JPH04161085A - Synchronous motor control method - Google Patents

Abstract

PURPOSE:To realize highly accurate torque control by arbitrarily varying the angle between the direction of rotor flux and the direction of stator current of a synchronous motor thereby controlling torque generation of the motor. CONSTITUTION:When a rotational position detector 2 detects an actual rotational angle thetaA of a synchronous motor 1, a current operating section 4 generates a sine wave current having desired phase and amplitude corresponding to the rotational angle thetaA and a target torque TT. An amplifier 3 then amplifies the sine wave and feeds the amplified current to the synchronous motor 1. In other words, torque is controlled by controlling the phase angle and the amplitude. According to the constitution, highly accurate torque control is realized through a hardware having rough control accuracy of current amplitude.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a synchronous motor control method for controlling the torque generated by the synchronous motor to a desired value, and in particular, to a method for controlling the torque, speed, and position of the synchronous motor. This relates to a control method.

[Prior Art] Conventionally, when controlling a synchronous motor using a permanent magnet in the rotor, torque control with the highest torque generation efficiency is performed by orthogonalizing the magnetic flux generated by the rotor and the current on the stator side.

Assuming that the magnetic flux distribution in the air gap is sinusoidal, the three-phase armature current i is controlled as follows according to the rotor position θ. where Δ is the current amplitude.

At this time, the torque generated by the synchronous motor is as follows.

T, =-・kl・■・Φ・・・・・・・・・(1)
Here, km is a proportionality constant and Φ is an effective magnetic flux.

Therefore, the motor generated torque T. is independent of θ and is proportional to ■. That is, since the magnitude of the generated torque is proportional to the current amplitude on the stator side, the configuration of the control system is also facilitated.

[Problems to be Solved by the Invention] As described above, in the conventional system, the control torque obtained is determined only by the amplitude of the commanded current and does not depend on θ.

Normally, this method is sufficient, but since the torque resolution is determined only by the current amplitude factor, precise control of the current amplitude is required in order to perform precise torque control.

In order to precisely control the current amplitude, it is conceivable to monitor the current amplitude using, for example, a microcomputer-controlled A/D converter and perform feedback control using the D/A converter. In such a configuration, the resolution of current amplitude control is determined by the accuracy of the D/A converter. When the maximum value of the command current is assigned to the maximum output of the D/A converter, the minimum control current is determined by the minimum bit of the D/A converter.

For example, when trying to command current in the positive and negative directions using an 8-bit D/A converter, the minimum current is 1/1/2 of the maximum current.
It is 128. Therefore, the minimum generated torque of the motor is the maximum torque of 17128, and more precise torque control is not possible with this method.

[! ! Means for Solving the Problem] According to the present invention, the torque generated by the motor is controlled by arbitrarily changing the angle formed between the magnetic flux direction of the rotor of the synchronous motor and the current direction of the stator.

[Embodiments] Two preferred embodiments of the present invention (a first embodiment and a second embodiment) will be described below with reference to the accompanying drawings. The first embodiment embodies the principle of the present invention, and the second embodiment further applies the first embodiment to position control and rotational speed control.

First Embodiment> FIG. 1 is a diagram illustrating a motor control device according to a first embodiment. In the figure, this control device detects the actual rotation angle θ1 of the synchronous motor. A detector 2, a current calculation unit 4 which generates a sine wave i current having a desired phase ψ and amplitude l according to its rotation angle θ and a target torque value TA, and a current amplification of this sine wave i to generate the A torque control system with an amplifier 3 feeding a synchronous motor. In this first embodiment, the torque is controlled by controlling the phase angle ψ and the amplitude ■.

In the torque control method of this first embodiment, the three-phase armature current is controlled as follows.

・・・・・・・・・・・・(2) Motor torque T generated at this time. is T, =-・k
It is expressed as l・Φ・I−cosψ (3). If k3・Φ is fixed, To
If the relationship between and ■·cosψ can be controlled while maintaining a proportional relationship, the control will be smooth. Therefore, consider controlling the amplitude and ψ that can maintain this proportional relationship.

Transforming equation (3), To=to-I-cosV=K·I. −−−・−(
4). Here, K = 3/2·k,·Φ. Equation (4) means that by controlling the two variables I and ψ, a proportional relationship between To and 1·cos ψ can be maintained. In other words, ■.

and T. Two variables I and ψ are determined so that they can be controlled while maintaining the proportional relationship. Therefore, I=I. +δ・・・・・・(5) If we set δ as a constant, equation (4) becomes (Eng.+δ)
・cosψ=1. ......(6). δ
If is a positive constant, then from equation (6), ■. Even if and δ are set to arbitrary values, ψ can be obtained according to the following. The relationship expressed by equation (7) is illustrated in FIG. 2.

For example, δ = engineering. Then, I=I. +δ=2I0, that is, the current I flowing through the motor is ■. By doubling the torque angle and controlling the torque angle to 60 degrees, the current flowing through the motor can be doubled and the same torque as the conventional method can be generated. Also, δ
By increasing , the motor current can be increased as desired.

In this way, once the target torque air is determined, T corresponding to this torque air. ψ and engineering so as to occur. is (7)
It can be calculated according to the equation (5), and the desired torque air can be generated by outputting a current according to the equation (5).

The current calculation unit 4 uses the above 1 and ψ to calculate the three-phase armature current from equation (2).

iu = I・sin (θ, +ψ) iv = I・sin (θ, +ψ−2π/3) 1 *
= I·sin (θ1+ψ−4π/3) Thus, in the method of the first embodiment, the generated torque T. In order to control the current amplitude I and the phase A, it has become possible to control the current amplitude I and the phase A in relation to each other.

Second Embodiment> According to FIG. 3, a second embodiment is a further development of the first embodiment.
An example will be explained. This second embodiment relates to the configuration of a speed control system for a synchronous motor. Here, 1 is a synchronous motor, 2 is a detector for the actual rotational position θ of the motor, 3 is an amplifier for supplying current to the motor 1, and 4 is a target current value based on the target torque T and motor rotational position θ. 5 is a detector for calculating the motor rotation speed; 6 is a comparator for generating a position error Δθ from the target rotational position θa and the actual motor rotational position θ1; 7 is a comparator 6 is an amplifier that amplifies the position error Δθ calculated and converts it into a target rotation speed; 8 is a comparator that generates a speed error from the target rotation speed output from the amplifier 7 and the actual motor rotation speed; 9 is a comparator that generates a speed error from the target rotation speed output from the amplifier 7; An amplifier 10 amplifies this speed error, an integrator 10 integrates this speed error, and an adder 11 that adds the outputs of 9 and 10 to generate a target torque value.

First, when the target rotational position θ1 is input to the comparator 6, the motor rotational position θ is read and the position error △ is calculated from the difference between the two.
θ is generated. This position error is input to the amplifier 7,
It is converted into a target rotational speed and input to the comparator 8. The comparator 8 reads the motor rotation speed from the detector 5 and generates a speed error. The speed error generated by comparator 8 is
It is input to 9 amplifiers and 10 integrators. Both outputs are summed by 11 adders, and the output becomes the target torque value.

The current calculation unit 4 generates a three-phase target current value i from the target torque value Tr and the motor rotation position θ1 which is the second output. The amplifier 3 supplies a phase current corresponding to the target current value to the synchronous motor 1 to rotate the motor.

As a result, the position and speed of the morph are detected by the morph position detector 2 and the morph rotation speed detector 5.

FIG. 5 shows a step response according to the conventional method when the resolution of the target current value is 1/128 in the position control system shown in the first embodiment. The horizontal axis represents the rotation angle θ, and the vertical axis represents the target current value. It can be seen that there are parts where the current resolution drops significantly around angles of 0.015 and 0.02. On the other hand, FIG. 4 shows the same configuration in which the above embodiment is applied to the target current value generation algorithm. From a comparison of both figures, it can be seen that the position control system to which the present invention is applied exhibits better characteristics.The present invention can be modified in various ways without departing from the spirit thereof.

In the above two embodiments, as an algorithm for generating the target current value, the amplitude of the target current value is set to a value slightly larger than the value calculated by the conventional method, and the phase control of the target current value is controlled within a small angle range. I mentioned the case where Other possible methods include the following.

■: Lo is fixed at the maximum value, and the generated torque is controlled only by controlling the phase A.

■: In the small torque range, the method according to the above embodiment or ■
The conventional method (fixed at ψ=90 degrees) is used in the large torque range.

(2) In the above embodiment, δ was fixed, but the relationship between δ and 1 is changed.

[Effects of the Invention] By using the present invention, even with a hardware configuration in which current amplitude control accuracy is rough, torque control becomes much more precise than in conventional systems. Therefore, effects such as a reduction in hardware costs and an improvement in control accuracy can be expected.

[Brief explanation of the drawing]

Fig. 1 is a basic configuration diagram of a preferred first embodiment of the present invention, Fig. 2 is a diagram explaining the control principle of the first embodiment, and Fig. 3 is a configuration diagram of a second embodiment of the present invention. 4 shows the step response waveform of the position control system using the above embodiment, and FIG. 5 shows the step response waveform of the position control system using the conventional method. , > −, , , '−2

Claims (5)

[Claims] (1) A method for controlling a synchronous motor, comprising controlling the torque generated by the motor by arbitrarily changing the phase angle between the magnetic flux direction of the rotor of the synchronous motor and the current direction of the stator. (2) The method for controlling a synchronous motor according to claim 1, characterized in that the motor generated torque is controlled by further changing the amplitude of the stator current. (3) When determining the phase angle and amplitude of the stator current, the amplitude and phase of the stator current are controlled so that the motor generated torque is proportional to the target torque. The method of controlling the synchronous motor described. (4) A method for controlling a synchronous motor according to any one of claims 1 to 3, characterized in that the motor rotation speed is controlled by further associating motor rotation speed information. (5) A method for controlling a synchronous motor according to any one of claims 1 to 3, characterized in that the motor rotational position is controlled by further associating motor rotational position information.