Angle detection system and angle detection method

Abstract

To enable easy adjustment of an initial position of a resolver.SOLUTION: A control device of an angle detection system controls the speed of a motor based on a speed estimation value based on an angle detection value of a resolver and a speed command of a desired value. The control device is configured to be capable of generating an angle detection value in which an offset from a true value of the angle of the motor contained in the angle detection value of the resolver is compensated for based on the initial position of the resolver. When estimating the initial position of the resolver, the control device drives the motor such that the speed estimation value is smaller than the speed command of the desired value, thereby generating a state in which the drive current of the motor is limited to a predetermined upper limit value, estimates the initial position of the resolver based on a position at which the difference between the speed command of the desired value and the speed estimation value is smaller in the limited state, and controls the speed of the motor such that the speed estimation value based on the compensated angle detection value becomes the speed command of the desired value when the speed of the motor is controlled using the initial position of the resolver.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to an angle detection system and an angle detection method.

Background Art

[0002] A resolver is used to detect the angle of a rotor of a motor connected to a shaft by detecting the angle (rotational position) of its shaft. Some resolvers can detect the absolute position with respect to its reference position. When improving the detection accuracy of an angle detection system, it has sometimes been difficult to adjust the initial position of the resolver to align the reference position of the resolver with the reference position of the motor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide an angle detection system and an angle detection method capable of easily adjusting the initial position of a resolver.

Means for Solving the Problems

[0005] The angle detection system of the embodiment includes a resolver and a control device. The resolver detects the angle of the motor. The control device controls the speed of the motor based on a speed estimation value based on the angle detection value of the resolver and a speed command of a desired value. The control device is configured to be able to generate an angle detection value obtained by compensating for an offset with respect to the true value of the angle of the motor included in the angle detection value of the resolver based on the initial position of the resolver. When estimating the initial position of the resolver, a state is generated in which the drive current of the motor is limited to a predetermined upper limit value by driving the motor using a speed command of the desired value that is larger than the speed estimation value. Based on the position where the speed estimation value becomes larger in the limited state, the initial position of the resolver is estimated. When controlling the speed of the motor using the initial position of the resolver, the speed of the motor is controlled such that the speed estimation value based on the compensated angle detection value becomes the speed command of the desired value.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

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Figure 7

Modes for Carrying Out the Invention

[0007] Hereinafter, an angle detection system, a motor drive system, and an angle detection method according to an embodiment will be described with reference to the drawings. Note that the drawings are schematic or conceptual, and the distribution of functions of each part is not necessarily the same as that in reality.

[0008] In the following description, components having the same or similar functions are denoted by the same reference numerals. And the redundant description of these components may be omitted. In the embodiment, "connected" includes being electrically connected. "Based on XX" means "based at least on XX", and may include cases based on another element in addition to XX. "Based on XX" is not limited to the case of directly using XX, and may include cases based on something obtained by performing operations or processing on XX. "XX or YY" is not limited to either XX or YY, and may include both XX and YY. This is the same when there are three or more selectable elements. "XX" and "YY" are arbitrary elements (for example, arbitrary information). An "inverter" is a power converter that outputs alternating current, and includes, for example, a DC / AC converter. A "motor" is a rotating electrical machine such as an induction motor driven by alternating current power. The "rotation speed of the motor" may be simply referred to as the "speed of the motor".

[0009] The "measured value of current" shown in the following description refers to the actual measured value of current, an index value indicating the actual magnitude of current, or an estimated value indicating the magnitude of current.

[0010] (Embodiment) FIG. 1 is a block diagram illustrating a motor drive system 1 according to an embodiment. For example, the motor drive system 1 includes a motor speed control device 10. The motor speed control device 10 is an example of a rotation position correction device. The motor drive system 1 may further include a motor 2 (denoted as M in FIG. 1), and a resolver 2A (denoted as SS in FIG. 1). The motor drive system 1 is an example of an angle detection system.

[0011] The motor speed control device 10 is connected to the motor 2 and the resolver 2A. The motor speed control device 10 controls the speed of the motor 2 so that the actual speed of the motor 2 detected by the resolver 2A matches the desired speed command value ω * .

[0012] The motor 2 includes a plurality of windings, and each winding is connected to the output of an inverter 30 described later. The inverter 30 is an example of a power converter. For example, the inverter 30 converts the DC power supplied from a DC power source 20 (described as DC in the figure) and drives the motor 2. For example, when AC from the inverter 30 flows through each winding, the motor 2 rotates due to electromagnetic action. For example, the shaft of the resolver 2A is mechanically connected to the shaft of the motor 2 by a method such as flange coupling, and the shaft of the resolver 2A rotates in conjunction with the rotation of the shaft of the motor 2.

[0013] The resolver 2A generates an AC signal according to the position of its own shaft. For example, the resolver 2A detects the magnetic flux excited by the current in the primary winding with the secondary winding. The voltage or current excited in the secondary winding becomes an AC signal including phase information corresponding to the angle difference between the direction of the excited magnetic flux and the direction of the secondary winding. The resolver 2A generates the AC signal as a detection signal of the position of its own shaft.

[0014] Note that the resolver 2A of the embodiment includes a signal converter inside. The signal converter generates an index value indicating the angle of the shaft of the resolver 2A, that is, an index value indicating the angle of the shaft of the motor 2 (referred to as an angle detection value θe2), based on the AC signal corresponding to the position of its own shaft. In other words, this resolver 2A generates and outputs an angle detection value θe2 corresponding to the detection result of the angle of the shaft of the motor 2. The signal converter includes an electronic circuit for signal processing. Therefore, the signal output by the signal converter may include an angle offset. Note that this signal converter may be configured separately outside the resolver 2A or may be included as a part of the motor speed control device 10 described later. In the following description, the case where it is built into the resolver 2A will be described.

[0015] For example, the motor speed control device 10 is a control device for the inverter 30 that drives the motor 2. The motor speed control device 10 is an example of a rotational position correction device.

[0016] The motor speed control device 10 includes a rotational position correction unit 3, a speed control unit 5, a current control unit 6, a PWM control unit 7 (denoted as PWM in the figure), a current value conversion unit 8, and a reference position estimation unit 9. Note that the speed control unit 5, the current control unit 6, and the PWM control unit 7 are examples of control units. General methods may be applied to this control.

[0017] The speed control unit 5 multiplies the speed deviation between the speed command value ω * and the speed estimated value ωFBK of the motor 2 by a predetermined speed response gain to generate a command value for the drive torque. The speed command value ω * is supplied from a host control device such as a programmable controller (PLC), for example. The speed command value ω * has a desired value set and is maintained at that value until the next value is set. The speed estimated value ωFBK of the motor 2 will be described later.

[0018] The current control unit 6 is connected to the output of the speed control unit 5. The current control unit 6 outputs a voltage command value V * generated according to the difference between the command value for the drive torque supplied from the speed control unit 5 and the estimated value of the torque current component supplied to the motor 2 (referred to as current iFBK).

[0019] The PWM control unit 7 drives the motor 2 by controlling the inverter 30 by PWM control (Pulse Width Modulation control). For example, the input of the PWM control unit 7 is connected to the output of the current control unit 6, and its output is connected to the inverter 30. The PWM control unit 7 outputs a gate control signal for the inverter 30 so as to drive the motor 2 according to the voltage command value V * generated by the current control unit 6.

[0020] For example, current transformers CT for detecting the phase current of each phase may be provided in the wiring connected to the output of the inverter 30. The current transformers CT may be provided in at least two of the wirings of each phase of the three-phase alternating current.

[0021] The current value conversion unit 8 generates a current detection value iFBK, which is an index value of the magnitude of the phase current, based on the instantaneous value of the phase current detected by the current transformer CT and the reference phase θ0 corresponding to the rotation of the motor 2. The current control unit 6 may perform current control using the current detection value iFBK.

[0022] The reference position estimation unit 9 estimates the initial position of the resolver 2A connected to the motor 2 of the motor drive system 1. The initial position is the reference position of the resolver 2A associated with the reference position of the rotor of the motor 2. In other words, the initial position is the reference position on the electrical signal output by the resolver 2A with respect to the mechanical reference position of the rotor of the motor 2. When the rotor of the motor 2 is at the reference position, the state where the reference positions of the resolver 2A coincide is the ideal state. However, the initial position of the resolver 2A may not be 0. The reference position estimation unit 9 estimates the initial position of the resolver 2A based on the magnitude of the phase current (current detection value iFBK) and the speed estimation value ωFBK, which will be described later. Details of this will be described later.

[0023] The first input of the rotational position correction unit 3 is connected to the output of the resolver 2A. For example, the rotational position correction unit 3 receives the angle detection value θe2 output from the resolver 2A and uses it for speed control of the motor 2. The second input of the rotational position correction unit 3 is connected to the output of the reference position estimation unit 9. For example, the rotational position correction unit 3 uses the position correction command value output by the reference position estimation unit 9 for rotational position correction.

[0024] For example, the rotational position correction unit 3 includes a detection value correction unit 31 and a speed conversion unit 32. The detection value correction unit 31 includes a correction value generation unit 31a and a subtractor 31b. The correction value generation unit 31a generates an angle adjustment amount Δθc corresponding to the position correction command value based on the position correction command value output by the reference position estimation unit 9. The subtractor 31b subtracts the angle adjustment amount Δθc from the angle detection value θe2 to generate an angle estimation value θe1. The angle adjustment amount Δθc is an example of angle correction information.

[0025] The speed conversion unit 32 acquires the angle estimation value θe1 generated by the detection value correction unit 31, and generates the aforementioned speed estimation value ωFBK and the like based on the angle estimation value θe1.

[0026] Note that the motor speed control device 10 includes, for example, a processor such as a CPU. By the processor executing a predetermined program, some or all of the functional units such as the rotation position correction unit 3, the speed control unit 5, the current control unit 6, the PWM control unit 7, the current value conversion unit 8, and the reference position estimation unit 9 may be realized, or the above may be realized by a combination of electrical circuits (circuitry). The motor speed control device 10 may use the storage area of the internal storage unit to execute the transfer process of each data and the arithmetic process for analysis by executing a predetermined program by the processor.

[0027] Next, with reference to FIGS. 2 to 4, a case of correcting the deviation (offset) of the angle information generated in the detection result of the resolver 2A will be described.

[0028] FIGS. 2 and 3 are diagrams for explaining the relationship between the magnitude of the angle adjustment amount Δθc added to the angle detection value in the embodiment, the speed ω of the motor 2, and the current I.

[0029] As a result of coupling the axis of the resolver 2A to the axis of the motor 2, a mechanical offset may occur between the reference position of the axis of the motor 2 and the reference position of the axis of the resolver 2A. Also, an electrical offset may occur between the reference position of the axis of the resolver 2A and the angle information converted by the converter. When these offsets occur, it becomes difficult to accurately detect the position of the axis of the motor 2 from the signal output by the resolver 2A. Hereinafter, when explaining without distinguishing between the mechanical offset and the electrical offset, it is simply referred to as the "offset of the output value". For example, if the offset of the output value is 0, the initial position is adjusted so that the combined value of the mechanical offset and the electrical offset becomes 0.

[0030] Figs. 2(a) and (b) show the relationship between the speed ω of the motor 2 and the drive current I flowing through the motor 2 when an angle adjustment amount is added to the output value of the resolver 2A in an ideal situation where there is no offset in the output value of the resolver 2A. For example, the horizontal axes in Figs. 2(a) and (b) indicate the magnitude of the added angle adjustment amount, and the origin thereof is associated with both the reference position of the axis of the motor 2 and the reference position of the axis of the resolver 2A.

[0031] As shown in Figs. 2(a) and (b), when the motor 2 is driven at a speed command value ω * the drive current I decreases in value when the added angle adjustment amount is 0, and increases in value as the added offset Δθc increases. When conducting such a test, it is necessary to be careful so that an excessive current does not flow.

[0032] Figs. 3(a) and (b) show the relationship between the speed ω of the motor 2 and the drive current I flowing through the motor 2 when an angle adjustment amount is added to the output value of the resolver 2A in a situation where an offset (θoffset) has occurred in the output value of the resolver 2A. For example, the horizontal axes in Figs. 3(a) and (b) indicate the magnitude of the added angle adjustment amount, and the origin thereof is associated with the reference position of the axis of the motor 2. θoffset indicates the offset that has occurred in the output value of the resolver 2A.

[0033] As shown in FIGS. 3(a) and 3(b), when the motor 2 is driven by a speed command value ω * the drive current I becomes smaller when the added angle adjustment amount Δθc is θoffset, and the value becomes larger as the added angle adjustment amount Δθc deviates from θoffset. When conducting such a test, it is necessary to pay attention so that an excessive current does not flow. In this way, by adjusting the magnitude of the added angle adjustment amount Δθc and identifying the magnitude of the angle adjustment amount Δθc when the value of the drive current I becomes smaller, the magnitude of the offset included in the output value of the resolver 2A can be identified.

[0034] Referring to FIG. 4, the process for canceling the offset of the output of the embodiment will be described. FIG. 4 is a flowchart of the process for canceling the offset of the output of the embodiment.

[0035] The rotation position correction unit 3 of the motor speed control device 10 determines an initial value as the starting point of the angle adjustment amount Δθc added to the output value of the resolver 2A to a predetermined angle (step SA1). The predetermined angle may be determined to be an arbitrary angle within one rotation of the motor 2. The motor speed control device 10 scans the angle adjustment amount Δθc so as to make one round according to the following procedure.

[0036] For example, the reference position estimation unit 9 detects the magnitude of the current value corresponding to the angle adjustment amount Δθc based on the output of the current value conversion unit 8 (step SA2). The motor speed control device 10 records the magnitude of the current value in association with each angle of the angle adjustment amount Δθc (step SA3). The rotation position correction unit 3 changes the magnitude of the angle adjustment amount Δθc by a predetermined amount (step SA4). The motor speed control device 10 determines whether or not the scan for making one round of the angle adjustment amount Δθc has ended (step SA5). As a result, if the scan for making one round has not ended, the motor speed control device 10 repeats the process from step SA2.

[0037] After the scan for making one round is completed, the reference position estimation unit 9 compares the magnitudes of the current values at each angle and selects the angle indicating the smallest current value (step SA6). The reference position estimation unit 9 identifies the selected angle as an offset included in the output value of the resolver 2A, sets the magnitude of the angle adjustment amount Δθc generated by the correction value generation unit 31a to the angle selected in step SA6 (step SA7), and ends a series of processes.

[0038] According to this procedure, the angle adjustment amount Δθc corresponding to the offset included in the output value of the resolver 2A can be determined. The motor speed control device 10 drives the motor 2 using this angle adjustment amount Δθc.

[0039] According to the above embodiment, the motor drive system 1 (angle detection system) includes a resolver 2A and a motor speed control device 10. The motor speed control device 10 is based on a speed estimated value ωFBK based on an angle detection value of the resolver 2A that detects the angle of the motor 2, and a speed command ω of a desired value * to control the speed of the motor 2. The motor speed control device 10 is configured to be able to generate an angle detection value obtained by compensating for an offset with respect to the true value of the angle of the motor 2 included in the angle detection value of the resolver 2A based on the initial position of the resolver 2A. The motor speed control device 10 generates an adjustment angle detection value during a detection period for detecting an offset from the true value of the angle of the motor 2, and based on the speed estimated value ωFBK based on the adjustment angle detection value and a speed command ω of a desired value * to control the speed of the motor 2. The motor speed control device 10 uses the detected value of the drive current of the motor 2 detected during the above detection period in association with the adjustment angle detection value to estimate the initial position of the resolver 2A. Thereby, the motor drive system 1 can easily adjust the initial position of the resolver 2A.

[0040] Note that the upper-level device may set the magnitude of the speed command value ω * when adjusting the reference position of the resolver 2A to a magnitude such that excessive current does not flow through the motor 2.

[0041] The speed control unit 5, the current control unit 6, and the PWM control unit 7 are such that when the speed estimated value ωFBK is the speed command value ω *The motor 2 is controlled so as to achieve this. The speed control unit 5, the current control unit 6, and the PWM control unit 7 are examples of control units that control the motor 2.

[0042] Note that the motor speed control device 10 may estimate the initial position of the resolver 2A based on the adjustment angle detection value when the detected value of the drive current of the motor 2 detected during the above detection period is smaller.

[0043] (Modification of the Embodiment) With reference to FIGS. 5 to 7, a modification of the embodiment will be described. In the above embodiment, one method of maintaining the speed of the motor 2 and scanning the reference position is exemplified, but the method is not limited to this. Instead, in this modification, a case will be described in which the reference position is scanned while maintaining the current by limiting the drive current of the motor 2 to a predetermined value. According to this modification, there is no need to pay attention to the drive current of the motor 2 becoming excessive. This will be described in detail below.

[0044] The motor speed control device 10 of the modification limits the drive current of the motor 2 within a predetermined range during the detection period of the initial position of the resolver 2A. Note that either the current control unit 6 or the PWM control unit 7 may be configured to limit the drive current of the motor 2 within a predetermined range. For example, the current control unit 6 may limit the drive current of the motor 2 within a predetermined range by limiting the command value of the drive voltage by a limit value specified by control. The PWM control unit 7 may limit the drive current of the motor 2 within a predetermined range by limiting the DUTY of the gate pulse by a limit value specified by control. This limitation is performed by control from the reference position estimation unit 9 described later.

[0045] FIGS. 5 to 7 respectively correspond to FIGS. 2 to 4 described above. FIGS. 5 and 6 are diagrams for explaining the relationship between the magnitude of the angle adjustment amount Δθc added to the angle detection value of the modification, the speed ω of the motor 2, and the current I.

[0046] In the cases shown in FIGS. 5 and 6, it is conditional to limit the drive current to a predetermined magnitude (upper limit value UL). For example, as the upper limit value UL of the drive current, a value smaller than the magnitude of the drive current flowing when the motor 2 is driven at the speed command value ω * is set. As a result, during the adjustment of the reference position, a state is formed in which a sufficient drive current cannot flow with respect to the magnitude of the speed command value ω * . Therefore, the speed of the motor 2 is always insufficient with respect to the speed command value ω * .

[0047] FIGS. 5(a) and 5(b) show the relationship between the drive current I flowing through the motor 2 and the speed ω of the motor 2 when an angle adjustment amount Δθc is added to the output value of the resolver 2A in an ideal situation where there is no offset in the output value of the resolver 2A.

[0048] As shown in FIGS. 5(a) and 5(b), when the drive current of the motor 2 is limited by the upper limit value UL, the speed of the motor 2 does not reach the speed corresponding to the speed command value ω * . The speed of the motor 2 becomes faster when the added offset is 0, and becomes slower as the added angle adjustment amount Δθc increases.

[0049] FIGS. 6(a) and 6(b) show the relationship between the drive current I flowing through the motor 2 and the speed ω of the motor 2 when an angle adjustment amount Δθc is added to the output value of the resolver 2A in a situation where an offset occurs in the output value of the resolver 2A.

[0050] As shown in FIGS. 6(a) and 6(b), when the drive current I is limited by the upper limit value UL even when trying to drive the motor 2 at the speed command value ω * , the speed command value ω *It does not reach the corresponding speed. The speed of the motor 2 is the fastest when the added angle adjustment amount Δθc is θoffset, and becomes slower as the added angle adjustment amount Δθc deviates from θoffset. In this way, by adjusting the magnitude of the offset Δθc to be added and identifying the magnitude of the angle adjustment amount Δθc when the value of the speed ω of the motor 2 is the largest, the magnitude of the offset θoffset included in the output value of the resolver 2A can be identified.

[0051] Referring to FIG. 7, a process for canceling the offset θoffset of the output value of the resolver 2A of the modified example will be described. FIG. 7 is a flowchart of a process for canceling the offset of the output of the modified example.

[0052] The rotation position correction unit 3 of the motor speed control device 10 determines an initial value as a starting point of the angle adjustment amount Δθc added to the output value of the resolver 2A to a predetermined angle (step SB1). The predetermined angle may be determined to be an arbitrary angle within one rotation of the motor 2. The motor speed control device 10 scans the angle adjustment amount Δθc so as to make one round according to the following procedure.

[0053] For example, the reference position estimation unit 9 detects the speed ω of the motor 2 corresponding to the angle adjustment amount Δθc based on the output of the current value conversion unit 8 (step SB2). The motor speed control device 10 records the speed ω of the motor 2 in association with each angle of the offset Δθc (step SB3). The rotation position correction unit 3 changes the magnitude of the angle adjustment amount Δθc by a predetermined amount (step SB4). The motor speed control device 10 determines whether or not the scanning for making one round of the angle adjustment amount Δθc has ended (step SB5). As a result, if the scanning for making one round has not ended, the motor speed control device 10 repeats the process from step SB2.

[0054] After the scanning for making one round is completed, the reference position estimation unit 9 compares the magnitudes of the speeds ω of the motor 2 at each angle and selects the angle indicating the largest value (step SB6). The reference position estimation unit 9 identifies the selected angle as an offset included in the output value of the resolver 2A, sets the magnitude of the angle adjustment amount Δθc generated by the correction value generation unit 31a to the angle selected in step SB6 (step SB7), and finishes a series of processes.

[0055] According to this procedure, the angle adjustment amount Δθc corresponding to the offset included in the output value of the resolver 2A can be determined. The motor speed control device 10 drives the motor 2 using this angle adjustment amount Δθc.

[0056] According to the above-described modification, the motor drive system 1 generates an adjustment angle detection value during a detection period for detecting an offset from the true value of the angle of the motor 2, and based on the speed estimation value ωFBK based on the adjustment angle detection value and a desired speed command ω * controls the speed of the motor 2, associates the speed estimation value detected during the detection period with the adjustment angle detection value and uses it to estimate the initial position of the resolver 2A. Thereby, the motor drive system 1 can easily adjust the initial position of the resolver 2A.

[0057] Note that the motor speed control device 10 may estimate the initial position of the resolver 2A based on the adjustment angle detection value when the speed estimation value detected during the above detection period is larger. The motor speed control device 10 may limit the drive current flowing through the motor 2 during the above detection period and detect the speed estimation value.

[0058] According to at least one embodiment described above, the angle detection system includes a resolver and a control device. The resolver detects the angle of the motor. The control device controls the speed of the motor based on a speed estimated value based on the angle detection value of the resolver and a speed command of a desired value. The control device is configured to be able to generate an angle detection value obtained by compensating for an offset with respect to the true value of the angle of the motor included in the angle detection value of the resolver based on the initial position of the resolver, and generates an adjustment angle detection value during a detection period for detecting the offset from the true value of the angle of the motor, and controls the speed of the motor based on the speed estimated value based on the adjustment angle detection value and a speed command of a desired value, and associates and uses the detected value of the current of the motor or the speed estimated value detected during the detection period with the adjustment angle detection value to estimate the initial position of the resolver. Thereby, the angle detection system can easily adjust the initial position of the resolver.

[0059] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, as well as in the invention described in the claims and the equivalent scope thereof.

Description of Reference Numerals

[0060] 1 Motor drive system, 2 Motor, 3 Rotation position correction unit, 4 History information processing unit, 5 Speed control unit, 6 Current control unit, 7 PWM control unit, 8 Current value conversion unit, 9 Reference position estimation unit, 10 Motor speed control device (rotation position correction device), 20 DC power supply, 30 Inverter, 31 Detection value correction unit, 32 Speed conversion unit

Claims

1. A resolver that detects the angle of the motor; a control device that controls the speed of the motor based on a speed estimate based on an angle detection value of the resolver and a speed command of a desired value; Equipped with The control device includes: a resolver angle detection value that is generated by compensating for an offset with respect to a true value of the motor angle, the offset being included in the resolver angle detection value, based on an initial position of the resolver; When estimating an initial position of the resolver, generating a state in which a drive current of the motor is limited to a predetermined upper limit value by driving the motor using a speed command of the desired value that is greater than the speed estimation value, and estimating an initial position of the resolver based on a position where the speed estimation value becomes the largest in the limited state; When the speed of the motor is controlled by utilizing the initial position of the resolver, a speed control for the motor so that a speed estimate based on the compensated angle detection value becomes a speed command of a desired value; Angle detection system.

2. The predetermined upper limit of the drive current is set to a predetermined speed command value (ω ＊ ) should be smaller than the magnitude of the drive current that flows when the The angle detection system according to claim 1 .

3. A computer that controls the speed of the motor based on a speed estimate based on an angle detection value of a resolver that detects an angle of the motor and a speed command of a desired value, a resolver angle detection value that is generated by compensating for an offset with respect to a true value of the motor angle, the offset being included in the resolver angle detection value, based on an initial position of the resolver; When estimating an initial position of the resolver, generating a state in which a drive current of the motor is limited to a predetermined upper limit value by driving the motor using a speed command of the desired value that is greater than the speed estimation value, and estimating an initial position of the resolver based on a position where the speed estimation value becomes the largest in the limited state; When the speed of the motor is controlled by utilizing the initial position of the resolver, a step of controlling the speed of the motor so that a speed estimate based on the compensated angle detection value becomes a speed command of a desired value; The angle detection method includes:

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