KR20110058074A - Maximizing efficiency control of induction motor for ac forklift truck - Google Patents

Abstract

PURPOSE: A method for controlling the maximum efficiency of an induction motor for an AC forklift truck is provided to improve the operation efficiency of an AC forklift truck by increasing the charging time of a battery through the maximum torque with the minimum current. CONSTITUTION: A stator resistance and a stator inductance are measured by applying a no-load current according to the driving state of an induction motor(S7,S12). A stator inductance function is produced through approximation by using stator inductance with regard to the current of a magnetic flux part(S15). Factors affecting the vector control of the induction motor are controlled by controlling the no-load current using the stator inductance function.

Description

MAXIMIZING EFFICIENCY CONTROL OF INDUCTION MOTOR FOR AC FORKLIFT TRUCK}

The present invention relates to an induction motor for an AC electric forklift, and more particularly, by changing an excitation current according to a load in a vector control by using a property in which an inductance component is greatly changed according to a flux current in an induction motor of an AC electric forklift. The present invention relates to a method for controlling the maximum operating efficiency of an induction motor for an AC electric forklift truck to increase the efficiency of an induction motor.

In general, in an induction motor for an AC electric forklift truck, the current is divided into a magnetic flux current and a torque current, and the position of the magnetic flux is determined by adjusting the magnitude of the magnetic flux current.

The magnetic flux can be expressed as the product of the current flowing through the inductance. In the case of a general induction motor, the magnetic flux is linearly controlled assuming that the inductance is constant.

However, in the case of induction motors for AC electric forklifts, the nonlinear characteristics between the magnetic flux current and the magnetic flux appear strongly, so if the relationship between the two is linearly assumed and controlled like a general induction motor, it is desired in most magnetic flux current ranges. I can't let go.

That is, in the case of general induction motor, mutual inductance and stator and rotor inductance can be known from the design value of the motor.If the design value is not known, the inductance is calculated using the three-phase voltage, rated frequency and rated current of the motor nameplate. This is estimated using an algorithm to which the following equations are applied.

[Equation 1]

[Equation 2]

&Quot; (3) "

&Quot; (4) "

At this time, the induction motor is operated at the no-load rated speed, and the stator inductance L _s can be obtained by measuring the current and voltage in the operation and substituting it in [Equation 4].

On the assumption that no-load rated speed, the d-axis voltage (V _d ) as shown in [Equation 1] is expressed as the product of the stator resistance (R _s ) and the magnetic flux current (I _d ), and [Equation 2] and Since the q-axis voltage (V _q ) can be expressed as the product of the driving frequency (ω _e ) according to the motor rotation speed, the stator inductance (L _s ), and the magnetic flux current (I _d ) of the equation (3) Equation 4 can be derived through the process.

Therefore, the stator inductance (λ _d ) obtained through the above process can be applied to the linear relationship between the magnetic flux and the current as shown in Equation 5 below.

[Equation 5]

L_s는 상수

L _s is a constant

However, the stator inductance (L _s) of the induction motor for AC electric forklift is the graph of Fig. 1 as well as the constants are changed, the magnetic flux minute current (I _d) flux minute current (I _d) for the efficient operation changes due to, depending on Will produce the same error.

That is, in FIG. 1, if magnetic flux as much as λ ₂ is required when the torque of T _q is applied to the induction motor of an AC electric forklift truck, the current of I ₁ is flowed as a flux component current in the linear relation (dotted line in FIG. 1). However, in practice (solid line in Fig. 1), a magnetic flux of λ ₁ is formed and an error of about 16% occurs, so that the torque component current flows about 40% more to make a torque of T _q .

In this case, the overall current flows about 10% more, which is the main cause of lowering the operating efficiency.

In particular, AC electric forklift due to the use of battery current is increased to approximately 10% is displayed with lethal weaknesses in 1st charge time, so that magnetic flux minute current (I _1, I ₂₎ and the magnetic flux (λ _1, λ ₂ In order to apply the relationship of) as practically as possible, accurate estimation of stator inductance according to the flux currents is required.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and measures the stator inductance of an induction motor before driving the induction motor of an AC electric forklift, and measures the stator inductance together with the function of the stator inductance according to the change of the flux current. Is automatically obtained and based on this, the control method is implemented so that the maximum torque can be achieved with the minimum current in the entire operating area of the AC electric forklift truck. The purpose of this study is to derive the function of the stator inductance for the no-load current to drive the forklift and to provide the maximum operating efficiency control method of the induction motor for AC electric forklift.

The maximum operating efficiency control method of the present invention AC motor forklift for induction motor for achieving the above object, by applying a no-load current without driving the induction motor to measure the stator resistance, step by step while driving the induction motor at rated speed A measuring step of measuring stator inductance by applying a no-load current; A function derivation step of repeating the measuring step while increasing a flux current to a current of a maximum operating region and deriving a function of the stator inductance by an approximation process using a stator inductance for the flux current measured in the repetition process; And a control step of changing the factors directly affecting the vector control of the induction motor by adjusting the no-load current using a function of the stator inductance derived in the function derivation step. Including to proceed.

The stator measurement may include: controlling torque current to zero and reducing and applying a flux current at a constant ratio with respect to a rated current as a target current; Calculating an average of the first d-axis flux voltages for a predetermined time after stabilizing by gradually increasing the applied flux currents; Applying the flux current as much as the rated current; Calculating an average of the second d-axis flux voltages for a predetermined time after stabilizing by gradually increasing the applied flux currents; Calculating a stator resistance from the calculated first and second d-axis magnetic flux voltages; It includes.

In addition, the constant ratio is 3/4 in applying the magnetic flux component current at a constant ratio with respect to the rated current.

In addition, when measuring the stator resistance, the magnetic flux current is set to a different value near the rated current, but the difference between the two values is set not to be large, and the magnetic flux current is stabilized after a time sufficiently larger than the time constant. It is measured when the state (normal state) is reached.

In addition, the stator inductance, the magnetic flux current of the minimum operating area by applying a flux current to drive the induction motor at a rated speed; Directly applying, as a three-phase current, a flux current of a minimum operating region applied to drive the induction motor at a rated speed, at a driving frequency; Calculating stator inductance by calculating the average of the stator resistance calculated when the induction motor reaches the rated speed, as well as the torque component current and q-axis voltage for a predetermined time, and the measurement frequency according to the driving of the induction motor; It further includes.

In addition, the magnitude of the no-load current to be applied in measuring the stator inductance is to determine the actual operating range in advance to set the range, and when the no-load current is applied stepwise enough time greater than the time constant, the no-load current is It is a measurement in a stabilized state.

The controlling may include updating (updating) the stator inductance according to the period of the speed controller so that the changing factors of the induction motor are synchronized with the period of the speed controller; It will continue to include more.

In the control step, the mutual inductance and the rotor inductance are changed according to the updated stator inductance, and the rotor time constants and torque constants and ratings, which are factors of the induction motor, according to the change of the mutual inductance and rotational inductance. The flux current is updated (updated) as well as the gain of the controller used for vector control is updated (updated).

The present invention measures the stator resistance of the induction motor before driving the induction motor of the AC electric forklift, and measures the stator inductance, and automatically calculates the function of the stator inductance according to the change of the magnetic flux current. As a result, the control method is designed to produce the maximum torque with the minimum current in the entire operating area of the AC electric forklift. This increases the charging time of the battery of the AC electric forklift and uses the same battery in the AC electric forklift. In the case of a full charge, the forklift can be driven for a longer time and the efficiency of each operating area of the AC electric forklift can be expected.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

2 is a flowchart illustrating a process of measuring a stator inductance of a stator resistance and a no-load current of an induction motor of an AC electric forklift according to an embodiment of the present invention, and FIG. 3 is a diagram illustrating a no-load current obtained by FIG. 2 according to an embodiment of the present invention. A block flow diagram showing a method of applying to a vector control of an induction motor of an AC electric forklift using a function of stator inductance is shown.

2 and 3, the derivation of the function of the stator inductance for the no-load current according to an embodiment of the present invention is the first step of measuring the stator resistance, the second step of measuring the stator inductance, and the third to derive the function Steps.

The first step is to measure the stator resistance (R _s ) by applying a quiescent current without driving the induction motor (300).

That is, in the state in which the torque component current I _q of the speed controller 100 is controlled to zero as shown in FIG. 2, the derivation function for the stator resistance R _s of FIG. The magnetic flux current I _d is applied to 200 at a constant ratio with respect to the rated current I _d1 as the target current (S1) (S2).

In this case, the constant ratio is preferably 3/4 in applying the magnetic flux current I _d at a constant ratio with respect to the rated current I _d1 , but it is not necessarily limited to this numerical value and may be changed. It can be.

Next, the derivation function for the stator resistance R _s of FIG. 2 is stabilized by gradually increasing the magnetic flux current I _d applied to the current controller 200, and then stabilizes the first d-axis magnetic flux for a predetermined time. The average of the minute voltages V _d1 is calculated (S3) (S4).

Next, the derivation function for the stator resistance R _s of FIG. 2 is stabilized by gradually increasing the applied magnetic flux current I _d after applying the magnetic flux current I _d by the rated current I _d2 . After that, the average of the second d-axis flux voltage V _d2 is calculated for a predetermined time (S5) (S6).

Then, the stator resistance R _s as shown in Equation 6 below can be calculated from the calculated first and second d-axis magnetic flux voltages V _d1 (V _d2 ) (S7).

&Quot; (6) "

Here, when measuring the stator resistance (R _s ), the magnetic flux current (I _d ) is set to a different value near the rated current (I _d1 ) (I _d2 ), but is set such that the difference between the two values is not large. For example, it is good to measure when the magnetic flux current I _d reaches a stabilized state (steady state) after a time sufficiently larger than the time constant.

The second step is to measure the stator inductance (L _s ) by applying a gradual no-load current while driving the induction motor 300 at a rated speed.

That is, the derivation function for the stator resistance R _s of FIG. 2 drives the induction motor 300 at the rated speed by applying the magnetic flux current I _d by the magnetic flux current of the minimum operating region (S8). In order to drive the induction motor 300 at the rated speed, the three-phase is loaded with the flux current I _d of the minimum operating area applied from the speed controller 100 to the current controller 200 at the command frequency ω _e ^* . Directly applied as a current (S9) (S10).

Next, the stator resistance R _s calculated when the induction motor 300 reaches the rated speed, as well as the torque current (I _q ) and q-axis voltage (V _q ) for a predetermined time, and the induction motor. If the average of the measured frequency (ω _e ) according to the driving of (300) is obtained (S11), it is possible to calculate the stator inductance (L _s ) as shown in Equation 7 (S12).

[Equation 7]

Here, the magnitude of the no-load current to be applied in measuring the stator inductance (L _s ) is determined by grasping the actual operating range in advance, and after a time sufficiently larger than the time constant when the no-load current is applied in stages. It is good to measure in the state (normal state) where the said no-load current was stabilized.

The third step is performed by the stator inductance generation function according to step S15 of FIG. 2, and the step S15 is repeated by repeating the first and second steps while increasing the flux current I _d to the current of the maximum operating region. (S13) (14), a function of the stator inductance L _s can be derived by an approximation process using the stator inductance L _s for the magnetic flux current I _d measured in the repetition process. (S15)

On the other hand, as shown in Figure 3 attached by using a function of the stator inductance (L _s ) derived through the stator inductance generation function 500, after adjusting the no-load current has a direct effect on the vector control of the induction motor 300 By changing the giving factors, it is possible to control the maximum operating efficiency of the induction motor 300.

That is, the stator inductance Ls is updated in the motor factor update function 600 by using a function of the stator inductance L _s derived through the stator inductance generation function 500 at every speed control cycle. In the case of (update), the mutual inductance and the rotor inductance change according to the updated stator inductance Ls, and accordingly, the rotor time constant T _r and the torque constant K _t, which are factors of the induction motor 300, are changed. ), The rated magnetic flux current I _{d_rate} , and the resistance R _x are newly updated (updated), and the gain K of the speed controller 200 used for the vector control made by the controller gain calculator 700. _{p, i, a_sc} ) and the gains K _{p, i, a_cc} of the current controller 200 are updated (updated), as well as the slip frequency of the slip frequency calculator 800 applied to the speed controller 200. ω _sl ) may be changed.

That is, the slip frequency calculator 800 measures the measured current I _dq of the magnetic flux and the torque fed back from the induction motor 300, the command flux λ _d output from the field weakening function processor 400, and , The amount of change in the slip frequency (ω _sl ) by calculating the stator inductance (L _s ) output from the stator inductance generation function unit 500 and the rotor time constant (T _r ) output from the motor factor update function unit 600. This is to output to the speed controller 100.

Then, the command torque output from the speed controller 200 to the current controller 300 is output from the gain K _{p, i, a_sc} and the slip frequency ω _sl of the _updated speed controller 200. The current I _q is adjusted so that the command voltage V _dq including the magnetic flux and torque voltages output from the current controller 300 to the induction motor 100 is changed, and thus the induction motor ( 100) is capable of producing the maximum torque with the minimum current in the entire operating area of the AC electric forklift, as well as driving the forklift for a longer time with a single charge as the battery charging time of the AC electric forklift becomes longer. It is possible to increase the driving efficiency for each operation area of the forklift.

Hereinafter, the present invention is not limited to the above-described specific preferred embodiments, and various modifications can be made by those skilled in the art without departing from the gist of the present invention as claimed in the claims. Of course, such changes are within the scope of the claims.

1 is a graph showing a linear relationship between a magnetic flux current and a magnetic flux according to the related art.

2 is a flowchart illustrating a process of measuring stator inductances for stator resistance and no-load current of an induction motor of an AC electric forklift according to an embodiment of the present invention.

FIG. 3 is a block diagram illustrating a method of applying to vector control of an induction motor of an AC electric forklift using the function of stator inductance with respect to the no-load current obtained by FIG. 2 according to an embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

100; Speed controller 200; Current controller

300; Induction motor 400; Weak field function processing unit

500; Stator inductance generation function 600; Motor Factor Update Function

700; A controller gain calculator 800; Sleep frequency calculator

Claims (3)

A measuring step of measuring stator inductance by applying a quiescent current while driving the induction motor, and applying a stepless quiescent current while driving the induction motor at a rated speed; A function derivation step of repeating the measuring step while increasing a flux current to a current of a maximum operating region and deriving a function of the stator inductance by an approximation process using a stator inductance for the flux current measured in the repetition process; And, A control step of changing a factor that directly affects vector control of an induction motor by adjusting a no-load current by using a function of stator inductance derived in the function derivation step; Method for deriving the function of the stator inductance for no-load current, characterized in that proceeding, including. The method of claim 1, wherein the control step, Updating (update) the stator inductance according to the period of the speed controller such that the changing factors of the induction motor are synchronized with the period of the speed controller; Maximum operating efficiency control method of the induction motor for AC electric forklift, characterized in that further comprising. The method of claim 2, wherein the control step, The mutual inductance and rotor inductance are changed according to the updated stator inductance, and the rotor time constant, torque constant, and rated flux current, which are factors of induction motor, are updated according to the change of mutual inductance and rotation inductance. In addition, the maximum operating efficiency control method of the induction motor for AC electric forklift, characterized in that the gain of the controller used for the vector control is updated (updated).

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