RU1800659C - Device for induction heating - Google Patents

Abstract

Usage: as a power source for electrotechnological installations, as well as as an electronic part of household induction cookers. The device comprises a single-phase rectifier on four diodes 1-4, connected to the output of the alternating voltage generator 5, with an inductive-capacitive filter on elements 6,7 and an inverter in the form of a series circuit from a parallel circuit formed by an inductor 8 and a compensating capacitor 9, and a key element (transistor) 10 with a control unit made in the form of two circuits, respectively consisting of a multivibrator 11, a voltage divider 12, a comparator 13. an amplifier 14, the output of which is connected to the control electrode 10, and a fixed delay circuit 15, an integrator 16 with a zero input, a second comparator 17, a shaper 18. 1 ill.

Description

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The invention relates to a converter technology and can be used as a power source for electrotechnological installations, in particular as a power source for domestic induction electric stoves.

The purpose of the invention is to expand the range of control of the output power of an induction heating device.

The drawing shows a diagram of a device for induction heating.

The device contains a single-phase rectifier on four diodes 1-4, connected by an input to the output of an alternating voltage generator B, and by an output connected to an input of an inductive-capacitive filter on inductor b and capacitor 7, the output of which is connected to the input of an inverter made in the form of a serial circuit from a parallel circuit formed by an inductor 8 and a compensating capacitor 9, and a key element 10, and a control unit, the output of which is connected to the control electrode of the key element. The control unit is made in the form of a multivibrator 11, the output of which through the voltage divider 12 is connected to the non-inverting input of the first comparator 13, the output of which is connected to the input of the amplifier 14, the output of the multivibrator is also connected to the input of the fixed delay element 15 and the first input of the integrator 16, the second input of which connected to the output of the fixed delay element, and the output to the non-inverting input of the second comparator 17, the output of which through the former 18 is connected to the inverting input of the first comparator. The inverting input of the second comparator is connected to the output of the unit for setting the output power level 19, the output of the amplifier serves as the output of the control unit.

A device for induction heating operates as follows.

The alternating voltage of the generator 5 is converted by the rectifier into an alternating voltage, having a ripple with a double frequency of the output voltage of the generator 5. The voltage from the output of the rectifier is filtered by the filter elements 6,7 and fed to the input of the inverter. The inverter key element 10 is turned on at positive half-cycles of the output alternating voltage (positive potential on the cover of the compensating capacitor 9 connected to the collector of the key element 10). The conduction interval of element 10 is adjustable and varies from a minimum value corresponding to a minimum output power level set by the fixed delay element 15 to half the period of the output alternating voltage. Multivibrator 11 generates pulses

a rectangular shape with a frequency of the output alternating voltage of the device equal to the resonance frequency of the load circuit of the elements 8.9. The pulses from the output of the multivibrator 11 are fed to the inputs of voltage divider 12, a fixed delay element 15 and the first input (zeroing input) of integrator 16. From the output of voltage divider 12, pulses of reduced amplitude are fed to

5 non-inverting input of the first comparator 13. From the output of the fixed delay element 15, the pulses shifted by the delay interval are fed to the second input of the integrator 16.

0 At the output of the integrator 16, in the interval of the pulse, the voltage increases linearly. This voltage is applied to the non-inverting input of the second comparator 17. The inverting input of the second comparator.

5 of the radiator 17, the voltage of the reference of the output power level is supplied from the output of the task unit 19. Until the voltage of the output of the integrator 16 is lower than the voltage from the output of the task block 19,

At the output of the second comparator 17, the voltage is negative, and at the output of the driver 18 is positive (close to zero). The output of the forming 18 is connected to the inverting input

5 of the first comparator 13. The voltage at the output of the first comparator 13 is positive. This voltage is amplified by the amplifier 14 and applied to the control electrode of the key element 10.

0 Key element 10 goes into open state. After the voltage at the output of the integrator 16 exceeds the voltage at the output of the unit for setting the level of output power 19, at the output of the second

5 of the comparator 17, the voltage will become positive. This will cause the first comparator 13 to switch, since the voltage level at its inverting input will exceed the voltage level at the non-inverting input. When switching the first comparator. 13, key element 10 transitions to the locked state. The integrator 16 is reset at negative half-cycles of the output variable

5 device voltages. At the same time, the voltage at the non-inverting input of the first comparator 13 is zero, and a small positive voltage is present at the inverting input, which keeps the first comparator 13 in a state of negative output voltage. As a result, key element 10 continues to be in a locked state.

By varying the voltage level at the output of the output power level setting unit 19, the on-state interval of the key element 10 on the output frequency period is adjusted from the minimum value determined by the delay interval of the element 15 to a maximum equal to half the period of the output alternating voltage of the device. In this case, the output frequency of the induction heating device remains unchanged, and the output power is regulated over a wide range.

The voltage divider 12 is based on a resistive circuit. Its application allows the use of a power source with a single voltage level in the control unit. Shaper 18 may be made based on a rectifier circuit. The output power level reference unit 19 is a variable gain resistive divider. The remaining elements of the control unit are based on integrated circuits 119 GG, 553, 554, 564 series.

Compared with the prototype, the inventive device for induction heating has a 1.8-1.9 times wider range of output power control. Deep power control in the inventive device is carried out without changing the output frequency. In this case, the minimum level of output power is determined by the duration of the minimum interval of the on state of the key element during the period of the output alternating voltage. The output power control range of the claimed device can reach 90-95% of the maximum output power level. The frequency control range of the output power of the device selected for the prototype, with frequency control, is limited by the requirements of the standard and the ability to go into the region of sound frequencies and is 50-55% of the maximum power level.

Claims (1)

SUMMARY OF THE INVENTION A device for induction heating, comprising a single-phase rectifier connected by an input to the output of an alternating voltage generator, and by an output connected to an input of an inductive-capacitive filter, the output of which is connected to an input of an inverter made in the form of a series circuit from a key element and a parallel circuit, formed by a compensating capacitor and inductor, and a control unit, the output of which is connected to the control electrode of the key element, characterized in that. that, in order to expand the range of regulation of the output power, the control unit is made in the form of a multivibrator, the output of which is connected via a voltage divider to the non-inverting input of the first comparator, with the input of the fixed delay element and the zero input of the integrator, the second input of which is connected to the output of the fixed delay element, and the output - with the non-inverting input of the second comparator, the inverting input of which is connected to the output of the unit for setting the output power level, and the output through the former n to the inverting input of the first comparator output connected to the input of an amplifier whose output is the output of the control unit.