JP2010074868A - Motor drive control circuit and electric power steering apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor drive control circuit, which is manufactured at low cost, and to provide an electric power steering apparatus. <P>SOLUTION: In this motor drive control circuit 40, a shunt resistor 45, which can detect a current accurately by switch elements UL, VL and WL, is connected beforehand between a motor drive circuit 43 and the negative electrode (GND) of a DC power supply 14. The detection results of AC currents Iu, Iv and Iw by each switch element UL, VL and WL are corrected by correction coefficients Ku, Kv and Kw that are generated from the detection results of the AC currents Iu, Iv and Iw by each switch element UL, VL and WL and the detection results of the AC current Is by the shunt resistor 45. Thereby, if the shunt resistor 45 is accurate, a plurality of phase current detecting elements, which are connected severally to a plurality of switch series circuits 43U, 43V and 43W, can be made inexpensive ones with low accuracy. Accordingly, the motor drive control circuit 40 can be manufactured at low cost. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a motor drive control circuit for driving and controlling a multiphase AC motor and an electric power steering apparatus having the motor drive control circuit.

A conventional motor drive control circuit of this type is provided with a bridge circuit for generating a multiphase AC current from a DC output of a DC power supply and energizing the multiphase AC motor. A plurality of switch series circuits connected in parallel between the electrodes. And in order to feedback-control a polyphase alternating current, the phase current detection element (for example, shunt resistance) was connected in series with each switch series circuit, and each phase current was detected (for example, refer to patent documents 1). ).
JP-A-6-98564 (paragraph [0013], FIG. 1)

  However, in the conventional motor drive control circuit described above, in order to accurately detect each phase current, the number of high-accuracy phase current detection elements is provided according to the phase, so that the motor drive control circuit becomes expensive. It was.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a motor drive control circuit and an electric power steering device that can be manufactured at low cost.

  The motor drive control circuit (40) according to the invention of claim 1 made to achieve the above object comprises a plurality of switch series circuits (43U, 43V,...) Connected in parallel between positive and negative electrodes of a DC power supply (14). 43W) is provided with a pair of switch elements (UH, UL, VH, VL, WH, WL) in series, and a pair of switch elements (UH, UL) in each switch series circuit (43U, 43V, 43W). , VH, VL, WH, WL), a plurality of branch circuits (42U, 42V, 42W) are connected to each phase winding (19U, 19V, 19W) of the multiphase AC motor (19). A plurality of bridge circuits (43) and a plurality of switch series circuits (43U, 43V, 43W) connected to the switch circuits (43U, 43V, 43W), respectively. By turning on and off the phase current detection elements (UH, UL, VH, VL, WH, WL) and the switch elements (UH, UL, VH, VL, WH, WL), the DC current from the DC power supply (14) A phase detection current (Iu, Iv, Iw) is generated and applied to the multiphase AC motor (19), and a current detection result detected by the phase current detection elements (UH, UL, VH, VL, WH, WL) In the motor drive control circuit (40) having a control circuit (44) that feedback-controls the multiphase AC currents (Iu, Iv, Iw), one of the positive and negative electrodes of the DC power supply (14) at one end Is connected to the other end, and a plurality of switch series circuits (43U, 43V, 43W) are commonly connected to the other end, and current can be detected accurately from the phase current detection elements (UH, UL, VH, VL, WH, WL). Correction current detection The control circuit (44) is provided with a child (45), and the control circuit (44) has a specific phase in which current flows only in one phase current detection element among the plurality of phase current detection elements (UH, UL, VH, VL, WH, WL). From the current detection result by the phase current detection element (UH, UL, VH, VL, WH, WL) and the current detection result by the correction current detection element (45) obtained in Step 1, each phase current detection element (UH, UL, Correction data (Ku, Kv, Kw) for correcting the current detection result of VH, VL, WH, WL) is generated, and the phase current in a phase other than the specific phase is generated using the correction data (Ku, Kv, Kw). It is characterized in that the current detection result by the detection elements (UH, UL, VH, VL, WH, WL) is corrected.

  In the present invention, “correcting the current detection result by the phase current detection element in a phase other than the specific phase using the correction data” means “current detection result by the phase current detection element in the specific phase using the correction data”. Is not excluded.

  According to a second aspect of the present invention, in the motor drive control circuit (40) according to the first aspect, the pair of switch elements (UH, UL, VH, VL, WH, WL) are MOSFETs, and each phase current is detected. The elements (UH, UL, VH, VL, WH, WL) are characterized in that they are shared by one switch element in the plurality of switch series circuits (43U, 43V, 43W).

  An electric power steering device (11) according to a third aspect of the invention includes the motor drive control circuit (40) according to the first or second aspect, and includes a multiphase AC motor (19) as a drive source. Has characteristics.

[Invention of Claim 1]
In the motor drive circuit of the present invention, a multiphase AC current flows through the phase windings of the plurality of switch series circuits and the multiphase AC motor in the bridge circuit by turning on and off the switch elements of the plurality of switch series circuits in the bridge circuit. Each phase current included in the multiphase AC current is detected by a plurality of phase current detection elements connected to a plurality of switch series circuits and subjected to feedback control. Further, in the present invention, for a plurality of phase current detection elements, one correction current detection element capable of detecting a current more accurately than the phase current detection elements is connected to a common connection portion of the plurality of switch series circuits in the bridge circuit. It is provided between the DC power supply. Here, in the specific phase in which the current flows only in one phase current detection element among the plurality of phase current detection elements, the current flowing in the one phase current detection element and the current flowing in the correction current detection element coincide with each other. To do. Thereby, the same current can be detected by the phase current detection element and the correction current detection element, respectively, and correction data for correcting the deviation can be generated. Since the phase current detection element having a specific phase is switched between the plurality of phase current detection elements, the correction data unique to each of the plurality of phase current detection elements can be generated by one correction current detection element. Since the correction data is used to correct the current detection result by the phase current detection element having a phase other than the specific phase, the detection accuracy of each phase current is improved, and stable feedback control can be performed.

  Thus, in the motor drive control circuit of the present invention, a correction current detection element capable of detecting current more accurately than the phase current detection element is provided between the DC power supply and the bridge circuit, and a plurality of phase current detections are provided. Since the current detection result by the element is configured to be corrected based on the current detection result of the one correction current detection element, if the current detection accuracy of the correction current detection element is high, a plurality of switches are connected in series. A plurality of phase current detection elements respectively connected to the circuit can be made inexpensive with low accuracy. In other words, the number of high-accuracy current detection elements that were conventionally required in accordance with the number of phases of the bridge circuit can be reduced to one regardless of the number of phases. It can be manufactured at low cost.

[Invention of claim 2]
According to the invention of claim 2, since the phase current detection element is also used as one switch element in the plurality of switch series circuits, the phase current detection element is compared with the case where the phase current detection element is connected to each switch direct circuit separately from the switch element. Thus, the cost can be further reduced and the motor drive control circuit can be reduced in size.

[Invention of claim 3]
According to the electric power steering apparatus of the third aspect, since the motor drive control circuit according to the first or second aspect is provided, the electric power steering apparatus can be manufactured at low cost.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. The vehicle 10 shown in FIG. 1 includes an electric power steering device 11, and the steering operation by the driver corresponds to a three-phase AC motor 19 (the “multi-phase AC motor” of the present invention. Hereinafter, simply “motor 19”. The steered wheels 12, 12 can be steered with assistance. Specifically, the inter-steering wheel shaft 16 is passed between the pair of steered wheels 12, 12, and the inter-steering wheel shaft 16 is inserted into the cylindrical housing 18. Both ends of the inter-steering wheel shaft 16 are connected to the steered wheels 12 and 12 via tie rods 17 and 17, and the cylindrical housing 18 is fixed to the main body of the vehicle 10. In addition, a large-diameter portion 18D is provided in an axial intermediate portion of the cylindrical housing 18, and a motor 19 is built in the large-diameter portion 18D. The motor 19 includes a stator 20 that is fitted and fixed to the inner surface of the cylindrical housing 18, and a cylindrical rotor 21 that is loosely fitted inside the stator 20. The inter-steering wheel shaft 16 passes through the inside of the rotor 21. In addition, a rotational position sensor 25 (for example, a resolver) for detecting the rotational position θ1 of the rotor 21 is provided at one end of the large-diameter portion 18D of the cylindrical housing 18.

  A ball screw nut 22 is assembled on the inner surface of the rotor 21. Further, a ball screw portion 23 is formed at an intermediate portion in the axial direction of the inter-steering wheel shaft 16. The ball screw mechanism 24 is constituted by the ball screw nut 22 and the ball screw portion 23, and when the ball screw nut 22 rotates together with the rotor 21, the ball screw portion 23 moves directly with respect to the cylindrical housing 18, whereby the steered wheels 12, 12 are moved. Steer.

  A rack 30 is formed on one end of the inter-steering wheel shaft 16, and a pinion 31 provided at the lower end of the steering shaft 32 is engaged with the rack 30. A steering wheel 33 is attached to the upper end portion of the steering shaft 32.

  A steering angle sensor 34 and a torque sensor 35 are attached to the steering shaft 32 to detect the steering angle θ2 of the steering 33 and the steering torque Tf applied to the steering shaft 32. A vehicle speed sensor 36 for detecting the vehicle speed V based on the rotation of the steered wheel 12 is provided in the vicinity of the steered wheel 12.

  The motor 19 is driven and controlled by a motor drive control circuit 40. As shown in FIG. 2, the motor drive control circuit 40 includes a motor drive circuit 43 (corresponding to the “bridge circuit” of the present invention) and a motor control circuit 44 (corresponding to the “control circuit” of the present invention). ing. The motor control circuit 44 includes a command value determination unit 41 and an inverter control unit 42.

  The DC power supply 14 is formed by connecting a booster circuit 39 to the battery 38, boosting the output voltage of the battery 38 by the booster circuit 39, and applying it to the motor drive circuit 43. The battery 38 receives power from an alternator (not shown) linked to the engine.

  The motor drive circuit 43 is a three-phase circuit in which U, V, and W-phase switch series circuits 43U, 43V, and 43W are connected in parallel between a positive electrode and a negative electrode (GND) of a booster circuit 39 that is connected to a battery 38. It is a bridge circuit. The U-phase switch series circuit 43U is provided with an upper switch element UH and a lower switch element UL connected in series, and the motor 19 is connected to a power supply line 42U branched from the middle of both the switch elements UH and UL. The U-phase winding 19U is connected. Similarly, the V-phase switch series circuit 43V is provided with an upper-side switch element VH and a lower-stage switch element VL, and a V-phase winding 19V of the motor 19 is connected to a feeding line 42V branched from the middle thereof. The W-phase switch series circuit 43W is provided with an upper-stage switch element WH and a lower-stage switch element WL, and a W-phase winding of the motor 19 is connected to a power supply line 42W branched from the middle of them. 19W is connected. Further, the switch element groups UH, UL, VH,... Are composed of, for example, N-channel MOSFETs, and the gates of these MOSFETs are connected to the motor control circuit 44 (inverter control unit 42). The feed lines 42U, 42V, and 42W correspond to “branch circuits” of the present invention.

  The command value determination unit 41 acquires each detection result (steering torque Tf, steering angle θ2 of the steering wheel 33, vehicle speed V) from the torque sensor 35, the steering angle sensor 34, and the vehicle speed sensor 36, and commands the motor drive current to the motor 19. The value Iq1 * is determined.

  The inverter control unit 42 acquires the command value Iq1 * of the motor drive current from the command value determination unit 41 and drives the switch elements UH, UL, VH,. For this purpose, the inverter control unit 42 generates the command values Vu1 *, Vv1 *, Vw1 * shown in FIG. 4A and the triangular wave K based on the command value Iq1 *. A method for generating the command values Vu1 *, Vv1 *, Vw1 * from the motor drive current command value Iq1 * is publicly known (for example, Japanese Patent Application Laid-Open No. 2006-340551), and detailed description thereof is omitted. The motor control circuit 44 performs so-called “triangular wave comparison method” PWM control based on the command values Vu1 *, Vv1 *, Vw1 * and the triangular wave K. As a result, as shown in the graph of FIG. 4B, for example, three-phase alternating currents Iu, Iv, and Iw indicated by sinusoidal waveforms that are 120 degrees out of phase with each other are fed via the feed lines 42U, 42V, and 42W. It is output from the motor drive circuit 43 to the motor 19.

  Here, in the graph of FIG. 4B, when the sine wave indicating the three-phase alternating currents Iu, Iv, Iw is “positive”, current flows from the motor drive circuit 43 to the motor 19 and “negative” In this phase, a current flows from the motor 19 to the motor drive circuit 43. For example, the U-phase current Iu flows from the motor drive circuit 43 to the motor 19 when the electrical angle θ1 is 0 <θ1 <60 [deg], 240 <θ1 <360 [deg], and 60 <θ1 <240. When [deg], the current flows from the motor 19 to the motor drive circuit 43. The V-phase current Iv flows from the motor drive circuit 43 to the motor 19 when 0 <θ1 <180 [deg], and from the motor 19 to the motor drive circuit 43 when 180 <θ1 <360 [deg]. It flows to. The W-phase current Iw flows from the motor drive circuit 43 to the motor 19 when the electrical angle θ1 is 120 <θ1 <300 [deg], and 0 <θ1 <120 [deg] and 300 <θ1 <360 [ deg] from the motor 19 to the motor drive circuit 43. In addition, the motor 19 of this embodiment is a Y connection (star connection).

  By the way, there are the following two patterns in the current conduction pattern between the motor drive circuit 43 and the motor 19. That is, the first energization pattern in which current flows from any one of the three phases U, V, and W to the other two phases (in this embodiment, the electrical angle θ1 is 60 <θ1 <120 [deg], 180 <θ1 <240 [deg], 300 <θ1 <360 [deg]), and a second energization pattern in which current flows from any two of the three phases to the other one (this embodiment) Then, the electrical angle θ1 is 0 <θ1 <60 [deg], 120 <θ1 <180 [deg], 240 <θ1 <300 [deg].

  FIG. 3A is an example of the first energization pattern, and the broken-line arrows in FIG. 3 indicate three-phase alternating currents Iu, Iv, when the electrical angle θ1 of the rotor 21 is 300 <θ1 <360 [deg]. The flow of Iw is shown. In this case, a current Iu flows into the U-phase winding 19U of the motor 19 from the upper stage side of the U-phase switch series circuit 43U via the feed line 42U, and the current Iu becomes a U-phase current. The current Iu is divided into the V and W phase windings 19V and 19W of the motor 19 and flows into the V phase current Iv and the W phase current Iw, respectively. The currents Iv and Iw flowing through the phase windings 19V and 19W flow into the V and W phase switch series circuits 43V and 43W through the feed lines 42V and 42W, flow through the lower switch elements VL and WL, and further merge. It flows to the negative electrode (GND) of the DC power supply 14.

  FIG. 3B shows an example of the second energization pattern. The broken line arrows in FIG. 3 indicate three-phase alternating currents Iu and Iv when the electrical angle θ1 of the rotor 21 is 0 <θ1 <60 [deg]. , Iw. In this case, currents Iu and Iv flow into the U and V phase windings 19U and 19V of the motor 19 from the upper side of the U-phase switch series circuit 43U and the V-phase switch series circuit 43V via the power supply lines 42U and 42V, respectively. It becomes U-phase current and V-phase current. Further, the currents Iu and Iv flowing through the phase windings 19U and 19V are merged and flow into the W-phase winding 19W to become a W-phase current. The current Iw flowing through the W-phase winding 19W flows into the W-phase switch series circuit 43W through the power supply line 42W, flows through the lower switch element WL, and further flows to the negative electrode (GND) of the DC power supply 14.

  The motor drive control circuit 40 performs feedback control on the three-phase alternating currents Iu, Iv, Iw output to the motor 19. Therefore, in the motor drive control circuit 40 of the present embodiment, as shown in FIG. 2, among the switch series circuits 43U, 43V, and 43W, the potential difference Vu between both ends of the lower-side switch elements UL, VL, and WL. Vv and Vw are input to the motor control circuit 44 (specifically, the inverter control unit 42) through amplifier circuits 44P, 44P and 44P provided in the motor drive circuit 43. The motor control circuit 44 calculates currents Iu, Iv, and Iw that actually flow through the switch series circuits 43U, 43V, and 43W from the potential differences Vu, Vv, and Vw and the on-resistance values Ron of the switch elements UL, VL, and WL. .

  Here, since each switch element UL, VL, WL, which is a MOSFET, generates heat due to a switching operation associated with PWM control, the on resistance value Ron varies. In addition, since the ON resistance value Ron varies among the same products, errors are likely to occur in the detection results of the currents Iu, Iv, and Iw by the switch elements UL, VL, and WL.

  Therefore, in this embodiment, in order to correct the detection results of the currents Iu, Iv, and Iw by the switch elements UL, VL, and WL, the current detection accuracy is between the motor drive circuit 43 and the negative electrode (GND) of the DC power supply 14. A high shunt resistor 45 (corresponding to the “correction current detecting element” of the present invention) is provided, and the potential difference Vs at both ends of the shunt resistor 45 is supplied to the motor control circuit 44 through the amplifier circuit 45P provided in the motor drive circuit 43. It has been input (see FIG. 2). The shunt resistor 45 has a temperature coefficient of resistance smaller than that of the switch elements UL, VL, and WL, and can accurately detect a current. Here, as shown in FIG. 3B, a current flows from any two phases (U, V phase) of the three phases U, V, W to the other one phase (W phase). In phase, the current (Iw) that flows through the lower one side switch element (WL) of the other one phase (W phase) matches the current Is that flows through the shunt resistor 45.

  This completes the description of the configuration of the present embodiment. Next, the effect of this embodiment is demonstrated. The inverter control unit 42 includes a CPU, a ROM, and a RAM (not shown), and the current detection program PG1 (see FIG. 5) stored in the ROM is executed by the CPU at a predetermined cycle, so that U, V, and W phase currents are obtained. Iu, Iv, and Iw are detected and corrected.

  When the current detection program PG1 is executed, first, the electrical angle θ1 of the rotor 21 is acquired from the rotational position sensor 25 provided in the motor 19 (S1).

  Next, it is determined whether or not the electrical angle θ1 is 0 <θ1 <60 [deg] (S2). That is, a current flows from the U and V phases toward the W phase (the state shown in FIG. 3B), and the current flows only to the switch element WL among the three switch elements UL, VL, and WL on the lower stage side. It is determined whether or not it is a “specific phase for the phase”.

  When the electrical angle θ1 is not 0 <θ1 <60 [deg] (NO in S2), the process proceeds to step S3. On the other hand, when the electrical angle θ1 is 0 <θ1 <60 [deg] (YES in S2), the potential difference Vw of the switch element WL is acquired, and the potential difference Vw and the known on-resistance value Ron of the switch element WL are acquired. The current Iw flowing through the W-phase switch series circuit 43W (switch element WL) is calculated from (for example, a catalog value) (S21).

  Next, the potential difference Vs of the shunt resistor 45 is acquired, and the current Is flowing through the shunt resistor 45 in the “specific phase for the W phase” is calculated from the potential difference Vs and the resistance value Rs of the shunt resistor 45 (S22). That is, in steps S21 and S22, the same current is detected by the switch element WL and the shunt resistor 45, respectively. Here, the detection result of the current Is by the shunt resistor 45 is more accurate than the detection result of the current Iw calculated from the potential difference Vw of the switch element WL and the on-resistance value Ron.

  Then, correction data for correcting the detection result of the current Iw by the switch element WL is generated from the detection results of the currents Iw and Is (S23). Specifically, a ratio obtained by dividing the current detection result by the shunt resistor 45 by the current detection result of the switch element WL is calculated, and the calculation result is set as a correction coefficient Kw for the current detection result of the switch element WL. That is, when the same current is detected by the switch element WL and the shunt resistor 45, the correction coefficient Kw <1 when the current detection result by the switch element WL is larger than the current detection result by the shunt resistor 45, and the correction coefficient when it is small. Kw> 1.

  If NO in step S2, it is determined whether or not the electrical angle θ1 is 120 <θ1 <180 [deg] (S3). That is, whether or not the current flows from the V and W phases toward the U phase, and among the three switch elements UL, VL, and WL on the lower stage, the current flows only to the switch element UL. Is determined.

  When the electrical angle θ1 is not 120 <θ1 <180 [deg] (NO in S3), the process proceeds to step S4. On the other hand, when the electrical angle θ1 is 120 <θ1 <180 [deg] (YES in S3), the potential difference Vu of the switch element UL is acquired, and the potential difference Vu and the known on-resistance value of the switch element UL are obtained. The current Iu flowing through the U-phase switch series circuit 43U (switch element UL) is calculated from Ron (for example, catalog value) (S31).

  Next, the potential difference Vs of the shunt resistor 45 is acquired, and the current Is flowing through the shunt resistor 45 in the “specific phase for the U phase” is calculated from the potential difference Vs and the resistance value Rs of the shunt resistor 45 (S32). That is, in steps S31 and S32, the same current is detected by the switch element UL and the shunt resistor 45, respectively. Here, the detection result of the current Is by the shunt resistor 45 is more accurate than the detection result of the current Iu calculated from the potential difference Vu of the switch element UL and the on-resistance value Ron.

  Then, a ratio obtained by dividing the current detection result of the shunt resistor 45 by the current detection result of the switch element UL is calculated, and the calculation result is a correction coefficient Ku (corresponding to “correction data” of the present invention) for the current detection result of the switch element UL. (S33). That is, when the same current is detected by the switch element UL and the shunt resistor 45, the correction coefficient Ku <1 when the current detection result by the switch element UL is larger than the current detection result by the shunt resistor 45, and the correction coefficient when it is small. Ku> 1.

  If NO in step S3, it is determined whether or not the electrical angle θ1 is 240 <θ1 <300 [deg] (S4). That is, whether or not the current flows from the U and W phases toward the V phase, and the current flows only to the switch element VL among the three switch elements UL, VL, and WL on the lower stage. Is determined.

  When the electrical angle θ1 is not 240 <θ1 <300 [deg] (NO in S4), the process proceeds to step S5. On the other hand, when the electrical angle θ1 is 240 <θ1 <300 [deg] (YES in S4), the potential difference Vv of the switch element VL is acquired, and the potential difference Vv and the known on-resistance value of the switch element VL are obtained. A current Iv flowing through the V-phase switch series circuit 43V (switch element VL) is calculated from Ron (for example, catalog value) (S41).

  Next, the potential difference Vs of the shunt resistor 45 is acquired, and the current Is flowing through the shunt resistor 45 in the “specific phase for the V phase” is calculated from the potential difference Vs and the resistance value Rs of the shunt resistor 45 (S42). That is, in steps S41 and S42, the same current is detected by the switch element VL and the shunt resistor 45, respectively. Here, the detection result of the current Is by the shunt resistor 45 is more accurate than the detection result of the current Iv calculated from the potential difference Vv of the switch element VL and the on-resistance value Ron.

  Then, a ratio obtained by dividing the current detection result by the shunt resistor 45 by the current detection result of the switch element VL is calculated, and the calculation result is calculated as a correction coefficient Kv for the current detection result of the switch element VL (corresponding to “correction data” of the present invention) (S43). That is, when the same current is detected by the switch element VL and the shunt resistor 45, the correction coefficient Kv <1 when the current detection result by the switch element VL is larger than the current detection result by the shunt resistor 45, and the correction coefficient when it is small. Kv> 1.

  In step S5 following the above steps S2 to S4, the potential difference Vw of the lower W-side switch element WL is acquired, and the W-phase current Iw calculated from the potential difference Vw and the on-resistance value Ron of the switch element WL is obtained. The detection result is multiplied by the correction coefficient Kw to correct the detection result of the current Iw by the switch element WL (S5). In the case of “specific phase for the W phase”, the detection result of the current Iw corrected by the process of step S5 matches the detection result of the current Is by the shunt resistor 45 detected in step S22. The detection result by the resistor 45 may be directly used as the detection result of the W-phase current Iw. That is, the present process (S5) of correcting the detection result of the current Iw by multiplying the detection result of the current Iw by the correction coefficient Kw may be omitted.

  Next, the potential difference Vu of the U-phase lower-side switch element UL is acquired, and the detection result of the U-phase current Iu calculated from the potential difference Vu and the ON resistance value Ron of the switch element UL is multiplied by the correction coefficient Ku. Thus, the detection result of the current Iu by the switch element UL is corrected (S6). In the case of “specific phase for the U phase”, the detection result of the current Iu corrected by the process of step S6 matches the detection result of the current Is by the shunt resistor 45 detected in step S32. The detection result by the resistor 45 may be used as the detection result of the U-phase current Iu as it is. That is, the present process (S6) of correcting the detection result of the current Iu by multiplying the detection result of the current Iu by the correction coefficient Ku may be omitted.

  Next, the potential difference Vv of the V-phase lower switch element VL is acquired, and the detection result of the V-phase current Iv calculated from the potential difference Vv and the on-resistance value Ron of the switch element VL is multiplied by the correction coefficient Kv. Thus, the detection result of the current Iv by the switch element VL is corrected to a more accurate value (S7). In the case of “specific phase for the V phase”, the detection result of the current Iv corrected by the process of step S7 matches the detection result of the current Is by the shunt resistor 45 detected in step S42. The detection result by the resistor 45 may be used as the detection result of the V-phase current Iv as it is. That is, the present process (S7) of correcting the detection result of the current Iv by multiplying the detection result of the current Iv by the correction coefficient Kv may be omitted.

  The above is the description of the current detection program PG1, and the motor control circuit 44 detects the U, V, and W phase currents Iu, Iv that are actually detected by the switch elements UL, VL, WL and corrected by the current detection program PG1. , Iw, feedback control is performed on the currents Iu, Iv, Iw flowing through the U, V, W phases of the motor drive circuit 43 (phase windings 19U, 19V, 19W of the motor 19).

  As described above, in the motor drive control circuit 40 of the present embodiment, the shunt resistor 45 that can detect the current more accurately from the switch elements UL, VL, WL between the motor drive circuit 43 and the negative electrode (GND) of the DC power supply 14. Is provided, and each switch is determined by a correction coefficient Ku, Kv, Kw generated from the detection result of the currents Iu, Iv, Iw by the switch elements UL, VL, WL and the detection result of the current Is by the shunt resistor 45. Since the detection results of the currents Iu, Iv, and Iw by the elements UL, VL, and WL are corrected, if the current detection accuracy of the shunt resistor 45 is high, they are connected to the plurality of switch series circuits 43U, 43V, and 43W, respectively. The three phase current detection elements (switch elements UL, VL, WL) can be made inexpensive with low accuracy. In other words, the number of high-precision current detection elements that are conventionally required in accordance with the number of phases of the motor drive circuit 43 can be reduced to one regardless of the number of phases. The electric power steering device 11 can be manufactured at low cost.

  Further, since the switching elements UL, VL, WL for generating the three-phase alternating current from the direct current output also serve as the phase current detection elements for detecting the currents Iu, Iv, Iw, the switching element groups UH, UL , VH,..., VH,... Can be further reduced in cost compared with the case where the phase current detection element is connected to each switch series circuit 43U, 43V, 43W. It can be downsized.

[Second Embodiment]
The motor drive control circuit 40 of this embodiment is shown in FIG. 6 and amplifies the potential differences Vu, Vv, Vw of the upper switch elements UH, VH, WH of the switch series circuits 43U, 43V, 43W of the respective phases. The circuit 44P, 44P, 44P is taken into the motor control circuit 44, and one end of the shunt resistor 45 is connected to the positive electrode of the DC power source 14 and the other end is connected in common to each switch series circuit 43U, 43V, 43W. The potential difference Vs of 45 is taken into the motor control circuit 44 through the amplifier circuit 45P. Other configurations are the same as those of the first embodiment, and the same components are denoted by the same reference numerals and redundant description is omitted.

  Next, the operation of the present embodiment will be described based on the flowchart of FIG. The inverter control unit 42 detects and corrects U, V, and W phase currents Iu, Iv, and Iw by causing the CPU to execute a current detection program PG2 (see FIG. 7) stored in a ROM (not shown) at a predetermined cycle. I do. In the present embodiment, among the three phases U, V, and W, the phase in which current flows from the U phase to the other V and W phases (300 <θ1 <360 [deg] in FIG. 4B) is The “specific phase” for the U phase, and the phase in which current flows from the V phase to the U and W phases ((60 <θ1 <120 [deg] in FIG. 4B)) is the “specific phase” for the V phase. The phase in which current flows from the W phase to the U and V phases (180 <θ1 <240 [deg] in FIG. 4B) is the “specific phase” for the W phase.

  When the current detection program PG2 is executed, first, the electrical angle θ1 of the rotor 21 is acquired from the rotational position sensor 25 provided in the motor 19 (S1).

  Next, it is determined whether or not the electrical angle θ1 is 60 <θ1 <120 [deg] (S200). That is, the current flows from the V phase toward the U and W phases, and among the three upper switching elements UH, VH, and WH, the current flows only to the switching element VH. Determine whether or not.

  When the electrical angle θ1 is not 60 <θ1 <120 [deg] (NO in S200), the process proceeds to step S300. On the other hand, when the electrical angle θ1 is 60 <θ1 <120 [deg] (YES in S200), the potential difference Vv of the switch element VH through which the current flows among the upper three switch elements UH, VH, and WH is acquired. Then, the current Iv flowing through the V-phase switch series circuit 43V (switch element VH) is calculated from the potential difference Vv and the known on-resistance value Ron (for example, catalog value) of the switch element VH (S201).

  Next, the potential difference Vs of the shunt resistor 45 is acquired, and the current Is flowing through the shunt resistor 45 in the “specific phase for the V phase” is calculated from the potential difference Vs and the resistance value Rs of the shunt resistor 45 (S202). The detection result of the current Is is a more accurate value than the detection result of the current Iv by the switch element VH.

  Then, a ratio obtained by dividing the current detection result by the shunt resistor 45 by the current detection result of the switch element VH is calculated, and the calculation result is set as a correction coefficient Kv for the current detection result of the switch element VH (S203).

  If NO in step S200, it is determined whether or not the electrical angle θ1 is 180 <θ1 <240 [deg] (S300). That is, whether a current flows from the W phase toward the U and V phases, and among the three upper switching elements UH, VH, and WH, the current flows only to the switching element WH. Is determined.

  When the electrical angle θ1 is not 180 <θ1 <240 [deg] (NO in S300), the process proceeds to step S400. On the other hand, when the electrical angle θ1 is 180 <θ1 <240 [deg] (YES in S300), the potential difference Vw of the switch element WH through which the current flows among the upper three switch elements UH, VH, and WH is acquired. Then, the current Iw flowing through the W-phase switch series circuit 43W (switch element WH) is calculated from the potential difference Vw and the known on-resistance value Ron (for example, catalog value) of the switch element WH (S301).

  Next, the potential difference Vs of the shunt resistor 45 is acquired, and the current Is flowing through the shunt resistor 45 in the “specific phase for the W phase” is calculated from the potential difference Vs and the resistance value Rs of the shunt resistor 45 (S302). The detection result of the current Is is a more accurate value than the detection result of the current Iw by the switch element WH.

  Then, a ratio obtained by dividing the current detection result by the shunt resistor 45 by the current detection result of the switch element WH is calculated, and the calculation result is set as a correction coefficient Kw for the current detection result of the switch element WH (S303).

  If NO in step S300, it is determined whether or not the electrical angle θ1 is 300 <θ1 <360 [deg] (S400). That is, a current flows from the U phase to the V and W phases (state shown in FIG. 3A), and the current flows only to the switch element UH among the upper three switch elements UH, VH, and WH. It is determined whether or not it is a “specific phase for the phase”.

  When the electrical angle θ1 is not 300 <θ1 <360 [deg] (NO in S400), the process proceeds to step S500. On the other hand, when the electrical angle θ1 is 300 <θ1 <360 [deg] (YES in S400), the potential difference Vu of the switch element UH through which the current flows among the upper three switch elements UH, VH, and WH is acquired. Then, the current Iu flowing through the U-phase switch series circuit 43U (switch element UH) is calculated from the potential difference Vu and the known on-resistance value Ron (for example, catalog value) of the switch element UH (S401).

  Next, the potential difference Vs of the shunt resistor 45 is acquired, and the current Is flowing through the shunt resistor 45 in the “specific phase for the U phase” is calculated from the potential difference Vs and the resistance value Rs of the shunt resistor 45 (S402). The detection result of the current Is is a more accurate value than the detection result of the current Iu by the switch element UH.

  Then, a ratio obtained by dividing the current detection result by the shunt resistor 45 by the current detection result of the switch element UH is calculated, and the calculation result is set as a correction coefficient Ku for the current detection result of the switch element UH (S403).

  In step S500 following the process in step S400, the potential difference Vw of the upper-side switch element WH of the W phase is acquired and corrected to the detection result of the current Iw calculated from the potential difference Vw and the on-resistance value Ron of the switch element WH. The coefficient Kw is multiplied to correct the detection result of the W-phase current Iw by the switch element WH to a more accurate value (S500). When “a specific phase for the W phase” (180 <θ1 <240 [deg]), the detection result of the current Iw corrected by the process of step S500 is the current by the shunt resistor 45 detected in step S302. Since it coincides with the detection result of Is, the detection result by the shunt resistor 45 may be directly used as the detection result of the W-phase current Iw. That is, the present process (S500) of correcting the detection result of the current Iw by multiplying the detection result of the current Iw by the correction coefficient Kw may be omitted.

  Next, the potential difference Vu of the U-phase upper-side switch element UH is obtained, and the detection result of the U-phase current Iu calculated from the potential difference Vu and the ON resistance value Ron of the switch element UH is multiplied by the correction coefficient Ku. The detection result of the current Iu by the switch element UH is corrected to a more accurate value (S600). When “a specific phase for the U phase” (300 <θ1 <360 [deg]), the detection result of the U-phase current Iu corrected by the process of step S600 is the shunt resistance detected in step S402. Therefore, the detection result of the shunt resistor 45 may be used as it is as the detection result of the U-phase current Iu. That is, the present processing (S600) of correcting the detection result of the current Iu by multiplying the detection result of the current Iu by the correction coefficient Ku may be omitted.

  Next, the potential difference Vv of the V-phase upper-side switch element VH is acquired, and the detection result of the V-phase current Iv calculated from the potential difference Vv and the on-resistance value Ron of the switch element VH is multiplied by the correction coefficient Kv. The detection result of the current Iv by the switch element VH is corrected to a more accurate value (S700). When “specific phase for the V phase” (60 <θ1 <120 [deg]), the detection result of the V-phase current Iv corrected by the processing in step S700 is the shunt resistance calculated in step S202. Therefore, the detection result of the shunt resistor 45 may be used as it is as the detection result of the V-phase current Iv. That is, this processing (S700) of correcting the detection result of the current Iv by multiplying the detection result of the current Iv by the correction coefficient Kv may be omitted.

  The above is the description of the current detection program PG2 of the present embodiment, and the present embodiment has the same effects as the first embodiment.

[Other Embodiments]
The present invention is not limited to the above-described embodiment. For example, the embodiments described below are also included in the technical scope of the present invention, and various other than the following can be made without departing from the scope of the invention. It can be changed and implemented.

  (1) In the first and second embodiments, the present invention is applied to a motor drive control circuit 40 for a so-called rack electric power steering apparatus in which a cylindrical motor 19 and a steered wheel shaft 16 are connected by a ball screw mechanism. Although an example is shown, the present invention may be applied to a motor drive control circuit for a pinion electric power steering apparatus in which a motor is connected to a shaft between steered wheels by a rack and pinion mechanism, and the motor is geared in the middle of the steering shaft. The present invention may be applied to a motor drive control circuit for a connected column electric power steering apparatus.

  (2) In the first and second embodiments, the switch element groups UH, UL, VH,... Of the motor drive circuit 43 are N-channel MOSFETs, but are P-channel MOSFETs. Also good.

  (3) In the first and second embodiments, the shunt resistor 45 is used as the correction current detecting element. However, the current detecting element is not limited to the shunt resistor, and other current detecting elements (for example, a Hall element or a current (Trans).

  (4) In the first and second embodiments, one of the pair of switch elements provided in each of the switch series circuits 43U, 43V, and 43W also serves as a phase current detection element for detecting the currents Iu, Iv, and Iw. However, in addition to the switch element groups UH, UL, VH,..., Each switch series circuit 43U, 43V, 43W has an inexpensive phase current that is less accurate than the shunt resistor 45 as a correction current detection element. A detection element may be connected.

  (5) In the first and second embodiments, the connection of the motor 19 is a star connection, but may be a delta connection.

  (6) In the first and second embodiments, the present invention is applied to the motor drive control circuit 40 of the three-phase AC motor 19, but the present invention is applied to the motor drive control circuit of a multiphase AC motor other than the three-phase motor. May be applied.

  (7) In the first and second embodiments, the switch series circuits 43U, 43V, and 43W are connected to the switch series circuits 43U, 43V, and 43W by the switch element on the shunt resistor 45 side of the power supply lines 42U, 42V, and 42W. Although the flowing currents Iu, Iv, and Iw are detected, the currents Iu, Iv, and Iw may be detected by a switch element on the side opposite to the shunt resistor 45.

  Specifically, in the first embodiment, a shunt resistor 45 is provided between the motor drive circuit 43 and the negative electrode (GND) of the DC power supply 14, and the currents Iu, Iv are generated by the lower-side switch elements UL, VL, WL. , Iw are detected, but the currents Iu, Iv, Iw may be detected by the upper-side switch elements UH, VH, WH. In the second embodiment, the shunt resistor 45 is provided between the motor drive circuit 43 and the positive electrode of the DC power supply 14, and the currents Iu, Iv, Iw are detected by the upper-side switch elements UH, VH, WH. However, the currents Iu, Iv, and Iw may be detected by the lower-side switch elements UL, VL, and WL.

The conceptual diagram of the vehicle carrying the electric power steering device which concerns on 1st Embodiment of this invention. Circuit diagram of electric power steering system Circuit diagram showing wiring between motor drive circuit and motor (A) Graph showing sinusoidal command value and triangular wave, (B) Graph showing waveform generated by PWM control Current detection program flowchart Circuit diagram of an electric power steering apparatus according to the second embodiment Current detection program flowchart

Explanation of symbols

11 Electric Power Steering Device 14 DC Power Supply 19 Three-phase AC Motor (Multi-phase AC Motor)
19U, 19V, 19W Phase winding 40 Motor drive control circuit 42U, 42V, 42W Feed line (branch circuit)
43 Motor drive circuit (bridge circuit)
43U, 43V, 43W Switch series circuit 44 Motor control circuit (control circuit)
45 Shunt resistor (correction current detection element)
Iu, Iv, Iw Three-phase AC current Ku, Kv, Kw Correction coefficient (correction data)
PG1, PG2 Current detection program UH, UL, VH, VL, WH, WL Switch element (phase current detection element)

Claims (3)

A plurality of switch series circuits connected in parallel between the positive and negative electrodes of a DC power supply are provided with a pair of switch elements in series, and a plurality of branches branched from between the pair of switch elements in each switch series circuit A bridge circuit formed by connecting a branch circuit to each phase winding of a multiphase AC motor;
A plurality of phase current detection elements connected to the plurality of switch series circuits and capable of detecting a current flowing through each switch series circuit;
A multiphase AC current is generated from the DC output of the DC power supply by turning on and off each switch element and applied to the multiphase AC motor, and a current detection result detected by the phase current detection element is acquired. In a motor drive control circuit comprising a control circuit for feedback control of the polyphase alternating current,
One of the positive and negative electrodes of the DC power supply is connected to one end, and the plurality of switch series circuits are commonly connected to the other end, and a correction current detection element capable of detecting a current more accurately than the phase current detection element Provided,
The control circuit includes a current detection result obtained by the phase current detection element acquired in a specific phase in which current flows only in one phase current detection element among the plurality of phase current detection elements, and a current detection element for correction. Generates correction data for correcting the current detection result of each phase current detection element from the current detection result, and corrects the current detection result by the phase current detection element in a phase other than the specific phase using the correction data A motor drive control circuit. The pair of switch elements are MOSFETs,
2. The motor drive control circuit according to claim 1, wherein each of the phase current detection elements is also used as one of the switch elements in the plurality of switch series circuits.   3. An electric power steering apparatus comprising the motor drive control circuit according to claim 1 and comprising the multiphase AC motor as a drive source.

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