Motor control device

Abstract

A motor control device (11) is provided with a command value computation unit (31) and a disturbance observer unit (33). The command value computation unit computes a command value (T*) for controlling a motor (12) of a mechanical device (13). The disturbance observer unit estimates a disturbance (Tld) acting on the mechanical device on the basis of the command value and rotation information (θ) regarding the motor and corrects the command value on the basis of the estimated disturbance. The disturbance observer unit includes an estimator (33A) that has a nominal plant (P^). The nominal plant is a model that simulates the mechanical device, and is constituted only by an inertia term from among an inertia term, a viscosity term, and a rigidity term. The estimator estimates the disturbance on the basis of the difference between output of the mechanical device in response to the command value and output of the nominal plant in response to the command value.

Description

Motor control device

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

[0002] Conventionally, there have been motor control devices that control motors of mechanical devices. For example, the motor control device disclosed in Patent Document 1 has a command value calculation unit and a disturbance observer unit. The command value calculation unit calculates a command value for controlling the motor. The disturbance observer unit estimates a disturbance acting on the mechanical device based on the command value and motor rotation information, and corrects the command value based on the estimated disturbance.

[0003] The disturbance observer unit has parameters that are adjusted to suppress vibrations caused by disturbances with specific frequencies. By adjusting the parameters, it is possible to compensate for only the effects of disturbances with specific frequencies. The disturbances are, for example, torque ripples of a motor.

[0004] International Publication No. 2023 / 053212

[0005] The frequency of torque ripple can change depending on the angular velocity of the motor. Therefore, depending on the operating state of the mechanical device, the frequency of torque ripple may fall outside the target frequency range for compensating for the effects of disturbances. In this case, there is a concern that the effectiveness of suppressing vibrations caused by disturbances may decrease.

[0006] A motor control device according to one aspect of the present disclosure includes a command value calculation unit and a disturbance observer unit. The command value calculation unit is configured to calculate a command value for controlling a motor of a mechanical device. The disturbance observer unit is configured to estimate a disturbance acting on the mechanical device based on the command value and rotation information of the motor, and to correct the command value based on the estimated disturbance. The disturbance observer unit includes an estimator having a nominal plant. The nominal plant is a model simulating the mechanical device and is composed of only the inertia term out of an inertia term, a viscosity term, and a stiffness term. The estimator is configured to estimate the disturbance based on the difference between an output of the mechanical device corresponding to the command value and an output of the nominal plant corresponding to the command value.

[0007] Fig. 1 is a block diagram of a motor control device according to a first embodiment. Fig. 2 is a block diagram of the motor control device of Fig. 1. Fig. 3 is a graph showing frequency characteristics of disturbances after compensation by the disturbance observer unit of Fig. 2. Fig. 4 is a block diagram of a motor control device according to a second embodiment.

[0008] First Embodiment A motor control device according to a first embodiment will be described. As shown in FIG. 1 , a motor control device 11 controls a motor 12. The motor 12 generates torque for driving a mechanical device 13 on which the motor 12 is mounted. The motor 12 is, for example, a three-phase brushless motor. The motor 12 has a rotation angle sensor 12A. The rotation angle sensor 12A detects a rotation angle θ of the motor 12. The rotation angle θ of the motor 12 is rotation information of the motor 12.

[0009] The motor control device 11 includes a microcomputer 21, an inverter 22, and a current sensor 23. The microcomputer 21 is a processing circuit and includes a command value calculation unit 31 and a feedback calculation unit 32. These calculation units are functional parts realized by the CPU (Central Processing Unit) of the microcomputer 21 executing a control program. The microcomputer 21 includes a memory for storing the control program. The memory includes computer-readable media such as RAM (Random Access Memory) and ROM (Read Only Memory). However, realizing each calculation unit by software is just one example, and at least some of the calculation units may be realized by hardware circuits such as logic circuits.

[0010] The command value calculation unit 31 calculates a state variable S ｓｖ Based on this, the torque command value T ＊ The torque command value T ＊ is the target value of the torque to be generated by the motor 12. The feedback calculation unit 32 calculates the torque command value T ＊ Based on this, the current command value I ＊ The current command value I ＊is the target value of the current supplied to the motor 12. The feedback calculation unit 32 calculates the current command value I ＊ and the value of the current Im of the motor 12 detected by the current sensor 23 .

[0011] The inverter 22 operates based on a drive signal generated by the feedback calculation unit 32. The inverter 22 has a plurality of switching elements. The inverter 22 performs a switching operation based on the drive signal to generate a current command value I ＊ The power generated by the inverter 22 is supplied to the motor 12 via a power supply path formed by a bus bar, a cable, or the like. As a result, the motor 12 generates power according to the current command value I ＊ , and thus the torque command value T ＊ A torque corresponding to the

[0012] 2, the motor control device 11 has a disturbance observer 33. The disturbance observer 33 detects a disturbance T applied to the plant P. ｌｄ and estimate the disturbance T ｌｄ The plant P is an actual plant that is the object of actual control, that is, a mechanical device 13. ｌｄ Compensation for the effect of disturbance T ｌｄ In controlling a system subjected to a disturbance T ｌｄ Considering the characteristics of the disturbance T ｌｄ This means reducing the influence of disturbance T ｌｄ is a nonlinear torque, for example, a torque ripple of the motor 12. The torque ripple is a disturbance that occurs periodically in response to the rotation of the motor 12.

[0013] The control system of the motor 12 controls the state variable S of the mechanical device 13. ｓｖ The torque command value T for the motor 12 is calculated based on the ＊ It is a feedback control system that determines the torque command value T ＊ When a current is supplied from the inverter 22 to the motor 12 in accordance with ｍTherefore, the torque command value T ＊ to the rotation angle θ of the motor 12 are subject to control in the feedback control system.

[0014] The disturbance observer 33 calculates the torque command value T ＊ and the output of the plant P. An example of the output of the plant P is the rotation angle θ of the motor 12. The disturbance observer unit 33 receives the torque command value T ＊ and the rotation angle θ of the motor 12. ｌｄ Estimate.

[0015] The disturbance observer unit 33 may be configured by a hardware circuit such as a logic circuit. The disturbance observer unit 33 may also be referred to as a disturbance observer circuit. The disturbance observer unit 33 may be a functional part realized by the CPU of a computer executing a control program.

[0016] The disturbance observer unit 33 includes an estimator 33A and a first subtractor 33B. The estimator 33A calculates the disturbance T ｌｄ The disturbance T ｌｄ is a nonlinear torque that occurs in the machine 13, which is an actual plant, other than the torque generated by the motor 12, and that affects the rotation angle θ. The estimator 33A calculates an estimated disturbance T based on the nominal plant P^. ｌｄ ^ is calculated. Estimated disturbance T ｌｄ ^ is the disturbance T ｌｄ The nominal plant P^ is a model that simulates the machine 13, which is an actual plant.

[0017] The transfer function of the nominal plant P^ has only an inertia term, as shown in the following equation (1): P^=1 / (J·s ２ ) ...(1) "J" is the inertia coefficient that models the moment of inertia of the mechanical device 13. "s" is the Laplace operator. " / " represents division, and "·" represents multiplication.

[0018] The estimator 33A calculates the rotation angle θ of the motor 12, which is the output of the plant P, and the torque command value T ＊The estimator 33A takes in the rotation angle θ of the motor 12 and the torque command value T ＊ Based on this, the estimated disturbance T ｌｄ Calculate ^, where "^" indicates an estimated value.

[0019] The estimator 33A calculates the difference Δθ between the rotation angle θ of the motor 12 and the estimated rotation angle θ^ of the motor 12, for example, as shown in the following equation (2). The rotation angle θ of the motor 12 is calculated based on the torque command value T ＊ The estimated rotation angle θ^ of the motor 12 is obtained as the output of the plant P with respect to the torque command value T ＊ is obtained as the output of the nominal plant for

[0020] Δθ=θ−θ^ (2) For example, as shown in the following equation (3), the estimator 33A multiplies the difference Δθ between the rotation angle θ of the motor 12 and the estimated rotation angle θ^ of the motor 12 by the observer gain L to obtain the estimated disturbance T ｌｄ The symbol "·" represents multiplication.

[0021] T ｌｄ ^=Δθ·L (3) The first subtractor 33B subtracts the torque command value T calculated by the command value calculation unit 31. ＊ From the estimated disturbance T ｌｄ The first compensated torque command value T ｃ１ ＊ The first compensated torque command value T ｃ１ ＊ is the disturbance T ｌｄ The torque command value T ＊ is.

[0022] Torque command value T ＊ The transfer function from the rotation angle θ of the motor 12 is expressed by the following equation (4): θ={1 / (J·s ２ )・T ＊ ...(4) The disturbance observer unit 33 detects the disturbance T ｌｄ The disturbance T applied to the machine 13 after the effect of ｌｄ is the compensated disturbance T ｌｄｃ The disturbance after compensation T ｌｄｃ is expressed by the following equation (5).

[0023] Tｌｄｃ =T ｌｄ -T ｌｄ ^ ... (5) < Compensated disturbance T ｌｄｃ As shown in FIG. 3, the frequency characteristic of the compensated disturbance T ｌｄｃ The frequency characteristic of is defined by the relationship between frequency and gain. In FIG. 3, the horizontal axis represents frequency and the vertical axis represents gain. ｌｄｃ The frequency of a specific frequency f ｃ In the following case, the compensated disturbance T ｌｄｃ The gain of the compensated disturbance T ｌｄｃ The frequency of a specific frequency f ｃ Above this, the gain increases rapidly with increasing frequency.

[0024] Ideally, the minimum value of the gain is negative infinity. ＊ From a specific frequency f ｃ A disturbance T with a frequency ｌｄ Therefore, a specific frequency f ｃ A disturbance T with a frequency ｌｄ Vibration of the mechanical device 13 due to the vibration is suppressed.

[0025] However, the transfer function of the nominal plant P^ has only an inertia term, as shown in the above equation (1). Therefore, the disturbance observer 33 calculates all elements other than the nominal plant P^, including the torque ripple component, that is, all elements other than the inertia, as the disturbance T ｌｄ and the estimated disturbance T ｌｄ The disturbance observer unit 33 also cancels, for example, the stiffness component and the viscosity component of the mechanical device 13, which is the plant P. For this reason, depending on the mechanical device 13, there is a risk that the convergence or stability of the operation of the mechanical device 13 may decrease.

[0026] Therefore, the motor control device 11 may have the following configuration. <First compensation unit 41> As shown in Fig. 2, the motor control device 11 has a first compensation unit 41. The first compensation unit 41 calculates the torque command value T ＊The first compensator 41 includes a load model 41A and a second subtractor 41B.

[0027] The load model 41A is a model that simulates the mechanical load of the motor 12. The load model 41A has a stiffness term and a viscosity term. The load model 41A takes in the rotation angle θ of the motor 12, which is the output of the plant P. The load model 41A calculates the load torque T ｌ Calculate the load torque T ｌ is expressed by the following equation (6).

[0028] T ｌ = K θ + C s θ ... (6) "K" is a stiffness coefficient that models the stiffness of the mechanical device 13, and "C" is a viscosity coefficient that models the friction of the mechanical device 13. The stiffness coefficient K and the viscosity coefficient C may be the same as or different from the stiffness coefficient and viscosity coefficient of the mechanical device 13, which is the plant P. "s" is the Laplace operator. "θ" is the rotation angle of the motor 12. "·" represents multiplication.

[0029] Depending on the specifications, the load model 41A may have only a stiffness term or only a viscosity term. ＊ From the load torque T ｌ The second compensated torque command value T ｃ２ ＊ The second compensated torque command value T ｃ２ ＊ is the torque command value T ＊ The disturbance observer unit 33 calculates the second compensated torque command value T ｃ２ ＊ Using the estimated disturbance T ｌｄ Calculate ^.

[0030] When the motor control device 11 has a load model 41A, the torque command value T ＊ The transfer function from the rotation angle θ of the motor 12 is expressed by the following equation (7): θ={1 / (J·s ２ +C・s+K)}・T ＊...(7) "θ" is the rotation angle of the motor 12. "J" is the inertia coefficient that models the moment of inertia of the mechanical device 13. "K" is the stiffness coefficient that models the stiffness of the mechanical device 13. "C" is the viscosity coefficient that models the friction of the mechanical device 13. "s" is the Laplace operator. "T ＊ " is a torque command value. " / " represents division and "-" represents multiplication.

[0031] As can be seen from equation (7), the torque command value T ＊ The transfer function from the rotation angle θ of the motor 12 includes all of the inertia term, viscosity term, and stiffness term. That is, the rotation angle θ of the motor 12, which is the output of the plant P, reflects all of the inertia, viscosity, and stiffness.

[0032] Effects of the First Embodiment The first embodiment provides the following effects: (1-1) The motor control device 11 includes a command value calculation unit 31 and a disturbance observer unit 33. The command value calculation unit 31 calculates a command value for controlling the motor 12 of the plant P. The plant P is a mechanical device 13. The command value may be, for example, a torque command value T ＊ The disturbance observer unit 33 detects the disturbance T applied to the plant P based on the command value and the rotation information of the motor 12. ｌｄ and estimate the estimated disturbance T ｌｄ The rotation information of the motor 12 is, for example, the rotation angle θ of the motor 12. The disturbance observer unit 33 includes an estimator 33A having a nominal plant P^. The nominal plant P^ is a model that simulates the plant P, and is composed of only the inertia term among the inertia term, the viscosity term, and the stiffness term. The estimator 33A calculates the torque command value T ＊ The output of the plant P and the torque command value T ＊ Based on the difference between the output of the nominal plant P^ and the output of the disturbance T ｌｄ The disturbance T ｌｄ Estimating the disturbance T ｌｄ The estimated disturbance T ｌｄ ＾ The purpose is to calculate the following.

[0033] According to this configuration, the estimator 33A calculates all elements other than the nominal plant P^, i.e., all elements other than inertia, as the disturbance T ｌｄ Therefore, the estimated disturbance T ｌｄ Based on the torque command value T ＊ By correcting the disturbance T ｌｄ The correction can be performed by, for example, reducing the torque command value T ＊ From the estimated disturbance T ｌｄ The nominal plant P^ is a model consisting of only inertia terms, and is therefore simple. "Simple" means that it is simpler than the nominal plant P^, which also includes viscous terms and stiffness terms. For example, the stiffness term includes variable factors such as road surface conditions. In contrast, the inertia term can be derived relatively easily from the system specifications of the mechanical device 13. For this reason, the nominal plant P^, which includes only inertia terms, is easier to design than the nominal plant P^, which includes stiffness terms or viscous terms.

[0034] (1-2) The motor control device 11 may have a first compensation unit 41. The first compensation unit 41 compensates for the influence of the correction of the command value by the disturbance observer unit 33 based on rotation information of the motor 12. The rotation information of the motor 12 is, for example, the rotation angle θ of the motor 12. The command value is, for example, a torque command value T ＊ The first compensation unit 41 has a load model 41A that simulates the mechanical load of the motor 12. The load model 41A is, for example, a model that is composed of a viscosity term and a stiffness term. The first compensation unit 41 reflects the output of the load model 41A in response to the rotation information of the motor 12 in the command value. The output is a load torque T ｌ The reflection is, for example, the torque command value T ＊ From the load torque T ｌ The solution is to subtract

[0035] This configuration makes it possible to obtain a command value to which a viscosity component and a stiffness component are assigned. Furthermore, robustness of the control can be ensured. Second Embodiment Next, a motor control device according to a second embodiment will be described. This embodiment has a configuration basically similar to that of the first embodiment shown in FIGS. 1 to 3. Therefore, the same members and configurations as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

[0036] According to the first embodiment, the load model 41A calculates the torque command value T ＊ However, the load model 41A only has a stiffness term and a viscosity term. In other words, the load model 41A does not accurately represent the state of the actual plant P, and therefore there is a risk that necessary information may be lost from the output of the plant P. The necessary information differs depending on the mechanical device 13, but is, for example, information about the output of the plant P in the low frequency range of 10 Hz or less. In this way, depending on the mechanical device 13, the disturbance T ｌｄ There may be frequency regions where it is preferable not to compensate for the effect of

[0037] Therefore, in this embodiment, the following configuration is adopted as the motor control device 11. As shown in FIG. 4, the motor control device 11 has a second compensation unit 42 instead of the first compensation unit 41. The second compensation unit 42 calculates the estimated disturbance T ｌｄ ^, the torque command value T ＊ The second compensation unit 42 includes a high pass filter (HPF) 42A and a third subtractor 42B.

[0038] The high-pass filter 42A is a filter that attenuates frequency components of the electrical signal below a cutoff frequency, but does not attenuate frequency components higher than the cutoff frequency. The cutoff frequency is set to a low frequency range of, for example, 10 Hz or less.

[0039] The high-pass filter 42A is configured to filter the estimated disturbance T calculated by the estimator 33A. ｌｄThe high-pass filter 42A takes in the estimated disturbance T ｌｄ ^, the frequency components lower than the cutoff frequency are attenuated. ｌｄ The component of ^ is the disturbance T ｌｄ is not used to compensate for the effect of the estimated disturbance T after filtering by the high-pass filter 42A. ｌｄ ^ is the processed estimated disturbance T ｌｄ_ｆｉｌ ^.

[0040] The third subtractor 42B subtracts the torque command value T ＊ From the processed estimated disturbance T ｌｄ_ｆiｌ ^ is subtracted to obtain the second compensated torque command value T ｃ２ ＊ The disturbance observer unit 33 calculates the second compensated torque command value T ｃ２ ＊ Using the estimated disturbance T ｌｄ Calculate ^.

[0041] As described above, the high-pass filter 42A filters the estimated disturbance T in the frequency domain below the cutoff frequency. ｌｄ The disturbance observer 33 cuts off the disturbance T ｌｄ This is a frequency range where it is preferable not to compensate for the influence of the torque command value T ＊ Therefore, the rotation angle θ of the motor 12, which is the output of the plant P, does not include the torque command value T ＊ The components are reflected.

[0042] <Advantages of the Second Embodiment> In addition to the advantages described in the previous section (1-1), the second embodiment has the following advantages: (2-1) The motor control device 11 includes a second compensation unit 42. The second compensation unit 42 calculates the estimated disturbance T ｌｄ The influence of the correction of the command value by the disturbance observer unit 33 is compensated for based on the torque command value T ＊ The second compensator 42 has a high-pass filter 42A that is set to a specific cutoff frequency. The second compensator 42 calculates the estimated disturbance Tｌｄ The output of the high-pass filter 42A for ^ is reflected in the command value. The output is the processed estimated disturbance T ｌｄ_ｆｉｌ The reflection is, for example, the torque command value T ＊ From the processed estimated disturbance T ｌｄ_ｆｉｌ The answer is to subtract ^.

[0043] According to this configuration, the high-pass filter 42A filters the estimated disturbance T ｌｄ The cutoff frequency is set by the disturbance observer 33, for example, when the disturbance T ｌｄ The compensation is set based on a frequency range in which it is preferable not to compensate for the influence of the cutoff frequency. Since the frequency range components equal to or lower than the cutoff frequency are not removed from the command value, the command value components in the frequency range equal to or lower than the cutoff frequency can be reflected in the output of the plant P. The output of the plant P is, for example, the rotation angle θ of the motor 12.

[0044] Other Embodiments The first and second embodiments may be modified as follows: The command value calculation unit 31 calculates the state variable S ｓｖ Based on the torque command value T ＊ is calculated, and the calculated torque command value T ＊ Based on this, the current command value I ＊ The feedback calculation unit 32 may calculate the current command value I ＊ Based on this, feedback control of the current Im of the motor 12 is performed.

[0045] In this case, however, the motor control device 11 is provided with a first multiplier 33C. The first multiplier 33C is provided on the calculation path between the estimator 33A and the first subtractor 33B. The first multiplier 33C multiplies the estimated disturbance T ｌｄ ^ is multiplied by the first gain to obtain the current command value I ＊ First correction value I ｃ１ The first correction value I ｃ１ is the disturbance T ｌｄ This is the current value required to cancel out the vibration caused by the

[0046] The first subtractor 33B subtracts the torque command value T ＊ to the first correction value I ｃ１ The first compensated current command value I ｃ１ ＊ The first compensated current command value I ｃ１ ＊ is the disturbance T ｌｄ The current command value I ＊ The estimator 33A calculates the rotation angle θ of the motor 12 and the first compensated current command value I ｃ１ ＊ Based on this, the estimated disturbance T ｌｄ Even in this way, the disturbance T having the frequency to be suppressed is ｌｄ It is possible to compensate for the effect of

[0047] Furthermore, when the motor control device 11 has a load model 41A, a second multiplier 41C is provided in the motor control device 11. The second multiplier 41C is provided on the calculation path between the load model 41A and the second subtractor 41B. The second multiplier 41C multiplies the load torque T calculated by the load model 41A by ｌ is multiplied by the second gain to obtain the current command value I ＊ Second correction value I ｃ２ The second correction value I ｃ２ is the current command value I ＊ is a current value for imparting a stiffness component and a viscosity component to the

[0048] The second subtractor 41B calculates the current command value I ＊ to the second correction value I ｃ２ The second compensated current command value I ｃ２ ＊ The second compensated current command value I ｃ２ ＊ is the current command value I ＊ The disturbance observer unit 33 calculates the compensated current command value I ｃ２ ＊ Using the estimated disturbance T ｌｄ In this way, the current command value I ＊Therefore, the rotation angle θ of the motor 12, which is the output of the plant P, is affected by the current command value I ＊ The stiffness component and viscosity component of the

[0049] The estimator 33A calculates the torque command value T ＊ or current command value I ＊ Instead of the above, the motor torque may be taken in as the output of the plant P. The motor torque is the torque generated by the motor 12. The estimator 33A calculates an estimated disturbance T based on the rotation angle θ of the motor 12 and the torque generated by the motor 12. ｌｄ The torque of the motor 12 can be determined based on the rated output and rotation speed of the motor 12, for example.

[0050] The disturbance observer 33 calculates the angular velocity ω of the motor 12. ｍ may be taken as the output of the plant P. ｍ is the rotation speed of the motor 12. In this case, the disturbance observer unit 33 acquires the estimated angular speed of the motor 12 as the output of the nominal plant P^. The disturbance observer unit 33 acquires the angular speed ω of the motor 12 ｍ and the estimated angular velocity of the motor 12, and calculates the disturbance T ｌｄ Compensates for the effect of angular velocity ω ｍ is the rotation information of the motor 12. ｍ can be obtained, for example, by differentiating the rotation angle θ of the motor 12 detected by the rotation angle sensor 12A with respect to time.

[0051] The mechanical device 13 may be an electric power steering device. The motor 12 is an assist motor. The assist motor generates an assist torque that is applied to a steering mechanism of the vehicle. The assist torque is a torque that assists the steering of the steering wheel and is torque in the same direction as the steering direction of the steering wheel. The steering mechanism includes a steering shaft connected to the steering wheel and a turning shaft that turns the steered wheels of the vehicle. The assist torque is applied to the steering shaft or the turning shaft. The command value calculation unit 31 calculates a torque command value T for the assist motor in accordance with the steering torque detected by the torque sensor. ＊ The steering torque is the torque applied to the steering wheel. The steering torque is calculated by the state variable S ｓｖ is.

[0052] The disturbance observer 33 measures all elements other than inertia as disturbance T ｌｄ and the estimated disturbance T ｌｄ Therefore, there is a risk that necessary information will be lost from the output of the plant P. If the mechanical device 13 is an electric power steering device, the information that will be lost is, for example, road surface information. The road surface information includes the road surface reaction force transmitted to the steering wheel via the steered wheels. From the viewpoint of ensuring a good steering feel at the steering wheel, it is preferable that the road surface information be reflected in the output of the plant P. Therefore, if the mechanical device 13 is an electric power steering device, it is preferable to provide a second compensation unit 42 in the motor control device 11. In this way, it is possible to reflect the road surface information in the output of the plant P.

[0053] The mechanical device 13 may be a steer-by-wire type steering device. The motor 12 is a reaction motor or a steering motor. The reaction motor generates a steering reaction torque applied to a steering shaft of the vehicle. The steering reaction torque is a torque in the opposite direction to the steering direction of the steering wheel. The command value calculation unit 31 calculates a torque command value T for the reaction motor in accordance with the steering torque detected by the torque sensor. ＊The steering motor generates a steering torque for steering the steered wheels of the vehicle. The command value calculation unit 31 calculates a torque command value T ＊ The steering angle is calculated based on the rotation angle θ of the motor 12 detected by the rotation angle sensor 12A, for example. The steering torque and the steering angle are calculated based on the state variable S ｓｖ is.

[0054] The mechanical device 13 is not limited to a steering device of a vehicle. The mechanical device 13 may be, for example, a machine tool driven by the motor 12.

Claims

1. A motor control device comprising: a command value calculation unit configured to calculate a command value for controlling a motor of a mechanical device; and a disturbance observer unit configured to estimate a disturbance acting on the mechanical device based on the command value and rotation information of the motor, and to correct the command value based on the estimated disturbance, wherein the disturbance observer unit includes an estimator having a nominal plant, the nominal plant being a model simulating the mechanical device and consisting of only the inertia term out of an inertia term, a viscosity term, and a stiffness term, and the estimator is configured to estimate the disturbance based on the difference between the output of the mechanical device in response to the command value and the output of the nominal plant in response to the command value.

2. A motor control device as described in claim 1, further comprising a first compensation unit configured to compensate for the effect of correction of the command value by the disturbance observer unit based on rotation information of the motor, wherein the first compensation unit has a load model that simulates the mechanical load of the motor, the load model being a model composed of the viscosity term and the stiffness term, and the first compensation unit is configured to reflect the output of the load model in response to the rotation information of the motor in the command value.

3. A motor control device as described in claim 1, further comprising a second compensation unit configured to compensate for the effect of correction of the command value by the disturbance observer unit based on the estimated disturbance, the second compensation unit having a high-pass filter set to a specific cutoff frequency, and the second compensation unit configured to reflect the output of the high-pass filter with respect to the estimated disturbance in the command value.

4. A motor control device according to any one of claims 1 to 3, wherein the mechanical device is a steering device of a vehicle, and the motor generates torque to be applied to the steering device.

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