KR100398223B1 - Method of Controlling Torque and Power of Induction Motor - Google Patents

Abstract

In the torque and output control method of an induction motor which adjusts the torque-minute current to adjust the boundary point between the constant torque area and the constant output area of the induction motor, the torque current value is constant from the start of the induction motor to an arbitrary speed point. Maintaining the torque torque current value so as to approach the rated torque current value by varying the torque current value from the arbitrary speed point, and the threshold value is adjusted as the torque current value is adjusted. Torque and output control method of the induction motor, characterized in that it comprises a step correspondingly adjusted.

Description

Torque and Power Control Method of Induction Motor {Method of Controlling Torque and Power of Induction Motor}

The present invention relates to a torque and power control method of an induction motor, and more particularly, to a torque and power control method of an induction motor for controlling torque and power of an induction motor by adjusting the magnitude of the torque component current of the induction motor. will be.

In general, an induction motor is a kind of AC motor driven by receiving AC power. It is composed of a stator that does not rotate and a rotor that can rotate. When a magnetic field is generated by applying a current to the stator winding, the induction motor is induced. Current flows to generate torque, and the torque is caused to rotate the rotor.

The induction motor as described above may control the speed of the induction motor by adjusting the frequency and voltage level of the power supplied to the induction motor.

Induction motors are currently used as powertrains in fuel electric vehicles, pure electric vehicles and in-line hybrid electric vehicles. Controlling the output and torque of these induction motors is the most important factor in determining the power performance of a car. have. Therefore, controlling constant torque and constant output in vector control of induction motors is very important for electric vehicles.

1 shows a general output characteristic curve of a conventional induction motor. It can be seen that the characteristic curve shows a constant torque characteristic below the reference speed (3600 rpm) and a constant output characteristic above. Also, from the start of the stall area, the output is drastically reduced due to the intrinsic characteristics of the induction motor and the inverter.

In general, when the induction motor is operated, a counter electromotive voltage is generated according to the rotational speed. When the counter electromotive voltage is increased proportionally according to the rotational speed, the counter electromotive force becomes larger than the driving voltage applied to the motor. Weak field control reduces the magnetic flux in inverse proportion to the rotational speed.

In other words, the magnetic flux is inversely reduced according to the rotational speed of the motor, thereby reducing the torque, thereby preventing the counter voltage from becoming larger than the driving voltage.

However, if the magnetic flux is reduced in inverse proportion to the rotational speed as described above, the loss of the driving torque in the high speed region is so large that the field weakening region is controlled as described above to make the maximum use of the driving torque in the high speed region. .

Assuming that the operating state of the induction motor is a steady state (no load, constant speed operation), the voltage and current constraints of the inverter determined by Equation 1 and the stator synchronous coordinate system voltage equation (motor equation) according to Equation 2 are combined. 2, the voltage limit appears as an ellipse and the current limit appears as a circle in the current plane.

: Flux coordinate flux current

: Current of synchronous coordinate system torque

: Magnetic flux voltage of synchronous coordinate system

: Torque Voltage for Synchronous Coordinate System

: Stator resistance

: Rpm

Stator inductance

Leakage factor

On the other hand, the synchronous coordinate system magnetic flux current from Equation 3, which is a relation between the rated current and the rated torque Can be obtained.

Using the synchronous coordinate system flux current obtained from Equation 3, the starting point of the field weakening area can be obtained. First, if you know the rated stator voltage or rated output, you can get the starting point of the field weakening area.

(1) If the rated stator voltage is known

In this case, the starting point of the field weakening area can be known from Equation 4 below.

(rpm)

(2) If you know the rated output

The field weakening start point obtained above is changed according to the stator voltage or the rated value of the stator current. However, if the power limit or the torque limit is increased or decreased at a constant rate, the field weakening start point is maintained at a constant value, and the starting point of the field weakening area can be known from Equation 5 below.

Rated power

Rated torque

: Number of stimulus pairs

: Slip frequency

On the other hand, the high speed operation characteristic of the induction motor is obtained from the current limit condition and the voltage limit condition to obtain the starting point of the stall operation region so as to operate at the maximum torque.

If the voltage drop component in the resistance is ignored, the following equation (6) is obtained from equations (1) and (2).

In addition, the combination of the electric currents that make the maximum torque while satisfying the voltage limit condition is shown in Equation 7 below.

Substituting Equation 7 into the current limiting equation provides a relationship as shown in Equation 8 below.

By extracting the field weakening operation / stall operation starting point of the spindle motor according to the above contents, the constant output operation region of the motor can be extracted. Equation 9 below again shows the field weakening driving start point and the stall driving starting point.

: Starting point of weak field

Stall starting point

In general, the field weakening starting point has the same value if the motor has the same rated torque and rated power. However, the starting point of the stall area depends on the characteristics of the motor. In the case of the spindle motor, the larger the value of the starting point of the stall area, the wider the constant power area becomes, which is advantageous, and is the most important factor in determining the performance of the spindle motor.

However, in the related art, there is a problem in that the boundary point between the constant torque region and the constant output region cannot be changed by keeping the torque current of the induction motor constant from the beginning. That is, there is a problem that the operating range of the induction motor is considerably narrowed because the boundary point having excellent power characteristics and the boundary point having excellent acceleration performance cannot be changed as necessary.

Therefore, the present invention has been made to solve the above problems, the object of the present invention is to adjust the magnitude of the torque component current to adjust the boundary point of the constant torque area and the constant output area of the motor to operate the induction motor according to the characteristics It is to provide a torque and output control method of the induction motor to enable the.

1 is an output characteristic curve of a conventional induction motor.

2 is a voltage limit curve and a current limit curve of an induction motor in a current plane.

3 is an output and torque characteristic curve according to the torque component current change according to the present invention.

In order to achieve the above object, the present invention, in the torque and output control method of the induction motor for controlling the boundary point between the constant torque area and the constant output area of the induction motor by changing the torque component current, the torque component of the induction motor Setting a boundary point between the constant torque area and the constant output area as a reference speed point when the current value is kept constant at the rated torque current value from the initial start to the stall start point; and the set constant torque area and the constant output area Maintaining a constant torque current value from the start of the induction motor to an arbitrary speed point on the basis of the reference speed point; and changing the torque value current value from the arbitrary speed point to change the rated torque current value. Adjusting the torque current value so that the torque current value approaches; In accordance with the present invention, the torque-minute current value is maintained to be greater than the rated torque-minute current value up to the arbitrary speed point, and in the case of the first case where the arbitrary speed point is smaller than the reference speed point, the arbitrary speed point is determined. Controlling the output characteristic of the induction motor to be a boundary point between the torque area and the constant output area, and in the step of keeping the torque-minute current value constant, the torque-minute current value up to the arbitrary speed point at the rated torque-minute current. In the second case where the speed is smaller than the value and the arbitrary speed point is the reference speed point, the point where the torque current value starts to coincide with the rated torque current value is the boundary point between the constant torque area and the constant output area. Torque of the induction motor, characterized in that for controlling the output characteristics of the induction motor to be It provides a power control method.

In addition, in order to achieve the above object, the present invention, in the first case, the torque current value in the section in which the torque current value starts to match the rated torque current value from the boundary point is represented by the following equation 1): It provides a torque and output control method of the induction motor, characterized in that shown.

Equation 1)

: Torque current value

: Boundary point between constant torque region and constant output region

: Constant current value from start to weak field start point

: Speed variable

In addition, in order to achieve the above object, in the second case, the torque current value in the section from the reference speed point to the boundary point is represented by the following formula 2) Torque of the induction motor, And an output control method.

Equation 2)

: Torque current value

: Reference speed point

: Constant current value from start to reference speed point

: Speed variable

Meanwhile. It is preferable that the reference speed is 3600 rpm.

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

3 illustrates torque and output changes according to the change in the torque component current according to the present embodiment. On the other hand, since the flux current includes the intrinsic magnetic characteristics of the induction motor, the flux current must always be kept constant.

First, in the case of (2), the current according to the torque is obtained by a conventional method. ) Is the rated torque current value When the constant current is supplied to the induction motor, This is a method of obtaining the output characteristic curve according to the change of).

In the case of (1), according to the present invention, the torque component current is initially kept high and is inversely proportional to the speed. At this time, the torque current in the section in which the torque current is reduced in inverse proportion to the speed is expressed by the following equation (10).

As mentioned above, the weak point starting point Is the reference speed Torque current is controlled up to (3600 rpm) In the above, a constant current is maintained.

The method of (1) as described above can be used in the case where it is desired to maintain the output while maintaining the high torque characteristic, and as a result, the power characteristic of the electric vehicle is improved because the constant power region is widened.

In the case of (3), according to the present invention, a low torque characteristic is maintained in the low speed region, but the torque characteristic current is increased by increasing the torque-minute current above the reference speed (3600 rpm) to maintain a constant output. At this time, the torque current in the rising section is controlled as in Equation 11 below.

The method of (3) as described above can be used when the output is desired while maintaining low torque characteristics, and as a result, the acceleration performance of the electric vehicle is improved.

As described above, according to the present invention, by adjusting the magnitude of the torque-minute current of the induction motor, there is an effect that can improve the power characteristics and acceleration performance of the electric vehicle as necessary.

Claims (5)

In the torque and output control method of the induction motor for varying the torque current to adjust the boundary point between the constant torque area and the constant output area of the induction motor, Setting a boundary point between the constant torque area and the constant output area as a reference speed point when the torque current value of the induction motor is constantly maintained at the rated torque current value from the initial start to the stall start point; Maintaining a constant torque current value from the start of the induction motor to an arbitrary speed point on the basis of the reference speed point at the boundary point between the set constant torque area and the constant output area; Adjusting the torque current value so as to approach the rated torque current value by changing the torque current value from the arbitrary speed point; As the torque component current value is adjusted, the torque component current value is maintained to be greater than the rated torque component current value up to the predetermined speed point, and in the first case where the arbitrary speed point is smaller than the reference speed point, Controlling the output characteristic of the induction motor so that any speed point is a boundary point between the constant torque area and the constant output area, and in the step of maintaining the torque-minute current value constant, the torque-minute current value up to the arbitrary speed point. Is kept smaller than the rated torque-minute current value, and in the second case where the arbitrary speed point is the reference speed point, the point where the torque-minute current value starts to coincide with the rated torque-current current value is a constant torque range. Controlling an output characteristic of the induction motor to be a boundary point of a constant output region. Torque and output control method of an induction motor, characterized in that. delete The method of claim 1, In the first case, the torque and output control method of the induction motor, characterized in that the torque current value is expressed by the following formula 1) in the section where the torque current value starts to match the rated torque current value from the boundary point. . Equation 1) : Torque current value : Boundary point between constant torque region and constant output region : Constant current value from start to weak field start point : Speed variable The method of claim 1, In the second case, the torque current value in the range from the reference speed point to the boundary point is represented by the following equation (2), the torque and output control method of the induction motor. Equation 2) : Torque current value : Reference speed point : Constant current value from start to reference speed point : Speed variable The method according to any one of claims 1 to 4, Torque and output control method of the induction motor, characterized in that the reference speed is 3600 rpm.