4 relates to a pole-switchable induction motor in which an arbitrary ratio between the numbers of poles can be obtained, and in which an arbitrary number of turns can be selected, to thereby achieve a very wide operating range and stabilize the operation when the number of poles is changed. This pole-switchable induction motor includes a rotor having a squirrel-cage winding, a stator having at least one group of a first winding having 2npoles and a second winding having 2mpoles wound around the same stator core, a first inverter connected to the first winding, and a second inverter connected to the second winding.PTL 1 relates to an electric power steering apparatus including a motor control command output device that outputs a first command value generated with a first command value calculation means and a second command value calculated with a second command value calculation means 34, 35 based on a current value including a current value of each motor drive system added with a motor drive system current addition means, as a motor control command to a two-system motor drive system composed of a motor and a drive circuit for driving the motor.Keep ListPatent Document(s)PTL 1: JP 2012-76 644 APTL 2: DE 10 2013 202 400 A1PTL 3: DE 10 2013 201 918 A1PTL 4: DE 10051621 A1SUMMARY OF THE INVENTIONTechnical ProblemIn the method discussed in PTL 1, it is necessary to detect as many current values as the number of channels included in the system. In the case of a system that detects a DC bus current of the inverter or a current flowing between a lower or upper arm of each phase of the inverter and a DC bus (hereinafter referred to as "three-shunt current"), it is necessary to add, as many times as the number of channels included in the system, a process for calculating a three-phase AC current flowing to a motor coil on the basis of the detected DC bus current or three-shunt current and a process for transforming the calculated three-phase AC current into a dq-axis current. In addition, in the case of a system that detects a three-phase alternating current flowing to the motor coil, it is necessary to add, as many as the number of channels included in the system, a process for transforming the detected three-phase alternating current into the dq-axis current.In this way, in the method discussed in PTL 1, it is difficult to reduce a computational load in a control device for a system including inverters and motors of multiple channels. In this regard, an object of the present invention is to reduce a computational load of the control device without reducing responsiveness of current control (torque control).Solution to the ProblemThe aforementioned object is achieved by the invention according to independent claim 1. Specifically, an inverter control apparatus including at least first and second inverters includes: a current detector that detects a current flowing through a main circuit of the first inverter; a current controller that generates a voltage command value of the first inverter on the basis of a detected current and a current command; and a voltage command predictor that generates a voltage command value of the second inverter on the basis of a variation of the voltage command value of the first inverter.Advantageous Effects of the InventionSince the present invention has the above-mentioned configurations, it is possible to reduce a calculation load of the control device without reducing the responsiveness of the current control (torque control).Brief Description of the Drawings[FIG. 1( a)] FIG. 1( a) is a diagram illustrating an electric power steering apparatus according to a first embodiment.[FIG. 1( b)] FIG. 1( b) is a diagram illustrating a configuration of a control device 280 according to the first embodiment.[FIG. 2 ] FIG. 2 is a diagram illustrating a processing sequence of a three-phase AC calculator 300 according to the first embodiment.[FIG. 3] FIG. 3 is a diagram illustrating a relationship among a PWM signal, a three-phase alternating current, and a direct current bus current.[FIG. 4( a)] FIG. 4( a) is a diagram illustrating a current path under a switching mode 1 of FIG. 3.[FIG. 4( b)] FIG. 4( b) is a diagram illustrating a current path under a switching mode 2 of FIG. 3.[FIG. 4( c)] FIG. 4( c) is a diagram illustrating a current path under a switching mode 3 of FIG. 3.[FIG. 4( d)] FIG. 4( d) is a diagram illustrating a current path under a switching mode 4 of FIG. 3.[FIG. 5 ] FIG. 5 is a diagram showing a processing sequence of an abc-to-dq transformer 310.[FIG. 6 ] FIG. 6 is a diagram illustrating a processing sequence of a current command generator 330.[FIG. 7 ] FIG. 7 is a diagram illustrating a map for the first d-axis current command and a map for the first q-axis current command.[FIG. 8] FIG. 8 is a diagram illustrating a processing sequence of a current controller 320.[FIG. 9 ] FIG. 9 is a diagram illustrating a processing sequence of a dq-to-abc transformer 350.[FIG. 10 ] FIG. 10 is a diagram illustrating a processing sequence of a PWM modulator 370 according to the first embodiment.[FIG. 11 ] FIG. 11 is a diagram illustrating a processing sequence of a voltage command predictor 340 according to the first embodiment.[FIG. 12 ] FIG. 12 is a diagram illustrating a processing sequence of a dq-to-abc transformer 360.[FIG. 13 ] FIG. 13 is a diagram illustrating a processing sequence of the PWM modulator 380 according to the first embodiment.[FIG. 14( a)] FIG. 14( a) is a diagram illustrating an electric power steering apparatus according to a second embodiment.[FIG. 14( b)] FIG. 14( b) is a diagram illustrating a configuration of a control device 280 according to the second embodiment.[FIG. 15] FIG. 15 is a diagram illustrating a processing sequence of a three-phase AC calculator 300 according to the second embodiment.[FIG. 16] FIG. 16 is a diagram illustrating a processing sequence of an abnormality detector 295 according to the second embodiment.[FIG. 17] FIG. 17 is a diagram illustrating a relationship between a first DC bus current IdcA and a first ground current igA.[FIG. 18] FIG. 18 is a diagram showing a processing sequence of a voltage command predictor 340 according to the second embodiment.[FIG. 19] FIG. 19 is a diagram illustrating a processing sequence of the PWM modulator 370 according to the second embodiment.[FIG. 20 ] FIG. 20 is a diagram illustrating a processing sequence of the PWM modulator 380 according to the second embodiment.DESCRIPTION OF EMBODIMENTSA case where an inverter control device according to the present invention is applied to an electric power steering device will now be described. Note that in each drawing, like reference numerals denote like elements, and will not be described repeatedly.First Embodiment(Outline of Electric Power Steering Apparatus)FIG. 1( a) is a diagram illustrating an electric power steering apparatus according to the first embodiment.The electric power steering apparatus according to the first embodiment includes a battery 10, a first inverter 20, a shunt resistor 90, an amplifier 100, a gate drive circuit 390 of the first inverter 20, a second inverter 120, a gate drive circuit 400 of the second inverter 120, a controller 280, a motor 110, an angle detector 190, an output shaft 200 of the motor 110, a transmission 210, a manual steering transmission 250, tie rods 260, vehicle wheels 270, a rod 220, a torque sensor 230, and a driver-operated steering 240. The shunt resistor 90 according to the first embodiment is provided to detect a DC bus current IdcA (hereinafter referred to as a first DC bus current IdcA) of the first inverter 20. The amplifier 100 is provided to amplify a voltage between both ends of the shunt resistor 90. The angle detector 190 is provided to detect a magnetic pole position of a rotor of the motor 110.The electric power steering device is configured to apply a motor drive device to the steering device to reduce (assist) a driver's operation load for the steering 240. When a driver turns the steering 240, torque is transmitted through the rod 220 and the transmission 210 to the manual steering transmission 250. The torque transmitted to the manual steering gear 250 is compensated by a torque generated in the motor 110, and is transmitted to the left and right vehicle wheels 270 through the left and right tie rods 260. As a result, the left and right vehicle wheels 270 are steered.The battery 10 is connected to DC sides of the first and second inverters 20 and 120 to supply a DC voltage to the first and second inverters 20 and 120. A negative electrode side of the battery 10 and a low potential side bus of the DC side of the first inverter 20 are connected to each other through the shunt resistor 90. Although it is assumed here that the shunt resistor 90 is connected to the negative electrode side of the battery 10 and the low potential side bus of the first inverter 20, the shunt resistor may be connected between a positive electrode side of the battery 10 and a high potential side bus of the DC side of the first inverter 20. Alternatively, the shunt resistor may be connected between the positive electrode side (negative electrode side) of the battery 10 and the high potential side bus (low potential side bus) of the DC side of the second inverter 120. Alternatively, the shunt resistor may be connected between any one of the upper arms of each phase (lower arms of each phase) of the first and second inverters 20 and 120 and the high-potential-side bus (low-potential-side bus), respectively. Alternatively, a Hall current sensor may be provided on the AC bus side of each phase in one of the first and second inverters 20 and 120.The three-phase AC bus side of the first inverter 20 is connected to a first three-phase coil wound around a stator of the motor 110. The three-phase AC bus side of the second inverter 120 is connected to the second three-phase coil wound around the stator of the motor 110.The switching elements 30 to 80 of the upper and lower arms of each phase of the first inverter 20 are turned on or off based on the first PWM signals SupA, SunA, SvpA, SvnA, SwpA, and SwnA generated by the controller 280 to convert the DC voltage supplied from the battery 10 into a three-phase AC voltage having a variable voltage and a variable frequency. Similarly, the switching elements 130 to 180 of the upper and lower arms of each phase of the second inverter 120 are turned on or off based on the second PWM signals SupB, SunB, SvpB, SvnB, SwpB, and SwnB generated by the controller 280 to convert the DC voltage supplied from the battery 10 into a three-phase AC voltage having a variable voltage and a variable frequency. In addition, the first and second inverters 20 and 120 apply the transformed three-phase AC voltage to the first and second three-phase coils wound around the stator of the motor 110 to generate the three-phase AC current in the first and second three-phase coils, respectively.The motor 110 generates a rotating magnetic field depending on the three-phase alternating current flowing to the first and second three-phase coils wound around the stator, and generates torque for accelerating or decelerating a rotor (not illustrated) based on the generated rotating magnetic field. In addition, the motor 110 outputs the generated torque to the output shaft 200 and supplies the torque to the manual steering gear 250 via the gear 210.A main circuit of the first inverter 20 according to the first embodiment includes switching elements 30 to 80. The switching elements 30 to 80 are formed by combining a metal oxide semiconductor field effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT) and a diode. A circuit configuration of the first inverter 20 according to the first embodiment is similar to that of the related art and will not be described in detail here.The switching element 30 of the upper U-phase arm of the first inverter 20 is turned on or off on the basis of the first PWM signal SupA voltage-boosted by the gate drive circuit 390. Similarly, the switching elements 40, 50, 60, 70, and 80 of the first inverter 20 are turned on or off based on the first PWM signals SunA, SvpA, SvnA, SwpA, and SwnA, respectively, which are voltage-boosted by the gate drive circuit 390.The main circuit of the second inverter 120 is also formed similarly to that of the first inverter 20. The switching element 130 of the upper U-phase arm of the second inverter 120 is turned on or off based on the second PWM signal SupB. Similarly, the switching elements 140, 150, 160, 170, and 180 of the second inverter 120 are turned on or off based on the second PWM signals SunB, SvpB, SvnB, SwpB, and SwnB, respectively, which are voltage-boosted by the gate drive circuit 400.(Processing of Control Device 280)A configuration and processing details of the control device 280 will be described with reference to FIG. 1( b). The controller 280 includes a carrier generator 290, a three-phase AC calculator 300, an abc-to-dq transformer 310, a current controller 320, a current command generator 330, a voltage command predictor 340, dq-to-abc transformers 350 and 360, and PWM modulators 370 and 380. As shown in FIG. 1( a), the controller 280 receives a first DC bus current Idc Detected by the shunt resistor 90 and the amplifier 100, a magnetic pole position θ of the rotor of the motor 110 detected by the angle sensor 190, and a torque Tsdetected by the torque sensor 230 and transmitted from the steering 240 to the rod 220.The three-phase AC calculator 300 acquires the first DC bus current IdcA flowing to the first inverter 20 at the timing determined on the basis of a relationship between a triangular wave carrier Carrier and the first three-phase AC voltage commands vuA*, vvA*, and vwA*. This triangular wave carrier carrier is generated in carrier generator 290 and the first three phase AC commands vuA*, vvA*, and vwA* are generated in dq-to-abc transformer 350 described below. In addition, the three-phase AC calculator 300 calculates the first three-phase AC currents iuA, ivA, and iwA flowing to the first three-phase coil of the motor 110 based on the detected first DC bus current IdcA.The abc-to-dq transformer 310 calculates a first d-axis current idA flowing to the d-axis of the motor 110 and a first q-axis current iqA flowing to the q-axis based on the first three-phase alternating currents iuA, ivA, and iwA and the magnetic pole position θ of the rotor of the motor 110. The current command generator 330 generates a first d-axis current command idA* and a first q-axis current command iqA* of the motor 110 on the basis of the magnetic pole position θ and the rotor torque Ts of the motor 110. The current controller 320 generates a first d-axis voltage command vdA* and a first q-axis voltage command vqA* using proportional-plus-integral control or the like such that the first d-axis current idA and the first q-axis current iqA coincide with the first d-axis current command idA* and the first q-axis current command iqA*, respectively.The dq-to-abc transformer 350 calculates the first three-phase AC voltage commands vuA*, vvA*, and vwA* on the basis of the first d-axis voltage command vdA*, the first q-axis voltage command vqA*, and the magnetic pole position θ of the rotor of the motor 110. The PWM modulator 370 generates the first PWM signals SupA, SunA, SvpA, SvnA, SwpA, and SwnA of the upper and lower arms of each phase of the first inverter 20 on the basis of the first three-phase AC voltage commands vuA*, vvA*, and vwA* and the triangular wave carrier carrier carrier.The voltage command predictor 340 predicts a second d-axis voltage command vdB* and a second q-axis voltage command vqB* based on the first d-axis voltage command vdA* and the first q-axis voltage command vqA*. The dq-to-abc transformer 360 generates second three-phase AC voltage commands vuB*, vvB*, and vwB* based on the second d-axis voltage command vdB* and the second q-axis voltage command vqB*. The PWM modulator 380 generates PWM signals SupB, SunB, SvpB, SvnB, SwpB, and SwnB of the upper and lower arms of each phase of the second inverter 120 on the basis of the second three-phase AC voltage commands vuB*, vvB*, and vwB* and the triangular wave carrier carrier carrier.In the first embodiment, the voltage command predictor 340 predicts the second d-axis voltage command vdB* and the second q-axis voltage command vqB* based on the first d-axis voltage command vdA* and the first q-axis voltage command vqA*. Alternatively, the second three-phase AC commands vuB*, vvB*, and vwB* may be predicted based on the first three-phase AC commands vuA*, vvA*, and vwA*.In this way, as compared with a method of detecting the DC bus currents of all channels by generating the voltage command of the inverter of the second channel and generating the voltage command of the inverter of all channels on the basis of current control such as proportional component control, it is possible to remarkably reduce processing loads for a current detection process, a three-phase AC calculation process, an abc-to-dq transformation process, and a current control process. That is, it is possible to reduce a calculation amount for controlling the second inverter 120 and the motor 110.(Processing of Three-Phase AC Calculator 300)FIG. 2 is a diagram illustrating a processing sequence of the three-phase AC calculator 300. As described above in connection with FIG. 1( b), the three-phase AC calculator 300 acquires the first DC bus current IdcA flowing to the first inverter 20 at the timing determined based on a relationship between the triangular wave carrier and the first three-phase AC voltage commands vuA*, vvA*, and vwA*, and calculates the first three-phase AC currents iU, iVA, and iWA based on the acquired first DC bus current IdcA.In FIG. 2, a first maximum phase voltage command is defined as a first X-phase AC voltage command vxA*, a first intermediate phase voltage command is defined as a first Y-phase AC voltage command vyA*, and a first minimum phase voltage command is defined as a first Z-phase AC voltage command vzA*. That is, subscripts "x, y, and z" of vxA*, vyA*, vzA*, ixA, iyA, and izA of FIG. 2 are replaced with one of "u, v, and w" depending on a relationship of the maximum phase, the intermediate phase, and the minimum phase of the first three-phase AC commands vuA*, vvA*, and vwA*.In step a- 1, it is determined whether or not the first X-phase AC voltage command vxA* (first maximum-phase voltage command) is higher than the triangular wave carrier carrier carrier. When vxA* is higher than the carrier, it is determined in step a- 2 whether or not the first Y-phase AC voltage command vyA* (first inter-phase voltage command) is lower than the triangular wave carrier carrier. When vyA* is lower than the carrier, the process proceeds to step a-3. When vyA* is not lower than the carrier, it is determined in step a-8 whether or not the first Z-phase AC voltage command vzA* (first minimum-phase voltage command) is lower than the triangular wave carrier carrier.In step a-3, it is determined whether or not the first time counter value Tcnt1 is larger than a predetermined threshold value Tth1. If Tcnt1 is not larger than Tth1, Tcnt1 is incremented in step a-7, and then step a-3 is repeated. When Tcnt1 is larger than Tth1, in step a-4, the first DC bus current IdcA is detected and the first X-phase AC current ixA is calculated based on formula (1). [Formula 1]Then, in step a- 5, the first X-phase alternating current ix The first Z-phase alternating current iz Calculated in step a- 10 are substituted into formula (2) to calculate the first Y-phase alternating current iyA. [Formula 2]In step a-6, the first time counter value Tcnt1 is reset to zero, and the process returns to step a-1.When it is determined in step a- 8 that the first Z-phase AC voltage command vzA* (first minimum-phase voltage command) is lower than the triangular wave carrier Carrier, it is determined in step a- 9 whether or not the first time counter value Tcnt1 is larger than a predetermined threshold value Tth1. If Tcnt1 is not larger than Tth1, Tcnt1 is incremented in step a-11, and then step a-9 is repeatedly processed. When Tcnt1 is larger than Tth1, the first DC bus current IdcA is detected in step a-10, and the first Z-phase AC current izA is calculated based on formula (3). [Formula 3]When it is determined in step a- 8 that the first Z-phase AC voltage command vzA* (first minimum-phase voltage command) is not lower than the triangular wave carrier carrier carrier, the process proceeds to step a- 6 so that the first of the timer value Tcnt1 is reset to zero, and then the process returns to step a- 1. This similarly applies to a case where it is determined in step a- 1 that the first X-phase AC voltage command vxA* (first maximum phase voltage command) is not higher than the triangular wave carrier carrier.FIG. 3 is a diagram illustrating a relationship among the PWM signals SupA, SvpA, and SwpA of the first upper arm of each phase, the first three-phase alternating currents iuA, ivA, and iwA, and the first direct current bus current IdcA. A principle of calculating the first three-phase AC currents iuA, ivA, and iwA from the first DC bus current IdcA using the three-phase AC calculator 300 will be described with reference to FIG. 3.In FIG. 3, the maximum phase, the intermediate phase, and the minimum phase are set to the U phase, the V phase, and the W phase, respectively. In addition, the three-phase alternating currents iuA, ivA, and iwA are defined as positive when flowing from the first inverter 20 to the three-phase coil of the motor 110. In addition, the first DC bus current IdcA is defined as positive when it flows from the low potential side bus of the first inverter 20 to the negative electrode side of the battery 10.The PWM signals SupA, SvpA and SwpA of the first upper arm of each phase are generated by comparing the first three-phase AC voltage commands vuA*, vvA* and vwA* and the carrier carrier carrier. That is, the PWM signal SupA is turned on when vuA* is higher than carrier and turned off when vuA* is lower than carrier. The same applies to the PWM signals Svp SwpA.In the first upper arm PWM signals of each phase generated in this manner, a switching mode 1 is set when SupA, SvpA, and SwpA are all turned on. In addition, a switching mode 2 is set when SupA and SvpA are turned on and SwpA is turned off. In addition, a switching mode 3 is set when SupA is turned on and SvpA and SwpA are turned off. Further, a switching mode 4 is set when SupA, SvpA, and SwpA are all turned off.Although described in detail below with reference to FIG. 1, as shown in FIG. 4, in the switching mode 1, the first d three-phase alternating currents iuA, ivA, and iwA flow, but the first direct current bus current IdcA does not flow. In the switching mode 2, the first DC bus current IdcA becomes "-iwA". In the switching mode 3, the first DC bus current IdcA is "iuA". In the switching mode 4, similarly to the switching mode 1, the first three-phase alternating currents iuA, ivA, and iwA flow, but the first direct current bus current IdcA does not flow.Therefore, the first three-phase alternating currents iuA, ivA, and iwA are calculated using the formulas (4) to (6), respectively, based on the processing sequence of FIG. 2 and the first direct-current bus current IdcA detected in the switch modes 2 and 3. [Formula 4] [Formula 5] [Formula 6]FIG. 4 is a diagram illustrating a current path of the first three-phase alternating currents iuA, ivA, and iwA and the first direct current bus current IdcA corresponding to the switching mode of FIG. 3. FIG. 4( a) illustrates the shift mode 1, FIG. 4( b) illustrates the shift mode 2, FIG. 4( c) illustrates the shift mode 3, and FIG. 4( d) illustrates the shift mode 4.In the switching mode 1, the first three-phase alternating currents iuA, ivA, and iwA flow only between the switching elements 30, 50, and 70 of the upper arm of each phase and the three-phase coil (not illustrated) of the motor 110. Therefore, since no current flows to the shunt resistor 90, the first DC bus current Idc becomes zero.In the switching mode 2, the first W-phase alternating current iwA flows through the switching element 80 of the lower W-phase arm and the shunt resistor 90 to the negative electrode side of the battery 10. in addition, the first W-phase alternating current iwA flowing from the positive electrode side of the battery 10 is mixed with the first V-phase alternating current ivA flowing from the switching element 50 of the upper V-phase arm in the U-phase direction to form the first U-phase alternating current iuA, and the U-phase alternating current iuA flows through the switching element 30 of the upper U-phase arm to the U-phase coil (not illustrated) of the motor 110. Therefore, in the switching mode 2, since the first W-phase alternating current iwA flows to the shunt resistor 90, the first direct current bus current Idc becomes the first W-phase alternating current iwA. At this time, however, the first DC bus current IdcA has a positive direction and the first W-phase AC current iwA has a negative direction. Therefore, a relationship between the first DC bus current Idc The first W-phase AC current iw Expressed as Formula (7). Formula (7) is equivalent to Formula (4) described above. [Formula 7]In the switching mode 3, the first U-phase alternating current iuA flows through the battery 10 and the switching element 30 of the U-phase upper arm to the U-phase coil (not illustrated) of the motor 110. The first U-phase alternating current iuA flowing to the U-phase coil (not illustrated) is branched into the V-phase coil (not illustrated) and the W-phase coil (not illustrated) of the motor 110 as the first V-phase alternating current ivA and the first W-phase alternating current iwA. In addition, the first V-phase alternating current ivA flowing from the V-phase coil (not illustrated) to the lower V-phase leg switching element 60 is mixed with the first W-phase alternating current iwA flowing from the W-phase coil (not illustrated) to the lower W-phase leg switching element 80 to form the first U-phase alternating current iuA, and the first U-phase alternating current iuA flows to the shunt resistor 90, the first DC bus current Idc to the first U-phase AC current iuA. At this time, the first DC bus current has a positive direction. Therefore, a relationship between the first DC bus current Idc The first U-phase AC current iu Expressed as Formula (8). Formula (8) corresponds to Formula (5) described above. [Formula 8]In the switching mode 4, the first three-phase alternating currents iuA, ivA, and iwA flow only between the switching elements 40, 60, and 80 of the lower arm of each phase and the three-phase coil (not illustrated). Therefore, since no current flows to the shunt resistor 90, the first DC bus current Idc becomes zero.According to the first embodiment, on the basis of such a relationship, the first three-phase alternating currents iuA, ivA, and iwA are calculated using the first direct-current bus current IdcA flowing to the shunt resistor 90.(Processing of abc-to-dq transformer 310)FIG. 5 is a diagram showing a processing sequence for calculating the first d-axis current id The first q-axis current iqAusing the abc-to-dq transformer 310.In step b- 1, the first three-phase AC currents iuA, ivA, and iwA calculated by the three-phase AC calculator 300 are detected. In step b- 2, the magnetic pole position θ of the rotor of the motor 110 detected by the angle sensor 190 is detected. In step b- 3, the first three-phase alternating currents iuA, ivA, and iwA and the magnetic pole position θ of the rotor of the motor 110 in formula (9) are employed to calculate the first d-axis current idA and the first q-axis current iqA. [Formula 9](Processing of Current Command Generator 330)FIG. 6 is a diagram illustrating a processing sequence for generating the first d-axis current command idA* and the first q-axis current command iqA* using the current command generator 330.In step c-1, the torque Ts detected by the torque sensor 230 is detected. In step c- 2, the magnetic pole position θ of the rotor of the motor 110 detected by the angle sensor 190 is detected. In step c- 3, an electric angular velocity ω of the rotor of the motor 110 is calculated based on Formula (10). [Formula 10]In step c- 4, the first d-axis current command idA* and the first q-axis current command iqA* are set according to the torque Ts and the electrical angular velocity ω. A specific example of the processing will be described with reference to FIG. 7.FIG. 7 shows a map of the first d-axis current command and a map of the first q-axis current command obtained by setting the torque Ts and the electrical angular velocity ω on the ordinate and the abscissa, respectively. These maps are stored in advance in a memory (not illustrated) of the current command generator 330, and the first d-axis current command idA*(x, y) and the first q-axis current command iqA*(x, y) in an array (x, y) corresponding to the torque Ts detected in step c- 1 and the angular electric speed calculated in step c- 3 are retrieved from the memory.(Processing of Current Controller 320)FIG. 8 is a diagram illustrating a processing sequence for generating the first d-axis voltage command vdA* and the first q-axis voltage command vqA* using the current controller 320.In step d- 1, the first dq-axis current commands idA* and iqA* set by the current command generator 330 are acquired. In step d- 2, the first dq axis currents idA and iqA calculated by the abc-to-dq transformer 310 are detected. In step d- 3, the first dq-axis current differences Δid Δiq Calculated based on formula (11). [Formula 11]Further, in step d- 4, the first dq-axis voltage commands vdA* and vqA* are calculated on the basis of the first dq-axis current differences ΔidA and ΔiqA calculated in step d- 3 and formula (12). Here, dq-axis proportional gains Kpd and Kpq and dq-axis integral gains Kid and Kiq are stored in advance in the memory (not illustrated) of the current controller 320. [Formula 12]Processing of dq-to-abc transformer 350)FIG. 9 is a diagram illustrating a processing sequence for calculating the first three-phase AC voltage commands vuA*, vvA*, and vwA* using the dq-to-abc transformer 350.In step e- 1, the first dq-axis voltage commands vdA* and vqA* calculated by the current controller 320 are acquired. In step e- 2, the magnetic pole position θ of the rotor of the motor 110 detected by the angle sensor 190 is detected. In step e- 3, the first dq-axis voltage commands vdA* and vqA* acquired in step e- 1 and the magnetic pole position θ of the rotor of the motor 110 acquired in step e- 2 are substituted into formula (13) to calculate the first three-phase AC voltage commands vuA*, vvA*, and vwA*. [Formula 13](Processing of PWM modulator 370)FIG. 10 is a diagram illustrating a processing sequence for generating the first PWM signals SupA, SunA, SvpA, SvnA, SwpA, and SwnA of the upper and lower arms of each phase of the first inverter 20 using the PWM modulator 370.In step f- 1, the first three-phase AC voltage commands vuA*, vvA*, and vwA* calculated by the dq-to-abc transformer 350 are acquired. Subsequently, in step f- 2, it is determined whether or not the first U-phase AC voltage command vuA* detected in step f- 1 is equal to or greater than the triangular vibration carrier carrier.When vuA* is equal to or larger than carrier in step f- 2, the first U-phase lower arm PWM signal SunA is set to OFF in step f- 3, and then the first U-phase upper arm PWM signal SupA is set to ON in step f- 4. Otherwise, if vuA* is not greater than or equal to carrier in step f-2, the first U-phase upper arm PWM signal SupA is set to OFF in step f-5, and then the first U-phase lower arm PWM signal SunA is set to ON in step f-6.In step f- 7, it is determined whether or not the first V-phase AC voltage command vvA* detected in step f- 1 is equal to or greater than the triangular vibration carrier carrier Carrier. When vvA* is equal to or larger than carrier, the first V-phase lower arm PWM signal SvnA is set to OFF in step f- 8, and then the first V-phase upper arm PWM signal SvpA is set to ON in step f- 9. Otherwise, if vvA* is not greater than or equal to carrier, the first upper V-phase arm PWM signal SvpA is set to OFF in step f-10, and then the first lower V-phase arm PWM signal SvnA is set to ON in step f-11.In step f- 12, it is determined whether or not the first W-phase AC voltage command vwA* detected in step f- 1 is equal to or greater than the triangular vibration carrier carrier carrier. When vwA* is equal to or larger than carrier, the PWM signal SwnA of the first W-phase lower arm is set to OFF in step f-13, and then the PWM signal SwpA of the first W-phase upper arm is set to ON in step f-14. Otherwise, when vwA* is not greater than or equal to carrier, the PWM signal SwpA of the first upper W-phase arm is set to OFF in step f-15, and then the PWM signal SwnA of the first lower W-phase arm is set to ON in step f-16.By generating the PWM signals SupA, SunA, SvpA, SvnA, SwpA, and SwnA of the first upper and lower arms of each phase in this manner, it is possible to allow an average value of the PWM voltage of the UVW phase output from the first inverter 20 to match the first three-phase AC voltage commands vuA*, vvA*, and vwA*. Such a method of generating the PWM signals is generally known as a triangular wave comparison method. Alternatively, without limiting the triangular wave comparison method, other methods such as a space vector modulation method may also be used as a method for generating the PWM signals.(Operation of Gate Driving Circuit 390)The gate drive circuit 390 amplifies voltages of the PWM signals SupA to SwnA of the first upper and lower arms of each phase generated by the PWM modulator 370, and outputs the amplified voltages to the gates of the switching elements 30 to 80 of the upper and lower arms of each phase of the first inverter 20.As a result, the switching elements 30 to 80 of the upper and lower arms of each phase of the first inverter 20 are turned on or off depending on the PWM signals SupA to SwnA of the first upper and lower arms of each phase.(Processing of Voltage Command Predictor 340)FIG. 11 is a diagram illustrating a processing sequence for predicting the second d-axis voltage command vdB* and the second q-axis voltage command vqB* based on the first d-axis voltage command vdA* and the first q-axis voltage command vqA* using the voltage command predictor 340 according to the first embodiment.In step g- 1, the first dq-axis voltage commands vdA* and vqA* calculated by the current controller 320 are acquired. In step g- 2, the first dq-axis voltage commands vdA* and vqA* acquired in step g- 1 and previous values vdAold* and vqAold* of the first dq-axis voltage commands set in step g- 4 are substituted into formula (14) to calculate the first voltage differences ΔvdA* and Δ vqA*. [Formula 14]In step g- 3, the first dq-axis voltage command differences ΔvdA* and ΔvqA* calculated in step g- 2 and previous values vdBo* and vqBo* of the second dq-axis voltage commands set in step g- 4 described below are substituted into formula (15) to generate the second dq-axis voltage commands vdB* and vqB*. [Formula 15]In step g- 4, the first dq-axis voltage commands vdA* and vqA* acquired in step g- 1 and the second dq-axis voltage commands vdB* and vqB* generated in step g- 3 are employed in formula (16) to set the previous values vdAold* and vqAold* of the first dq-axis voltage commands and the previous values vdBo* and vqBo* of the second dq-axis voltage commands. [Formula 16]By generating the second dq-axis voltage commands vdB* and vqB* in this manner, it is possible to remarkably reduce processing loads for a current detection process, a three-phase AC calculation process, an abc-to-dq transformation process, and a current control process, compared to a method of detecting the DC bus currents of all channels and generating the voltage commands of the inverters of all channels using current control such as proportional component control. That is, it is possible to reduce a computation amount for controlling the second inverter 120 and the motor 110.According to the first embodiment, as a configuration of the voltage command predictor 340, the first dq-axis voltage command differences ΔvdA* and Δ vqA* are directly added to the previous values vdBo* and vqBo* of the second dq-axis voltage commands, as expressed in Formula (15). Alternatively, for example, by multiplying ΔvdA* and ΔvqA* by a predetermined coefficient and then adding them to vdBo* and vqBo*, a difference in circuit parameter or the like between the first and second inverters 20 and 120 may be compensated.Alternatively, the voltage command predictor 340 may be configured using, for example, a method of calculating the second dq-axis voltage commands vdB* and vqB* by obtaining a ratio between the first dq-axis voltage commands vdA* and vqA* and the previous values vdAold* and vqAold* of the first dq-axis voltage commands and multiplying this ratio by the previous values vdBold* and vqBold* of the second dq-axis voltage commands. Such a method does not deviate from the subject matter of the invention, that is, the voltage command value of the second inverter is generated based on variation of the voltage command value of the first inverter.(Processing of dq-to-abc transformer 360)FIG. 12 is a diagram illustrating a processing sequence for generating the second three-phase AC voltage commands vuB*, vvB*, and vwB* on the basis of the second d-axis voltage command vdB* and the second q-axis voltage command vqB* using the dq-to-abc transformer 360. Basic operation is similar to operation of dq-to-abc transformer 350 of FIG. 9. That is, the dq-axis second voltage commands vdB* and vqB* acquired in step h- 1 and the magnetic pole position θ of the rotor of the motor 110 acquired in step h- 2 are employed in formula (17) to calculate the three-phase second AC voltage commands vuB*, vvB*, and vwB*. [Formula 17](Processing of PWM modulator 380)FIG. 13 is a diagram illustrating a processing sequence for generating the second PWM signals SupB, SunB, SvpB, SvnB, SwpB, and SwnB of the upper and lower arms of each phase of the second inverter 20 using the PWM modulator 380. The basic concept is similar to that of FIG. 10 and will not be described in detail here.(Operation of Gate Driving Circuit 400)The gate drive circuit 400 amplifies voltages of the PWM signals SupB to SwnB of the second upper and lower arms of each phase generated by the PWM modulator 380, and inputs the amplified voltages to the gates of the switching elements 130 to 180 of the upper and lower arms of each phase of the second inverter 120.As a result, the switching elements 130 to 180 of the upper and lower arms of each phase of the second inverter 120 are turned on or off depending on the PWM signals SupB to SwnB of the second upper and lower arms of each phase.Second Embodiment(Outline of Electric Power Steering Apparatus)FIG. 14( a) is a diagram illustrating an electric power steering apparatus according to the second embodiment.The electric power steering apparatus according to the second embodiment has a configuration different from that of the first embodiment as described below. The electric power steering apparatus according to the second embodiment includes a shunt resistor 95 for detecting a DC bus current IdcB (hereinafter referred to as "second DC bus current IdcB") of the second inverter 120, and an amplifier 105 for amplifying a voltage between both ends of the shunt resistor 95. The controller 280 receives first and second DC bus currents IdcA and IdcB, respectively. In addition, as described below in connection with FIG. 14( b), the control device 280 according to the second embodiment includes a detection current selector 285 that selects any one of the first and second DC bus currents IdcA and IdcB as a detection current, and an abnormality detector 295. With the aid of such parts, it is possible to detect any abnormality such as a ground fault or overcurrent in each channel with high accuracy and improve a fail-safe functionality.In the electric power steering apparatus according to the second embodiment, the DC bus currents of each channel are sequentially switchingly detected. The voltage command of the inverter of the channel in which the DC bus current is detected is generated by a current controller such as the proportional-integral controller. The voltage command of the inverter of the channel in which the DC bus current is not detected is generated by adding a difference between the previous value and the last value of the voltage command of the inverter at which the DC bus current is detected to the voltage command one calculation cycle before the inverter of the channel at which the DC bus current is not detected.By generating the voltage command of the inverter of each channel in this manner, it is possible to remarkably reduce the processing loads for a current detection process, a three-phase AC calculation process, an abc-to-dq transformation process, and a current control process, compared to a method of detecting the DC bus currents of all channels and generating the voltage commands of the inverters of all channels using a typical current control such as a proportional-integral control.(Processing of Control Device 280)A configuration and processing details of the control device 280 according to the second embodiment will be described with reference to FIG. 14( b). The controller 280 includes a detection current selector 285, a carrier generator 290, an abnormality detector 295, a three-phase AC calculator 300, an abc-to-dq transformer 310, a current controller 320, a current command generator 330, a voltage command predictor 340, dq-to-abc transformers 350 and 360, and PWM modulators 370 and 380.The detection current selector 285 selects any one of the first and second DC bus currents IdcA and IdcB as a detection current. Here, it is assumed that the detection current selector 285 sequentially switches the first and second DC bus currents IdcA and IdcB at every predetermined timing.When the detection current selector 285 selects the first DC bus current IdcA, the three-phase AC calculator 300 detects the first DC bus current IdcA at a timing determined on the basis of a relationship between the three-phase AC voltage commands triangular wave carrier carrier and the first three-phase AC voltage commands vuA*, vvA*, and vwA*. The three-phase AC calculator 300 calculates the first three-phase AC currents iuA, ivA, and iwA flowing to the first three-phase coil of the motor 110 based on the detected first DC bus current IdcA. In addition, the three-phase AC calculator 300 sets the calculated first three-phase AC currents iuA, ivA, and iwA as the three-phase AC currents iu, iv, and iw for a single channel.In this case, the abnormality detector 295 detects the first DC bus current IdcA and the three-phase AC currents iu, iv, and iw for a single channel (i.e., the first three-phase AC currents iuA, ivA, and iwA) calculated by the three-phase AC calculator 300 at the timing determined based on a relationship between the triangular wave carrier and the first three-phase AC commands vuA*, vvA*, and vwA*. The abnormality detector 295 determines whether an abnormality (such as a ground fault or overcurrent) exists in the channel including the first inverter 20 and the motor 110 based on the detected first DC bus current IdcA and the first three-phase AC currents iuA, ivA, and iwA.When the detection current selector 285 selects the second DC bus current IdcB, the three-phase AC calculator 300 detects the second DC bus current IdcB at the timing determined based on a relationship between the triangular wave carrier Carrier and the second three-phase AC voltage commands vuB*, vvB, and vwB*. The three-phase AC calculator 300 calculates the second three-phase AC currents iuB, ivB, and iwB flowing to the second three-phase coil of the motor 110 based on the detected second DC bus current IdcB. In addition, the three-phase AC calculator 300 sets the calculated second three-phase AC currents iuB, ivB, and iwB as the three-phase AC currents iu, iv, and iw for a single channel.In this case, the abnormality detector 295 detects the second DC bus current IdcB and the three-phase AC currents iu, iv, and iw for a single channel (i.e., the second three-phase AC currents iuB, ivB, and iwB) calculated by the three-phase AC calculator 300 at the timing determined based on a relationship between the triangular wave carrier and the second three-phase AC commands vuB*, vvB*, and vwB*. The abnormality detector 295 determines whether an abnormality (such as a ground fault or overcurrent) exists in the channel including the second inverter 120 and the motor 110, based on the detected second DC bus current IdcB and the second three-phase AC currents iuB, ivB, and iwB.The abc-to-dq transformer 310 calculates the d-axis current id flowing to the d-axis and the q-axis current iq flowing to the q-axis for a single channel of the motor 110 based on the three-phase alternating currents iu, iv, and iw for a single channel and the magnetic pole position θ of the rotor of the motor 110.The current command generator 330 generates the d-axis current command id* and the q-axis current command iq* for a single channel of the motor 110 based on the magnetic pole position θ and the rotor torque Ts of the motor 110.The current controller 320 generates the d-axis voltage command vd* and the q-axis voltage command vq* for a single channel such that the d-axis current id and the q-axis current iq for a single channel match the d-axis current command id* and the q-axis current command iq* for a single channel.When the detection current selector 285 selects the first DC bus current IdcA, When the voltage command predictor 340 sets the dq-axis voltage commands vd* and vq* for a single channel as the first dq-axis voltage commands vdA* and vqA*, and calculates the second dq-axis voltage commands vdB* and vqB* by adding the differences ΔvdA* and Δ vqqA* between the last first dq-axis voltage commands vdA* and vqA* and the first dq-axis voltage commands vdAold* and vqAold* before a single calculation cycle to the second dq-axis voltage commands vdBold* and vqBold* before a single calculation cycle.When the detection current selector 285 selects the second DC bus current IdcB, When the voltage command predictor 340 sets the dq-axis voltage commands vd* and vq* for a single channel as the second dq-axis voltage commands vdB* and vqB*, and calculates the first dq-axis voltage commands vdA* and vqA* by adding the differences ΔvdB* and Δ vqqB* between the last second dq-axis voltage commands vdB* and vqB* and the second dq-axis voltage commands vdBold* and vqBold* before a single calculation cycle to the first dq-axis voltage commands vdAold* and vqAold* before a single calculation cycle.The dq-to-abc transformer 350 calculates the first three-phase AC voltage command vuA*, vvA*, and vwA* based on the first d-axis voltage command vdA*, the first q-axis voltage command vqA*, and the magnetic pole position θ of the rotor of the motor 110. The PWM modulator 370 generates the first PWM signals SupA, SunA, SvpA, SvnA, SwpA, and SwnA of the upper and lower arms of each phase of the first inverter 20 on the basis of the first three-phase AC voltage commands vuA*, vvA*, and vwA*, the triangular wave carrier carrier, and a first ground fault determination flag FaultA 1 and a first overcurrent determination flag FaultA 2 generated by the abnormality detector 295.The dq-to-abc transformer 360 calculates the second three-phase AC voltage commands vuB*, vvB*, and vwB* based on the second d-axis voltage command vdB*, the second q-axis voltage command vqB*, and the magnetic pole position θ of the rotor of the motor 110. The PWM modulator 380 generates the second PWM signals SupB, SunB, SvpB, SvnB, SwpB, and SwnB of the upper and lower arms of each phase of the second inverter 120 on the basis of the second three-phase AC voltage commands vuB*, vvB*, and vwB*, the triangular wave carrier carrier, and a second ground fault determination flag FaultB 1 and a second overcurrent determination flag FaultB 2 generated by the abnormality detector 295.The carrier generator 290, the abc-to-dq transformer 310, the current command generator 330, the current controller 320, and the dq-to-abc transformers 350 and 360 are similar to those of the first embodiment and will not be described in detail repeatedly.(Processing of Detection Current Selector 285)As described above, the detection current selector 285 sequentially selects any one of the first DC bus current IdcA and the second DC bus current IdcB at a predetermined timing. In addition, the detection current selector 285 sets any one of the first DC bus current IdcA and the second DC bus current IdcB as the DC bus current Idc for a single channel.Here, the timing for switching the selection between the first DC bus current Idc The second DC bus current IdcB set to a predetermined time interval. Preferably, the timing for switching the selection is set to a time period in which all upper arms of each phase of the inverters are turned on and all lower arms of each phase are turned off, or a time period in which all lower arms of each phase are turned on and all upper arms of each phase are turned off.(Processing of Three-Phase AC Calculator 300)FIG. 15 is a diagram illustrating a processing sequence of the three-phase AC calculator 300 according to the second embodiment. As described above, the three-phase AC calculator 300 calculates the three-phase AC currents iu, iv, and iw for a single channel on the basis of any one of the first DC bus current IdcA and the second DC bus current IdcB.In FIG. 15, similarly to FIG. 2, the indices corresponding to the maximum phase, the intermediate phase, and the minimum phase are denoted by "x, y, and z".In step j- 1, the three-phase AC calculator 300 determines whether or not the detection current selector 285 selects the first DC bus current IdcA.When the detection current selector 285 selects the first DC bus current IdcA, by processing of steps j-2 to j-12, the first three-phase AC currents iuA, ivA, and iwA are set as the three-phase AC currents iu, iv, and iw for a single channel. Processing for this case is substantially similar to the processing sequence described above in connection with FIG. 2 in the first embodiment, and will not be described in detail repeatedly. However, the formulas (1), (2) and (3) are replaced with the formulas (18), (19) and (20). [Formula 18] [Formula 19] [Formula 20]Meanwhile, when the detection current selector 285 selects the second DC bus current IdcA in step j- 1, the second three-phase AC currents iuB, ivB, and iwB are set as the three-phase AC currents iu, iv, and iw for a single channel by the processing of steps j- 13 to j- 22. The processing in this case is also similar to the processing sequence described above in connection with FIG. 2 in the first embodiment, and will not be described in detail repeatedly. However, the formulas (1), (2) and (3) are replaced with the formulas (21), (19) and (22). [Formula 21] [Formula 22]By calculating the three-phase alternating currents in this manner, it is possible to calculate the three-phase alternating currents iuA, ivA, and iwA flowing to the first three-phase coil when the detection current selector 285 selects the first direct current bus current IdcA. In addition, when the detection current selector 285 selects the second DC bus current IdcB, it is possible to calculate the three-phase AC currents iuB, ivB, and iwB flowing to the second three-phase coil.A relationship between the PWM signals of the upper arm of each phase, which are generated by comparison between the three-phase AC command and the carrier, the three-phase AC current and the DC bus current is similar to that of FIG. 3 and will not be described repeatedly. In addition, the current paths of the three-phase alternating current and the direct current bus current corresponding to the switching mode of the inverter are similar to those of FIG. 4 and will not be described repeatedly.(Processing of Abnormality Detector 295)FIG. 16 is a diagram illustrating a processing sequence for determining whether an abnormality (such as a ground fault or overcurrent) exists in the channel based on the DC bus current and the three-phase AC current using the abnormality detector 295.The abnormality detector 295 determines whether or not the detection current selector 285 selects the first DC bus current IdcA in step k- 1.When the detection current selector 285 selects the first DC bus current IdcA in step k-1, it is determined in step k-2 whether the first X-phase AC voltage command vxA* (first maximum-phase voltage command) is lower than the triangular wave carrier carrier. When vxA* is lower than the carrier, the process proceeds to step k-3. When vxA* is not lower than the carrier, the process proceeds to step k-7.In step k-3, it is determined whether or not the second time counter value Tcnt2 is larger than a predetermined threshold value Tth2. If Tcnt2 is not larger than Tth2, Tcnt2 is incremented in step k-14, and then step k-3 is repeated. When Tcnt2 is larger than Tth2, the detected first DC bus current IdcA is substituted at step k-4 in formula (23) to calculate the first ground current igA. The expression of the first ground current igA in the formula (23) will be described below with reference to FIG. 17. [Formula 23]Then, in step k-5, it is determined whether or not the first ground current igA is larger than a predetermined threshold value Igth. When the first ground current igA is larger than Igth, the first ground fault determination flag FaultA 1 is set to ON (occurrence of a ground fault) in step k- 6, and the process proceeds to step k- 7. If igA is not greater than Igth, the process proceeds to step k-7 without executing step k-6.Meanwhile, when the detection current selector 285 does not select the first DC bus current IdcA in step k-1, steps k-15 to k-19 are processed instead of steps k-2 to k-6, so that it is determined whether or not a ground fault occurs in the inverter of the second channel. Here, the second ground current igB is calculated based on formula (24). [Formula 24]In step k-7, the second time counter value Tcnt2 is reset to zero.Subsequently, the abnormality detector 295 determines whether or not an overcurrent occurs in steps k- 8 to k- 13.In step k- 8, it is determined whether an amount |iu| of the U-phase alternating current iu calculated by the three-phase alternating current calculator 300 is larger than a predetermined threshold value Ith. When |iu| is not greater than the predetermined threshold Ith, it is determined in step k-12 whether the magnitude |iv| of the V-phase alternating current iv is greater than the predetermined threshold Ith. When |iv| is not greater than the predetermined threshold Ith, it is determined in step k- 13 whether the magnitude | iw| of the W-phase alternating current iw is greater than the predetermined threshold Ith.When it is determined in steps k-8, k-12, and k-13 that an amount of |iu|, |iv|, and |iw| is greater than the predetermined threshold Ith, it is determined in step k-9 whether or not the detection current selector 285 selects the first DC bus current IdcA. When the detection current selector 285 selects the first DC bus current IdcA, the first overcurrent determination flag ErrorA 2 is set to ON (occurrence of an overcurrent) in step k- 10. When the detection current selector 285 does not select the first DC bus current IdcA, the second overcurrent determination flag ErrorB 2 is set to ON (occurrence of an overcurrent) in step k- 11.By determining an abnormality (such as a ground fault or an overcurrent) in this manner, it is possible to specify whether or not an abnormality occurs in the channel including the first inverter 20 and the first three-phase coil or whether or not an abnormality occurs in the channel including the second inverter 120 and the second three-phase coil.Alternatively, although the abnormality detector 295 according to the second embodiment is configured to determine the occurrence of a ground fault and an overcurrent, the occurrence of either a ground fault or an overcurrent may be determined.FIG. 17 is a diagram illustrating a relationship between the first DC bus current Idc The first ground current ig Detected by setting all upper arms of each phase to OFF and setting all lower arms of each phase to ON when a ground fault occurs between the W phase and the ground in the channel including the first inverter 20 and the first three-phase coil.FIG. 17( a) illustrates a mode in which the first ground current igA flows from the W phase to the ground side. FIG. 17( b) illustrates a mode in which the first ground current igA flows from the ground to the W-phase side. When no ground fault occurs as described in connection with FIG. 4( d), no current flows to the shunt resistor 90, but when a ground fault occurs, a ground current igA flows to the shunt resistor 90 and a shunt resistor 98 as shown in FIG. 17. Therefore, the first DC bus current IdcA detected when all upper arms of each phase are set to OFF and all lower arms of each phase are set to OFF is the first ground current igA, and the relationship expressed in the above-described formula (23) is established.A ground fault occurring in the channel including the second inverter 120 and the second three-phase coil is similar to that occurring in the channel including the first inverter 20 and the first three-phase coil as described above, and will not be described repeatedly.(Processing of Voltage Command Predictor 340)FIG. 18 is a diagram illustrating a processing sequence for calculating the first dq-axis voltage commands vdA* and vqA* and the second dq-axis voltage commands vdB* and vqB* using the voltage command predictor 340 according to the second embodiment.The voltage command predictor 340 acquires the dq-axis voltage commands vd* and vq* for a single channel calculated by the current controller 320 in step I- 1. In addition, in step I-2, it is determined whether or not the detection current selector 285 selects the first DC bus current IdcA.When it is determined in step I- 2 that the detection current selector 285 selects the first DC bus current IdcA, the dq-axis voltage commands vd* and vq* for a single channel acquired in step I- 1 are set as the first dq-axis voltage commands vdA* and vqA* in step I- 3 based on formula (25). [Formula 25]Then, in step I- 4, the first dq-axis voltage commands vdA* and vqA* and the previous values vdAold* and vqAold* of the first dq-axis voltage command set in step I- 6 described below are substituted into formula (14) to calculate the first dq-axis voltage command differences ΔvdA* and Δ vqA*. In addition, in step I- 5, the first dq-axis voltage command differences ΔvdA* and ΔvqA* and the previous values vdBo* and vqBo* of the second dq-axis voltage command set in step I- 6 described below are substituted into formula (15) to generate the second dq-axis voltage commands vdB* and vqB*.In step I- 6, the voltage command predictor 340 sets the first dq-axis voltage commands vdA* and vqA* calculated in step I- 3 and the second dq-axis voltage commands vqA* and vqB* calculated in step I- 5 in formula (16) to set previous values vdAold* and vqAold* of the first dq-axis voltage command and previous values vdBo* and vqBo* of the second dq-axis voltage command.On the other hand, when it is determined in step I- 2 that the detection current selector 285 does not select the first DC bus current IdcA, the dq-axis voltage commands vd* and vq* for a single channel acquired in step I- 1 are set as the second dq-axis voltage commands vdB* and vqB* in step I- 7 on the basis of formula (26). [Formula 26]Then, in step I- 8, the dq-axis second voltage commands vdB* and vqB* and the previous values vdBo* and vqBo* of the dq-axis second voltage command set in step I- 6 are substituted into formula (27) to calculate the dq-axis second voltage command differences ΔvdB* and Δ vqB*. [Formula 27]In step I- 9, the second dq-axis voltage command differences ΔvdB* and Δ vqB* and the previous values vdAold* and vqAold* of the first dq-axis voltage command set in step I- 6 are substituted into formula (28) to generate the first dq-axis voltage commands vdA* and vqA*. [Formula 28]In step I- 6, the voltage command predictor 340 sets the dq-axis second voltage commands vdB* and vqB* calculated in step I- 7 and the dq-axis first voltage commands vdA* and vqA* generated in step I- 9 in formula (16) to set the previous values vdAold* and vqAold* of the first dq-axis voltage command and the previous values vdBo* and vqBo* of the second dq-axis voltage command.By generating the first dq-axis voltage commands vdA* and vqA* and the second dq-axis voltage commands vdB* and vqB* in this way, it is possible to remarkably reduce processing loads for a current detection process, a three-phase AC calculation process, an abc-to-dq transformation process, and a current control process, compared to a method of detecting the DC bus currents of all channels and generating the voltage commands of the inverters of all channels using current control such as proportional component control. That is, it is possible to reduce a computation amount for controlling the first inverter 20, the second inverter 120, and the motor 110.(Processing of PWM modulator 370)FIG. 19 is a diagram illustrating a processing sequence of the PWM modulator 370 according to the second embodiment.The PWM modulator 370 determines whether or not the first ground fault determination flag FaultA 1 generated by the abnormality detector 295 is set to ON (occurrence of a ground fault) in step m- 1. When the first ground fault determination flag FaultA 1 is not set to ON (occurrence of a ground fault), it is determined in step m- 3 whether the first overcurrent determination flag FaultA 2 generated by the abnormality detector 295 is set to ON (occurrence of an overcurrent).When the first ground fault determination flag FaultA 1 is set to ON (occurrence of ground fault) in step m- 1 or when the first overcurrent determination flag FaultA 2 is set to ON (occurrence of overcurrent) in step m- 3, the PWM modulator 370 sets all of the first PWM signals SupA, SunA, SvpA, SvnA, SwpA, and SwnA to OFF in step m- 2.When the first overcurrent determination flag ErrorA 2 is not set to ON (occurrence of an overcurrent) in step m- 3, the PWM modulator 370 processes steps f- 1 to f- 16 of FIG. 10 in step m- 4.By generating the first PWM signals SupA, SunA, SvpA, SvnA, SwpA, and SwnA in this manner, it is possible to stop switching of the switching elements of the upper and lower arms of each phase of the first inverter 20 (maintain the OFF states) when the first ground fault determination flag FaultA 1 is set to ON or the first overcurrent determination flag FaultA 2 is set to ON. When both the first ground fault determination flag FaultA 1 and the first overcurrent determination flag FaultA 2 are set to OFF, an average value of the PWM voltage of the UVW phase output from the first inverter 20 may be set to the first three-phase AC voltage commands vuA*, vvA*, and vwA*.(Processing of PWM modulator 380 of the second embodiment)FIG. 20 is a diagram illustrating a processing sequence of the PWM modulator 380 according to the second embodiment. The processing sequence of FIG. 20 is substantially similar to the processing sequence of FIG. 19, and will not be described in detail repeatedly.Similarly to the PWM modulator 370, the PWM modulator 380 according to the second embodiment may stop switching (maintaining the OFF states) of switching the switching elements of the upper and lower arms of each phase of the second inverter 120 (maintaining the OFF states) when the second ground fault determination flag FaultB 1 is set to ON or the second overcurrent determination flag FaultB 2 is set to ON. When both the second ground fault determination flag FaultB 1 and the second overcurrent determination flag FaultB 2 are set to OFF, an average value of the PWM voltage of the UVW phase output from the second inverter 120 may be set to the second three-phase AC voltage commands vuB*, vvB*, and vwB*.This application claims priority right based on Japanese Patent Application No. 2016-000328, filed in the Japan Patent Office on Jan. 5, 2016, the entire contents of which are incorporated herein by reference.List of reference characters10 Battery 20 First inverter 30 to 80 Switching element of the first inverter 90, 95 Shunt resistor 98 Ground fault resistor 100, 105 Amplifier 110 Motor 120 Second inverter 130 to 180 Switching element of the second inverter 190 Angle detector for detecting the magnetic pole position of the rotor of the motor 200 Motor output shaft 210 Transmission 220 Rod 230 Torque sensor 240 Steering 250 Hand steering gear 260 Tie rod 270 Vehicle wheel 280 Controller 285 Detection current selector 290 Carrier generator 295 Abnormality detector 300 Three-phase AC calculator 310 abc-to-dq transformer 320 Current controller 330 Current command generator 340 Voltage command predictor 350, 360 dq-to-abc transformer 370, 380 PWM modulator 390 Gate drive circuit of the first inverter 400 Gate drive circuit of the second inverter

Claims

An inverter control apparatus comprising: at least a first and a second inverter (20, 120); a current detector that detects a current flowing through a main circuit of the first inverter (20); a current controller (320) that generates a voltage command value of the first inverter (20) based on a detected current and a current command; and a voltage command predictor (340) that generates a voltage command value of the second inverter (120) based on a variation of the voltage command value of the first inverter (20), wherein the current detector sequentially switchingly detects a current flowing through the main circuit of the first inverter (20) and a current flowing through the main circuit of the second inverter (120), the current controller (320) generates the voltage command value of the first inverter (20) based on the detected current and a predetermined current command during a current detection period of the first inverter (20), and the voltage command predictor (340) generates the voltage command value of the second inverter (120) during the current detection period of the first inverter (20) by adding a variation of the voltage command value of the first inverter (20) to the previous voltage command value of the second inverter (120).The inverter control apparatus according to claim 1, wherein the current controller (320) generates a voltage command value of the second inverter (120) based on the detected current and a predetermined current command during a current detection period of the second inverter (120), and the voltage command predictor (340) generates the voltage command value of the first inverter (20) during the current detection period of the second inverter (120) by adding a variation of the voltage command value of the second inverter (120) to the previous voltage command value of the first inverter (20).The inverter control apparatus according to any one of claims 1 to 2, wherein the current detector detects a DC bus current flowing to a DC bus of the first inverter (20).The inverter control apparatus according to any one of claims 1 to 2, wherein the current detector detects a current flowing between a lower or upper arm of each phase of the first inverter (20) and a DC bus.The inverter control apparatus according to any one of claims 1 to 2, wherein the current detector detects a current flowing to a three-phase AC output line of the first inverter (20).The inverter control apparatus according to any one of claims 1 to 5, further comprising an abnormality detector (295) that detects an abnormality in the first inverter (20) based on a current detected by the current detector.The inverter control apparatus according to claim 6, wherein the abnormality detector (295) stops (turns off) switching of all upper and lower arms of each phase of the first inverter (20) in a case where a DC bus current of the first inverter (20) detected when all lower arms of each phase of the first inverter (20) are set to ON is larger than a predetermined threshold value.The inverter control device according to claim 6 or 7, wherein the abnormality detector (295) stops (turns off) switching of all upper and lower arms of each phase of the first inverter (20) in a case where a three-phase alternating current of the first inverter (20) is greater than a predetermined threshold value.A motor driving device, comprising: the inverter control device according to any one of claims 1 to 8; and a motor (110) including: a first coil connected to the first inverter (20); a second coil connected to the second inverter (120); a stator on which the first and second coils are wound.An electric power steering apparatus mounted with the motor drive apparatus according to claim 9.

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