Current detection device, motor control device, and electric power steering device

Abstract

The current detection device includes: a current detection unit (35a-35f) that detects a current flowing through a switching element of a lower arm (or an upper arm); a correction value calculation unit (50b) that calculates an offset correction value based on a detected value of the current detected by the current detection unit during a period in which the switching element is off in PWM control, and holds and updates the calculated offset correction value; and a correction unit (50c) that corrects a detected value of the current detected by the current detection unit during a period in which the switching element is on by the offset correction value held by the correction value calculation unit, and the correction value calculation unit does not perform updating of the offset correction value in a case where a duty ratio of the PWM control is below a lower limit value of the duty ratio (or above an upper limit value of the duty ratio).

Description

Technical Field

[0001] This invention relates to a current detection device, a motor control device, and an electric power steering device. Background Technology

[0002] As a unit for driving electric motors, pulse width modulation (PWM) control is known. In PWM control, a switching element is turned on and off by a PWM signal with a duty cycle corresponding to the command value, and a voltage corresponding to the duty cycle is applied to the electric motor. The current flowing through the electric motor due to this voltage application is detected by a current detector, and the difference between the target value and the current detection value is used as the deviation for generating the command value.

[0003] In this structure, although the current flowing through the electric motor should be zero, sometimes the current detected by the current detector is not zero. This current is called the offset current, and the detected current value by the current detector is the value obtained by adding the offset current to the actual current flowing through the electric motor. Therefore, the offset current is the cause of the error in the detected current value in the current detector.

[0004] If an offset error occurs (i.e., an error caused by offset current), the detected current value will not be consistent with the actual current flowing through the electric motor, thus making it impossible to control the electric motor current according to the settings. For example, in an electric power steering system that assists vehicle steering, if an offset error occurs in the control of the electric motor that generates steering assistance force, torque pulsation may sometimes occur during steering, causing discomfort to the driver.

[0005] Therefore, the power steering device of Patent Document 1 below includes: a current detection unit that detects the current flowing through a switching element as the current flowing through an electric motor; and a correction unit that corrects the detection value of the current detection unit. This correction unit obtains an offset correction value based on the current detected by the current detection unit during the period when the switching element is off in PWM control, and uses the offset correction value to correct the current detected by the current detection unit during the period when the switching element is on.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Specification of Japanese Patent No. 4474896 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] However, when trying to detect the offset current generated in a current detector that detects the current flowing through the switching element in PWM control, the offset current is sometimes not detected accurately.

[0011] This invention was made with regard to the above-mentioned problems, and its purpose is to detect with high precision the offset current generated in a current detector that detects the current of the switching elements of a multiphase inverter in PWM control.

[0012] Methods for solving problems

[0013] To achieve the above objectives, one aspect of the current detection device of the present invention includes: a current detection unit that detects the current flowing through a switching element based on the voltage drop of a resistive element connected in series with a switching element of either the upper or lower arm of a PWM-controlled multiphase inverter; a correction value calculation unit that calculates an offset correction value based on the detected current value obtained by the current detection unit during the period when the switching element is off in PWM control, and maintains and updates the calculated offset correction value; and a correction unit that corrects the detected current value obtained by the current detection unit during the period when the switching element is on using the offset correction value maintained by the correction value calculation unit. When the switching element is a switching element of the lower arm and the duty cycle of the PWM control is below the lower duty cycle limit, or when the switching element is a switching element of the upper arm and the duty cycle is above the upper duty cycle limit, the correction value calculation unit does not update the offset correction value.

[0014] Another aspect of the present invention provides a motor control device comprising: a multiphase inverter having switching elements; the aforementioned current detection device for detecting the current flowing through the switching elements; and a controller for controlling the multiphase inverter based on the current value detected by the current detection device.

[0015] Another embodiment of the electric power steering device of the present invention includes the above-described motor control device and a multiphase motor controlled by the motor control device, wherein the multiphase motor provides steering assistance force to the vehicle's steering system.

[0016] Invention Effects

[0017] According to the present invention, the offset current generated in a current detector that detects the current of the switching elements of a multiphase inverter can be detected with high precision in PWM control. Attached Figure Description

[0018] Figure 1 This is a structural diagram illustrating an example of an electric power steering system according to an embodiment.

[0019] Figure 2This is a schematic diagram showing an example of an Electronic Control Unit (ECU).

[0020] Figure 3 This is a schematic diagram showing another example of an electronic control unit (ECU).

[0021] Figure 4 This is a circuit diagram illustrating an example of the structure of a current sensing unit.

[0022] Figure 5 This is a block diagram illustrating an example of the functional structure of the control unit.

[0023] Figure 6 This is a block diagram of an example of a current detection value correction unit.

[0024] Figure 7 (a) is a timing diagram showing the on and off periods of the switching element of the lower arm, (b) is a schematic timing diagram of the output value of the current detection unit, and (c) is a schematic timing diagram of the offset correction value.

[0025] Figure 8 (a) is a timing diagram showing the on and off periods of the switching element of the lower arm when the duty cycle is small, and (b) is a schematic timing diagram of the output value of the current detection unit.

[0026] Figure 9 This is a flowchart illustrating an example of a method for setting offset correction values.

[0027] Figure 10 This is a structural diagram showing a first variation of the electric power steering system.

[0028] Figure 11 This is a structural diagram showing a second variation of the electric power steering system.

[0029] Figure 12 This is a structural diagram showing a summary of the third variation of the electric power steering system. Detailed Implementation

[0030] The embodiments of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, the embodiments of the present invention shown below illustrate apparatus and methods for embodying the technical concept of the present invention, but the technical concept of the present invention does not limit the structure, arrangement, etc., of the constituent components to the following content. The technical concept of the present invention can be modified in various ways within the technical scope defined by the technical solutions described in the claims.

[0031] (structure)

[0032] Figure 1This is a schematic structural diagram illustrating an example of an electric power steering (EPS) device. The steering wheel (steering handle) 1's steering shaft (steering shaft, handle shaft) 2 is connected to the steering wheels 8L and 8R via a reduction gear (worm gear) 3 constituting a reduction mechanism, universal joints 4a and 4b, pinion rack mechanism 5, tie rods 6a and 6b, and further via wheel hub units 7a and 7b.

[0033] The pinion rack mechanism 5 has a pinion 5a connected to a pinion shaft that transmits steering force from a universal joint 4b and a rack 5b that meshes with the pinion 5a. The rotational motion transmitted to the pinion 5a is converted into linear motion in the vehicle width direction by the rack 5b.

[0034] A torque sensor 10 for detecting steering torque Th is installed on the steering shaft 2. In addition, a steering angle sensor 14 for detecting steering angle θh of steering wheel 1 is installed on the steering shaft 2.

[0035] Additionally, the motor 20, which assists in the steering force of the steering wheel 1, is connected to the steering shaft 2 via a reduction gear 3. This specification describes an example where the motor 20 is a three-phase motor, but the number of phases of the motor 20 may not be three.

[0036] The electronic control unit (ECU) 30, which controls the electric power steering system, is powered by the battery 13 and receives the ignition key signal via the ignition switch 11.

[0037] The ECU30 calculates the current command value of the auxiliary control command based on the steering torque Th detected by the torque sensor 10, the vehicle speed Vh detected by the vehicle speed sensor 12, and the steering angle θh detected by the steering angle sensor 14. It then controls the current supplied to the motor 20 (U-phase current I1u, V-phase current I1v, W-phase current I1w) by compensating the current command value.

[0038] Furthermore, the steering angle sensor 14 is not necessary. The steering angle θh can also be calculated by adding the motor rotation angle θm obtained from the rotation angle sensor 21 that detects the rotation angle of the rotating shaft of the motor 20 to the torsion angle of the torsion bar of the torque sensor 10.

[0039] Alternatively, the steering angles of the steering wheels 8L and 8R can be used instead of the steering angle θh. For example, the steering angle can also be detected by measuring the displacement of the rack 5b.

[0040] ECU30 may include, for example, a computer containing peripheral components such as a processor and storage devices. The processor may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit).

[0041] Storage devices can be any of semiconductor storage devices, magnetic storage devices, and optical storage devices. Storage devices may include registers, cache memory, ROM (Read Only Memory) used as main storage, and RAM (Random Access Memory), etc.

[0042] The functions of ECU30 described below are achieved, for example, by the processor of ECU30 executing a computer program stored in a storage device.

[0043] Alternatively, the ECU30 can be formed using dedicated hardware for performing the various information processing described below.

[0044] For example, ECU30 may also include functional logic circuits configured in general-purpose semiconductor integrated circuits. For example, ECU30 may also have programmable logic devices (PLDs) such as field-programmable gate arrays (FPGAs).

[0045] Figure 2 This is a structural diagram showing an example of an ECU 30 according to an embodiment. The ECU 30 includes a control calculation unit 31, a gate drive circuit 32a, an inverter 33a, a motor speed calculation unit 34, and current detection units 35a to 35c.

[0046] The control calculation unit 31 calculates the current command value, which is the control target value of the drive current of the motor 20, based at least on the steering torque Th, and outputs the voltage control command values ​​V1u, V1v, and V1w obtained by compensating for the current command value to the gate drive circuit 32a. The voltage control command values ​​V1u, V1v, and V1w are the U-phase voltage control command value of the U-phase coil, the V-phase voltage command value of the V-phase coil, and the W-phase voltage command value of the W-phase coil, respectively.

[0047] The gate drive circuit 32a calculates the duty cycles Du, Dv, and Dw of the PWM signals that drive the U-phase coil, V-phase coil, and W-phase coil based on the voltage control command values ​​V1u, V1v, and V1w. The gate drive circuit 32a outputs the PWM signals according to the calculated duty cycles Du, Dv, and Dw to the inverter 33a.

[0048] Inverter 33a has a three-phase bridge connected between the positive side line and the ground line, the positive side line being connected to the DC power supply Vdc and supplied with DC power.

[0049] The three-phase bridge includes pairs of switching elements, in which the upper arms of the U-phase, V-phase, and W-phase switching elements Q1u1, Q1v1, and Q1w1 are connected in series with the lower arms of the U-phase, V-phase, and W-phase switching elements Q1u2, Q1v2, and Q1w2 respectively. The U-phase current I1u supplied to the U-phase coil of the motor 20 is supplied from the connection point of the switching elements Q1u1 and Q1u2, the V-phase current I1v supplied to the V-phase coil is supplied from the connection point of the switching elements Q1v1 and Q1v2, and the W-phase current I1w supplied to the W-phase coil is supplied from the connection point of the switching elements Q1w1 and Q1w2.

[0050] Shunt resistors r1u, r1v, and r1w are connected in series between the switching elements Q1u2, Q1v2, and Q1w2 in the lower arms of phases U, V, and W, and the grounding wire. The current detection units 35a to 35c, described later, can detect the current flowing through the switching elements Q1u2, Q1v2, and Q1w2 in the lower arms by detecting the voltage drop generated in the shunt resistors r1u, r1v, and r1w.

[0051] Alternatively, shunt resistors r1u, r1v, and r1w can be placed between the switching elements Q1u1, Q1v1, and Q1w1 of the upper arm of phase U, phase V, and phase W and the positive terminal line. The current detection units 35a to 35c can also detect the current flowing through the switching elements Q1u1, Q1v1, and Q1w1 of the upper arm.

[0052] The motor speed calculation unit 34 calculates the motor rotation angle θm (e.g., motor electrical angle) of the motor 20 based on the detection signal of the rotation angle sensor 21 and outputs it to the control calculation unit 31.

[0053] The current detection units 35a to 35c output the detected values ​​I1ud, I1vd, and I1wd of the current flowing through the switching elements Q1u2, Q1v2, and Q1w2 of the lower arm based on the voltage drop generated in the shunt resistors r1u, r1v, and r1w.

[0054] Figure 4 This is a circuit diagram illustrating an example of the structure of the current detection unit 35a. The current detection unit 35a includes: a differential amplifier circuit 36 ​​that generates a current detection signal corresponding to the magnitude of the voltage drop generated in the shunt resistor r1u; and a low-pass filter (LPF) 37 connected to the output of the differential amplifier circuit 36. Current detection units 35b and 35c are similar. Furthermore, in Figure 4 In this context, Vcc is a specified voltage generated by the power generation circuit, which can be, for example, 5V.

[0055] In the current detection unit 35a configured in this way, even if the voltage drop generated in the shunt resistor r1u is zero (i.e. the current flowing through the shunt resistor r1u is zero), the detection value of the current detection unit 35a is sometimes not zero (i.e. the detection value includes the offset current).

[0056] Such offset current is generated, for example, due to the deterioration of the differential amplifier circuit 36 ​​over the years and the temperature change of the current detection unit 35a.

[0057] Figure 3 This is a structural diagram illustrating other examples of ECU30 implementation methods. Figure 3 The ECU 30 controls the dual-winding motor 20. The dual-winding motor has two windings, in which a first system coil and a second system coil are wound within the same motor housing, and a common rotor is rotated by the coils of the two systems. The ECU 30 includes a control calculation unit 31, a first system gate drive circuit 32a and a first system inverter 33a for driving the first system coil of the motor 20, a second system gate drive circuit 32b and a second system inverter 33b for driving the second system coil, a motor speed calculation unit 34, and current detection units 35a to 35f. Figure 3 The structure of the motor speed calculation unit 34 and Figure 2 The structure of the motor speed calculation unit 34 is the same.

[0058] The control calculation unit 31 calculates the current command value, which is the control target value of the drive current of the motor 20, based at least on the steering torque Th, and outputs the voltage control command values ​​V1u, V1v, V1w, V2u, V2v, and V2w obtained by compensating for the current command value to the first system gate drive circuit 32a and the second system gate drive circuit 32b. The voltage control command values ​​V1u, V1v, and V1w are the U-phase voltage control command value, V-phase voltage command value, and W-phase voltage command value of the first system coil, respectively, and the voltage control command values ​​V2u, V2v, and V2w are the U-phase voltage control command value, V-phase voltage command value, and W-phase voltage command value of the second system coil, respectively.

[0059] The first system gate drive circuit 32a calculates the duty cycles Du, Dv, and Dw of the U-phase, V-phase, and W-phase PWM signals driving the first system coils based on the voltage control command values ​​V1u, V1v, and V1w. The first system gate drive circuit 32a outputs the PWM signals according to the calculated duty cycles Du, Dv, and Dw to the first system inverter 33a.

[0060] Figure 3 The structure of the first system gate drive circuit 32a, the first system inverter 33a, and the current detection units 35a-35c are similar to those of the first system gate drive circuit 32a, the first system inverter 33a, and the current detection units 35a-35c. Figure 2The drive circuit 32a, inverter 33a, and current detection units 35a to 35c have the same structure.

[0061] The second system gate drive circuit 32b calculates the duty cycles Du, Dv, and Dw of the U-phase, V-phase, and W-phase PWM signals that drive the second system coils based on the voltage control command values ​​V2u, V2v, and V2w. The second system gate drive circuit 32b outputs the PWM signals according to the calculated duty cycles Du, Dv, and Dw to the second system inverter 33b.

[0062] The second system inverter 33b has a three-phase bridge connected between the positive side line and the ground line, the positive side line being connected to the DC power supply Vdc and supplied with DC power.

[0063] The three-phase bridge includes pairs of switching elements, in which the upper arms of the U-phase, V-phase, and W-phase switching elements Q2u1, Q2v1, and Q2w1 are connected in series with the lower arms of the U-phase, V-phase, and W-phase switching elements Q2u2, Q2v2, and Q2w2 respectively. The U-phase current I2u supplied to the first system coil of the motor 20 is supplied from the connection point of the switching elements Q2u1 and Q2u2, the V-phase current I2v is supplied from the connection point of the switching elements Q2v1 and Q2v2, and the W-phase current I2w is supplied from the connection point of the switching elements Q2w1 and Q2w2.

[0064] Shunt resistors r2u2, r2v2, and r2w2 are connected in series between the switching elements Q2u2, Q2v2, and Q2w2 in the lower arms of phases U, V, and W, and the grounding wire. The current detection units 35d to 35f, described later, can detect the current flowing through the switching elements Q2u2, Q2v2, and Q2w2 in the lower arms by detecting the voltage drop generated in the shunt resistors r2u, r2v, and r2w.

[0065] Alternatively, shunt resistors r2u, r2v, and r2w can be placed between the switching elements Q2u1, Q2v1, and Q2w1 on the upper arm of phases U, V, and W and the positive terminal line. The current detection units 35d to 35f can also detect the current flowing through the switching elements Q2u1, Q2v1, and Q2w1 on the upper arm.

[0066] Current detection units 35d to 35f output the detected current values ​​I2ud, I2vd, and I2wd based on the voltage drop generated in the shunt resistors r2u, r2v, and r2w, respectively, of the current flowing through the switching elements Q2u2, Q2v2, and Q2w2 in the lower arm. The structure of current detection units 35d to 35f is similar to that of reference units. Figure 4 The structure of the current detection unit 35a described herein is the same.

[0067] Figure 5This is a block diagram illustrating an example of the functional structure of the control and arithmetic unit 31. Furthermore, the following description only depicts the functional structure for controlling the inverter 33a of a single system. Figure 3 In the structure of inverters 33a and 33b that have two systems, each inverter independently possesses the functional structure described below.

[0068] The control calculation unit 31 includes a current command value calculation unit 40, subtractors 41 and 42, a current limiting unit 43, a proportional-integral (PI) control unit 44, a 2-phase / 3-phase conversion unit 45, a current detection value correction unit 46a to 46c, a 3-phase / 2-phase conversion unit 47, and an angular velocity conversion unit 48, and drives the motor 20 through vector control.

[0069] The current command value calculation circuit 40 calculates the q-axis current command value Iq0 and the d-axis current command value Id0 that should flow to the motor 20 based on the steering torque Th, vehicle speed Vh, motor rotation angle θm of motor 20 and rotational angular velocity ω of motor 20.

[0070] On the other hand, the detection values ​​I1ud, I1vd, and I1wd of the U-phase current, V-phase current, and W-phase current of the motor 20 in the current detection units 35a to 35c are input to the current detection value correction units 46a to 46c.

[0071] The current detection value correction units 46a to 46c calculate the U-phase current I1u, V-phase current I1v, and W-phase current I1w by removing the offset current from the detected values ​​I1ud, I1vd, and I1wd. The structure and operation of the current detection value correction units 46a to 46c will be described later.

[0072] The U-phase current I1u, V-phase current I1v, and W-phase current I1w are converted into d-q axis currents id and iq by the 3-phase / 2-phase conversion unit 47.

[0073] Subtractors 41 and 42 calculate the q-axis deviation current Δq0 and the d-axis deviation current Δd0 by subtracting the feedback currents iq and id from the q-axis current command value Iq0 and the d-axis current command value Id0, respectively.

[0074] The current limiting unit 43 limits the upper limits of the q-axis deviation current Δq0 and the d-axis deviation current Δd0. The limited q-axis deviation current Δq and d-axis deviation current Δd are then input to the PI control unit 44.

[0075] The PI control unit 44 calculates voltage command values ​​vq and vd that make the q-axis deviation current Δq and the d-axis deviation current Δd zero, respectively. The 2-phase / 3-phase conversion unit 45 converts the voltage command values ​​vd and vq into U-phase voltage control command values ​​V1u, V-phase voltage command values ​​V1v, and W-phase voltage command values ​​V1w, respectively, and outputs them to the gate drive circuit 32a.

[0076] The angular velocity conversion unit 48 calculates the rotational angular velocity ω of the motor 20 based on the time change of the motor rotation angle θm. These motor rotation angles θm and rotational angular velocities ω are input to the current command value calculation unit 40 for vector control.

[0077] Figure 6 This is a block diagram of an example of a current detection value correction unit 46a. Current detection value correction units 46b and 46c also have the same structure as current detection value correction unit 46a. Current detection value correction unit 46a includes a scaling conversion unit 50a, a correction value calculation unit 50b, a subtractor 50c, a gain correction value storage unit 50d, and a multiplier 50e.

[0078] The scaling conversion unit 50a outputs the detection value I1ud from the current detection unit 35a that detects the U-phase current and converts it into a current value in digital form. For example, the scaling conversion unit 50a can convert the detection value I1ud into a current value by multiplying it by a predetermined coefficient.

[0079] The correction value calculation unit 50b dynamically calculates the offset correction value used to correct the offset error (i.e., the error caused by the offset current) generated in the current detection unit 35a during the PWM control of the ECU 30, and maintains and updates the calculated offset correction value. That is, the correction value calculation unit 50b calculates the offset error periodically or at any time during the PWM control, and updates the previously calculated and maintained offset error using the newly calculated offset error.

[0080] The correction value calculation unit 50b calculates the offset correction value based on the current detection value I1ud detected by the current detection unit 35a during the period when the switching element Q1u2 of the lower arm of phase U is open. For example, the current detection value I1ud detected by the current detection unit 35a during the period when the switching element Q1u2 is open can be used as the offset correction value.

[0081] For example, the correction value calculation unit 50b can calculate the average of N detection values ​​output by the current detection unit 35a during the period when the switching element Q1u2 is off, during a specified period of time (hereinafter sometimes referred to as "detection value collection period P"), as the offset correction value (N is a natural number greater than or equal to 1). In this case, the correction value calculation unit 50b updates the held offset correction value for each detection value collection period P using the newly calculated offset correction value.

[0082] For example, if the length of the detection value collection period P is set to 1 [sec] seconds, and the period during which the correction value calculation unit 50b obtains the output of the current detection unit 35a during the period when the switching element Q1u2 is off is set to 1 [ms], then the average value of 1000 detection values ​​can be calculated as the offset correction value.

[0083] In addition, the correction value calculation unit 50b can obtain the output of the current detection unit 35a in each PWM cycle, or it can obtain it in multiple cycles of the PWM cycle.

[0084] Figure 7 (a) is a timing diagram showing the on and off periods of the switching element Q1u2. Figure 7 (b) is a schematic timing diagram of the output value I1ud of the current detection unit 35a. Figure 7 (c) is a schematic timing diagram of the offset correction value. Figure 7 The output value I of (b) ON and I OFF These are the stable values ​​of the output I1ud during the on-time and off-time of the switching element Q1u2, respectively.

[0085] The correction value calculation unit 50b can acquire the output value I1ud of the current detection unit 35a at sampling times s1, s2, ... sN during a detection value collection period P that starts at time t0 and ends at time t1, and calculate the average of the N acquired output values ​​I1ud as the offset correction value.

[0086] In addition, the sampling times s1, s2, ... sN can be set to, for example, the off-time P of the switching element Q1u2. OFF The central moment.

[0087] Figure 8 (a) is a timing diagram showing the on and off periods of the switching element Q1u2 on the lower arm of phase U when the duty cycle Du of phase U is small. Figure 8 (b) is a schematic timing diagram of the output value of the current detection unit 35a.

[0088] like Figure 4 As shown, an LPF37 is arranged in the output section of the current detection unit 35a. Therefore, when the switching element Q1u2 is switched, as Figure 7 (b) Figure 8 As shown in (b), the waveform of the output value of the current detection unit 35a is passivated.

[0089] Therefore, when the duty cycle Du of phase U is small, it is sometimes impossible to properly sample the detection value I1ud during period a by disconnecting the circuit. For example, when in Figure 8 When sampling the current detection value I1ud of the current detection unit 35a at sampling time s1 shown in (b), the stable value I during the disconnection period is compared. OFF Larger detection values ​​are sampled.

[0090] Therefore, the correction value calculation unit 50b stops updating the offset correction value of the U phase when the duty cycle Du of the U phase is below the lower limit Dth (e.g., 14%) (in other words, it does not update the offset correction value of the U phase when the duty cycle Du is below the lower limit Dth). For example, if the duty cycle Du of the U phase is detected to be below the lower limit Dth at any time during a certain detection value collection period P, the correction value calculation unit 50b sets the duty cycle reduction detection flag F1 from off to on. When the duty cycle reduction detection flag F1 is on at the end of the detection value collection period P, the correction value calculation unit 50b stops updating the currently held offset correction value of the U phase based on the offset correction value I1ud collected during the detection value collection period P (in other words, it does not update). The correction value calculation unit 50b can receive duty cycle information related to the duty cycles Du, Dv, and Dw from the gate drive circuit 32a.

[0091] Similarly, in the current detection value correction unit 46b of phase V, the update of the offset correction value of phase V is stopped when the duty cycle Dv of phase V is below the lower limit value Dt (in other words, the update of the offset correction value of phase V is not performed when the duty cycle Dv is below the lower limit value Dt). In the current detection value correction unit 46c of phase W, the update of the offset correction value of phase W is also stopped when the duty cycle Dw of phase W is below the lower limit value Dt (in other words, the update of the offset correction value of phase W is not performed when the duty cycle Dw is below the lower limit value Dt).

[0092] For example, even if the duty cycle Du of phase U is greater than the lower limit Dth, but the duty cycle Dv of phase V or the duty cycle Dw of phase W is less than or equal to the lower limit Dth, the correction value calculation unit 50b can stop updating the offset correction value of phase U (in other words, even if the duty cycle Du is greater than the lower limit Dth, but the duty cycle Dv or Dw is less than or equal to the lower limit Dth, the offset correction value of phase U is not updated). This is because when the duty cycles Dv and Dw of phase V and phase W are small, the time when the correction value calculation unit 50b obtains the detection value I1ud of the current detection unit 35a is close to the time when the switching elements in phase V and phase W are switched on and off, thus avoiding the influence of noise that may be caused by switching.

[0093] For example, if the correction value calculation unit 50b detects at any time during a certain detection value collection period P that the duty cycle Dv and Dw have fallen below the lower limit value Dth, the correction value calculation unit 50b sets the duty cycle reduction detection flag F1 from off to on. If the duty cycle reduction detection flag F1 is on at the end of the detection value collection period P, the correction value calculation unit 50b stops updating the offset correction value of the currently held U phase based on the offset correction value I1ud collected during the detection value collection period P (in other words, it does not perform the update of the offset correction value of the currently held U phase based on the offset correction value I1ud collected during the detection value collection period P).

[0094] Similarly, in the V-phase current detection value correction unit 46b, even if the duty cycle Dv of the V-phase is greater than the lower limit Dth, the update of the V-phase offset correction value can be stopped if the duty cycles Du and Dw of the U-phase and W-phase are below the lower limit Dt (in other words, even if the duty cycle Dv is greater than the lower limit Dth, the update of the V-phase offset correction value is not performed if the duty cycles Du and Dw are below the lower limit Dt). Furthermore, in the W-phase current detection value correction unit 46c, even if the W-phase duty cycle Dw is greater than the lower limit Dt, the update of the W-phase offset correction value can be stopped if the duty cycles Du and Dv of the U-phase and V-phase are below the lower limit Dt (in other words, even if the duty cycle Dw is greater than the lower limit Dt, the update of the W-phase offset correction value is not performed if the duty cycles Du and Dv are below the lower limit Dt).

[0095] Furthermore, when the shunt resistors r1u, r1v, and r1w are placed between the switching element of the upper arm of phase U, phase V, and phase W and the positive terminal line, the update of the offset correction value is stopped when the duty cycle is above the upper limit (in other words, the update of the offset correction value is not performed when the duty cycle is above the upper limit).

[0096] Furthermore, the correction value calculation unit 50b can also prevent the update of the offset correction value of phase U based on the detection value I1ud when the current detection unit 35a detects that the current detection value I1ud exceeds the upper limit value Ith during the period when the switching element Q1u2 is off (in other words, the offset correction value of phase U is not updated based on the detection value I1ud when the detection value I1ud exceeds the upper limit value Ith). The upper limit value Ith can be appropriately set to a magnitude that cannot be imagined as an offset current (e.g., 1 ampere).

[0097] For example, if a detection value I1ud exceeds the upper limit Ith at any time during a certain detection value collection period P, the correction value calculation unit 50b sets the U-phase anomaly detection flag F2u from off to on. If the U-phase anomaly detection flag F2u is on at the end of the detection value collection period P, the correction value calculation unit 50b stops updating the currently held U-phase offset correction value based on the offset correction value calculated based on the detection value I1ud collected during the detection value collection period P (in other words, it does not update the currently held U-phase offset correction value based on the offset correction value calculated based on the detection value I1ud collected during the detection value collection period P).

[0098] Furthermore, even if the detected current value I1vd by the current detection unit 35b exceeds the upper limit value Ith during the period when the switching element Q1v2 of phase V is off, or the detected current value I1wd by the current detection unit 35c exceeds the upper limit value Ith during the period when the switching element Q1w2 of phase W is off, the correction value calculation unit 50b may not prohibit the updating of the offset correction value of phase U (in other words, the offset correction value of phase U can be updated even if the detected value I1vd exceeds the upper limit value Ith or the detected value I1wd exceeds the upper limit value Ith). This is because even if an abnormal value is detected in phase V or phase W, as long as no abnormal value is detected in phase U, the calculation of the offset correction value will not be hindered.

[0099] Similarly, in the V-phase current detection value correction unit 46b, if the detection value I1vd detected by the current detection unit 35b exceeds the upper limit value Ith, the V-phase abnormal value detection flag F2v can be set from off to on, prohibiting the update of the V-phase offset correction value based on the detection value I1vd exceeding the upper limit value Ith (in other words, the V-phase offset correction value is not updated based on the detection value I1vd exceeding the upper limit value Ith). Furthermore, if the W-phase current detection value correction unit 46c detects that the detection value I1wd of the current detection unit 35c exceeds the upper limit value Ith, the W-phase abnormal value detection flag F2w can be set from off to on, prohibiting the update of the W-phase offset correction value based on the detection value I1wd exceeding the upper limit value Ith (in other words, the W-phase offset correction value is not updated based on the detection value I1wd exceeding the upper limit value Ith).

[0100] Reference Figure 6 The subtractor 50c corrects the detected value I1ud by subtracting the offset correction value held by the correction value calculation unit 50b from the detected value I1ud of the current detected by the current detection unit 35a during the period when the switching element Q1u2 is turned on.

[0101] The multiplier 50e multiplies the specified gain stored in the gain correction value storage unit 50d with the subtraction result of the correction value calculation unit 50b, and outputs the product as the corrected U-phase current I1u.

[0102] Figure 9 This is a flowchart illustrating an example of the method for setting the offset correction value in the current detection value correction units 46a to 46c. Furthermore, in the following flowchart description, the detection value I1ud of the U-phase current detection unit 35a of the first system and the detection value I2ud of the U-phase current detection unit 35d of the second system are collectively referred to as "detection value Iud," the detection value I1vd of the V-phase current detection unit 35b of the first system and the detection value I2vd of the V-phase current detection unit 35e of the second system are collectively referred to as "detection value Ivd," and the detection value Iwd1 of the W-phase current detection unit 35c of the first system and the detection value I2wd of the W-phase current detection unit 35f of the second system are collectively referred to as "detection value Iwd."

[0103] In step S1, the duty cycle reduction detection flag F1, the U-phase abnormal value detection flag F2u, the V-phase abnormal value detection flag F2v, and the W-phase abnormal value detection flag F2w are set to off. Additionally, the value of the counter variable CNT is initialized to 0.

[0104] In step S2, the detection value Iud of phase U is detected.

[0105] In step S3, it is determined whether the duty cycle Du of phase U is below the lower limit Dth. If the duty cycle Du of phase U is below the lower limit Dth (step S3: Yes), the process proceeds to step S4. If the duty cycle Du of phase U is not below the lower limit Dth (step S3: No), the process proceeds to step S5.

[0106] In step S4, the duty cycle reduction detection flag F1 is set to "on". Then, the process proceeds to step S5.

[0107] In step S5, it is determined whether the detection value Iud of phase U exceeds the upper limit value Ith. If the detection value Iud of phase U exceeds the upper limit value Ith (step S5: Yes), the process proceeds to step S6. If the detection value Iud of phase U does not exceed the upper limit value Ith (step S5: No), the process proceeds to step S7.

[0108] In step S6, the U-phase abnormal value detection flag F2u is set to "on". Then, the process proceeds to step S7.

[0109] In step S7, the detection value Ivd of phase V is detected.

[0110] In step S8, it is determined whether the duty cycle Dv of phase V is below the lower limit Dth. If the duty cycle Dv of phase V is below the lower limit Dth (step S8: Yes), the process proceeds to step S9. If the duty cycle Dv of phase V is not below the lower limit Dth (step S8: No), the process proceeds to step S10.

[0111] In step S9, the duty cycle reduction detection flag F1 is set to "on". Then, the process proceeds to step S10.

[0112] In step S10, it is determined whether the detection value Ivd of phase V exceeds the upper limit value Ith. If the detection value Ivd of phase V exceeds the upper limit value Ith (step S10: Yes), the process proceeds to step S11. If the detection value Ivd of phase V does not exceed the upper limit value Ith (step S10: No), the process proceeds to step S12.

[0113] In step S11, the V-phase abnormal value detection flag F2v is set to "on". Then, the process proceeds to step S12.

[0114] In step S12, the detection value Iwd of phase W is detected.

[0115] In step S13, it is determined whether the duty cycle Dw of phase W is below the lower limit Dth. If the duty cycle Dw of phase W is below the lower limit Dth (step S13: Yes), the process proceeds to step S14. If the duty cycle Dw of phase W is not below the lower limit Dth (step S13: No), the process proceeds to step S15.

[0116] In step S14, the duty cycle reduction detection flag F1 is set to "on". Then, the process proceeds to step S15.

[0117] In step S15, it is determined whether the detection value Iwd of phase W exceeds the upper limit value Ith. If the detection value Iwd of phase W exceeds the upper limit value Ith (step S15: Yes), the process proceeds to step S16. If the detection value Iwd of phase W does not exceed the upper limit value Ith (step S15: No), the process proceeds to step S17.

[0118] In step S16, the W-phase abnormal value detection flag F2w is set to "on". Then, the process proceeds to step S17.

[0119] In step S17, it is determined whether the count variable CNT is greater than or equal to N. If the count variable CNT is greater than or equal to N (step S17: Yes), it is determined that the collection period P of a detection value has expired, and the process proceeds to step S19. If the count variable CNT is not greater than or equal to N (step S17: No), the process proceeds to step S18.

[0120] In step S18, the value of the counter variable CNT is incremented by 1, and the process returns to step S2.

[0121] In step S19, it is determined whether the duty cycle reduction detection flag F1 is enabled. If the duty cycle reduction detection flag F1 is enabled (step S19: Yes), the process proceeds to step S26. In this case, the offset correction values ​​for phase U, phase V, and phase W are not updated.

[0122] If the duty cycle reduction detection flag F1 is not turned on (step S19: No), proceed to step S20.

[0123] In step S20, it is determined whether the U-phase anomaly detection flag F2u is enabled. If the U-phase anomaly detection flag F2u is enabled (step S20: Yes), the process proceeds to step S22. In this case, the U-phase offset correction value is not updated. If the U-phase anomaly detection flag F2u is not enabled (step S20: No), the process proceeds to step S21.

[0124] In step S21, the new offset correction value for the U phase is calculated, and the currently maintained offset correction value is updated. Then, the process proceeds to step S22.

[0125] In step S22, it is determined whether the V-phase anomaly detection flag F2v is enabled. If the V-phase anomaly detection flag F2v is enabled (step S22: Yes), the process proceeds to step S24. In this case, the V-phase offset correction value is not updated. If the V-phase anomaly detection flag F2v is not enabled (step S22: No), the process proceeds to step S23.

[0126] In step S23, a new offset correction value for phase V is calculated, and the currently maintained offset correction value is updated. Then, the process proceeds to step S24.

[0127] In step S24, it is determined whether the W-phase anomaly detection flag F2w is enabled. If the W-phase anomaly detection flag F2w is enabled (step S24: Yes), the process proceeds to step S26. In this case, the offset correction value of the W-phase is not updated. If the W-phase anomaly detection flag F2w is not enabled (step S24: No), the process proceeds to step S25.

[0128] In step S25, a new offset correction value for phase W is calculated, and the currently maintained offset correction value is updated. Then, the process proceeds to step S26.

[0129] In step S26, it is determined whether the ignition switch 11 is off. If the ignition switch 11 is off (step S26: Yes), the process ends. If the ignition switch 11 is not off (step S26: No), the process returns to step S1.

[0130] (Modified Example)

[0131] The above description illustrates an example of applying the rotation angle detection device of the present invention to a column-assisted electric power steering system, also known as an upstream-assisted system. However, the rotation angle detection device of the present invention can also be applied to a downstream-assisted electric power steering system. Hereinafter, examples of applying the rotation angle detection device of the present invention to electric power steering systems using a single pinion-assisted system, a rack-assisted system, and a double pinion-assisted system will be described as examples of downstream-assisted electric power steering systems.

[0132] Furthermore, in the case of downstream auxiliary methods, for waterproofing purposes, the motor 20, rotation angle sensor 21, and ECU 30 do not need to be separate structures, but can be arranged as follows: Figures 10-12 The dashed line shows an integrated MCU (Motor Control Unit).

[0133] Figure 10 This illustrates a structural example of the rotation angle detection device of the present invention applied to an electric power steering system with single pinion assist. The steering wheel 1 is connected to one side of the intermediate shaft via a universal joint 4a of the steering shaft 2. Additionally, an input side shaft 4c with a torsion bar (not shown) is connected to the other side of the universal joint 4b.

[0134] The pinion rack mechanism 5 includes a pinion (gear) 5a, a rack 5b, and a pinion shaft 5c. The input side shaft 4c is connected to the pinion rack mechanism 5 via a torsion bar (not shown), which twists due to the deviation in the rotation angle between the input side shaft 4c and the pinion rack mechanism 5. The torque sensor 10 electromagnetically measures the torsion angle of the torsion bar as the steering torque Th of the steering wheel 1.

[0135] The motor 20, which provides steering force to the auxiliary steering wheel 1, is connected to the pinion shaft 5c via the reduction gear 3. The rotation angle sensor 21 calculates the rotation angle information of the motor rotation shaft of the motor 20 in the same manner as in the above embodiment.

[0136] Figure 11 This illustrates a structural example of applying the rotation angle detection device of the present invention to an electric power steering device using a rack-assisted method. A helical groove (not shown) is formed on the outer peripheral surface of the rack rod 5b, and a similarly led helical groove (not shown) is also formed on the inner peripheral surface of the nut 51. A ball screw is formed by arranging multiple rolling elements in the rolling path formed by these helical grooves.

[0137] A belt 54 is wound around a drive pulley 52 connected to the rotating shaft 20a of the motor 20 that provides steering force to the auxiliary steering wheel 1, and a driven pulley 53 connected to a nut 51. The rotational motion of the rotating shaft 20a is converted into the linear motion of the rack 5b. The rotation angle sensor 21 calculates the rotation angle information of the motor rotating shaft of the motor 20 in the same manner as in the above embodiment.

[0138] Figure 12 This illustrates a structural example of the rotation angle detection device of the present invention applied in an electric power steering system with dual pinion assist. In addition to the pinion shaft 5c and pinion 5a, the electric power steering system with dual pinion assist also has a second pinion shaft 55, a second pinion 56, and a rack rod 5b having a first rack tooth (not shown) meshing with the pinion 5a and a second rack tooth (not shown) meshing with the second pinion 56.

[0139] The second pinion shaft 55 is connected to the motor 20, which has the steering force of the auxiliary steering wheel 1, via the reduction gear 3. The rotation angle sensor 21 calculates the rotation angle information of the motor rotation shaft of the motor 20 in the same way as in the above embodiment.

[0140] (Effects of the implementation method)

[0141] (1) The ECU 30 includes: current detection units 35a to 35f, which detect the current flowing through the switching element based on the voltage drop of a resistor element connected in series with the switching element of either the upper or lower arm of the PWM-controlled multiphase inverter; a correction value calculation unit 50b, which calculates an offset correction value based on the detected current value of the current detected by the current detection units 35a to 35f during the period when the switching element is off in PWM control, and maintains and updates the calculated offset correction value; and a correction unit 50c, which corrects the detected current value of the current detected by the current detection units 35a to 35f during the period when the switching element is on based on the offset correction value maintained by the correction value calculation unit 50b. If either of the aforementioned switching elements is a lower arm switching element and the duty cycle of the PWM control is below the lower duty cycle limit, or if either of the aforementioned switching elements is an upper arm switching element and the duty cycle is above the upper duty cycle limit, the correction value calculation unit 50b does not update the offset correction value.

[0142] Therefore, it is possible to avoid the reduction in offset current detection accuracy due to the inability to properly sample the detection values ​​of current detection units 35a to 35f during the period when the switching element of the lower arm is open when the duty cycle is small. Alternatively, it is possible to avoid the reduction in offset current detection accuracy due to the inability to properly sample the detection values ​​of current detection units 35a to 35f during the period when the switching element of the upper arm is open when the duty cycle is large. As a result, the offset current generated in the current detector that detects the current of the switching element of the multi-phase inverter can be detected with high accuracy in PWM control.

[0143] (2) If the switching element of either of the above is a switching element of the lower arm and the duty cycle of at least one phase of the multiphase inverter is below the lower duty cycle limit, or if the switching element of either of the above is a switching element of the upper arm and the duty cycle of at least one phase of the multiphase inverter is above the upper duty cycle limit, the offset correction value of the other phases of the multiphase inverter may not be updated.

[0144] Therefore, when calculating the offset correction values ​​for other phases, the influence of noise caused by the switching of switching elements can be avoided.

[0145] (3) The correction value calculation unit 50b can calculate the average value of the current detected by the current detection units 35a to 35f during the specified length of time that the switching element is disconnected as the offset correction value.

[0146] This allows for the removal of minute noise in the detection values ​​of the current detection units 35a to 35f.

[0147] (4) The correction value calculation unit 50b may not update the offset correction value based on the detection value exceeding the upper limit if the current detected by the current detection unit 35a to 35f exceeds the upper limit during the period when the switching element is off.

[0148] Therefore, it is possible to avoid the reduction in the detection accuracy of the offset current due to abnormal detection values ​​of the current detection units 35a to 35f.

[0149] (5) If the current detected by the current detection units 35a to 35f exceeds the upper limit value in any phase of the multiphase inverter during the period when the switching element is off, and the current detected by the current detection units 35a to 35f does not exceed the upper limit value in other phases of the multiphase inverter during the period when the switching element is off, the offset correction value in other phases can be updated.

[0150] Even if an outlier is detected in one phase, it will not hinder the calculation of the offset correction value as long as no outliers are detected in other phases. Therefore, by not prohibiting the updating of the offset correction value in other phases, it is possible to prohibit the updating of the offset correction value to a certain extent.

[0151] Explanation of reference numerals in the attached figures

[0152] 1…Steering wheel, 2…Steering shaft, 3…Reduction gear, 4a, 4b…Universal joint, 4c…Input side shaft, 5…Pinary rack and pinion mechanism, 5a…Pinary gear, 5b…Rack, 5c…Pinary gear shaft, 6a, 6b…Tie rod, 7, 7b…Wheel hub unit, 8L, 8R…Steering wheel, 10…Torque sensor, 11…Ignition switch, 12…Vehicle speed sensor, 13…Battery, 14…Steering angle sensor, 20…Motor, 20a…Rotating shaft, 21…Rotation angle sensor, 30…Electronic control unit, 31…Control and computing unit, 32a…First system gate drive circuit, 32b…Second system gate drive circuit, 33a…First system inverter, 33b…Second system inverter, 3 4…Motor speed calculation unit, 35a~35f…Current detection unit, 36…Differential amplifier circuit, 37…Low-pass filter (LPF), 40…Current command value calculation unit, 41, 42, 50c…Subtractor, 43…Current limiting unit, 44…Proportional-integral control unit, 45…2-phase / 3-phase conversion unit, 46a~46c…Current detection value correction unit, 47…3-phase / 2-phase conversion unit, 48…Angular velocity conversion unit, 50a…Scale conversion unit, 50b…Correction value calculation unit, 50c…Correction unit, 50d…Gain correction value storage unit, 50e…Multiplier, 51…Nut, 52…Drive pulley, 53…Driven pulley, 54…Belt, 55…Second pinion shaft, 56…Second pinion.

Claims

1. A current detection device, characterized in that, have: The current detection unit detects the current flowing through the switching element based on the voltage drop of the resistive element connected in series with the switching element of either the upper or lower arm of the PWM-controlled multiphase inverter. The correction value calculation unit calculates the offset correction value based on the current detection value detected by the current detection unit during the period when the switching element is off in PWM control, and maintains and updates the calculated offset correction value. as well as The correction unit corrects the detected current value by the current detection unit during the period when the switching element is turned on, using the offset correction value maintained by the correction value calculation unit. When the switching element is a lower arm switching element and the duty cycle of the PWM control is below the lower duty cycle limit, or when the switching element is an upper arm switching element and the duty cycle is above the upper duty cycle limit, the correction value calculation unit does not update the offset correction value. When the switching element is a lower arm switching element and the duty cycle in at least one phase of the multiphase inverter is below the lower duty cycle limit, or when the switching element is an upper arm switching element and the duty cycle in at least one phase of the multiphase inverter is above the upper duty cycle limit, the correction value calculation unit does not update the offset correction value in the other phases of the multiphase inverter.

2. The current detection device according to claim 1, characterized in that, The correction value calculation unit calculates the average value of the current detected by the current detection unit during the specified length of time the switching element is off as the offset correction value.

3. The current detection device according to claim 1 or 2, characterized in that, If the detected current value detected by the current detection unit exceeds the upper limit value during the period when the switching element is off, the correction value calculation unit does not update the offset correction value based on the detected value exceeding the upper limit value.

4. The current detection device according to claim 3, characterized in that, If the current detected by the current detection unit in any phase of the multiphase inverter exceeds the upper limit value during the period when the switching element is open, and the current detected by the current detection unit in other phases of the multiphase inverter does not exceed the upper limit value during the period when the switching element is open, the correction value calculation unit updates the offset correction value in the other phases.

5. A motor control device, characterized in that, have: A multiphase inverter, which has switching elements; The current detection device according to any one of claims 1 to 4 detects the current flowing through the switching element; as well as The controller controls the multiphase inverter based on the current value detected by the current detection device.

6. An electric power steering device, characterized in that, have: The motor control device according to claim 5; and A multiphase motor, which is controlled by the motor control device. The electric power steering device provides steering assistance to the vehicle's steering system through the multiphase motor.

7. A current detection device, characterized in that, have: The current detection unit detects the current flowing through the switching element based on the voltage drop of the resistive element connected in series with the switching element of either the upper or lower arm of the PWM-controlled multiphase inverter. The correction value calculation unit calculates the offset correction value based on the current detection value detected by the current detection unit during the period when the switching element is off in PWM control, and maintains and updates the calculated offset correction value. as well as The correction unit corrects the detected current value by the current detection unit during the period when the switching element is turned on, using the offset correction value maintained by the correction value calculation unit. When the switching element is a lower arm switching element and the duty cycle of the PWM control is below the lower duty cycle limit, or when the switching element is an upper arm switching element and the duty cycle is above the upper duty cycle limit, the correction value calculation unit does not update the offset correction value. If the detected current value by the current detection unit exceeds the upper limit value during the period when the switching element is off, the correction value calculation unit does not update the offset correction value based on the detected value exceeding the upper limit value. If the current detected by the current detection unit in any phase of the multiphase inverter exceeds the upper limit value during the period when the switching element is open, and the current detected by the current detection unit in other phases of the multiphase inverter does not exceed the upper limit value during the period when the switching element is open, the correction value calculation unit updates the offset correction value in the other phases.

8. A motor control device, characterized in that, have: A multiphase inverter, which has switching elements; The current detection device of claim 7 detects the current flowing through the switching element; and The controller controls the multiphase inverter based on the current value detected by the current detection device.

9. An electric power steering device, characterized in that, have: The motor control device according to claim 8; and A multiphase motor, which is controlled by the motor control device. The electric power steering device provides steering assistance to the vehicle's steering system through the multiphase motor.

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