JP2010268579A - Permanent magnet synchronous electric motor system and magnetic field control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a permanent magnet synchronous electric motor system which is simple in constitution, high in accuracy, low in cost, and capable of controlling a magnetic field in a wide range, and to provide a magnetic field control method for the motor system. <P>SOLUTION: The permanent magnet synchronous electric motor system 10 includes a control device 12 which has a power supply 15 variable in voltage and frequency, and performs control for weakening the magnetic field, by making a d-axis current flow from the stator side of a permanent magnet synchronous electric motor 11 toward an orientation in which the magnetic flux of a permanent magnet of the permanent magnet synchronous electric motor 11 is weakened, when the permanent magnet synchronous electric motor 11 is operated at a high speed exceeding the basic speed. The magnetic flux of the permanent magnet is set to a value smaller than a rated magnetic flux corresponding to the basic speed. The control device 12 includes: a first speed control system 13, which generates a required torque characteristic by setting the value of a q-axis current crossing the d-axis current at right angles to be larger than a value of a rated q-axis current, corresponding to the rated magnetic flux in a low-speed region equal to or lower than the basic speed; and a second speed control system 14 which generates a required output characteristic, by adjusting the values of the d-axis current and the q-axis current respectively in a high-speed region. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a permanent magnet synchronous motor system that obtains constant output characteristics and step-down output characteristics by field control and a field control method thereof.

For example, as described in Patent Document 1, a permanent magnet synchronous motor can be operated at high speed by field weakening with a substantially constant voltage as in field control of a separately excited DC shunt motor. A method of increasing the speed of the permanent magnet synchronous motor by supplying a current that weakens the magnetic flux from the stator side to weaken the magnetic flux is used. For this reason, the method of controlling the field current to be small in inverse proportion to the speed increase as in the case of a DC motor cannot be adopted, and a magnetic flux weakening current that increases substantially in proportion to the speed increase must be supplied from the power source. . Therefore, when the field control range is wide, for example, there is a problem that the stator current becomes considerably large with respect to the requirement of constant output characteristics. In particular, there is a problem that the required voltage of the variable voltage and variable frequency power supply becomes very large as compared with the field weakening control of the DC motor. For this reason, it has been difficult to apply a standardized voltage rated inverter to a wide field control of a permanent magnet synchronous motor. Therefore, means for boosting the inverter voltage and a method of switching the winding of the permanent magnet synchronous motor so as to reduce the back electromotive force of the motor (for example, see Patent Document 2) have been proposed and put into practical use.

Japanese Patent Application Laid-Open No. 2004-129381 JP-A-2005-354807

However, since the method of switching the windings of the motor requires a winding switching circuit and its control device, a winding switching circuit and its control device are provided between the inverter that drives the permanent magnet synchronous motor and the permanent magnet synchronous motor. There arises a problem that a space to be arranged must be secured. In addition, since the number of power lines necessary for switching the winding is drawn from the permanent magnet synchronous motor, there is a problem that the number of wirings increases.

The present invention has been made in view of such circumstances, and provides a permanent magnet synchronous motor system and a field control method thereof capable of performing a wide range of field control with a simple configuration with high accuracy and low cost.

A permanent magnet synchronous motor system according to the present invention that meets the above-mentioned object is provided with a power source having a variable voltage and frequency, and the rotor of the permanent magnet synchronous motor is used during high-speed operation exceeding the base speed of the permanent magnet synchronous motor. In a permanent magnet synchronous motor system having a control device that controls field weakening by flowing a d-axis current from the stator side of the permanent magnet synchronous motor in a direction to weaken the magnetic flux of the installed permanent magnet,
The magnetic flux of the permanent magnet synchronous motor is designed to be smaller than the rated magnetic flux corresponding to the base speed,
The control device increases the value of the q-axis current orthogonal to the d-axis current in a low speed region equal to or lower than the base speed to be larger than the value of the rated q-axis current corresponding to the rated magnetic flux. The permanent magnet synchronous motor is requested by adjusting the values of the d-axis current and the q-axis current in a first speed control system that generates torque characteristics required for the motor and a high speed region exceeding the base speed. And a second speed control system for generating the output characteristics to be generated.

In the permanent magnet synchronous motor system according to the present invention, the first speed control system has a characteristic load angle when a stator phase current of the permanent magnet synchronous motor becomes a minimum with respect to a torque generated by the permanent magnet synchronous motor. And the load angle of the permanent magnet synchronous motor is preferably matched with the characteristic load angle.

In the permanent magnet synchronous motor system according to the present invention, the second speed control system may reduce the d-axis current to 0 or the permanent magnet in a speed region where the speed of the permanent magnet synchronous motor is equal to or lower than a preset critical speed. Holding the stator phase current of the synchronous motor at a value corresponding to the characteristic load angle that minimizes the torque generated by the permanent magnet synchronous motor, adjusting the q-axis current value and the stator phase voltage, In the speed region exceeding the critical speed, it is preferable to adjust the value of the q-axis current while adjusting the value of the d-axis current and performing field control.

A field control method for a permanent magnet synchronous motor system according to the present invention that meets the above-described object is provided by using a power source having a variable voltage and frequency at the time of high-speed operation exceeding the base speed of the permanent magnet synchronous motor. In a field control method of a permanent magnet synchronous motor system for performing field weakening control by flowing a d-axis current from the stator side of the permanent magnet synchronous motor in a direction to weaken the magnetic flux of the permanent magnet mounted on the rotor of the permanent magnet,
The permanent magnet synchronous motor magnetic flux of the permanent magnet is designed to be smaller than the rated magnetic flux corresponding to the base speed,
In the low speed region below the base speed, the torque required for the permanent magnet synchronous motor is set by making the q-axis current value orthogonal to the d-axis current larger than the rated q-axis current value corresponding to the rated magnetic flux. In the high speed region exceeding the base speed, the values of the d-axis current and the q-axis current are adjusted to generate the output characteristics required for the permanent magnet synchronous motor.

In the field control method for a permanent magnet synchronous motor system according to the present invention, the characteristic load angle when the stator phase current of the permanent magnet synchronous motor is minimum with respect to the torque generated by the permanent magnet synchronous motor in the low speed region. And the load angle of the permanent magnet synchronous motor is preferably matched with the characteristic load angle.

In the field control method for a permanent magnet synchronous motor system according to the present invention, in the high speed region, when the speed of the permanent magnet synchronous motor is equal to or lower than a preset critical speed, the d-axis current is set to 0 or the permanent magnet synchronous motor. The q-axis current value and the stator phase voltage are adjusted while maintaining the stator phase current at a value corresponding to the characteristic load angle at which the stator phase current is minimum with respect to the torque generated by the permanent magnet synchronous motor. When exceeding, it is preferable to adjust the value of the q-axis current while adjusting the value of the d-axis current and performing field control.

In the permanent magnet synchronous motor system and its field control method according to the present invention, the magnetic flux of the permanent magnet of the permanent magnet synchronous motor is designed to be smaller than the rated magnetic flux corresponding to the base speed. It is possible to reduce the maximum voltage when performing field control at high speed operation exceeding the base speed of the permanent magnet synchronous motor using, for example, a booster or a motor for boosting the voltage of a power source whose voltage and frequency are variable There is no need to add a winding switching circuit for switching windings and a control device therefor, the configuration of the permanent magnet synchronous motor system is simplified, and reliability can be improved and costs can be reduced.
Further, by designing the permanent magnet magnetic flux of the permanent magnet synchronous motor to a value smaller than the rated magnetic flux, for example, the use of rare metal, which is an expensive magnetic material, can be reduced, and the cost of the permanent magnet synchronous motor can be reduced. It can meet the recent requirements for derare metal.

In the permanent magnet synchronous motor system and the field control method thereof according to the present invention, the characteristic load angle when the stator phase current of the permanent magnet synchronous motor becomes the minimum with respect to the torque generated by the permanent magnet synchronous motor is obtained, and the permanent magnet synchronous motor When the load angle is matched with the characteristic load angle, it is possible to suppress an increase in stator phase current caused by designing the magnet magnetic flux to be smaller than the rated value.

In the permanent magnet synchronous motor system and the field control method thereof according to the present invention, a critical speed is preset in the high speed region of the permanent magnet synchronous motor, and the d-axis current is set to 0 or zero in the permanent magnet synchronous motor. Maintaining the stator phase current at a value corresponding to the characteristic load angle that minimizes the torque generated by the permanent magnet synchronous motor, adjusting the q-axis current value and stator phase voltage, and exceeding the critical speed range Then, when adjusting the value of the q-axis current while adjusting the value of the d-axis current and performing the field control, it is possible to suppress an increase in the stator phase current caused by designing the magnetic flux to be smaller than the rated value. . As a result, the efficiency at high speed operation exceeding the base speed of the permanent magnet synchronous motor can be improved.

It is explanatory drawing of the permanent-magnet synchronous motor system which concerns on one embodiment of this invention. It is explanatory drawing which shows the relationship between a stator phase current, a torque, and a load angle in the field control method of the permanent magnet synchronous motor system which concerns on one embodiment of this invention. It is explanatory drawing which shows the relationship between the load angle and torque in the field control method of the permanent magnet synchronous motor system, and the conventional method with a constant load angle of 90 °. It is explanatory drawing which shows the relationship between the speed, d-axis current command, and q-axis current command in the field control method of the permanent magnet synchronous motor system. It is explanatory drawing which shows the relationship between q-axis current and a torque at the time of setting the operating speed in the field control method of the permanent magnet synchronous motor system as a parameter. It is explanatory drawing which shows the relationship between the speed, torque, voltage, and phase current in the field control method of the permanent magnet synchronous motor system which concerns on a modification. It is explanatory drawing which shows the relationship between the speed when not adjusting a stator phase voltage in the high speed area | region below a critical speed, a torque, a voltage, and a phase current. It is explanatory drawing which shows the relationship between the speed, torque, voltage, and phase current in the conventional field control method. It is explanatory drawing which shows the comparison of the efficiency of the permanent magnet synchronous motor in the field control method of the permanent magnet synchronous motor system which concerns on one embodiment of this invention, and the conventional field control method. It is explanatory drawing which shows the efficiency of the permanent magnet synchronous motor in the case where a stator resistance is designed small by the field control method of the permanent magnet synchronous motor system which concerns on one embodiment of this invention, and the conventional field control method.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
As shown in FIG. 1, a permanent magnet synchronous motor system 10 according to an embodiment of the present invention includes a permanent magnet synchronous motor 11 and a control device 12 that performs field control of the permanent magnet synchronous motor 11 by vector control. Yes. Here, the magnetic flux of the permanent magnet of the permanent magnet synchronous motor 11 is designed to be smaller than the rated magnetic flux, for example, 75%. Here, the recommended value of the magnetic flux design of the permanent magnet is 50% or more and 75% or less of the rated magnetic flux.

Then, the control device 12 can obtain the torque characteristics required for the permanent magnet synchronous motor 11 when the speed (rotational speed) of the permanent magnet synchronous motor 11 is in a low speed region below the base speed (rated rotational speed). As described above, the first speed control system 13 that performs operation control for making the value of the q-axis current orthogonal to the d-axis current larger than the value of the rated q-axis current corresponding to the rated magnetic flux, and the rotational speed of the permanent magnet synchronous motor 11 Control in which the values of the d-axis current and the q-axis current are adjusted so that the output characteristics required by the permanent magnet synchronous motor 11, for example, the constant output characteristics, can be obtained in the high speed region exceeding the base speed. And a second speed control system 14 for performing This will be described in detail below.

The first and second speed control systems 13 and 14 detect a load of the PWM inverter 15 which is an example of a power source having a variable voltage and frequency for operating the permanent magnet synchronous motor 11 and the operating permanent magnet synchronous motor 11. The first absolute value encoder 16 that is an example of a load detector that performs the operation and the second absolute value that is an example of a magnetic pole position detector that detects the magnetic pole position (rotation angle) θ _r of the permanent magnet synchronous motor 11 that is in operation. The speed output from the encoder 16a, the speed detector 17 for calculating the rotational speed ω _rn of the permanent magnet synchronous motor 11 from the output of the second absolute value encoder 16a, and the speed output from the operation control panel (not shown) of the permanent magnet synchronous motor system 10 The speed control PI controller 18 that compares the command ω _rn ^* with the rotational speed ω _rn output from the speed detector 17 and PI-amplifies the deviation to generate the original torque command T _ec. have.

The first speed control system 13 generates a torque command T _en ^* from the original torque command T _ec output from the PI controller 18, and the original speed control system 13 based on the torque command T _en ^* output from the limiter 19. And function generators 20 and 21 for generating the phase current command i _snv ^* and the original load angle command δ _v ^* , respectively. Here, the limiter 19 is intended to limit the torque command _{T en} ^* to the allowable value for the original torque command _{T ec} (torque demand), for example, the torque command _{T en} ^* is -2.0P. u. ~ +2.0 p. u. It is limited to the range.

Here, in the function generators 20 and 21, when the stator phase current of the permanent magnet synchronous motor 11 becomes the minimum with respect to the generated torque of the permanent magnet synchronous motor 11, the ratio of the generated torque / stator phase current is the maximum. Characteristic load angle of the permanent magnet synchronous motor 11 is calculated from the torque command T _en ^* to the original phase current command i _snv ^* and the original load angle command δ so that the load angle of the permanent magnet synchronous motor 11 matches the characteristic load angle. _v ^* is determined. As a result, it is possible to compensate for the torque reduction caused by designing the permanent magnet magnetic flux of the permanent magnet synchronous motor 11 to a value smaller than the rated magnetic flux while suppressing an increase in the stator phase current.

The second speed control system 14 synchronizes the permanent magnet in the voltage and field control range based on the original torque command T _ec output from the PI controller 18 and the rotational speed ω _rn output from the speed detector 17. A q-axis current component calculator 22 for calculating the original q-axis current command i _qsn ^* so as to decrease the q-axis current component in proportion to the speed increase so that the electric motor 11 has a required constant output characteristic; An original d-axis current command i _dsn ^* that generates a command signal that determines a d-axis current component that weakens the magnetic flux of the permanent magnet of the permanent magnet synchronous motor 11 during field control is calculated based on the rotational speed ω _rn that is the output of the generator 17. the d-axis current component computing unit 23, generates original q-axis current command _{i QSN} ^* and the vector operation from the original d-axis current command _{i dsn} ^* original phase current command _{i SNF} ^* and the original load angle command [delta] _F ^*, respectively And a voltage and field control phase current computing unit 24. Accordingly, in the speed region where the speed of the permanent magnet synchronous motor 11 is a preset speed, for example, a critical speed or less corresponding to 150% of the base speed, for example, the d-axis current is changed to the stator phase of the permanent magnet synchronous motor 11. The value of the q-axis current and the stator phase voltage can be adjusted while maintaining a value corresponding to the characteristic load angle at which the current is minimum with respect to the torque generated by the permanent magnet synchronous motor 11, and the speed exceeds the critical speed. In the region, the value of the q-axis current can be adjusted while performing field control by adjusting the value of the d-axis current.

The first, second speed control system 13 and 14, which is the output original phase current command from the function generator 20 the rotational speed is below base speed of the permanent magnet synchronous motor 11 i _SNV ^* phase current command i and _sn ^*, phase current voltage and field control phase current computing unit which is the output original phase current command from the 24 i _SNF ^* and the phase current command i _sn ^* when the rotational speed of the permanent magnet synchronous motor 11 exceeds the base speed When the rotational speed of the command selector 25 and the permanent magnet synchronous motor 11 is lower than the base speed, the original load angle command δ _v ^* , which is an output from the function generator 21, is used as the load angle command δ ^*, and the rotation of the permanent magnet synchronous motor 11 is performed. A load angle command selector 26 that uses the original load angle command δ _F ^* , which is an output from the voltage and field control phase current calculator 24 when the speed exceeds the base speed, as a load angle command δ ^* is provided.

Further, the first and second speed control systems 13 and 14 rotate the permanent magnet synchronous motor 11 which is the output of the load angle command δ ^* output from the load angle command selector 26 and the second absolute value encoder 16a. The phase angle command θ _s ^* obtained as the sum of the angle θ _r and the phase current command i _sn ^* output from the phase current command selector 25 are used as the stator phase current command i _as ^* of the three-phase a, b, and c coordinates ^. , _i ^bs _*, and a current command unit 27 to be input to the PWM inverter 15 converts the _{i cs} ^*.

Here, among the stator phase currents i _as , i _bs , and i _cs input from the PWM inverter 15 to the permanent magnet synchronous motor 11, for example, the stator phase currents i _cs and i _bs are current sensors 28 and 29. Each is detected and input to the PWM inverter 15. On the other hand, the stator phase current i _as is obtained from i _cs and i _bs by a known vector operation. The PWM inverter 15 compares the obtained stator phase currents i _as , i _bs , i _cs with the stator phase current commands i _as ^* , i _bs ^* , i _cs ^* inputted from the current command device 27. Then, current control is performed so that the deviation becomes zero.

Then, the field control method of the permanent magnet synchronous motor system 10 which concerns on one embodiment of this invention is demonstrated.
The field control method of the permanent magnet synchronous motor system 10 uses a PWM inverter 15 which is an example of a power source having a variable voltage and frequency, and performs permanent magnet synchronous motor during high speed operation exceeding the base speed of the permanent magnet synchronous motor 11. The permanent magnet synchronous motor 11 performs field weakening control by flowing a d-axis current from the stator side of the permanent magnet synchronous motor 11 in the direction of weakening the magnetic flux of the permanent magnet mounted on the rotor of the permanent magnet 11. Is designed to be smaller than the rated magnetic flux corresponding to the base speed, and in the low speed region below the base speed, the q-axis current value orthogonal to the d-axis current is the rated q-axis current value corresponding to the rated magnetic flux. The torque characteristic required for the permanent magnet synchronous motor 11 is generated to be larger, and in the high speed region exceeding the base speed, the values of the d-axis current and the q-axis current are adjusted to change the permanent magnet synchronous power. The output characteristics required for the motive 11 are generated. Details will be described below.

In the low speed region, the value of the q-axis current must be increased in order to cause the permanent magnet synchronous motor 11 to generate the required torque. At this time, in order to reduce the load of the PWM inverter 15, the stator phase current It is necessary to suppress the increase. Here, since the stator phase current of the permanent magnet synchronous motor 11 is the vector sum of the d-axis current and the q-axis current, the stator phase current of the permanent magnet synchronous motor 11 is in relation to the torque generated by the permanent magnet synchronous motor 11. Characteristic load angle when the generated torque / stator phase current ratio is maximized, and the d-axis current and the load angle of the permanent magnet synchronous motor 11 match the characteristic load angle. The q-axis current is controlled (vector control of the permanent magnet synchronous motor 11).

Now, let the stator phase currents of the three-phase a, b, and c coordinates of the permanent magnet synchronous motor 11 be i _as , i _bs , and i _cs . Each stator phase current is
i _as = is _s sin (ω _r t + δ) (1)
i _bs = i _s sin (ω _r t + δ−2π / 3) (2)
i _cs = i _s sin (ω _r t + δ + 2π / 3) (3)
Given in. Here, _{i s} is the amplitude value of the stator phase current (A), omega _r is the rotor speed (rad / sec), [delta] is the load angle (torque angle) rotor field and the phase of the stator current (rad ) And t are time (sec).

The d-axis current i _ds and the q-axis current i _{qs at} the rotor reference coordinates d and q coordinates of the stator phase currents i _as , i _bs , and i _cs are given by equation (4).

By substituting the equations (1), (2), and (3) into the equation (4), the equation (5) is obtained.

On the other hand, the voltages V _ds (V) and V _qs (V) of the permanent magnet synchronous motor 11 expressed by the rotor reference coordinate d and the q axis are given by the equation (6).

The torque Te (N−m) is given by the equation (7).
Te = (3/2) · (P / 2) · [λ _af i _qs + (L _d −L _q ) i _{qs ids} ] (7)
Note that _RS is q-axis and d-axis stator winding resistance (Ω), L _q and L _d are q-axis and d-axis inductance (H), and _λaf is rotor flux linkage (Wb-turn). ), P is the differential operator = d / dt, and P is the number of poles.

Here, in order to simplify the description of the invention, voltage, current, speed, torque, stator winding resistance, d-axis inductance, and q-axis inductance are expressed by a unit method (pu method).
Now, the base voltage is V _B (V), the base current is I _B (A), the base speed (base speed) is ω _B (rad / sec), and the base rotor flux _linkage is λ _afB (Wb-turn). Then, the base resistance R _B becomes V _B / I _B (Ω), the base inductance L _B becomes V _B / (ω _B · I _B ) (H), and the stator winding resistance R _Sn expressed by the unit method is R _S / _R B _(p.u.), respectively d-axis inductance _{L dn} and the q-axis inductance _{L dn} expressed in unit normal _{L d / L B (p.u.} ), L q / L B (p.u .). Further, the q-axis voltage V _qsn and the d-axis voltage V _dsn expressed by the unit method are V _qs / V _B (pu) and V _ds / V _B (pu), respectively, and are expressed by the unit method. The rotor speed ω _rn is ω _r / ω _B (pu), and the rotor flux _linkage λ _afn expressed in the unit method is λ _af / λ _afB .

Here, the base torque _T B _(N-m), is defined as T B (N-m) = (3/2) · (P / 2) · λ afB · I B. Then, the torque p. u. The value is expressed as T _en = T _e / T _B. As a result, equation (6) can be expressed by the unit method as equation (8).

Moreover, (7) Formula can be represented by a unit method like (9) Formula.
T _en = i _sn [λ _{afn sin} δ + (1/2) (L _dn −L _qn ) i _sn sin 2δ] (9)

In the field control method of the permanent magnet synchronous motor system 10 of the present embodiment, the rotor flux _linkage λ _afn expressed in the unit method is _set to 1.0 p. u. Smaller, for example, 0.75 p. u. 1.0 p. u. The stator phase current i _sn that generates torque is 1.0 p. u. Become bigger. Therefore, the stator phase current i _sn is 1.0 p. u. In order to suppress the increase, the load angle δ at which the ratio of T _en / i _sn is maximized is calculated, and the load angle of the permanent magnet synchronous motor 11 matches this value δ using this load angle δ as a command value. Thus, the phase angle of the stator phase current i _sn is controlled. In this case, the relationship of the stator phase current _{i sn} the load angle [delta] (rad), the expression _(9), in the form of a T en _{/ i sn,} determined as _{d (T en / i sn)} / dδ = 0 be able to. The result is as shown in equation (10). Here, a ₁ = L _dn −L _qn .
δ = cos ⁻¹ [(− (λ _afn / 4a ₁ i _sn ) − ((λ _afn / 4a ₁ i _sn ) ²
+ (1/2)) ^1/2 ) (10)
Therefore, the load angle δ that maximizes T _en / i _sn can be determined for i _sn if L _dn , L _qn , and λ _afn are known.

In FIG. 2, L _dn = 0.4347 p. u. , L _qn = 0.6988 p. u. , Λ _afn = 1.0 and 0.75 p. u. As the load angle δ with respect to the stator phase current _{i sn} from equation (10) shows a result of calculation, respectively torque _{T en} from (9). As shown in FIG. 2, λ _afn is 0.75 p. u. In the case of 1.0 p. u. Of about 1.3 p. u. Stator phase current of 2.0 p. u. To generate torque, approximately 2.3 p. u. It can be seen that the stator phase current is required. 1.0p the λ _afn. u. Compared with the comparative example which designed and adopted control which maximizes T _en / i _sn , the performance is certainly lowered.

However, it can be explained that the performance is improved by adopting the control that maximizes T _en / i _sn when the load angle is usually 90 ° (π / 2 rad) constant control. . That is, in the conventional method in which the load angle = π / 2 (rad) is constant, 1.0 p. u. 1.0 p. u. Stator current of 2.0 p. u. 2.0 p. u. The permanent magnet magnetic flux is 0.75 p. u. In spite of the small design, 2.0 p. u. The required stator phase current for torque is 2.67 p. u. Rather, about 2.3 p. u. And the stator phase current is small. If a ₁ = L _dn −L _qn = −0.2641 p. u. Not -0.3169 p. u. Then 2.0 p. u. The stator current required for torque is about 2.2 p. u. It can be.

Note that the characteristics shown in FIG. 2, it is possible to determine the load angle δ stator phase currents i _sn for the torque T _en, set to function generator 20 functions (10), the torque command T _en ^* Can generate the original phase current command i _snv ^*, and when the function of the equation (9) is set in the function generator 21, the original load angle command δ _v ^* is generated based on the torque command T _en ^*. be able to.

In FIG. 3, L _dn = 0.4347 p. u. , L _qn = 0.6988 p. u. , Λ _afn = 0.75 p. u. The stator phase current i _sn is 2.3 p. u. And 1.3 p. u. It shows the (10) the relationship of the torque T _en represented by load angle δ and (9) of the formula in the case of. FIG. 3 shows that the stator phase current i _sn in the conventional method with a constant load angle of 90 ° is 2.0 p. u. And 1.0 p. u. The relationship between torque and load angle in the case of is also shown. FIG. 3 shows 2.0 p. u. In order to generate the torque, the stator phase current i _sn is set to 2.3 p. u. By increasing the load angle from 90 ° B point to B ′ point, the torque moves from point A to point A ′, indicating that the same torque can be generated.

On the other hand, in the high speed region, the d-axis current is fixed to the permanent magnet synchronous motor 11 in a speed region where the speed of the permanent magnet synchronous motor 11 is a predetermined speed or less, for example, a critical speed corresponding to 150% of the base speed. While maintaining the value corresponding to the characteristic load angle at which the child phase current is minimum with respect to the torque generated by the permanent magnet synchronous motor 11, the value of the q-axis current and the stator phase voltage are adjusted, and the speed region exceeding the critical speed Then, the value of the q-axis current is adjusted while performing field control by adjusting the value of the d-axis current. Here, as a field control method, a direct field weakening control method in which a d-axis current, which is a magnetic flux weakening current component of a permanent magnet, is given as a function of only the speed of the permanent magnet synchronous motor 11, the speed of the permanent magnet synchronous motor 11, and There are two indirect field weakening control schemes that provide a flux weakening current component as a function of torque. Here, the simplest direct field weakening control method will be described.

The voltage of the permanent magnet synchronous motor 11 operating at a certain speed is as shown in the equations (11) and (12) when p = 0 in the equation (8).
V _qsn = R _sn i _qsn + ω _rn (L _dn i _dsn + λ _afn ) (11)
V _dsn = −ω _rn L _qn i _qsn + R _sn i _dsn (12)
Here, the phase voltage V _{sn in} the case of i _qsn = 0 is obtained by the equation (13).
V _sn ² = V _qsn ² + V _dsn ²
= Ω _rn ² (L _dn i _dsn + λ _afn ) ² + R _sn ² i _dsn ² (13)

From the equation (13), the maximum speed ω _rn (max) achievable by the field weakening control is obtained as the equation (14), and the maximum allowable field weakening d-axis current component i _dsn is obtained as the equation (15).
ω _rn (max) = (V _sn ² −R _sn ² i _dsn ² ) ^1/2 / (λ _afn + L _dn i _dsn ) (14)
i _dsn <−λ _afn / L _dn (15)
That is, in the direct field control, the limit of the equation (15) is satisfied, and the command value of i _dsn is generated as a function of the speed of the permanent magnet synchronous motor 11. Accordingly, the d-axis current component calculator 23 in FIG. 1 calculates and outputs a command value for i _dsn based on the equations (14) and (15).

FIG. 4 shows an example of the characteristic of the d-axis current command i _dsn ^* that weakens the magnetic flux of the permanent magnet, which is obtained as a function of the speed of the permanent magnet synchronous motor 11. In this case, up to a critical speed (1.5 times the base speed), the d-axis current component i _dsn, which is the load angle that maximizes the torque / current ratio, is set to i _dsn = −0.4 p. u. Set to. As shown in FIG. 4, when the d-axis current command i _dsn ^* with respect to the speed is determined, the q-axis current command i _qsn ^* can be calculated from the torque for obtaining the constant output characteristics. For this, i _qsnb × (1 / ω _rn ) is adopted as the first approximate value i _qsn1 , i _sn1 is obtained from a vector sum with i _dsn ^*, and torque T _en is calculated by equation (9).

Here, i _qsnb1 is a critical axis q-axis current. This value is compared with the torque of the constant output characteristic, and convergence calculation is performed so that the difference is reduced to obtain i _snnn , and the obtained i _snnn is determined as i _qsn ^* . I _qsn ^{* in} FIG. 4 is calculated by the procedure described above for i _qsn ^* for 100% output when the magnetic flux of the permanent magnet is designed to be 75% of the rating. In FIG. 4, in order to generate the rated torque at the base speed, the current is 100% or more below the base speed.

The calculation of i _qsn ^* is performed by the q-axis current component calculator 22 of FIG. FIG. 5 shows this relationship obtained as the torque and q-axis current characteristics using the operation speed as a parameter. From Figure 5, in the high-speed operation field current is increased, for the same torque request, q-axis current command i _QSN ^* is slightly smaller. In the q-axis current component calculator 22, among the characteristics shown in FIG. 5, for example, ω _rn is set to 4.0 p. It is also possible to generate an approximate value of i _qsn ^* in FIG. Also, the accurate i _qsn ^* determined from the characteristics of FIG. 5 can be generated by the q-axis current component calculator 22.

In this way, in the field control, the torque of the permanent magnet synchronous motor 11 which becomes smaller corresponding to the weakening of the magnetic flux of the permanent magnet is calculated from the field current command, and the torque required torque obtained by PI amplification of the control deviation of the speed controller. A q-axis current command i _qsn ^* coinciding with T _ec is calculated and set. Here, when i _dsn ^* and i _qsn ^* are obtained, the voltage and field control phase current calculator 24 calculates the original phase current command i _snF ^* and the original load angle command δ _F ^* by the following equations.
i _snF ^* = (i _dsn ^{* 2} + i _qsn ^{* 2} ) ^1/2 (16)
δ _F ^* = tan ⁻¹ (i _qsn ^* / i _dsn ^* ) (17)

The outputs of the voltage and field control phase current calculator 24, i _snF ^* and δ _F ^*, are given to the current command unit 27, and perform vector control of voltage and field control in a high speed region exceeding the base speed. However, when the obtained original phase current command i _snF ^* exceeds the maximum allowable current of the PWM inverter 15, i _snF ^* is limited to the allowable current. Here, this function is provided in the voltage and field control phase current calculator 24. The maximum value of i _dsn ^{* in} FIG. 4, that is, the maximum field control current given by the equation (15) is i _dsn <−0.75 / 0.4.347 = −1.725 p. I am satisfied with u.

FIG. 6 shows a field control method of the permanent magnet synchronous motor system 10 according to the modification, and the magnetic flux of the permanent magnet is set to 75% of the rated magnetic flux and the voltage control range 1 in response to the request for a wide field control of 1: 6. : 1.5, field control range 1: 4, L _dn = 0.4 p. u. , L _qn = 0.616 p. u. , R _sn = 0.042 p. u. The relationship between voltage, torque, phase current, and speed is shown.

FIG. 7 shows a case where the magnetic flux of the permanent magnet is designed to be 75% of the rated magnetic flux, the voltage control range is 1: 1.5, and the field control range is 1: 4 in response to the wide field control requirement of 1: 6. _dn = 0.4 p. u. , L _qn = 0.616 p. u. , R _sn = 0.042 p. u. FIG. 8 is an explanatory diagram showing the relationship between the speed, torque, voltage, and phase current when the stator phase voltage is not adjusted in the high speed region below the critical speed.

As shown in FIG. 6, the maximum value of the necessary voltage is suppressed to about 250% of the base voltage despite the high speed operation of 6 times the base speed. Moreover, the phase current at the maximum speed is slightly lower than the characteristic when the voltage control of 1: 1.5 shown in FIG. 7 is not performed. However, in this case, the voltage is 250% or less.

FIG. 8 shows the characteristics obtained when the conventional field control is performed with the magnetic flux of the permanent magnet as 100% of the rated magnetic flux and the field control range of 1: 6. The voltage at maximum speed is as high as about 350%. Indeed, in the case of FIG. 6, the current below the base speed exceeds 100%, but in the field control range, it is smaller than the current of FIG. 8 when the magnet magnetic flux is designed to be 100%. This means that the efficiency of the permanent magnet synchronous motor 11 at the maximum field control speed is improved.

Fig. 9 shows the calculated efficiency characteristics when the iron loss is ignored, the mechanical loss is assumed to be 1% of the rated capacity, and the windage loss is assumed to be 2% of the rated capacity at the maximum speed. As shown in the figure, below the base speed, the magnetic flux was designed below the rated value, so the efficiency decreased due to the increase in copper loss, but the speed was 4 p. On the maximum speed side exceeding u, the efficiency of the present invention is higher than that of the conventional method.

As described above, in the present embodiment, the magnetic flux of the permanent magnet is designed to be smaller than 100% of the rated value to suppress the voltage increase in the field control and to suppress the increase in current for obtaining the same torque characteristics. For this reason, in the low speed region below the base speed, an operation command is given for the load angle at which the torque / current ratio is maximized. Further, in the high speed region below the critical speed, the load angle at which the torque / current ratio is maximized is commanded, and the stator phase voltage is adjusted to achieve constant output characteristics, thereby suppressing an increase in current. Further, in the high speed region exceeding the critical speed, the q-axis current is adjusted while adjusting the d-axis current and performing field control.

By controlling in this way, it becomes possible to suppress the maximum voltage of the PWM inverter 15 below the rated voltage, and it is possible to realize a wide range of constant output and field control. That is, in the wide range constant output control by the field control of 1: 6 required for the hybrid car, there is no need for means for boosting the voltage of the PWM inverter 15 or means for switching and using the motor windings. Therefore, the control device 12 is simplified, and there is an advantage that the reliability is improved and the cost is reduced for a hybrid car.

In addition, the problem of current increase below the base speed when the magnetic flux of the permanent magnet is designed to be below the rated value is commanded by calculating the load angle at which the torque / current ratio is maximized. Explained how to make it as small as possible. Of course, as a measure for reducing the temperature rise of the permanent magnet synchronous motor 11 due to the increase in current, a known measure of increasing the cooling capacity of the permanent magnet synchronous motor 11 or designing the stator resistance of the permanent magnet synchronous motor 11 to be small. Can be adopted. If a measure for designing the stator resistance of the permanent magnet synchronous motor 11 to be small is adopted, as shown in FIG. 10, characteristics that are more efficient than the conventional method can be obtained in the entire speed control range. FIG. 10 shows a case where the stator resistance is designed to be 60% under the same conditions as in FIG.

As described above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the configuration described in the above-described embodiment, and the matters described in the scope of claims. Other embodiments and modifications conceivable within the scope are also included.
For example, although the direct field weakening control method has been described as the field control method, it is naturally applicable to the indirect field weakening control method. In this case, as is well known, the optimum d-axis current command i _dsn ^* at the time of field control is determined by trial and error by utilizing the fact that the mutual flux linkage and the maximum torque of the permanent magnet synchronous motor have a substantially linear relationship. Next, a method is employed in which the necessary q-axis current command i _qsn ^* is determined by calculating back from the torque. If the function generator of FIG. 1 generates the current obtained by such a procedure, it is clear that the permanent magnet synchronous motor system by the indirect field weakening control method and its field control method can be realized.
In the speed range where the speed of the permanent magnet synchronous motor is lower than the critical speed, the d-axis current is set to 0, the q-axis current value and the stator phase voltage are adjusted, and the d-axis current is exceeded in the speed range exceeding the critical speed. The q-axis current value may be adjusted while performing field control by adjusting the value of.

10: permanent magnet synchronous motor system, 11: permanent magnet synchronous motor, 12: control device, 13: first speed control system, 14: second speed control system, 15: PWM inverter, 16: first absolute value Encoder, 16a: second absolute encoder, 17: speed detector, 18: PI controller, 19: limiter, 20, 21: function generator, 22: q-axis current component calculator, 23: d-axis current component Calculator: 24: Voltage and field control phase current calculator, 25: Phase current command selector, 26: Load angle command selector, 27: Current commander, 28, 29: Current sensor

Claims (6)

The permanent magnet is provided with a power supply having a variable voltage and frequency so that the magnetic flux of the permanent magnet attached to the rotor of the permanent magnet synchronous motor is weakened during high-speed operation exceeding the base speed of the permanent magnet synchronous motor. In a permanent magnet synchronous motor system having a control device that controls field weakening by flowing d-axis current from the stator side of the synchronous motor,
The magnetic flux of the permanent magnet synchronous motor is designed to be smaller than the rated magnetic flux corresponding to the base speed,
The control device increases the value of the q-axis current orthogonal to the d-axis current in a low speed region equal to or lower than the base speed to be larger than the value of the rated q-axis current corresponding to the rated magnetic flux. The permanent magnet synchronous motor is requested by adjusting the values of the d-axis current and the q-axis current in a first speed control system that generates torque characteristics required for the motor and a high speed region exceeding the base speed. And a second speed control system for generating the output characteristics to be output. 2. The permanent magnet synchronous motor system according to claim 1, wherein the first speed control system has a characteristic load when a stator phase current of the permanent magnet synchronous motor becomes a minimum with respect to a torque generated by the permanent magnet synchronous motor. A permanent magnet synchronous motor system characterized in that an angle is calculated and a load angle of the permanent magnet synchronous motor is matched with the characteristic load angle. 3. The permanent magnet synchronous motor system according to claim 1, wherein the second speed control system is configured such that the speed of the permanent magnet synchronous motor is in a speed region equal to or lower than a preset critical speed. The d-axis current is kept at 0 or a value corresponding to a characteristic load angle at which the stator phase current of the permanent magnet synchronous motor is minimum with respect to the torque generated by the permanent magnet synchronous motor, A permanent magnet synchronous motor system that adjusts the value of the q-axis current while performing field control by adjusting the value of the d-axis current in a speed region exceeding the critical speed by adjusting a stator phase voltage. . In the direction of weakening the magnetic flux of the permanent magnet mounted on the rotor of the permanent magnet synchronous motor during high speed operation exceeding the base speed of the permanent magnet synchronous motor using a power source with variable voltage and frequency, In the field control method of a permanent magnet synchronous motor system that controls field weakening by flowing d-axis current from the stator side of the magnet synchronous motor,
The permanent magnet synchronous motor magnetic flux of the permanent magnet is designed to be smaller than the rated magnetic flux corresponding to the base speed,
In the low speed region below the base speed, the torque required for the permanent magnet synchronous motor is set by making the q-axis current value orthogonal to the d-axis current larger than the rated q-axis current value corresponding to the rated magnetic flux. And generating output characteristics required for the permanent magnet synchronous motor by adjusting the values of the d-axis current and the q-axis current in a high speed region exceeding the base speed, respectively. Field control method for permanent magnet synchronous motor system. 5. The field control method for a permanent magnet synchronous motor system according to claim 4, wherein a characteristic load when a stator phase current of the permanent magnet synchronous motor becomes a minimum with respect to a torque generated by the permanent magnet synchronous motor in the low speed region. A field control method for a permanent magnet synchronous motor system, characterized in that an angle is calculated and a load angle of the permanent magnet synchronous motor is matched with the characteristic load angle. 6. The field control method for a permanent magnet synchronous motor system according to claim 4, wherein, in the high speed region, when the speed of the permanent magnet synchronous motor is equal to or lower than a preset critical speed, the d axis While maintaining the current at 0 or a value corresponding to the characteristic load angle at which the stator phase current of the permanent magnet synchronous motor is minimum with respect to the torque generated by the permanent magnet synchronous motor, the value of the q-axis current and the stator phase A field control method for a permanent magnet synchronous motor system, wherein a voltage is adjusted and if the critical speed is exceeded, the value of the d-axis current is adjusted to adjust the value of the q-axis current while performing field control.

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