RU2665671C2 - Pulse width modulation signals generation method for direct current motors control - Google Patents

Abstract

FIELD: power equipment.SUBSTANCE: invention relates to the power conversion equipment, namely to controlled direct current electric motors. Pulse width modulation signals generating method for the DC motors controlling, including the universal computer based control system, digital communication channel using the rs-485 start-stop interface protocol, rs-485 digital start-stop communication channel interface circuit with the electronic power key and the controlled DC motor, at that, the pulse signal generation for the DC motor control is carried out in the control computer itself, and the pulse control signal is transmitted via the communication channel with the rs-485 start-stop data transfer protocol, to the electronic power key, wherein the transmitted signal pulse start-stop units are divided into control action periods, in which series of the certain number of the start-stop interface protocol signal bytes is software-based generated, which in the integral level is the required current value, which sets the DC motor speed.EFFECT: technical result is the device design simplification, increase in its reliability.1 cl, 7 dwg

Description

The present invention relates to power conversion technology, namely, to controlled DC electric motors, and can also be used in various fields of production.

Known devices for generating PWM signals (pulse width modulation), containing the circuit formation, coding and power elements. They form signals based on individual generators, decoders, logic circuits, or individual software microprocessor devices. The output signals transmitted to the DC motor always have a digital format - signal 0 and signal 1. The term "PWM" defines the type of control signals - pulse.

However, known devices have the following disadvantages. They are implemented in the form of microcircuits, printed circuit boards, etc. electronics products. They take place, have the possibility of physical wear and tear, and breakdowns. The industry produces many control devices for DC motors. The cost of control devices is approaching the cost of engines. The control circuit performs the functions of: receiving commands from the upper-level program, generating the desired shape of the PWM signal, transmitting the pulse signal to the engine through an electronic key. These complex functions require command analysis systems, their decryption and conversion. Such devices add to the cost of control systems and reduce their reliability.

Of the known technical solutions, the closest in technical essence to the claimed method (prototype) is a PWM module and control device [L1] Figure 1 shows a block diagram of a prototype. It consists of a control system 1, a digital communication line 2, a printed circuit board of a signal conditioner 3, on which a microprocessor and an electronic key 4 are located. This system controls the motor 5.

In the proposed method, the microprocessor is excluded, thereby reducing cost and increasing reliability.

The figure 2 shows the functional diagram of the inventive method. It consists of a control system 6, a digital communication line 7 via the start-stop protocol rs-485 data exchange, and a power switch 8 with a circuit for interfacing with the signals of the rs-485 data bus. This system controls the motor 9.

The purpose of the claimed method is to reduce the cost of control systems, increase the reliability of products by eliminating complex microprocessor products.

This goal is achieved by the fact that the control system performs the function of generating signals for the motor. Since an electronic key requires a pulse signal, the signal transmission scheme is implemented in the standard start-stop digital industrial interface of the rs-485 protocol [L3], [L4].

The figure 3 shows a diagram of a pairing of an electronic key with a digital interface 10 of the protocol rs-485. Scheme 11 is highlighted by a dashed line and consists of diodes VD1 VD2, separating the positive and negative pulse signal to control the electronic key KT829. The key opens from the positive part of the impulse. Resistances R1 and R2 create the required current to open the electronic key with the positive part of the pulse, and the mode of closing the key with the negative part of the pulse. The electronic key controls the DC motor 12.

The electronic key is made on a transistor type KT829. Capacitor C1 smoothes the pulsed pulsations of an electronic switch on a DC motor. The supply voltage depends on the type of motor and the capabilities of the transistor, and in the above diagram it is possible up to 45 ... 100 volts depending on the type of electronic switch.

The digital channel of the start-stop protocol rs-485 is formed on the circuit by the usb-rs-485 converter. Any other existing computer interface is allowed that forms the digital channel of the rs-485 start-stop protocol.

To generate a PWM signal to a DC motor, in the minimum version, it is possible to transmit signal codes x00 to xFF (0000-0000 and 1111-1111 in bit record). The minimum ensemble of the 1st byte of the PWM signal consists of 9 signals x00, x01, x03, x07, x0F, x1F, x3F, x7F, xFF.

The figure 4 shows a sequence diagram of 5 bytes of code x07 and figure 5 presents a diagram of a similar sequence, 5 bytes of code x00.

A digital start-stop signal is generated from the start interval always starting with a logic level of 0. Next, 8 intervals are formed, each of 0 or 1, depending on the transmitted information. The information section ends with a stop interval, always a logical 1 signal.

In figures 4 and 5, the X-time is displayed along the axis, the Y-axis shows the voltage on the output bus relative to the common power bus. The average current is defined as the average current in the output bus. The average current in figures 4 and 5 is highlighted by a thickened line and its level is indicated.

Obviously, the average (integral) current at the load with a sequence of all x00 will be minimal. And the maximum current can be formed by transmitting a sequence of xFF signals. Intermediate currents form the signals of the existing ensemble for one byte.

Figure 6 shows the PWM signal variants of one byte. Calculation of the possible number of current values is carried out at clock intervals. The period consists of 8 bits, the 1st start interval and the 1st stop interval. Only 10. The signal transmission time can vary from the 1st clock interval - this is the start interval and transmission of code x00. Till 9 - the xFF code is transferred. The signal-to-period ratio (duty cycle ratio) varies from 1/10 to 9/10. A total of 9 output current values for setting the speeds of DC motors.

от лат. singularis - единственный, особенный, сингулярность в философии (от лат. singularis - единственный) - единичность существа, события, явления.To increase accuracy, it is necessary to form such an ensemble of signals that the average (integral) current is unique, i.e. singular.

from lat. singularis - the only, special, singularity in philosophy (from lat. singularis - the only one) - the unity of being, event, phenomenon.

Consider the formation of the average current for a series of signals of 8 bytes. The period for accounting for the average current consists of 8 bytes, these are 10 * 8 clock intervals. It turns out that the gradation of duty cycle varies from 8/80 to 72/80 on an interval of 8 bytes.

The figure 7 shows the gradation of currents for a series of 8 bytes. Using a series of 8 bytes increases the gradation of the average (integral) current to 8 * 9 = 72 steps. Using 80 bytes in a series increases the gradation to 80 * 9 = 720 steps. Thus, increasing the number of bytes in the series, the accuracy of the PWM signal generation can be increased to any given reasonable value.

To form the required engine speeds, it is assumed to use computers with the Windows operating system and transfer data blocks via the start-stop channel rs-485. Previously, the program forms data blocks into files. In the control mode, the program transfers data files to the rs-485 start-stop channel and the engine rotates at the required speed. The transfer of certain data files means the rotation of the DC motor at a certain speed and the absence of transfer - stops the rotation.

The software testing the control of the DC motor by this method is given in [L5]. The program comes with open source code and can be implemented in any programming language and operating system and shows the principle of generating a control signal. The electronic key is dependent on the engines used and the calculation of such electronic keys is given in [L6].

Information sources

1. DC motor control module (prototype) URL: http://ellab.su/catatog/bukd/bukdpt/

2. Engine control modules URL: http://electrum-av.com/en/silovye-moduli-so-vstroennym-upr/moduli-upravleniya-dvigatelvami.html

3. Description of the rs-485 standard: http://ru.wikipedia.org/wiki/RS-485

4. Interfaces rs-485: http.b: // www ookasutp.ru/Chapter2_3.aspx

5. Description of the DC motor control program http://www.shabronov.narod.ru/temp/tenis_bam_v2/

6. Calculation of transistor keys: http://life-prog.ru/1_40865_raschet-tranzistornih-klyuchey.html

7. Justification for using rs-485 with an explanation of expert comments: http: /shabronov_s2.dyn-dns.ru/temp/dp1_pat_uvedomlenie_sh/

Claims (1)

A method for generating pulse-width modulation signals for controlling DC motors, including a control system based on a universal computer, a digital communication channel using the RS-485 start-stop interface protocol, an RS-485 digital start-stop communication channel interface circuit with an electronic power switch, and controlled DC motor, characterized in that the formation of a pulse signal for controlling the DC motor is carried out in the control computer itself, and the pulse signal is controlled The line is transmitted via a communication channel with the RS-485 start-stop protocol for data transmission to an electronic power switch, and the pulse start-stop blocks of the transmitted signal are divided into control periods in which a series of a certain number of bytes of the start-stop interface protocol is generated by software signals, constituting in the integrated level the value of the required current, which sets the speed of rotation of the DC motor.

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