CN110662320A - Composite resonance heating circuit and frequency control method thereof - Google Patents

Composite resonance heating circuit and frequency control method thereof Download PDF

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Publication number
CN110662320A
CN110662320A CN201910902757.2A CN201910902757A CN110662320A CN 110662320 A CN110662320 A CN 110662320A CN 201910902757 A CN201910902757 A CN 201910902757A CN 110662320 A CN110662320 A CN 110662320A
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China
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unit
zero
voltage
crossing
resonant
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韦伟平
雷丽萍
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Dongguan Double Power Supply Technology Co Ltd
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Dongguan Double Power Supply Technology Co Ltd
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/06—Control, e.g. of temperature, of power
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

The invention discloses a composite resonance heating circuit, which comprises a power converter and a resonance heater, wherein alternating current voltage with adjustable frequency f is output between two output ends of the power converter; the heating loop also comprises a resonant heater, and the resonant heater comprises a near-end capacitor unit, a de-loop cable and a far-end resonant unit; wherein the near-end capacitor unit, the return cable, the far-end resonance unit and the return cable are connected in sequence, and the far-end resonance unit has a fixed partHaving a resonant frequency f01When the resonant heating circuit works, f is kept in the circuit01The composite resonance circuit can conveniently transmit high-frequency current to a far end to realize electromagnetic induction heating. The invention also provides a control method of the composite resonance heating circuit, and the working condition of the far-end resonance unit adjusts the frequency f of the sinusoidal alternating current output by the power converter, so that the far-end resonance unit can accurately work at the resonance point, and the circuit can obtain good resonance heating effect.

Description

Composite resonance heating circuit and frequency control method thereof
Technical Field
The invention belongs to the technical field of induction heating circuits, and particularly relates to a composite resonant circuit.
Background
Induction heating is an advanced heating technique that has advantages not found in conventional heating methods, such as: the induction heating technology is widely applied to the fields of smelting, casting, hot forging, welding, material surface heat treatment and the like at present, and becomes an indispensable technology in the industries of metallurgy, national defense, manufacturing and the like.
The development of induction heating technology has been widely used in more and more specific industrial scenarios to date. For example, in order to protect a steel structure and achieve the effects of water resistance, corrosion resistance and the like of the steel structure on the surface of a ship, a naval vessel, an airplane or other large steel structures, operators usually coat paint with corresponding functions on the surface of a steel structure body after the steel structure body is formed. Once the original paint layer is peeled off, damaged or aged, the original paint layer needs to be removed integrally and then coated again. In the process of removing the original paint layer, the induction heating technology becomes an application technology which is considered by operators preferentially due to the characteristics of high heating efficiency, no contact with a workpiece to be processed, strong controllability and the like.
The existing induction heating technology is generally used for constructing a circuit by adopting a series resonance principle in order to better adapt to the processing occasion of paint removal on the surface of a large-scale steel structure.
Please refer to fig. 1. When an induction heating circuit is constructed by using a series resonance principle, the circuit generally comprises a power supply E, a near-end transformer T1, a series capacitor C, a transmission cable L1, a far-end transformer T2 and an inductor L2 from the aspect of circuit principle; the power supply E, the near-end transformer T1, the series capacitor C, the transmission cable L1, the far-end transformer T2 and the inductor L2 are connected in sequence.
From the above circuit principle, when the circuit is in operation, the power supply E outputs an alternating voltage with a certain frequency, the series capacitor C is connected with the inductor L2 to form a series resonant structure, and the series resonant structure has its natural resonant frequency, and the magnitude of the natural frequency is determined by the magnitude of the capacitive reactance of the series capacitor C1 and the magnitude of the inductive reactance of the inductor L2.
When the frequency of the alternating voltage output by the power supply is equal to the natural resonant frequency of the series resonant structure, the series resonant structure resonates, and at the moment, the inductor L2 obtains the maximum current in the full frequency domain range, the current generates an alternating magnetic field, and further, induced electromotive force is generated on the surface of the workpiece to be processed, so that heating is realized.
However, as can be seen from the resonance characteristic of the series resonant circuit, when the circuit reaches the resonance point, a high-frequency alternating current with a large amplitude flows into both the series capacitor C1 and the inductor L2, and at this time, for the series capacitor C1, due to the defects of the existing capacitor manufacturing technology, the series capacitor C1 inevitably has a dielectric loss, which further causes a power loss on the series capacitor C1, which not only increases the reactive power in the circuit, but also generates a large amount of heat on the series capacitor C1, which seriously affects the stability of the circuit itself; in the case of the inductor L2, since the inductor L2 is a coil formed by winding a plurality of turns of conducting wires, when a high-frequency large current flows into the inductor L2, a local overcurrent phenomenon inevitably occurs due to the skin effect and proximity effect of the conductor, and further heat is generated in an overcurrent area, and the inductor L2 is burned out in a severe case. Since the circuit is applied to a high voltage environment, it is known from the resonance characteristic of the series resonant circuit that when the series resonant circuit is in a resonant state, the series capacitor C1 and the inductor L2 both have Q times of overvoltage with respect to the source voltage, and therefore, when the series resonant circuit is in a resonant state, not only a high frequency large current but also an overvoltage occurs to the series capacitor C1 and the inductor L2, so that the current and voltage resistance characteristics of the series capacitor C1 and the inductor L2 are very strict.
When the series resonance principle is adopted to apply the induction heating technology, from the structural principle level of the device, a power supply E, a near-end transformer T1 and a series capacitor C are commonly arranged at the near end close to an external three-phase network voltage port in the equipment, a far-end transformer T2 and an inductor L2 are arranged at the far end far away from the external three-phase network voltage port together, the movable far-end heater is manufactured, the near end and the far end are connected through a transmission cable L1, the far-end heater is convenient for an operator to move randomly, and heating and paint removal treatment is carried out on different area ranges of the surface of a large steel structure.
It can be seen from the above structural principle of the device that, due to the distributed inductance on the transmission cable L1, the current will lose a certain amount of energy on the transmission cable during the current transmission process, so the length of the transmission cable L1 will be very limited, which greatly limits the operating radius of the operator. Furthermore, because the power density of the far-end transformer T2 is too high, the far-end heater itself generates heat seriously, and therefore, a water cooling circulation system must be provided in the far-end heater at the same time, which results in a large volume, heavy weight, inconvenient movement of the far-end heater, and the whole induction heating device is very heavy and cannot obtain a good heating effect.
Disclosure of Invention
In order to solve the above problems, an object of the present invention is to provide a composite resonant heating circuit, which fully utilizes distributed parasitic inductance on a return cable, combines a series resonant structure and a parallel resonant structure to realize transmission of high frequency current at any distance, realizes resonance at a far-end resonant unit, and generates a high frequency alternating current to generate a high frequency alternating magnetic field to realize induction heating.
The composite resonant heating circuit is simple in structure, good in stability, convenient to control, light, handy, simple and convenient, and good in use experience.
Another objective of the present invention is to provide a control method for a composite resonant heating circuit, which is based on the composite resonant heating circuit, and utilizes the current signal and the voltage signal obtained from the heating main loop to determine the operating condition of the remote resonant unit, and further adjusts the frequency f of the sinusoidal alternating current output by the power converter according to the operating condition, so as to ensure that the remote resonant unit can accurately operate at the resonant point, and ensure that the circuit obtains a good resonant heating effect.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the invention provides a composite resonance heating circuit, which comprises a power converter and a resonance heater.
The power converter comprises a rectifying module, a filtering module, a voltage regulating module, an inverting module and a transformer, wherein the input end of the rectifying module is connected with an external three-phase network voltage; when the circuit works, the current on the primary side of the transformer is taken as a current signal, and the voltage at two ends of the parallel capacitor is taken as a voltage signal.
The resonant heater comprises a near-end capacitor unit, a return circuit removing cable and a far-end resonant unit, wherein the far-end resonant unit comprises a heating inductor and a parallel capacitor, and the heating inductor is connected with the parallel capacitor in parallel. One end of the near-end capacitor unit is connected with one output end of the power supply, the other end of the near-end capacitor unit is connected with one common end of the heating inductor and the parallel capacitor through a loop-removing cable, and the other common end of the heating inductor and the parallel capacitor is connected with the other output end of the power supply through another loop-removing cable; the remote resonance unit has a natural resonance frequency f01When the resonant heating circuit works, f is kept in the circuit01。
After the external three-phase network voltage is rectified, filtered, regulated, inverted and transformed by the transformer, the secondary side of the transformer is used for obtaining alternating voltage with adjustable voltage amplitude and adjustable frequency by the power converter.
In the resonant heating circuit provided by the invention, once the heating inductor and the parallel capacitor are set, the inductive reactance of the heating inductor and the capacitive reactance of the parallel capacitor can be known, and f can be further deduced01And the magnitude of the inductive reactance of the heating inductor and the magnitude of the capacitive reactance of the parallel capacitor together determine the magnitude of the quality factor Q of the remote resonant unit.
Adjusting the frequency f of the AC voltage, when f is obtained in the circuit01When the remote resonance unit reaches its resonance point, the remote resonance unit is connected with the remote resonance unitThe resonance characteristic of the coupled resonance circuit is known, at this time, the whole far-end resonance unit is resistive, the voltage at two ends of the far-end resonance unit reaches the maximum value in the full frequency domain range, and alternating current which is always Q times of the source current is obtained on the heating inductor.
Further, the near-end capacitance unit comprises at least one series capacitor and at least one gating switch; the series capacitors are arranged in one-to-one correspondence with the gating switches, and one end of each series capacitor is connected with one output end of the power converter; the other end of each series capacitor is connected with one end of a corresponding gating switch, and the other end of each gating switch is connected with a loop-removing cable; when the gating switch is switched on, the corresponding series capacitor is connected into the circuit, and when the gating switch is switched off, the corresponding series capacitor is disconnected with the circuit; the capacitive reactance of each series capacitor is not equal to each other.
From the circuit structure, the near-end capacitor unit and the far-end resonance unit are connected through a de-loop cable, and since distributed inductance is inevitably parasitic on the de-loop cable, f is obtained in the circuit01When the far-end resonant unit is wholly resistive, the circuit formed by the connection of the near-end capacitor unit, the distributed inductance parasitic on the de-loop cable and the far-end resonant unit is equivalent to an LCR series resonant circuit, and analysis shows that the equivalent LCR series resonant circuit also has a corresponding inherent resonant frequency f02The natural resonant frequency f02The magnitude of the resonant frequency is determined by the magnitude of the capacitive reactance of the near-end capacitive unit, the magnitude of the inductive reactance of the distributed inductance parasitic on the open-loop cable, the magnitude of the mutual inductance between the two open-loop cables, and the magnitude of the equivalent impedance of the far-end resonant unit.
After the circuit is built, the circuit is simultaneously provided with the inherent resonance of the remote resonance unitFrequency f01Natural resonant frequency f of equivalent LCR series resonant loop02When designing parameters of each electronic component in the circuit, f should be ensured02And f01The values are as close as possible, so that f is obtained in the circuit01In the process, the equivalent LCR series resonance circuit is also close to the resonance working point, so that the electric energy provided by the external three-phase network voltage can be ensured to be consumed by most resistive far-end resonance units and transmitted to an external workpiece in the form of an alternating magnetic field, a good heating effect is obtained, the switching devices in the inverter module can be ensured to work in a weak inductance or resistive state, the switching stress is reduced, and the switching loss is reduced.
Once the de-loop cable is selected, the inductive reactance of the distributed inductance parasitic on the de-loop cable and the mutual inductance between the two de-loop cables are determined, at the moment, the on-off conditions of different gating switches are changed, the series capacitors with different capacitive reactance sizes are connected into the circuit, and the inherent resonant frequency f of the LCR series resonant loop can be adjusted02Guarantee f02And f01The values are as close as possible.
Furthermore, the resonant heater also comprises a series inductor, the series inductor is arranged between the gating switch and the return-circuit removing cable, one end of the series inductor is connected with the gating switch, and the other end of the series inductor is connected with the corresponding return-circuit removing cable. The heating circuit is connected with a series inductor, so that on one hand, the influence of the inductive reactance of the heating inductor on the total inductive reactance of the heating circuit can be reduced as much as possible, and the resonant heater can accurately work at the required resonant frequency; on the other hand, the current signal and the voltage signal sampled in the circuit can accurately reflect the resonance condition of the remote resonance unit.
Furthermore, the resonant heating circuit further comprises an inverter controller, and the inverter controller comprises:
the voltage zero-crossing detection unit is used for detecting a zero-crossing point of a voltage signal;
the voltage zero-crossing pulse generating unit is used for generating corresponding pulses at the zero-crossing points of the voltage signals;
the current zero-crossing detection unit is used for detecting the zero-crossing point of the current signal;
the current zero-crossing pulse generating unit is used for generating corresponding pulses at the zero-crossing points of the current signals;
the phase comparison unit is used for comparing the phases between the two paths of input pulses;
a phase difference amplifying unit for amplifying the phase difference;
the PFM adjusting unit is used for adjusting the output frequency of the inversion module;
the inversion driving unit is used for generating control pulses aiming at the inversion module;
taking the current on the primary side of the transformer as a current signal, and taking the voltage at two ends of the parallel capacitor as a voltage signal; the current signal is connected to the current zero-crossing detection unit, and the output end of the current zero-crossing detection unit is connected with the current zero-crossing pulse generation unit; the current zero-crossing detection unit detects the zero crossing point of the current signal, the voltage signal is accessed to the voltage zero-crossing detection unit, and the output end of the voltage zero-crossing detection unit is connected with the voltage zero-crossing pulse generation unit; a voltage zero-crossing detecting unit detects a zero-crossing point of the voltage signal;
the output ends of the current zero-crossing pulse generating unit and the voltage zero-crossing pulse generating unit are connected into the phase comparison unit together, and the phase difference between the current zero-crossing pulse generating unit and the voltage zero-crossing pulse generating unit is compared;
the output end of the phase comparison unit is connected with the phase difference amplification unit, and the phase difference amplification unit amplifies the phase difference. The output end of the phase difference amplifying unit is connected with the PFM adjusting unit; the PFM adjusting unit outputs a PFM modulating signal aiming at the phase difference, and the output end of the PFM adjusting unit is connected with the inversion driving unit; the inversion driving unit generates inversion driving pulses according to the PFM modulation signal, and the inversion driving pulses are connected into the inversion module to correspondingly change the working condition of the inversion module.
Obtaining current signal on the primary side of the transformer, obtaining voltage signal at two ends of the parallel capacitor, comparing the phase difference between the two, if there is phase difference between them, it represents that the far-end resonance unit does not reach its resonance working point at this moment, using said phase difference to make PFM modulation, and making said PFM modulationFurther adjusting the working condition of the inversion module, and adjusting the frequency f of the sinusoidal alternating voltage output between the two output ends of the power converter at the next moment, so that the frequency f further approaches to the natural resonant frequency f01After continuous detection and adjustment, finally obtaining f ═ f01。
Compared with the prior art, the composite resonance heating circuit provided by the invention has the advantages that the resonance characteristic of parallel resonance is utilized, high-frequency large current can be conveniently obtained on the heating inductor, a good induction heating effect is obtained, the circuit structure is simple and stable, and the electrical performance is excellent.
Drawings
Fig. 1 is a schematic diagram of an induction heating technique implemented by applying the principle of series resonance in the prior art.
Fig. 2 is a schematic circuit diagram of a composite resonant heating circuit implemented in an embodiment of the present invention, in which:
m1 is a rectifying module, M2 is a filtering module, M3 is a voltage regulating module, and M4 is an inverting module;
c2 is series capacitance, K2 is a gate switch, L21 is series inductance, L22 is the total equivalent result of distributed inductance parasitic on the de-looping cable and mutual inductance generated between the two de-looping cables, C1 is parallel capacitance, and L1 is heating inductance.
Fig. 3 is a schematic structural diagram of a composite resonant heating device implemented in an embodiment of the present invention, in which E is a power converter, L21 is a series inductor, L22 is a return cable, C1 is a parallel capacitor, and L1 is a heating inductor.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In order to achieve the purpose, the technical scheme of the invention is as follows:
please refer to fig. 2.
In this embodiment, a composite resonant heating circuit is provided.
The resonant heating circuit comprises a heating loop, and the heating loop comprises a power converter and a resonant heater.
The power converter comprises a rectifying module M1, a filtering module M2, a voltage regulating module M3, an inverting module M4 and a transformer T, wherein the input end of the rectifying module M1 is connected with an external three-phase network voltage, the rectifying module M1, the filtering module M2, the voltage regulating module M3, the inverting module M4 and the transformer T are sequentially connected, and an alternating current voltage with adjustable frequency f is output between two output ends of a secondary side of the transformer T; when the circuit works, the current on the primary side of the transformer is taken as a current signal, and the voltage at two ends of the parallel capacitor is taken as a voltage signal.
The resonant heater comprises a near-end capacitor unit, a return circuit removing cable and a far-end resonant unit; the remote resonance unit comprises a heating inductor L1 and a parallel capacitor C1, and the heating inductor L1 is connected with the parallel capacitor C1 in parallel; one end of the near-end capacitor unit is connected with one output end of the power converter, the other end of the near-end capacitor unit is connected with one common end of the heating inductor L1 and the parallel capacitor C1 connected with a previous loop cable, the other common end of the heating inductor L1 and the parallel capacitor C1 is connected with the other output end of the power converter through a loop-removing cable, distributed inductors are generated on each loop-removing cable, mutual inductance is generated between the two loop-removing cables, and the total equivalent result is L22.
In the present embodiment, the near-end capacitor unit includes at least one series capacitor C2 and at least one gate switch K2; the series capacitors C2 are arranged in one-to-one correspondence with the gating switches K2, and one end of each series capacitor C2 is connected with one output end of the inverter module M3; the other end of each series capacitor C2 is respectively connected with one end of a corresponding gating switch K2, the other end of each gating switch K2 is connected with one end of a series inductor L21 in series, and the other end of the series inductor L21 is connected with a far-end resonance unit through a loop-through cable; when the gating switch K2 is switched on, the corresponding series capacitor C2 is switched in the circuit, and when the gating switch K2 is switched off, the corresponding series capacitor C2 is disconnected with the circuit; the capacitive reactance of each series capacitor C2 is not equal to each other.
Furthermore, the resonant heating circuit further comprises an inverter controller, and the inverter controller comprises:
the voltage zero-crossing detection unit is used for detecting a zero-crossing point of a voltage signal;
the voltage zero-crossing pulse generating unit is used for generating corresponding pulses at the zero-crossing points of the voltage signals;
the current zero-crossing detection unit is used for detecting the zero-crossing point of the current signal;
the current zero-crossing pulse generating unit is used for generating corresponding pulses at the zero-crossing points of the current signals;
the phase comparison unit is used for comparing the phases between the two paths of input pulses;
a phase difference amplifying unit for amplifying the phase difference;
the PFM adjusting unit is used for adjusting the output frequency of the inversion module;
the inversion driving unit is used for generating control pulses aiming at the inversion module;
taking the current on the primary side of the transformer T as a current signal, and taking the voltage at two ends of a parallel capacitor C1 as a voltage signal; the current signal is connected to the current zero-crossing detection unit, and the output end of the current zero-crossing detection unit is connected with the current zero-crossing pulse generation unit; the current zero-crossing detection unit detects the zero crossing point of the current signal, the voltage signal is accessed to the voltage zero-crossing detection unit, and the output end of the voltage zero-crossing detection unit is connected with the voltage zero-crossing pulse generation unit; a voltage zero-crossing detecting unit detects a zero-crossing point of the voltage signal;
the output ends of the current zero-crossing pulse generating unit and the voltage zero-crossing pulse generating unit are connected into the phase comparison unit together, and the phase difference between the current zero-crossing pulse generating unit and the voltage zero-crossing pulse generating unit is compared;
the output end of the phase comparison unit is connected with the phase difference amplification unit, and the phase difference amplification unit amplifies the phase difference. The output end of the phase difference amplifying unit is connected with the PFM adjusting unit; the PFM adjusting unit outputs a PFM modulating signal aiming at the phase difference, and the output end of the PFM adjusting unit is connected with the inversion driving unit;
please refer to fig. 3:
the embodiment also provides a device structure based on the composite resonant heating circuit.
The structure is that the power converter E and the series capacitor C2 are arranged near the near end of the external three-phase network voltage port, the parallel capacitor C1 and the heating inductor L1 are arranged together at the far end far away from the external three-phase network voltage port, and the near end and the far end are connected through a loop-removing cable L22.
It can be seen from the above structure principle that the device using the composite resonance heating circuit has a simple structure, the far-end resonance unit can normally work as long as the parallel capacitor C1 and the heating inductor L1 with large flow capacity and strong pressure resistance are reasonably selected, the whole size of the device is small, the heating problem of the device is not serious, the maintenance is convenient, the operation is convenient, and the user experience is good.
The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (9)

1. A composite resonance heating circuit comprises a power converter, wherein the input end of the power converter is connected with an external three-phase network voltage, and an alternating voltage with adjustable frequency f is output between two output ends of the power converter;
the resonant heating circuit is characterized by further comprising a resonant heater, wherein the resonant heater comprises a near-end capacitor unit, a return-circuit removing cable and a far-end resonant unit, one end of the near-end capacitor unit is connected with one output end of a power supply, the other end of the near-end capacitor unit is connected with one end of the far-end resonant unit through the return-circuit removing cable, and the other end of the far-end resonant unit is connected with the other output end of the power supply through the other return-circuit removing cable;
the remote resonance unit has a natural resonance frequency f01When the resonant heating circuit works, f is kept in the circuit01。
2. The composite resonant heating circuit of claim 1, wherein the remote resonant unit comprises a heating inductor and a parallel capacitor, two ends of the parallel capacitor are respectively connected to two de-loop cables, and the heating inductor is connected in parallel with the parallel capacitor.
3. The composite resonant heating circuit of claim 2, wherein the proximal capacitor unit comprises at least one series capacitor and at least one gate switch; the series capacitors are arranged in one-to-one correspondence with the gating switches, and one end of each series capacitor is connected with one output end of the power converter; the other end of each series capacitor is connected with one end of a corresponding gating switch, and the other end of each gating switch is connected with the parallel capacitor through a de-loop cable;
when the gating switch is switched on, the corresponding series capacitor is connected into the circuit, and when the gating switch is switched off, the corresponding series capacitor is disconnected with the circuit;
the capacitive reactance of each series capacitor is different from each other.
4. The composite resonant heating circuit of claim 3, wherein the resonant heater further comprises a series inductor, the series inductor is disposed between the gating switch and the return cable, one end of the series inductor is connected to the gating switch, and the other end of the series inductor is connected to the corresponding return cable.
5. The composite resonant heating circuit of claim 4, wherein the power converter comprises a rectifying module, a filtering module, a voltage regulating module, an inverting module and a transformer, the rectifying module, the filtering module, the voltage regulating module, the inverting module and the transformer are connected in sequence, an input end of the rectifying module is connected with an external three-phase network voltage, and an alternating voltage with an adjustable frequency f is output between two output ends of a secondary side of the transformer;
the current on the primary side of the transformer is taken as a current signal, and the voltage at two ends of the parallel capacitor is taken as a voltage signal.
6. The composite resonant heating circuit of claim 5, further comprising an inverter controller, the inverter controller comprising:
the voltage zero-crossing detection unit is used for detecting a zero-crossing point of a voltage signal;
the voltage zero-crossing pulse generating unit is used for generating corresponding pulses at the zero-crossing points of the voltage signals;
the current zero-crossing detection unit is used for detecting the zero-crossing point of the current signal;
the current zero-crossing pulse generating unit is used for generating corresponding pulses at the zero-crossing points of the current signals;
the phase comparison unit is used for comparing the phases between the two paths of input pulses;
a phase difference amplifying unit for amplifying the phase difference;
the PFM adjusting unit is used for adjusting the output frequency of the inversion module;
the inversion driving unit is used for generating control pulses aiming at the inversion module;
the current signal is connected to a current zero-crossing detection unit, and the output end of the current zero-crossing detection unit is connected with a current zero-crossing pulse generation unit; the voltage signal is connected to a voltage zero-crossing detection unit, and the output end of the voltage zero-crossing detection unit is connected with a voltage zero-crossing pulse generation unit;
the current zero-crossing pulse generating unit and the output end of the voltage zero-crossing pulse generating unit are connected to the phase comparing unit together;
the output end of the phase comparison unit is connected with the phase difference amplification unit, and the output end of the phase difference amplification unit is connected with the PFM regulation unit; the output end of the PFM regulating unit is connected with the inversion driving unit;
the output end of the inversion driving unit is connected with the inversion module, and the inversion driving unit generates inversion driving pulses to control the operation of the inversion module.
7. A method of frequency control of a composite resonant heating circuit, the method comprising the steps of:
s1: obtaining a signal: taking the current on the primary side of the transformer as a current signal, and taking the voltage at two ends of the parallel capacitor as a voltage signal;
s2: and (3) phase comparison: comparing to obtain the phase difference between the current signal and the voltage signal;
s3: frequency adjustment: and correspondingly adjusting the power converter according to the phase difference between the current signal and the voltage signal, and changing the frequency f of the alternating voltage output between the two output ends of the power converter so that the current signal and the voltage signal are in phase.
8. The frequency control method of a composite resonant heating circuit of claim 7, wherein said S2: the phase comparison specifically comprises:
s21: the current signal is accessed to a current zero-crossing detection unit, and the current zero-crossing detection unit detects the zero crossing point of the current signal; the voltage signal is accessed to a voltage zero-crossing detection unit, and the voltage zero-crossing detection unit detects the zero crossing point of the voltage signal;
s22: the current zero-crossing pulse generating unit generates a current zero-crossing pulse corresponding to the zero crossing point of the current signal, and the voltage zero-crossing pulse generating unit generates a voltage zero-crossing pulse corresponding to the zero crossing point of the voltage signal;
s23: the current zero-crossing pulse and the voltage zero-crossing pulse are connected into a phase comparison unit together, and the phase difference of the current zero-crossing pulse and the voltage zero-crossing pulse is compared;
s24: the phase difference is accessed to a phase difference amplifying unit, and the phase difference amplifying unit amplifies the phase difference.
9. The frequency control method of a composite resonant heating circuit of claim 7, wherein said S3: the frequency adjustment specifically comprises:
s31: the amplified phase difference is connected into a PFM regulating unit, and the PFM regulating unit outputs a PFM modulation signal aiming at the phase difference;
s31: the PFM modulation signal is connected to an inversion driving unit, the inversion driving unit generates an inversion driving pulse according to the PFM modulation signal, and the inversion driving pulse is connected to an inversion module to correspondingly change the working condition of the inversion module.
CN201910902757.2A 2019-09-24 2019-09-24 Composite resonance heating circuit and frequency control method thereof Pending CN110662320A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113784470A (en) * 2021-08-31 2021-12-10 河北工业大学 Induction heating system based on LLC

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113784470A (en) * 2021-08-31 2021-12-10 河北工业大学 Induction heating system based on LLC
CN113784470B (en) * 2021-08-31 2023-07-25 河北工业大学 LLC-based induction heating system

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