JP2011050217A - Controller for induction motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller for an induction motor which can switch a control method in any output state by smoothly changing an exciting current and a torque current of the induction motor. <P>SOLUTION: The controller for an induction motor calculates a current command value according to a torque command value and a rotating speed of an induction motor IM and drives the induction motor using a three-phase AC current corresponding to the calculated current command value. The controller for the induction motor comprises a vector control current component command calculating unit 11-1 for calculating a current that makes a target magnetic flux of the induction motor constant at a given torque command value, a maximum efficiency control current component command calculating unit 11-2 for calculating a current that minimizes a loss of the induction motor at a given torque command value, a current component command calculating unit 11-3 on switching a control method for calculating a current when switching the current command value, and a motor driving unit (12, 13, 14) that makes the current in the induction motor follow the current command value. The controller for the induction motor controls the output torque of the induction motor so that it may have a value corresponding to the torque command value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an induction motor control apparatus.

As a method for controlling an induction motor used as a driving power source for an industrial vehicle such as a forklift, a primary current I ₁ (current flowing through a stator) is divided into an excitation current Id and a torque current Iq and controlled, and PG ( PG vector control using a pulse generator for speed detection is widely adopted. As is well known, the PG vector control has a different meaning from the vector control described later.

  A thick line on the Id-Iq characteristic diagram of FIG. 5A shows an example of vector control (Id = constant) and maximum efficiency control (Id: Iq = arbitrary) widely used as a control method of the induction motor. It is.

  Vector control (Id = constant) makes the magnetic flux Φd constant by making the excitation current Id constant at a predetermined slip speed, and changes the torque current Iq in proportion to the desired torque. This control method is excellent in the response and stability of the motor, and is considered advantageous for the operation performance of the forklift.

  On the other hand, the maximum efficiency control (Id: Iq = arbitrary) is a control method for suppressing copper loss and iron loss by reducing the excitation current Id and the magnetic flux Φd by appropriately setting the ratio of Id: Iq. It is.

  FIG. 5B shows one method of maximum efficiency control, in which the ratio of Id: Iq is controlled to an appropriate constant value in the low torque region.

As shown in FIG. 5 (b), even for the same torque output, Id: substantially the Iq 1: If 1, copper loss ^{_{P 1Loss = I 1 2 × R}} 1 of the motor primary side is a minimum Thus, the copper loss can be suppressed by reducing the excitation current Id. R ₁ is the primary resistance value. Further, reducing the exciting current Id reduces the magnetic flux Φd, and can suppress iron loss.

  By the way, forklifts frequently accelerate and decelerate while the road surface condition frequently changes due to the friction coefficient μ of the traveling road surface, steps, roughness, etc., so the responsiveness and stability of the traveling motor deteriorates. It may lead to a decrease in operability and safety. Therefore, it is required to achieve high efficiency without deteriorating responsiveness and stability.

  So far, several methods have been proposed to compensate for responsiveness and stability while applying maximum efficiency control. The method is roughly divided into two as follows.

First method: Method for improving the responsiveness and stability of maximum efficiency control Second method: A method for switching and selectively using the control method As a remarkable example of the first method, the induction motor control described in Patent Document 1 There is a device. This example is used as a technique for improving the torque response while changing the magnetic flux by using a low-pass filter characteristic and suppressing the current peak value.

  As a second method, there is a method of switching the control method when the device is stopped for industrial use, but it is not suitable for a vehicle in which the environment and the operating condition frequently change. For example, Patent Document 2 targets the driving of an elevator, operates with maximum efficiency control when there is no occupant or during steady operation with the occupant, and vector control (Id = constant) during acceleration and deceleration with the occupant. A vector control device to be operated is described. In an elevator or the like, it is sufficient to switch the control method when the apparatus is stopped or to switch the control method gently in a predetermined operation. However, this is not suitable for vehicles whose environment and operating conditions frequently change.

  On the other hand, Patent Document 3 proposes a control device for an induction motor that is proposed for a vehicle as another example of the second method and switches a control method at a certain point on the Id-Iq characteristic diagram. . Briefly speaking, this control device is a method of switching to a method of controlling torque by excitation current Id and torque current Iq with a constant sliding speed in the low torque region (maximum efficiency control), and controlling torque by slipping in the high torque region. However, the control method can be selectively used only for the low torque region and the high torque region, that is, the restricted output state.

Japanese Patent No. 2914106 JP 2000-184800 A JP-A-10-210800

  If switching to vector control can be performed quickly when the environment or operating conditions change during operation with maximum efficiency control in steady state, the response and stability can be improved while suppressing losses such as copper loss and iron loss. Can be secured.

  However, as shown at the tip of two arrows in FIG. 5B, the points indicating the excitation current Id and the torque current Iq by the two control methods are not close to each other on the Id-Iq characteristic diagram even if the torque is the same. In this case, if the vector control (Id = constant) and the maximum efficiency control (Id: Iq = arbitrary) are to be switched alternately and suddenly, a large current may flow rapidly and normal operation may not be possible.

  An object of the present invention is a method of switching the control method as the second method, and smoothly changes the excitation current Id and the torque current Iq of the induction motor by a new means, and the control method in an arbitrary output state It is an object of the present invention to provide a control device for an induction motor that can be switched.

  An induction motor control device according to an aspect of the present invention calculates a current command value according to a torque command value and a rotation speed of the induction motor, and drives the induction motor with a three-phase alternating current corresponding to the calculated current command value. A first current calculation unit that calculates a current that makes the target magnetic flux of the induction motor constant at a given torque command value, and calculates a current that minimizes the loss of the induction motor at a given torque command value A second current calculation unit, a third current calculation unit for calculating a current at the time of switching between the first current calculation unit and the second current calculation unit, that is, a current command value switching, and A motor drive unit that causes the current flowing through the induction motor to follow the current command value, and controls the output torque of the induction motor to be a value corresponding to the torque command value.

  The third current calculation unit stores a plurality of types of constant torque curves that are preliminarily measured with respect to the excitation current Id and the torque current Iq of the induction motor and are defined as a constant torque curve defined by Id × Iq = constant. Based on the torque value stored in the constant torque curve map, the combination of the excitation current and the torque current is changed so that the output torque of the induction motor is constant with respect to a constant torque command. It is preferable to perform an operation. The third current calculation unit preferably performs current calculation for updating the torque current so as to follow the updated torque command value when the output torque of the induction motor is updated and applied.

  According to the present invention, it is possible to provide a control device capable of smoothly changing the excitation current Id and the torque current Iq of the induction motor and switching the control method in an arbitrary output state.

  When such an induction motor control device is applied to an induction motor used as a driving power source for an industrial vehicle such as a forklift, the control method can be switched according to a request from the vehicle from any state. It is. For example, vector control (Id = constant) in situations such as when a sudden acceleration command is input or the tire is idling due to slipping and the vehicle's traction control (slip prevention control) is started during energy saving operation by maximum efficiency control Can be switched smoothly. As a result, it is possible to realize both the energy saving of the vehicle and the ease of operability.

It is a block block diagram of embodiment of the induction motor control apparatus by this invention. The Id-Iq characteristic figure for demonstrating the 1st operation example of the induction motor control apparatus shown by FIG. The Id-Iq characteristic figure for demonstrating the 2nd operation example of the induction motor control apparatus shown by FIG. The Id-Iq characteristic figure for demonstrating the 3rd operation example of the induction motor control apparatus shown by FIG. The Id-Iq characteristic figure for demonstrating an example of the conventional vector control and maximum efficiency control is shown.

[Configuration and operation of the invention]
As described above, as shown at the tips of the two arrows in FIG. 5B, the points indicating the excitation current Id and the torque current Iq according to the two control methods are close to each other on the Id-Iq characteristic diagram even when the torque is the same. If not, when trying to switch the vector control (Id = constant) and the maximum efficiency control (Id: Iq = arbitrary) alternately and suddenly, a large current may flow rapidly and normal operation may not be possible.

FIG. 1 shows a block configuration of an embodiment of an induction motor control apparatus according to the present invention. In addition to the current component command calculation unit 11 that can be said to be a characteristic part of the present invention, the present induction motor control device has a current component with an excitation current command value Ids ^* and a torque current command value Iqs ^* from the current component command calculation unit 11 as inputs. Control circuit 12, voltage command calculation circuit 13 that receives d-axis voltage command value Vds ^* and q-axis voltage command value Vqs ^* from current component control circuit 12, and U-phase voltage command value Vus ^* from voltage command calculation circuit 13 , including V-phase voltage command value ^Vvs *, W-phase voltage command value Vws ^* a as an input U-phase voltage Vus, V-phase voltage Vvs, the PWM inverter 14 to output a W-phase voltage Vws. The current component control circuit 12, the voltage command calculation circuit 13, and the PWM inverter 14 function as a motor driving unit that collectively causes the current flowing through the induction motor IM to follow the current command value.

  The induction motor control device also includes a current component calculation circuit 16 that receives the U-phase current detection value Ius from the U-phase current detector 15-1 and the V-phase current detection value Ivs from the V-phase current detector 15-2 as inputs. The slip frequency calculation circuit 17 receives the excitation current calculation value Ids and the torque current calculation value Iqs from the current component calculation circuit 16, the slip frequency calculation value ωs ′ from the slip frequency calculation circuit 17, and the speed detector of the induction motor IM. 18 includes an adding unit 19 that adds the detected value ωr from the speed (angular frequency) 18 and an integrator 20 that calculates the angle θ by integrating the addition result (angular frequency) ω from the adding unit 19. The calculated angle θ is input to the voltage command calculation circuit 13 and the current component calculation circuit 16. The excitation current calculation value Ids and the torque current calculation value Iqs from the current component calculation circuit 16 are also input to the current component control circuit 12.

The induction motor control device further includes a current ratio map data table 21 that receives the speed detection value ωr. In the current ratio map data table 21, a combination of the ratio of the torque current command value Iqs ^* to the excitation current command value Ids ^* measured in advance is registered as map data, and the table is referred to based on the speed detection value ωr. Current ratio Iqs ^* / Ids ^* .

The current component command calculation unit 11 which is a main part of the induction motor control device according to the present invention receives a torque command and an excitation current command from a host device (not shown), and obtains a current ratio Iqs ^* / Ids ^* from the current ratio map data table 21. receive. The current component command calculation unit 11 is a vector control current component command calculation unit 11-1 that receives an excitation current command and is responsible for vector control, and a maximum efficiency control current component command that is responsible for maximum efficiency control upon receiving a current ratio Iqs ^* / Ids ^*. The calculation unit 11-2 includes a control method switching current component command calculation unit 11-3 that is responsible for switching between vector control and maximum efficiency control.

  The vector control current component command calculation unit 11-1 functions as a first current calculation unit that calculates a current that makes the target magnetic flux of the induction motor IM constant at a given torque command value, and a maximum efficiency control current component command calculation unit 11-2 functions as a second current calculation unit that calculates a current that minimizes the loss of the induction motor at a given torque command value. On the other hand, the current component command calculation unit 11-3 at the time of switching the control method calculates a current at the time of switching between the first current calculation unit and the second current calculation unit, that is, at the time of switching the current command value. Functions as a current calculator.

  Next, a control method switching procedure realized by the current component command calculation unit 11 in the induction motor control device will be described.

Step 1
First, before and after the transition in the case of shifting from steady operation to steady operation of the same torque with a different control method will be described. As described above, if the control method is different, the combination of the excitation current Id and the torque current Iq is different even with the same torque. In order to keep the torque T the same, it is necessary to make Φd × Iq the same from Equation 1 below.

但し、ｐはポール数、Ｌｒは回転子自己インダクタンス、Ｍは相互インダクタンスで固定値であり、Φｄはｄ軸磁束である。

Here, p is the number of poles, Lr is the rotor self-inductance, M is the mutual inductance, and Φd is the d-axis magnetic flux.

  Assuming that the d-axis magnetic flux Φd and the excitation current Id are in a proportional relationship, if the product Id × Iq of the excitation current Id and the torque current Iq is the same, Φd × Iq is also the same and the torque is the same. Therefore, by increasing or decreasing the excitation current Id and the torque current Iq while keeping the same Id × Iq, the same torque can be obtained even if the control method is switched. An example is shown in FIG.

  FIG. 2 shows switching between vector control (Id = constant) and one of maximum efficiency control, which controls the Id: Iq ratio to an appropriate constant value in the low torque region. It is an example of a technique. Both ends of the arrow, which is the intersection of the constant torque curve and the Id-Iq line of each control method, indicate a combination of Id and Iq according to each control method at a certain torque.

Step 2
Next, the transition of the above operation will be described.

  The transfer function representing the response of the d-axis magnetic flux Φd with respect to the increase / decrease of the excitation current Id is expressed by the following formula 2.

但し、ｓはラプラス演算子、Ｒｒは回転子抵抗である。

Here, s is a Laplace operator, and Rr is a rotor resistance.

  Therefore, the d-axis magnetic flux Φd becomes a first-order lag response with respect to the excitation current Id with a time constant Lr / Rr. The change amounts ΔId and ΔIq of the excitation current Id and the torque current Iq and the change amount ΔT of the torque T can be expressed by the following equation (3).

  Therefore, the torque current Iq is decreased and increased so that Id × Iq becomes constant after giving a first-order lag with the time constant Lr / Rr to the increase and decrease of the excitation current Id. Thereby, Φd × Iq can be kept constant and the torque can be kept constant. An example is shown in FIGS.

  FIG. 2 shows an example of a technique for switching between vector control (Id = constant) and maximum efficiency control (Id: Iq = arbitrary). The point indicating the torque current Iq and the excitation current Id giving the first order lag moves on the arrow line and reaches one of the end points. For this purpose, the control method switching current component command calculation unit 11-3 includes a storage unit in which a plurality of constant torque curves (Id × Iq = constant) are registered as a constant torque curve map.

FIG. 3 shows an example of a technique for selectively using vector control (Id = constant) and maximum efficiency control (Id: Iq map). Similar to the method of FIG. 2, the point indicating the torque current Iq and the excitation current Id giving the first order lag moves on the line of the arrow and reaches one of the end points. For this reason, the control component switching current component command calculation unit 11-3 determines that the output torque of the induction motor IM is constant with respect to a constant torque command based on the torque value stored in the constant torque curve map. The calculation is performed to change the combination of the excitation current Id and the torque current Iq so that the excitation current command value Ids ^* and the torque current command value Iqs ^* are output. In FIG. 3, Id: Iq in the shaded area is registered in the current ratio map data table 21 as current ratio map data for maximum efficiency control.

Step 3
Next, a case where the torque command is updated during the transition of the above operation will be described.

  Based on the d-axis magnetic flux Φd at the time when the torque command is updated, the current component command calculation unit 11 updates the command value of the torque current Iq. Based on the updated torque, d-axis magnetic flux Φd and torque current Iq, the excitation current Id and torque current Iq are calculated in the procedure of step 2 so as to keep Φd × Iq constant. An example is shown in FIG.

FIG. 4 shows an example of a technique for switching between vector control (Id = constant) and maximum efficiency control (Id: Iq map). The point indicating the torque current Iq and the exciting current Id giving the first order lag moves on the line of the arrow, and after updating the torque command, it reaches one of the end points along the updated constant torque curve. For this reason, when the torque command value of the induction motor IM is updated and given, the current component command calculation unit 11-3 at the time of switching the control method changes the torque current command value so as to follow the updated torque command value. Current calculation for updating Iqs ^* is performed and output. Also in FIG. 4, Id: Iq in the shaded area is registered in the current ratio map data table 21 as current ratio map data for maximum efficiency control.

  By the above method, the control method can be smoothly switched while keeping the output torque constant.

  According to the above embodiment, the excitation current Id and the torque current Iq of the induction motor can be smoothly changed, and the control method can be switched in an arbitrary output state.

  When such an induction motor control device is applied to an induction motor used as a driving power source for an industrial vehicle such as a forklift, the control method can be switched according to a request from the vehicle from any state. It is. For example, vector control (Id = constant) in situations such as when a sudden acceleration command is input while the vehicle is in energy saving operation by maximum efficiency control, or when a tire is idling due to slipping and traction control (slip prevention control) of the vehicle is started. Can be switched smoothly. As a result, it is possible to realize both the energy saving of the vehicle and the ease of operability.

  The present invention applies vector control that uses an induction motor and decomposes and controls the primary current into an excitation current Id and a torque current Iq, and is required to satisfy both responsiveness, stability, and efficiency, or other purposes. If the control method is required to be switched, application is possible.

15-1, 15-2 Current detector 18 Speed detector 19 Adder 20 Integrator

Claims (3)

In the induction motor control device that calculates the current command value according to the torque command value and the rotation speed of the induction motor, and drives the induction motor with a three-phase alternating current corresponding to the calculated current command value,
A first current calculation unit that calculates a current that makes the target magnetic flux of the induction motor constant at a given torque command value;
A second current calculation unit for calculating a current that minimizes the loss of the induction motor at a given torque command value;
A third current calculation unit that calculates a current at the time of switching between the first current calculation unit and the second current calculation unit, that is, a current command value;
A motor drive unit that causes the current flowing through the induction motor to follow the current command value;
An induction motor control device that controls the output torque of the induction motor to be a value corresponding to the torque command value.   The third current calculation unit stores in the storage device a plurality of types of constant torque curves that are preliminarily measured with respect to the excitation current Id and torque current Iq of the induction motor and are defined as Id × Iq = constant, and a constant torque curve map. Based on the torque value stored in the torque constant curve map, an operation for changing the combination of the excitation current and the torque current so that the output torque of the induction motor is constant with respect to a constant torque command is performed. The induction motor control device according to claim 1, wherein the induction motor control device is performed.   When the output torque of the induction motor is updated and given, the third current calculation unit performs a current calculation for updating the torque current so as to follow the updated torque command value. The induction motor control device according to claim 2.

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