RU2514129C1 - System for controlling electrical heating temperature - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: system for controlling electrical heating temperature comprises an industrial controller as a control device; a multivibrator connected to the output of said controller; a line of power field-effect transistors controlled through the multivibrator from the discrete output of the controller and operating in pulsed mode as switching elements; a thermocouple connected to the input of the controller through a normalising transducer as a temperature sensor; controller and multivibrator power supply units; a three-phase step-down transformer which powers the power part of the system through a diode rectifier; a capacitor unit which smoothes voltage at the output of the rectifier.

EFFECT: preventing phase skew in the mains, preventing current surge, high accuracy of control, high energy efficiency by reducing power loss.

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Description

The invention relates to the field of electrical engineering, electronics and automatic temperature control.

Known temperature control devices during operation of industrial and domestic facilities, for example, the temperature controller of a heating device described in RF patent No. 93161, decl. November 9, 2009, IPC G05D 23/00, which contains a logic device with a control element, temperature sensors, a remote control device. The main disadvantage of this temperature controller is the low level of controlled power of the heaters, low accuracy of temperature control.

To increase the controlled power of the heater allows the "Station control electric heating circuit" (St. RF №26856, declared. 09.07.2002, IPC G05D 23/00), adopted as a prototype, including a circuit breaker, electrical heating switch (CE), microcontroller, module control and monitoring (MUK), current meter (IT), and temperature sensors (DT), characterized in that it is additionally equipped with an independent trip unit (HP) and limit temperature sensors (DPT), connected together in series, the number of which is more than 3 , as a CE she with holds a pair of contactless triacs (C), as IT transformers; moreover, the number of DTs is from 1 to 9, and the MUK consists of a control circuit C, a megohmmeter, a current magnitude control circuit, an HP emergency circuitry, and a solid-state motor circuit.

The disadvantages of this device are:

- the use of triacs operating in a pulse-width mode as switching elements, which leads to a distortion of the shape of the sinusoidal signal;

- when working on a powerful heater in such a device, a phase imbalance in the supply network will occur due to switching only two of the three phases using triacs;

- the occurrence of high currents when directly connecting a high-power heater to the mains.

A well-known object cannot be used to control heating elements of high power, because in a powerful heater with a stepwise change in the supply voltage due to triac control, large inrush currents will occur, which will lead to low regulation accuracy.

An electric heating temperature control system is proposed, which includes an industrial controller as a control device; multivibrator connected to its output; a line of powerful field-effect transistors controlled by a multivibrator as switching elements; a thermocouple connected to the controller input via a normalizing converter as a temperature sensor; power supplies for the controller and multivibrator; a three-phase step-down transformer that provides power to the power part of the system through a diode rectifier; block of capacitors, smoothing the voltage at the output of the rectifier. This system is characterized in that a step-down transformer is introduced into it and control is carried out by its secondary winding, and a line of field-effect transistors operating in a pulsed mode is selected as switching elements, thereby ensuring minimal power loss. A galvanic isolation is introduced into the system, separating the power unit from the information one, which provides protection for the controller.

The proposed device will eliminate the possibility of phase imbalance in the supply network through the use of a three-phase transformer. In addition, the transition to direct current control and the introduction of capacitors as smoothing filters will exclude current surges on the heating element in contrast to triac control. Also, the use of field effect transistors operating in a pulsed mode as controlled keys will save energy by reducing the power dissipated by them. The system can be easily expanded by connecting additional sensors and actuators to the controller, as well as easily integrated into the general automation system of the enterprise due to the presence of unified communication interfaces in the industrial controller.

To explain the described device in figure 1 shows its schematic diagram. Designations in the diagram:

C1-C3 - capacitors (smoothing filter);

C4 - capacitor 1 nF;

R1 - resistor 10 kOhm;

R2-R9, R11-R19 - 10 Ohm resistors;

R10 - resistor 100 kOhm;

Rн - heating element;

T1-T16 - a line of powerful field-effect transistors;

Tr1 - three-phase transformer;

VD1-VD6 - rectifier diodes;

VU1 - optocoupler;

DD1 - timer chip;

DD2, DD4 - power supplies for the controller and multivibrator;

DD3 - industrial controller;

DD5 - rated converter.

The proposed device operates as follows. In the initial state, the controller issues a multivibrator shutdown signal, field-effect transistors are closed, and the heater is turned off. Then, in accordance with the regulation algorithm, the controller, receiving information about the current temperature value from the temperature sensor (thermocouple) through the normalizing transducer, supplies an enable signal to the multivibrator, which gives out pulsed signals with a certain duty cycle to the gates of the field-effect transistors, thereby opening and including them heater. Using the two-position control algorithm as an example, the operation of the device will look as follows. If the current temperature is less than the set value, the controller turns on the multivibrator, and he, in turn, turns on the heater. As soon as the current temperature has become higher than the set one, the controller turns off the multivibrator and heater, the process repeats.

The described system is implemented as a prototype.

Thus, the proposed device allows you to:

- eliminate the possibility of phase imbalance in the supply network;

- eliminate inrush currents;

- increase the accuracy of regulation;

- increase energy efficiency by reducing power losses.

Claims (1)

An electric heating temperature control system, consisting of an electric heating switch, an industrial controller, a temperature sensor (thermocouple), characterized in that a three-phase transformer with primary windings fed from a three-phase network is introduced into it, midpoints of the secondary windings connected to each other and to the “case” , and diodes are included in each line of their output circuits, the cathodes of which are connected to the positive plates of the block of electrolytic capacitors, load resistance, and drains of the powerful field line transistors, their sources are connected to the “case”, and the gates are connected through low-resistance resistors to the output (3) of an integrated timer assembled according to the circuit of a standby multivibrator with an RC-timing circuit, powered by a first DC source connected to one of the phases of a three-phase network, and the input circuit of the multivibrator is connected through the galvanic isolation element to the collector of its transistor, the input circuit of the galvanic isolation is connected to the discrete input of the controller, to the analog input of which through the normalizing conversion The temperature sensor (thermocouple) is connected, the normalizing converter, controller and galvanic isolation optocoupler are supplied from the second DC source connected to one of the phases of the three-phase network.

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