JPH10210800A - Controller for induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the output torque of an induction motor accurately even in a region subjected to limitation by the power supply voltage. SOLUTION: In a region I of relatively low torque, an exciting current command Id* and a torque current command Iq* are varied along a maximum efficiency line and the output torque of an induction motor is controlled by (Id*, Iq*). In a region III of relatively high torque, output torque of the induction motor is controlled by Iq*/Id*, i.e., the slip, and a margin BC for the limit line due to limitation of power supply voltage is imparted with respect to the (Id*, Iq*). Terminal voltage of the induction motor is fixed at a level corresponding to the power supply voltage because the margin BC is imparted, and the output torque can be controlled accurately by the slip.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a control device for controlling an induction motor.

[0002]

2. Description of the Related Art An induction motor is used as a drive motor for an electric vehicle, and its output is controlled by dividing a motor primary current into an excitation current component Id and a torque current component Iq. Vector control is well known. Here, Id is a component that causes the induction motor to generate the secondary magnetic flux Φ2, and Iq is a component that causes the induction motor to generate the output torque T.

[0003] FIG. 6 shows that T and (I
d, Iq). T is proportional to Id × Iq because T is a torque generated by the linkage between Iq and Φ2. Therefore, (Id, Iq) that can realize a certain T
, A curve denoted as “constant torque line” in the figure is obtained. Further, the constant torque line relating to the larger T is located on the higher current side in the figure as compared with the constant torque line relating to the smaller T. On the other hand, when the efficiency of the induction motor is maximized (Id, Iq), a straight line labeled “Maximum efficiency line” is obtained in the figure (here, iron loss and magnetic saturation are ignored). There). Therefore, if T is to be increased while maintaining the maximum efficiency, (Id,
The exciting current command value Id ^* and the torque current command value Iq ^*, which are the control target values of Iq), may be increased together along this maximum efficiency line.

However, in practice, the voltage of a power supply for supplying a primary current to an induction motor is finite. Therefore, when (Id ^* , Iq ^* ) and (Id, Iq) are increased along the maximum efficiency line in FIG. 6, eventually, the "power supply voltage and the power supply voltage" which are substantially elliptical curves as shown in FIG. Output limitation due to motor terminal voltage ". That is, (Id ^* ,
As the motor terminal voltage necessary to realize (Id, Iq) equal to Iq ^* ) becomes equal to the voltage of the power supply for supplying the primary current to the induction motor, the motor terminal voltage increases. Beyond this point (Id ^* , Iq ^* )
Even if is increased, it is not possible to realize (Id ^* , Iq ^* ) due to the lack of the actual power supply voltage with respect to the required motor terminal voltage, which causes problems including insufficient torque. The maximum efficiency line when taking this output limitation into account is shown in FIG.
As shown in FIG. 6, from the origin (Id, Iq) = (0, 0) to the point A, that is, the point where the required motor terminal voltage and the applicable power supply voltage become equal, a straight line (region I) as shown in FIG. The portion having a larger current than the point A is a line having a curve (region II) along the line of the output limitation in FIG. In region I, the output torque T is increased by increasing both (Id ^* , Iq ^* ), whereas in region II, Iq ^* is increased to increase T and Id ^*.
And the motor terminal voltage is reduced to the power supply voltage value.

[0005]

Here, since the output limiting line shown in FIG. 7 is a line determined by the correlation between the power supply voltage and the motor terminal voltage, the line in the area II in FIG. In order to give (Id ^* , Iq ^* ) such that (Id, Iq) accurately follows the maximum efficiency line, the back electromotive force of the induction motor to be controlled can be accurately estimated for various operating ranges and conditions. I have to. In practice, however, it has been difficult to achieve such accuracy, and it has heretofore been difficult to maximize the efficiency of the induction motor and control the output torque to a desired value.

One of the objects of the present invention is to maximize the efficiency of an induction motor without accurate estimation of the back EMF by introducing different control techniques in areas where relatively large output torque is required. Another object of the present invention is to make it possible to control the output torque to a desired value and to appropriately realize desired motor characteristics.

[0007]

In order to achieve the above object, a control device according to the present invention provides an exciting current component Id of a primary current flowing through an induction motor according to a value of an exciting current command Id ^*. Component Iq is converted to torque current command Iq ^*
And when the determined (Id ^* , Iq ^* ) is given to the current command output means, the output torque T of the induction motor becomes (Id ^* , Iq ^* ).
d ^*, Iq ^*) of the product Id ^* × Iq ^* at a value determined T ^* becomes equal to as, its (Id ^*, and a current control means for determining a value of Iq ^*), was determined (Id ^*, Iq ^* ) To the current command output means, T becomes (Id ^* , Iq
^* ) Determined by the slip control means for determining the value of (Id ^* , Iq ^* ) and the current control means so as to become a value T ^* corresponding to the slip s determined by the ratio Iq ^* / Id ^{* of} ( ^* ). I
In the low torque region I where the value of d ^* , Iq ^* ) is smaller than the limit line in the current vector space due to the power supply voltage, the current control means determines that the value is higher in the higher torque region III where the current is larger. From the slip control means, (Id ^* , Iq
^* ) To the current command output means, and a control switching means (see FIG. 1).

In the present invention, for the region I where only a relatively small T can be obtained, T ^* is realized by controlling (Id, Iq) with (Id ^* , Iq ^* ) as the target. Conversely, in the region III where a relatively large T must be realized, T ^* is realized by the target control of s. Here, in the induction motor, T when the motor terminal voltage is constant is determined by s as shown in FIG. On the other hand, in the region on the higher current side than the limit line caused by the power supply voltage, the region is limited by the power supply voltage.
The terminal voltage of the induction motor can be considered constant. Therefore, as shown in FIG. 1, as shown in FIG. 1, a region III in which a difference (distance between points B and C) between (Id, Iq) and (Id ^* , Iq ^* ) is generated, and the target control of s is performed for this region. , T ^* can be realized with maximum efficiency.
At that time, it is not necessary to accurately estimate the back electromotive force of the induction motor.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. For the sake of simplicity, the constant names, variable names, command names, and the like used in the above description will be used.

FIG. 3 shows an example of the system configuration of an electric vehicle to which the present invention is applied. In this system, a three-phase induction motor 10 is used as a vehicle driving motor, and a discharge output of a vehicle-mounted battery 12 is output from an inverter 1.
At 4, DC is converted to three-phase AC and supplied to the induction motor 10. The control device 16 controls the inverter 1 according to the required acceleration / deceleration detected as the accelerator opening, the brake pedal force, and the like.
By controlling the switching patterns Su, Sv, Sw of the U, V, and W phase switching elements in 4, the torque corresponding to the required acceleration / deceleration is output from the induction motor 10. The rotation sensor 18 in the figure detects the rotor angular velocity ω of the induction motor 10, and the current sensors 20u, 20v and 20w
Detects the U, V, and W phase currents Iu, Iv, and Iw, and the voltage sensor 21 detects the voltage VB of the battery 12.

FIG. 4 shows an internal functional configuration of the control device 16 according to an embodiment of the present invention. In the figure, torque command generator 2
2 incorporates, for example, a map that gives the rotation speed of the induction motor 10 versus the maximum output torque characteristic.
The current motor rotation speed (= ω / 2π × 60, where ω is rad / sec and the motor rotation speed is rpm) is referred to. As a result, after obtaining the maximum torque that can be output at the current rotational speed, the torque command generation unit 22 realizes the required acceleration / deceleration by dividing the maximum torque by the accelerator opening and the brake pedal force. A torque command T ^* indicating the torque required for the above is generated. The current command generation unit 24 which are arranged at a subsequent stage, based on the T ^* and omega (I
d ^* , Iq ^* ) and the slip angular velocity command ωs ^* are derived. The procedure will be described later.

On the other hand, the three-phase / two-phase conversion unit 26 includes Iu, I
The detected values of v and Iw are calculated using the motor electrical angle θ (Id,
Iq). The adders 28d and 28q determine the differences Id ^* -Id and Iq between the command value and the detected value with respect to the motor current.
^* -Iq is calculated, and the proportional control units 30d and 30q perform a proportional control operation. The adders 34d and 34q calculate the kp × (Id ^* −Id) and kp obtained by the proportional control operation.
The back electromotive force term generated by the back electromotive force term generator 32 is added to × (Iq ^* −Iq). 2-phase / 3-phase converter 36
Are the voltage commands (Vd ^* , V
q ^* ) is converted to Su, Sv, Sw using θ and output. .theta. is obtained by obtaining the sum of .omega. and .omega.s ^* , that is, the rotational angular velocity of the magnetic flux by the adder 38, and integrating this by the integrator 40. In the above description, kp is a proportional control gain. Further, as for the two-phase / three-phase conversion and the three-phase / two-phase conversion, a conventionally well-known technique can be used, and thus the description is omitted.

One of the features of the control device 16 shown in FIG.
Instead of using PI control, which is relatively frequently used for current control of an induction motor, P control that does not generate an integral term is used. This is because the motor terminal voltages required to realize (Id ^* , Iq ^* ), that is, (Vd ^* , V
Even if the voltage determined by q ^* ) exceeds the voltage that can be actually applied from the battery 12 to the terminal of the induction motor 10 via the inverter 14, the current control becomes unstable due to the divergence of the integral term. This is to prevent it. Therefore, according to the present embodiment, even when a large back electromotive force is generated because the induction motor 10 is operated at a high rotation speed or when the voltage of the battery 12 is reduced, the current control is relatively small. It is stable. In this regard,
For example, refer to the disclosure of Japanese Patent Application Laid-Open No. 64-69289 relating to a system for driving an induction motor by an AC power supply.

Another feature of the control device shown in FIG.
A back electromotive force term is generated, and this is generated by the proportional control units 30d and 30q.
That is, the steady-state current deviation is suppressed by adding to the output. The back electromotive force term can be generated in accordance with the common sense of those skilled in the art using each constant (secondary inductance L2, secondary resistance R2, mutual inductance M, etc.) of the induction motor 10. This at least partially compensates for the disadvantage of the P control over the PI control, that is, the disadvantage that a steady-state deviation is likely to occur.

Another feature of the control device shown in FIG. 4 is that, in a region I in FIG. 1, T ^* is realized by controlling (Id, Iq) with (Id ^* , Iq ^* ) as a target. And region I
In II, the control method is switched for each area, in which T ^* is realized by controlling the slip angular velocity ωs with ωs ^* as a target. That is, it is difficult to accurately estimate the back electromotive force over various operating ranges and various conditions.
If the current control is performed along the line of the output limitation by the power supply voltage and the motor terminal voltage as in the region II in the middle, inaccuracy of the control cannot be avoided. Therefore, instead, the control of T by s (where ωs is proportional to s) focusing on the slip versus output torque characteristic when the motor terminal voltage is constant shown in FIG. 3 is introduced. Thereby, in this embodiment,
High-efficiency operation can be accurately performed in the high torque region.

FIG. 5 shows a schematic functional configuration of the current command generator 24. This figure is a diagram for explaining the functions, and the embodiment of the present invention is not limited to hardware or software. In addition, various calculation procedures can be replaced with a map or the like.

In the figure, an area I command determining unit 42 is Id × I
The relation of q = (L2 / M ² ) × T and the condition Iq = k × Iq (where k is a constant) of the maximum efficiency line shown in FIG.
By substituting T = T ^* , (Id, Iq) necessary to realize T ^* by current control, ie, (Id ^* , Id)
q ^* ), and this (Id, Iq) is calculated as ωs = (R
By substituting into the relationship of 2 / L2) × (Iq / Id), ωs ^* indicating ωs to be obtained when the obtained (Id ^* , Iq ^* ) is output is determined. On the other hand, region II
The I command determining unit 44 obtains s necessary for realizing T ^* by referring to the slip versus output torque characteristics when the motor terminal voltage is a value equivalent to VB, and further uses this s to obtain ω
s ^* , and further convert this ωs ^* to ωs = (R2 / L2)
× (Iq / Id) by substituting into ωs, Iq /
Id is calculated, so that Iq ^* / Id ^* becomes equal to this Iq / Id and monotonically increases with respect to T ^* , that is, such that a margin portion BC in FIG. 1 occurs (Id ^* ,
Iq ^* ). The control switching unit 46 supplies the current command output unit 48 with (Id ^* , Iq ^* ) determined by the region I command determination unit 42, and the current command output unit 48
(Id ^* , Iq ^* ) is output to d and 28q. However,
(Id ^* , I
q ^* ), the (Id ^* , I ^*
When the motor terminal voltage necessary to realize (q ^* ) as (Id, Iq) will exceed the VB equivalent value, the control switching unit 46 determines the (Id ^*) determined by the region I command determination unit 42 ^. , Iq ^* ) instead of the region III command determining unit 4
The (Id ^* , Iq ^* ) determined in step 4 is supplied to the current command output unit 48.

As described above, in the region III, the flow can be actually performed under the restriction by VB or the like (Id, Iq).
By applying (Id ^* , Iq ^* ) larger by BC than that of the inverter 14, a voltage corresponding to VB from the inverter 14 side, that is, the highest voltage that can be extracted from the inverter 14 is applied to the induction motor 10. As a result, a state where the control of T by s can be performed as shown is obtained. Further, in this state, since the control of T by s (directly ωs) is executed, T ^* can be accurately realized even if a slight deviation occurs in the current command and the voltage command. As a result, VB
Even at the time of a decrease, high efficiency, high torque, and high precision control can be realized.

[0019]

As described above, according to the present invention,
In region III where relatively large T must be realized, T ^* is realized by target control of s, so T ^* is achieved at maximum efficiency without accurately estimating the back electromotive force of the induction motor. As a result, desired motor characteristics can be realized.

[Brief description of the drawings]

FIG. 1 shows the principle of torque control according to the present invention.
It is an Iq top view.

FIG. 2 is a characteristic diagram showing characteristics of slip s versus output torque T when the motor terminal voltage is constant.

FIG. 3 is a block diagram showing an example system configuration of an electric vehicle to which the present invention is applied;

FIG. 4 is a block diagram illustrating a functional configuration of a control device according to an embodiment of the present invention.

FIG. 5 is a block diagram illustrating a functional configuration of a current command generation unit.

FIG. 6 is a diagram illustrating a maximum efficiency line and a constant torque line of a motor when an output limitation by a power supply voltage and a motor terminal voltage is not considered.

FIG. 7 is a diagram showing output limitation by a power supply voltage and a motor terminal voltage.

FIG. 8 is a diagram showing a maximum efficiency line when an output limitation by a power supply voltage and a motor terminal voltage is considered.

[Explanation of symbols]

Reference Signs List 10 induction motor, 12 battery, 14 inverter, 16 control device, 18 rotation sensor, 20u, 20
v, 20w current sensor, 21 voltage sensor, 22 torque command generator, 24 current command generator, 26 three-phase /
Two-phase converter, 28d, 28q, 34d, 34q, 38
Adder, 30d, 30q proportional controller, 32 back electromotive force term generator, 36 2-phase / 3-phase converter, 40 integrator, 4
2 area I command determination unit, 44 area III command determination unit,
46 control switching section, 48 current command output section, T ^* torque command, Id ^* excitation current command, Iq ^* torque current command, ωs ^* slip angular velocity command, VB battery voltage,
Id Excitation current component of motor primary current, Iq Torque current component of motor primary current.

Claims (1)

[Claims] 1. A current command output means for controlling an exciting current component of a primary current flowing through an induction motor according to a value of an exciting current command, and controlling a torque current component according to a value of a torque current command. When the current command and the torque current command are given to the current command output means, the excitation current command and the torque current are set so that the output torque of the induction motor becomes equal to a value determined by the product of the excitation current command and the torque current command. Current control means for determining the value of the command; and when the determined excitation current command and torque current command are given to the current command output means, the output torque of the induction motor is determined by the ratio of the excitation current command and the torque current command. A slip control means for determining the values of the excitation current command and the torque current command so as to have a value corresponding to the determined slip, and an excitation determined by the current control means. In the low torque region where the values of the magnetic current command and the torque current command are smaller than the limit line on the current vector space caused by the power supply voltage, the current control means is used, and in the high torque region where the current is large, the slip control is performed. Control switching means for supplying an exciting current command and a torque current command to the current command output means from the means.