KR20020007050A - Method and System for Sensorless Field Orientation Control of AC Motor - Google Patents

Abstract

PURPOSE: A method and system for controlling a field orientation of an AC motor is provided to control a sensorless AC motor by using a high frequency signal, and ensure a superior control function regardless of a load condition. CONSTITUTION: A controlling system of a sensorless AC motor includes a position controller(10), a speed controller(20), a compensator(30), a current controller, a field orientation controller, and a position and speed interpolator(140). The current controller includes a PI controller(40), a low pass filter(50), an axis transformer(60), an inverter(70), and an axis transformer(80). The field orientation controller includes an axis transformer(90), a band pass filter(100), a pre-processor(110), a correction controller(120) and an integrator(130).

Description

Magnetic flux reference control method and system for AC motors {Method and System for Sensorless Field Orientation Control of AC Motor}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic flux reference control method and system for an AC motor, and more particularly, to a magnetic flux reference control method and control system for an AC motor that controls an AC motor using the polarity of the AC motor in a high frequency region.

AC motors have been recently used in various fields of the industry that require high performance control due to the advantages of maintenance and repair due to the mechanical wear of the brush and commutator pieces compared to the DC motor.

The AC motor can control the position and speed of the rotor only by knowing the position of the magnetic flux. In order to control the position and the speed of the rotor, a rotor position and speed detection sensor such as a rotary encoder has been conventionally used.

However, the method of using such a rotor position and speed detection sensor increases the price of the AC motor system due to the cost for installing the rotor position and speed detection sensor, and is also used to control the signal output from the detection sensor. There is a problem in that the control system is complicated because of the conversion to a signal. In addition, the signal output from the detection sensor is vulnerable to the electromagnetic noise (Electromagnetic Noise), there is a problem that the control of the AC motor system is difficult because the detector detection signal provides wrong information in the AC motor environment to which high frequency is applied.

Since the method using the rotor position and the speed detection sensor has the above problems, a sensorless control method for finding the position of the magnetic flux without the position and the speed detection sensor has been studied in recent years.

Such sensorless control methods can be broadly classified into two types, namely, a method using back electromotive force and a method using magnetic salience. Although good results are obtained at medium speed or high speed using the counter electromotive force, there is a problem in that reliability is low in a low speed region where voltage disturbance is large because the magnitude of the counter electromotive force is proportional to the speed of the rotor. In addition, the conventional method of using the polarity has been used a method of inputting a voltage signal during the sampling period, a method using a rotating high frequency signal, such a method still has difficulty in controlling the rotor position and speed.

The present invention is to solve the above problems, it is an object of the present invention to provide an AC motor control method and control system for controlling a sensor-less AC motor using a high frequency signal.

Another object of the present invention is to provide an AC motor control method and control system having excellent control performance regardless of load conditions by controlling the AC motor by controlling the current of the control shaft.

Figure 1 shows the change in torque magnitude per unit current according to the d-axis current and q-axis current of the AC motor.

Figure 2 shows the change in the magnitude of the d-axis current according to the q-axis current representing the maximum torque per unit current.

Figure 3 shows the terminal impedance according to the position of the rotor in the no-load condition of the embedded permanent magnet motor (IPMM) according to the above equation (4).

4 shows the change of the average value Zha of the high frequency impedance according to the d-axis current and the q-axis current.

5 shows the change of the peak value Zhp of the high frequency impedance according to the d-axis current and the q-axis current.

6 shows the angle at the minimum high frequency impedance according to the load torque ( ) Shows the change.

7 shows the estimated flux axis and measurement axis in the synchronous coordinate system.

Figure 8 illustrates a sensorless AC motor control system in an embodiment of the present invention.

Fig. 9 shows the d-axis current preprocessor at constant voltage injection.

Fig. 10 shows the q-axis current preprocessor at constant voltage injection.

The sensorless control method of the AC motor of the present invention sets an estimated control axis in a synchronous coordinate system, applies a pulsating high frequency signal to the estimated magnetic flux axis, and applies an impedance in a signal measuring axis of the synchronous coordinate system indicated by the applied high frequency signal. The control axis is obtained using the impedance difference in the axis orthogonal to the signal measurement axis of the synchronous coordinate system, and the position and speed of the rotor are obtained based on the control axis.

It is preferable to use the polarity of the magnitude of the impedance that is obtained according to the error between the actual magnetic flux axis and the estimated magnetic flux axis to obtain the control axis.

Obtaining the magnetic flux axis separates the components of the pulsating signal on the estimated measurement axis into components of two measurement axes orthogonal to each other, and calculates the motor impedance in the two measurement axes from the measured values of the components on the two measurement axes. desirable.

The magnetic flux axis may be determined using the difference between the motor impedances of the two measurement axes.

Preferably, the components on the two measurement axes comprise a first measurement axis that is out of phase by π / 4 from the estimated magnetic flux axis and a second measurement axis that is out of phase by π / 4 from the estimated magnetic flux axis.

When the components of the two axis axes are composed of the first and second measurement axes described above, it is preferable to determine the position of the estimated magnetic flux axis to minimize the difference between the motor impedances of the two measured axes. Do.

The pulsating high frequency signal injected into the estimated magnetic flux axis of the synchronous coordinate system is a voltage input signal, and in this case, the measured values of the two measuring axes are preferably current.

The magnetic flux reference control system of the AC motor of the present invention receives a current controller for controlling a constant high frequency voltage to be input to the AC motor, and receives the output current of the AC motor, and estimates the output current of the input AC motor by the estimated magnetic flux axis and the estimated magnetic flux. And a magnetic flux reference control unit that separates an axis component perpendicular to an axis and obtains a position and a velocity of an actual magnetic axis by using an error between the estimated magnetic flux axis current component and the axis current component perpendicular to the estimated magnetic flux axis.

The apparatus may further include a position speed controller configured to control the position and the speed of the rotor of the AC motor by receiving the position and the speed of the actual magnetic flux shaft obtained from the magnetic flux reference unit.

The field-oriented control member is converted into an output synchronization coordinate system in the still coordinate system receives the current and the phase by π / 4 behind the output estimate the current flux shaft axis and the estimated phase to the magnetic flux axis π / 4 as long as the alternating current motor A shaft converter separating the preceding shaft component, a band pass filter for filtering a specific frequency band component of the output current component of the shaft converter, a correction controller for obtaining the speed of the rotor by receiving the output value of the band pass filter, It includes an integrator that receives the actual rotor speed and finds the position of the rotor.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

In this embodiment, the motor is controlled using the difference between the impedance of the magnetic flux axis (d axis) of the AC motor and the axis (q axis) perpendicular to the magnetic flux axis. Hereinafter, the impedance difference between the magnetic flux axis and the axis perpendicular to the magnetic flux axis will be described. Explain.

First, the principle of controlling an AC motor to produce high efficiency is demonstrated.

The torque of the AC motor is shown in Equation 1 below.

Ld: d-axis inductance component, Lq: q-axis inductance component, id: d-axis current, iq: q-axis current, P: number of poles

In an ideal case, the torque of the AC motor is output as in Equation (1).

Figure 1 shows the change in torque magnitude per unit current according to the d-axis current and q-axis current of the AC motor.

As shown in Fig. 1, the torque per unit current of the actual AC motor is shown.

Figure 2 shows the change in the magnitude of the d-axis current according to the q-axis current representing the maximum torque per unit current.

FIG. 2 is an orthogonal graph in the direction of the Id axis and the Iq axis of the curved surface generating the maximum torque of FIG.

To increase the efficiency of AC motors, the maximum torque per unit current must be generated. Therefore, by controlling the d-axis current according to the graph shown in FIG. 2, the efficiency of the AC motor can be controlled to be high.

Hereinafter, the polarity of the AC motor will be described using the voltage expression of the AC motor.

Equation 2 is a formula showing the voltage of the terminal terminal of the AC motor.

vd = d-axis terminal voltage, vq = q-axis terminal voltage, Ld = d-axis inductance, Lq = q-axis inductance, p = time constant, id = d-axis current, iq = q-axis current, Ke = proportional a constant, Rotor angular velocity

Here, the voltage component with speed in the zero or low frequency operating region is very small and therefore can be ignored (i.e., In this case, if a high frequency superposition signal is applied, the impedance in the high frequency region is expressed by Equation 3 below.

Zdh = synchronous coordinate system d-axis impedance, Zqh = synchronous coordinate system q-axis impedance

The polarity is generated by alternating currents such as synchronous reluctance machines (SYRMs) and embedded permanent magnet machines (IPMMs), or magnetic fluxes such as IM and SMPMMs. The appearing AC motor has a high frequency impedance in the d-axis and a high frequency impedance in the q-axis as shown in Equation 3 below.

The high-frequency impedance of the motor stator for any angle in the stationary coordinate system corresponds to the difference between the synchronous coordinate system d-axis impedance and the synchronous coordinate system q-axis impedance, which can be derived from Equation 3 and is given by Equation 4.

Zha = average value of high frequency impedance, Zhp = peak value of high frequency impedance, Angle at minimum high frequency impedance, Rotor position

Figure 3 shows the terminal impedance according to the position of the rotor in the no-load condition of the embedded permanent magnet motor (IPMM) according to the above equation (4).

As shown in Fig. 3, as the frequency increases, the difference in impedance in Equation 4 increases.

4 shows the change of the average value Zha of the high frequency impedance according to the d-axis current and the q-axis current.

5 shows the change of the peak value Zhp of the high frequency impedance according to the d-axis current and the q-axis current.

6 shows the angle at the minimum high frequency impedance according to the load torque ( ) Shows the change.

As shown in Fig. 4, the average value of the high frequency impedance decreases as the stator current increases, and as shown in Fig. 5, the peak value of the high frequency impedance decreases as the load current increases, because of the magnetic saturation. As shown in Fig. 6, the angle at the minimum ) Moves slightly with the change in the stator current, due to magnetic saturation.

Hereinafter, the principle of the present invention to find the position of the magnetic flux axis for controlling the motor position and speed using this salient polarity will be described.

In the rotation of the impedance rotating magnetic flux axis in the high frequency range magnetic flux axis is greater than the impedance of the vertical axis, since the impedance of the salient-pole according to the position of injecting a high frequency signal, when θ is 0, that is, rotating magnetic flux axis is a high-frequency signal In this case, it can be seen that the impedance in the rotating magnetic flux shaft is maximum. In other words, the position of the axis for injecting the high frequency signal becomes the rotating magnetic flux axis so that the magnitude of the impedance measured at the axis for injecting the high frequency signal is maximized. Therefore, the arbitrary position θ is set as the estimated magnetic flux axis, the high frequency signal is injected into the estimated magnetic flux axis, the impedance at the estimated magnetic flux axis is measured, the estimated magnetic flux axis is changed, and the magnitude of the impedance at the estimated magnetic flux axis is maximum. Find the position of the estimated magnetic flux axis, and determine the position as the position of the magnetic flux.

When the magnitude of the impedance in the estimated magnetic flux axis is maximum, since the two components spaced π / 4 from the estimated magnetic flux axis are the same, the present embodiment sets the estimated magnetic flux axis to simplify the algorithm for finding the position of the estimated magnetic flux axis. Then, the component of the estimated magnetic flux axis is separated into two measuring axis components separated by π / 4 from the estimated magnetic flux axis, and the positions of the estimated magnetic flux axes having the same impedance of the two measuring axis components are found. That is, if the impedances of the two measurement axis components are the same, the impedance of the estimated magnetic flux axis is maximum, and if the impedance of the estimated magnetic flux axis is maximum, the actual magnetic flux axis is correctly found.

7 shows the estimated flux axis and measurement axis in the synchronous coordinate system.

As shown in FIG. 7, two pulsating high frequency signals injected into the estimated magnetic flux axes are spaced by π / 4 from the estimated magnetic flux axes, and are orthogonal to each other, Separate into components. For measurement The axis is out of phase by the estimated flux axis by π / 4 The axis is out of phase by π / 4 than the estimated flux axis.

If the actual flux axis of the rotor and the estimated flux axis coincide, Signal measured on the axis, If the signals measured on the axes are the same, but the actual flux axis of the rotor and the estimated flux axis do not coincide, the signals measured on the two measuring axes are different.

A system for controlling an AC motor by using the principle of finding an actual magnetic flux axis as described above will be described below.

Figure 8 illustrates a sensorless AC motor control system in an embodiment of the present invention.

As shown in FIG. 8, the sensorless AC motor control system of the embodiment of the present invention includes a position controller 10, a speed controller 20, a compensator 30, a current controller (CC), a magnetic flux reference controller ( field orientation controller (FOC), position and velocity interpolators 140.

The current controller includes a PI controller 40, a low pass filter (LPF, 50), an axis converter 60, an inverter 70, and an axis converter 80, and the flux reference controller FOC is an axis converter 90. , Bandpass filter 100, preprocessor 110, crystal controller 120, integrator 130.

Hereinafter, a sensorless AC motor control method according to an embodiment of the present invention will be described with reference to the drawings.

First, the operator (A1) is the rotor position command value ( ) Is estimated rotor position value ( ), And input the difference to the position controller 10. The position controller 10 is a speed command value of the rotor ( ) And the operator A2 is the speed command value ( Estimated rotor speed () ), And input the difference to the speed controller 20. The speed controller 20 has a reference value of q-axis current ( Calculate) and print it. The multiplexer (MUX) is a reference value of the d-axis current designated by the compensator 30 ( ) And the reference value of q-axis current ( ), And the resulting d-axis q-axis composite current reference value ( )

The current control unit CC controls the input of a desired current value to the stator of the AC motor, which will be described in detail below.

Operator (A3) is the d-axis q-axis composite current reference value ( ) And feedback d-axis q-axis composite current value of AC motor ( Is obtained, and the difference is input to the PI controller 40. PI controller 40 is based on the input value of the d-axis q-axis reference voltage input value ( ) The calculator A4 uses the d-axis q-axis reference voltage input value ( ) And the high frequency voltage value input to the d-axis ( ) And input it to the axis converter 60. The axis converter 60 converts the input value from the synchronous coordinate system to the stationary coordinate system and outputs it. The inverter 70 appropriately converts the AC motor input voltage value which has been converted, and inputs it to the AC motor stator.

Output current of AC motor ( ), And the axis translator 80 converts the static coordinate system into a synchronous coordinate system. The current converted to the synchronous coordinate system is passed through the low pass filter (LPF, 50) to remove the ripple component. ) Is input to the calculator A3 to control the constant current to be input to the AC motor.

On the other hand, the output current of the AC motor ( ), The flux reference control unit (FOC) obtains the rotor position and the rotor speed value.

Hereinafter, the operation of the magnetic flux reference controller will be described.

Axis converter 90 is the output current of the AC motor ( ), The stop coordinate system is converted into a synchronous coordinate system, and the output current of the AC motor ( ) Than the measuring axis of the synchronous coordinate system. The phase is divided into components of the axis ahead and components of the axis backward. Axial-converted current components are filtered through a band pass filter (BPF) 100 so that the current components in a particular high frequency band desired ( ), And the preprocessor 110 uses the current component to calculate the square value of the d-axis current component ( ) And the square of the q-axis current component ( )

Fig. 9 shows the d-axis current preprocessor at constant voltage injection.

Fig. 10 shows the q-axis current preprocessor at constant voltage injection.

The correction controller 120 calculates the square value of the d-axis current component ( ) And the square of the q-axis current component ( ) Position of the actual rotor flux The operation principle of the correction controller will be described below.

The input of the correction controller 120 is shown in Equation 5 below.

Here, if the estimation error is in a small range (i.e. Equation 5 can be approximated as Equation 6 below.

Angle with minimum impedance Is moved by the stator current. When this angle is compensated, the frequency response characteristic of the estimated rotor flux with respect to the actual rotor flux is expressed by Equation 7 below.

At this time, the equation of the correction controller is shown in Equation 8 below.

By the same principle as above, the correction controller uses the speed of rotor flux ( )

Integrator 130 is the speed of the rotor flux ( ) By integrating the position of the rotor flux ( ) Thus, the flux reference control unit (FOC) uses the output current of the motor to determine the speed of the rotor magnetic flux ( ) And location ( ) Can be obtained.

The calculator A5 Estimated rotor position using )

The position and speed estimator 140 compensates for the speed and position of the rotor magnetic flux obtained from the flux reference controller (FOC) by taking into account slip and noise in induction motors. It is fed back to A2) and used for position control and speed control.

What has been described above is only an embodiment of the present invention, and various changes can be made without departing from the technical scope of the present invention. In particular, in the present embodiment, a method of inputting a high frequency voltage is described, but the AC motor can be controlled by inputting a high frequency current.

According to the AC motor control method and system for controlling a sensorless AC motor by using the high frequency signal according to the present invention, it is possible to control the AC motor by controlling the current of the control shaft so as to have control performance regardless of the load condition.

Claims (12)

In the magnetic flux reference control method of the AC motor, A first step of setting the estimated magnetic flux axis in the synchronous coordinate system; Applying a high frequency signal pulsating to the estimated magnetic flux axis; A third step of obtaining a magnetic flux axis by using an impedance difference in the estimated magnetic flux axis of the synchronous coordinate system indicated by the applied high frequency signal and an impedance difference in an axis orthogonal to the estimated magnetic flux axis of the synchronous coordinate system; And And a fourth step of obtaining a position and a speed of the rotor based on the magnetic flux shaft. The method of claim 1, The third step of obtaining the magnetic flux axis, the magnetic flux reference control method of the AC motor, characterized in that to use the polarity of the impedance magnitude appearing according to the error between the actual magnetic flux axis and the estimated magnetic flux axis. The method of claim 1, The third step of obtaining the magnetic flux axis separates the components of the signal pulsating on the estimated magnetic flux axis into components of two measurement axes orthogonal to each other, and calculates the motor impedance of the two measurement axes from the measured values of the components on the two measurement axes. Process of calculation; And The magnetic flux reference control method of the AC motor, characterized in that it comprises the step of determining the magnetic flux axis by using the difference in the motor impedance in the two measurement axes. The method of claim 3, The components on the two measuring axes are composed of a first measuring axis that is out of phase by π / 4 from the estimated magnetic flux axis and a second measuring axis that is out of phase by π / 4 from the estimated magnetic flux axis. How to control the flux reference. The method of claim 4, wherein When the components of the two axis axes consist of the first and second measurement axes, the position of the estimated magnetic flux axis that minimizes the difference between the motor impedances of the calculated two measurement axes is determined as the magnetic flux axis. Magnetic flux reference control method of AC motor. The method of claim 1, The pulsating high frequency signal injected into the estimated magnetic flux axis of the synchronous coordinate system is a voltage input signal, and in this case, the measured values of the two measuring axes are currents. The method of claim 6, When the pulsating high frequency signal injected into the estimated magnetic flux axis of the synchronous coordinate system is a voltage input signal, a current which is a measured value of each measuring axis, Squared with Since the difference in the square of is proportional to the admittance measured in each measurement axis, the position of the estimated magnetic flux axis that minimizes the difference in the square of the current value, which is the measured value of each measurement axis, is determined by the magnetic flux axis. How to control the flux reference. The method of claim 1, The pulsating high frequency signal injected into the estimated magnetic flux axis of the synchronous coordinate system is a current input signal, and in this case, the measured values of the two measuring axes are voltages. The method of claim 8, When the pulsating high frequency signal injected into the estimated magnetic flux axis of the synchronous coordinate system is a current input signal, a voltage that is a measured value of each measuring axis, Squared with The magnetic flux reference control method of an AC motor, characterized in that for determining the position of the estimated magnetic flux axis to minimize the difference in the square of. In the AC motor control system, which controls the AC motor, A current control unit controlling a high frequency voltage to be input to the AC motor; The output current of the AC motor is input, and the output current of the input AC motor is separated into an estimated magnetic flux axis and an axis component perpendicular to the estimated magnetic flux axis, and the estimated flux axis current component and an axis current component perpendicular to the estimated magnetic flux axis The magnetic flux reference control system of an AC motor, characterized in that it comprises a magnetic flux reference control unit for calculating the position and the speed of the actual magnetic flux axis using the error. In claim 10, And a position speed controller configured to control the position and the speed of the rotor of the AC motor by receiving the position and the speed of the actual magnetic flux shaft obtained from the magnetic flux reference controller. In claim 10, The magnetic flux reference control unit, The output current of the AC motor is received and converted from the stationary coordinate system to the synchronous coordinate system, and the output current is separated into an axis whose phase is π / 4 behind the estimated magnetic flux axis and an axis component whose phase is π / 4 ahead of the estimated magnetic flux axis. Axial converter, A band pass filter for filtering a specific frequency band component of the output current component of the axial converter; A correction controller configured to obtain a speed of the rotor by receiving the output value of the band pass filter; And an integrator for inputting the actual rotor speed of the correction controller to obtain the position of the rotor.