Motor control device

Abstract

A motor control device for controlling a multi-phase motor (21) for an SBW control system is provided, which is capable of reducing heat generation in circuit elements by dissipating load energy according to an operating sequence of a motor control, whereby the number of elements is reduced. In the motor control device, a control circuit (40, 90) controls the electrical conduction of a control current to the respective windings (21a to 21c) of the respective phases.In the electrical line control performed during the actuation of the multiphase motor (21), (i) the control circuit (40, 90) continuously holds an electrically conductive switching element (31 to 33) in an electrical line path to the winding of an electrically conductive phase in an on state during an actuation current rise period; during an actuation current hold period, the control circuit (40, 90) alternately switches on the electrically conductive switching element (31 to 33) and a reverse-flux switching element (34 to 36) by means of a PWM control; and (iii) during an actuation current decay period, the control circuit (40, 90) holds the electrically conductive switching element (31 to 33) and the reverse-flux switching element (34 to 36) in an off state.

Description

The present invention relates to a motor control device. A shift-by-wire (SBW) system is a method of controlling a vehicle's transmission mechanism via a motor control device. In an SBW system, a switched reluctance motor (SRM), typically a three-phase motor, is controlled by a motor control circuit within a motor control unit. The motor's rotation is transmitted via gears to a shaft, which in turn drives a shift-by-wire mechanism at a specific angle. This allows for the switching of gear positions, such as Park (P), Reverse (R), Neutral (N), and Drive (D). In such a control system, the motor control device, for example, holds a switching element, located in an electrical conductor path to a coil or winding of an electrically conductive phase (which is to be made electrically conductive), in an on state at the point of increase of the control current, in order to shorten the rise time of the control current. Since sufficient torque is readily ensured at the point of initiation of electrical conductivity, high-speed motor control is achieved. When the control current drops or decays, the switching element corresponding to the energized phase is held in an off state, and thus the current disappears quickly, and the torque becomes zero. In such a case, in a configuration where an H-bridge circuit is used as an electrical line circuit to the motor or electric motor, freewheeling diodes are used to reverse a motor control current. As a result, a forward voltage Vf is generated across the diode during electrical conduction to the motor coil or winding, even during a current reversal. This generates continuous heat in the diode, dependent on the time-integrated power, which is represented by "drive current x forward voltage". Therefore, it is necessary to use a diode with a high thermal resistance with respect to reverse current, leading to increased costs and size. On the other hand, there is a technique for controlling a potential difference generated in a reversing current path at the point of reversal during electrical conduction to the motor winding, reducing it to nearly zero using a switching element such as a MOS transistor. However, with this technique, the potential difference is controlled according to the magnitude of the drive current to dissipate energy stored in the motor winding. That is, control according to the operating sequence of the motor control circuit is not implemented. Furthermore, since the H-bridge circuit is used, the number of elements forming the circuit increases, leading to increased costs and size. The configuration and technique described above are described, for example, in JP 2012-125096A and JP 2000-358397A. JP 2017-200284A describes a switched reluctance motor with a three-phase half-bridge circuit as the motor control inverter and a control unit for controlling the inverter circuit. The inverter circuit comprises pairs of switching elements for each phase, each consisting of a series-connected upper and lower switching element. The control unit is configured to switch between a single-phase current control mode, in which current is intended to flow to each phase of the three-phase coil; a two-phase current control mode, in which the current is intended to flow on a two-phase basis; and a three-phase current control mode, in which current is intended to flow to all coils of the three phases simultaneously. In the single-phase current control mode, when the current is to be increased, the first switching element of the series circuit is switched on, and the corresponding reverse-flow switching element of the series circuit is switched off.Conversely, if the current is to be reduced, the reverse flow switching element is switched on, and the first switching element is switched off. JP 2019-33620A describes a motor control device in which a rotary angle calculation unit 51 calculates a motor rotation angle. A setpoint unit defines a motor angle setpoint for stopping the motor. A drive control unit controls the motor drive so that the motor angle corresponds to the motor angle setpoint. A voltage sensing unit detects a battery voltage, which serves as the input voltage for a motor driver. In a stop control operation to stop the motor, the drive control unit changes the number of phases of the coils that generate a braking current according to the battery voltage. JP 2013-150491A describes a control device for a switched reluctance motor, which is controlled by switching an electric current flowing through a winding of each phase of the reluctance motor using a semiconductor switch. The control device ensures that the semiconductor switch is in the on state when an electrical voltage is applied in the forward direction to a body diode of the semiconductor switch, thus allowing an electric current to flow through the body diode into the semiconductor switch. JP 2006-230074A describes a motor drive system consisting of a motor and a motor control circuit for driving the motor. The system includes a reverse current circuit, which comprises switching elements for distributing reverse currents between the motor control circuit and the motor coils, as well as diodes. When rotating flux currents are generated by the motor's excitation, the motor drive system allows the reverse current circuit to become conductive. Further state of the art is described in DE 100 13 151 A1, JP 2012 - 125 096 A and JP 2000 - 358 397 A. It is an object of the present invention to provide a motor control device for implementing SBW control that is capable of reducing heat generation in circuit elements by dissipating load energy according to an operating sequence of a motor control, while the number of elements is small or low. This object is achieved by a motor control device with the features of claim 1 and by a motor control device with the features of claim 5. The dependent claims are directed to advantageous embodiments of the invention. According to one aspect of the present invention, a motor control device is designed to control a multiphase motor having three or more phases for shift-by-wire control (electrical switching). The motor control device comprises: several electrically conductive switching elements arranged in electrical conduction paths to coils or windings of the respective phases of the multiphase motor; several reverse-flux switching elements arranged in reverse-flux paths of the coils or windings of the respective phases; several diodes connected in parallel to the reverse-flux switching elements; and a control circuit designed to perform electrical conduction control of a control current to the respective coils or windings. In the electrical conduction control of the control current to the respective coils or windings,During windings, which is carried out during the control of the multiphase motor, (i) the control circuit controls the corresponding electrically conductive switching element in the electrical conduction path to the coil or winding of an electrically conductive phase in such a way that it is continuously held in an on state; (ii) during a control current holding period, the control circuit controls the corresponding electrically conductive switching element and the corresponding reverse-flux switching element by means of PWM control in such a way that they are switched on alternately; and (iii) during a control current decay period, the control circuit controls both the corresponding electrically conductive switching element and the corresponding reverse-flux switching element in such a way that they are held in an off state. Before describing the operation, the energy dissipation of the reverse current, caused by the electrical connection to the coil or winding, is described. The time required for the energy dissipation of the reverse current is monitored by the potential difference induced in the reverse-current switching element or the diode in the reverse-current path. With the electrical connection to the coil or winding described above, it is not necessary to perform energy dissipation during the control current holding period. If the control current is reversed during the control current holding period, because the reversing current switching element is activated in the reversing current path, the potential difference becomes essentially zero. Therefore, heat generation by the switching element described above can be prevented. According to the configuration described above, the control circuit, in the electrical line control of the control current to the coils or windings of the respective phases, continuously keeps the electrically conductive switching element in the electrical line path in the on state during the control current rise period of the multi-phase motor. During the control current hold period, the control circuit alternately switches the electrically conductive switching element and the reverse-flux switching element on and off using PWM control. Consequently, heat generation in the reverse-flux switching element and the diode due to the reverse current can be reduced during the control current hold period. Furthermore, during the drive current decay period, the control circuit holds both the electrically conductive switching element and the reverse-flux switching element in the off state. As a result, the reverse current, caused by the interruption of the current flow to the coil or winding of the electrically conductive phase, can flow through the reverse-flux path via the diode instead of through the reverse-flux switching element during the drive current decay period. Consequently, energy dissipation is facilitated, and the current can be quickly reduced to zero. In the case where such a motor control device is used for SBW control, a small operating angle of the motor in a single actuation and the length of the interval for each actuation are operating characteristics. Therefore, in SBW control, the frequency of energy dissipation through the diode connected in parallel to the reverse-flux switching element in an actuation performed to move or change the switching position can be lower than in other motor products. Since the interval for each actuation is long, even if the switching element generates heat, the heat can be dissipated by the next actuation. The above and further problems, features, and advantages of the present invention will become clear with reference to the following detailed description and the accompanying drawings, in which identical parts are designated by the same reference numerals. The drawings show: Fig. 1 a diagram representing an electrical configuration of a motor control device or electric motor control device according to a first embodiment; Fig. 2 a diagram representing a schematic structure of an SBW system; Fig. 3 a timing diagram of a motor control unit according to the first embodiment; Fig. 4 a flow diagram of the motor control unit according to the first embodiment; Fig. 5 a flow diagram of a motor control unit according to a second embodiment; Fig. 6 a timing diagram of the motor control unit according to the second embodiment; Fig.Figure 7 shows a diagram illustrating an electrical configuration of a motor control device according to a third embodiment; Figure 8 shows a flowchart of a motor control unit according to the third embodiment; Figure 9 shows a diagram illustrating an electrical configuration of a motor control device according to a fourth embodiment; and Figure 10 shows a diagram illustrating an electrical configuration of a motor control device according to a fifth embodiment. First embodiment The first embodiment of the present invention is described below with reference to Figs. 1, 2, 3 to 4. As shown in Fig. 1, a motor control device 100 comprises a motor unit 20 and a motor control unit 30. The motor control device 100 receives electrical power from a drive power source, such as a vehicle battery 1. The motor control device 100 controls the operation of a three-phase motor (electric motor) 21 of the motor unit 20, thereby controlling the operation of an SBW system via a drive force transmission unit 2. A rotational force output by the three-phase motor 21 is transmitted to a switching range changer mechanism (hereinafter referred to simply as the changer mechanism) 4 via a shaft 3 as an output shaft and is transmitted to the drive force transmission unit 2. The motor unit 20 contains the three-phase motor 21, a coding sensor 22, and a speed reduction mechanism 23 consisting of gears. The rotational force from the three-phase motor 21 is transmitted to the shaft 3 via the speed reduction mechanism 23. The three-phase motor 21 is a switched reluctance motor (SRM) and has a rotor with a magnetic core having a predetermined number of salient pole sections. The three-phase motor 21 contains coils or windings 21a, 21b, and 21c of a stator corresponding to three phases: a U-phase, a V-phase, and a W-phase. The rotor is rotated by attractive forces caused by the application of DC currents to these windings 21a, 21b, and 21c. The first ends of windings 21a to 21c are connected together to a common connection point, and the common connection point is connected to a power supply line L1.The second ends of the windings 21a to 21c selectively conduct currents through the motor control unit 30. The coding sensor 22 detects the rotational position of the rotor of the three-phase motor 21. The motor control unit 30 receives a rotational position signal from the coding sensor 22. The rotational force of the shaft of the three-phase motor 21 is reduced by the speed reduction mechanism 23 and then transmitted to the shaft 3. The motor control unit 30 contains six n-channel MOS transistors 31 to 36 and a control circuit 40. The six MOS transistors 31 to 36 each have body diodes (hereinafter simply referred to as diodes) 31a to 36a. The six MOS transistors 31 to 36 include electrically conductive MOS transistors 31 to 33 and reverse-flux MOS transistors 34 to 36. The electrically conductive MOS transistors 31 to 33 are arranged corresponding to the three phases, i.e., the U-phase, the V-phase, and the W-phase, and serve as electrically conductive switching elements for conducting control currents as motor control currents to energize the windings 21a to 21c. The reverse-flow MOS transistors 34 to 36 are arranged in accordance with the three phases and serve as reverse-flow switching elements to reverse the drive current.The electrically conductive MOS transistors 31 to 33 are referred to simply as electrically conductive MOSs 31 to 33 in the following and are each labelled E-MOS in the drawings. The reverse-flux MOS transistors 34 to 36 are referred to simply as reverse-flux MOSs 34 to 36 in the following and are each labelled R-MOS in the drawings. The motor control unit 30 has terminals A and B, which are connected to the respective positive and negative terminals of the vehicle battery 1, and a DC voltage is applied to these terminals. Terminal A is connected to the power supply line L1, and terminal B is connected to a power supply line L2 via a current-sensing resistor 37. In a configuration where a relay or an upper ECU is connected to the vehicle battery 1, the positive and negative terminals of the vehicle battery 1 are connected via the relay or the upper ECU to terminal A and terminal B of the motor control unit 30. The electrically conductive MOS 31 and the reverse-flux MOS 34 are connected in series between the power supply lines L1 and L2. Similarly, the electrically conductive MOS 32 and the reverse-flux MOS 35 are connected in series between the power supply lines L1 and L2, and the electrically conductive MOS 33 and the reverse-flux MOS 36 are connected in series between the power supply lines L1 and L2. The electrically conductive MOS 31 to 33 are located on a low voltage side, and the reverse-flux MOS 34 to 36 are located on a high voltage side. The power supply line L1 is connected to the common terminal to which the first ends of windings 21a to 21c of the three-phase motor 21 are connected.A common connection point between the reverse-flux MOS 34 and the electrically conductive MOS 31, a common connection point between the reverse-flux MOS 35 and the electrically conductive MOS 32 and a common connection point between the reverse-flux MOS 36 and the electrically conductive MOS 33 are accordingly connected to the second ends of the windings 21a to 21c. The control circuit 40 comprises a computing circuit 41 and a drive circuit 42. Specifically, the control circuit 40 is provided by a microcomputer. The drive circuit 42 applies gate drive signals to the gates of the MOS transistors 31 to 36. The computing circuit 41 controls the electrically conductive MOS transistors 31 to 33 and the reverse-flux MOS transistors 34 to 36 via the drive circuit 42. The computing circuit 41 uses a terminal voltage of the current sensing resistor 37 to detect a motor drive current Im. Fig. 2 shows a schematic structure of the switching range change mechanism 4 of the SBW system and a drive force transmission unit 2 of a parking lock, which are controlled by the motor control device 100. The control of the motor 20 is controlled by the motor control unit 30, and the motor 20 serves as a drive source for the switching mechanism 4. The changeover mechanism 4 includes a locking plate 5, which is fixed to the shaft 3, a locking spring 6, and similar components. The changeover mechanism 4 transmits the rotational driving force of the shaft 3, which is output by the speed reduction mechanism 23, to a manual valve 7 and a parking lock element 8 of the drive force transmission unit 2. The locking plate 5 has a pin 5a that projects along the shaft 3 and engages in a groove at the top of the manual valve 7. When the locking plate 5 is driven to rotate by the motor 20, the pin 5a is rotated, and the manual valve 7 is moved back and forth in its axial direction by a drive force transmitted via a section of the manual valve 7 that engages the pin 5a. The manual valve 7 is arranged in a valve body 9. As the manual valve 7 moves back and forth in the axial direction, the switching range or switching position range is changed. The locking plate 5 has four recesses 5b on an outer circumference that contact the locking spring 6 to hold the manual valve 7 in respective positions corresponding to the switching ranges. The rotational position of the locking plate 5 is held by the force of the locking spring 6 in the position of any one of the recesses 5b. The recesses 5b correspond, from the near end of the locking spring 6, to the switching ranges of D (Drive / Drive / D position), N (Neutral), R (Reverse), and P (Park). The position at which the locking plate 5 is rotated furthest in the positive direction is the D position, and the position at which the locking plate 5 is rotated furthest in the negative direction is the P range. The parking locking element 8 comprises a parking rod 10, a cone 11, a parking pawl 12, a shaft section 13, and a parking gear 14. The parking rod 10 moves the cone 11 in the direction of arrow P when the locking plate 5 pivots in the negative direction of rotation, which is opposite to the positive direction of rotation. As a result, the parking pawl 12 is pushed upwards in the direction of arrow L, and the projection 12a and the parking gear 14 engage, thereby locking the parking gear 14. The following describes the operation of the configuration described above with reference to Fig. 3 and Fig. 4. The three-phase motor 21 of the present embodiment generates a magnetic force when the windings 21a, 21b, and 21c of the U, V, and W phases successively and selectively conduct motor control currents according to a predetermined conduction pattern. As a result, the projections of the magnetic body forming the rotor are successively magnetically attracted and rotated, thereby generating a rotational torque. This means that for each of the windings 21a to 21c of the respective phases, the motor control current Im is increased to a target current value Ia, set to a predetermined level, during a current rise period Tr. During a current hold period Tk following the current rise period Tr, the motor control current Im is controlled to maintain the target current value Ia. During a current decay period Td following the current hold period Tk, the motor control current Im drops to zero. In this case, the electrical conduction to the respective windings 21a to 21c of the three-phase motor 21 is controlled by the control circuit 40 by activating and controlling the electrically conductive MOSFETs 31 to 33 and the reverse-flux MOSFETs 34 to 36, which are arranged corresponding to the three phases. In the following, the winding 21a of the U-phase, the winding 21b of the V-phase and the winding 21c of the W-phase are also referred to as U-phase winding 21a, V-phase winding 21b and W-phase winding 21c.Furthermore, the phase to whose winding the motor control current is supplied is also referred to as an electrically conductive phase or energized phase. Fig. 3 shows an electrical conduction pattern for the U-phase winding 21a, the V-phase winding 21b, and the W-phase winding 21c. Here, the electrical conduction pattern of the U-phase winding 21a is described as an example. The control circuit 40 controls the drive of the electrically conducting MOS 31, which is arranged in an electrical conduction path, and the reverse-flux MOS 34 such that the motor drive current Im is directed to the U-phase winding 21a. In Fig. 3, Vg1 represents a gate voltage applied to the electrically conducting MOS, and Vg2 represents a gate voltage applied to the reverse-flux MOS. Initially, during the current rise period Tr, the control circuit 40 holds the reverse-flux MOS 34 in an off state and controls the electrically conductive MOS 31, so that it is switched on at time t0. The control circuit 40 then holds the electrically conductive MOS 31 in an on state during the current rise period Tr. When the electrically conductive MOS 31 is switched on, the voltage from the vehicle battery 1 is applied to the winding 21a via the electrically conductive MOS 31. As a result, the motor control current Im is induced, which flows in the winding 21a, and the value of the motor control current Im continues to rise during the current rise period Tr. When the current value, which is detected via the current sensing resistor 37, reaches a target current value Ia at time t1, the control circuit 40 ends the current rise period Tr and transitions to the current holding period Tk. During the current holding period Tk, the control circuit 40 controls the electrically conductive MOS 31 and the reverse-flux MOS 34 via PWM control to alternately switch them on at times t1, t2, t3, etc., in order to maintain the motor control current Im at the set current value Ia. That is, during the current holding period Tk, the electrically conductive MOS 31 and the reverse-flux MOS 34 are controlled in such a way that they exhibit on and off patterns with opposite phases. Thus, the electrically conductive MOS 31 and the reverse-flux MOS 34 are switched on alternately. The control circuit 40 then switches off the electrically conductive MOS 31 and the reverse-flux MOS 34 at time t4, when the detection signal from the coding sensor 22 changes, thus terminating electrical conduction to the U-phase winding 21a. In this case, the energy stored in the coil 21a is dissipated by flowing through a reverse-flux path formed via the body diode 34a of the reverse-flux MOS 34, and becomes zero at time t5. Vemb in Fig. 3 represents the potential difference in the reverse current path of winding 21a during the current holding period Tk and the current decay period Td according to the present embodiment, and Vcmp represents the potential difference of a comparative example. Since the reverse current MOS 34 is switched on during the current holding period Tk in the present embodiment, no potential difference occurs during the current holding period Tk, as shown in Fig. 3. On the other hand, in a conventional method, as shown in the comparative example in Fig. 3, a reverse current path is formed via the body diode. Therefore, a potential difference corresponding to the forward voltage Vf of the diode occurs during the current holding period Tk. This means that during the current holding period Tk of the present embodiment, there is no need to dissipate the energy via the body diode 34a of the reverse-flux MOSFET 34. The control circuit 40 switches on the reverse-flux MOSFET 34 to reverse the motor control current Im of the winding 21a, and thus the potential difference in the reverse-flux path can become almost zero. Fig. 4 shows a sequence of motor control by the control circuit 40. The control circuit 40 initiates the motor control in response to a switching range change request from a higher-level ECU or similar. Initially, in step S100, the control circuit 40 starts current monitoring. In this case, the control circuit 40 monitors the motor control current Im based on the terminal voltage of the current sensing resistor 37. When any of the electrically conductive MOSs 31 to 33 is switched on, the motor control current Im is directed to the corresponding winding 21a to 21c of the corresponding phase and flows through the current sensing resistor 37. Thus, the computing circuit 41 reads the voltage across the current sensing resistor 37 to detect the motor control current Im. Then, in step S110, the control circuit 40 switches on, for example, the electrically conductive MOS 31 from among the electrically conductive MOSs 31 to 33 to effect electrical conduction to the U-phase winding 21a, and maintains the electrically conductive MOS 31 in the on-state. In this case, electrical conduction can be initiated for a single phase or for multiple phases. Then, in the subsequent step S120, the control circuit 40 maintains the on-state of the electrically conductive MOS 31 until the motor control current Im flowing in the U-phase winding 21a reaches a predetermined setpoint Ia. When the motor control current Im reaches the predetermined setpoint Ia, the control circuit 40 proceeds to step S130. In step S130, the control circuit 40 alternately switches on the electrically conductive MOS 31 of the U-phase and the reverse-flux MOS 34 of the U-phase via PWM control to maintain the motor control current Im, which flows in the U-phase winding 21a, at a constant level. The control circuit 40 then repeatedly executes steps S130 and S140. When the motor 20 rotates and the output of the coding sensor 22 changes, the control circuit 40 proceeds to step S150. In step S150, the control circuit 40 determines whether the motor rotation quantity Mr has reached a setpoint Mtg, that is, whether the reversing mechanism 4 has rotated to the position of the setpoint angle. If it is determined that the motor rotation quantity Mr has not reached the setpoint Mtg, that is, if the motor rotation quantity Mr is insufficient, the control circuit 40 proceeds to step S160. In step S160, the control circuit 40 holds the electrically conducting MOS 31 and the reverse-flux MOS 34 of the U-phase in the off state to initiate a decrease or decay of the motor control current Im. Afterward, the control circuit 40 returns to step S110. When the control circuit 40 returns to step S110, it performs the electrical conduction control described above for one of the windings 21a to 21c of the next phase to be electrically conducted, while overlapping with the decay period Td of the motor control current Im of the current phase. Note that the phase for holding the electrically conducting MOS and the reverse-flux MOS in the off state in step S160 does not need to be present for all electrically conducting phases. In step S110, the next electrical conduction step can be performed after the decay period Td of the motor control current Im has ended. The control circuit 40 then repeats steps S110 to S160 until the motor rotation quantity Mr reaches the setpoint Mtg. When the motor rotation quantity Mr reaches the setpoint Mtg in step S150, the control circuit 40 proceeds to step S170. In step S170, the control circuit 40 controls the electrically conductive MOSs 31 to 33 and the reverse-flux MOSs 34 to 36 of all phases such that they are kept in the off state. Consequently, when the control of the motor 20 is stopped, the switching range change is terminated. In the embodiment described here, during the current holding period Tk, the control circuit 40 switches off the electrically conductive MOS corresponding to the electrically conductive phase and switches on the reverse-flux MOS corresponding to the electrically conductive phase during the electrical conduction to the windings 21a to 21c. Since the diodes 34a to 36a are not used to reverse the current in the reverse-flux path, heat generation can be prevented in this configuration during the current holding period Tk. During the current decay period Td, the control circuit 40 switches off the electrically conducting MOS and the reverse-flux MOS of the electrically conducting phase. Since the diodes 34a to 36a are used to reverse the current in the reverse-flux path, the current can return to zero within a short time by dissipating the energy. In the present embodiment, the control circuit for conducting electrical current to the three-phase motor 21 is formed by the three electrically conductive MOSs 31 to 33 and the three reverse-flux MOSs 34 to 36. Therefore, the number of switching elements can be halved compared to a configuration in which an H-bridge circuit is arranged at the terminals of the respective windings of the three phases. In the embodiment described above, the control circuit 40 is provided, for example, by a microcomputer. However, the control circuit 40 is not limited to the example described above, but can also be provided by an IC containing logic circuits, or a combination of the microcomputer and the IC. Second embodiment A second embodiment is described below with reference to Figures 5 and 6. The configurations that differ from the first embodiment are mainly described below. In the present embodiment, the electrical configuration is similar to that of the first embodiment. However, the control at the point of stopping the electrical conduction to the windings 21a to 21c differs in part from the control carried out in the motor control circuit of the first embodiment. As shown in Fig. 5, the control circuit 40 of the present embodiment performs steps S100 to S160 in a similar manner to the first embodiment. However, the control circuit 40 performs a different control action at the time the motor control is stopped than in the first embodiment, as shown in step S170a. When, in step S150, the control circuit 40 determines that the motor rotation quantity Mr has reached the setpoint Mtg, the control circuit 40, in the next step S170a, switches the electrically conductive MOS of the electrically conductive phase to the off state and the reverse-flux MOS of the electrically conductive phase to the on state. As a result, a braking action is applied to the rotor of the three-phase motor 21 to stop the motor control, and the switching range change is completed. Fig. 6 is a timing diagram that schematically shows a sequence of control operation by the control circuit 40 for the three-phase windings 21a to 21c of the three-phase motor 21. In this control system, at time t10, which is the start of electrical conduction to the three-phase motor 21, the control circuit 40 simultaneously conducts electrical current to two windings, for example, to the U-phase winding 21a and the V-phase winding 21b. In this case, the electrical conduction of each phase is carried out in a similar manner to the first embodiment. At time t11, the control circuit 40 stops the electrical conduction to the U-phase winding 21a and starts the electrical conduction to the W-phase winding 21c. At time t12, the motor control current Imw of the W-phase winding 21c reaches the target current value Ia. In this case, the control circuit 40 switches the electrically conductive MOS 31 and the reverse-flux MOS 34 for the U-phase winding 21a to the off state as described above. Therefore, the motor control current Imu of winding 21a is caused to flow through diode 34a as a reverse current. As a result, a potential difference Vf is generated across diode 34a in the reverse-flux path, and the motor control current Imu is diverted as a reverse current, so that it is essentially zero at time t12. The control circuit 40 then switches the electrically conductive MOSs 32 and 33 and the reverse-flux MOSs 35 and 36 off in order to stop electrical conduction to the V-phase winding 21b and the W-phase winding 21c as electrically conductive phases at time t13. Thus, the currents Imv and Imw of windings 21b and 21c are reversed so that they flow through the respective diodes 35a and 36a. At time t13, the control circuit 40 also starts electrical conduction to the U-phase winding 21a. As a result, a potential difference Vf occurs in the two reverse flux paths due to the diodes 35a and 36a, and thus the reverse currents Imv and Imw are diverted so that at time t14 they are essentially zero while electrical conduction to the U-phase winding 21a is carried out. Thus, when the rotational speed of the rotor of the three-phase motor 21 reaches the setpoint through electrical conduction to the three-phase windings 21a to 21c in the manner described above, the control circuit 40 stops the electrical conduction to the W-phase winding 21c, the electrically conductive phase, at time t21. At this time, the control circuit 40 switches off the electrically conductive MOS 33 and switches on the reverse-flux MOS 36 to maintain the motor control current Imw after time t22. Time t22 is the time at which the current Imw of winding 21c becomes zero when the reverse-flux MOS 36 is switched off, as shown by a dashed line in Fig. 6. Since, in the present embodiment, the reverse-flux MOS 36 is held in the on-state at time t21, the current Imw becomes essentially zero at time t23, which is after time t22, as shown by a thick solid line in Fig. 6. Thus, the time for dissipating energy to exert a braking effect is extended. As a result, the rotor of the three-phase motor 21 is stopped at a predetermined position. To stop the rotor even more reliably, it is also possible in this case to conduct electrical current to another phase to produce a torque in the direction opposite to the motor's direction of rotation. In the second embodiment described above, similar effects to those in the first embodiment can be achieved by implementing the motor control in a similar manner. Since the reverse-flow MOSFET is switched on when the rotor control is stopped because the three-phase motor 21 has reached the predetermined rotational speed, a braking effect is exerted, and the rotor can be stopped quickly. Third embodiment A third embodiment is described below with reference to Figures 7 and 8. The main focus here is on the configurations that differ from the first embodiment. The present embodiment features a configuration that implements a control mechanism to prevent overheating when the reverse current is caused to flow through diodes 34a to 36a of the reverse-flux MOSFETs 34 to 36. This means that in the motor control unit 50, temperature sensing elements 51 to 53 are arranged for detecting temperatures near the reverse-flux MOSFETs 34 to 36. The temperature sensing elements 51 to 53 use, for example, thermistors or similar devices. The computing circuit 41 of the control circuit 40 receives temperature sensing signals from the temperature sensing elements 51 to 53. Since the reverse-flux MOSFETs 34 to 36 have diodes 34a to 36, the temperatures of the reverse-flux MOSFETs 34 to 36 and the diodes 34a to 36a can be detected by the temperature sensing elements 51 to 53. The control circuit 40 changes the motor control pattern according to the temperatures of the reverse-flux MOSFETs 34 to 36, which are detected by the temperature sensing elements 51 to 53. Fig. 8 shows the sequence of the motor control. When the motor control is started, the control circuit 40 begins monitoring the motor control current Im and the temperature T in step S100a. When monitoring the motor control current Im, the control circuit 40 uses the terminal voltage of the current sensing resistor 37 to detect the motor control current Im. When monitoring the temperature T, the control circuit 40 uses the detection signals from the temperature sensing elements 51 to 53 to detect the respective temperatures T of the reverse-flux MOSFETs 34 to 36. The control circuit 40 performs similar processing in steps S110 to S150 and S170 as in the first embodiment. If, in step S150, it is determined that the motor rotation quantity Mr has not yet reached the setpoint Mtg, the control circuit 40 proceeds to step S180. In step S180, the control circuit 40 determines whether the detected temperature of the temperature sensing element 51 to 53, corresponding to the electrically conductive phase, is equal to or greater than a predetermined temperature. In other words, in step S180, it is determined whether the heating value Q of the temperature sensing element corresponding to the electrically conductive phase is equal to or greater than a predetermined value Qpred. If the result of the determination in step S180 is "no," that is, if, for example, the electrically conductive phase is the U-phase and the temperatures of the reverse-flux MOS 34 and the diode 34a, which are detected by the temperature sensing element 51, have not increased to or above the predetermined temperature, the control circuit 40 performs the processing in step S160 similarly to the first embodiment. Therefore, the control circuit 40 switches off the electrically conductive MOS 31 and the reverse-flux MOS 34, which correspond to the electrically conductive phase. This causes the reverse current of winding 21a of the U-phase, as the electrically conductive phase, to flow through the diode 34a and be discharged as described above. In this way, the reverse current drops. If, on the other hand, the result of the determination in step S180 is yes, that is, if, for example, the U-phase is the electrically conductive phase and the temperature of the reverse-flux MOS 34, which is detected by the temperature sensing element 51 of the U-phase, has reached or exceeds the predetermined temperature, the control circuit 40 proceeds to step S190. In step S190, the control circuit 40 switches off the electrically conductive MOS 31, which corresponds to the electrically conductive phase, and switches on the reverse-flux MOS 34, which corresponds to the electrically conductive phase. As a result, the reverse current of winding 21a of the U-phase, the electrically conductive phase, flows through the reverse-flux MOSFET 34 instead of through diode 34a. Even though the drive current decay period is extended in this case, the voltage across the reverse-flux MOSFET 34 is essentially zero. Thus, heat generation is reduced compared to the configuration where the reverse current flows through diode 34a. The control circuit 40 then returns to step S110 and proceeds to the electrical conduction step for the next phase. As the next electrical conduction step, the control circuit 40 performs step S110 for one of the windings 21a to 21c of the phase to be conducted next and carries out the electrical conduction control described above. The control circuit 40 repeats steps S110 to S160 described above. When it is determined in step S150 that the motor rotation quantity Mr has reached the setpoint Mtg, the control circuit 40 proceeds to step S170 and holds the electrically conducting MOSs 32, 34, and 36 and the reverse-flux MOSs 31, 33, and 35 of all electrically conducting phases in the off state. Thus, when the control of the motor 20 is stopped, the switching range change is completed. In the third embodiment described above, the temperature sensing elements 51 to 53 are arranged corresponding to the respective adjacent reverse-flux MOSs 34 to 36. If the rotational speed of the three-phase motor 21 has not reached the setpoint and electrical conduction to the winding of the electrically conductive phase is stopped, the control circuit 40 switches off the electrically conductive MOS and switches on the reverse-flux MOS only if the detected temperature of the temperature sensing element corresponding to the electrically conductive phase is equal to or greater than the predetermined temperature. In this operation, which causes the reverse current to flow through diodes 34a to 36a, which are connected in parallel to the respective reverse-flux MOSFETs 34 to 36, in order to dissipate energy quickly, when an overheating condition is expected, the reverse current is also directed to flow through the reverse-flux MOSFETs 34 to 36. This reduces heat generation and protects the reverse-flux MOSFETs 34 to 36 from thermal destruction. Depending on the specifications, characteristics, and conditions of use of the three-phase motor 21, as well as the element characteristics of the reverse-flux MOSs 34 to 36, the present embodiment can be used. If the present embodiment is used appropriately depending on these conditions, the advantageous effects described above can be achieved. Note that the present embodiment can be used for the configuration of the second embodiment. Fourth embodiment A fourth embodiment is described below with reference to Fig. 9. The main focus here is on the configurations that differ from the first embodiment. In the present embodiment, a motor control unit 60 has current sensing resistors 61 to 63 instead of the current sensing resistor 37. This means that in the present embodiment, the current sensing resistors 61 to 63 are arranged between the electrically conductive MOSs 31 to 33 and the power supply line L2, corresponding to the U, V, and W phases, in contrast to the first embodiment, where the current sensing resistor 37 is arranged to detect the motor control current Im jointly, independently of the electrically conductive phase. The detected voltages of the current sensing resistors 61 to 63 are provided to the computing circuit 41. Therefore, similar effects to those in the first embodiment can be achieved in the fourth embodiment. Furthermore, the motor control current Im can be measured independently for each electrically conductive phase. Fifth embodiment A fifth embodiment is described below with reference to Fig. 10. The following mainly describes the configurations that differ from the first embodiment. In the present embodiment, a motor control unit 70 of a motor control device 101 has twelve MOS transistors 71 to 82. The MOS transistors 71 to 82 each have body diodes 71a to 82a. The MOS transistors 72, 74, 76, 78, 80, and 82 serve as the electrically conductive MOS transistors, and the MOS transistors 71, 73, 75, 77, 79, and 81 serve as the reverse-flux MOS transistors. The unit of MOS transistors 71 to 74, the unit of MOS transistors 75 to 78, and the unit of MOS transistors 79 to 82 are each configured as an H-bridge circuit and are arranged corresponding to the windings 21a to 21c of the respective phases of the three-phase motor 21. The control circuit 90 contains a computing circuit 91 and a drive circuit 92 and controls the MOS transistors 71 to 82 in a similar manner to the control circuit 40 described above. The detection signal from the current detection resistor 37 is provided to the computing circuit 91. Here, a configuration similar to that of the conventional system is used. The control circuit 90 performs the motor control in a similar manner to the first embodiment. In this case, the control circuit 90 performs the electrical conduction to the windings 21a to 21c of the respective phases as follows. Regarding the electrical conduction of the U-phase winding 21a during the current rise period Tr, the control circuit 90, for example, switches on the reverse-flux MOS 71 and the electrically conductive MOS 74, which form the H-bridge circuit, to conduct the motor control current to the U-phase winding 21a. Since in this case the SRM is operated independently of the current direction to the winding 21a, the control circuit 90 can achieve the electrical conduction by switching on the reverse-flux MOS 73 and the electrically conductive MOS 72. Subsequently, during the current-hold period Tk, the electrically conductive period during which the switch-on control is alternately performed by the PWM control, the control circuit 90 alternately and repeatedly performs the operation to switch on the reverse-flow MOSFET 71 and the electrically conductive MOSFET 74, and the operation to switch on the reverse-flow MOSFETs 71 and 73 while the electrically conductive MOSFET 74 is off, in order to establish the reverse-flow path for the reverse current. The reverse-flow path can be established by switching on the electrically conductive MOSFETs 72 and 74 while the reverse-flow MOSFET 71 is off. During the current decay period Td, the control circuit 90 switches off the reverse-flux MOS 71 and the electrically conductive MOS 74, so that all MOSs 71 to 74 forming the H-bridge circuit are in the off state. In this case, the reverse current of the U-phase winding 71a flows through the diodes 72a and 73a. This creates a potential difference in the reverse-flux path, and the energy is dissipated. In the fifth embodiment described above, the state in which the reverse current flows in the reverse flow path, where the potential difference is essentially zero, and the state in which energy dissipation is caused by the reverse currents flowing through the diodes 72a and 73a in the reverse flow paths are also suitably and distinguishably achieved and used. Therefore, an operation can be realized that reduces or prevents heat generation by the reverse flow MOSs 71 and 73. Other embodiments The present invention is not limited to the embodiments described above, but can be modified in various ways within the scope of the invention. For example, the following modifications and extensions are possible. The multi-phase motor is not limited to the three-phase motor 21, but can be a multi-phase motor with four or more phases. The electrically conductive MOSs can be located on the high-voltage side, and the reverse-flux MOSs can be located on the low-voltage side. In this case, the first ends of windings 21a to 21c are connected to a common connection point, and this common connection point can be connected to ground. The electrically conductive switching element and the reverse-flux switching element are not limited to MOS transistors, but can be provided by any switching element such as IGBTs. The diodes forming the reverse flux paths are not limited to body diodes. External diodes can also be used. In this case, the diodes are connected at least in parallel with the reverse flux switching elements. In summary, a motor control device according to one embodiment is designed to control a multi-phase motor 21 having three or more phases for shift-by-wire control, wherein each phase contains a winding 21a to 21c.The motor control device includes: several electrically conductive switching elements 31, 32, 33, 72, 74, 76, 78, 80, 82, which are arranged in electrical conduction paths to the windings 21a to 21c of the respective phases of the multiphase motor 21; several reverse flux switching elements 34, 35, 36, 71, 73, 75, 77, 79, 81, which are arranged in reverse flux paths of the windings 21a to 21c; several diodes 34a, 35a, 36a, 71a, 73a, 75a, 77a, 79a, 81a, which are connected in parallel to the respective reverse-flux switching elements 34, 35, 36, 71, 73, 75, 77, 79, 81; and a control circuit 40, 90, which is designed to carry out an electrical line control for directing a control current as a motor control current to the respective windings 21a to 21c. In the electrical line control, which is carried out for the respective windings during the control of the multiphase motor 21, (i) the control circuit 40, 90 controls the corresponding electrically conductive switching element in the electrical line path to the winding of an electrically conductive phase in such a way that it is continuously held in an on state; (ii) in a control current holding period, the control circuit 40, 90 controls the corresponding electrically conductive switching element and the corresponding reverse-flux switching element in such a way that they are alternately switched on by a PWM control; and (iii) in a control current decay period, the control circuit 40, 90 controls the corresponding electrically conductive switching element and the corresponding reverse-flux switching element in such a way that they are held in the off state. According to one embodiment, the control circuit 40, 90 in the electrical line control, which is carried out at a time when the control of the multi-phase motor 21 stops, controls the reverse current switching element of the electrically conductive phase in the control current decay period in such a way that it is kept in the on state. According to one embodiment, the motor control device also includes a temperature sensing element 51, 52, 53, which is arranged to detect the temperature of a respective reverse flow switching element 34, 35, 36, 71, 73, 75, 77, 79, 81. If the temperature detected by the temperature sensing element 51, 52 and 53 is equal to or greater than a predetermined temperature, the control circuit 40 controls the corresponding reverse flow switching element during the control current decay period such that it is switched on or is already switched on. According to one embodiment, the multiphase motor 21 is a switched reluctance motor, and first ends of the windings 21a to 21c of all phases are connected together with a connection of a drive current supply or drive power supply 1. While only selected exemplary embodiments and examples have been chosen to illustrate the present invention, it is obvious to the person skilled in the art that various changes and modifications are possible without departing from the scope of the invention as specified in the related claims. Furthermore, the above description of the exemplary embodiments and examples of the present invention is merely illustrative and does not limit the invention as specified in the related claims.

Claims

Motor control device (100, 101) designed to control a multiphase motor (21) having three or more phases for shift-by-wire control, each phase containing a winding (21a to 21c), the motor control device (100, 101) comprising: several electrically conductive switching elements (31, 32, 33, 72, 74, 76, 78, 80, 82) arranged in electrical conduction paths to the windings (21a to 21c) of the respective phases of the multiphase motor (21); several reverse-flux switching elements (34, 35, 36, 71, 73, 75, 77, 79, 81) arranged in reverse-flux paths of the windings (21a to 21c); several diodes (34a, 35a, 36a, 71a, 73a, 75a, 77a, 79a, 81a), which are connected in parallel to the respective reverse flow switching elements (34, 35, 36, 71, 73, 75, 77, 79, 81);and a control circuit (40, 90) designed to perform electrical line control for directing a control current to the respective windings (21a to 21c), wherein in the electrical line control performed for the respective windings (21a to 21c) during control of the multiphase motor (21), the control circuit (40, 90): (i) during a control current rise period, controls the corresponding electrically conductive switching element (31, 32, 33, 72, 74, 76, 78, 80, 82) in the electrical line path to the winding (21a to 21c) of an electrically conductive phase such that it is continuously held in an on state; (ii) during a control current hold period, controls the corresponding electrically conductive switching element (31, 32, 33, 72, 74, 76, 78, 80, 82) and controls the corresponding reverse flow switching element (34, 35, 36, 71, 73, 75, 77, 79, 81) such that they are switched on alternately to each other by means of a PWM control;and (iii) during a control current decay period, controls the corresponding electrically conductive switching element (31, 32, 33, 72, 74, 76, 78, 80, 82) and the corresponding reverse-flux switching element (34, 35, 36, 71, 73, 75, 77, 79, 81) such that they are held in an off state, causing a reverse current to flow through the diode (34a, 35a, 36a, 71a, 73a, 75a, 77a, 79a, 81a) which is connected in parallel to the corresponding reverse-flux switching element (34, 35, 36, 71, 73, 75, 77, 79, 81). Motor control device (100, 101) according to claim 1, wherein in the electrical line control, which is carried out at a time of stopping the control of the multi-phase motor (21), the control circuit (40, 90) controls the reverse current switching element (34, 35, 36, 71, 73, 75, 77, 79, 81) of the electrically conductive phase in the control current decay period such that it is kept in the on state. Motor control device (100, 101) according to claim 1 or 2, further comprising: a temperature sensing element (51, 52, 53) arranged to detect the temperature of the respective reverse flow switching element (34, 35, 36, 71, 73, 75, 77, 79, 81), wherein, if the temperature detected by the temperature sensing element (51, 52, 53) is equal to or greater than a predetermined temperature, the control circuit (40) controls the corresponding reverse flow switching element (34, 35, 36, 71, 73, 75, 77, 79, 81) during the control current decay period such that it is switched on. Motor control device (100, 101) according to one of claims 1 to 3, wherein the multiphase motor (21) is a switched reluctance motor, and first ends of the windings (21a to 21c) of all phases are connected to a connection of a drive power supply (1). Motor control device (100, 101) designed to control a multiphase motor (21) having three or more phases for shift-by-wire control, each phase containing a winding (21a to 21c), the motor control device (100, 101) comprising: several electrically conductive switching elements (31, 32, 33, 72, 74, 76, 78, 80, 82) arranged in electrical conduction paths to the windings (21a to 21c) of the respective phases of the multiphase motor (21); several reverse-flux switching elements (34, 35, 36, 71, 73, 75, 77, 79, 81) arranged in reverse-flux paths of the windings (21a to 21c); several diodes (34a, 35a, 36a, 71a, 73a, 75a, 77a, 79a, 81a), which are connected in parallel to the respective reverse flow switching elements (34, 35, 36, 71, 73, 75, 77, 79, 81);and a control circuit (40) designed to perform electrical line control for directing a control current to the respective windings (21a to 21c), wherein in the electrical line control performed for the respective windings (21a to 21c) during control of the multiphase motor (21), the control circuit (40): (i) during a control current rise period, controls the corresponding electrically conductive switching element (31, 32, 33, 72, 74, 76, 78, 80, 82) in the electrical line path to the winding (21a to 21c) of an electrically conductive phase such that it is continuously held in an on state; (ii) during a control current hold period, controls the corresponding electrically conductive switching element (31, 32, 33, 72, 74, 76, 78, 80, 82) and the corresponding Reverse flow switching element (34, 35, 36, 71, 73, 75, 77, 79, 81) is controlled in such a way that they are switched on alternately to each other by a PWM control;and (iii) during a control current decay period, controls the corresponding electrically conductive switching element (31, 32, 33, 72, 74, 76, 78, 80, 82) and the corresponding reverse-flow switching element (34, 35, 36, 71, 73, 75, 77, 79, 81) such that they are held in an off state, the motor control device (100, 101) also has a temperature sensing element (51, 52, 53) arranged to detect a temperature of the respective reverse-flow switching element (34, 35, 36, 71, 73, 75, 77, 79, 81), and when the temperature detected by the temperature sensing element (51, 52, 53) is equal to or greater than a predetermined temperature, the control circuit (40) controls the corresponding reverse flow switching element (34, 35, 36, 71, 73, 75, 77, 79, 81) during the control current decay period such that it is switched on.;

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