SU754626A1 - Apparatus for control of dirent current electric motor - Google Patents

Description

The invention relates to the field of electrical engineering, in particular to devices for controlling a direct current electric motor, and can be used in those industries where a high speed drive is required in a wide range of motor speed control, for example, in a machine tool industry.

A device for controlling a DC motor, consisting of a summing amplifier, two phase control units, logic circuits, a speed feedback sensor and a power converter, is known. In this case, a reference signal and a feedback signal from the output of the speed feedback sensor are fed to the inputs of the summing amplifier. The output of the summing amplifier is connected to the inputs of the phase control units. The outputs of the phase control units are connected to the inputs of logic circuits, and the outputs of the latter - to the inputs of the power converter. Such a structure of the electric drive allows in a relatively simple electrical circuit to obtain a wide range of control of the rotational speed of the executive engine [1].

2

The disadvantage of this drive, inherent in general electric drives with linear regulators, is a significant decrease in performance in the lower part of the control range. This is due to the fact

₅ that at low frequencies of rotation of the electric motor with a small initial mismatch, the amplitude of the control signal from the output of the summing amplifier is insufficient for fast processing of this error due to the inherent nonlinearities and inertia of water.

Thus, in electric drives with a linear regulator, there is a contradiction between the need to provide a wide range of speed control and high speed throughout the whole range.

The closest technical solution to the present invention is a device for controlling a DC motor, comprising a power converter, a speed sensor, a linear channel and a nonlinear control channel, a two-position switch, and a reference signal comparison unit for speed signals, to the output of which the channel inputs are connected

3

754626

four

linear and nonlinear control and two-position switch, and the outputs of the linear and nonlinear control channels through the output switching contacts of the switching unit are connected to the input of the power converter [2].

In the specified device, the control frequency of the rotational speed in which the limiting speed is ensured is insignificant. At low rotational frequencies with a small initial error in this drive only the linear control channel works, therefore, its speed does not differ from the speed of the drive with a linear regulator.

The purpose of the invention is to increase the speed of the reversing electric drive in a wide range of speed control.

This goal is achieved by the fact that in the device the nonlinear control channel is made in the form of a series-connected nonlinear function converter, which is the channel input, and an adder, the second input of which is connected to the output of the speed sensor.

FIG. 1 shows a block diagram of the device; in fig. 2 is a diagram of its operation (in Fig. 2a there is a diagram of a variation of a CW; Fig. 26 and in the diagrams of a change of ωτ and signals at the outputs of a linear 5 and nonlinear 6 control channels).

The device comprises a power converter 1 connected in series, connected to the electric motor 2, a speed feedback sensor 3 and a reference signal comparison element 4. In addition, a linear 5 and a nonlinear 6 control channels and a switch 7 for two positions are connected to the output of the .4 comparison element with their inputs. The channel 6 of the nonlinear control is made in the form of a series-connected nonlinear functional converter 8 and an adder 9, the second input of which is connected to the output of the speed feedback sensor 3. The output of the adder 9 is the output of the channel 6 nonlinear control. The outputs of the linear 5 and nonlinear 6 control channels through the output switching contacts of the switch 7 are connected to the input of the power Converter 1.

The drive works as follows.

At the initial time ίο (see Fig. 2a), the input of the comparison element 4 supplies a control signal corresponding to a predetermined rotational speed. At the output of the comparison element 4, a deviation signal appears, a larger response threshold Δ of the switch 7. Switch 7 is activated, closing the output contacts 10 and 11, and connects the output of the nonlinear control channel 6 to the input of the power converter 1.

When this to the input of the power Converter 1 is applied to the control signal

ν = Ρ (Δω) + Κω _τ , (1) where Ρ (Δω) is the nonlinear function of the deviation of the current rotation frequency;

Δω = AZ — ωτ ^{at the} output of the nonlinear functional converter 8;

From - the current frequency of rotation of the electric motor;

K - scale factor.

In expression (1), the nonlinear function

Ρ (Δω) is designed to create an engine acceleration, providing forced testing of the deviation of the controlled variable from the target, and the component Cat for ensuring equal speed in the whole range of speed control.

When the deviation decreases to Δ (at time ί s, Fig. 26), switch 7 is activated, closing contacts 12 and 11 and respectively, opening contacts 10 and 11, and connects the input of power converter 1 to the output of the linear control channel 5. Starting from 1z and as long as / Δω / <Δ, the power converter 1 is controlled by a linear, for example, PID control law.

The nonlinear function Ρ (Δω) is formed on the basis of the requirement of the maximum speed of the drive, and depends on its parameters, the specified quality of the transient process and the control range that determines the value of the switching threshold. Obtaining the analytical expression of the function Ρ (Δω) is difficult, usually it is constructed as a graph when synthesizing the structure of the electric drive using a digital computer or is selected experimentally. In the particular case, the function Ρ (Δω) can be approximated, for example, by the following expression:

(and! 51§п Δω with Δ </ Δω / <Δ ,; Ca51 £ p Δω with Δ, <ω / <Δ $, ..

υ3δΐ§ηΔω at / Δω /> L where Δι, Δg are the threshold values of the deviation at the output of the comparison element 4;

U, and g, iz are the control actions of constant amplitude, with U u <υ® <

<from; Δ <Δ ι <Δ ъ

The amplitudes of the control actions C ι Of and the corresponding deviation threshold values Δ, Δι, Δ g are determined during the synthesis of the drive structure; at the output of the linear control channel 5.

At the site ί ό — ί + the electric drive works out a control jump

at the entrance. The magnitude of the input action corresponds to the nominal frequency of 5

754626

6

engine cover. At the moment ίο Δ ω> Δ g, the switch 7, closing the contacts 11 and 10, connects to the input of the power converter 1 the output of the nonlinear 6 control channel, on which the control signal V is generated in accordance with the expression (1). In this case, the magnitude of the control signal is such that in the section ίο — ίι the electric motor acquires the maximum permissible acceleration ω ^ ,, and moves with this acceleration until the moment of time <.

At time ί <, the deviation Δω becomes less than Dg, the control signal V decreases in accordance with (2). The acceleration developed by the engine also decreases to ωι <ώβ »β and remains constant in the ί a — Hb section. At the time ί ζ deviation Δω <Δι, the control signal V decreases again, respectively, the acceleration developed by the engine 2, up to the value of Fa and remains constant in section ίζ — Ъ · At time 1c, the deviation Δω <Δ and switch 7, opening contacts 10 and 11 and closing contacts 12 and 11, connects the output of channel 5 to the input of the power converter. Under the action of the signal from the output of channel 5, the electric motor 2 switches to the braking mode, and when ώ »0 is reached - to the steady rotation mode.

In section 1z — ί <πρΗ, the constant transducer signal of the power converter 1 is controlled by the linear channel 5. At the moment управление +, the control at the input of the comparison element 4 is reversed. on nonlinear.

The reverse speed is the same. In the section ί <—ί _{5, the} engine is decelerated, and in the section — разβ accelerates with the maximum permissible acceleration.

& time ίβ / Δω / <Lg and there is a decrease in the value of the control signal V in accordance with the expression (2). Further, the movement is carried out similarly to the movement in areas ί a — ί +

In a similar way, the engine freezes down with a certain ₄₅ decrease in the driving force (Δ <</ Δω / <Δι, section ίβ — ίιο) ·

Thus, the formation of a nonlinear control as a sum of a signal from the output of a nonlinear functional converter and a signal proportional to the current rotational speed of the electric motor reduces the threshold value of the switch 7 and leads to a significant increase in the range of the speed control of the engine in which it operates

nonlinear control, providing high speed when developing control or disturbing influences. In this case, the greatest gain in speed is provided in the lower part of the range of regulation of the frequency of rotation of the wide-adjustable electric drive.

The parameters of the nonlinear functional converter 8 and the linear control channel 5 coefficients are selected so that when switching the control of the power converter 1 to linear control, the electric motor 2 goes to a predetermined rotational speed ω ₃ with allowable overshoot (in the particular case, the choice of the corresponding linear control channel coefficients an aperiodic process is provided.) At the same time, high speed of the electric drive is achieved in a wide range of regulation rotational speed of the executive engine.

The proposed device is actually quasi-optimal in speed, and to ensure speed close to optimal, it only needs one switch regardless of the order of the differential equation describing the system.

Claims (1)

Claim A device for controlling a DC motor, comprising a power converter, a speed sensor, a linear channel and a nonlinear control channel, a two-position switch and a block for comparing reference signals and speed feedback, the output of which is connected to the inputs of a linear and non-linear control channels and two switch positions, and the outputs of the linear and nonlinear control channels through the output switching contacts of the switching unit are connected to the input of the power converter, differing scheesya in that, in order to improve drive performance in a wide range of speed control, nonlinear control channel configured as a series-connected non-linear functional inverter being input kanala- and the adder, the second input of which is connected to the output of the speed sensor.