JP2007189897A - Method for controlling ac motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an AC motor control method, which accurately measures the primary resistance in a motor that affects the vector control by a large amount and obtains precision vector control characteristic, even when the motor temperature changes. <P>SOLUTION: This method measures the secondary time constant and the inertial moment of the motor, prior to operation, and calculates the DC excitation time Tset, based on them. To quickly decelerate and stop the AC motor, this method makes a constant DC current flow via an inverter for a Tset time, beginning when a deceleration command reaches the proximity of stoppage frequency. In addition, primary resistance is obtained in the motor, from the ratio of the motor voltage that is to be applied to the motor current. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control method for an AC motor including an auto-tuning function for automatically measuring a motor constant using an inverter device for variable speed control of the AC motor.

In general-purpose inverters and the like for variable speed control of induction motors, high starting torque at low speed and reduction in speed fluctuation rate are required. In order to meet this requirement, speed sensorless vector control without using a speed sensor that controls the excitation current of the induction motor to be constant and gives a slip frequency proportional to the torque current to control the speed and vector control using the speed sensor have become widespread. is doing. In such control, it is necessary to compensate for the impedance voltage drop of the motor constant. Therefore, auto-tuning processing is performed to measure the motor constants such as actual primary resistance and secondary resistance using an inverter, and vector control is performed based on the measured values. Of the motor constants, the primary resistance and the secondary resistance vary by several tens of percent depending on the temperature of the motor. For this reason, it is desirable to always measure during operation. However, since it takes a long time to measure, conventionally, measurement is performed before starting or after stopping the motor as described in JP-A-5-297079, for example. Further, methods for measuring the primary resistance and the secondary resistance are described, for example, in JP-A-6-59000 and JP-A-6-98595. In general, a DC voltage is applied from an inverter, a DC current is passed through the motor winding, and the primary resistance r1 is measured from the ratio of the DC voltage and the DC current (measurement by DC excitation). The secondary resistor r2 applies a single-phase AC voltage from the inverter, causes an AC current to flow through the motor winding, and measures the primary + secondary combined resistance (r1 + r2) from the values of effective power and AC current (single-phase AC). Measurement by excitation). Next, r2 is obtained by subtracting r1 measured by DC excitation from this value (r1 + r2). Note that these measurement times generally take several seconds.

  When measuring at the time of start-up at the time of vector control operation without a speed sensor or with a speed sensor, it is possible to measure an accurate motor constant because it is measured at the motor temperature immediately before the start-up. For this reason, there is an advantage that the constant speed control characteristic with a small speed fluctuation with respect to the load is improved. However, if measurement is not performed in a short time after the start command, acceleration will be delayed, which may cause a problem and limited applications. On the other hand, when performing the auto-tuning process after the speed sensorless vector control operation, there is a certain amount of time until the next start-up, which can be applied to various applications. However, in the conventional example, the motor constant measurement operation is started by applying the inverter voltage after the motor is stopped. In the case of a general-purpose inverter, generally the gate voltage of the inverter is cut off when the speed command reaches the stop frequency. However, the motor rotates for a while due to the inertia of the load. When the moment of inertia is large, it takes time to stop. Further, in the case of a general-purpose inverter without a speed sensor, there is a problem that it is very difficult to determine whether or not the motor has stopped.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for controlling an AC motor that can accurately measure a primary resistance of a motor that greatly affects vector control on a general-purpose basis, and that can provide accurate vector control characteristics even when the motor temperature changes. There is.

  As a first means for achieving the above object, when the AC motor is decelerated and stopped, a constant DC current is applied to the motor winding line by the inverter for a desired time from when the speed command or the inverter frequency reaches near the stop frequency. By applying a voltage so as to flow and performing this direct current excitation process, a brake torque is generated in the motor, and the primary resistance of the motor is measured from the ratio of the voltage applied to the motor and the current flowing in the motor. Also, vector control was performed based on the measured motor constant.

  As a second means, a DC excitation time for applying a constant DC current to the motor winding line is measured, and the inertia moment J of the load and the secondary time constant T2 of the motor are measured by measuring the motor constant before the vector control operation. The DC excitation time was calculated based on the value of, and the DC excitation time was varied according to J and T2.

  As a third means, when a constant DC current is passed through the motor winding line and a vector control start command (forward or reverse switch-on operation) is input while measuring the motor constant, the motor constant measurement operation is stopped. Then, we decided to accelerate by switching to vector control operation.

  According to the present invention, every time the vehicle is decelerated and stopped, the DC excitation process is performed from the vicinity of the stop frequency and the time considering the moment of inertia of the load and the secondary time constant of the motor. Accordingly, there is an effect that the primary resistance r1 can be accurately measured from the voltage command applied to the motor and the motor current in combination with stopping the motor early. As a result, the measurement can be performed in an optimum time corresponding to the application having various inertia loads, so that there is an effect that there is versatility. In addition, since vector control is performed using this measurement value, there is an effect that accurate vector control can be obtained.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, an AC power source 1 is converted into a DC power source through a rectifier circuit 2 and a smoothing capacitor 3. Further, during normal vector control operation, the inverter input voltage Vdc is PWM controlled by the inverter 4 to generate an AC voltage, whereby the induction motor 5 is controlled at a variable speed. The software configuration of the control device 6 using a one-chip microcomputer includes a speed command pattern generation / start / stop determination means 7, a speed sensorless vector control means 8, and an auto tuning processing means 9. The speed command pattern generation and start / stop judgment means 7 generates a speed command f1 ^* acceleration / deceleration pattern based on the target speed command fn, stop frequency command (equivalent to start frequency) fs, and acceleration / deceleration rate set value. It also outputs start and stop commands for auto tuning operation that measures vector control and motor constants based on forward and reverse start commands and operation stop commands. Next, the speed sensorless vector control means 8 accelerates or decelerates according to the speed command f1 ^* . In this case, speed control is performed based on various motor constants such as the primary resistance r1 and the output of the motor current detector 10. Further, the speed sensorless vector control means 8 compensates the voltage drop due to the primary impedance so that the induced voltage of the induction motor 5 becomes constant, and outputs the primary voltage command of the motor. Furthermore, the primary frequency is controlled by giving a slip frequency proportional to the current contributing to the torque, and a PWM signal (gate signal) is output based on the magnitude of the primary voltage vector and the primary frequency command, and the gate circuit 11 The inverter 4 is controlled via As a result, the actual speed is controlled so as to substantially follow the speed command f1 ^* .

Next, the auto-tuning process 9 is divided into a motor constant measurement process that measures only once before driving and a primary resistance measurement process that measures every deceleration stop after driving. These processes are induced by controlling the inverter 4. A DC voltage or a single-phase AC voltage is applied to the electric motor 5 to determine the electrical constant of the induction motor 5 from the output values iu, iw of the current detector 10.

Hereinafter, the main part of the present invention will be described in detail with reference to FIGS. FIG. 2 shows a flowchart of the auto-tuning process before operation. First, the primary + secondary combined resistance (r1 +) is calculated from the effective power of the motor and the magnitude of the motor current by the single-phase AC excitation method described in JP-A-6-98595.
r2) is obtained. Next, the primary resistance r1 is obtained based on the DC excitation method described in Japanese Patent Publication No. 2580101. Therefore, the secondary resistance r2 is obtained by subtracting the r1 measurement value from the (r1 + r2) measurement value. Next, steady operation is performed by the method described in JP-A-6-265607, and the self-inductance L2 of the motor is obtained from the inverter output voltage, effective current, and reactive current. Next, acceleration / deceleration operation is performed by the method described in JP-A-61-88780, and the moment of inertia J of the motor and the load is measured.

  After the above measurement operation is completed, the DC excitation time Tset is calculated. Tset is determined from the motor secondary time constant T2 = L2 / r2 and the moment of inertia J. As will be described in detail in the control block diagram of FIG. 4, since the voltage applied to the motor does not reach a steady state, the DC excitation time TsetA by T2 is about 4 times the secondary time constant T2 of the motor after the DC excitation current control is started. Is approximated by Equation (1).

(Equation 1)
TsetA ≒ 4 x T2
Next, the estimated time Tstop from the speed at the stop frequency fs until the motor stops is approximated by Equation 2.

(Equation 2)
Tstop≈J × (2π × fs / pt) / (Tm0 / 2)
Here, J is the moment of inertia, fs is the stop frequency, pt is the number of pole pairs of the motor, and Tm0 is the rated torque of the motor. (2π × fs / pt) is the rotational angular velocity of the motor at the start of DC excitation. Also, Tm0 / 2 considers the brake torque at the time of starting DC excitation as Tm0, and this brake torque decreases as the speed decreases, and the slip frequency of the induction motor becomes zero at the motor speed zero, so the brake torque becomes zero. . Therefore, it is considered that Tm0 is equivalent to the rated torque of the motor by flowing a DC excitation current corresponding to the rated current of the motor. Further, it is considered that the brake torque decreases almost linearly from Tm0 until the motor stops, and the average brake torque is set to Tm0 / 2. The brake torque at the time of direct current excitation is approximated by Equation 2 because it varies depending on the rated slip frequency of the motor, the secondary time constant T2, the direct current excitation current, and the like. next,
The larger of TsetA and Tstop is the DC excitation time Tset, which is set via the upper and lower limiters. The upper limiter is determined from the thermal overload capability of the power elements constituting the inverter, and the lower limiter is about 1 second.

Next, the operation flow after operation is shown in FIG. When a stop command is input during the vector control operation, the speed command f1 ^* is gradually lowered, and when the stop frequency fs is reached, the vector control is terminated and DC excitation is started. As a result, the motor is braked and the primary resistance r1 is continuously measured. If the DC excitation time exceeds Tset, the r1 measurement value is stored in the memory and the r1 measurement is terminated.

  Next, FIG. 4 shows a control block diagram of DC excitation control and r1 measurement. Based on the DC excitation phase command θd, the U-phase and W-phase motor current detection values iu and iw are converted to dq (converting the current in the fixed coordinates into the current in the rotation coordinates) by Equation 3 to obtain Id and Iq. Note that the DC excitation phase command θd is a phase command in vector control at the end of vector control. Further, iu and iw are direct currents, and Id is also a direct current amount.

(Equation 3)
Id = iu · cos θd − ((iu + 2 iw) / √3) sin θd
Iq = −iu · sin θd − ((iu + 2iw) / √3) cos θd
Next, the current control system is composed of a d-axis current control means 13 and a q-axis current control means 14, and the d-axis current control means 13 (proportional + integral) so that the Id detection value coincides with the DC excitation current command Id ^*. ) Compensate and output d-axis voltage Vd ^* . On the other hand, the q-axis current control means 14 compensates for the Iq detection value to be zero (proportional + integration) and outputs the q-axis voltage Vq ^* . The dq / uvw conversion means 15 converts the rotational coordinate voltage into the fixed coordinate voltage, performs the calculation of Formula 4, outputs three-phase voltage commands Vu ^* , Vv ^* , Vw ^* , and the gate signal generation means 16. The gate signal is output via Since θd is constant, the inverter frequency becomes zero, and Vu ^* , Vv ^* ,
Vw ^{* is} also a DC voltage command.

(Equation 4)
Vu ^* = Vd ^* · cos θd−Vq ^* · sin θd
Vw ^* = − Vu / 2−√3 (Vd ^* · sin θd + Vq ^* · cos θd) / 2
Vv ^* = − (Vu ^* + Vw ^* )
In such a configuration, Vq ^* is almost zero, and the DC voltage applied to the motor is equivalent to Vd ^{* in a} steady state. However, Vd ^* is a command value, and includes an error voltage ΔVd due to a dead time provided so that the power elements of the positive and negative arms constituting the inverter are not short-circuited and an on-voltage drop of the power element (Vd ^* −ΔVd). ) Is the true DC voltage applied to the motor. Therefore, the primary resistance calculation means 17 performs calculation of Formula 5 to measure the primary resistance r1. ΔVd varies slightly depending on the phase command θd, but is set in advance based on the dead time and the ON voltage drop of the power element.

(Equation 5)
r1 = (Vd ^* −ΔVd) / Id
Next, Vd ^* in Formula 5 is attenuated by the first-order lag of the second-order time constant T2 of the motor from the time when DC excitation is started, and approaches a steady value at about four times T2. This is initially a voltage of (r1 + r2), and in a steady state, a voltage of only r1. For this purpose, TsetA in FIG.
Measured after direct current excitation for about 4 times longer than T2. This improves the measurement accuracy. Furthermore, since the slip frequency is generated when the electric motor is rotating, Vd ^* does not reach a steady state. For this reason, a measurement error of r1 occurs. Therefore, the measurement accuracy is improved by calculating the estimated motor stop time Tstop shown in FIG. 2, performing DC excitation for a time longer than Tstop, applying the brake, and measuring the primary resistance after the motor stops.

Next, FIG. 5 shows a time chart of the control operation in the present invention. When the start switch is turned on, the speed command f1 ^* increases from the starting frequency fs to the target speed fn according to the acceleration rate, and is accelerated so that the actual speed follows f1 ^* . Further, when the stop switch is turned on, f1 ^* decreases, and when the stop frequency fs is reached, the gate signal is turned off and the gate signal is utilized by the control block shown in FIG. 4 to perform the direct current excitation operation. As a result, the brake works and the speed decreases. Note that the rate at which the speed decreases (the rate of temporal speed reduction) varies depending on the moment of inertia J, but the stop time Tstop is estimated from Equation 2 to determine the DC excitation time Tset. As a result, the measured value r1 is stored after the time Tset when it is estimated that the motor has stopped, and the gate signal is turned off. Thereby, the brake is applied and stopped in a short time, and the voltage command Vd ^* is measured in a constant steady state, so that r1 can be measured with high accuracy. In addition, the DC excitation time can be shortened.

  Next, FIG. 6 shows a time chart when a start command is input during DC excitation. In this case, the DC excitation operation is stopped in order to give priority to activation, and acceleration is performed by performing vector control based on the previously measured r1 measurement value.

The control block diagram which shows one Example of this invention. The flowchart figure which shows the auto-tuning process before the driving | operation of this invention. The flowchart figure which shows the control after the driving | operation of this invention. The control block diagram of DC excitation control and primary resistance measurement. The time chart figure which shows the driving | operation operation | movement of this invention. The time chart figure at the time of starting command entering during the direct current excitation of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... AC power source, 2 ... Rectifier circuit, 3 ... Smoothing capacitor, 4 ... Inverter, 5 ... Induction motor, 6 ... Control device, 7 ... Speed command pattern generation and start / stop judgment means, 8 ... Speed sensorless vector control means, DESCRIPTION OF SYMBOLS 9 ... Auto tuning processing means, 10 ... Current detector, 11 ... Gate circuit, 12 ... dq conversion means, 13 ... d-axis current control means, 14 ... q-axis current control means, 15 ... dq / uvw conversion means, 16 ... Gate signal generating means, 17... Primary resistance calculating means.

Claims (2)

  A voltage source inverter converts the DC voltage into AC or DC and supplies it to the AC motor. The auto-tuning operation means measures the AC motor constant from the motor current detection value, and controls the voltage source inverter based on the measured value. Then, in the control apparatus for the AC motor comprising vector control operation means for vector control of the AC motor, when the AC motor is decelerated to a stop, the inverter is used to drive the motor from the time when the speed command or the inverter output frequency reaches near the stop frequency. A control apparatus for an AC motor, wherein a voltage is applied so that a constant DC current flows for a desired time, and a primary resistance of the motor is measured from a ratio of a voltage applied to the motor and a current flowing through the motor. A voltage source inverter converts the DC voltage into AC or DC and supplies it to the AC motor. The auto-tuning operation means measures the AC motor constant from the motor current detection value, and controls the voltage source inverter based on the measured value. In the control apparatus for the AC motor comprising the vector control operation means for vector controlling the AC motor,
A control apparatus for an AC motor, wherein a DC excitation time for supplying a constant DC current to the motor is varied according to a load moment of inertia and a secondary time constant of the motor.

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