Motor control device

Abstract

Provided is a control device capable of estimating a motor output torque in a unified manner without deteriorating the accuracy of feedback control, torque monitoring, and the like. As a functional structure when a motor is controlled by rectangular wave control, the motor control device is provided with: a power factor calculation unit that obtains a power factor on the basis of a voltage phase command and current phases of a d-axis current and a q-axis current obtained by converting a three-phase current on the basis of a rotation angle of the motor; a reference power factor calculation unit that obtains a reference power factor on the basis of a torque command for the motor; a current correction unit that corrects the d-axis current and the q-axis current using a power factor ratio, which is a ratio between the power factor and a reference power factor; and a torque estimation unit that estimates the torque of the motor on the basis of the corrected d-axis current, the corrected q-axis current, and a torque estimation map in which the torque is set on the basis of the d-axis current and the q-axis current.

Description

Technical Field

[0001] This invention relates to a device for controlling a motor via an inverter, particularly a device for controlling a three-phase synchronous motor. Background Technology

[0002] For controlling such motors, PWM control and rectangular wave control are known. In PWM control, the three-phase current is converted into d-axis and q-axis currents using the motor's rotation angle, and the torque (or voltage) is estimated based on the mapping. This is sometimes called the dq-axis mapping method. Conversely, in rectangular wave control, the torque (or voltage) is estimated based on the current amplitude, voltage amplitude, motor speed, and power factor. This is sometimes called the effective power method. Generally, when the motor is actually running, voltage control based on PWM control is executed when the induced voltage is lower than the system voltage (low-to-medium speed region), and rectangular wave voltage control is executed when the induced voltage reaches the system voltage (high-speed region); the two control methods coexist.

[0003] On the other hand, in PWM control, the d-axis and q-axis currents are calculated based on the motor's rotation angle, making it susceptible to the accuracy of the rotation angle detection. However, in feedback control, both the command and estimated values ​​for calculating the control deviation are based on the motor's rotation angle, and the difference between them cancels out the detection accuracy. Therefore, as long as the feedback control itself is performed correctly, there is no problem. In contrast, in rectangular wave control (effective power mode), since control is not based on the motor's rotation angle, it is less affected by sensor detection accuracy, external interference, etc., and has higher durability. Conversely, if estimated values ​​based on the d-axis and q-axis currents are used in feedback control or torque monitoring, only these estimated values ​​become affected by the accuracy of the motor rotation angle detection; therefore, the control deviation or feedback control error may increase. In addition, it is possible to unify the torque estimation value used in feedback control to the value obtained by the effective power method. However, the torque estimation based on the effective power method is based on the premise that the voltage of the rectangular wave is fixed. In contrast, in PWM control, the voltage modulation is the premise. Therefore, it is difficult to use the torque estimation based on the effective power method in PWM control.

[0004] Patent Document 1 discloses a technical solution aimed at improving the control accuracy of motor torque based on rectangular wave control. The control system described in Patent Document 1 includes a control device that performs feedback control to adjust voltage phase commands. It calculates a first value for the control deviation using the product of a current amplitude command and a power factor command, and a second value using the product of the actual current amplitude and the actual power factor. Therefore, in the control system described in Patent Document 1, the current amplitude is calculated as the magnitude of the current vector, thus improving the control accuracy of the motor's output torque without being affected by the detection accuracy of the rotation angle sensor.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 7435189 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] In a three-phase synchronous motor, as described above, due to the influence of the induced voltage, PWM control and rectangular wave control are switched and executed according to the motor speed. Correspondingly, if the estimation of the motor output torque used for feedback control and torque monitoring is switched to an estimation based on dq-axis mapping and an estimation based on effective power, the control may become complex, and the torque fluctuations associated with the control switching may increase. In the control system described in Patent Document 1, the torque estimation in rectangular wave control is based on effective power; therefore, an output torque estimation different from that based on PWM control is performed, allowing for improvements in control simplification and elimination of torque fluctuations.

[0010] This invention was made in view of the above-mentioned technical problems, and its purpose is to provide a control device that can estimate the motor output torque in a uniform manner without compromising the accuracy of feedback control, torque monitoring, etc.

[0011] Methods for solving problems

[0012] To achieve the above objectives, the present invention provides a motor control device that uses an inverter to convert direct current to alternating current and control a motor. The device is characterized by comprising, as a functional structure for controlling the motor via rectangular wave control, a power factor calculation unit that calculates a power factor based on the current phase and voltage phase commands of the d-axis and q-axis currents, wherein the d-axis and q-axis currents are obtained by converting the three-phase currents based on the rotation angle of the motor; a reference power factor calculation unit that calculates a reference power factor based on a torque command for the motor; a current correction unit that corrects the d-axis and q-axis currents using the ratio of the power factor to the reference power factor, i.e., a power factor ratio; and a torque estimation unit that estimates the torque of the motor based on the corrected d-axis and q-axis currents and a torque estimation mapping, wherein the torque estimation mapping is obtained by setting the torque based on the d-axis and q-axis currents.

[0013] Invention Effects

[0014] According to the present invention, a mapping for estimating torque is used in the dq-axis mapping method to obtain the estimated torque. In this case, when the motor is controlled by a rectangular wave, the d-axis current and q-axis current are corrected according to the ratio of the reference power factor to the actual power factor, i.e., the power factor ratio. The corrected current value is used as the independent variable, and the estimated torque value is obtained according to the mapping. Therefore, in both rectangular wave control and PWM control, the motor torque can be estimated using the dq-axis mapping method, thus simplifying control without compromising the accuracy of the torque estimation. Attached Figure Description

[0015] Figure 1 This is a block diagram illustrating the functional structure of the control device in an embodiment of the present invention.

[0016] Figure 2 This is a block diagram illustrating the functional structure of the torque monitoring unit in an embodiment of the present invention.

[0017] Figure 3 (a) is a graph showing the relationship between power factor and induced voltage, (b) is a graph showing the relationship between current amplitude and induced voltage, and (c) is a graph showing the relationship between induced voltage and AC power.

[0018] Figure 4 This is a flowchart illustrating an example of control performed in an embodiment of the present invention.

[0019] Explanation of reference numerals in the attached figures

[0020] 1: Control device; 2: PWM control unit; 2a: dq current value calculation unit; 2b: Feedback control unit; 2c: PWM generation unit; 3: Square wave control unit; 3a: Power conversion unit; 3b: Feedback control unit; 3c: Power calculation unit; 3d: Square wave generation unit; 4: Control mode switching determination unit; 5: Realization torque monitoring unit; 5a: Torque estimation unit; 5b: Monitoring unit; 5c: Reference power factor calculation unit; 5d: Power factor calculation unit; 5e: Current correction unit; Id: d-axis current; Iq: q-axis current. Detailed Implementation

[0021] Next, embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, the embodiments described below are merely examples of how the present invention can be implemented and are not intended to limit the scope of the invention.

[0022] In embodiments of the present invention, the motor, the inverter that converts DC to AC and controls the motor, and the energy storage device that serves as the power source can be conventionally known structures such as those described in Patent Document 1. The control device 1 in embodiments of the present invention is primarily composed of a microcomputer consisting of an arithmetic unit (CPU), storage units (RAM, ROM), and an interface (I / F). It is configured to use various input data (input signals) and pre-stored data to perform calculations according to a prescribed program, output the calculation results as control command signals, and monitor the calculation results.

[0023] The output control command signal is the inverter control signal for controlling the inverter. For this control, PWM control and rectangular wave control are performed. Furthermore, as a result of this control, the torque output by the motor (realized torque) is monitored. Figure 1 The functional structure of the control device 1, which possesses these functions, is illustrated in the block diagram. First, taking an example of the input data (hereinafter sometimes referred to as input signals), the inputs are the d-axis current Id (A: amperes) and the q-axis current Iq (A: amperes). The motor is a three-phase synchronous motor; the three-phase currents (U-phase current, V-phase current, W-phase current) are converted based on the motor's rotation angle, and their d-axis current Id and q-axis current Iq are calculated. Additionally, the voltage phase θv (deg, degrees) is input to calculate the power in the rectangular wave control and to obtain a torque estimate for torque monitoring. Furthermore, the voltage amplitude |V|, calculated based on the system voltage VH and modulation rate Vr, and the motor speed are input. A torque command is also input. The torque command, for example, can be the driving torque for driving (acceleration) calculated in an electric vehicle equipped with a motor based on the accelerator pedal angle and vehicle speed. Furthermore, a control mode signal selected based on the motor speed or modulation rate is input. Here, the selected control modes are rectangular wave control and PWM control.

[0024] The control device 1 includes a PWM control unit 2, which generates a pulse signal (PWM) for controlling the inverter. The PWM control unit 2 includes a dq current value calculation unit 2a, which calculates the d-axis current value Id and the q-axis current value Iq. A predetermined correlation exists between the d-axis current Id and the q-axis current Iq and the torque output by the motor. This correlation can be prepared in advance as a torque mapping determined using the d-axis current Id and the q-axis current Iq as independent variables. The torque is provided as a torque command, and the mapping is pre-stored as data. Therefore, the dq current value calculation unit 2a calculates the command values ​​of the d-axis current Id and the q-axis current Iq based on the torque and mapping according to the torque command. Sometimes, the method of calculating the command value of the d-axis current Id (Id command) and the command value of the q-axis current Iq (Iq command) using the mapping and torque is called the dq-axis mapping method.

[0025] The actual torque output by the motor may sometimes differ from the indicated torque due to external interference such as deviations in the detection accuracy of the rotation angle. A feedback control unit 2b is provided in the PWM control unit 2, which performs feedback control to correct this control deviation. The detected values ​​of the d-axis current Id and the q-axis current Iq are input to the feedback control unit 2b. The difference between these detected values ​​and the command values ​​(Id command, Iq command) calculated by the dq current value calculation unit 2a is used as the control deviation, and the voltage command value is calculated accordingly. This feedback control can be a conventionally known control such as PID control, and the coefficients in its formula can be determined through experiments, simulations, etc.

[0026] The PWM control unit 2 includes a PWM generation unit 2c, which generates a pulse signal for controlling the motor based on the voltage command obtained in this way. Motor control based on this PWM generation unit 2c can be performed in the same way as conventional control.

[0027] Next, the rectangular wave control unit 3 will be described. The rectangular wave control unit 3 generates and outputs a rectangular wave for controlling the motor. For this purpose, firstly, a power conversion unit 3a is provided to convert the indicated torque into power. This power can be calculated using a so-called effective power method, and the torque can be converted into power using the following previously known relationship between voltage amplitude, current amplitude, motor rotation angle, and torque.

[0028] Mathematical Formula 1

[0029]

[0030] A feedback control unit 3b is provided in the rectangular wave control unit 3. This feedback control unit 3b uses the difference between the indicated torque and the actual torque output by the motor as a control deviation and performs feedback control. The actual power value supplied or consumed by the motor is input to this feedback control unit 3b. This power value can be calculated based on the d-axis current Id, the q-axis current Iq, and the phase difference θv of these currents with the q-axis current Iq as a reference. A power calculation unit 3c is provided in the rectangular wave control unit 3, which performs this calculation.

[0031] The feedback control unit 3b uses the difference between the power command value calculated based on the command torque and the power value calculated by the power calculation unit 3c as the control deviation and calculates the voltage command value. This feedback control can be a conventionally known control such as PID control, and the coefficients in its formula can be determined through experiments, simulations, etc.

[0032] The rectangular wave control unit 3 is provided with a rectangular wave generation unit 3d, which generates a rectangular wave for controlling the motor based on the voltage command obtained in this way. As for motor control, the control based on the rectangular wave generation unit 3d can be the same as conventional control.

[0033] As a control mode for the motor, the aforementioned PWM control and rectangular wave control can be switched or selected based on the modulation rate or motor speed, or based on the relationship between system voltage and induced voltage. The relationship between the control mode and the modulation rate is as described in Patent Document 1 above. The control device 1 is provided with a control mode switching determination unit 4, which determines the actual control mode used in motor control based on the control mode thus determined. As an inverter control signal, a control signal (a pulse signal or rectangular wave signal based on PWM control) is output based on the control mode selected by the control mode switching determination unit 4.

[0034] On the other hand, the control device 1 is equipped with a torque monitoring unit 5, which monitors for any abnormalities in the actual torque output of the motor. Its basic functions are as follows: to estimate the actual torque output of the motor, compare this estimated torque value with the commanded torque, and monitor for any abnormalities where the deviation exceeds a predetermined reference value. The torque monitoring unit 5 is equipped with a torque estimation unit 5a, which calculates the estimated torque value. The aforementioned d-axis current Id and q-axis current Iq are input to the torque estimation unit 5a. In addition, the phase difference θv of these currents, with the q-axis current Iq as a reference, and a signal indicating the control mode are also input. Based on these input data, the torque estimation unit 5a calculates the torque using a dq-axis mapping method. The calculated torque is an estimated value for the actual torque output of the motor. The torque monitoring unit 5 is equipped with a monitoring unit 5b, which compares this estimated torque value with the torque commanded by the motor and determines whether any abnormalities exist. As a result of torque comparison, the determination can be as follows: cases where the deviation is above a preset reference value are considered "abnormal", and cases where the deviation is less than the reference value are considered "normal".

[0035] In embodiments of the present invention, the d-axis current Id and the q-axis current Iq are further corrected, and a torque estimate is obtained. For example, the torque monitoring unit 5 is configured to perform this correction using the power factor ratio. Figure 2 This is a block diagram illustrating its functional structure. First, in order to calculate the power factor ratio, a reference power factor calculation unit 5c and a power factor calculation unit 5d are provided. The reference power factor is the power factor calculated based on the torque command, which can be calculated based on the input torque command, voltage amplitude |V|, and motor speed, etc., using the above equation (1). The power factor is the cosine of the phase difference between the apparent power and the effective power. The power factor calculation unit 5d calculates the power factor based on the above d-axis current Id and q-axis current Iq.

[0036] A current correction unit 5e is provided, which corrects the d-axis current Id and the q-axis current Iq based on these reference power factors and power factors. First, in order to perform this correction, the ratio of the reference power factor to the power factor (=reference power factor / power factor), i.e., the power factor ratio, is calculated. Furthermore, since the current value correction is performed when the motor is under rectangular wave control, the power factor ratio is set to "1" when PWM control is executed. Therefore, a signal indicating the control mode, the d-axis current Id, and the q-axis current Iq are input to the current correction unit 5e. By multiplying the detected d-axis current Id and q-axis current Iq by the power factor ratio (Id×power factor ratio, Iq×power factor ratio) respectively, the corrected d-axis current value and the corrected q-axis current value are obtained, thereby performing correction based on the current correction unit 5e. Based on the corrected d-axis current value and the corrected q-axis current value obtained in this way, the torque estimation unit 5a calculates the torque estimation value by dq-axis mapping.

[0037] Here, we explain the technical significance of using the power factor ratio to correct the d-axis current Id and the q-axis current Iq. The torque estimation mapping (torque estimation mapping) calculated based on the d-axis current Id and the q-axis current Iq is based on the following equation (2).

[0038] Mathematical formula 2

[0039] T=Pn(φ*Iq+(Ld-Lq)*Id*Iq)…(2)

[0040] In addition, T represents torque, and Pn represents the number of pole pairs of the motor. Let Ld be the induced voltage, Lq be the d-axis inductance, and Lq be the q-axis inductance. It can be said that the torque estimation mapping is based on the above equation (2) and the induced voltage... It is manufactured with each inductor Ld and Lq fixed. However, the induced voltage... Sometimes deviations occur due to the temperature of the motor rotor. In addition, the inductors Ld and Lq sometimes vary depending on the motor. Therefore, these factors can sometimes be the main reasons for the deviation between the estimated torque calculated from the mapping and the actual torque.

[0041] On the other hand, the estimation of torque based on the effective power mode is based on the following equation (3).

[0042] Mathematical Formula 3

[0043]

[0044] In addition, |V| represents the voltage amplitude, N represents the motor speed, θi represents the current phase, and θv represents the voltage phase.

[0045] It can be said that if the voltage amplitude |V| and the motor speed N are fixed, then equation (3) maps the above torque estimate to the induced voltage in equation (2) above. The inductors Ld and Lq are replaced with power factors (cosθ), and the torque is defined.

[0046] Furthermore, in reality, the power factor is relative to the induced voltage. The changes in inductances Ld and Lq are proportional. Therefore, it can be assumed that the prescribed relationship between the torque estimation value based on the dq-axis mapping method and the torque estimation value based on the effective power method holds true. If the torque estimation is performed based on the effective power method, it can be correlated with the induced voltage. The actual torque is uniquely maintained regardless of the changes in each inductor Ld and Lq.

[0047] However, when controlling the motor output using the effective power method, an accurate torque estimation value cannot be obtained if the torque is estimated based on the dq-axis mapping method using the detected d-axis current Id and q-axis current Iq. To correct this, a correction based on the aforementioned power factor ratio is performed.

[0048] As mentioned above, if the induced voltage If all inductors Ld and Lq are under the same conditions (i.e., the same motor and the same induced voltage), then the same torque will be calculated in both equations (2) and (3) above. Furthermore, in equation (3), even if the induced voltage... The changes in inductors Ld and Lq, along with variations in the power factor, cause the current amplitude |I| to increase or decrease, thereby maintaining a constant torque. Figure 3 The relationship is shown in the figure.

[0049] Figure 3 (a) shows the relationship between the power factor and the induced voltage, with the power factor increasing proportionally to the increase in the induced voltage. Figure 3 (b) shows the relationship between the current amplitude and the induced voltage. Based on the product of the current amplitude and the power factor, the power command is fed back for control, and therefore the current amplitude is reduced accordingly to the increase in the power factor. Figure 3 (c) shows the relationship between induced voltage and AC power, by increasing or decreasing the current amplitude |I| in accordance with the change in induced voltage, so that the AC power (i.e. shaft torque) is approximately constant.

[0050] If this relationship is applied to equation (2), the power factor will be relative to the induced voltage. And considering the changes in each inductor Ld and Lq, it is possible to pre-measure the power factor when creating the torque estimation map, and use this power factor as a reference power factor to calculate the ratio (power factor ratio) to the current power factor. Based on this power factor ratio, the d-axis current Id and the q-axis current Iq are corrected. That is, the following can be calculated:

[0051] Corrected d-axis current Id = Id × power factor ratio

[0052] Correct the q-axis current Iq = Iq × power factor ratio.

[0053] In PWM control, the power factor ratio is set to "1". Therefore, the torque estimate will follow the feedback of equation (2) above, and the desired torque estimate value can be obtained. In addition, in rectangular wave control, feedback is performed based on equation (3) above. However, since the corrected d-axis current Id and corrected q-axis current Iq, which are corrected by the power factor ratio as described above, are used, the obtained estimate torque is consistent with the value based on the torque estimate mapping. That is, the monitoring of the torque can be unified to the dq-axis mapping method.

[0054] Next, refer to Figure 4 The flowchart shown illustrates an example of control in an embodiment of the present invention. Figure 4 The control process for calculating the estimated torque value is shown, executed by the control device 1 of the present invention. First, the control mode is determined in step S1. Figure 4 In the example shown, it is determined whether the control mode is rectangular wave control. In step S1, if it is determined to be rectangular wave control, the process proceeds to step S2 and the power factor is calculated. This calculation can be performed based on the following formula.

[0055] Mathematical expression 4

[0056] θi=tan -1 (Iq / Id)

[0057] Pf = cos(θv - θi)

[0058] In addition, θi is the current phase, θv is the voltage phase command, and Pf is the power factor.

[0059] In addition, the reference power factor is calculated in step S3. The reference power factor is obtained based on a pre-prepared reference power factor mapping. The reference power factor mapping is a mapping that determines the reference power factor using motor speed and torque command values ​​as parameters, and is created according to each voltage amplitude |V| (= inverter voltage × modulation rate). However, the reference power factor mapping is as follows: the power factor is measured under the same conditions as when creating the torque estimation mapping used in the dq axis mapping method. Furthermore, the execution order of steps S2 and S3 is arbitrary; either one can be performed first, or they can be performed simultaneously in parallel.

[0060] In step S4, the ratio of the power factor obtained in steps S2 and S3 to the reference power factor is calculated (power factor ratio = reference power factor / power factor). Using the obtained power factor ratio, the detected d-axis current Id and q-axis current Iq are corrected. In step S5, the corrected d-axis current Id and corrected q-axis current Iq are calculated and used as current values ​​for torque estimation. Then, in step S6, using these corrected d-axis currents Id and corrected q-axis currents Iq as independent variables, the torque estimation value is obtained according to the torque estimation mapping. After that, the process temporarily ends. Figure 4 The routine is as follows. Here, the torque estimation mapping is the same mapping used in the dq axis mapping method, except that the independent variable is the corrected current value.

[0061] On the other hand, if the control mode determined in step S1 is PWM control, proceed to step S7 and obtain the d-axis current Id and q-axis current Iq. Then, proceed to step S6 to calculate the torque estimation value based on the torque estimation mapping, and then temporarily end the process. Figure 4 This is a routine. It is based on the torque estimation of the usual dq axis mapping method.

[0062] Finally, Figure 4 In the control example shown, the power factor ratio is used to correct the d-axis current Id and the q-axis current Iq. By using this correction value, torque estimation for torque monitoring can be performed using the dq-axis mapping method. That is, the torque estimation used for torque monitoring in PWM control and rectangular wave control can be unified without amplifying errors such as deviations in the estimated values, thus simplifying the control process.

Claims

1. A motor control device, wherein the motor control device uses an inverter to convert DC to AC and control the motor, characterized in that, As a functional structure for controlling the motor via rectangular wave control, the motor control device includes: The power factor calculation unit calculates the power factor based on the current phase and voltage phase commands of the d-axis current and q-axis current, which are obtained by converting the three-phase current based on the rotation angle of the motor. A reference power factor calculation unit calculates a reference power factor based on a torque command for the motor. The current correction unit corrects the d-axis current and the q-axis current using the ratio of the power factor to the reference power factor, i.e., the power factor ratio. as well as The torque estimation unit estimates the torque of the motor based on the corrected d-axis current, the corrected q-axis current, and a torque estimation mapping, wherein the torque estimation mapping is obtained by setting the torque according to the d-axis current and the q-axis current.

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