JPH07123761A - Methods for controlling and estimating output torque of motor drive system - Google Patents

Abstract

PURPOSE:To inexpensively make a motor drive system to follow a command without vibrating the output torque of the system by estimating the output torque signal required for the control of the output torque from a speed sensor fitted to a motor without providing any torque sensor on the shaft of the motor. CONSTITUTION:At the time of making a torsion system composed of a motor 7 which drives a load 9 and elastic shaft 8 which connects the load 9 with the motor 7 to follow a command without vibrating its output torque Ts by only using a speed detector fitted to the motor 7, three stable poles which decide the response characteristic of the system are first decided. When the poles are decided to -pa, -pb, and -pc, the gain of each control loop is calculated from the poles and the machine constants rho and omegao of a plant based on formulae I, II, and III and inputted to each control block. Then a cut-off frequency omegac is appropriately decided by taking the noise condition at the actual operating time into account and the coefficient of each software observation instrument is decided from the frequency omegac and the machine constants of the plant. Finally, the calculated coefficients are respectively inputted to the software observation instruments.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torsion system consisting of a shaft for connecting a motor and a load, and uses only a speed sensor attached to the motor without providing a shaft torque sensor to prevent or suppress torsional vibration and The present invention relates to a control system obtained by estimating torque and a torque sensorless control algorithm.

[0002]

2. Description of the Related Art In the axial torque control of a torsion system, an axis torque sensor is generally provided on the axis, and control is performed based on some control theory based on a deviation between a command torque and a torque detection signal from the axis torque sensor. Therefore, it has been conventionally impossible to control the shaft torque without providing a torque sensor. Furthermore, according to the shaft torque sensor method,
The torque detection signal contains a lot of noise, and some special signal processing is required to make it a signal that can be used for control.
It is well known that the price of sensors is high and the cost of products is much higher.

[0003]

In a motor drive system having a shaft with low rigidity, a torque sensor is not provided on the shaft, and a shaft torque signal required for shaft torque control is estimated from a speed sensor attached to the motor, The first object of the present invention is to use the estimated torque signal to inexpensively cause the shaft torque to follow the command without vibrating. Further, in order to suppress the shaft vibration, it is necessary to feed back signals such as a differential value of the shaft torque, and it is a second object of the present invention to provide an algorithm for surely estimating these signals by software without delay. Is.

[0004]

In order to facilitate understanding of the present invention, a dynamic characteristic analysis of the system will be described first.

The block of the system including the electric motor, the load and the elastic shaft is represented as shown in FIG. 3, and the equation of motion is well known as in equations (1), (2) and (3). expressed. In FIG. 3, 7 is an electric motor, 8 is an elastic shaft,
Reference numeral 9 is a load machine, and 10 is a torque generation coefficient.

[0006]

[Equation 1]

However, ωm, ωl, Ts, u, and Tl are the speed of the electric motor 7 and the load machine 9, the axial torque generated in the shaft, the control input applied to the electric motor, and the load torque applied to the load, respectively. Jm, Dm, Kt are the inertia of the motor,
The viscous friction coefficient and the torque generation coefficient are represented, Jl and Dl represent the inertia of the load machine and the viscous friction coefficient, and Kc represents the spring constant of the shaft.

In order to make the model easy to handle in axial torque control, the differential equations of the state variables ωm, Ts and Ts (hereinafter referred to as φ) and Tl are used, and the equations of motion of equations (1), (2) and (3) are , Is expressed by the following equation of state.

[0009]

[Equation 2]

Here, the transfer function from the control input u applied to the electric motor to the shaft torque Ts is given by equation (8), ignoring a slight viscous friction in the system.

[0011]

[Equation 3]

Ρoωo is the motor coefficient Jm, the load inertia J
1, the mechanical constants of the axial spring constant Kc are parameters defined by the equations (9) and (10), which respectively represent the ratio of the load inertia to the total inertia and the torsion system resonance angular frequency. .

[0013]

[Equation 4]

Looking at the characteristic polynomial of the denominator of the equation (8) that determines the characteristic of the system, the damping coefficient (the coefficient corresponding to s) is 0.
And it can be seen that it is a typical secondary vibration system. In fact, the viscous friction contributes somewhat to the effect of damping it in the system, but only slightly.

Therefore, in order to suppress the torsional vibration, it is necessary to give a system equivalent to a damping term from the control input. It corresponds to the differential feedback of the shaft torque. This may be due to the PID control law as shown in FIG.

FIG. 1 shows a torque sensorless shaft torque control principle showing the technical idea of the present invention. 1 is a controlled object, 2 is a speed sensor, 3 is a soft observer, 4 is a proportional integrator, and 5 is a proportional integrator. Differential gains, 61 and 62 are adders. From FIG. 1, the transfer function from the torque command T * to the shaft torque Ts is given by equation (11).

[0017]

[Equation 5]

That is, the differential gain Kd is the damping term (s =
It is understood that the vibration suppression effect is achieved by entering the (multiplication term). Further, the three characteristic poles of the closed loop system can be freely adjusted by the three gains Kp, Ki and Kd.

It is necessary to feed back the shaft torque and its differential signal to the control side described above, but since the signal is not directly measured, the observer theory is modified here and the soft observer is based on the mechanical constant of the plant. With the above configuration, the shaft torque, the shaft torque differential value, and the load torque are estimated from the control input signal applied to the electric motor and the detection signal of the speed sensor attached to the electric motor.

The soft observer 3 is as shown in FIG. Here, FIG. 2 is a diagram showing the principle of the soft observer according to the present invention. That is, the soft observer is represented by the following equation of state.

[0021]

[Equation 6]

However, ωc represents a cutoff frequency freely decided by the designer, and means that high frequency noise higher than that is attenuated. X of soft observer output
b, xc, and xd correspond to a shaft torque signal, a shaft torque differential value signal, and a load torque signal, respectively. In this way it is guaranteed that the observed signal will gradually converge to the actual signal. Moreover, it is pointed out that the feedback of the signal does not affect the control loop. Except for the first initial deviation, it is completely equivalent to using the true signal.

[0023]

In FIG. 1, the differential gain 5 gives a damping term to the system to prevent or suppress torsional vibration.
In the torque adjustment loop, the proportional integrator in the proportional integrator 4 adjusts the follow-up speed to the command torque T *, and the integrator serves to eliminate the command follow-up offset. In the soft observer 3 shown in FIG. 2, the cutoff frequency ωc plays a role of determining the speed of convergence and cutting off higher frequency observation noise.

[0024]

The present invention will be described in more detail with reference to specific system application examples. That is, in the torsion system consisting of the electric motor that drives the load and the elastic shaft that connects the load and the electric motor,
In an application that uses only the speed detector attached to the electric motor to follow the command without vibrating the shaft torque,
First, determine the three stable poles that determine the system response characteristics.

For example, when -pa, -pb, -pc are determined, the mechanical constants of these poles and plant, ρ, ωo.
From the equations (17), (18), (1
9) Calculate and put in each control block.

Next, looking at the noise situation during actual operation,
The cutoff frequency ωc is appropriately determined, and each coefficient of the soft observer is determined from the cutoff frequency and the mechanical constant of the plant. Finally, each calculated coefficient may be input to the soft observer.

[0027]

As described above, according to the present invention, the signals corresponding to the shaft torque and the shaft torque differential value required for the torsional vibration control are extrapolated by a software observer or a feedback system is provided. Thus, an inexpensive control method capable of suppressing torsional vibration can be provided.

[Brief description of drawings]

FIG. 1 is a system diagram showing a torque sensorless shaft torque control principle showing the technical idea of the present invention.

FIG. 2 is a diagram showing the principle of a soft observer according to the present invention.

FIG. 3 is a system diagram showing a torsion system control target block.

[Explanation of symbols]

 1 Control object 2 Speed sensor 3 Soft observer 4 Proportional integrator 5 Differential gain 7 Electric motor 8 Elastic shaft 9 Load machine 10 Torque generation coefficient T * Command torque u Control input torque Ts Axial torque φ Axial torque differential value estimated value ωo Torsional coefficient Resonance angular frequency ωm Motor speed ωl Load machine speed Tl Load disturbance ωc Cutoff frequency

[Equation 7]

Claims (2)

[Claims] 1. A method for controlling a command torque to follow a command torque while suppressing vibration of a shaft torque of a low-rigidity shaft connecting a load and a motor for driving the load, wherein an output value of a speed sensor attached to the motor is controlled. A soft observation means is provided to obtain the value of the shaft torque and its differential value by inputting, and a derivative of the estimated shaft torque is obtained by proportionally integrating the deviation between the command torque and the estimated value of the shaft torque. A shaft torque control method for an electric motor drive system, wherein a torque command is obtained by applying a value. 2. A method of estimating a torsional shaft torque generated on an elastic shaft connecting a motor and a load and a differential value thereof, wherein a control input applied to the motor, an output signal of a motor speed sensor, a mechanical constant of a plant are arbitrarily set. By configuring the soft observer (3) of order 4 based on the specified cutoff frequency, the state variable (x
b) and the state variable (xc) are used as an estimated value of the axial torque and its differential value, and an axial torque estimation method for an electric motor drive system.