Motor control device

Abstract

This motor control device is provided with: a control unit that performs sensorless control on a brushless motor having three phases; and a determination unit that determines whether or not there is an out-of-step of the brushless motor (BM). The control unit performs sensorless control on the basis of the estimated d-axis output current (Ids), the estimated q-axis output current (Iqs), the estimated d-axis instruction voltage (Vdc), the estimated q-axis instruction voltage (Vqc), and the estimated rotational speed ([omega] s). The determination unit calculates a determination voltage (Vqj) on the basis of the estimated d-axis output current (Ids), the estimated q-axis output current (Iqs), and the estimated rotational speed ([omega] s). Furthermore, when a voltage deviation (hV), which is the difference between the determination voltage (Vqj) and the estimated q-axis instruction voltage (Vqc), exceeds a determination threshold value (Hs), it is determined that an out-of-step has occurred. For example, as the estimated rotational speed ([omega] s) increases, the determination unit determines the determination threshold value (Hs) to increase.

Description

Technical Field

[0001] The present disclosure relates to a motor control device. Background Art

[0002] Patent document 1 describes the following contents for the purpose of detecting out-of-step with a simple structure that does not require the addition of current detectors and voltage detectors. The model voltage calculation unit 10 uses a PM motor model based on the voltage equation of the PM motor 2 to calculate the dq axis model voltages vd* and vq* according to the speed indicated by the speed of the PM motor and the dq axis current indicated by the current, and the out-of-step determination unit 11 determines whether the PM motor has lost step by comparing the model voltage with the voltage indications vd and vq of the inverter. In addition, when calculating the model voltage, the dq axis current detection value can be used instead of the current indication of the PM motor. Furthermore, it is possible to perform out-of-step determination using only the model voltage of the q axis component.

[0003] When the brushless motor operates properly, the synchronous speed (rotation speed of the magnetic field when an alternating current is applied) is equal to the actual rotation speed of the rotor (synchronous state). If the load on the motor is too large, a state in which the synchronous speed and the actual rotation speed are inconsistent (out-of-step state) may occur. In the out-of-step state, a deviation (error) occurs between the speed indication (also called "target rotation speed") and the actual rotation speed. In Patent Document 1, in the judgment of out-of-step, since the above-mentioned model voltage is calculated based on the speed indication (target rotation speed), there is a case where the judgment produces an error.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2010-252503 Summary of the invention

[0005] An object of the present invention is to provide a structure capable of reliably determining a step-out of a brushless motor in a motor control device that performs sensorless control on the brushless motor.

[0006] A motor control device (MS) according to the present invention comprises: a control unit (BC) for performing sensorless control on a brushless motor (BM) having three phases; and a determination unit (BH) for determining whether the brushless motor (BM) has lost step.

[0007] In the motor control device (MS) involved in the present invention, the control unit (BC) performs the sensorless control based on the estimated d-axis and q-axis output currents (Ids, Iqs), the estimated d-axis and q-axis indicated voltages (Vdc, Vqc) and the estimated rotation speed (ωs). Moreover, the determination unit (BH) calculates the determination voltage (Vqj) based on the estimated d-axis and q-axis output currents (Ids, Iqs) and the estimated rotation speed (ωs), and determines that the step-out occurs when the difference between the determination voltage (Vqj) and the estimated q-axis indicated voltage (Vqc), that is, the voltage deviation (hV) reaches the determination threshold value (Hs). For example, the determination unit (BH) determines the determination threshold value (Hs) to be larger as the estimated rotation speed (ωs) increases.

[0008] In the motor control device (MS) according to the present invention, the determination unit (BH) determines the determination voltage (Vqj) assuming that the brushless motor (BM) is not out of step and rotates at the estimated rotation speed (ωs). Specifically, the determination unit (BH) calculates a first component (Sv1=R·Iqs) corresponding to a voltage drop in the brushless motor (BM) based on the estimated q-axis output current (Iqs), calculates a second component (Sv2=ωs(φ+Ld·Ids)) corresponding to a back electromotive force in the brushless motor (BM) based on the estimated rotation speed (ωs) and the estimated d-axis output current (Ids), and determines the determination voltage (Vqj) as the sum of the first component (Sv1) and the second component (Sv2) (Vqj=Sv1+Sv2).

[0009] According to the above configuration, the estimated rotation speed ωs is used for the step-out determination of the brushless motor BM, and the voltage deviation hV is determined as a state quantity that appropriately expresses the degree of step-out. This improves the determination accuracy and enables reliable determination. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a block diagram for explaining an embodiment of the motor control device MS.

[0011] Figure 2 It is a block diagram for explaining the determination unit BH. DETAILED DESCRIPTION

[0012] <Symbols of components, etc. and expressions of magnitude relations of values>

[0013] In the following description, components, calculation processes, signals, characteristics, and values ​​marked with the same symbols, such as "BM", have the same function. In addition, the magnitude relationship of the values ​​of various state quantities (Hs, hV, etc.) is expressed based on their magnitudes (absolute values). According to the rotation direction of the motor, the positive and negative (+ / -) signs of the current, voltage, etc. are marked. For example, a positive sign is marked when the motor is driven in the forward direction, and a negative sign is marked when the motor is driven in the reverse direction. In other words, the sign of the state quantity is different according to the rotation direction of the motor. In addition, the voltage deviation hV is calculated as the difference between the determination voltage Vqj and the estimated q-axis indication voltage Vqc, but the sign is opposite according to the calculation method of the voltage deviation hV. In other words, the sign of the voltage deviation hV is opposite when it is calculated as "hV=Vqj-Vqc" and when it is calculated as "hV=Vqc-Vqj". Therefore, in the following description, in order to avoid cumbersome description, the magnitude (or height) of the value is expressed based on the absolute value (magnitude) of the value.

[0014] <Embodiment of Motor Control Device MS>

[0015] Reference Figure 1 The block diagram of the embodiment of the motor control device MS is used to explain the embodiment of the motor control device MS. The brushless motor BM is a synchronous motor provided with three-phase coils of the U phase, the V phase and the W phase. The brushless motor BM is controlled (driven) by the motor control device MS. The brushless motor BM adopts a sensorless structure. Therefore, there is no position sensor (rotation angle sensor) for detecting the position (i.e., rotation angle) of the rotor of the brushless motor BM.

[0016] The motor control device MS that drives the brushless motor BM is composed of a control unit BC and a determination unit BH.

[0017] <<Control Department BC<<

[0018] Since the brushless motor BM is a sensorless type, the control unit BC performs sensorless control (also called "sensorless vector control"). Sensorless control is a well-known motor driving method (for example, refer to Japanese Patent Publication No. 2008-011616, Japanese Patent Publication No. 2019-208329, and Japanese Patent Publication No. 2022-110307). The control unit BC is briefly described below.

[0019] In the control unit BC, the brushless motor BM is driven by vector controlling the current of the d-axis component and the current of the q-axis component orthogonal to the d-axis. "D-axis, q-axis" are control axes in the rotating coordinates (also called "d-q coordinates") of vector control. The "d-axis" extends in the direction of the magnetic flux axis of the permanent magnet, and the "q-axis" extends in the torque direction. Here, the d-axis is orthogonal to the q-axis. In a brushless motor with a rotation angle sensor, the actual d-axis and the actual q-axis (also called "actual d-axis, actual q-axis" or "true d-axis, true q-axis") are identified based on the detection result of the rotation angle sensor (i.e., the rotation angle).

[0020] Since the sensorless brushless motor BM does not have a rotation angle sensor, the d-axis and q-axis are inferred to perform vector control (i.e., sensorless vector control). In sensorless control, the control axis inferred as the d-axis of the rotating coordinate is called the "inferred d-axis (or, virtual d-axis)". In addition, the control axis inferred as the q-axis of the rotating coordinate is called the "inferred q-axis (or, virtual q-axis)". The inferred d-axis is orthogonal to the inferred q-axis, which is the same as the relationship between the actual d-axis and the actual q-axis. In addition, the error between the actual d-axis, the actual q-axis and the inferred d-axis, the inferred q-axis is recorded as the "axis error Δθ (angle error)".

[0021] The current indication values ​​in the inferred d-axis and the inferred q-axis are called "inferred d-axis indicated current Idc, inferred q-axis indicated current Iqc". Furthermore, the currents generated in the inferred d-axis and the inferred q-axis corresponding to the inferred d-axis indicated current Idc and the inferred q-axis indicated current Iqc are called "inferred d-axis output current Ids, inferred q-axis output current Iqs". The inferred d-axis output current Ids and the inferred q-axis output current Iqs are inferred based on the three-phase detection currents Ius, Ivs, and Iws (U-phase, V-phase, and W-phase detection currents). The inferred d-axis output current Ids and the inferred q-axis output current Iqs are also called "inferred d-axis inferred current Ids, inferred q-axis inferred current Iqs (or, inferred d-axis response current Ids, inferred q-axis response current Iqs)".

[0022] The control unit BC is composed of an instruction current calculation block IC, an instruction voltage calculation block VC, a first coordinate conversion block ZC, a second coordinate conversion block ZS, and a speed estimation block WS.

[0023] In the indicated current calculation block IC, the estimated d-axis indicated current Idc and the estimated q-axis indicated current Iqc are calculated based on the indicated rotational speed ωc (the target value of the motor rotational speed) and the estimated rotational speed ωs (the estimated value of the motor rotational speed). Specifically, in the indicated current calculation block IC, the estimated rotational speed ωs calculated by the speed estimation block WS is subtracted from the indicated rotational speed ωc. Then, based on the calculation result "ωc-ωs" (referred to as "rotational speed error Δω"), the estimated d-axis indicated current Idc that the estimated d-axis output current Ids should follow is determined. In addition, in the indicated current calculation block IC, the estimated q-axis indicated current Iqc that the estimated q-axis output current Iqs should follow is calculated based on the estimated d-axis indicated current Idc, etc. That is, the indicated currents Idc and Iqc in the estimated d-axis and the estimated q-axis are calculated in such a way that the rotational speed error Δω becomes "0" and the estimated rotational speed ωs is consistent with the indicated rotational speed ωc. The indicated current calculation block IC performs processing for making the estimated rotation speed ωs coincide with the indicated rotation speed ωc, and functions as a "speed controller (controller for controlling the rotation speed)".

[0024] In the indicated voltage calculation block VC, the estimated d-axis and estimated q-axis indicated voltages Vdc and Vqc (target values) are calculated based on the estimated d-axis and estimated q-axis indicated currents Idc and Iqc (target values) and the estimated d-axis and estimated q-axis output currents Ids and Iqs (output values). In the indicated voltage calculation block VC, the indicated voltages Vdc and Vqc in the estimated d-axis and estimated q-axis are calculated so that the current errors "Iqc-Iqs" and "Idc-Ids" in the estimated q-axis and estimated d-axis are both "0" and the estimated d-axis output currents Ids and estimated q-axis output currents Iqs are consistent with the estimated d-axis indicated currents Idc and estimated q-axis indicated currents Iqc. Since the indicated voltage calculation block VC is a processing block for making the estimated d-axis output currents Ids and estimated q-axis output currents Iqs consistent with the estimated d-axis indicated currents Idc and estimated q-axis indicated currents Iqc, it functions as a "current controller (controller for controlling the estimated current)".

[0025] In the first coordinate conversion block ZC, the U-phase, V-phase, and W-phase indicated voltages Vuc, Vvc, and Vwc (target values) are calculated based on the estimated d-axis and estimated q-axis indicated voltages Vdc and Vqc (target values). Specifically, the U-phase, V-phase, and W-phase indicated voltages Vuc, Vvc, and Vwc are determined by converting the estimated d-axis indicated voltage Vdc and the estimated q-axis indicated voltage Vqc from two-phase coordinates to three-phases based on the estimated rotation angle θs calculated by the speed estimation block WS. The U-phase, V-phase, and W-phase indicated voltages Vuc, Vvc, and Vwc are output to the inverter INV.

[0026] In the inverter INV, based on the U-phase, V-phase, and W-phase indicated voltages Vuc, Vvc, and Vwc, the brushless motor BM is powered by PWM control (pulse width modulation control) to drive the brushless motor BM. Specifically, the pulse width modulated signal is determined according to the U-phase, V-phase, and W-phase indicated voltages Vuc, Vvc, and Vwc. Moreover, according to the signal, the switching element (MOS-FET, IGBT, etc.) is controlled to adjust the U-phase, V-phase, and W-phase supply currents Ius, Iuv, and Iws (also called "detection current") supplied to the brushless motor BM. In other words, as a result of the U-phase, V-phase, and W-phase indicated voltages Vuc, Vvc, and Vwc, the U-phase, V-phase, and W-phase supply currents Ius, Iuv, and Iws are controlled.

[0027] In order to detect the motor currents Ius, Iuv, and Iws supplied from the inverter INV to the brushless motor BM, a current sensor IA is provided. Since the phase difference of the U-phase, V-phase, and W-phase supply currents Ius, Iuv, and Iws is known, the current sensor IA can also be used to detect the supply currents of two of the three phases (for example, the U-phase detection current Ius and the V-phase detection current Ivs) and infer the supply current of the remaining one phase (for example, the W-phase detection current Iws). That is, by detecting the supply currents of at least two of the three phases using the current sensor IA, the current actually supplied to the three phases is detected.

[0028] In the second coordinate conversion block ZS, the estimated d-axis output current Ids and the estimated q-axis output current Iqs are calculated based on the U-phase, V-phase, and W-phase detection currents Ius, Iuv, and Iws. Specifically, the estimated d-axis output current Ids and the estimated q-axis output current Iqs are determined by converting the detection currents Ius, Iuv, and Iws from three-phase coordinates to two-phases based on the estimated rotation angle θs calculated by the speed estimation block WS. Here, the estimated d-axis and estimated q-axis output currents Ids and Iqs (output values) correspond to the estimated d-axis and estimated q-axis indicated currents Idc and Iqc (input values, target values).

[0029] In the speed estimation block WS, the estimated rotation speed ωs and the estimated rotation angle θs are calculated based on the estimated d-axis output current Ids and the estimated q-axis output current Iqs. In the speed estimation block WS, the estimated rotation speed ωs is first calculated. Then, the estimated rotation speed ωs is integrated to determine the estimated rotation angle θs. When calculating the estimated rotation speed ωs, a well-known method such as a current introduction method, a high-order harmonic superposition method, a flux observer method, and an extended induced voltage method is used.

[0030] For example, in the speed estimation block WS, as shown in the blowing part XWS, the control amount of the PLL control when the axis error Δθ is controlled to follow "0 (target value)" is determined as the estimated rotation speed ωs. Here, in the PLL control (Phase Locked Loop), feedback control is applied based on the input periodic signal, and a phase-synchronized signal is output from another oscillator.

[0031] Since the target value of the axis error Δθ is set to "0", the axis error Δθ is input to the PLL control block. In the PLL control block, the axis error Δθ is multiplied by the proportional gain Kp to calculate the proportional term. In addition, the axis error Δθ is time-integrated and multiplied by the integral gain Ki to calculate the integral term. Then, the sum of the proportional term and the integral term is determined as the estimated rotation speed ωs (i.e., "ωs=Kp·Δθ+Ki·∫Δθ·dt"). Furthermore, the estimated rotation speed ωs is time-integrated to determine the estimated rotation angle θs (i.e., "θs=∫ωs·dt").

[0032] For example, in the speed estimation block WS, the calculation method of the axis error Δθ (the angle error between the actual q-axis and the estimated q-axis) is used separately based on the rotation speed. When the rotation speed is small (at low speed), the axis error Δθ is determined based on the harmonic superposition method. In the harmonic superposition method (also called the "interference superposition method"), a high-frequency voltage of a pulse (or a sine wave) is superimposed (applied) to the estimated d-axis indicated voltage Vdc. And, based on the amplitude change of the high-frequency component of the estimated q-axis output voltage Iqs at this time, the axis error Δθ is estimated.

[0033] In contrast, when the rotation speed is high (at high speed), the axis error Δθ is calculated based on the extended induced voltage method. In the extended induced voltage method, the axis error Δθ (angle error) is calculated by estimating the induced voltage from the voltage and current. Specifically, the axis error Δθ is estimated based on the estimated rotation speed ωs (the previous value in the calculation cycle), the estimated d-axis output current Ids, the estimated q-axis output current Iqs, and the estimated d-axis indicated voltage Vdc and the estimated q-axis indicated voltage Vqc.

[0034] The estimated rotation speed ωs calculated by the speed estimation block WS is input to the indicated current calculation block IC and the determination unit BH. In addition, the estimated rotation angle θs calculated by the speed estimation block WS is input to the first coordinate conversion block ZC and the second coordinate conversion block ZS.

[0035] <<Judgment Unit BH>>

[0036] In the determination unit BH, it is determined whether there is a step-out in the brushless motor BM. In a brushless motor with a rotation angle sensor, the coil phase most suitable for generating torque is always determined based on the information of the rotation angle, so there is no step-out (asynchronous rotation of the rotating magnetic field and the rotor with permanent magnets). However, in a brushless motor without a rotation angle sensor, the synchronization of the rotating magnetic field and the rotor is performed by inference, so there is a possibility of step-out when the load is high or when the load changes suddenly.

[0037] In the determination unit BH, whether or not a step-out occurs is determined based on the estimated rotation speed ωs, the estimated q-axis indicated voltage Vqc, the estimated d-axis output current Ids, and the estimated q-axis output current Iqs. Furthermore, if it is determined that a step-out occurs, the determination signal Fd is output toward the indicated current operation block IC. For example, the determination signal Fd is sent as a control flag (also referred to as a "determination flag"). Specifically, in the determination flag Fd, "0" indicates that no step-out occurs, and "1" indicates that a step-out occurs. Therefore, the moment (corresponding operation cycle) when the step-out occurs is when "Fd=0" transitions to "Fd=1".

[0038] In the command current calculation block IC of the control unit BC, a process for recovering from the out-of-step state is executed based on the determination flag Fd. For example, the command rotation speed ωc is reduced from the moment "Fd=1" is received.

[0039] <Detailed configuration of determination unit BH>

[0040] Reference Figure 2 The detailed structure of the determination unit BH is described in the block diagram of FIG. The estimated rotation speed ωs, the estimated q-axis indicated voltage Vqc, the estimated d-axis output current Ids, and the estimated q-axis output current Iqs are input to the determination unit BH. In the determination unit BH, the deviation hV (voltage deviation) between the determination voltage Vqj calculated based on the estimated rotation speed ωs, the estimated d-axis output current Ids, and the estimated q-axis output current Iqs and the estimated q-axis indicated voltage Vqc is calculated. And, by comparing the voltage deviation hV with the determination threshold value Hs, it is determined whether the brushless motor BM has lost step.

[0041] The determination unit BH is composed of a determination voltage calculation block VJ, a voltage deviation calculation block HV, a determination threshold calculation block HS, and a determination processing block HN.

[0042] In the judgment voltage calculation block VJ, the judgment voltage Vqj is calculated based on the estimated rotation speed ωs, the estimated d-axis output current Ids, and the estimated q-axis output current Iqs. The "judgment voltage Vqj" is the voltage to be applied to the estimated q-axis when the brushless motor BM is assumed to be not out of step and rotates at the estimated rotation speed ωs. Specifically, the judgment voltage Vqj is determined based on equation (1).

[0043] Vqj=R·Iqs+ωs·(φ+Ld·Ids)…Equation (1)

[0044] Here, "R" represents the resistance value (nominal value) of the brushless motor BM, "φ" represents the linkage flux (nominal value) of the brushless motor BM, and "Ld" represents the d-axis inductance (nominal value) of the brushless motor BM. Here, the "nominal value" is the average value of the measured data.

[0045] The first term Sv1 (= "R·Iqs") of the formula (1) is equivalent to the voltage drop in the brushless motor BM when the estimated q-axis output current Iqs is energized. In addition, the second term Sv2 (= "ωs·(φ+Ld·Ids)") of the formula (1) is equivalent to the back electromotive force in the brushless motor BM when it rotates at the estimated rotation speed ωs. Therefore, in the calculation of the judgment voltage Vqj, the first term Sv1 (also called "first component") equivalent to the voltage drop in the brushless motor BM is calculated based on the estimated q-axis output current Iqs. In addition, the second term Sv2 (also called "second component") equivalent to the back electromotive force in the brushless motor BM is calculated based on the estimated rotation speed ωs and the estimated d-axis output current Ids. Moreover, the sum of the first component Sv1 and the second component Sv2 is determined as the judgment voltage Vqj.

[0046] In the voltage deviation calculation block HV, a voltage deviation hV, which is a difference between the determination voltage Vqj and the estimated q-axis indicated voltage Vqc, is calculated based on the determination voltage Vqj and the estimated q-axis indicated voltage Vqc. For example, the voltage deviation hV is determined based on equation (2).

[0047] hV=Vqj-Vqc…Formula (2)

[0048] As described above, the judgment voltage Vqj is a voltage corresponding to the estimated q-axis indicated voltage Vqc in a state where no step-out occurs and the brushless motor BM is properly operating at the estimated rotation speed ωs. Therefore, the difference between the judgment voltage Vqj and the estimated q-axis indicated voltage Vqc, that is, the voltage deviation hV, is a state quantity (state variable) indicating the degree (magnitude) of step-out. Therefore, the greater the degree of step-out of the brushless motor BM (the difference between the indicated rotation speed ωc and the actual motor rotation speed), the greater the voltage deviation hV is calculated.

[0049] For example, when the brushless motor BM is not out of step and is properly driven by the sensorless control (i.e., the estimated rotation speed ωs is substantially consistent with the actual motor rotation speed), the estimated q-axis indicated voltage Vqc is equal to the judgment voltage Vqj. Therefore, in this state, the voltage deviation hV is "0". In contrast, when the brushless motor BM is out of step and its rotation is completely stopped (i.e., the estimated rotation speed ωs is generated, but the actual rotation speed is "0"), the estimated q-axis indicated voltage Vqc does not include the second component Sv2 corresponding to the back electromotive force. Therefore, the voltage deviation hV is consistent with the second component Sv2. Therefore, when the brushless motor BM is out of step and the actual motor rotation speed is "0", "hV = ωs·(φ+Ld·Ids) = Sv2" is calculated. That is, the maximum value of the voltage deviation hV is the second component Sv2, and the voltage deviation hV changes in the range from "0" to the second component Sv2.

[0050] In the determination threshold calculation block HS, the determination threshold Hs is calculated based on the estimated rotation speed ωs. The "determination threshold Hs" is a threshold for determining whether there is a step-out. The calculation map Zhs, which is a characteristic for calculating the determination threshold Hs, is pre-set as a characteristic of the determination threshold Hs relative to the estimated rotation speed ωs. And, this characteristic Zhs is stored in the microprocessor in the motor control device MS. According to the pre-set calculation map Zhs, the larger the estimated rotation speed ωs is, the larger the determination threshold Hs is determined to be.

[0051] As described above, when the brushless motor BM is operating properly (i.e., when no step-out occurs), the voltage deviation hV is determined to be "0" because the judgment voltage Vqj is equal to the estimated q-axis indicated voltage Vqc. However, in the motor control device MS, the detection results Ius, Ivs, and Iws (current detection values) of the current sensor IA include deviations (errors). Similarly, in the brushless motor BM, there are deviations in the resistance value R, the interlinkage flux φ, the inductance Ld of the d-axis, and the inductance Lq (inductance coefficient) of the q-axis. In addition, the detection value (Ius, etc.) of the current sensor IA and the characteristics (R, φ, etc.) of the brushless motor BM vary depending on the temperature, etc. Therefore, in the state where the brushless motor BM is not step-out (i.e., the state of "hV=0"), the characteristic Zes of the error Es included in the sensorless control is calculated in advance. This error Es is called a "steady-state error", and its characteristic Zes is called a "steady-state error characteristic". The steady-state error Es is an error stably included in the sensorless control due to errors (deviation, fluctuation) such as the detection value of the current sensor IA and the characteristics of the brushless motor BM.

[0052] The maximum value (worst value) of the steady-state error Es is determined for each motor rotation speed using the motor rotation speed as a parameter in the above-mentioned combination of the deviation and the temperature condition. Furthermore, the maximum value of the steady-state error Es is plotted with respect to the motor rotation speed, and the steady-state error characteristic Zes is set. That is, the steady-state error Es occurs within a range Hes (referred to as a "steady-state error range") surrounded by the horizontal axis (axis for estimating the rotation speed ωs) and the steady-state deviation characteristic Zes.

[0053] The calculation map Zhs for calculating the determination threshold value Hs is set to be always larger than the steady-state error characteristic Zes. Specifically, the calculation map Zhs is set by adding a predetermined margin (margin value) to the steady-state error characteristic Zes. Thus, for example, when the estimated rotation speed ωs is a value ω1, the determination threshold value Hs corresponding to the calculation map Zhs is calculated to be larger by a margin value mj than the steady-state error Es corresponding to the steady-state error characteristic Zes. Since the determination threshold value Hs is not included in the range Hes (steady-state error range) of the steady-state error Es, a step-out can be correctly determined.

[0054] In the steady-state error characteristic Zes, the higher the motor rotation speed, the larger the steady-state error Es. In order to effectively avoid the determination threshold Hs being included in the error range of the steady-state error Es, the larger the estimated rotation speed ωs is, the larger the calculation map Zhs is set. And, an upper limit value hx is set for the calculation map Zhs. In addition, a lower limit speed ωo is set for the calculation map Zhs so as to limit the out-of-step determination when the estimated rotation speed ωs is low. That is, when the estimated rotation speed ωs is lower than the lower limit speed ωo, the determination involving the out-of-step is not performed. Here, the "upper limit value hx" and the "lower limit speed ωo" are pre-set specified values ​​(constants).

[0055] In the determination processing block HN, the presence or absence of a step-out is determined based on the comparison between the voltage deviation hV and the determination threshold value Hs. This determination is called "step-out determination". In the determination processing block HN, the step-out determination is performed based on "whether the voltage deviation hV reaches the determination threshold value Hs". Specifically, when the voltage deviation hV is lower than the determination threshold value Hs, the occurrence of a step-out is denied. On the other hand, when the voltage deviation hV is higher than the determination threshold value Hs, the time Tx (called "duration time") during which the state (i.e., the state in which the voltage deviation hV reaches the determination threshold value Hs) is counted from the moment (corresponding operation cycle) when the situation is first satisfied (i.e., the time Tx in which the voltage deviation hV reaches the determination threshold value Hs) is continued. And, when the duration Tx of the state of "hV ≥ Hs" reaches the determination time tx, the occurrence of a step-out is confirmed. Here, the "determination time tx" is a predetermined value (constant) set in advance. In the determination processing block HN, "Fd = 0" is output when the occurrence of a step-out is denied, and "Fd = 1" is output when the occurrence of a step-out is confirmed.

[0056] The method for determining the judgment threshold Hs is summarized. The judgment threshold Hs is calculated based on the estimated rotation speed ωs and the pre-set calculation map Zhs. According to the calculation map Zhs, the larger (higher) the estimated rotation speed ωs is, the larger the judgment threshold Hs is determined to be. The calculation map Zhs is set to be larger than the steady-state error characteristic Zes. Thus, the judgment threshold Hs is determined to be always larger than the steady-state error Es included in the sensorless control. As a result, the influence of the steady-state error Es is reduced in the out-of-step judgment.

[0057] <Summary of implementation methods>

[0058] Hereinafter, embodiments of the motor control device MS will be summarized.

[0059] In the motor control device MS, there are provided a control unit BC for performing sensorless control on a brushless motor BM having three phases and a determination unit BH for determining whether the brushless motor BM has lost step. In the control unit BC, sensorless control is performed based on an estimated d-axis output current Ids, an estimated q-axis output current Iqs, an estimated d-axis indicated voltage Vdc, an estimated q-axis indicated voltage Vqc, and an estimated rotation speed ωs. Here, the estimated d-axis output current Ids and the estimated q-axis output current Iqs are calculated based on the detection currents of at least two phases of the three phases (that is, at least two of the detection currents Iua, Iva, and Iwa). The estimated d-axis indicated voltage Vdc and the estimated q-axis indicated voltage Vqc are determined based on the estimated d-axis output current Ids and the estimated q-axis output current Iqs. The estimated rotation speed ωs is determined based on the estimated d-axis output current Ids and the estimated q-axis output current Iqs.

[0060] In the determination unit BH, the determination voltage Vqj is calculated based on the estimated d-axis output current Ids, the estimated q-axis output current Iqs, and the estimated rotation speed ωs. And when the difference between the determination voltage Vqj and the estimated q-axis indication voltage Vqc, that is, the voltage deviation hV reaches the determination threshold value Hs (that is, when the voltage deviation hV is greater than the determination threshold value Hs), it is determined that a step-out occurs. The larger the estimated rotation speed ωs is, the larger the determination threshold value Hs is determined to be. Since the determination voltage Vqj for step-out determination is calculated based on the estimated rotation speed ωs, the determination error is reduced.

[0061] In the determination unit BH, the determination voltage Vqj is determined on the assumption that the brushless motor BM is not out of step and is rotating at the estimated rotation speed ωs. In detail, the determination voltage Vqj is calculated as the sum of the first component Sv1 corresponding to the voltage drop in the brushless motor BM and the second component Sv2 corresponding to the back electromotive force in the brushless motor BM (i.e., "Vqj = Sv1 + Sv2"). Here, the first component Sv1 is calculated based on the estimated q-axis output current Iqs (specifically, "Sv1 = R·Iqs"). In addition, the second component Sv2 is calculated based on the estimated rotation speed ωs and the estimated d-axis output current Ids (specifically, "Sv2 = ωs·(φ+Ld·Ids)").

[0062] The judgment voltage Vqj is determined to correspond to a state in which no step-out occurs and the motor rotation speed is the estimated rotation speed ωs. Therefore, the difference between the judgment voltage Vqj and the estimated q-axis indication voltage Vqc, that is, the voltage deviation hV, represents the degree (size) of step-out. In detail, in the voltage deviation hV, the degree of step-out is expressed according to the change of the second component Sv2 equivalent to the back electromotive force. For example, when the brushless motor BM is driven normally (that is, when no step-out occurs), the voltage deviation hV is determined to be "0". In contrast, the situation in which the brushless motor BM is completely stopped (that is, the situation in which the motor rotation speed is "0") is the worst state in step-out. In this worst state, since no back electromotive force is generated, the voltage deviation hV is determined to be equal to the second component Sv2. According to the above structure, since the degree of step-out of the sensorless brushless motor BM is appropriately expressed, a reliable step-out judgment can be performed.

[0063] In the determination unit BH, the calculation map Zhs for calculating the determination threshold value Hs is set to be larger than the characteristic Zes (steady-state error characteristic) of the error Es included in the sensorless control. As a result, the determination threshold value Hs is always calculated to be a value larger than the steady-state error Es. In other words, the determination threshold value Hs is not included in the steady-state error range Hes, but is determined outside it. As a result, the influence of the steady-state error Es is avoided in the step-out determination.

[0064] In the steady-state error characteristic Zes, the steady-state error Es increases as the motor rotation speed increases. In addition, the second component Sv2 indicating the degree of out-of-step changes according to the estimated rotation speed ωs. Therefore, in the calculation map Zhs for calculating the determination threshold Hs, the larger the estimated rotation speed ωs is, the larger the determination threshold Hs is determined to be. As a result, the determination threshold Hs can effectively avoid the steady-state error range Hes, and the out-of-step determination can be appropriately performed.

[0065] In the determination unit BH, when the estimated rotation speed ωs is less than the predetermined speed ωo, the execution of the out-of-step determination is prohibited. When the motor rotation speed is low, it is difficult to ensure the accuracy of the estimated rotation speed ωs. In addition, when the motor rotation speed is low, the possibility of out-of-step is lower than when the motor rotation speed is high. Therefore, in the case of "ωs<ωo", the out-of-step determination is not performed. As a result, the reliability of the out-of-step determination is improved.

Claims

1. A motor control device, comprising a control unit for performing sensorless control on a brushless motor having three phases and a determination unit for determining whether the brushless motor has lost step, wherein: The control unit performs the sensorless control based on the estimated d-axis output current, the estimated q-axis output current, the estimated d-axis indicated voltage, the estimated q-axis indicated voltage, and the estimated rotational speed. The determination unit calculates a determination voltage based on the estimated d-axis output current, the estimated q-axis output current and the estimated rotation speed, and determines that the step-out has occurred when a voltage deviation reaches a determination threshold, wherein the voltage deviation is a difference between the determination voltage and the estimated q-axis indicated voltage.

2. The motor control device according to claim 1, wherein: The determination unit determines the determination threshold value to be larger as the estimated rotation speed is larger.

3. The motor control device according to claim 1 or 2, wherein: The determination unit determines the determination voltage assuming that the brushless motor is not out of step and is rotating at the estimated rotation speed.

4. The motor control device according to claim 3, wherein: The determination unit is composed of: Based on the estimated q-axis output current, a first component corresponding to the voltage drop in the brushless motor is calculated. Based on the estimated rotation speed and the estimated d-axis output current, a second component corresponding to the back electromotive force in the brushless motor is calculated. The determination voltage is determined as the sum of the first component and the second component.

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