Motor control device, motor control method, and motor control system

Abstract

The invention relates to a motor control device, a motor control method and a motor control system. In the following structure, the length of a current detection section is changed based on the voltage of a DC power supply of an inverter. In a current detection section corresponding to a combination of ON and OFF of a PWM signal, an output signal of a one-shunt current detector is sampled to detect a phase current of a motor, and the motor is controlled via an inverter on the basis of the detected phase current. As a result, it is possible to easily suppress a change in motor torque caused by a change in inverter voltage.

Description

Technical Field

[0001] The present invention relates to a motor control device, a motor control method and a motor control system. Background Art

[0002] The motor control device of Patent Document 1 includes: a PWM signal generation unit that generates PWM (Pulse Width Modulation) signals with mutually offset phases; an inverter circuit driven by the PWM signal; a single shunt resistor for detecting the motor current in each phase; a current detection unit that detects the motor current of the first phase at a first timing and the motor current of the second phase at a second timing based on the current flowing through the shunt resistor; and a correction unit that corrects the detected value of the motor current of the first phase according to a first offset value and corrects the detected value of the motor current of the second phase according to a second offset value.

[0003] Furthermore, the motor control device of Patent Document 1 includes a power supply voltage detection unit that detects a power supply voltage applied to the inverter circuit, and an offset value changing unit that changes a first offset value and a second offset value according to the power supply voltage detected by the power supply voltage detection unit.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-121204 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, in order to prevent the motor torque from changing due to the increase or decrease in the voltage of the inverter's DC power supply (hereinafter referred to as the inverter voltage), when the offset value is changed according to the inverter voltage, since the suppression of torque changes depends on the resolution of current detection, there is a problem that it is difficult to easily suppress the change in motor torque caused by the change in the inverter voltage.

[0009] The present invention has been made in view of the existing actual situation, and an object of the present invention is to provide a motor control device, a motor control method, and a motor control system that can easily suppress changes in motor torque caused by changes in inverter voltage.

[0010] Means for solving problems

[0011] According to the present invention, in one embodiment thereof, in the following structure, the length of the current detection interval is changed based on the voltage of the DC power supply. The structure is a structure in which the output signal of a current detector that detects the current flowing between an inverter driven by a PWM signal and the DC power supply of the inverter is sampled in the current detection interval corresponding to the combination of on (ON) and off (OFF) of the PWM signal to detect the phase current of the motor, and the motor is controlled via the inverter based on the detected phase current.

[0012] Effects of the Invention

[0013] According to the present invention, it is possible to easily suppress a change in motor torque caused by a change in inverter voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a block diagram showing the overall structure of a motor control system.

[0015] Figure 2 This is a block diagram showing functional units related to correction of the current detection interval width.

[0016] Figure 3 This is a timing chart showing the current detection period in the 1-shunt method.

[0017] Figure 4 It shows Figure 3 Circuit diagram showing the flow of current in the current detection interval A.

[0018] Figure 5 It shows Figure 3 Circuit diagram showing the flow of current in the current detection interval B.

[0019] Figure 6 This is a timing chart showing a process of shifting the phase of a PWM signal.

[0020] Figure 7 2 is a timing chart showing the difference in offset caused by the difference in inverter voltage.

[0021] Figure 8 1 is a timing chart showing correction of the current detection interval width according to the inverter voltage.

[0022] Figure 9 : is a timing chart showing the correlation between the current detection interval width and the offset amount.

[0023] Figure 10 : is a flowchart showing the process of limiting the current detection interval width.

[0024] Figure 11This is a flowchart showing a process of performing correction according to the rotation speed condition.

[0025] Figure 12 This is a flowchart showing a process of adding hysteresis to execution and stop of correction.

[0026] Figure 13 This is a block diagram showing the low-pass filter processing function of the inverter voltage signal.

[0027] Figure 14 This is a block diagram showing a low-pass filter processing function of an output signal of a segment width correction unit.

[0028] Figure 15 : is a timing chart showing the time diffusion process of the interval width correction.

[0029] Figure 16 This is a line graph showing the steering torque when the current detection interval width is not corrected.

[0030] Figure 17 : is a line graph showing the steering torque when the current detection interval width is corrected. DETAILED DESCRIPTION

[0031] Hereinafter, embodiments of a motor control device, a motor control method, and a motor control system according to the present invention will be described with reference to the accompanying drawings.

[0032] Figure 1 1 is a system diagram showing a basic configuration of a motor control system 1 including a motor control device.

[0033] Furthermore, the motor control system 1 is applied to, for example, controlling a motor that generates steering force in an electric power steering device mounted on a vehicle.

[0034] The motor control system 1 includes a motor 2 , an inverter circuit 3 , a current detector 4 , an inverter voltage detector 5 , and a motor control device 6 .

[0035] The motor 2 is a three-phase brushless motor having a three-phase winding group consisting of a U-phase coil, a V-phase coil, and a W-phase coil.

[0036] The motor 2 includes a rotor angle sensor 2A that detects the angle of a rotor of the motor 2 .

[0037] The inverter circuit 3 is a three-phase bridge circuit composed of six switching elements 3a-3f. It converts the DC power supply 7 into three-phase AC using PWM signals to drive the motor 2 with a sinusoidal wave (in other words, 180-degree current conduction).

[0038] As the switching elements 3 a to 3 f , semiconductor switching elements such as FETs (Field effect transistors) are used.

[0039] Furthermore, the inverter circuit 3 includes a smoothing capacitor 8 connected in parallel with the DC power supply 7 .

[0040] The current detector 4 is a device that detects the current flowing between the inverter circuit 3 and the DC power supply 7 , that is, the bus current of the inverter circuit 3 .

[0041] The current detector 4 includes a shunt resistor 4A connected in series between the inverter circuit 3 and ground, and detects the current by converting the potential difference between both ends of the shunt resistor 4A into a current value.

[0042] That is, the motor control system 1 is a system that detects the phase current of each phase of the motor 2 using a single-shunt method, and the current detection value by the current detector 4 is sampled at a timing corresponding to the combination of the PWM signals of each phase.

[0043] Furthermore, the inverter voltage detector 5 detects the voltage of the DC power supply 7 serving as the power supply of the inverter circuit 3 , in other words, the inverter voltage.

[0044] The motor control device 6 is an electronic control device including a microcomputer 61 as a control unit or a control means.

[0045] The microcomputer 61 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like.

[0046] The motor control device 6 includes functional units such as a motor control unit 6A, a switching signal generating unit 6B, and an analog / digital converter 6C (hereinafter referred to as an AD converter 6C).

[0047] The motor control unit 6A is a functional unit executed by the microcomputer 61 as software.

[0048] The motor control unit 6A performs AD conversion on the analog output signal of the current detector 4 at a predetermined timing using the AD converter 6C, and obtains the output of the current detector 4 , that is, the detected value of the bus current of the inverter circuit 3 , as a digital signal.

[0049] Then, the motor control unit 6A calculates the current of each phase based on the output of the current detector 4, compares the calculated current of each phase with the command current, and performs feedback control to correct the current of each phase so that the current of each phase approaches the command current, thereby implementing PWM control of the switching elements 3a-3f of the inverter circuit 3.

[0050] The switching signal generating unit 6B acquires the switching timings THiu*, TLou*, THiv*, TLov*, THiw*, and TLow* generated by the motor controlling unit 6A (specifically, the switching timing setting unit 20 described later).

[0051] The switching signal generating unit 6B then generates switching signals, i.e., PWM signals (in other words, gate signals), for the switching elements 3a-3f of the inverter circuit 3 based on the switching timings THiu*, TLou*, THiv*, TLov*, THiw*, and TLow*, using the carrier period Tc as a time reference, and supplies the generated PWM signals to the switching elements 3a-3f of the inverter circuit 3.

[0052] The motor control unit 6A has various functional units including a current detection unit 11, a rotation angle / rotation speed detection unit 12, an angular velocity calculation unit 13, a three-phase dq axis conversion unit 14, a first phase compensation unit 15, a current control unit 16, a dq axis three-phase conversion unit 17, a second phase compensation unit 18, a PWM duty cycle calculation unit 19, a switch timing setting unit 20, an AD timing setting unit 21, an inverter voltage detection unit 22, and a carrier frequency setting unit 23.

[0053] The current detection unit 11 reproduces the three-phase currents Iu, Iv, and Iw flowing through the motor 2 based on the motor rotation speed ω and the bus current IDC of the inverter circuit 3 .

[0054] Furthermore, the current detection unit 11 sets a current detection interval in which the current detector 4 can detect the phase current of the maximum voltage phase and a current detection interval in which the current detector 4 can detect the phase current of the minimum voltage phase, based on the combination of on and off states of the PWM signal. The current detection unit 11 calculates the phase current of the intermediate voltage phase based on the detected values ​​of the phase current of the maximum voltage phase and the detected values ​​of the phase current of the minimum voltage phase.

[0055] The rotation angle / speed detection unit 12 obtains the output of the rotor angle sensor 2A, outputs a signal of the motor electrical angle θe0, further calculates the motor speed ω from the difference between the previous value and the current value of the motor electrical angle θe0, and outputs a signal of the motor speed ω.

[0056] The angular velocity calculation unit 13 calculates the electrical angular velocity ωe from the difference between the current value and the previous value of the motor electrical angle θe0 and outputs a signal of the electrical angular velocity ωe.

[0057] The first phase compensator 15 obtains signals of the motor electrical angle θe0 , the electrical angular velocity ωe, and the carrier period Tc set by the carrier frequency setting unit 23 .

[0058] Then, the first phase compensator 15 outputs a signal of the motor electrical angle θe1 ​​in which the motor electrical angle θe0 is corrected as if the rotation angle was detected at the current detection timing, taking into account the time difference between the current detection timing and the rotation angle detection timing.

[0059] The three-phase dq-axis converter 14 performs coordinate conversion for vector control to convert the three-phase AC current into a two-axis DC current based on the three-phase currents Iu, Iv, and Iw and the motor electrical angle θe1, and outputs a signal of the flux (d-axis) current Id and a signal of the torque (q-axis) current Iq.

[0060] The current control unit 16 is based on the command current Id * 、Iq * , actual current Id, Iq and electrical angular velocity ωe, outputs the d-axis command voltage Vd* and q-axis command voltage Vq* signals so that the actual current Id, Iq obtained by the three-phase dq axis conversion unit 14 follows the d-axis command current Id provided from the outside * , q-axis command current Iq * .

[0061] The second phase compensator 18 obtains the signals of the motor electrical angle θe0, the electrical angular velocity ωe, and the carrier period Tc, and outputs a signal of the motor electrical angle θe2 which corrects the motor electrical angle θe0 as if the rotation angle detection was performed at the voltage reflection timing, taking into account the time deviation between the voltage reflection timing and the timing of the rotation angle detection.

[0062] The dq-axis 3-phase conversion unit 17 performs coordinate conversion to convert the 2-axis voltage instructions Vd* and Vq* for vector control into 3-phase voltage instructions Vu*, Vv*, and Vw* based on the d-axis instruction voltage Vd* and the q-axis instruction voltage Vq*, and the motor electrical angle θe2, and outputs the signals of the 3-phase voltage instructions Vu*, Vv*, and Vw*.

[0063] The inverter voltage detection unit 22 obtains the output of the inverter voltage detector 5 and detects the inverter voltage VINV, that is, the voltage of the DC power supply 7 which is the power supply of the inverter circuit 3 .

[0064] The PWM duty ratio calculation unit 19 calculates three-phase command duty ratios DUu*, DUv*, and DUw* based on the ratios of the three-phase voltage commands Vu*, Vv*, and Vw* to the inverter voltage VINV.

[0065] The switching timing setting unit 20 compares the three-phase command duty ratios DUu*, DUv*, and DUw* with the carrier period Tc, and outputs the switching timings THiu*, TLou*, THiv*, TLov*, THiw*, and TLow* of the switching elements 3a to 3f of the inverter circuit 3, respectively.

[0066] The switching signal generating unit 6B uses the carrier period Tc as a time reference and generates the switching signals, i.e., PWM signals, for the switching elements 3a-3f of the inverter circuit 3 based on the switching timings THiu*, TLou*, THiv*, TLov*, THiw*, and TLow*, and provides the generated PWM signals to the switching elements 3a-3f of the inverter circuit 3.

[0067] The AD timing setting unit 21 sets AD timings TADI, TADθ, and TADV for AD-converting the bus current IDC, the motor electrical angle θe0, and the inverter voltage VINV of the inverter circuit 3 based on the switching timings THiu*, TLou*, THiv*, TLov*, THiw*, and TLow*.

[0068] The AD converter 6C performs AD conversion, that is, samples the bus current IDC, the motor electrical angle θe0, and the inverter voltage VINV based on the AD timings TADI, TADθ, and TADV, using a signal synchronized with a control cycle generated based on the carrier cycle Tc.

[0069] Then, the motor control unit 6A obtains the switching timings THiu*, TLou*, THiv*, TLov*, THiw*, and TLow* of the switching elements 3a-3f based on the bus current IDC, the motor electrical angle θe0, and the inverter voltage VINV sampled by the AD converter 6C.

[0070] The carrier frequency setting unit 23 selects one of a plurality of previously set carrier cycles Tc based on the control conditions of the motor 2 and the like, and sets a control cycle Tcc that is an integral multiple of the carrier cycle Tc.

[0071] Then, the carrier frequency setting unit 23 outputs signals of the carrier period Tc and the control period Tcc to the angular velocity calculation unit 13, the first phase compensation unit 15, the current control unit 16, the second phase compensation unit 18, the switch timing setting unit 20, the switch signal generation unit 6B, the AD timing setting unit 21 and the AD conversion unit 6C.

[0072] Furthermore, if there is a detection error in the motor electrical angle θe0 detected by the rotor angle sensor 2A, the angular velocity ωe calculated by the angular velocity calculation unit 13 may vibrate.

[0073] Therefore, the angular velocity calculation unit 13 obtains the angular velocity ωe by including a process of removing the vibration component of the angular velocity ωe using a digital filter.

[0074] Figure 2 1 is a block diagram showing a characteristic configuration of the motor control unit 6A of the motor control system 1 in the present embodiment.

[0075] The motor control unit 6A of the motor control system 1 has Figure 1 In addition to the basic configuration shown, the current detection interval width correction unit 24 , the PWM phase manipulation amount calculation unit 25 , and the current detection possibility determination unit 26 are further provided.

[0076] Here, the current detection interval width corrector 24 is a functional unit that corrects the width of the current detection interval (in other words, the duration of the current detection interval) during which the current detection unit 11 detects the phase current of the motor 2 , based on the inverter voltage VINV.

[0077] The PWM phase manipulation amount calculation unit 25 is a functional unit that calculates an amount by which the phases of the PWM signals of the respective phases are shifted from each other in order to ensure the width of the current detection interval set by the current detection interval width correction unit 24 .

[0078] Furthermore, the current detection possibility determination unit 26 determines whether current detection is possible based on whether the width of the current detection interval is set to be equal to or greater than a minimum width, and outputs information on the current detection possibility to the current detection unit 11 and the current control unit 16 .

[0079] The current detection interval is an interval in which the current corresponding to the phase current of one of the three phases flows to the shunt resistor 4A, and is an interval from the timing of the combined switching of the on / off switching signals, i.e., the PWM signals, of the switching elements 3a-3f to the AD conversion and sampling of the output signal of the current detector 4.

[0080] Moreover, the width of the current detection interval is set to be longer than a reference time that takes into account the delay time of the switching elements 3a-3f, the stabilization time of the circuit, the AD conversion time, etc., and the time point that has passed at least the reference time since the timing of the combined switching of the on and off of the PWM signal is set as the AD conversion timing, that is, the end of the current detection interval.

[0081] Hereinafter, the functions of the current detection interval width correction unit 24 , the PWM phase manipulation amount calculation unit 25 , and the current detection possibility determination unit 26 will be described in detail.

[0082] The current detection interval width correction unit 24 obtains a reference value TSPini as a reference length of the current detection interval width and an input value INP including the inverter voltage VINV, calculates and outputs a current detection interval width TSPadj and a current detection timing correction value TADIadj obtained by correcting the reference value TSPini according to the inverter voltage VINV.

[0083] The correction of the current detection interval corresponding to the inverter voltage VINV performed by the current detection interval width correction unit 24 is a process for performing the following operation: even if the inverter voltage VINV changes, the offset generated in the current detected by the current detector 4 of the single-shunt current sensor in the current detection interval is fixed.

[0084] Then, the current detection interval width correction unit 24 increases the current detection interval width TSPadj as the inverter voltage VINV decreases.

[0085] In order to ensure the current detection interval width TSpadj, the PWM phase operation amount calculation unit 25 calculates and outputs the switching timing correction values ​​ΔTHiu*, ΔTLou*, ΔTHiv*, ΔTLov*, ΔTHiw*, and ΔTLow* based on the current detection interval width TSpadj and the three-phase command duty ratios DUu*, DUv*, and DUw*.

[0086] That is, when the current detection interval width TSpadj cannot be ensured without performing the process of shifting the phases of the PWM signals of each phase, the PWM phase operation amount calculation unit 25 sets the phase shift amount of the PWM signal so that the current detection interval width TSpadj is ensured by shifting the phases of the PWM signals.

[0087] Here, in the correction of the current detection interval width TSPadj corresponding to the inverter voltage VINV, since the lower the inverter voltage VINV, the longer the current detection interval width TSPadj, the lower the inverter voltage VINV, the larger the phase shift amount in the process of shifting the phases of the PWM signals to ensure the current detection interval width TSPadj is set to.

[0088] Therefore, when the three-phase command duty ratios DUu*, DUv*, and DUw* are the same, the lower the inverter voltage VINV, the larger the phase offset of the PWM signal is set. This is equivalent to implementing a process in which the lower the inverter voltage VINV, the longer the current detection interval width TSPadj is.

[0089] Then, the switching timing setting unit 20 calculates and outputs the switching timings THiu*, TLou*, THiv*, TLov*, THiw*, and TLow* based on the three-phase command duty ratios DUu*, DUv*, and DUw*, the carrier period Tc, and the switching timing correction values ​​ΔTHiu*, ΔTLou*, ΔTHiv*, ΔTLov*, ΔTHiw*, and ΔTLow*.

[0090] That is, the switching timing setting unit 20 corrects the basic switching timings THiu*, TLou*, THiv*, TLov*, THiw*, and TLow* calculated based on the three-phase command duty ratios DUu*, DUv*, and DUw* and the carrier period Tc based on the switching timing correction values ​​ΔTHiu*, ΔTLou*, ΔTHiv*, ΔTLov*, ΔTHiw*, and ΔTLow*.

[0091] The AD timing setting unit 21 calculates the current detection timing TADI based on the switching timings THiu*, TLou*, THiv*, TLov*, THiw*, TLow*, the current detection timing correction value TADIadj, and the carrier period Tc, and outputs a signal of the current detection timing TADI to the AD converter 6C.

[0092] The current detection possibility determination unit 26 determines whether the current detector 4 can detect the phase current based on the current detection interval width reference value TSPini and the switching timings THiu*, TLou*, THiv*, TLov*, THiw*, and TLow*, and outputs a signal indicating the determination result.

[0093] Hereinafter, the detection process of the phase current of the motor 2 in the motor control system 1 will be described in detail.

[0094] Figure 3-Figure 5 This is a diagram for explaining basic bus current detection processing.

[0095] Figure 3 One embodiment of the relationship between the U-phase, V-phase, and W-phase PWM signals 101 , 102 , and 103 and the bus current 104 detected by the current detector 4 is shown.

[0096] The PWM signals 101 , 102 , and 103 are PWM signals supplied to the switching elements of the upper arms of the respective phases, and the switching elements of the upper arms and the switching elements of the lower arms are driven in a complementary manner.

[0097] exist Figure 3 In FIG. 1 , the U-phase PWM signal 101 is turned on at a U-phase ON timing 105 and is turned off at a U-phase OFF timing 108 .

[0098] Furthermore, the V-phase PWM signal 102 is turned on at a V-phase ON timing 106 and is turned off at a V-phase OFF timing 109 .

[0099] Furthermore, the W-phase PWM signal 103 is turned on at the W-phase ON timing 107 and is turned off at the W-phase OFF timing 110 .

[0100] Here, the ON / OFF timings of the PWM signals 101 , 102 , and 103 are in the order of U-phase ON timing 105 , V-phase ON timing 106 , W-phase ON timing 107 , W-phase OFF timing 110 , V-phase OFF timing 109 , and U-phase OFF timing 108 in time series.

[0101] Then, in Figure 3 The on period of the U-phase PWM signal 101 is the longest, the on period of the W-phase PWM signal 103 is the shortest, and the on period of the V-phase PWM signal 102 is in the middle. The U-phase is the maximum voltage phase, the W-phase is the minimum voltage phase, and the V-phase is the intermediate voltage phase.

[0102] The bus current 104 detected by the current detector 4 is zero when the U-phase PWM signal 101 , the V-phase PWM signal 102 , and the W-phase PWM signal 103 are all on, that is, during the on period of the W-phase PWM signal.

[0103] Furthermore, the bus current 104 detected by the current detector 4 is zero when the U-phase PWM signal 101 , the V-phase PWM signal 102 , and the W-phase PWM signal 103 are all OFF, that is, before the U-phase ON timing 105 and after the U-phase OFF timing 108 .

[0104] On the other hand, the current detection interval A in which the U-phase PWM signal 101 is on, the V-phase PWM signal 102 is on, and the W-phase PWM signal 103 is off is a first current detection interval in which the W-phase current Iw flows through the shunt resistor 4A of the current detector 4 .

[0105] Figure 4 The on / off states of the switching elements 3 a - 3 f in the current detection interval A are shown.

[0106] In the current detection interval A, the switching element 3a of the upper arm of the U phase is turned on, the switching element 3b of the lower arm of the U phase is turned off, the switching element 3c of the upper arm of the V phase is turned on, the switching element 3d of the lower arm of the V phase is turned off, the switching element 3e of the upper arm of the W phase is turned off, and the switching element 3f of the lower arm of the W phase is turned on.

[0107] Therefore, in the current detection interval A, the current flowing from the switching element 3a of the upper arm of the U phase to the U phase of the motor 2 and the current flowing from the switching element 3c of the upper arm of the V phase to the V phase of the motor 2 converge at the connection part of the star connection, and the current flows to the shunt resistor 4A of the current detector 4 through the W phase of the motor 2 and the switching element 3f of the lower arm of the W phase.

[0108] Therefore, the bus current 104 detected by the current detector 4 in the current detection interval A becomes the negative W-phase current Iw. By detecting the current flowing through the shunt resistor 4A in the current detection interval A, the phase current Iw of the minimum voltage phase, namely the W-phase, can be detected.

[0109] In the present embodiment, in the star-connected three-phase winding of the motor 2 , the current flowing from the connection portion of the three-phase winding to the winding is a negative current, and the current flowing from the winding to the connection portion is a positive current.

[0110] The current detection section B in which the U-phase PWM signal 101 is on, the V-phase PWM signal 102 is off, and the W-phase PWM signal 103 is off is a section in which the U-phase current Iu flows through the shunt resistor 4A of the current detector 4 .

[0111] Figure 5 The on / off states of the switching elements 3 a - 3 f in the current detection interval B are shown.

[0112] In interval B, the switching element 3a of the upper arm of the U phase is turned on, the switching element 3b of the lower arm of the U phase is turned off, the switching element 3c of the upper arm of the V phase is turned off, the switching element 3d of the lower arm of the V phase is turned on, the switching element 3e of the upper arm of the W phase is turned off, and the switching element 3f of the lower arm of the W phase is turned on.

[0113] Therefore, in the current detection period B, the current flowing from the switching element 3 a of the upper arm of the U phase to the U phase of the motor 2 branches from the star-connected connection portion into the V phase and the W phase.

[0114] Then, the current flowing into the V phase passes through the switching element 3 d of the lower arm of the V phase, and the current flowing into the W phase passes through the switching element 3 f of the lower arm of the W phase. The current flowing into the V phase and the current flowing into the W phase merge and flow through the shunt resistor 4A of the current detector 4.

[0115] Here, since the sum of the V-phase current and the W-phase current is the U-phase current, the current detected by the current detector 4 in the second current detection interval, i.e., the current detection interval B, becomes the positive U-phase current Iu. By detecting the current flowing through the shunt resistor 4A in the current detection interval B, the phase current Iu of the maximum voltage phase, i.e., the U-phase, can be detected.

[0116] Furthermore, the three-phase currents Iu, Iv, and Iw satisfy the relationship "Iu + Iv + Iw = 0." Therefore, if W-phase current Iw is detected in current detection interval A and U-phase current Iu is detected in current detection interval B, V-phase current Iv can be calculated using the relationship "Iu + Iv + Iw = 0."

[0117] That is, if the current detector 4 detects the phase currents of two phases out of the three phases, the phase current of the remaining phase can be obtained by calculation without being detected by the current detector 4 .

[0118] As a combination pattern of the on / off of the PWM signals 101, 102, 103 that can detect the two-phase current by the current detector 4 within one PWM cycle, according to the combination of the maximum voltage phase, the minimum voltage phase, and the intermediate voltage phase, except Figure 3 In addition to the modes shown, there are the following 5 modes.

[0119] When the maximum voltage phase is the U phase and the minimum voltage phase is the V phase, the negative V phase current Iv can be detected by the current detector 4 in the interval where the U phase PWM signal 101 is on, the V phase PWM signal 102 is off, and the W phase PWM signal 103 is on, and the positive U phase current Iu can be detected by the current detector 4 in the interval where the U phase PWM signal 101 is on, the V phase PWM signal 102 is off, and the W phase PWM signal 103 is off.

[0120] In addition, when the maximum voltage phase is the V phase and the minimum voltage phase is the W phase, the negative W phase current Iw can be detected by the current detector 4 in the interval where the U phase PWM signal 101 is on, the V phase PWM signal 102 is on, and the W phase PWM signal 103 is off, and the positive V phase current Iv can be detected by the current detector 4 in the interval where the U phase PWM signal 101 is off, the V phase PWM signal 102 is on, and the W phase PWM signal 103 is off.

[0121] In addition, when the maximum voltage phase is the V phase and the minimum voltage phase is the U phase, the negative U-phase current Iu can be detected by the current detector 4 in the interval where the U-phase PWM signal 101 is off, the V-phase PWM signal 102 is on, and the W-phase PWM signal 103 is on, and the positive V-phase current Iv can be detected by the current detector 4 in the interval where the U-phase PWM signal 101 is off, the V-phase PWM signal 102 is on, and the W-phase PWM signal 103 is off.

[0122] In addition, when the maximum voltage phase is the W phase and the minimum voltage phase is the U phase, the negative U-phase current Iu can be detected by the current detector 4 in the interval where the U-phase PWM signal 101 is off, the V-phase PWM signal 102 is on, and the W-phase PWM signal 103 is on, and the positive W-phase current Iw can be detected by the current detector 4 in the interval where the U-phase PWM signal 101 is off, the V-phase PWM signal 102 is off, and the W-phase PWM signal 103 is on.

[0123] Furthermore, when the maximum voltage phase is the W phase and the minimum voltage phase is the V phase, the negative V-phase current Iv can be detected by the current detector 4 in the interval where the U-phase PWM signal 101 is on, the V-phase PWM signal 102 is off, and the W-phase PWM signal 103 is on, and the positive W-phase current Iw can be detected by the current detector 4 in the interval where the U-phase PWM signal 101 is off, the V-phase PWM signal 102 is off, and the W-phase PWM signal 103 is on.

[0124] As described above, the interval in which the phase current can be detected by the current detector 4 is determined by the on / off combination of the PWM signals 101, 102, and 103. However, the length of the interval in which the on / off combination of the PWM signals 101, 102, and 103 is maintained varies depending on the three-phase command duty ratios DUu*, DUv*, and DUw*, and thus the necessary length of the current detection interval cannot be ensured.

[0125] Therefore, the PWM phase operation amount calculation unit 25 of the motor control unit 6A maintains the pulse width corresponding to the three-phase command duty ratios DUu*, DUv*, and DUw*, and shifts the phases of the PWM signals, thereby ensuring the necessary length of the current detection interval (in other words, the current detection interval width).

[0126] Figure 6 This is a timing chart illustrating a process of shifting the phases of PWM signals, and illustrates a case where the current detector 4 detects the phase current Iu of the maximum voltage phase, that is, the U phase, and the phase current Iw of the minimum voltage phase, that is, the W phase.

[0127] Figure 6 The upper part shows the PWM signals in a state where the processing of shifting the phases of the PWM signals is not performed.

[0128] also, Figure 6 The middle portion of shows the PWM signal in a state where the phases of the PWM signals are shifted in order to ensure the reference value T SPini of the current detection interval width.

[0129] and then, Figure 6The lower portion shows PWM signals in a state where the phases of the PWM signals are shifted in order to ensure a current detection interval width TSPadj (TSPadj>TSPini) obtained by correcting the reference value TSPini of the current detection interval width according to the inverter voltage VINV.

[0130] exist Figure 6 In the upper portion of , the U-phase current detection interval width 201 is the difference between the U-phase closing timing and the V-phase closing timing, and the W-phase current detection interval width 202 is the difference between the W-phase closing timing and the V-phase closing timing.

[0131] The U-phase current detection interval width 201 and the W-phase current detection interval width 202 vary according to the three-phase command duty ratios DUu*, DUv*, and DUw*, but the minimum interval width required for current detection is predetermined as a reference value TSPini.

[0132] The reference value T SPini of the current detection interval width is determined by taking into account the delay time of the switching elements 3 a - 3 f, the dead time to prevent the switching elements of the upper arm and the switching elements of the lower arm from being turned on simultaneously, the settling time of the circuit that amplifies and detects the voltage drop generated when current flows through the shunt resistor 4A, and the AD conversion time required for the AD converter 6C to sample the amplified voltage drop.

[0133] Therefore, if the current detection interval width is shorter than the reference value T SPini, the motor control unit 6A cannot obtain a stable current detection value and cannot use it for motor control.

[0134] Therefore, in current detection, it is necessary to ensure a current detection interval width greater than the current detection interval width reference value TSPini, and sample the output of the current detector 4 as a phase current detection value after at least the current detection interval width reference value TSPini has passed from the start point of the current detection interval.

[0135] The motor control unit 6A Figure 6 When the U-phase current detection interval width 201 and the W-phase current detection interval width 202 in the state where the phase shifting process is not performed are shorter than the reference value TSPini, in order to ensure the current detection interval of the reference value TSPini, as shown in FIG. Figure 6 As shown in the middle part of , a process is implemented to shift the phases of the PWM signals.

[0136] Specifically, the PWM phase operation amount calculation unit 25 of the motor control unit 6A calculates the value obtained by subtracting the U-phase current detection interval width 201 from the reference value TSPini, that is, the shortfall in the current detection interval width, as the U-phase PWM offset 203 (in other words, the offset of the U-phase PWM signal). Similarly, the value obtained by subtracting the W-phase current detection interval width 202 from the reference value TSPini is calculated as the W-phase PWM offset 204 (in other words, the offset of the W-phase PWM signal).

[0137] Then, the switching timing setting unit 20 of the motor control unit 6A applies the U-phase PWM offset 203 to the U-phase on timing and the U-phase off timing, and performs offset processing to delay the phase of the U-phase PWM signal by an amount corresponding to the U-phase PWM offset 203. Similarly, the switching timing setting unit 20 applies the W-phase PWM offset 204 to the W-phase on timing and the W-phase off timing, and performs offset processing to advance the phase of the W-phase PWM signal by an amount corresponding to the W-phase PWM offset 204.

[0138] The switching timing setting unit 20 of the motor control unit 6A makes the U-phase current detection interval width 205 and the W-phase current detection interval width 206 after the offset processing equal to the reference value T SPini by the above-mentioned offset processing of the PWM signal.

[0139] Then, the AD timing setting unit 21 of the motor control unit 6A sets the U-phase current detection timing 208 to the end point of the U-phase current detection interval width 205 after the offset processing (in other words, the U-phase closing timing after the offset processing), and sets the W-phase current detection timing 207 to the end point of the W-phase current detection interval width 206 after the offset processing (in other words, the V-phase closing timing).

[0140] In this way, if the current detection interval width of the reference value TSPini is ensured by offset processing of the PWM signal, the output of the current detector 4 can be sampled as the phase current detection value after the delay time of the switching elements 3a-3f, the stabilization time of the circuit, etc., and the motor control unit 6A can control the motor current with high precision.

[0141] Furthermore, in the present embodiment, the current detection interval width correction unit 24 of the motor control unit 6A has a function of correcting the reference value TSPini according to the inverter voltage VINV to set the current detection interval width TSPadj (TSPadj≧TSPini).

[0142] Furthermore, even when the PWM phase operation amount calculation unit 25 of the motor control unit 6A ensures a current detection interval width TSPadj that is longer than the reference value TSPini, as shown in FIG. Figure 6As shown in the lower part of , a process of shifting the phases of the PWM signals is also implemented.

[0143] In detail, when the U-phase current detection interval width 201 and the W-phase current detection interval width 202 are smaller than the current detection interval width TSPadj, the PWM phase operation amount calculation unit 25 of the motor control unit 6A calculates the value obtained by subtracting the U-phase current detection interval width 201 from the current detection interval width TSPadj as the U-phase PWM offset 209, and calculates the value obtained by subtracting the W-phase current detection interval width 202 from the current detection interval width TSPadj as the W-phase PWM offset 210.

[0144] Then, the switching timing setting unit 20 of the motor control unit 6A applies the U-phase PWM offset 209 to the U-phase on timing and the U-phase off timing, and performs offset processing to delay the phase of the U-phase PWM signal by an amount corresponding to the U-phase PWM offset 209. Similarly, the switching timing setting unit 20 applies the W-phase PWM offset 210 to the W-phase on timing and the W-phase off timing, and performs offset processing to advance the phase of the W-phase PWM signal by an amount corresponding to the W-phase PWM offset 210.

[0145] The switching timing setting unit 20 of the motor control unit 6A makes the offset U-phase current detection interval width 211 and the offset W-phase current detection interval width 212 equal to the current detection interval width TSpadj by the offset processing of the PWM signal.

[0146] Then, the AD timing setting unit 21 of the motor control unit 6A sets the U-phase current detection timing 213 to any position between the U-phase current detection interval width 205 and the U-phase current detection interval width 211 starting from the V-phase closing timing, thereby enabling stable detection of the U-phase current Iu.

[0147] Similarly, the AD timing setting unit 21 of the motor control unit 6A can stably detect the W-phase current Iw by setting the W-phase current detection timing 214 to any position between the W-phase current detection interval width 206 and the W-phase current detection interval width 212 starting from the W-phase closing timing.

[0148] In addition, although Figure 6 The mode for detecting positive U-phase current and negative W-phase current is described as an example, but it is obvious that for other phase current detection modes, the required current detection interval width can be ensured by offset processing that shifts the phases of PWM signals.

[0149] Next, the current detection interval width TSPadj corrected according to the inverter voltage VINV will be described.

[0150] Figure 7 1 is a timing chart showing that changes in the three-phase currents in each interval AG of the PWM cycle differ depending on the level of the inverter voltage VINV.

[0151] In section A where the U-phase PWM signal 101 is off, the V-phase PWM signal 102 is off, and the W-phase PWM signal 103 is off, the phase current circulates through the switching elements of the lower arm of the inverter circuit 3 and the motor 2 .

[0152] At this time, the voltages of the three phases are equal, and the voltages converted to the d-axis and q-axis are zero, so the currents of the phases hardly change.

[0153] Furthermore, in section B where U-phase PWM signal 101 is off, V-phase PWM signal 102 is on, and W-phase PWM signal 103 is off, the current changes so as to flow from V-phase to U-phase and W-phase, V-phase current 305 increases, and U-phase current 301 and W-phase current 309 decrease.

[0154] Furthermore, in section C where U-phase PWM signal 101 is off, V-phase PWM signal 102 is on, and W-phase PWM signal 103 is on, the current changes so as to flow from V-phase and W-phase to U-phase, V-phase current 305 and W-phase current 309 increase, and U-phase current 301 decreases.

[0155] The absolute value of the slope of the current change in section C decreases compared to section B in the V-phase current 305 , increases compared to section B in the U-phase current 301 , and is the same as section B in the W-phase current 309 .

[0156] In addition, in the interval D where the U-phase PWM signal 101 is on, the V-phase PWM signal 102 is on, and the W-phase PWM signal 103 is on, the phase current circulates through the switching element of the upper arm of the inverter circuit 3 and the motor 2, and similarly to the interval A, the current of each phase hardly changes.

[0157] In addition, in the interval E where the U-phase PWM signal 101 is on, the V-phase PWM signal 102 is off, and the W-phase PWM signal 103 is on, the current changes so as to flow from the U-phase and W-phase to the V-phase, the V-phase current 305 decreases, and the U-phase current 301 and the W-phase current 309 increase.

[0158] Furthermore, in interval F where U-phase PWM signal 101 is on, V-phase PWM signal 102 is off, and W-phase PWM signal 103 is off, the current changes so as to flow from the U-phase to the V-phase and W-phase, and V-phase current 305 and W-phase current 309 decrease, while U-phase current 301 increases.

[0159] The absolute value of the slope of the current change in section F decreases in the V-phase current 305 , increases in the U-phase current 301 , and remains the same in the W-phase current 309 , compared to section E.

[0160] In section G where the U-phase PWM signal 101 is off, the V-phase PWM signal 102 is off, and the W-phase PWM signal 103 is off, similar to section A, the phase current refluxes through the lower switching element of the inverter circuit 3 and the motor 2 .

[0161] As described above, the waveforms of the currents of each phase vibrate in the interval AG of the PWM cycle. Therefore, the U-phase average current 302 , the V-phase average current 306 , and the W-phase average current 310 flowing on average in the PWM cycle are regarded as the phase currents actually flowing to the respective phases of the motor 2 .

[0162] Here, there is a V-phase current offset 307, which is the difference between the V-phase detection current at the end point of the interval E in which the V-phase current can be detected and the V-phase average current 306. In addition, there is a U-phase current offset 303, which is the difference between the U-phase detection current at the end point of the interval F in which the U-phase current can be detected and the U-phase average current 302.

[0163] That is, when the current flowing through the shunt resistor 4A serving as the DC bus resistance is detected in each current detection interval, the current is detected as a value deviated from the average current of the current actually flowing through each phase.

[0164] Therefore, when the current flowing to the shunt resistor 4A is detected as the phase current in each current detection interval, it is necessary to correct the offset of the detected current by pre-measuring the above-mentioned offset value and storing it, and to calculate the average current actually flowing through each phase based on the current detected in each current detection interval.

[0165] For example, when all three-phase command duty ratios DUu*, DUv*, and DUw* are set to the same value, the average current of each phase becomes zero, but the phase current detected in a single current detection interval becomes a value offset from the average current, so this value can be stored as an offset value.

[0166] In addition, if the U-phase current waveform 304 when the inverter voltage VINV is a high voltage is compared with the U-phase current waveform 301 when the inverter voltage VINV is a low voltage, then in terms of the slope of the current change in the intervals B, C, E, and F where the current can be detected, the U-phase current waveform 304 at high voltage is larger than the U-phase current waveform 301 at low voltage, and the current change is more rapid.

[0167] Therefore, when the inverter voltage VINV increases or decreases, the V-phase current offset 307 and the U-phase current offset 303 also increase or decrease.

[0168] Therefore, when the detection current is corrected using an offset correction value that is fixed regardless of the inverter voltage VINV, if the inverter voltage VINV changes, an offset occurs between the actual offset amount and the offset correction value used to correct the detection current.

[0169] Then, the motor control is continued in a state where the detection current used for motor control deviates from the actual current actually flowing through the motor 2 , whereby the actual current flowing through the motor 2 deviates from the command current, causing the motor torque to vary.

[0170] Therefore, in order to prevent the motor torque from changing due to the increase or decrease of the inverter voltage VINV, it is necessary to cope with the actual offset amount that changes according to the inverter voltage VINV.

[0171] However, in order to effectively suppress the variation in the motor torque by changing the offset correction value used for correcting the current detection value according to the inverter voltage VINV, the detection resolution of the current detector 4 must be sufficient.

[0172] For example, if the current detection resolution in the electric power steering device using motor 2 is insufficient, a unit change in the current detection resolution causes a change in the motor torque. Such a change in the motor torque causes the driver to feel uncomfortable through the steering wheel as a change in steering feel.

[0173] Generally, there is a trade-off between the measurable current range and the current detection resolution.

[0174] Therefore, in order to ensure a measurable phase current range and improve detection resolution, it is necessary to perform switching processing of detection resolution such that the detection resolution is set high in a low current region and low in a high current region.

[0175] However, switching the current detection resolution requires adding a detection circuit, changing the software, and the like, which increases system costs.

[0176] Therefore, the motor control unit 6A of this embodiment is configured not to change the offset correction value of the detection current used to correct the increase or decrease of the inverter voltage VINV, but to adjust the offset generated in the detection current by correcting the current detection interval width and the current detection timing, so that a fixed offset correction value can be applied even if the inverter voltage VINV increases or decreases.

[0177] According to such a configuration, the response to the offset amount that changes according to the inverter voltage VINV does not depend on the current detection resolution but depends on the current detection interval width, the resolution of the current detection timing, and the motor inductance.

[0178] The current detection interval width and the resolution of the current detection timing are determined by the clock frequency for counting the PWM cycle, and the clock frequency varies depending on the microcomputer 61 and the oscillator.

[0179] For example, in the motor control of an electric power steering device, if it is assumed that the current detection resolution is approximately 0.1A, the clock frequency for counting the PWM cycle is 80MHz, and the motor inductance is 70uH, the current change per clock is approximately 0.001A. Therefore, adjusting the current detection interval width and the current detection timing is equivalent to increasing the current detection resolution by 100 times.

[0180] On the other hand, in order to improve the detection resolution of the current by 100 times, the current measurement range needs to be reduced to 1 / 100, which is difficult to achieve.

[0181] For example, in an electric power steering device, it is necessary to measure a current within a range of approximately ±100 A during motor control.

[0182] Furthermore, even if the resolution of the AD converter used when the microcomputer 61 detects the current can be changed, it will need to be increased by 128 times, that is, by 7 bits, which leads to an increase in cost.

[0183] Furthermore, although the detection resolution of the current can be improved, there is a problem that the resolution of the voltage applied to the motor 2 has a limit.

[0184] In contrast, when the offset generated in the detected current is adjusted by correcting the current detection interval width and the current detection timing, the current resolution does not need to be switched by hardware or software, and both the current detection range and the current resolution can be achieved.

[0185] Furthermore, since the phase current can be adjusted finer than the detection resolution of the phase current, the adjustment of the motor torque and the steering feel can be improved, and the adjustment of the offset amount that changes according to the inverter voltage VINV can be improved.

[0186] Furthermore, since the offset of the detection current can be adjusted finer than the detection resolution of the phase current and is not dependent on the detection resolution of the phase current, it is possible to reduce costs by reducing the detection resolution of the phase current.

[0187] Furthermore, there is no need to change the offset correction value according to the inverter voltage VINV, and there is no need to measure the inverter voltage VINV and the slope of the offset amount in advance.

[0188] Next, the amount of change in the current in the current detection interval is determined.

[0189] For the dq axes, if d-axis voltage Vd, q-axis voltage Vq, resistance R, d-axis current Id, q-axis current Iq, d-axis inductance Ld, q-axis inductance Lq, motor speed ω, and interlinkage flux φ are set, then the circuit equation of Equation 1 holds.

[0190] [Formula 1]

[0191]

[0192] Then, solving the circuit equation of Formula 1 for dId / dt and dIq / dt yields Formula 2.

[0193] [Formula 2]

[0194]

[0195] Here, if the voltage drop and the rotation speed caused by the phase current and the phase resistance are sufficiently low to be negligible, it can be regarded as ω=0 and RI=0, and Equation 2 can be approximated as Equation 3.

[0196] [Formula 3]

[0197]

[0198] Then, the current variation amounts ΔId and ΔIq in the current detection section TSP are obtained by multiplying the slope by time using Equation 4.

[0199] [Formula 4]

[0200]

[0201] That is, the current fluctuation amounts ΔId and ΔIq in the current detection interval TSP are proportional to the width of the current detection interval and the inverter voltage VINV.

[0202] Then, from the current variations ΔId and ΔIq in the dq axes, variations ΔIu, ΔIv, and ΔIw of each phase can be calculated by two-phase to three-phase conversion. When the current detection interval TSP is sufficiently short, the above approximation holds.

[0203] Figure 8 1 is a timing chart showing a process of fixing the offset amount generated in the detection current by correcting the current detection interval width when the inverter voltage VINV changes, that is, the function of the current detection interval width correction unit 24 .

[0204] Figure 8 The left side shows the phase current and current detection interval width when the inverter voltage VINV is the reference voltage. Figure 8The right side of shows the phase current and the current detection interval width when the inverter voltage VINV is a voltage lower than the reference voltage.

[0205] When the inverter voltage VINV is equal to the reference voltage (refer to Figure 8 ), a difference between the V-phase detection current 401 detected at the end point of the interval C in which the V-phase current can be detected and the V-phase average current 402, that is, an offset 403 is generated.

[0206] Similarly, when the inverter voltage VINV is lower than the reference voltage (refer to Figure 8 ), the difference between the V-phase detection current 404 detected at the end point of the interval G in which the V-phase current can be detected and the V-phase average current 405, that is, the offset 406 is generated.

[0207] Here, the width of interval C (that is, the reference value TSPini of the current detection interval width) corrected according to the inverter voltage VINV is set as the width of interval G so that the offset 403 and the offset 406 become equal. In other words, even if the inverter voltage VINV changes from the reference voltage, the offset remains fixed.

[0208] In addition, the same applies to interval D and interval H that can detect the U-phase current. Based on the width of interval D when the inverter voltage VINV is the reference voltage, the width of interval H when the inverter voltage VINV is lower than the reference voltage is adjusted so that even if the inverter voltage VINV is lower than the reference voltage, the offset does not change compared to the reference voltage.

[0209] That is, the lower the inverter voltage VINV is than the reference voltage, the longer the current detection interval width correction unit 24 sets the current detection interval width than the reference value TSPini, thereby preventing the offset from changing even when the inverter voltage VINV is lower than the reference voltage.

[0210] If the inverter voltage VINV is different, the slope of the change in the detection current waveform in the current detection interval becomes different. If the slope is different, the change amount of the detection current in the current detection interval changes, and the difference between the detection current and the average current, that is, the offset, changes.

[0211] Here, the offset ΔOS is expressed by Equation 5 based on the inverter voltage VINV, the current detection interval width TSP, and the inductance L.

[0212] [Formula 5]

[0213]

[0214] Therefore, based on the relationship of Expression 5, the current detection interval width correction unit 24 changes the current detection interval width TSP so as to suppress a change in the offset amount ΔOS when the inverter voltage VINV changes from the reference voltage.

[0215] Specifically, the inverter reference voltage VINV0, the inverter detection voltage VINVx, the current detection interval width reference value TSPini, and the corrected current detection interval width TSPadj satisfy the relationship of Equation 6. The equation for calculating the current detection interval width TSPadj is as shown in Equation 7.

[0216] [Formula 6]

[0217]

[0218] [Formula 7]

[0219]

[0220] Therefore, the current detection interval width correction unit 24 can calculate, based on Equation 7, the current detection interval width TSPadj that provides the same offset as that generated when the inverter detection voltage VINVx is at the inverter reference voltage VINV0.

[0221] Figure 9 Schematically shows how the current detection interval width TSPadj is obtained based on Equation 7.

[0222] In straight line 407 having a larger slope than straight line 411, the difference between the value after fixed time 408 and the value before fixed time 409, i.e., offset 410, is greater than the difference between the value after fixed time 408 and the value before fixed time 409, i.e., offset 412, in straight line 411 having a smaller slope than straight line 407.

[0223] Therefore, by correcting the offset 412 of the straight line 411 with a relatively small slope to be equal to the offset 410 of the straight line 407 with a relatively large slope for a fixed time 413, an offset 414 equal to the offset 410 of the straight line 407 with a relatively large slope can be obtained for the straight line 411 with a small slope.

[0224] In this manner, even if the inverter voltage VINV fluctuates, the offset generated in the detection current can be fixed by correcting the current detection interval width.

[0225] Furthermore, when the inverter voltage VINV remains the same, if the current detection interval width becomes longer, the amplitude of the three-phase current within one PWM cycle increases, and power consumption and electromagnetic noise increase.

[0226] Without applying the correction of the current detection interval width corresponding to the inverter voltage VINV, when the inverter voltage VINV is low voltage, the power consumption and electromagnetic noise are reduced compared with those at high voltage. However, even if the correction of the current detection interval width corresponding to the inverter voltage VINV is applied, if the high voltage is used as the reference, the power consumption and electromagnetic noise at low voltage will not increase compared with those at high voltage.

[0227] In addition, if the rotation speed of the motor 2 increases, the command duty ratio under the PWM control increases, so the margin for ensuring the minimum current detection interval width required for current detection decreases. By applying the correction of the current detection interval width corresponding to the inverter voltage VINV, the current detection rate may decrease. However, by implementing the method described later, Figure 10 、 Figure 11 The processing shown can suppress a decrease in the current detection rate.

[0228] Furthermore, if an offset occurs in the detection current, the current that actually flows will be offset from the detection current by an amount corresponding to the offset.

[0229] By utilizing this characteristic, the actual current flowing can be adjusted by adjusting the offset.

[0230] Compared to changing the offset correction value in units of current detection resolution, changing the generated offset in units of the resolution based on the current detection interval width and the correction of the current detection timing allows the actual current to be adjusted more finely than the current detection resolution.

[0231] In addition, the current detection interval width correction unit 24 calculates the current detection interval width TSPadj when the inverter voltage VINV, the current command and the resolution of the detection current are set as the input value INP, so as to generate a value obtained by subtracting the remainder obtained by dividing the current command by the resolution of the detection current from the resolution of the detection current as the offset ΔOSadd.

[0232] That is, the current detection interval width correction unit 24 calculates the current detection interval width TSPadj according to Equation 8.

[0233] [Formula 8]

[0234]

[0235] In this manner, by correcting the current detection interval width, the offset is adjusted to be equal to the amount of excess or deficiency in the resolution of the detection current in the current command, thereby controlling the current actually flowing.

[0236] Figure 103 is a flowchart showing a process of limiting the current detection interval width TSPadj executed by the motor control unit 6A.

[0237] In step S501 , the motor control unit 6A calculates an upper limit value TSPul of the current detection interval width TSPadj based on the command duty ratio.

[0238] Next, the motor control unit 6A determines in step S502 whether the current detection interval width TSPadj exceeds the upper limit value TSPul.

[0239] Then, the motor control unit 6A proceeds to step S503 if the current detection interval width TSPadj exceeds the upper limit TSPul, and bypasses step S503 and proceeds to step S504 if the current detection interval width TSPadj does not exceed the upper limit TSPul.

[0240] In step S503 , the motor control unit 6A limits the current detection interval width TSPadj using the upper limit value TSPul.

[0241] That is, in step S502 , the motor control unit 6A sets the upper limit value TSPul as the current detection interval width TSPadj, thereby limiting the current detection interval width TSPadj to a range that does not exceed the upper limit value TSPul.

[0242] This can prevent misuse of the abnormal current detection interval width TSPadj.

[0243] In step S504, the motor control unit 6A determines whether the current detection interval width TSPadj is lower than a predetermined lower limit value TSP11.

[0244] The lower limit value TSP11 is predetermined in consideration of the delay time of the switching elements 3a-3f, the circuit stabilization time, the AD conversion time, etc., and is stored as a set value in a nonvolatile memory such as a ROM of the microcomputer 61.

[0245] Regarding the motor control unit 6A, if the current detection interval width TSPadj is lower than the lower limit value TSP11, the process proceeds to step S505. If the current detection interval width TSPadj is not lower than the lower limit value TSP11, the process directly ends this routine.

[0246] In step S505, the motor control unit 6A sets the lower limit value TSP11 as the current detection interval width TSPadj, thereby limiting the current detection interval width TSPadj to a range not lower than the lower limit value TSP11.

[0247] This makes it possible to avoid the influence of vibrations generated in the current detected in the current detection section having a width shorter than the lower limit value TSP11.

[0248] As described above, the motor control unit 6A implements Figure 10 The process shown in the flowchart of FIG. 1 limits the current detection interval width TSPadj to a value within a region sandwiched between the upper limit value TSPul and the lower limit value TSP11.

[0249] Figure 11 This is a flowchart showing the calculation process of the current detection interval width TSPadj executed by the motor control unit 6A, showing the process of limiting the correction of the current detection interval width corresponding to the inverter voltage VINV to when a predetermined condition is met, specifically, when the rotation speed is within a predetermined range.

[0250] In step S601 , the motor control unit 6A determines whether the motor rotation speed is within a predetermined low rotation speed region, in other words, whether the motor rotation speed is lower than a predetermined threshold value.

[0251] When the motor rotation speed is within the predetermined low rotation speed region, that is, when the rotation speed of the motor 2 is lower than the threshold value, the motor control unit 6A proceeds to step S602 .

[0252] In step S602 , the motor control unit 6A corrects the reference value TSPini according to the inverter voltage VINV and calculates the current detection interval width TSPadj.

[0253] On the other hand, when the motor rotation speed is outside the predetermined low rotation speed range, that is, when the rotation speed of the motor 2 exceeds the threshold value, the motor control unit 6A proceeds to step S603.

[0254] In step S603 , the motor control unit 6A outputs the reference value TSPini as the current detection interval width TSPadj as it is.

[0255] The low rotation speed region in which the current detection interval width TSPadj corresponding to the inverter voltage VINV is corrected is set based on a region in which the driver can feel changes in motor torque through the steering wheel, for example, when the motor 2 is a motor that generates steering force in an electric power steering device.

[0256] That is, the current detection interval width TSPadj is corrected according to the inverter voltage VINV in a limited area where the driver feels the change in motor torque, thereby reducing the change in motor torque felt by the driver.

[0257] This can prevent unnecessary correction of the current detection interval width TSPadj corresponding to the inverter voltage VINV in a region where the effect of suppressing changes in the motor torque is difficult to feel, thereby reducing the calculation load of the motor control unit 6A, that is, the microcomputer 61.

[0258] In addition, Figure 11 In the calculation process shown in the flowchart, the condition for whether the motor control unit 6A performs the correction of the current detection interval width TSPadj according to the inverter voltage VINV is set as the rotation speed of the motor 2, but the condition is not limited to the rotation speed.

[0259] For example, the motor control unit 6A can switch whether or not to perform correction of the current detection interval width TSPadj corresponding to the inverter voltage VINV based on a torque command or a PWM modulation rate instead of the rotation speed condition.

[0260] Furthermore, the motor control unit 6A can switch whether or not to perform correction of the current detection interval width TSPadj corresponding to the inverter voltage VINV based on a combination of a plurality of conditions among the rotation speed, the torque command, and the modulation rate.

[0261] Here, the motor control unit 6A does not perform correction of the current detection interval width TSPadj corresponding to the inverter voltage VINV, thereby switching between execution and stop of correction corresponding to the inverter voltage VINV based on the torque command and modulation rate conditions that generate torque changes exceeding the allowable level.

[0262] Figure 12 This is a flowchart showing another embodiment of the calculation process of the current detection interval width TSPadj executed by the motor control unit 6A, and shows a case where a hysteresis characteristic is given to the process of switching whether to perform correction of the current detection interval width TSPadj according to the inverter voltage VINV.

[0263] In step S701 , the motor control unit 6A determines whether the motor rotational speed is within a predetermined first rotational speed range, in other words, whether the motor rotational speed is lower than a first threshold value.

[0264] Then, when the motor rotation speed is within the first rotation speed range, the motor control unit 6A proceeds to step S702 , and after setting a command to perform correction of the current detection interval width TSPadj corresponding to the inverter voltage VINV, proceeds to step S705 .

[0265] On the other hand, when the motor rotation speed is not within the first rotation speed range, the motor control unit 6A proceeds to step S703 .

[0266] In step S703 , the motor control unit 6A determines whether the motor rotation speed is within a predetermined second rotation speed range, in other words, whether the motor rotation speed is lower than a second threshold (second threshold>first threshold).

[0267] Then, when the motor rotation speed is not within the predetermined second rotation speed range, that is, when the motor rotation speed is equal to or greater than the second threshold value, the motor control unit 6A proceeds to step S704.

[0268] In step S704 , the motor control unit 6A sets an execution instruction to cancel the correction of the current detection interval width TSPadj corresponding to the inverter voltage VINV.

[0269] On the other hand, when the motor rotation speed is lower than the second threshold value, the motor control unit 6A skips step S704 and proceeds to step S705.

[0270] In step S705 , the motor control unit 6A determines whether or not a command to correct the current detection interval width TSPadj corresponding to the inverter voltage VINV has been set.

[0271] Then, when the execution instruction is set, the motor control unit 6A proceeds to step S706 and executes correction of the current detection interval width TSPadj corresponding to the inverter voltage VINV.

[0272] On the other hand, when the execution instruction is canceled, the motor control unit 6A proceeds to step S707 and outputs the reference value TSPini as the current detection interval width TSPadj without executing correction corresponding to the inverter voltage VINV.

[0273] That is, if the motor rotation speed is lower than the first threshold, the motor control unit 6A starts to correct the current detection interval width TSPadj corresponding to the inverter voltage VINV, but thereafter, the correction process continues even if the motor rotation speed rises above the first threshold, and the correction process is stopped only when it becomes above a second threshold higher than the first threshold.

[0274] Such hysteresis characteristics can suppress repeated execution and stop of correction when the motor rotation speed fluctuates around the first threshold value, thereby improving the stability of correction control.

[0275] Next, a configuration for suppressing vibration of the motor torque due to a noise component generated in the detection value of the inverter voltage VINV in the correction process of the current detection interval width TSPadj corresponding to the inverter voltage VINV will be described.

[0276] Figure 13The structure shows that the signal of the inverter voltage VINV obtained by the current detection interval width correction unit 24 becomes a signal of the inverter voltage VINV after the noise component (that is, the high-frequency component) is removed by the digital low-pass filter 27, in other words, the signal of the inverter voltage VINV passes through the digital low-pass filter 27.

[0277] In addition, Figure 14 In the structure, the digital low-pass filter 28 removes the noise component from the signal of the current detection interval width TSPadj output by the current detection interval width correction unit 24, and similarly, the digital low-pass filter 29 removes the noise component from the signal of the current detection timing correction value TADIadj output by the current detection interval width correction unit 24.

[0278] Then, the PWM phase manipulation amount calculation unit 25 obtains the current detection interval width TSPadj signal passed through the digital low-pass filter 28 , and the AD timing setting unit 21 obtains the current detection timing correction value TADIadj signal passed through the digital low-pass filter 29 .

[0279] according to Figure 13 or Figure 14 The structure suppresses the motor torque vibration caused by the noise component generated in the detection value of the inverter voltage VINV.

[0280] Figure 15 3 is a timing chart showing a time diffusion process for correcting the current detection interval width TSPadj corresponding to the inverter voltage VINV.

[0281] Figure 15 The time diffusion processing shown is a processing that detects the phase current at a ratio of once to multiple cycles of PWM, and reduces the phase shift amount of the PWM signal when the PWM cycle of the phase current is not detected compared to when the PWM cycle of the phase current is detected. The above-mentioned multiple PWM cycles can be set as a control cycle for updating the duty cycle in PWM, for example.

[0282] exist Figure 15 In the embodiment, the period for updating the three-phase command duty ratios DUu*, DUv*, and DUw* is defined as a control period, and the control period is composed of N PWM periods from the first PWM period to the Nth PWM period.

[0283] Then, in the first PWM cycle, correction of the current detection interval width TSPadj according to the inverter voltage VINV is applied, and phase current is detected using the current detection interval width TSPadj corrected according to the inverter voltage VINV.

[0284] In each PWM cycle from the second PWM cycle to the Nth PWM cycle, the interval width obtained by subtracting the increase correction amount of the interval width of the difference between the current detection interval width TSPadj applied to the first PWM cycle and the reference value TSPini from the reference value TSPini and dividing it by "N-1" is set as the current detection interval width, so that the average of the current detection interval width in the control cycle is consistent with the reference value TSPini.

[0285] With this configuration, the PWM cycle in which the current detection interval width TSPadj increases from the reference value TSPini is reduced, and the amplitude of the three-phase current fluctuation can be reduced as an average of the control cycle, thereby suppressing increases in power consumption and electromagnetic noise.

[0286] Figure 16 as well as Figure 17 This is a graph showing the relationship between the steering torque generated by the motor 2 and the steering angle, depending on the level of the inverter voltage VINV, when the motor 2 is a motor that generates steering torque in the electric power steering device.

[0287] Figure 16 1 is a diagram showing the relationship between the steering torque and the steering angle in a state where the current detection interval width TSPadj corresponding to the inverter voltage VINV is not corrected, and shows how the steering torque generated by the motor 2 shifts when the inverter voltage VINV changes.

[0288] on the other hand, Figure 17 1 is a diagram showing the relationship between the steering torque and the steering angle in a state where the current detection interval width TSPadj corresponding to the inverter voltage VINV is corrected, and shows that even if the inverter voltage VINV changes, a steering torque of substantially the same level is generated.

[0289] That is, by correcting the current detection interval width TSPadj according to the inverter voltage VINV, the average current of each phase (actual phase current) can be obtained with high accuracy using a fixed offset correction value even if the inverter voltage VINV changes.

[0290] Then, if the average current of each phase (in other words, the actual phase current) can be calculated with high accuracy, the accuracy of the feedback control that performs correction action to make the phase current close to the command current is increased, thereby suppressing the change in steering torque caused by the change in inverter voltage VINV.

[0291] Furthermore, if the steering torque does not change even when the inverter voltage VINV changes, the change in steering feel will not be transmitted to the driver through the steering wheel, thereby preventing the driver from feeling uncomfortable.

[0292] The technical concepts described in the above embodiments can be used in appropriate combination as long as no contradiction occurs.

[0293] Furthermore, the present invention has been specifically described with reference to preferred embodiments. However, it is obvious that a person skilled in the art can adopt various modified forms based on the basic technical concept and teachings of the present invention.

[0294] For example, when the inverter voltage VINV becomes higher than the reference voltage, the motor control unit 6A can execute a process of shortening the current detection interval width compared to the reference value.

[0295] Furthermore, the motor control unit 6A can detect the phase current of the first phase among the three phases of the motor 2 in the first PWM cycle, and detect the phase current of the second phase in the second PWM cycle following the first PWM cycle.

[0296] Furthermore, the above-described embodiment employs a three-phase PWM method that uses a double-edge triangular carrier as a carrier signal for pulse centering. However, a three-phase PWM method using a single-edge triangular carrier as a carrier signal can also employ a method that changes the current detection interval width in accordance with the inverter voltage VINV and phase-shifts the PWM signal to ensure the current detection interval width.

[0297] Furthermore, the above-described current detector 4 is a resistance detection type current sensor using the shunt resistor 4A, but a magnetic field detection type current sensor can be employed as the current detector.

[0298] Description of Reference Numerals

[0299] 1: Motor control system, 2: Motor, 3: Inverter circuit, 4: Current detector, 4A: Shunt resistor, 5: Inverter voltage detector, 6: Motor control device, 6A: Motor control unit, 6B: Switching signal generation unit, 6C: AD conversion unit, 7: DC power supply, 20: Switching timing setting unit, 21: AD timing setting unit, 24: Current detection interval width correction unit, 25: PWM phase operation amount calculation unit, 61: Microcomputer (control unit, control unit).

Claims

1. A motor control device, the motor control device controlling a motor, The control unit of the motor control device performs the following operations: obtaining an output signal of a current detector that detects a current flowing between an inverter driven by a PWM signal and a DC power supply of the inverter, The output signal of the current detector is sampled in a current detection interval corresponding to a combination of on and off of the PWM signal to detect the phase current of the motor. controlling the motor via the inverter based on the detected phase current, obtaining a signal related to the voltage of the DC power supply, The length of the current detection interval is changed based on the voltage of the DC power supply.

2. The motor control device according to claim 1, wherein: The current detection section is a section from the timing of switching the on / off combination of the PWM signal to the time when the output signal of the current detector is sampled.

3. The motor control device according to claim 1, wherein: The control unit increases the length of the current detection interval as the voltage of the DC power supply decreases.

4. The motor control device according to claim 1, wherein: The control unit shifts the phases of the PWM signals to ensure a length of the current detection interval.

5. The motor control device according to claim 4, wherein: The control unit performs: The phase current is detected at a rate of 1 in multiple cycles of the PWM control cycle. When the PWM control period of the phase current is not detected, the amount of phase shift of the PWM signal is reduced compared to when the PWM control period of the phase current is detected.

6. The motor control device according to claim 5, wherein: The control unit sets the plurality of cycles as cycles for changing the duty ratio in PWM.

7. The motor control device according to claim 1, wherein: The control unit changes the length of the current detection interval within a region sandwiched between an upper limit value and a lower limit value.

8. The motor control device according to claim 1, wherein: The control unit changes the length of the current detection interval based on the voltage of the DC power supply when the rotation speed of the motor is within a predetermined range.

9. A motor control device, the motor control device controlling a motor, The control unit of the motor control device performs the following operations: obtaining an output signal of a current detector that detects a current flowing between an inverter driven by a PWM signal and a DC power supply of the inverter, The output signal of the current detector is sampled at a predetermined timing to detect the phase current of the motor. controlling the motor via the inverter based on the detected phase current, obtaining a signal related to the voltage of the DC power supply, The lower the voltage of the DC power supply, the greater the amount by which the phases of the PWM signals are shifted from each other.

10. A motor control method, which is a motor control method executed by a control unit, obtaining an output signal of a current detector that detects a current flowing between an inverter driven by a PWM signal and a DC power supply of the inverter, The output signal of the current detector is sampled in a current detection interval corresponding to a combination of on and off of the PWM signal to detect the phase current of the motor. controlling the motor via the inverter based on the detected phase current, obtaining a signal related to the voltage of the DC power supply, The length of the current detection interval is changed based on the voltage of the DC power supply.

11. A motor control system comprising: motor; Inverter, driven by PWM signal; a current detector that detects a current flowing between the inverter and a DC power supply of the inverter; and A control unit that performs: Obtaining the output signal of the current detector, The output signal of the current detector is sampled in a current detection interval corresponding to a combination of on and off of the PWM signal to detect the phase current of the motor. controlling the motor via the inverter based on the detected phase current, obtaining a signal related to the voltage of the DC power supply, The length of the current detection interval is changed based on the voltage of the DC power supply.

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