JPH04304184A - Vector control method for induction motor - Google Patents

Abstract

PURPOSE:To enhance secondary resistance compensation and to improve control characteristics of speed and current. CONSTITUTION:When vector control of an induction motor is carried out by means of first and second CPUs 21, 22, data fed from the first CPU 21 is stored in a common memory 23 and subsequently transmitted to the second CPU 22. At that time, an estimated value obtained by adding half of the variation of data omegao(primary angular frequency) is transmitted from the first CPU 21 to the second CPU 22.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a vector control method for an induction motor using two CPUs.

0002

2. Description of the Related Art Vector control of induction motors, which controls secondary magnetic flux and secondary current orthogonal thereto in a non-interfering manner, has been widely applied.

In the case of a three-phase induction motor, this vector control treats the current and magnetic flux as vectors in a d-q coordinate system of two orthogonal axes that rotate at the same speed as the rotating magnetic field generated by the power source.
This is a method of controlling by converting the calculation results into current command values for each phase of a three-phase power supply.

[0004] To describe the specific method, d-q
The voltage equation in the coordinate system is expressed by the following equation (1).

[0005]

[Math 1]

[0006] However, ωs=ω−ωr, Lσ=(L1L2
-M2)/L2.

[0007] Here, v1d and v1q are the primary voltage d, respectively.
, q-axis components, i1d and i1q are the d- and q-axis components of the primary current, respectively, λ2d and λ2q are the d- and q-axis components of the secondary magnetic flux, respectively.
R1, R2 are the primary and secondary resistances, respectively, L1, L2, and M are the primary, secondary, and exciting inductances, respectively. ω, ωr, and ωs are the primary power supply angular frequency, rotor angular frequency, and slip angular frequency, respectively. P represents d/dt.

If the d-axis is placed on the secondary magnetic flux in the d-q coordinate system, λ2q=0. At this time, λ2d=Φ2=constant, i2d=0, i2q=i2, and orthogonal control of torque and magnetic flux similar to a DC machine is possible.

On the other hand, the secondary magnetic flux has the following relationship.

0010

[Math 2]

According to the vector control condition, i2d=0,
From equation (2), λ2d=Mi1d.

[0012] Also, since λ2q=0, i1q=-L2/
M·i2q, and i1q is proportional to the torque current.

Next, from the fourth line of equation (1), equation (3) is obtained, and from this equation (3), the condition for the slip angular frequency is found.
ωs is expressed by equation (4).

[0014]

[Math 3]

The above are the vector control conditions when controlling the secondary magnetic flux so that it coincides with the d-axis. Therefore, in order to perform vector control, i1d is set to λ2d/M, and ω
It is necessary to control s so that equation (4) holds true.

Here, the resistance value of the secondary resistance R2 used to calculate the slip angular frequency ωs changes due to temperature changes such as the ambient temperature and self-heating of the rotor, so the change in resistance value is calculated based on the output voltage of the motor. It is necessary to estimate and correct the target value of the slip angular frequency ωs based on this change to compensate for fluctuations in generated torque due to changes in secondary resistance. If the change in secondary resistance is ignored, torque control accuracy and torque response will deteriorate. For example, if we use the inverter's output voltage as is, we can estimate the change in secondary resistance by 1
Since the change in the primary resistance is taken in, it is desirable that the signal used for estimation be a signal that is not affected by the primary resistance.

For this reason, a control circuit shown in FIG. 3 has already been proposed. 1 in the figure is the excitation current command section,
λ2d*/M* until the angular frequency ωr exceeds a certain value
Let the target value of 1d be i1d*, and if ωr exceeds a certain value, i
Decrease 1d*. Below, target values or ideal values are indicated with *. The deviation of the speed commands ωr* and ωr is set as i1q* through the speed amplifier 2, and the primary voltage on the d-q axis is calculated based on i1d* and i1q*. Ideal value v1d*, v1
If q* is calculated and the correction for voltage fluctuation due to changes in primary resistance and secondary resistance is controlled so that i1d*=i1d and i1q*=i1q, then P that controls i1d*=i1d
Δv1d is obtained for the I amplifier 31, i1q*=i1q
Δv1q is obtained for the PI amplifier 32 that controls the .DELTA.v1q. Δ
Since v1d and Δv1q both include voltage fluctuations due to changes in the primary resistance and secondary resistance, if the secondary resistance change is compensated for by finding a component that does not include voltage fluctuations due to the primary resistance change, the primary resistance Compensation that is not affected by changes becomes possible. Therefore, a rotational coordinate γ-δ axis is set in which the reference axis γ is placed on the vector of the primary current I1, and the primary voltage variation Δv1δ of this δ axis is determined by the slip correction calculation unit 33. This Δv1δ is expressed by a formula that does not include the primary resistance R1,
Therefore, it is not affected by the primary resistance R1.

FIG. 4 is a vector diagram showing the relationship between the d-q axis and the γ-δ axis, voltage and current, and FIG. 5 is a vector diagram showing the primary voltage fluctuation. In the figure, V1 and E are the primary voltages, respectively. , secondary voltage, Δv1 is the primary voltage fluctuation, Δv1γ, Δv1δ
are the γ-axis component and δ-axis component of the variation, respectively, and ψ is the γ-axis and d
The phase difference with the shaft, I0 is the excitation current, and I2 is the torque current. Δv1δ is expressed by the following equation (5).

[0019] Δv1δ=−Δv1d·sinψ+Δv1qcosψ…
(5) However, cosψ=I0/I1=i1d/i1γ,
sinψ=I2/I1=i1q/i1γ Then, the slip correction calculation unit 33 calculates 2 based on Δv1δ.
Correction amount Δωs of the slip angle frequency corresponding to the next resistance change
is obtained by calculation, and ωs obtained by the slip angular frequency calculation section 34
Let the added value of * and Δωs be the target value of the slip angular frequency,
The rotor angular frequency ωr is added to this to obtain the target value of the angular frequency ω=dθ/dt of the primary voltage. In FIG. 3, 35 is a polar coordinate conversion section, 36 is a coordinate conversion section, 41 is a PWM circuit, 4
2 is an inverter, IM is an induction motor, PP is a pulse pickup section, and 43 is a speed detection section.

[0020]

FIG. 6 shows a simplified version of the vector control circuit shown in FIG. 3 by dividing it into a speed control system and a current control system. In FIG. 6, 21 is the first CPU of the speed control system, and 22 is the second CPU of the current control system.
It is U. Here, the speed control system includes speed detection, speed amplifier, excitation command, slip angle frequency calculation, etc., and the calculations of this speed control system are executed at a relatively low speed (for example, a calculation cycle of about 1 to 5 mS). In addition, the current control system uses coordinate transformation,
These include voltage command calculation, current command calculation, current detection processing, PWM calculation, etc., and the calculations of this current control system are relatively high-speed processing (
For example, the calculation period is about 100 μS to 500 μS).

As described above, in the vector control system, two first and second CPUs 21 and 22 are generally used to share arithmetic processing. A general-purpose one-chip CPU is usually used for the speed control system, and a DSP for high-speed calculation is usually used for the current control system. First and second CPU21
, 22 are connected by a shared memory 23, and the first CPU
The angular frequency ωr or the primary angular frequency ω0 (
When the slip angular frequency calculation is executed by the first CPU 21, ω0 is used, and when the calculation is executed by the second CPU 22, ωr is used.
data such as the torque command i1q*, excitation i1d*, etc. are set in the shared memory 23. 2nd CPU
22 reads data set in the shared memory 23 and executes current control calculations every calculation cycle. This execution result is supplied to the inverter 25 via the base drive 24 as a PWM command. In the figure, 26 is an induction motor;
27 is a pulse pickup.

As shown in FIG. 6, when the calculations of the speed control system and the current control system are shared and executed by the two CPUs 21 and 22, the delay time due to the difference in the calculation cycle of the speed control system and the current control system, Due to the transmission delay time that occurs when ωr and ω0 calculated by the first CPU 21 are transmitted to the second CPU 22 through the shared memory 23, slippage occurs when calculating them in the current control system and controlling the actual motor. An error will occur. Because of this error, the Δ
V1δ or ΔV1δI becomes inaccurate and vector control conditions cannot be maintained, resulting in problems such as deterioration of accuracy of secondary resistance compensation and deterioration of speed control characteristics and current control characteristics.

The present invention has been made in view of the above circumstances, and aims to provide a vector control method for an induction motor that improves the accuracy of secondary resistance compensation and improves speed and current control characteristics. do.

[0024]

[Means and Operations for Solving the Problems] In order to achieve the above object, the present invention executes calculations for the speed control system in a first CPU, and executes calculations for the current control system in a second CPU. The second CPU reads these data stored in the shared memory and performs control calculations. In a method for vector-controlling an induction motor by controlling an inverter, the data of ωr or ω0 transmitted from the first CPU to the second CPU via the shared memory is set to the value at the midpoint of the speed control period. is characterized in that it is obtained as predicted data and then transmitted to the second CPU. Further, in the present invention, the data of ωr or ω0 is transmitted from the first CPU to the second CPU via the shared memory.
After the data is transmitted to U, the second CPU performs linear interpolation processing between the data.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. From the first CPU 21 to the second CPU shown in FIG.
The data (ωr or ω0) to be transmitted to U22 is assumed to be data ω0n*, which is a predicted value at the midpoint of the speed control cycle. This ω0n* is obtained from the following equation (1).

[0026] ω0n*=ω0n+(ω0n-ω0n-1)/2
...(1) However, ω0n: Current value of primary angular frequency (
midpoint value), ω0n-1: Previous value of primary angular frequency, ω
0n*: This is the current value (intermediate predicted value) of the data to be transmitted to the second CPU at the primary angular frequency.

The above equation (1) adds 1/2 of the change in ω0 to the current value ω0n to obtain the predicted value ω0n*, and this ω0n* is calculated as shown in FIG. That is, the previous value ω0n-1 is subtracted from the current value ω0n of the values obtained for each speed control period T to obtain an average value, and the current value ω0n is added to this average value. The ω0n* obtained in this way is transmitted to the second CPU 22, and the second CPU
22 calculates this ω0n* and sends out a PWM command. If such a control method is used, there will be no transmission delay time or delay time in the calculation cycle, and no slip errors will occur. Therefore, accurate vector control can be performed.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, from the first CPU 21, for example, ω
0 is transmitted to the second CPU 22, the second CPU
U22 uses this ω0 data to perform linear interpolation processing using the following equation (2).

[0029] ω0n*=ω0n-1*+(ω0n-ω0n-1)/N
...(2) However, N=T/t, T is the speed control period, t is the current control period, ω0n is the current value of the primary angular frequency, ω0n-1 is the previous value of the primary angular frequency, ω0n*
is the current value of the second CPU usage data of the primary angular frequency, ω
0n-1* is the previous value of the second CPU usage data of the primary angular frequency.

The above equation (2) is calculated from the current value ω0n to the previous value ω
The average value of N is obtained by subtracting 0n-1, and the previous value of the second CPU usage data is added to this average value of N. The thus obtained ω0n* is subjected to linear interpolation processing by the second CPU 22, and a PWM command is sent from the second CPU 22. By using such a control method, there is no transmission delay time or delay time in the calculation cycle, and no slip errors occur. Therefore, accurate vector control can be performed.

Note that when ω0n is transmitted from the first CPU 21, a reset process is performed with ω0n*=ω0n, and the calculation of equation (2) is performed using this ω0n* as an initial value until the next ω0n is transmitted. conduct.

[0032]

[Effects of the Invention] As described above, according to the present invention,
In a vector control method using first and second CPUs and a common memory, the transmission delay time that occurs when transmitting data from the first CPU to the second CPU via the common memory is eliminated, and the calculation cycle is By eliminating the delay time due to the difference in the slip frequency, vector control can be performed accurately with no errors in the slip frequency, and the advantage is that secondary resistance compensation and speed and current control characteristics can be improved.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram for explaining a first embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining a second embodiment of the invention.

FIG. 3 is a block diagram showing a conventional vector control device.

[Fig. 4] Vector diagram.

[Figure 5] Vector diagram.

FIG. 6 is a simplified block diagram of a conventional vector control device.

[Explanation of symbols]

21...First CPU 22...Second CPU 23...Shared memory 24...Base drive 25...Inverter

Claims (2)

[Claims] Claim 1: A first CPU executes calculations for the speed control system, and a second CPU executes calculations for the current control system, and the angular frequency ωr, primary angular frequency ω0, and torque command calculated by both CPUs are and excitation commands as data in a shared memory, the second CPU reads these data stored in the shared memory and performs control calculations, and then controls an inverter to vector-control the induction motor. from the first CPU to the second CPU via shared memory.
After obtaining the ωr or ω0 data to be transmitted to the CPU as data that predicts the value at the midpoint of the speed control cycle,
A vector control method for an induction motor, the method comprising transmitting data to a second CPU. 2. After transmitting the data of ωr or ω0 from the first CPU to the second CPU via the shared memory, the second CPU performs linear interpolation processing between the data. A vector control method for an induction motor according to claim 1.