JP2638949B2 - Control method of induction machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling an induction motor used in an electric vehicle or the like, and more particularly to an improvement in energy efficiency thereof.

[Prior Art] Conventionally, as torque control of an AC motor, vector control that considers a primary current to be decomposed into an excitation current and a torque current has been widely performed. In the vector control of the induction motor, the exciting current is usually set to a constant value, and the torque current is changed to control the output torque.

Japanese Patent Publication No. 61-59071 discloses field weakening control for reducing the exciting current when the rotation speed of the induction motor increases to a predetermined value.

Further, Japanese Patent Application Laid-Open No. 58-49092 discloses that when the induction motor is under a low load, the exciting current is reduced at a predetermined constant ratio to perform field weakening control.

There is also known a method in which the optimum excitation current value and torque current value are determined for each output torque by an experiment, and the excitation current value and the torque current value are controlled based on the experimental data.

The control for operating the induction motor at the maximum efficiency by changing the exciting current is performed by the IEEJ Rotary Machine Study Group.
85-3.

This conventional control determines the slip frequency so that copper loss is minimized, and controls the induction motor with high efficiency by changing the excitation current according to the slip frequency that is fixed without depending on the rotation speed. Is what you do.

[Problem to be Solved by the Invention] In such a conventional method of controlling an induction motor,
There were the following issues.

(A) When the exciting current is kept constant, there is a problem that a large amount of energy is lost when the load is low.

That is, when the excitation current is set to a constant value, it is necessary to fix the excitation current to a value corresponding to the required maximum torque. For this reason, in the low load region, there is a problem that the exciting current becomes unnecessarily large and energy loss increases. In particular, in the case of an induction motor as a drive source of an electric vehicle, there are many cases where the load is high, such as when starting, when rapidly accelerating, and when traveling uphill. Therefore, if the exciting current value is set in accordance with such a high torque, the energy loss at a low torque becomes extremely large.

(B) Even if the field weakening control is performed at a high rotation as described in JP-B-61-59071, the energy loss at a low load cannot be reduced.

(C) As described in JP-A-58-49092, if the field weakening control is performed at a low load, the energy loss can be reduced to some extent. However, the excitation current value cannot be optimized, and sufficient energy efficiency cannot be improved. Also, if the distribution of torque current and excitation current is changed,
Due to the first order delay of the magnetic flux with respect to the exciting current, the torque transiently becomes in proportion to the product of these, and the optimization control and the accurate torque control cannot be performed.

(D) According to the method of obtaining the optimum value from experimental data obtained in advance, appropriate excitation current and torque current can be set in a considerable number of cases, and energy loss can be reduced. However, in order to increase the accuracy by this method, the amount of experiment must be increased accordingly, and it is difficult to sufficiently cope with all cases due to the setting of experimental conditions.

(E) When the slip frequency is determined so as to minimize the copper loss, and thereby the exciting current is controlled, the iron loss component is ignored in the selection of the slip frequency, and therefore, regardless of the rotation speed, The slip frequency was constant. However, since the iron loss component actually forms a considerable loss, this conventional method has not been able to achieve the expected results sufficiently.

The present invention has been made to solve such a problem, and an optimal slip depending on a rotation speed, which minimizes a copper loss and an iron loss whose slip angular frequency is calculated from characteristic values of an induction motor. Excitation current,
It is an object of the present invention to provide a control method of an induction motor that can always keep energy efficiency optimal by changing a torque current and controlling an output torque.

[Means for Solving the Problems] The control method for an induction motor according to the present invention is a control method for an induction motor that controls power supply to the induction motor based on a torque command value. 2
From the characteristic values of the secondary side resistance, mutual inductance, secondary side reactance and iron loss resistance, the optimum slip angular frequency for minimizing copper loss and iron loss in the induction motor is calculated and calculated by the following equation, and ωsmin = [(R ₁ + R _M ) R ₂ ² / {M ² R ₂ + R ₁ (L ₂ + l ₂ ) ² }] ^0.5 (where ωsmin is the optimal slip angular frequency, R ₁ is the primary resistance, and R ₂ is the secondary resistance , M is the mutual inductance of the primary secondary, L ₂ is the secondary inductance, l ₂ is the secondary leakage inductance, R _M is iron loss resistance) at a given torque fluctuation region, the rotational speed by changing the core-loss resistance R _M according those, the optimum slip angular frequency ωsmin changed according to the rotational speed, obtains the excitation current and the torque current, the output torque of the induction motor according to the torque command value It is characterized by the following.

[Operation] According to the present invention, first, the primary resistance of the induction motor,
From the respective characteristic values of the secondary resistance, the mutual inductance, the secondary reactance, and the iron loss resistance, an optimum slip angular frequency that minimizes the copper loss and the iron loss of the induction motor is calculated and calculated in accordance with the rotation speed.

Then, using the optimum slip angle frequency, the exciting current and the torque current are changed, and the output torque is controlled to a predetermined value corresponding to the torque command.

As described above, in a state where the slip angle frequency is maintained at the optimum slip angle frequency, both the excitation current and the torque current are changed according to the torque command value, so that optimization control of energy efficiency can be performed in the entire rotation range, Energy loss can be minimized in both high and low load regions.

Embodiment An embodiment of an electric vehicle to which an induction motor control method according to the present invention is applied will be described with reference to the drawings.

DC power from the battery 10 is converted into predetermined AC power by switching control of a switching transistor (not shown) of the inverter main circuit 12, and the DC power is supplied to the induction motor.
Supplied to 14. Then, the drive of the induction motor 14 is controlled, so that the running of the electric vehicle is controlled.

The rotational speed ωr of the induction motor 14 is
Is detected by And this rotation speed ωr is the magnetic flux Φ
It is supplied to the 2 command circuit 18. The magnetic flux Φ2 is supplied to the command circuit 18. The magnetic flux Φ2 command circuit 18 generates a torque command value
Secondary magnetic flux [Phi ₂ obtained from tq ^* supplies to the vector control circuit 100, and supplies the .omega.s ^* command circuit 20.

Here, the torque command value Tq
^* Secondary magnetic flux [Phi ₂ obtained by the calculation is supplied from, but utilizes an optimal slip angular frequency ωsmin obtained by the optimum slip angular frequency calculation circuit 22 to calculate the secondary magnetic flux [Phi ₂ in this invention. Therefore, this optimal slip angular frequency ω
The calculation of smin will be described.

The calculation of the optimum slip angular frequency ωsmin is based on the fact that the copper loss and the iron loss of the induction motor 14 are minimized. Then, within a range in which the secondary magnetic flux is not saturated, the slip angular frequency ωs changes according to the rotational speed obtained by this calculation, that is, a specific slip angular frequency ωsm.
In order to make torque response equivalent to vector control,
The excitation current I ₀ obtained by differentiating the secondary magnetic flux [Phi _2. By doing so, the torque output can be accurately controlled even when the torque command Tq ^* changes.

FIG. 2 shows an equivalent circuit when the axis of the induction motor 14 is changed. According to this, the following relationship is established.

i ₁ d = {Φ ₂ + K · d / dt (Φ ₂ )} / M i ₁ q = K · ωs · Φ ₂ / M i ₂ d = − (1 / R ₂ ) × d / dt (Φ ₂ ) i ₂ q = −ωs · Φ ₂ / R ₂ where i ₁ d is a primary-side exciting current corresponding to I ₀ and i ₁ q is a primary-side torque current corresponding to It. And i ₂ d and i ₂ q are the current in the excitation direction and the current in the torque direction on the secondary side, respectively. Ωs is the slip angular frequency, and K is 2
Divided by the following side inductance L ₂ and the sum of the secondary-side leakage inductance the secondary resistance _{R 2 (K = (L 2} + l 2) / R 2,
Φ ₂ is a secondary magnetic flux.

Further, the output torque T is T = Φ ₂ · i ₂ q, which can be expressed as follows using the slipping frequency ωs.

T = ωsΦ ₂ ² · R ₂ Here, the energy loss L including copper loss and iron loss when current flows to the resistance in the induction motor 14 is obtained by multiplying the square of the current of each component by the resistance. Can be Then, in the steady state, dΦ / dt becomes 0, so the loss L is expressed by the following equation.

L = i ₁ d ² (R ₁ + R _M ) + i ₁ q ² R ₁ + (i ₂ d ² + i ₂ q ² ) R ₂ = T [｛1+ (L ₂ + l ₂ ) ² / M ² × R ₁ / R ₂ ｝ ωs + (R ₁ + R _M ) R ₂ / M ² × 1 / ωs] Here, R _M indicates iron loss resistance.

In order to obtain ωs that minimizes the loss L, that is, the optimal slip angular frequency ωsmin, the loss L is differentiated by ωs, and ωs that becomes zero is obtained. In this way, the optimum slip angular frequency ωsmin is obtained as in the following equation.

_{ωsmin = [(R 1 + R} M) R 2 2 / {M 2 · R 2 + R 1 (L 2 + l 2) 2}] 0.5 optimum slip angular frequency Omegasmin which thus determined is varied in response to the rotation ωr However, if the slip angular frequency ωs is kept at the optimum slip angular frequency ωsmin including the transition period, control can be performed with the loss L minimized.

Therefore, the optimum slip angle frequency calculation circuit 22 calculates the optimum slip angle frequency ωsmin from the characteristic value of the induction motor 14 as described above.
Is calculated.

Wherein each characteristic constant of the induction motor 14 is in practice varies with the motor temperature or motor speed, for example, primary resistance R _1, R ₂ increases with increasing temperature, and the iron loss resistance R _M together with increase in the rotational speed To increase. Therefore, the arithmetic circuit 22 determines the motor characteristic constants from the motor temperature and the motor rotation speed for the torque command value Tq ^* , and calculates the optimum slip angular frequency ωsmin based on the constants.

As previously mentioned, the characteristic that in the present invention was employed to account for iron loss which has been ignored for conventional motor efficiency as Factor to determine the optimum slip angular frequency ωsmin iron loss resistance R _M FIG. 4 shows the iron loss resistance R _M experimentally obtained by the no-load test and the restraint test.
It is understood that the iron loss resistance increases as the rotation speed increases as shown in the figure.

As described above, according to the present invention, the iron loss resistance _RM is inserted only on the primary side of the d-axis, as is apparent from FIG.
With no iron loss component on the primary side of the q-axis, the arithmetic operation of the arithmetic circuit 22 can be performed very easily.

Then, the optimum slip angular frequency ωsmin is supplied to a divider 24.
R ₂ is supplied with a torque command value Tq ^* multiplied, where these division is performed. This operation result is the root operator
The secondary magnetic flux Φ ₂ is further calculated at 28, and this is supplied to the magnetic flux Φ ₂ command circuit 18.

That is, the secondary flux [Phi ₂ is calculated calculated by the following equation.

The ^{_{Φ 2 = {Tq * · R}} 2 / ωsmin} 0.5, in the magnetic flux Φ2 command circuit 18 and .omega.s ^* command circuit 20, the maximum magnetic flux Φmax sought thus resulting secondary magnetic flux [Phi ₂ in advance Compare. This is the output voltage has an upper limit, and because the magnetic flux density can not be increased any more secondary magnetic flux [Phi ₂ to reach saturation, stores the limit value Φmax in consideration of these previously, which the determined by calculation This is to prevent the secondary magnetic flux command value Φ ₂ ^* to be compared and output from the secondary magnetic flux Φ ₂ from exceeding the maximum magnetic flux Φ max.

In other words, the magnetic flux Φ2 command circuit 18 when the secondary magnetic flux [Phi ₂ is greater than the maximum flux Φmax outputs the maximum flux Φmax place as a secondary magnetic flux command value [Phi ₂ ^* in the secondary flux [Phi _2.

[Phi ₂ ^* = [phi] max also, .omega.s ^* command circuit 20 is a secondary magnetic flux [Phi ₂ is the maximum magnetic flux [Phi
If it is larger than max, the following value is output as the slip angle frequency command value ωs ^* instead of the optimum slip angle frequency ωsmin.

ωs ^* = R ₂ · Tq ^* / Φmax ² As described above, when the secondary magnetic flux reaches the maximum value, by changing the slip angular frequency command value ωs ^*, which is kept constant, the same as the prior art can be obtained. The output torque can be followed automatically.

Next, the vector control unit 100 will be described. The configuration of the vector controller 100 are the same as those known conventionally, where the torque command value Tq ^*, 2 primary magnetic flux command value [Phi ₂ ^* and the rotational speed slip angular frequency command value .omega.r .omega.s
^The power supply angular frequency ω ₀ ^* obtained by adding ^* to the adder 32 is supplied. Then, an inverter control command value iu ^* , iv ^* , iw ^* is supplied to the inverter main circuit 12.

The divider 42 has a torque command value Tq ^* and a secondary magnetic flux command value Φ ₂
^* Is supplied, where the division of Tq ^* / Φ ₂ ^* is performed.
The calculation result is supplied to a constant multiplier 44, where it is multiplied by a constant to calculate a torque current command value It ^* , which is supplied to a 2 / 3-phase converter 46. Thus, the torque current command is expressed by the following equation.

^{It * = (Tq * / Φ} 2 *) × (L 2 + l 2) / M where, L ₂ is the secondary side Indakuansu of the induction motor 14,
l ₂ is the secondary leakage inductance of the induction motor 14, M is the mutual inductance of the primary side and the secondary side of the induction motor 14.

Further, the secondary magnetic flux command value Φ ₂ ^* is supplied to the constant multiplier 48, where it is multiplied by 1 / M. Then, this result is added to the result that the secondary magnetic flux command value Φ ₂ ^* is supplied to the adder 54 through the constant multiplier 50 and the differentiator 52, and the exciting current command value
I ₀ ^* is calculated. That is, the exciting current command is as follows.

I ₀ ^* = (Φ ₂ ^* / M) + d / dt ｛(Φ ₂ ^* / M) × (L ₂ + l ₂ ) / R ₂ ｝ Further, the calculation result and the magnetic flux Φ of the divider 42 are added to the divider 56.
The secondary magnetic flux command value Φ ₂ ^* from the second command circuit 18 is supplied,
Here, these divisions are performed. And this divider 56
Is calculated by the constant multiplier 58 in the secondary resistance of the induction motor 14.
Multiplied by R ₂ and the resulting slip angular frequency ωs
And supplies to ωs ^* command circuit 20. Here, the slip angular frequency ωs is as follows.

_{^{ωs = Tq * × R 2 /}} Φ 2 * 2 ωs * command circuit 20 is a secondary magnetic flux command [Phi ₂ is the maximum magnetic flux Φma
If it is smaller than x, the optimum slip angular frequency ωsmin is output as the slip angular frequency command ωs ^* , and the secondary magnetic flux command Φ ₂
Is larger than the maximum magnetic flux Φmax, the slip angular frequency command ωs resulting from the above calculation is output as the slip angular frequency command ωs ^* . This output value is added to the rotation speed ωr by the adder 32 and supplied to the 2/3 phase converter 46 as the power supply frequency ω ₀ ^* .

The 2 / 3-phase converter 46 receives the input torque current command It ^* ,
A three-phase current command value that controls switching in the inverter main circuit from the excitation current command I ₀ ^* and the power supply frequency ω ₀ ^*.
Output iu ^* , iv ^* , iw ^* .

The operation of the example shown in FIG.
It becomes like the flowchart shown in the figure.

Thus, the secondary flux [Phi ₂ is when the maximum magnetic flux Φmax smaller performed optimum efficiency control is varied in accordance with the optimum slip angular frequency ωsmin the rotational speed so as to minimize the copper loss and iron loss, 2 2 when the secondary magnetic flux exceeds the maximum magnetic flux Φmax
The same processing as the related art in which the next magnetic flux command value Φ ₂ ^* is fixed to the maximum magnetic flux Φmax is performed.

As described above, according to the present invention, since the optimum slip angular frequency ωsmin is determined so as to minimize both the copper loss and the iron loss, it is possible to achieve higher efficiency than before. FIG. 5 shows the characteristics of the optimum slip angle frequency ωsmin with respect to the motor rotation speed in the present invention. In the past, when the optimum slip angle frequency was used for control, this frequency was a constant value. according, in order to have considering iron loss resistance R _M as described above, the optimum slip angular frequency ωsmin with an increase in rotational speed is also understood to be increased.

[Effects of the Invention] As described above, according to the control method of the induction motor according to the present invention, by controlling the slip angular frequency to be the optimum slip angular frequency capable of minimizing copper loss and iron loss, control with less energy loss is performed. Is achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a system to which an induction motor control method according to one embodiment of the present invention is applied, FIG. 2 is an equivalent circuit diagram of the induction motor 14 of the embodiment, and FIG. 3 is an operation of the embodiment. FIG. 4 is a characteristic diagram showing characteristics of iron loss resistance and rotation speed in the embodiment, and FIG. 5 is a characteristic diagram showing characteristics of optimal slip angle frequency and rotation speed in the embodiment. is there. 10… Battery 12 …… Inverter main circuit 14 …… Induction motor 16 …… Tacho generator 18 …… Flux Φ2 command circuit 20… ωs ^* Command circuit 22 …… Minimum slip angle frequency calculation circuit R _M …… Iron loss resistance

Claims (1)

(57) [Claims] 1. An induction motor control method for controlling power supply to an induction motor based on a torque command value, comprising: a primary resistance, a secondary resistance, a mutual inductance, a secondary reactance, and an iron the optimum slip angular frequency to minimize the copper loss and iron loss in the induction motor from the characteristic values of the loss resistance is calculated is calculated by the following _{equation, ωsmin = [(R 1 +} R M) R 2 2 / {M 2 R 2 + R ₁ (L ₂ + l ₂ ) ² ｝] ^0.5 (where ωsmin is the optimal slip angular frequency, R ₁ is the primary resistance, R ₂ is the secondary resistance, M is the mutual inductance of the primary and secondary sides, L ₂ is the secondary inductance, l ₂ is the secondary leakage inductance, R _M is iron loss resistance) at a given torque fluctuation region, by changing the core-loss resistance R _M in accordance with the rotational speed, This optimum slip angle frequency ωsmin is changed according to the rotational speed, And determine the torque current, a control method for an induction motor the output torque of the induction motor, characterized in that the one corresponding to the torque command value.