JP2015033242A - Motor drive control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid formation of a closed circuit caused by ground fault and interphase short circuit.SOLUTION: A motor drive control device 38 includes a drive circuit 40 for driving a 3-phase brushless motor 32, semiconductor relays 48 interposed, one by one, among a neutral point 32n and coils 32u, 32v, 32w in respective phases of the brushless motor 32, and a control circuit 44 for controlling the drive circuit 40 and the semiconductor relay 48. The semiconductor relay 48 includes one switching parts 48us, 48vs, 48ws for switching operation respectively in its equivalent circuit, and diode parts 48ud, 48vd, 48wd which are connected in series so that two diodes have a forward direction in opposite directions in a bypass line which bypasses them. Since a current cannot pass through the diode parts 48ud, 48vd, 48wd, a closed circuit can be opened by turning off a part of the switching parts 48us, 48vs, 48ws according to a point where ground fault and interphase short circuit occur.

Description

  The present invention relates to a motor drive control device that drives and controls a motor.

  As a motor drive control device, a drive circuit for driving a brushless motor, a semiconductor relay interposed between a coil and a neutral point of each phase of the brushless motor, and a control circuit for controlling the drive circuit and the semiconductor relay are provided. Are known (for example, see Patent Document 1).

  Since such a semiconductor relay functions as a circuit breaker that interrupts the formation of an unintended closed circuit due to a ground fault or a short circuit between phases in a current-carrying line between a coil of each phase and a drive circuit, the brushless motor is, for example, an electric power When used as an assist motor in a steering device, even if a ground fault or a short circuit between phases occurs, the closed circuit formed due to these is opened to allow the steering force assist to be continued.

  Here, when the semiconductor relay has a parasitic diode that is inevitably formed due to its structure, a current flows in the forward direction of the parasitic diode even when the switching unit that performs the switching operation of the semiconductor relay is turned off. Therefore, there is a case in which formation of a closed circuit cannot be avoided, and in Patent Document 1, in each phase, two semiconductor relays are connected in series so that the forward directions of the parasitic diodes are opposite to each other. What is inserted between the neutral point is disclosed.

JP 2007-295658 A

  However, when the number of semiconductor relays interposed in each phase is two, the impedance of each phase is doubled and the motor efficiency is reduced, and the product cost of the motor is affected by the increase in the number of parts. There is a fear.

  In view of the above-described conventional problems, the present invention has an object to provide a motor drive control device that avoids the formation of a closed circuit due to a ground fault or a short circuit between phases without increasing the number of semiconductor relays. To do.

  For this reason, the motor drive control device according to the present invention is inserted one by one between a drive circuit for driving a motor having an N phase (N ≧ 2), a coil of each phase of the motor, and a neutral point. It is assumed that the semiconductor switching element includes a drive circuit and a control circuit that controls the semiconductor switching element. In such a motor drive control device, one of the semiconductor switching elements inserted between at least the (N-1) phase coil and the neutral point of the N phase performs a switching operation in its equivalent circuit. A switching unit; and a diode unit in which at least two diodes are connected in series so that the forward direction is reversed in a bypass line that bypasses the switching unit.

  According to the motor drive control device of the present invention, it is possible to avoid the formation of a closed circuit due to the occurrence of a ground fault or a short circuit between phases without increasing the number of semiconductor relays.

It is a schematic diagram showing an example of an electric power steering system. It is explanatory drawing which shows 1st Embodiment of a motor drive control apparatus. It is structural sectional drawing which shows an example of a semiconductor relay. It is a flowchart which shows a motor failure diagnosis process. It is explanatory drawing explaining generation | occurrence | production of the closed circuit by a ground fault. It is explanatory drawing explaining generation | occurrence | production of the closed circuit by a short circuit between phases. It is explanatory drawing which shows the brushless motor which inserted one semiconductor relay which has a diode part with a single forward direction. It is explanatory drawing which shows the brushless motor which inserted two semiconductor relays which have a single diode part in the forward direction. It is explanatory drawing which shows 2nd Embodiment of a motor drive control apparatus. It is a flowchart which shows the failure diagnosis process of a semiconductor relay. It is explanatory drawing which shows the combination of a semiconductor relay.

Hereinafter, a first embodiment for carrying out the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an example of an electric power steering system.

  The electric power steering system 10 includes a steering wheel 12 to which a steering operation by a driver is input, a steering shaft 14 connected to the steering wheel 12, and an intermediate connected to the steering shaft 14 via a first universal joint 16. The shaft 18, the pinion shaft 22 connected to the intermediate shaft 18 via the second universal joint 20, the pinion gear 24 that rotates integrally with the pinion shaft 22, and the pinion gear 24 that meshes with the pinion gear 24. A rack gear 26 that converts to linear motion and a tie rod 30 that transmits the motion of the rack gear 26 to the steering wheel 28 are provided.

  The electric power steering system 10 also steers by decelerating the output of the brushless motor 32 as an assist motor, which is a power source of the steering assist force, and the output of the brushless motor 32 in order to assist the steering force by the driver's steering operation. A reduction gear 34 that transmits to the shaft 14, a torque sensor 36 that detects a steering torque generated by a driver's steering operation, and a motor drive control device (inverter device) 38 that drives and controls the brushless motor 32 are provided.

  The torque sensor 36 detects the torque transmitted from the steering wheel 12 to the pinion gear 24 via the steering shaft 14 when the operator rotates the steering wheel 12, and outputs a torque signal corresponding to the torque. Output. For example, the torque sensor 36 detects a twisting amount of the steering shaft 14 by attaching a strain gauge to the steering shaft 14, or inserts a twisting spring mechanism such as a torsion bar in the middle of the steering shaft 14. Is detected, and torque is calculated based on the amount of twist.

  The speed reducer 34 is, for example, a speed reduction mechanism including a worm gear in which a screw gear (worm) and a helical gear (worm wheel) fixed concentrically to the steering shaft 14 are combined, or a speed reduction mechanism including a planetary gear. When the worm gear is used for the speed reducer 34, the output shaft 32a of the brushless motor 32 is concentrically connected to the worm so that the output of the brushless motor 32 is transmitted through the worm wheel meshing with the worm to the steering shaft. 14 is transmitted.

FIG. 2 shows an example of the internal configuration of the brushless motor 32 and the motor drive control device 38.
The brushless motor 32 is a three-phase DC synchronous motor, and includes U-phase, V-phase, and W-phase three-phase coils 32u, 32v, and 32w in a cylindrical stator (stator) (not shown). One ends of the phase coils 32u, 32v, 32w are connected to each other to form a star connection. Further, a rotor (permanent magnet rotor) (not shown) is rotatably provided in a space formed in the central portion of the stator, and the output shaft 32a of the brushless motor 32 described above is outward, that is, a reduction gear at the rotation center of the rotor. It is extended toward 34.

  The motor drive control device 38 includes a drive circuit (inverter circuit) 40 that drives the brushless motor 32, magnetic pole position detection means 42 that detects the magnetic pole position of the rotor, and a controller (control circuit) 44 that controls the drive circuit 40. It is equipped with.

  The drive circuit 40 has a circuit in which switching elements 40 ua, 40 ub, 40 va, 40 vb, 40 wa, and 40 wb are connected in a three-phase bridge, and a voltage Vb is supplied to this circuit from a power supply circuit (not shown). That is, one end of the upper switching elements 40ua, 40va, 40wa is connected to the power supply circuit, the other end is connected to one end of the lower switching elements 40ub, 40vb, 40wb, and the other ends of the lower switching elements 40ub, 40vb, 40wb are Connected to ground.

  In the drive circuit 40, the switching elements 40ua, 40ub, 40va, 40vb, 40wa, 40wb can perform a switching operation such as an FET (Field Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), or a bipolar transistor, for example. It is composed of semiconductor elements and includes anti-parallel diodes 40 uda, 40 udb, 40 vda, 40 vdb, 40 wda, 40 wdb, respectively. The control terminals (gate terminals) of the switching elements 40ua, 40ub, 40va, 40vb, 40wa, 40wb are connected to the controller 44, and on / off of the switching elements 40ua, 40ub, 40va, 40vb, 40wa, 40wb will be described later. As described above, control is performed by PWM (Pulse Width Modulation) operation by the controller 44.

  In the drive circuit 40, shunt resistors 46u, 46v, 46w are interposed between the ground and the lower switching elements 40ub, 40vb, 40wb. Both ends of the shunt resistors 46u, 46v, 46w are connected to a current detection circuit (not shown) in the controller 44. In the current detection circuit, based on the voltages at the both ends of the shunt resistors 46u, 46v, 46w. A current flowing through the brushless motor 32 is detected.

  The magnetic pole position detecting means 42 can use various sensors regardless of contact type or non-contact type, such as a resolver, a Hall element, a Hall IC, a magnetoresistive element, and a rotary encoder. The magnetic pole position signal is output to the controller 44.

  The controller 44 has a microcomputer, and calculates the motor applied voltage based on the torque signal from the torque sensor 36, the current detection values in the shunt resistors 46u, 46v, 46w, and the magnetic pole position signal from the magnetic pole position detection means 42. A motor voltage command value for control is calculated, and a motor voltage command signal corresponding to the motor voltage command value is modulated with a PWM carrier wave (triangular wave). The controller 44 generates a gate drive signal to be input to the control terminals of the switching elements 40ua, 40ub, 40va, 40vb, 40wa, and 40wb based on the six PWM signals whose widths are modulated. The signals are output to the control terminals 40ua, 40ub, 40va, 40vb, 40wa, and 40wb, respectively.

  Here, the motor drive control device 38 is a semiconductor relay that opens an unintended closed circuit due to a ground fault or a short circuit between phases in a current-carrying line between the coils 32u, 32v, 32w of each phase of the brushless motor 32 and the drive circuit 40. 48u, 48v, and 48w are further provided, and the semiconductor relays 48u, 48v, and 48w are inserted one by one between the coils 32u, 32v, and 32w of each phase in the brushless motor 32 and the neutral point 32n. Controlled individually or simultaneously.

  Each of the semiconductor relays 48u, 48v, and 48w has, in its equivalent circuit, two switching diodes 48us, 48vs, and 48ws that perform switching operation and two diodes in a forward direction by a bypass line that bypasses the switching units 48us, 48vs, and 48ws, respectively. Are connected in series so as to be opposite to each other, and diode parts 48ud, 48vd, 48wd.

  The semiconductor relays 48u, 48v, and 48w include, for example, MOSFETs (Metal-Oxide-Semiconductor Field-) in which a Schottky barrier diode (hereinafter referred to as “SBD”) is built in addition to a parasitic diode that is inevitably formed due to its structure. It may be a semiconductor switching element such as an effect transistor. Such a semiconductor switching element is a well-known device disclosed in, for example, Japanese Patent Laid-Open Nos. 7-15099 and 2010-81536.

FIG. 3 is a structural cross-sectional view of an N-channel vertical MOSFET as an example of the semiconductor relays 48u, 48v, and 48w.
The N-channel vertical MOSFET applied to the semiconductor relays 48u, 48v, and 48w includes a drain region 100, a base region 102, a source region 104, a drain electrode 106 connected to the drain region 100, a source region 104, and a base region, respectively. 102, a source electrode 108 connected to the gate electrode 102, a gate insulating film 110 covering the surface of the base region 102 exposed between the drain region 100 and the source region 104, and a gate electrode 112 disposed on the gate insulating film 110. .

The drain region 100 is composed of a first drain region 100a and a second drain region 100b. On the N-type (N ⁺ ) silicon substrate constituting the first drain region 100a, the second drain region 100b is formed. As a result, an N ⁻ type epitaxial layer is formed.

The base region 102 is formed by diffusing a P-type layer on the surface side of the epitaxial layer in the drain region 100. Further, a high-concentration N-type (N ⁺ ) layer is double-diffused near the surface of the P-type layer. As a result, the source region 104 is formed.

The base region 102 is formed by a different diffusion process in the region below the bonding surface with the source electrode 108 (the region sandwiched between the source regions 104 and 104) and the other regions, and the impurity concentrations thereof are different. Yes. That is, in the base region 102, the region below the bonding surface with the source electrode 108 is formed with a low concentration of the P-type semiconductor, and the impurity concentration is formed lower than the other regions. Further, N-type impurities are further ion-implanted into the surface of the source region 104 which has become an N ⁺ concentration region by the diffusion process, so that the N-type impurity on the very surface of the source region 104 has a high concentration.

  The source electrode 108 is formed by depositing a metal such as aluminum on the exposed portion of the base region 102 and the source region 104 (the portion not covered with the gate insulating film 110) and the gate insulating film 110 covering the gate electrode 112. As formed, the source electrode 108 is metal-semiconductor bonded to the exposed portions of the base region 102 and the source region 104.

  Since the very surface of the source region 104 has a high concentration of N-type impurities, the junction between the source electrode 108 and the source region 104 is an ohmic junction, but the region below the junction surface in the base region 102 is a P-type junction. Since the impurity concentration is low, the junction at the junction surface between the source electrode 108 and the base region 102 is a Schottky junction that forms a Schottky barrier on the junction surface.

  Therefore, the semiconductor relays 48u, 48v, and 48w include a PN junction diode inevitably generated by a PN junction between the base region 102 and the second drain region 100b, that is, a parasitic diode 114, while the source electrode 108 and the base electrode 102 The SBD 116 is formed by Schottky bonding at the bonding surface.

  When a positive voltage is applied to the gate electrode 112, an inversion layer is formed on the surface of the base region 102 facing the gate electrode 112 to form an N-type channel, and this portion performs switching operations 48 us, 48 vs. , 48ws, the semiconductor relays 48u, 48v, and 48w are configured so that the forward direction of the parasitic diode 114 and the SBD 116 are reversed in a bypass line that bypasses the switching units 48us, 48vs, and 48ws in the equivalent circuit, respectively. Are provided with diode parts 48ud, 48vd, and 48wd connected in series.

  In the semiconductor relays 48u, 48v, and 48w, the parasitic diode 114 connected in parallel to the switching units 48us, 48vs, and 48ws and the voltage applied between the source electrode 108 and the drain electrode 106 in any direction and No current flows through the bypass line passing through the SBD 116, that is, the diode portions 48ud, 48vd, and 48wd.

  In this embodiment, the switching elements 40ua, 40ub, 40va, 40vb, 40wa, 40wb in the drive circuit 40 are the semiconductor relays 48u that open a closed circuit due to a ground fault and a short circuit between phases in terms of the characteristics of the built-in diode. It is different from 48v and 48w.

  The above-described N-channel vertical MOSFET shown in FIG. 3 is merely an example of the semiconductor relays 48u, 48v, and 48w, and the semiconductor relays 48u, 48v, and 48w include switching units 48us, 48vs, and 48ws in their equivalent circuits. Any type of semiconductor switching element may be used as long as the diode switching units 48ud, 48vd, and 48wd are formed by connecting two diodes in series so that the forward direction is opposite to the bypass line. Therefore, the semiconductor relays 48u, 48v, and 48 are not limited to a planar type, a vertical type structure, and an N type, as in the N-channel vertical type MOSFET described above, and a trench type, a horizontal type structure, a P type, or the like may be used as appropriate. You can choose.

  As described above, the diodes incorporated in the semiconductor relays 48u, 48v, and 48w include the SBD 116 by Schottky junction at the junction surface between the source electrode 108 and the base electrode 102, and the base region 102 and the second drain region 100b. If the N layer of the source region 108 can be deepened in addition to the parasitic diode 114 by the PN junction, a parasitic diode formed by the PN junction between the base region 102 and the source region 104 may be used.

  In short, each of the semiconductor relays 48u, 48v, and 48w includes, in its equivalent circuit, at least two diodes on one switching unit 48us, 48vs, and 48ws that perform switching operation and a bypass line that bypasses the switching unit 48us, 48vs, and 48ws. And diode portions 48ud, 48vd, and 48wd connected in series so that the forward direction is reverse.

  FIG. 4 shows the contents of the motor failure diagnosis process executed by the controller 44 before the drive control of the brushless motor 32 by the motor drive control device 38 is started when the ignition key is turned on. .

  In step 1001 (abbreviated as “S1001” in the figure. The same applies hereinafter), first, all of the semiconductor relays 48u, 48v, and 48w are turned ON, and the coils 32u, 32v, and 32w of each phase are placed between the neutral point 32n. Is made conductive.

  In step 1002, whether or not a ground fault or an interphase short-circuit has occurred in the drive circuit 40 of the brushless motor 32 or the motor drive control device 38 is diagnosed by a known diagnosis method including the identification of the abnormality type and the occurrence location. .

  When it is diagnosed that no ground fault or inter-phase short-circuit has occurred, the brushless motor 32 and the drive circuit 40 are in a normal state in which no closed circuit is formed. In order to perform drive control of the motor 32, the motor failure diagnosis process is terminated (Yes). That is, the controller 44 controls the drive circuit 40 while controlling the semiconductor relays 48u, 48v, and 48w so as to keep all the coils 32u, 32v, and 32w of each phase and the neutral point 32n in a conductive state. To start.

  On the other hand, if it is diagnosed that a ground fault or an inter-phase short-circuit has occurred, it is an abnormal state in which a closed circuit is formed in the brushless motor 32, the drive circuit 40, or the like. Go to 1003 (No).

In step 1003, an abnormality process is performed to open a closed circuit due to a ground fault or a short circuit between phases.
Specifically, some, but not all, of the coils 32u, 32v, 32w of each phase and the neutral point 32n are in a non-conductive state depending on the location where the ground fault or inter-phase short-circuit occurs. Thus, the semiconductor relays 48u, 48v, and 48w are controlled.

  For example, as shown in FIG. 5, when a ground fault occurs in which the energization line connecting the drive circuit 40 and the W-phase coil 32w is connected to the ground with a relatively low impedance, the upper switching element 40ua and the lower switching In the energization mode in which the element 40vb is turned on, the neutral point 32n → the semiconductor relay 48v → the V phase coil 32v → the switching element 40vb → the ground → the ground fault location → the W phase coil 32w → the semiconductor relay 48w → the neutral point 32n. Although a circuit (shaded thick line in the figure) is formed, it is closed by controlling to turn off the semiconductor relay 48w so that the W-phase coil 32w and the neutral point 32n are in a non-conductive state. The circuit can be opened.

  Further, for example, as shown in FIG. 6, when an energization line connecting the drive circuit 40 and the V-phase coil 32v and an energization line connecting the drive circuit 40 and the W-phase coil 32w cause a short circuit between phases. A closed circuit (shaded thick line in the figure) is formed as follows: neutral point 32n → semiconductor relay 48v → V phase coil 32v → phase short circuit location → W phase coil 32w → semiconductor relay 48w → neutral point 32n. Either one of the semiconductor relay 48v and the semiconductor relay 48w so that either the V-phase coil 32v and the neutral point 32n or the W-phase coil 32w and the neutral point 32n are in a non-conductive state. The closed circuit can be opened by performing control to turn off.

  When the semiconductor relay 48v and the semiconductor relay 48w have a diode part 48vd and a diode part 48wd whose forward direction is directed only in a single direction, for example, only to the neutral point 32n, as shown in FIG. When a ground fault as shown in FIG. 5 or a short circuit between phases as shown in FIG. 6 occurs, even if the switching part 48ws of the semiconductor relay 48w is turned off, a closed circuit is formed through the diode part 48wd and is not opened. There is also a possibility. However, all of the semiconductor relays 48u, 48v, and 48w in the present embodiment are diode sections 48ud, 48u, 48v, 48w, which are connected in series so that the forward direction is reversed in a bypass line that bypasses the switching units 48us, 48vs, 48ws. 48vd and 48wd are provided. For this reason, since current cannot pass through the diode portions 48ud, 48vd, and 48wd, if the switching portion 48ws of the semiconductor relay 48w is turned off, the W-phase coil 32w and the neutral point 32n are not electrically connected. Therefore, it is possible to reliably avoid the formation of a closed circuit.

  As described above, the semiconductor relays 48u, 48v, and 48w are controlled so that some but not all of the coils 32u, 32v, and 32w of each phase and the neutral point 32n are in a non-conductive state. Even if an abnormality such as a ground fault or a short circuit between phases occurs, the drive control of the brushless motor 32 is continued using the phase in which no abnormality has occurred, so that the assist of the steering force by the electric power steering system 10 is incomplete. However, there is a need to continue. Depending on the application of the brushless motor 32, it may be controlled to turn off all the semiconductor relays 48u, 48v, and 48w by giving priority to the stop of the brushless motor 32.

  According to the motor drive control device 38 as described above, the diode units 48ud, 48vd, and 48wd in which at least two diodes are connected in series so that the forward direction is reversed in the bypass line that bypasses the switching units 48us, 48vs, and 48ws. The semiconductor relays 48u, 48v, and 48w that are provided are inserted one by one between the coils 32u, 32v, and 32w of each phase in the brushless motor 32 and the neutral point 32n.

  Therefore, in order to surely avoid the formation of a closed circuit, as shown in FIG. 8, in each phase, between the coils 32u, 32v, 32w and the neutral point 32n, the semiconductor relay 200u and the semiconductor relay 200u ′ The semiconductor relay 200v and the semiconductor relay 200v ′, and the semiconductor relay 200w and the semiconductor relay 200w ′ are respectively inserted, and the two semiconductor relays in each phase are connected to the parasitic diode 200ud and the parasitic diode 200ud ′, the parasitic diode 200vd and the parasitic diode 200vd. ′ And the parasitic diode 200wd and the parasitic diode 200wd ′ need not be connected in series so that their forward directions are opposite to each other, and the number of semiconductor relays is not increased.

  Therefore, in order to surely avoid the formation of a closed circuit, the motor efficiency is not reduced due to the increase in impedance of each phase, and the increase in the number of parts and the increase in product cost can be suppressed.

Next, a second embodiment for carrying out the present invention will be described. In addition, about the same structure as 1st Embodiment, the description is abbreviate | omitted or simplified by attaching | subjecting the same code | symbol.
FIG. 9 shows an example of the internal configuration of the brushless motor 32 and the motor drive control device 38.

  Compared with the first embodiment, the motor drive control device 38 of the present embodiment further includes a voltage stabilization means 50 used for diagnosing whether or not the semiconductor relays 48u, 48v, 48w are out of order. It is different in point.

  The voltage stabilization means 50 includes a pull-up resistor 50a as a first voltage stabilization means and pull-down resistors 50b and 50c as second voltage stabilization means. The pull-up resistor 50a includes an energization line for the U-phase coil 32u and a power supply circuit (not shown) that supplies the voltage Vb among the three energization lines connecting the drive circuit 40 and the coils 32u, 32v, and 32w of each phase. The pull-down resistors 50b and 50c are connected between the energization line for the V-phase coil 32v and the ground, and between the energization line for the W-phase coil 32w and the ground, respectively. The pull-up resistor 50a is not limited to the connection between the energization line for the U-phase coil 32u and the power supply circuit that supplies the voltage Vb, and supplies the energization line and the voltage Vb for the V-phase coil 32v or the W-phase coil 32w. In this case, the pull-down resistors 50b and 50c are connected to energization lines other than the energization line to which the pull-up resistor 50a is connected.

  The controller 44 includes an energization line connecting the U-phase coil 32u and the drive circuit 40, an energization line connecting the V-phase coil 32v and the drive circuit 40, and an energization line connecting the W-phase coil 32w and the drive circuit 40. The terminal voltage of each phase of the brushless motor 32 can be detected by a voltage detection circuit (not shown) in the controller 44.

  FIG. 10 shows that the semiconductor relays 48u, 48v, and 48w executed by the controller 44 before the drive control of the brushless motor 32 by the motor drive control device 38 is started when the ignition key is turned ON. The fault diagnosis process is shown. It should be noted that the present failure diagnosis processing is performed by a motor in order to determine at an early stage whether or not the motor failure diagnosis processing in the first embodiment described above can be performed by diagnosing whether or not the semiconductor relays 48u, 48v, and 48w have failed. It may be executed before the failure diagnosis process.

In step 2001, all the switching elements 40ua, 40ub, 40va, 40vb, 40wa, 40wb of the drive circuit 40 are turned off.
As shown in FIG. 8, in each phase, between the semiconductor relay 200u and the semiconductor relay 200u ′, between the semiconductor relay 200v and the semiconductor relay 200v ′, and between the semiconductor relay 200w and the semiconductor relay 200w ′, respectively. When the built-in parasitic diodes are connected in series so that the forward directions of the parasitic diodes are opposite to each other and are inserted between the coils 32u, 32v, 32w and the neutral point 32n, the failure of the two semiconductor relays in each phase In order to diagnose the above, it is necessary to control the switching elements 40 ua, 40 ub, 40 va, 40 vb, 40 wa, 40 wb of the drive circuit 40 to switch the direction of the current flowing in each phase. However, since the motor drive control device 38 of the present embodiment can perform failure diagnosis of the semiconductor relays 48u, 48v, and 48w without using the drive circuit 40, as will be described later, the switching elements 40ua, 40 ub, 40 va, 40 vb, 40 wa, and 40 wb are all turned off (OFF).

In step 2002, the U-phase semiconductor relay 48u is turned on (ON), and the V-phase semiconductor relay 48v and the W-phase semiconductor relay 48w are turned off (OFF).
In step 2003, it is determined whether the terminal voltages of the V phase and the W phase are normal.

  When the semiconductor relays 48u, 48v, 48w are normal, the U-phase coil 32u and the neutral point 32n are in a conductive state, but between the V-phase coil 32v and the neutral point 32n, and W Since the phase coil 32w and the neutral point 32n are in a non-conducting state, the detected terminal voltages of the V phase and the W phase are 0 level. Therefore, it is determined whether or not the V-phase and W-phase terminal voltages are 0 level, and more specifically, whether or not the V-phase and W-phase terminal voltages are less than (0 + α). Here, α is slightly reduced by the pull-down resistors 50b and 50c on the energization line connecting the V-phase coil 32v and the drive circuit 40 or the energization line connecting the W-phase coil 32w and the drive circuit, for example. This is an error for avoiding a misdiagnosis that causes an increase in terminal voltage not related to the failure of the semiconductor relays 48u, 48v, 48w, such as the influence of superimposed noise, to be caused by the failure of the semiconductor relays 48u, 48v, 48w.

  If the V-phase and W-phase terminal voltages are less than (0 + α), it is recognized that the V-phase and W-phase semiconductor relays 48v and 48w have not caused a short-circuit failure, so that the U-phase semiconductor relay 48u continues to fail. In order to make a diagnosis, the process proceeds to step 2004 (Yes).

  When the terminal voltage of V phase or W phase is (0 + α) or more, it cannot be diagnosed whether or not a short circuit failure has occurred in the U-phase semiconductor relay 48u, but at least the terminal voltage is (0 + α). The V-phase or W-phase semiconductor relays 48v and 48w thus turned on are contrary to the control command of the controller 44 to turn off the switch operation, and it is recognized that a short-circuit failure has occurred. Proceeding to 2006 (No), the failure occurrence of the V-phase or W-phase semiconductor relays 48v and 48w is determined.

In step 2004, the U-phase semiconductor relay 48u is turned off (OFF), and the V-phase semiconductor relay 48v and the W-phase semiconductor relay 48w are turned on.
In step 2005, it is determined whether or not the terminal voltage of the U phase is normal.

  When the semiconductor relays 48u, 48v, and 48w are normal, the conduction between the V-phase coil 32v and the neutral point 32n and between the W-phase coil 32w and the neutral point 32n Since the coil 32u and the neutral point 32n are in a non-conducting state, the detected U-phase terminal voltage is at the Vb level. Therefore, it is determined whether or not the U-phase terminal voltage is at the Vb level, more specifically, whether or not the U-phase terminal voltage is equal to or higher than (Vb−β). Here, β is an error provided for the same reason as α described above.

  When the U-phase terminal voltage is (Vb−β) or higher, it is recognized that the U-phase semiconductor relay 48u does not cause a short-circuit failure, so that all the semiconductor relays 48u, 48v, and 48w do not cause a short-circuit failure. And the fault diagnosis is terminated (Yes).

  When the U-phase terminal voltage is less than (Vb−β), the U-phase semiconductor relay 48 u is turned on against the control command of the controller 44 to turn off the switch operation, and a short-circuit failure occurs. Therefore, the process proceeds to step 2007 (No), and the occurrence of a failure in the U-phase semiconductor relay 48u is determined.

  According to the motor drive control device 38 of the second embodiment, as described in the first embodiment, the semiconductor relays 48u, 48v, and 48w each including a diode whose forward direction is reverse are respectively provided. The phase coils 32u, 32v, 32w and the neutral point 32n are inserted one by one, and the pull-up resistors 50a and the pull-down resistors 50b, 50c are connected to the energization lines of the respective phases.

  Therefore, in the motor drive control device 38 of the second embodiment, as shown in FIG. 8, in each phase, between the semiconductor relay 200u and the semiconductor relay 200u ′, between the semiconductor relay 200v and the semiconductor relay 200v ′, The semiconductor relay 200w and the semiconductor relay 200w ′ are connected in series so that the forward directions of the built-in parasitic diodes are opposite to each other, and between the coils 32u, 32v, 32w and the neutral point 32n. In order to individually diagnose the failure of the two semiconductor relays of each phase, as in the case where each is inserted, the switching elements 40ua, 40ub, 40va, 40vb, 40wa, 40wb of the drive circuit 40 are controlled to each phase. There is no need to switch the direction of the flowing current.

Therefore, in the motor drive control device 38 of the present embodiment, failure diagnosis of the semiconductor relays 48u, 48v, 48w can be easily performed without using the drive circuit 40.
In the first embodiment and the second embodiment described above, the semiconductor relays 48u, 48v, and 48w are all equivalent circuits, and at least two diodes are connected in a forward direction by a bypass line that bypasses the switching units 48us, 48vs, and 48ws. The diode portions 48ud, 48vd, and 48wd were connected in series so as to be reversed. However, as shown in FIG. 11, for example, when the energization line passing from the drive circuit 40 through the V-phase coil 32v is insulated, the W-phase semiconductor relay 48w ′ is replaced with an equivalent circuit of the switching unit 48ws ′. A diode line 48 wd ′ having a single diode characteristic in the forward direction may be provided in a bypass line that bypasses.

  In the first and second embodiments described above, the motor drive control device 38 controls the drive of the three-phase brushless motor 32. However, the motor drive control device 38 can be applied to any brushless motor having an N phase (N ≧ 2). Applicable. In this case, in order to open the closed circuit by the semiconductor relay or to diagnose the failure of the semiconductor relay, the semiconductor relay inserted between at least the (N-1) phase coil of the N phase and the neutral point is In the equivalent circuit, it is necessary to include a diode portion in which at least two diodes are connected in series so that the forward direction is reversed in a bypass line that bypasses the switching portion.

  Furthermore, in the first embodiment and the second embodiment described above, the brushless motor 32 is not limited to one driven based on the magnetic pole position signal from the magnetic pole position detecting means, and operates by sensorless driving. Also good.

  The electric power steering system 10 according to the first to third embodiments described above is a column assist system in which the portion where the brushless motor 32 transmits the steering assist force is the steering shaft 14, but the portion which transmits the steering assist force is the steering shaft. It is not limited to 14, but may be a so-called pinion assist type or rack assist type electric power steering system.

  Further, as in the first to third embodiments described above, not only the electric power steering system 10 that directly assists the steering force by the rotation of the assist motor, but also assists the steering force by the hydraulic pressure generated by the power of the assist motor. A so-called electro-hydraulic power steering system may be used.

  As mentioned above, although the invention made | formed by this inventor was concretely demonstrated based on embodiment, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the summary. Needless to say.

DESCRIPTION OF SYMBOLS 10 ... Electric power steering system, 32 ... Brushless motor, 32n ... Neutral point, 32u ... U phase coil, 32v ... V phase coil, 32w ... W phase coil, 38 ... Motor drive control device, 40 ... Drive circuit, 40ua ... U-phase upper switching element, 40 ub ... U-phase lower switching element, 40 va ... V-phase upper switching element, 40 vb ... V-phase lower switching element, 40 wa ... W-phase upper switching element, 40 wb ... W-phase lower switching element, 44 ... Control, 48u ... U phase semiconductor relay, 48v ... V phase semiconductor relay, 48w, 48w '... W phase semiconductor relay, 48us ... U phase semiconductor relay switching unit, 48vs ... V phase semiconductor relay switching unit, 48ws, 48ws '... W-phase semiconductor relay switching part, 48 ud ... U-phase semiconductor relay Diode section, 48vd ... V-phase semiconductor relay switching section, 48wd, 48wd '... W-phase semiconductor relay diode section, 50 ... voltage stabilizing means, 50a ... pull-up resistor, 50b, 50c ... pull-down resistor, 114 ... parasitic diode 116: Schottky barrier diode (SBD)

Claims (3)

A drive circuit for driving a motor having an N phase (N ≧ 2);
A semiconductor switching element inserted one by one between a coil and a neutral point of each phase of the motor;
A control circuit for controlling the drive circuit and the semiconductor switching element;
A motor drive control device comprising:
The semiconductor switching element inserted between at least the (N-1) phase coil of the N phase and the neutral point includes one switching unit that performs a switching operation in the equivalent circuit, and the switching unit. And a diode section in which at least two diodes are connected in series so that the forward direction is opposite to the bypass line.   Of the energization lines connecting the drive circuit and the coils of the respective phases, a first voltage stabilizing means for connecting the energization lines for some phases and a power source is provided, and for other phases other than the some phases 2. The motor drive control device according to claim 1, further comprising second voltage stabilization means for connecting the energization line and the ground.   Voltage generated in a current-carrying line for the other phase when the semiconductor switching element of the part of the phase is turned on and the semiconductor switching element of the other phase is turned off while the operation of the driving circuit is stopped The motor drive control device according to claim 2, wherein a failure of the semiconductor switching element of the other phase is diagnosed based on the above.