TWI383574B - Method and apparatus of field weakening for ac motor drives - Google Patents

Description

Field weakening control method and device for AC motor driver

The present invention relates to an AC motor drive having a field weakening control applied above a rated speed.

AC motor drive unit, including drive and AC motor. The driver consists of two parts: the power circuit and the control circuit. The main structure of the power circuit includes: rectifier module, DC link capacitor and frequency conversion module; the rectifier module can accept the input of single-phase or three-phase mains power, and rectify the alternating current into a DC power with chopping, and the DC link The capacitor provides a filtering effect of chopping DC power and serves as an input for the frequency conversion module, and the frequency conversion module includes a switching element that provides a three-phase pulse voltage output and is coupled to the input side of the AC motor through the driver. The control loop can generate a driving signal to control the switching element in the frequency conversion module Switching of pieces.

In addition to the external body, the AC motor includes an encoder coupled to the same shaft, which may be an incremental encoder or an absolute position encoder. The driver generates the stator current on the q-axis coordinate via the speed controller according to the rotor position and/or speed fed back by the encoder, and the established magnetic flux and the AC motor rotor flux on the d-axis coordinate Interaction, thereby achieving vector control of the AC motor.

The back electromotive force generated by the AC motor is proportional to the rotational speed. When the rotational speed rises and the voltage supplied by the DC link capacitor is insufficient to overcome the counter electromotive force generated by the AC motor, the AC motor is limited in the range of high speed operation; In order to operate the AC motor at a higher speed, in general, the driver will adjust the d-axis current to reduce the magnetic flux, thereby overcoming the counter electromotive force generated at high speed and increasing the operating speed range. This method is also generally The so-called weak magnetic control. The conventional weak magnetic control law [1] generates a command inversely proportional to the magnitude of the d-axis current according to the magnitude of the rotational speed, but in this prior art, it is not considered whether the output voltage of the driver reaches the maximum and the rated current of the motor. Restricted conditions, so it is not guaranteed to effectively achieve the maximum DC link voltage utilization and maximum output torque.

Reference materials:

[1] Vector control inverter controller parameter automatic adjustment method, Republic of China patent, case number: 84113378.

In view of the above problems, the main object of the present invention is to provide a field weakening control and device for an AC motor, which utilizes the switching period of the pulse width modulation control of the AC motor frequency converter minus the effective switching of the inverter control calculation. The sum of time, ie (T _A + T _B ), instantly generates an adaptive d-axis current command via the controller to achieve the utilization of the expandable DC link voltage, so that the AC motor has a higher speed than the rated speed The large output torque is used to solve the technical problems and potential shortcomings in the prior art.

Therefore, in order to achieve the above object, the present invention discloses an effective switching time (T _A , T _B ) of an effective voltage vector using a space vector modulation law to predict whether or not the DC link capacitor voltage is effectively utilized, when (T _A + T _B ) T _Z , where T _Z = switching period of pulse width modulation control, represents that the current voltage utilization of the DC link capacitor is larger in the linear region than the general modulation law. If the motor continues to increase the speed in this case, in addition to the condition of (T _A + T _B ) = T _Z , it must be achieved by using the technique of field weakening.

Therefore, in order to achieve the above object, the present invention discloses a use of T _Z (switching period of pulse width modulation control) as a reference command for achieving a large DC link capacitor voltage utilization rate, and the pulse wave of the AC motor frequency converter The switching period of the width modulation control is subtracted from the sum of the effective switching times calculated by the inverter control, ie (T _A + T _B ), and then the d-axis current is generated via a field weak current controller and a subsequent limiter. The command correction value can be used to automatically adjust the d-axis current to achieve the field weakening control.

In addition, with the method and apparatus disclosed by the present invention, the voltage vector magnitude when (T _A + T _B ) > T _Z is greater than the voltage vector magnitude of the maximum linear region, in this case, represents the inverter output voltage space vector trajectory. Will operate at the maximum limit of the hexagon, so when the stator current is limited by the maximum current, it means that the AC motor operates under the conditions of maximum voltage and maximum current, so the AC motor has a larger under weak magnetic control. Output torque.

The features and implementations of the present invention are described in detail below with reference to the preferred embodiments.

1 is a structural diagram of a vector control system of a field weakening control and device of an AC motor disclosed in the present invention, which mainly comprises a control structure 100 of a driver, a field weakening control device 200, an AC power source 300, and a power circuit architecture 400 of the driver. The current sensors 501 to 503 and the AC motor body and the encoders 601 to 602.

The AC motor driver is to achieve the vector control of the AC motor. The encoder 602 is used to obtain the position information of the AC motor body 601 and is fed back to the control structure 100 of the driver. After the counter 182, the information of the encoder can be converted into The angle at which the rotor of the AC motor is located. This angle can be used as the coordinate conversion of the first coordinate converter 161 and the second coordinate converter 162; and the speed estimator 181 can be used to obtain the speed feedback information of the AC motor. The current sensors 501-503 feedback the three-phase currents i _u , i _v and i _{w of the} motor, and convert the variables of the three-phase stationary coordinates into the variables of the two-phase synchronous rotating coordinates through the second coordinate converter 162. and Then, the first subtractor 121 and the third subtractor 123 are subtracted from the current command, and are adjusted by the d-axis current controller 131 and the q-axis current controller 133; the outputs of the two controllers are transmitted again. The two adders 112 and the third adder 113 add the compensation values of the voltage decoupling compensator 150, and then rotate the two-phase synchronous rotation coordinates via the first coordinate converter. and The variable is converted to a two-phase stationary coordinate to obtain a voltage space vector command for the spatial vector modulator 170. The relationship between the voltage space vector command and the sector is shown in Fig. 2A; the schematic diagram of the voltage space vector bit in the first interval (Sector 1) is shown in Fig. 2B; the voltage vector switch synthesized in Fig. 2B is switched. The switching timing and the schematic diagrams of T _A , T _B and T _{Z are} shown in Figure 2C, where T _A and T _B are the effective switching times respectively, and T _Z is the switching period of the pulse width modulation control, T _Z =1 /(KT _s ), T _s = sampling period of pulse width modulation control, K = constant. Finally, in order to send the energy of the commercial terminal to the AC motor body 601, the input is started from the AC power source 300, and the AC power is rectified into a DC power having a chopper through the rectifier module 401 and filtered by the DC link capacitor 402, and then the space vector modulator is used. 170 outputs a control signal to the inverter module 403 to drive the switching element to perform DC energy conversion.

In the full speed mode, there is the speed of the AC motor ω _r and the speed command The adjustment is made via the second subtractor 122 and through the speed controller 132, and the output of the controller is coupled to the first limiter 142, which can be used as a limit for the q-axis current command and the output torque, with respect to the limiter The limit value can be calculated by the limit value calculator 207 to prevent the driver or motor from operating above the maximum current.

The field weakening control device 200 disclosed in the present invention refers to the effective switching time of the effective voltage vector of the feedback space vector modulator 170, that is, T _A and T _B , which are added through the fourth adder 205 and pass through the low pass. The filter 204 filters out the high frequency signal and subtracts it from the switching period of the pulse width modulation control, that is, T _z , and subtracts it through the fourth subtractor 203, and then passes through a field weakening current controller 202. The adjustment is followed by a limiter 201 for ensuring that when (T _A + T _B ) > T _Z , the output of the limiter is a negative value i _{ds_fw} as the d-axis current command correction value. Finally, the output of the limiter is again commanded with the d-axis current, ie , added by the first adder 206 as an actual d-axis current command reference value, ie ; its value is calculated by the limit value calculator 207 Calculated, the limit value of the first limiter 142 can be obtained. This value is the limit value of the q-axis current command limiter. The maximum limit range and maximum linear range of the voltage vector of the space vector modulation law are shown in Fig. 2A. When (T _A + T _B ) = T _Z , the voltage vector is currently within the maximum limit range. The hexagonal trajectory rotates, so the voltage utilization is larger than the circular interval of the maximum linear range.

The simulation result of the field weakening control and device vector control system of the AC motor disclosed in the present invention is shown in FIG. 3, when the AC motor rotor speed reaches the rated speed (1.0 pu) or more, then T _A + T _B When the size is increased to above T _Z (1.0 pu), the field weakening control structure will act. Therefore, the d-axis current command correction value, i _{ds_fw} , can be seen from the _figure . At this time, the value starts to rise with the speed. Increase, in order to maintain a large voltage utilization of the DC link capacitor and overcome the increase of the back electromotive force of the AC motor; when the rotational speed tends to stabilize, the back electromotive force does not change any more, so the correction value will also be stabilized.

100‧‧‧Drive Control Architecture

200‧‧‧Weak magnetic control device

300‧‧‧AC power supply

400‧‧‧Power circuit architecture for drives

112‧‧‧Second adder

113‧‧‧ third adder

121‧‧‧First subtractor

122‧‧‧second subtractor

123‧‧‧ third subtractor

131‧‧‧d-axis current controller

132‧‧‧Speed Controller

133‧‧‧q-axis current controller

142‧‧‧First limiter

150‧‧‧Voltage decoupling compensator

161‧‧‧First coordinate converter

162‧‧‧Second coordinate converter

170‧‧‧ Space Vector Modulator

181‧‧‧Speed Estimator

182‧‧‧ counter

201‧‧‧Restrictor

202‧‧‧ weak magnetic current controller

203‧‧‧4th subtractor

204‧‧‧low pass filter

205‧‧‧fourth adder

206‧‧‧First Adder

207‧‧‧limit value calculator

401‧‧‧Rectifier Module

402‧‧‧DC link capacitor

403‧‧‧Variable frequency module

501‧‧‧ Current Sensor

502‧‧‧ Current Sensor

503‧‧‧ Current Sensor

601‧‧‧AC motor body

602‧‧‧Encoder

FIG. 1 is a structural diagram of a vector control system with a field weakening control and an AC motor of the device disclosed in the present invention.

Figure 2A to Figure 2C are the voltage space vector diagram of the space vector modulation law under the static coordinate, the voltage vector synthesis diagram of the space vector modulation interval 1, and the pulse wave pattern of the space vector modulation interval 1. .

Figure 3 is a simulation result of the vector control system of the field weakening control and device of the AC motor disclosed in the present invention.

100‧‧‧Drive Control Architecture

200‧‧‧Weak magnetic control device

300‧‧‧AC power supply

400‧‧‧Power circuit architecture for drives

112‧‧‧Second adder

113‧‧‧ third adder

121‧‧‧First subtractor

122‧‧‧second subtractor

123‧‧‧ third subtractor

131‧‧‧d-axis current controller

132‧‧‧Speed Controller

133‧‧‧q-axis current controller

142‧‧‧First limiter

150‧‧‧Voltage decoupling compensator

161‧‧‧First coordinate converter

162‧‧‧Second coordinate converter

170‧‧‧ Space Vector Modulator

181‧‧‧Speed Estimator

182‧‧‧ counter

201‧‧‧Restrictor

202‧‧‧ weak magnetic current controller

203‧‧‧4th subtractor

204‧‧‧low pass filter

205‧‧‧fourth adder

206‧‧‧First Adder

207‧‧‧limit value calculator

401‧‧‧Rectifier Module

402‧‧‧DC link capacitor

403‧‧‧Variable frequency module

501‧‧‧ Current Sensor

502‧‧‧ Current Sensor

503‧‧‧ Current Sensor

601‧‧‧AC motor body

602‧‧‧Encoder

Claims (8)

An AC motor driver weakening control method, which uses the switching period of the pulse width modulation control as a reference command and compares with the effective switching time of the inverter effective voltage vector, ie (T _A + T _B ), When the effective switching time of the effective voltage vector of the inverter is greater than the switching period of the pulse width modulation control, the discriminating enters the weak magnetic control. An AC motor drive weakening control method, which utilizes an effective switching time of an effective voltage vector, that is, (T _A + T _B ), is added by an adder, and is filtered by a low-pass filter After being divided, the switching period of the pulse width modulation control, that is, T _z , is subtracted by a subtractor, and then a weak current controller is used to generate a d-axis current command correction value and limit the value thereof; The d-axis current command correction value is then added to the d-axis current command via the adder as an actual d-axis current command reference value; the actual d-axis current command reference value is used to limit the q-axis current Command value. The AC motor driver weakening control method according to item 2 of the application scope, the switching period of the pulse width modulation control, T _Z =1/(KT _s ), T _s = sampling period of the pulse width modulation control , K = constant. The AC motor driver field weakening control method according to Item 2, wherein the d-axis current command correction value generated by the field weakening current controller limits the correction value of the d-axis current command to a negative value. value. The AC motor driver field weakening control method according to item 2 of the application scope, the limit value of the q-axis current command limiter, that is, , with the actual d-axis current command reference value, , the relationship is: , where I _{s (max)} = the maximum current of the AC motor. An AC motor drive field weakening control device is connected to a control structure of the driver. The input of the field weakening control device includes: an effective switching time of the effective voltage vector, that is, T _A and T _B ; and a d-axis current command , which is The output of the field weakening control device includes: an actual d-axis current command reference value, ie ; with the limit value of the q-axis current command limiter, ie The field weakening control device comprises: a fourth adder for adding the effective switching times (T _A and T _B ) of the effective voltage vectors of the control structure of the driver; a low pass filter, and the The four adder and the subtractor are connected to filter the high frequency signal of the effective switching time (T _A + T _B ) and output to the subtractor; a subtractor, which is associated with the low pass filter and the weak magnetic controller Interacting, for switching the pulse width modulation control switching period, that is, T _Z , subtracting the sum of the filtered effective switching times, that is, (T _A + T _B ) and outputting the difference to the field weak current control a weak magnetic current controller interposed with the subtractor and the limiter to ensure that the d-axis current command value is corrected when (T _A + T _B )>=T _Z ; a limiter And the weak magnetic current controller and the first adder are connected to limit the d-axis current command correction value to a negative value; a first adder, the limit value calculator, the control structure of the driver and The limiter is connected to the d-axis current command, ie And adding the limiter output value to obtain the actual d-axis current command reference value, ie Output to the drive's control architecture and limit value calculator; a limit value calculator that interfaces with the control architecture of the first adder and the driver to calculate the limit value of the q-axis current command limiter. The AC motor driver weakening control device according to item 6 of the application scope has a switching period of pulse width modulation control, T _Z =1/(KT _s ), T _s = sampling period of pulse width modulation control , K = constant. The limit value of the q-axis current command limiter of the AC motor driver field weakening control device as described in the scope of claim 6 , with the actual d-axis current command reference value, , the relationship is: , where I _{s (max)} = the maximum current of the AC motor.