CN112352378A - Motor control device, motor control method, and motor system - Google Patents

Abstract

In one embodiment, a motor control device of the present disclosure determines a command value of a current vector in a dq coordinate system that rotates in synchronization with a rotor, based on a torque command value, and includes: a processor and a memory, the memory recording the magnet interlinkage magnetic flux psi of the motor_aA predetermined coefficient a, d-axis inductance L_dAnd q-axis inductance L_qCoefficient b and number of pole pairs N defined by the difference_pp. When the processor receives the torque command value, the processor executes the following processing: (a) determining the number of relative pole pairs N of the torque command value_ppA coefficient c defined by the ratio of (A) to (B); (b) calculating the equation satisfying the torque ax +2bxy-c equal to 0 and making x²+y²Minimized values of x and y; (c) a vector having x as a q-axis component and y as a d-axis component is determined as a command value of the current vector.

Description

Motor control device, motor control method, and motor system

Technical Field

The present disclosure relates to a motor control device, a motor control method, and a motor system for a synchronous motor.

Background

In order to control a synchronous motor such as a permanent magnet synchronous motor, a vector control algorithm is used. In the vector control, it is necessary to determine a current vector in a dq coordinate system that rotates in synchronization with the rotation of the rotor, based on a speed command value or a torque command value. When determining the current vector, Maximum Torque/current (MTPA: Maximum Torque Per amp) control for maximizing Torque with respect to current is put to practical use. The MTPA control is a control for selecting a current vector having the smallest magnitude among current vectors generating the same torque. Hereinafter, the magnitude of the current vector is referred to as a "norm" in the present specification. In order to minimize the norm of the current vector under the same torque, it is necessary to determine the current vector so that the distance from the origin to the constant torque curve is shortest on the dq coordinate plane defining the current vector.

Such a determination of the current vector can be performed as follows. First, a table (or map) is prepared in advance in which a plurality of values of the torque are associated with a current vector that realizes each value with the minimum norm. When a torque command value is received during control of the motor, a corresponding current vector is read from the table.

The motor control device described in japanese laid-open patent publication 2016-100982 includes a map for defining a relationship between inductance and a current vector in order to reduce the amount of data in the table.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2016-100982

Disclosure of Invention

Problems to be solved by the invention

As described below, conventional maximum torque/current (MTPA) control has various problems. Embodiments of the present disclosure provide a new motor control device and motor control method that realize minimum current/torque control instead of maximum torque/current control. In addition, an embodiment of the present disclosure provides a motor system including the motor control device.

Means for solving the problems

In an exemplary embodiment, a motor control device according to the present disclosure determines a command value of a current vector in a dq coordinate system that rotates in synchronization with a rotor, based on a torque command value, and includes: a digital arithmetic circuit; and a memory in which a magnet linkage flux Ψ of the motor is recorded_aA predetermined coefficient a, d-axis inductance L_qAnd q-axis inductance L_qCoefficient b defined by the difference of (a) and the number of pole pairs N_ppAnd a digital arithmetic circuit which executes the following processing when receiving the torque command value: (a) determining the number of relative pole pairs N of the torque command value_ppA coefficient c defined by the ratio of (A) to (B); (b) calculating the equation satisfying the torque ax +2bxy-c equal to 0 and making x²+y²Minimized values of x and y; and (c) determining a vector having x as a q-axis component and y as a d-axis component as a command value of the current vector. The digital operation circuit calculates x²+y²The minimum values of x and y are determined by successive calculations based on newton's method.

In an exemplary embodiment, the motor system of the present disclosure includes the motor control device described above, a motor drive circuit connected to the motor control device, and a motor connected to the motor drive circuit.

In an exemplary embodiment, a motor control method of the present disclosure is a motor control method for determining a command value of a current vector in a dq coordinate system that rotates in synchronization with a rotor, based on a torque command value, the motor control method including:(1) determining the number of pole pairs N of the torque command value relative to the motor_ppA coefficient c defined by the ratio of (A) to (B); (2) when the magnetic flux Ψ is interlinked with the magnet of the motor_aA is a, and the d-axis inductance L_dAnd q-axis inductance L_qB, x is calculated to satisfy the torque equation ax +2bxy-c equal to 0²+y²Minimized values of x and y; and (3) determining a vector having x as a q-axis component and y as a d-axis component as a command value of a current vector, and calculating the command value so that x is equal to²+y²The minimum values of x and y are determined by successive calculations based on newton's method.

Effects of the invention

According to the embodiment of the present disclosure, since the algorithm for deriving the torque from the torque is not the forward solution that is conventionally performed for deriving the torque from the current vector, but the algorithm for deriving the reverse solution for deriving the current vector from the torque is performed, the conversion from the torque command value to the current command value can be performed without depending on a table or a map that requires an excessively large amount of data.

Drawings

Fig. 1 is a diagram schematically showing the configuration of a non-limiting exemplary embodiment of the motor control system of the present disclosure.

Fig. 2 is a diagram showing an example of a hardware configuration of the motor control device of the present disclosure.

Fig. 3 is a flowchart showing an example of steps of processing of an embodiment of the present disclosure.

Fig. 4 is a block diagram showing a configuration example in an embodiment of the motor control device of the present disclosure.

Detailed Description

Before describing the embodiments of the present disclosure, a "Forward solution (Forward MTPA)" in which a torque is derived from a current vector and a "reverse solution (Inverse MTPA)" in which a current vector is derived from a torque will be described first.

< Forward solution for deriving torque from current vector >

In the vector control theory, various quantities such as voltage, current, magnetic flux, and inductance can be expressed by a dq coordinate system that rotates in synchronization with the rotation of the rotor. The torque T generated by the 3-phase ac synchronous motor is represented by equation 1.

[ numerical formula 1]

T＝N_pp[Ψ_ai_q+(L_q-L_d)i_di_q]

Here, N is_ppIs the number of pole pairs, Ψ_aIs the interlinkage magnetic flux generated by the permanent magnet of the rotor. L is_dAnd L_qAre d-axis inductance and q-axis inductance, i, respectively_dAnd i_qRespectively d-axis current and q-axis current. The unit of torque is Newton-meter [ Nm ]]The unit of inductance is Henry [ H ]]The unit of current is ampere [ A ]]. The expression 1 is derived on the assumption that a sinusoidal current flows through the 3-phase stator windings with a phase difference of 2 pi/3. In addition, the inductance and the spatial higher harmonic components of the flux are ignored. When these harmonic components cannot be ignored, a small ripple appears in the torque, but since the harmonic components do not affect the average torque, the average torque (constant component) is equal to the torque of expression 1.

The first term on the right side of equation 1 is "magnet torque", and the second term is "reluctance torque". At L_dAnd L_qIn a motor having a non-salient polarity of the same size, such as a surface magnet motor (SPM), the torque is only the first term of magnet torque. In contrast, in a motor in which a permanent magnet is not attached to a rotor, for example, a Switched Reluctance Motor (SRM), the torque is only the reluctance torque of the second term. The torque of an embedded motor (IPM) in which a permanent magnet is embedded in the rotor has a total value of the magnet torque and the reluctance torque.

When a value of a target torque (torque command value) is given, a motor control device that executes vector control needs to determine a current vector required to achieve the torque. The current vector is a d-axis current I defined in the dq coordinate system_dAnd q-axis current I_qIs a vector of components, and can also pass through norm I_aAnd lead phase angle beta from q axis₁To be represented. Hereinafter, the norm of the current vector is sometimes referred to as "current norm",the leading phase angle of the current vector from the q-axis is referred to as the "current phase angle", or simply as the "phase angle".

d-axis current I_dAnd q-axis current I_qThe norm I is used as shown in the following numerical expression 2_aAnd phase angle beta₁To indicate.

[ numerical formula 2]

i_q＝I_acosβ₁

i_d＝I_asinβ₁

When this relationship is used, the torque T can also be expressed by the following expression 3.

[ numerical formula 3]

The efficient motor control is called high efficiency control, and representative example thereof is mtpa (maximum Torque Per amp) control. In the MTPA control, the current phase angle is determined so as to obtain the maximum torque with respect to a certain current norm. Since the current norm is proportional to the copper loss, MTPA can also be said to be a method of determining the current phase angle so as to obtain the maximum torque with respect to a predetermined copper loss. However, in a real motor, since there are losses such as iron loss and wind loss in addition to copper loss, MTPA does not necessarily give an optimal efficiency solution. However, MTPA is widely used because it is easy to model it. Particularly in the low-speed, high-torque domain where copper losses dominate, MTPA gives a solution that is sufficiently close to the optimal solution.

The MTPA problem is defined as the current norm I_aDetermining a current phase angle beta that maximizes the torque T under constant conditions₁. From equation 3, if L is_q-L_dWhen the current phase angle β is 0, the applied torque T is realized₁Uniquely determine, β₁0 deg.. On the other hand, in the case where the rotor does not include a permanent magnet as in the case of a reluctance motor, the interlinkage magnetic flux Ψ generated by the permanent magnet is generated_aIs zero, so at the current phase angle beta₁The torque T is maximum at 45 °. In this way, in the motor capable of ignoring one of the magnet torque and the reluctance torque, the current vector for realizing the torque T is uniquely determined in accordance with the torque T. However, when both the magnet torque and the reluctance torque are applied, such as in the case of an embedded magnet, there are innumerable current vectors that realize the applied torque T. Therefore, in order to perform MTPA control, it is necessary to fix the current norm I_aFinding a current phase angle beta at which the torque T is maximized₁。

Current phase angle beta for maximizing torque T₁Will pass through a current phase angle beta₁The numerical expression 4 obtained by differentiating the numerical expression 3 becomes 0.

[ numerical formula 4]

If the right side of equation 4 is set to zero, equation 5 is obtained.

[ numerical formula 5]

-Ψ_aI_asinβ₁+(L_q-L_d)I_a ²cos2β₁＝0

When L is_qAnd L_dWhen the difference is different, the current phase angle β is determined as follows by solving equation 5₁。

[ numerical formula 6]

As another solving method, the method has the characteristics that I is given_qAnd I_dIn the case of one of the methods, the other method is determined. According to this method, solutions I represented by the following equations are obtained_q、I_d。

[ number formula 7]

In both methods, one of 2 values of a predetermined current vector is fixed, and the other value is calculated using the MTPA condition. In the conventional MTPA control, for example, the current norm I is temporarily determined based on the torque command value T_aTo find the current norm I_aRelative current phase angle beta₁. In this method, the current norm I is arbitrarily determined at first_aTherefore, there is a problem that the minimum current for generating the torque command value cannot be obtained. As a countermeasure, there is a method of performing iterative calculations. However, in this case, the calculation time increases, and it is not clear that sufficient accuracy can be obtained by performing several calculations, and thus it is not practical. The conventional method solves the problem to be solved by the reverse solution method by the forward solution method.

Therefore, instead of performing the above calculation online, the minimum current to achieve the torque T is found with reference to a lookup table. Specifically, the "current norm and current phase angle" (or "I") for realizing each torque T with the smallest current is calculated in advance by using a plurality of different torques T_dAnd I_q") a table of these 2 variables, so that the table is generated offline and stored in memory. When a command value of torque T is given during online operation, the motor control device reads "current norm and current phase angle" (or "I") with reference to the table_dAnd I_q") these 2 variables. The calculation in advance may be performed using a solver calculation or the like. According to this method, the entire table needs to be reproduced for each motor. In addition, if the permanent magnet magnetic flux, inductance, or the like changes in the same motor, the table needs to be rewritten, and therefore, it is not possible to cope with a change in the temperature characteristics of the motor and a change with time.

In order to cope with the variation of the motor parameter, a large number of tables corresponding to various parameters can be theoretically prepared in advance. However, since enormous data is required, it is not practical. For example, in the current norm I_aAnd current phase angle beta₁When the data of (2) are each set to 16 bits, the current vectors are expressed with respect to the input of 1 variable (1 torque value)And 4 bytes of data are required. The current norm I corresponding to each torque value is prepared with the torque resolution set to 12 bit amount (4096)_aAnd current phase angle beta₁In the case of the data of (3), the data amount reaches 16.384 kbytes (═ 4 bytes × 2¹²). An inexpensive microcomputer has a ROM capacity of about 32 kbytes to 128 kbytes, and therefore it is uneconomical to consume a capacity of 16 kbytes in the table.

When the table amount is increased, the capacity is sharply increased. For example, when a table is prepared by expanding the torque resolution to 24 bits and 32 bits of current, the data amount is about 134 mbytes (8 bytes × 2 bytes)²⁴) Such a huge amount. At this scale, it is difficult to make and install a watch.

Consider a case where the calculation is performed by a Central Processing Unit (CPU) without depending on a table. The higher the number of clocks of the CPU, the higher the CPU cost (microcomputer cost) rises. Further, since the motor is driven in real time, when the motor is driven by a PWM signal having a carrier frequency of 20kHz, the signal needs to be updated every 50 μ sec. The MTPA calculation does not need to be updated in this cycle, but needs to be updated at 1msec to 10msec in consideration of the electrical time constant. Therefore, the number of clocks used in 1 calculation becomes small. If a large number of clocks are used in the MTPA control calculation, a rise in the CPU cost is caused accordingly. However, MTPA control itself is not necessary for motor driving, and therefore it is not allowed to increase the level of the microcomputer only for this reason.

< inverse solution for deriving current vector from torque >

In the embodiment of the present disclosure, upon receiving the torque command value, the motor control device derives the current vector by executing each process of the following motor control method.

(1) Determining the number of pole pairs N of the torque command value relative to the motor_ppA coefficient c defined by the ratio of (a) to (b).

(2) When the magnetic flux Ψ is interlinked with the magnet of the motor_aA is a, and the d-axis inductance L_dAnd q-axis inductance L_qB is a predetermined coefficient, and calculatesSatisfies ax +2bxy-c as a torque equation of 0 and makes x²+y²The minimized values of x and y.

(3) A vector having x as a q-axis component and y as a d-axis component is determined as a command value of the current vector.

In addition, x is calculated²+y²The minimum values of x and y are determined by successive calculations based on newton's method.

The above-described processing will be described in detail below.

Torque command value T versus number of pole pairs N_ppHas a ratio of T/N_pp. Here, as a simplest example, c ═ T/N is assumed_pp. In addition, the magnetic flux Ψ is linked by the magnets_aA predetermined coefficient a is set to a ═ Ψ_a. About d-axis inductance L_dAnd q-axis inductance L_qThe coefficient b defined by the difference (b) is (L)_q-L_q)/2. In addition, the q-axis component of the current vector is represented by i_qX, and i is given to the d-axis component of the current vector_d＝y。

Using a, b, c, x, and y as described above, equation 1 defining the torque equation can be modified to the following equation.

[ number formula 8]

With respect to the numerical expression 8, even if two sides are multiplied by an arbitrary number, e.g., the number of pole pairs N_ppThe equation also holds. In addition, the equation holds even if both sides are divided by the reference value of the torque. Therefore, a, b, and c can also be normalized in such a way that the above equations hold. For example, by applying a reference voltage V₀[V]Reference current I₀[A]Reference electrical angular velocity omega₀[rad/sec]The reference torque T can be obtained by substituting a voltage equation different for each motor₀. The torque T of the numerical expression 8 and the reference torque T may be set₀When c is equal to 1, a and b are normalized. A, b andeach parameter of c is not limited to a ═ Ψ_a、(L_q-L_q) /2 and T/N_ppThe standard value of these values may be used. The standard values a, b, and c also correspond to the "coefficients defined by … …" described above, respectively.

As is clear from the above definition, the coefficient c is a parameter depending on the torque T, and therefore, if a torque command value is given, the magnitude of the coefficient c is determined. The coefficients a and b have specific magnitudes depending on the motor. Therefore, the "inverse solution method" is to obtain a norm (x) of x and y satisfying equation 8 when the magnitude of coefficient c is specified in addition to coefficients a and b unique to the motor²+y²) Is the smallest x, y. In embodiments of the present disclosure, x and y are determined by newton's method. Specifically, under the constraint condition of equation 8, the norm (x) is determined by performing successive calculation based on newton's method²+y²) The smallest x and y.

< 3 Newton method for variables x, y, lambda

In this example, the solution is obtained by the lagrangian indeterminate multiplier method using the medium variable λ. Specifically, under the constraint condition of equation 8, x is obtained²+y²Minimized x, y, λ. At x²+y²When the minimum value is reached, the partial differential of f (x, y, λ) shown in the following expression 9 becomes zero.

[ numerical formula 9]

f(x，y，λ)＝x²+y²-λ(ax+2bxy-c)＝0

This is represented by equation 10.

[ numerical formula 10]

In order to simplify the differential expression in the description to be described later, expression 10 is rewritten to expression 11 below.

[ numerical formula 11]

In order to obtain the values of x, y, and λ satisfying the above equations, initial values x are given to the values₀、y₀、λ₀. As the initial values, solutions of x, y, and λ obtained when the previous torque command value is given may be used. If these initial values are true solutions in addition to the coefficients a, b, and c used in the present calculation, the following equations hold.

[ numerical formula 12]

However, in reality, the initial value rarely satisfies the above equation. Successive calculations based on newton's method were continued. Therefore, Δ x, Δ y, and Δ λ satisfying the following equations are used as the offset amount from the initial value.

[ numerical formula 13]

The following approximate expressions hold for Δ x, Δ y, and Δ λ.

[ numerical formula 14]

[ numerical formula 15]

[ number formula 16]

When numerical expression 13 is rewritten using numerical expression 11, the following numerical expression is obtained.

[ number formula 17]

Δ x, Δ y, and Δ λ are obtained from the above equations. Specifically, the inverse matrix of the matrix on the right side can be used for calculation. Then, as shown in the following equation, x is obtained using Δ x, Δ y, and Δ λ₁、y₁、λ₁As a candidate for a solution.

[ numerical formula 18]

By repeating this calculation, x, y, and λ that substantially satisfy the relationship of expression 11 are obtained. In other words, it is possible to determine the constraint condition satisfying equation 8 and let x²+y²The x-component and y-component of the minimized current vector.

The coefficients a and b are parameters specific to the motor and do not change in a short time. On the other hand, the coefficient c varies according to the torque command value. However, the change in the coefficient c is also small in a short time scale of, for example, about several milliseconds. Therefore, when torque command values are sequentially input in a short cycle of 1 second or less, the current vector (x, y) for realizing a new torque command value is approximated to the current vector (x, y) for realizing the previous torque command value. Therefore, if x, y, λ obtained as a result of the last calculation is used as the initial value x₀、y₀、λ₀The number of times of repeating the calculation is often 1. The number of times of repeating the calculation may be set to 2 or 3. This is also the same in the case of newton's method using 2 or 1 variables described later.

< 2 variable x, y Newton's method >

When λ is eliminated from the 3-dimensional simultaneous equation shown in equation 11 in which x, y, and λ are unknown numbers, equation 19 below is obtained.

[ number formula 19]

The initial value x to be used for successive calculation is determined in the same manner as the 3-variable Newton method₀、y₀Added Δ x, Δ y. Δ x and Δ y are expressed by the following equations.

[ number formula 20]

Specifically, the above formula is expressed by the following formula.

[ numerical formula 21]

When the inverse matrix of the matrix is used on the right side of the above equation, Δ x and Δ y are expressed by the following equations.

[ numerical formula 22]

By performing successive calculations using Δ x and Δ y, a current vector can be determined.

< 1 variable x Newton method >

When y is eliminated from the simultaneous equations expressed by equation 19, the following equation of degree 4 is obtained for x.

[ numerical formula 23]

H(x)＝4b²x⁴+acx-c²＝0

In this case, Δ x is obtained by the following equation.

[ numerical formula 24]

Specifically, the above formula is expressed by the following formula.

[ number formula 25]

Δ x is as follows.

[ number formula 26]

When x is determined by successive calculation, y is obtained from expression 19.

The current vector can be determined by any of the above methods. The calculation amount is smaller in the case of the newton method based on the 2 variable or the 1 variable than in the case of the newton method based on the 3 variable.

As described above, in the embodiment of the present disclosure, when the torque command value T is given, the current vector that realizes the torque command value T with the minimum norm can be determined by the newton method. According to the embodiment of the present disclosure, it is not necessary to prepare a table having an enormous amount of data in advance and store the table in the memory. The motor control device can determine the current vector by performing the calculation based on the above equation only 1 time, and there is no theoretical error. If the above calculation is performed every time the torque command value is updated, the current vector that minimizes the norm can be immediately obtained.

< exemplary embodiment >

Hereinafter, an example of the motor control device of the present disclosure will be described with reference to the drawings. In addition, unnecessary detailed description may be omitted. For example, detailed descriptions of already known matters and repetitive descriptions of substantially the same configuration may be omitted. This is to avoid unnecessarily obscuring the following description, and to thereby enable those skilled in the art to readily understand the same. The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the disclosure. It is not intended to limit the subject matter described in the claims.

Refer to fig. 1. Fig. 1 is a diagram showing a schematic configuration of a motor system according to an embodiment of the present disclosure. The motor system 1000 shown in fig. 1 includes: a permanent magnet synchronous motor (hereinafter, simply referred to as "motor") 300 including a rotor 30 and a stator 32; a motor drive circuit 200 for applying a voltage to a winding 34 included in a stator 32 of a motor 300; a current sensor 250 that measures a current flowing through the winding 34; and a motor control device 100 connected to the motor drive circuit 200.

The rotor 30 in the present embodiment has a plurality of permanent magnets embedded in an iron core. The embodiments of the present disclosure are not limited to this example. The rotor 30 may be rotated by generating only reluctance torque without a permanent magnet. The rotor 30 can take a variety of forms.

The motor drive circuit 200 is a power converter having an inverter as a main circuit. The main circuit includes a plurality of power semiconductor elements (not shown in fig. 1) as components. The motor control device 100 generates and outputs a control signal (gate signal) for switching each power semiconductor element in the motor drive circuit 200. In the illustrated example, the Current sensor 250 is a Current Transformer (CT), but the example of the Current sensor 250 is not limited thereto. When the motor drive circuit 200 has 1 or more shunt resistors, the current flowing through the winding 34 can be measured by measuring the voltage drop of each shunt resistor.

The illustrated motor control device 100 includes a processor 10 functioning as a "digital arithmetic circuit" and a memory 20 in which a software program for controlling the operation of the processor 10 is recorded. The processor 10 may be, for example, an Integrated Circuit (IC) chip such as a CPU or a digital signal processor. The memory 20 is a recording medium in which a computer program for controlling the operation of the processor 10 is stored. The memory 20 need not be a single recording medium, but may be a collection of a plurality of recording media. As described below, the memory 20 may include, for example, a semiconductor volatile memory such as a RAM, a semiconductor nonvolatile memory such as a flash ROM, and a storage device such as a hard disk drive. At least a portion of the memory 20 may be a removable recording medium.

Motor control device 100 in fig. 1 determines a command value of a current vector in a dq coordinate system that rotates in synchronization with rotation of rotor 30, based on a torque command value.

The memory 20 stores the magnetic flux Ψ of the motor_aA predetermined coefficient a, d-axis inductance L_dAnd q-axis inductance L_qCoefficient b defined by the difference of (a) and the number of pole pairs N_pp。

Upon receiving the torque command value, the processor (digital arithmetic circuit) 10 of the motor control device 100 executes the following processing.

(a) Determining the number of relative pole pairs N of the torque command value_ppA coefficient c defined by the ratio of (A) to (B);

(b) calculating a torque satisfying the torque equation ax +2bxy-c equal to 0 and making x equal to²+y²Minimized values of x and y; and

(c) a vector having x as a q-axis component and y as a d-axis component is determined as a command value of the current vector.

And, the processor 100 calculates x²+y²The minimum values of x and y are determined by successive calculations based on newton's method.

The contents of these processes are as described above, and the same explanation is not repeated here. The torque command value can be input to the processor 10 from an external higher-level computer or controller. Further, the torque command value may be generated inside the processor 10 based on a signal supplied from a computer or a controller to the processor 10.

In the embodiment of the present disclosure, the processor 10 calculates the values of x and y that minimize f (x), and calculates the values of x and y by successive calculations based on newton's method. Therefore, large table data is not required.

In the present embodiment, the memory 20 stores a lookup table including a plurality of values that differ depending on the state of the motor 300 for the coefficient a and/or the coefficient b. The state of the motor 300 may include an operating temperature of the motor, a degree of magnetic saturation, a degree of demagnetization of the permanent magnet in the case where the rotor 30 has the permanent magnet, and a period of use.

Processor 10 may also be based on magnet linkage flux Ψ_aD-axis inductance L_dAnd/or q-axis inductance L_qThe values of the coefficient a and/or the coefficient b recorded in the memory 20 are updated. As mentioned above, the coefficient a is defined by the magnet linkage flux Ψ_aThe strength of the permanent magnet of the motor 300 is determined. The strength of the permanent magnet may be reduced by thermal demagnetization during the operation of the motor. Therefore, when the strength of the permanent magnet changes, the value of the coefficient a can be updated based on the change. For example, the operating temperature of the motor or the winding current may be detected, and the coefficient a may be changed according to the temperature and/or the winding current. The temperature and/or winding current dependence of the coefficient a can be stored in the memory as table data. Further, a function for approximating the relationship may be stored in the memory. Coefficient b is formed by d-axis inductance L_dAnd q-axis inductance L_qThe difference of (b) is specified, so in the case where the inductance changes due to magnetic saturation, the coefficient b can be updated based on the change. The relation of the winding current to the coefficient b may also be stored in the memory as table data.

In the present embodiment, the processor 10 determines the command value of the voltage vector based on the difference between the measured value of the current vector and the command value of the current vector when receiving the measured value of the current vector.

The motor 300 in the present embodiment is an embedded permanent magnet synchronous motor, but the motor in the present disclosure is not limited to this example.

Fig. 2 is a diagram showing an example of the hardware configuration of the motor control device 100 in the motor module of the present disclosure.

Motor control apparatus 100 may have a hardware configuration shown in fig. 2, for example. The motor control device 100 in this example includes a CPU154, a PWM circuit 155, a ROM (read only memory) 156, a RAM (random access memory) 157, and an I/F (input/output interface) 158, which are connected to each other by a bus. Other circuits and devices (AD converters and the like) not shown may be connected to the bus. The PWM circuit 155 supplies a PWM signal to the motor drive circuit 200 of fig. 1. Programs and data that specify operations of the CPU154 are stored in at least one of the ROM156 and the RAM 157. Such a motor control device 100 can be realized by a general-purpose microcontroller of 32 bits, for example. Such a microcontroller may be formed, for example, from 1 or more integrated circuit chips.

Details of various operations performed by the motor control device 100 will be described later. Typically, various operations performed by the motor control device 100 are defined by a program stored in the memory 20. By updating a part or all of the contents of the program, a part or all of the operations of motor control device 100 can be changed. Such updating of the program may be performed using a recording medium in which the program is stored, or may be performed by wired or wireless communication. Communication can occur using the I/F158 of FIG. 2. In order to reduce the amount of computation by the CPU154 shown in fig. 2, part of various operations performed by the motor control device 100, for example, part of vector computation may be performed by a hardware circuit dedicated to computation by the motor control device 100.

Next, a basic flow of the motor control operation in the embodiment of the present disclosure will be described with reference to fig. 3.

First, in step S1, the CPU154 receives an input of a torque command value. Next, in step S2, the CPU154 determines coefficients a, b, and c for defining the torque equation (ax +2bxy-c is 0). The coefficient c has a magnitude depending on the torque command value received in step S1. In step S3, the CPU154 reads out the initial values of x and y for the above-described successive calculations based on newton' S method from the memory. Examples of the initial values are values of x and y calculated based on the previous torque command value. In step S4, the CPU154 determines to make x by using the newton method described above²+y²The minimized values of x and y. That is, the d-axis current command value and the q-axis current command value are determined. In step S5, the CPU154 updates or maintains the values of the coefficients a, b. The updating may be performed in case the state of the motor has changed.

Next, referring to fig. 4, the motor in the embodiment of the present disclosure is describedNon-limiting examples of exemplary configurations and operations of the control device will be described. In the illustrated example, motor control device 100 in motor system 1000 according to the present embodiment generates d-axis current command value i from torque command value T by the above-described processing_d ^*And q-axis current command value i_q ^*The current command value generation module. The motor control device 100 further includes a current control circuit 12, a first coordinate conversion circuit 14A, and a PWM circuit 16. The current control circuit 12 controls the d-axis current command value i_d ^*And q-axis current command value i_q ^*Determining a d-axis voltage command value V_d ^*And q-axis voltage command value V_q ^*. The first coordinate conversion circuit 14A converts the voltage command value from the dq coordinate system to the UVW coordinate system. The PWM circuit 16 is based on the voltage command value (V) output from the first coordinate conversion circuit 14A_u ^*、V_v ^*、V_w ^*) And generating a pulse width modulation signal. The structure and operation of these circuits 12, 14A, 16 follow a well-known example.

The motor control device 100 further includes a second coordinate conversion circuit 14B, a position detection circuit 18A, and a speed calculation circuit 18B. The second coordinate conversion circuit 14B detects a value i of the winding current i of the 3-phase U, V, W supplied from the inverter to the motor 300_u、i_vAnd is converted from the UVW coordinate system to the dq coordinate system. The position detection circuit 18A detects the mechanical angular position θ of the rotor in the motor 300_m. The speed arithmetic circuit 18B calculates the mechanical angular position theta of the rotor based on the rotational speed_mCalculating the mechanical angular velocity omega of the rotor_m。

D-axis current i converted into dq coordinate system from second coordinate conversion circuit 14B_dQ-axis current i_qA current control circuit 12 for applying a d-axis current command value i to the current control circuit_d ^*And q-axis current command value i_q ^*A comparison is made. A typical example of the current control circuit 12 is a Proportional Integral (PI) controller. According to the mechanical angular position theta of the rotor_mThe electrical angular position θ of the rotor is calculated. The electrical angular position θ of the rotor is used for seating between the dq coordinate system and the UVW coordinate systemAnd (5) standard conversion. Mechanical angular velocity ω of the rotor_mCan be used to determine the torque command value T.

A gate driver that generates a gate drive signal for switching the transistors in the inverter based on the PWM signal may be provided in a stage preceding the inverter of the motor drive circuit 200. These elements are well known and omitted for brevity.

A part or all of the circuits described above can be realized by an integrated circuit device. Such integrated circuit devices can typically be formed from 1 or more semiconductor components. The integrated circuit device may include an a/D converter that converts an analog signal from the position sensor into a digital signal, and an a/D converter that converts an analog signal from a sensor (not shown) that detects a current flowing in the winding of the motor 300 into a digital signal.

At least a portion of the inverter may also be included in the integrated circuit device. Such integrated circuit devices are typically implemented by interconnecting 1 or more semiconductor chips within 1 package. A part or all of the integrated circuit device can be realized by, for example, writing a program unique to the present disclosure in a general-purpose microcontroller unit (MCU).

The motor control device, the motor control method, and the motor system according to the present disclosure can be used for various synchronous motors requiring high-efficiency operation.

Description of the symbols

A 10 … processor (digital arithmetic circuit), 20 … memory, 100 … motor control device, 200 … motor control device, 300 … motor, 1000 … motor system.

Claims (9)

1. A motor control device for determining a command value of a current vector in a dq coordinate system that rotates in synchronization with a rotor, based on a torque command value, the motor control device comprising:

a digital arithmetic circuit; and

a memory for recording a magnet linkage flux Ψ of the motor_aA predetermined coefficient a, d-axis inductance L_qAnd q-axis inductance L_qCoefficient b defined by the difference of (a) and the number of pole pairs N_pp，

The digital arithmetic circuit executes the following processing when receiving a torque command value:

(a) determining the number of relative pole pairs N of the torque command value_ppA coefficient c defined by the ratio of (A) to (B);

(b) calculating the equation satisfying the torque ax +2bxy-c equal to 0 and making x²+y²Minimized values of x and y; and

(c) a vector having x as a q-axis component and y as a d-axis component is determined as a command value of the current vector,

the digital operation circuit calculates x²+y²The minimum values of x and y are determined by successive calculations based on newton's method.

2. The motor control device according to claim 1,

when the latest torque command value is received, the digital arithmetic circuit obtains the values of x and y determined from the latest torque command value, using the value determined based on the previously received torque command value as an initial value.

3. The motor control device according to claim 1 or 2,

the memory stores a lookup table containing a plurality of values different depending on the state of the motor for the coefficient a and/or the coefficient b.

4. The motor control device according to claim 3,

the state of the motor includes the operating temperature of the motor, the degree of magnetic saturation, the degree of demagnetization of the permanent magnet in the case where the rotor has the permanent magnet, and the period of use.

5. The motor control device according to claim 1 or 2,

the digital operation circuit is based on the magnet linkage flux Ψ_aD-axis inductance L_qAnd/or q-axis inductance L_qThe values of the coefficient a and/or the coefficient b recorded in the memory are updated.

6. The motor control apparatus according to any one of claims 1 to 5,

the digital operation circuit receives a measured value of a current vector and determines a command value of a voltage vector based on a difference between the measured value of the current vector and the command value of the current vector.

7. The motor control apparatus according to any one of claims 1 to 6,

the motor is an embedded permanent magnet synchronous motor.

8. An electric motor system is characterized by comprising:

the motor control device according to any one of claims 1 to 7;

a motor drive circuit connected to the motor control device; and

and the motor is connected with the motor driving circuit.

9. A motor control method for determining a command value of a current vector in a dq coordinate system rotating in synchronization with a rotor based on a torque command value,

the motor control method includes:

(1) determining the number of pole pairs N of the torque command value relative to the motor_ppA coefficient c defined by the ratio of (A) to (B);

(2) when the magnetic flux Ψ is interlinked by the magnets of the motor_aA is a, and the d-axis inductance L_dAnd q-axis inductance L_qB, x is calculated to satisfy the torque equation ax +2bxy-c equal to 0²+y²Minimized values of x and y; and

(3) a vector having x as a q-axis component and y as a d-axis component is determined as a command value of the current vector,

in calculating x²+y²The minimum values of x and y are determined by successive calculations based on newton's method.

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