CN113251395A - Steam generator's controlling means based on electromagnetic induction heating technique - Google Patents

Steam generator's controlling means based on electromagnetic induction heating technique Download PDF

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CN113251395A
CN113251395A CN202110119290.1A CN202110119290A CN113251395A CN 113251395 A CN113251395 A CN 113251395A CN 202110119290 A CN202110119290 A CN 202110119290A CN 113251395 A CN113251395 A CN 113251395A
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CN113251395B (en
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杨波
周博文
杨东升
李广地
朱晓琳
贺志盈
唐庆志
王欢
魏宏岩
赵满红
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Qiyan Shenyang Technology Center Co ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B1/00—Methods of steam generation characterised by form of heating method
    • F22B1/28—Methods of steam generation characterised by form of heating method in boilers heated electrically
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B35/00—Control systems for steam boilers
    • 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

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Abstract

The invention discloses a control device of a steam generator based on an electromagnetic induction heating technology, which comprises a rectifying part, a filtering part, a direct current voltage stabilizing part, an inverting part, a steam generating part, a driving part, a control part and a system power circuit, wherein the rectifying part is connected with the filtering part; the control part comprises a chopping control circuit, a control circuit of the inverter part, an IGBT drive circuit, a voltage detection circuit, a current detection circuit, a voltage and current protection circuit, a reset circuit and an output signal detection circuit; the control part not only controls the on and off of the IGBT in the inverter part by the driving circuit, but also controls the over-current, over-voltage and under-voltage protection of the IGBT. The invention adopts an AC-DC-AC circuit structure to lead the device to have better output power regulation mode and higher working efficiency. In addition, the output intermediate frequency alternating current is monitored in real time, and the stability of the output amplitude and frequency is ensured.

Description

Steam generator's controlling means based on electromagnetic induction heating technique
Technical Field
The invention relates to the technical field of electromagnetic heating, in particular to a control device of a steam generator based on an electromagnetic induction heating technology.
Background
With the rapid development of industrial technologies, steam generators are widely used, but a considerable proportion of steam generators using coal or other non-renewable energy as fuel still exist. Although the country has encouraged to improve the thermal efficiency of steam generation of the conventional boiler, the efficiency of steam generation is low, and the internal devices are complicated and difficult to maintain, and various pollutants are generated by combustion, causing a lot of environmental pollution problems. People are beginning to research novel technologies with high energy utilization rate and environmental protection, and one of the technologies is the induction heating technology. The electromagnetic induction heating steam generator mainly applies an eddy current heating principle, and rapidly-changed alternating current passes through a coil surrounding the outside of the steam generator to generate an alternating magnetic field, so that eddy current is generated on the surface of metal to heat. Compared with the traditional steam generator, the electromagnetic induction heating type steam generator has the characteristics of energy conservation, high efficiency and no pollution, thereby having great practical significance for researching the steam generator.
The core of the steam generator based on the electromagnetic induction heating technology is mainly concentrated on a control device of the steam generator, the steam generator is mainly divided into low frequency, medium frequency and high frequency according to different application occasions, and the medium frequency control is adopted in most of applications. The traditional induction heating control device mostly adopts a parallel resonance type, the circuit design of a parallel resonance type controller is mature, but the control device is too complex, the connecting line between the control device and a load cannot be too long, and the applicable occasions are limited. In order to enable the wide application of the electromagnetic induction heating steam generator, an electromagnetic induction heating technology with high efficiency, low loss and wide application range is urgently needed.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention provides a control device for a steam generator based on electromagnetic induction heating technology.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a control device of a steam generator based on an electromagnetic induction heating technology comprises: the device comprises a rectification part, a filtering part, a direct-current voltage stabilizing part, an inversion part, a steam generation part, a driving part, a control part and a system power circuit;
the input of the rectification part is three-phase alternating current which is input into the rectification part for rectification; after the rectifying circuit works stably, the rectifying circuit is in short circuit, and the output direct current is filtered by the filtering part; after filtering, the direct-current voltage stabilizing part, namely a chopper circuit is accessed to perform DC-DC chopping conversion; chopping and then switching in the inversion part to perform DC-AC conversion to generate intermediate frequency alternating current; connecting the medium-frequency alternating current generated by the inverter part to a surface coil wound on the steam generating part, i.e. a steam generator;
the control part comprises (1) controlling the chopper circuit; (2) controlling the inversion part; the control part controls the drive circuit to control the on and off of the IGBT in the inverter part on one hand, and controls the over-current, over-voltage and under-voltage protection of the IGBT on the other hand.
The rectification part adopts a three-phase bridge type uncontrollable rectification circuit which comprises 6 power diodes, namely VD1, VD2, VD3, VD4, VD5 and VD 6; VD1, VD3 and VD5 are connected with a common cathode, VD4, VD6 and VD2 are connected with a common anode, the anode of VD1 is connected with the cathode of VD4, the anode of VD3 is connected with the cathode of VD6, and the anode of VD5 is connected with the cathode of VD 2;
when the AC side line voltage UA＞UBWhen the voltage is zero, the diodes VD1 and VD6 are conducted, and the voltage at the direct current side is UAB(ii) a When the AC side line voltage UA＞UCWhen the voltage is zero, the diodes VD1 and VD2 are conducted, and the voltage on the direct current side is UAC(ii) a When the AC side line voltage UB＞UCWhen the voltage is zero, the diodes VD3 and VD2 are conducted, and the voltage on the direct current side is UBC(ii) a Namely, the output direct current voltage is the maximum value of the alternating current side line voltage.
The filter part is characterized in that two filter capacitors C1 and C2 are connected to a direct-current voltage output end of a three-phase bridge type uncontrollable rectifying circuit, and two resistors R2 and R3 are respectively connected to the C1 and the C2 on the filter capacitors in parallel, so that the voltage sharing effect is achieved, and the voltages applied to two ends of the capacitors C1 and C2 are the same; besides, two voltage dividing resistors R4 and R5 are connected to the direct current voltage output end of the three-phase bridge type uncontrollable rectifying circuit and used for detecting direct current side voltage.
The direct current voltage stabilizing part adopts a Sepic chopper circuit to adjust the amplitude of the voltage on the direct current side of the input inversion part so as to adjust the output power on the direct current side;
the amplitude of the voltage at the direct current side of the input inversion part is adjusted by adjusting the duty ratio alpha of the chopper circuit, and the calculation formula of the alpha is as follows:
Figure BDA0002921395150000021
Figure BDA0002921395150000022
wherein E is the rectified output voltage; u shape0Outputting voltage for the chopper circuit; t is tonAnd toffThe turn-on and turn-off times of the IGBT, respectively.
The inverter part adopts a single-phase bridge current type inverter circuit, an electromagnetic induction coil for heating and a series compensation capacitor C are connected in series to form a load of the single-phase bridge current type inverter circuit, and in order to ensure the stability of steam generation, the resonance frequency of a control system fluctuates in a set pass band.
The control part comprises a chopping control circuit, a control circuit of the inverter part, an IGBT drive circuit, a voltage detection circuit, a current detection circuit, a voltage and current protection circuit, a reset circuit and an output signal detection circuit;
the output of the chopper control circuit is used as the input of the direct-current chopper circuit to control the on and off of an IGBT in the chopper circuit;
the output of the control circuit of the inversion part is divided into two aspects: on one hand, the output is used as the input of the IGBT driving circuit, the inverter circuit is controlled to complete the inversion process, and the voltage and current protection circuit is controlled to protect the IGBT; on the other hand, the voltage detection circuit and the current detection circuit are controlled to detect the voltage and the current output by the inverter;
the IGBT driving circuit comprises two parts: one part is IGBT drive of a chopper circuit, the other part is IGBT drive of an inverter circuit, the IGBT drive of the chopper circuit is controlled by an SG3525 chip, and the IGBT drive of the inverter circuit is controlled by a DSP;
the IGBT drive, the voltage detection circuit, the current detection circuit, the voltage current protection circuit, the reset circuit and the output signal detection circuit of the inverter circuit are all controlled by a DSP and are all connected with the output of the DSP.
A pin 8 of the SG3525 chip is a soft start access end and is also an inverted input end of the PWM comparator; a soft start capacitor is connected, and because the voltage at two ends of the capacitor can not change suddenly, when the pin 8 is at a low level, the reverse input end of the PWM comparator is also at a low level, the PWM comparator outputs a high level, the output of the PWM latch is also at a high level, and the high level is added to an output transistor through two NAND gates to ensure that the output transistor can not be conducted; when the soft start capacitor is charged to enable the pin 8 of the SG3525 chip to be at a high level, the SG3525 works;
voltage is sent to a pin 1 of SG3525, the pin 1 is the reverse input end of an error amplifier, and a feedback signal is connected to the pin to form closed-loop control; PWM waves generated by SG3525 pass through an isolation driving circuit and then drive an IGBT in a chopper circuit; the reference voltage is connected to the same-direction input end (pin 2) of the error amplifier, and the sampling voltage of the output voltage is added to the reverse input end of the error amplifier; when the output voltage is increased, the output of the error amplifier is reduced, the high level time of PWM output is also prolonged, the on-time of the IGBT tube is shortened, and the steady state is realized.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in:
1. the control device of the steam generator based on the electromagnetic induction heating technology adopts an AC-DC-AC circuit structure, so that the device has a better output power regulation mode and higher working efficiency. The hardware control device monitors the output intermediate frequency alternating current in real time, and guarantees the stability of the output amplitude and frequency. Meanwhile, due to the existence of the protection and detection circuit, the safety and the stability of the device are greatly improved.
2. The rectifier part adopts three-phase alternating current input, adopts a three-phase uncontrollable rectifying circuit, is different from the traditional controllable rectifying circuit, has higher circuit power factor, is connected with a current limiting resistor at the direct current side to prevent the direct current side from overlarge current, is short-circuited after the rectifier works stably, and filters the output direct current through a filter capacitor.
3. The chopper circuit adopts a buck-boost chopper circuit, is mainly used for providing direct current with stable amplitude for an inverter circuit and transmitting the direct current to the inverter, is different from the conventional steam generator power supply circuit in that alternating current power measurement and regulation is adopted, and the invention changes the duty ratio of the chopper circuit to control the output voltage of a direct current side by using a direct current side power regulation mode so as to change the input voltage of the inverter and further change the output power. Meanwhile, the influence of the chopper circuit added with a power switch device on the circuit is reduced as much as possible.
Drawings
Fig. 1 is a schematic structural diagram of a control device of a steam generator based on an electromagnetic induction heating technology according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an AC-DC rectifying and filtering circuit according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a DC-DC chopper circuit in an embodiment of the present invention;
FIG. 4 is a schematic diagram of the operation of an inverter according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a power circuit in an embodiment of the invention;
FIG. 6 is a schematic diagram of a chopper control circuit in an embodiment of the present invention;
FIG. 7 is a schematic diagram of an IGBT drive circuit according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of a voltage and current detection circuit according to an embodiment of the present invention;
FIG. 9 is a schematic diagram of an over-voltage and current protection circuit according to an embodiment of the present invention;
FIG. 10 is a schematic diagram of an under-voltage circuit according to an embodiment of the present invention;
FIG. 11 is a schematic diagram of a reset circuit in an embodiment of the invention;
FIG. 12 is a schematic diagram of a synchronous signal conversion circuit according to an embodiment of the present invention;
fig. 13 is a schematic circuit diagram of a steam generating part according to an embodiment of the present invention.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
As shown in fig. 1, the structure of the control device of the steam generator based on the electromagnetic induction heating technology in the present embodiment includes: the device comprises a rectification part, a filtering part, a direct-current voltage stabilizing part, an inversion part, a steam generation part, a driving part, a control part and a system power circuit;
the input of the rectification part is three-phase alternating current which is input into the rectification part for rectification; after the rectifying circuit works stably, the rectifying circuit is in short circuit, and the output direct current is filtered by the filtering part; after filtering, the direct-current voltage stabilizing part, namely a chopper circuit is accessed to perform DC-DC chopping conversion; chopping and then switching in the inversion part to perform DC-AC conversion to generate intermediate frequency alternating current; connecting the medium-frequency alternating current generated by the inverter part to a surface coil wound on the steam generating part, i.e. a steam generator;
the control part comprises (1) controlling the chopper circuit; (2) controlling the inversion part; the control part controls the drive circuit to control the on and off of the IGBT in the inverter part on one hand, and controls the over-current, over-voltage and under-voltage protection of the IGBT on the other hand.
In this embodiment, the rectifying portion adopts a three-phase bridge type uncontrollable rectifying circuit, as shown in fig. 2, so that no three-phase half-controlled or full-controlled rectifying circuit is adopted, the circuit controls the output voltage of the circuit by controlling the firing angle, and thus the power factor of the circuit is low, and the harmonic amplitude changes along with the firing angle, which is easy to pollute the circuit.
The three-phase bridge type uncontrollable rectifying circuit comprises 6 power diodes which are respectively VD1, VD2, VD3, VD4, VD5 and VD 6; VD1, VD3 and VD5 are connected with a common cathode, VD4, VD6 and VD2 are connected with a common anode, the anode of VD1 is connected with the cathode of VD4, the anode of VD3 is connected with the cathode of VD6, and the anode of VD5 is connected with the cathode of VD 2;
when the AC side line voltage UA＞UBWhen the voltage is zero, the diodes VD1 and VD6 are conducted, and the voltage at the direct current side is UAB(ii) a When the AC side line voltage UA＞UCWhen the voltage is zero, the diodes VD1 and VD2 are conducted, and the voltage on the direct current side is UAC(ii) a When the AC side line voltage UB＞UCWhen the voltage is zero, the diodes VD3 and VD2 are conducted, and the voltage on the direct current side is UBC(ii) a Namely, the output direct current voltage is the maximum value of the alternating current side line voltage.
The filtering part is formed by connecting two filtering capacitors C1 and C2 at the direct current voltage output end of the three-phase bridge type uncontrollable rectifying circuit, and plays a role in filtering on the direct current side as shown in figure 2. Two resistors R2 and R3 are respectively connected in parallel to the filter capacitors C1 and C2 to play a role in voltage sharing, so that voltages applied to two ends of the capacitors C1 and C2 are the same; besides, two voltage dividing resistors R4 and R5 are connected to the direct current voltage output end of the three-phase bridge type uncontrollable rectifying circuit and used for detecting direct current side voltage. In fig. 2, R1 is a current limiting resistor for limiting the charging current of the capacitor and preventing the rectifier from overcurrent. The switching function on both sides of R1 is to short-circuit R1 after the converter has been operating steadily.
When the current of the rectifying part is continuous, and the loss of the switching tube is not considered, the rectifying part outputs voltage:
Ud＝2.34Uin (1)
Ud＝2.34×380＝889.2 (2)
in the formula: u shapedRepresents the dc side voltage after rectification; u shapeinRepresenting the input three-phase ac phase voltages.
Figure BDA0002921395150000051
In the formula: the peak value of the voltage born by the diode is UFM。
Considering safety factors, a certain safety margin is generally selected, which is 3 times of the peak value of the reverse voltage, so that:
Uvd＝3×537.32＝1611.96 (4)
in the formula of UvdIs the inverse peak voltage.
Since the circuit in this embodiment requires the final output power to be 6K, when considering the switching tube loss, U isdTaking 880, and setting η of the circuit to 0.85, then output current:
Figure BDA0002921395150000052
in the formula IdIs the output rectified current.
The current is therefore:
Figure BDA0002921395150000061
in the formula IvdIs the current flowing through the diode;
also in view of the safety margin, here again 3 times the diode current rating margin is taken as the current peak:
Figure BDA0002921395150000062
in summary, the rectifier diode of the present embodiment should be selected to be 20A/1700V.
The direct current voltage stabilizing part adopts a Sepic chopper circuit to adjust the amplitude of the voltage on the direct current side of the input inversion part so as to adjust the output power on the direct current side;
in this embodiment, fig. 3 shows the principle of the dc chopper circuit, since the output of the rectifier circuit is dc power, and for convenience, the dc power is shown as a dc power supply, and since the last output terminal is directly supplied to the input terminal of the inverter portion, the equivalent load portion is not shown in fig. 3. The circuit is a Sepic chopper circuit, and the basic working principle is as follows: when V is in an on state, the E-L1-V loop and the C1-V-L2 loop are conducted simultaneously, and L1 and L2 store energy. When V is in off state, E-L1-C-VD-load circuit and L2-VD-load circuit are conducted simultaneously, in this stage E and L1 supply power to load and charge C, and the energy stored in C is transferred to L2 when V is in on state.
The amplitude of the voltage at the direct current side of the input inversion part is adjusted by adjusting the duty ratio alpha of the chopper circuit, and the calculation formula of the alpha is as follows:
Figure BDA0002921395150000063
Figure BDA0002921395150000064
wherein E is the rectified output voltage; u shape0Outputting voltage for the chopper circuit; t is tonAnd toffThe turn-on and turn-off times of the IGBT, respectively.
In this embodiment, the dc voltage output by the rectifying circuit is 880, and the voltage finally output to the inverter is 600, so that the duty ratio α of the dc chopper circuit needs to be adjusted, and with the above formula, the formula of α can be derived as:
Figure BDA0002921395150000065
therefore, the duty ratio of the circuit is only required to be adjusted and set to be 0.59, so that stable direct current with the amplitude of 600 can be generated and transmitted to the inversion part.
The inverter part adopts a single-phase bridge current type inverter circuit, as shown in fig. 4, an electromagnetic induction coil for heating and a series compensation capacitor C are connected in series to form a load of the single-phase bridge current type inverter circuit, and in order to ensure the stability of steam generation, the resonance frequency of a control system fluctuates in a set pass band.
In this embodiment, as shown in fig. 4, a resistor R and an inductor L are connected in series to form an equivalent load of the induction coil. The compensation capacitor C is connected in series because the power factor is low. The capacitors C and L, R form a series resonant circuit. The bridge circuit has four bridge arms, and can be seen as being formed by combining two half-bridge circuits. The bridge arms 1 and 4 are used as one pair, the bridge arms 2 and 3 are used as the other pair, the two bridge arms in the pair are conducted simultaneously, and the two pairs are conducted for 180 degrees alternately. In the figure, VD1 and VD4, V1 and V4, VD2 and VD3, V2 and V3 are sequentially and alternately conducted.
In order to ensure that the resonant frequency of the system can fluctuate within a set range in the circuit, the circuit is generally represented by a passband, wherein the system frequency is required to be above 19kHz in order to ensure the stability of the generated steam, the resonant frequency of the circuit is 20kHz, and the bandwidth is 2 kHz. Therefore, the method comprises the following steps:
Figure BDA0002921395150000071
in the formula: omega0Representing the resonant frequency of the circuit; Δ ω represents the frequency bandwidth; q is the quality factor of the circuit.
The amplitude of the direct current voltage transmitted to the inverter circuit through the DC-DC chopper circuit is about 600, when the circuit works stably, at least a certain margin is selected, and the margin is uniformly set to be 2 times, namely about 1200, so that the direct current voltage is represented by the formula:
Figure BDA0002921395150000072
Figure BDA0002921395150000073
can deduce IvtThe expression of (a) is:
Figure BDA0002921395150000074
in the formula: p is the power to be output; cos phi is the power factor of the circuit; u, I are the effective values of the inverter output voltage and current; i isvtIs the effective value of the current flowing through the thyristor; u shapelIs the effective value of the load voltage.
For safety reasons, the capacity is also 2 times, and through the analysis, the IGBT tube of 40A/1200V of the Megner company is finally determined and selected, and the model is MBQ40T120 FDS.
In this embodiment, the system power supply circuit provides 15V voltage for the over-voltage and over-current protection circuit and the detection circuit, provides 5V voltage for the IGBT driving circuit, and designs a system power supply with different voltage output values, as shown in fig. 5, where the input voltage is an ac voltage, a fuse F is connected to the positive electrode of the input terminal, and a switch S1 is connected to the negative electrode, so that when the input phase voltage has faults such as short circuit, the input terminal can be timely disconnected, damage to the rear-end circuit device is prevented, and the safety of the circuit is ensured. In the embodiment, a gold sun LH10-10A05 alternating current-direct current conversion power supply is adopted, in order to be isolated from a back-end circuit, capacitors C7, C9, C13 and C15 are connected, the capacitors pass through filter capacitors C2 and C5, resistors R3 and R4 are connected in parallel to two ends of the filter capacitors C2 and C5, the effect of carrying out voltage equalization on the filter capacitors is achieved, the principle of the back part circuit is basically the same through inductors L1 and L2, and finally the voltage value required by the system is obtained through clamping diodes D1 and D2.
The control part comprises a chopping control circuit, a control circuit of the inverter part, an IGBT drive circuit, a voltage detection circuit, a current detection circuit, a voltage and current protection circuit, a reset circuit and an output signal detection circuit;
the output of the chopper control circuit is used as the input of the direct-current chopper circuit to control the on and off of an IGBT in the chopper circuit;
the output of the control circuit of the inversion part is divided into two aspects: on one hand, the output is used as the input of the IGBT driving circuit, the inverter circuit is controlled to complete the inversion process, and the voltage and current protection circuit is controlled to protect the IGBT; on the other hand, the voltage detection circuit and the current detection circuit are controlled to detect the voltage and the current output by the inverter;
the IGBT driving circuit comprises two parts: one part is IGBT drive of a chopper circuit, the other part is IGBT drive of an inverter circuit, the IGBT drive of the chopper circuit is controlled by an SG3525 chip, and as shown in figure 6, the IGBT drive of the inverter circuit is controlled by a DSP;
the IGBT drive, the voltage detection circuit, the current detection circuit, the voltage current protection circuit, the reset circuit and the output signal detection circuit of the inverter circuit are all controlled by a DSP and are all connected with the output of the DSP.
In fig. 6, the power input terminal is 15V, and the pin 8 of the SG3525 chip is both a soft start access terminal and an inverted input terminal of the PWM comparator; a soft start capacitor is connected, and because the voltage at two ends of the capacitor can not change suddenly, when the pin 8 is at a low level, the reverse input end of the PWM comparator is also at a low level, the PWM comparator outputs a high level, the output of the PWM latch is also at a high level, and the high level is added to an output transistor through two NAND gates to ensure that the output transistor can not be conducted; when the soft start capacitor is charged to enable the pin 8 of the SG3525 chip to be at a high level, the SG3525 works;
voltage is sent to a pin 1 of SG3525, the pin 1 is the reverse input end of an error amplifier, and a feedback signal is connected to the pin to form closed-loop control; PWM waves generated by SG3525 pass through an isolation driving circuit and then drive an IGBT in a chopper circuit; the reference voltage is connected to the same-direction input end (pin 2) of the error amplifier, and the sampling voltage of the output voltage is added to the reverse input end of the error amplifier; when the output voltage is increased, the output of the error amplifier is reduced, the high level time of PWM output is also prolonged, the on-time of the IGBT tube is shortened, and the steady state is realized.
The IGBT driving circuit in this embodiment is, as shown in fig. 7, an M57959L type IGBT driver by mitsubishi corporation, which has a desaturation detection and protection link inside the driver, and is capable of turning off the IGBT at a fast response but slow speed when an overcurrent occurs, and giving a fault signal to an external circuit. The logic control signal is input by a pin 13, the resistance values of the resistors R1 and R2 are basically fixed, the diode D1 is a fast recovery diode, and the bidirectional voltage stabilizing diodes D2 and D3 prevent the grid and the emitter of the IGBT from breaking down to damage the circuit. The required input voltage of the driver is 5V, the positive driving voltage output outwards is +15V, and the negative driving voltage is-10V.
The voltage and current detection circuit diagram in this embodiment is shown in fig. 8, wherein a hall voltage sensor CHV-25P/500V is applied to a sampling circuit of the voltage detection circuit, and the sensor can electrically isolate an analog signal at an input end from a digital signal at an output end, and can output an output voltage of-5V- + 5V. Because the DSP can only detect the voltage signal, the input signal is changed into a voltage of-2.5- +2.5V through the sampling circuit formed by the resistors R1 and R2. The voltage allowed by the analog/digital conversion of the DSP is 0-3V, so in order to convert the voltage of-2.5-2.5V to 0-3V, the operational amplifier U1 constitutes a voltage bias circuit together with R3, R4, R5, and R6.
Since some harmonic interference is included in the circuit, a filtering process is required to prevent noise generated by the harmonic from affecting the a/D sampling result. The operational amplifier U2, the capacitors C1 and C2 and the resistor R7 which are correspondingly configured form a first-order active filter, the front-end input voltage is isolated from the sampling voltage by adopting a voltage tracking mode, and the cutoff frequency is further changed by changing the sizes of the R7 and the C1. In order to avoid damaging the digital/analog input interface due to too high voltage, a 3V voltage regulator diode D1 is arranged at the interface.
The current detection circuit samples current through a current transformer, and sends the detected current obtained by sampling to the current detection circuit shown in the figure. After the sampling current is filtered by a capacitor C6, the current input is converted into a voltage signal by sampling resistors R14 and R15, in order to prevent harmonic interference, the circuit is a second-order low-pass filter circuit which is formed by an operational amplifier TL028, capacitors C1 and C5, resistors R7 and R17 together, the voltage with the amplitude of +/-3V is obtained, and similarly, the voltage can be identified by the A/D of a DSP, and two inverters are formed by the operational amplifiers TL0821 and TL0822, resistors R1, R2, R3, R5 and R16 and a slide rheostat R, so that the voltage of 0-3V is obtained. Also, a zener diode D1 is designed at the interface for circuit safety considerations.
As shown in fig. 9, the voltage-current protection circuit in this embodiment is configured to convert an ac voltage obtained by feedback into a dc voltage by forming a diode uncontrollable rectifying circuit through four diodes D1, D2, D3, and D4. And voltage drop is generated on the slide rheostat R1 and R2 through filtering of the capacitor C and is transmitted to an operational amplifier TL082, wherein the reference voltage of the homodromous input end is 15V, and the reverse end is 3V. When the output voltage is too high, the voltage of the non-inverting input terminal of the comparator becomes small, and when the output voltage is less than the reference voltage of the inverting input terminal by 3V, the comparator sends a low level, and at this time, the light emitting diode connected in series with R5 lights up as a fault display lamp, and then an interrupt signal is transmitted to the I/O port of the DSP through the operational amplifier TL 0821. The principle of the overcurrent protection is basically the same as that of the overvoltage protection, and therefore, the description thereof is omitted.
The undervoltage protection circuit in this embodiment is implemented by using an operational amplifier circuit, as shown in fig. 10, in which the voltage at the input terminal is 15V, and after the zener diode D1 is connected, the voltage is sent to the 1 terminal of the comparator Ua, and as with the overvoltage and current protection circuit, when an undervoltage fault occurs, the voltage drop at the forward input terminal starts to decrease, and when the voltage is lower than the reference voltage 3V at the reverse input terminal 2, the comparator outputs a low level, and the light emitting diode connected in series with the capacitor C2 is turned on, and transmits the generated fault signal to the DSP through the operational amplifier Ub, and performs corresponding processing.
In this embodiment, as shown in fig. 11, the reset circuit is configured such that the reset signal is completed by an interrupt subroutine of the DSP by transmitting a low level signal to the DSP. In the reset circuit, the resistors R4 and R7 charge the capacitor C2, when the capacitor charge reaches a certain value, the voltage at 5 end is always higher than the voltage at 4 end, and the output of the comparator U1 is high level. When restart is pressed, the SR terminal is at low level, the capacitor C2 discharges through the resistor R7, the 5 terminal voltage drops, and when the voltage is lower than the 4 terminal voltage, the comparator U1 outputs low level to be transmitted to the DSP.
In this embodiment, the synchronizing signal converting circuit is capable of tracking the frequency as shown in fig. 12, and in order to track the frequency, it is necessary to convert the current signal into a voltage signal having the same frequency. In the figure, a current signal is converted into a voltage signal through sampling resistors R1 and R2, the voltage signal is converted into a square wave signal with the same frequency through a voltage stabilizing diode D1, capacitors C3, C4, C5, C6 and C7, and resistors R3 and R4, the square wave signal is transmitted to AMC1200 for optical coupling isolation, and an analog signal is isolated from a digital signal. Finally, the signal generated by the isolation is filtered by a first-order low-pass filter circuit consisting of an operational amplifier, a capacitor C11 and a resistor R8, and is sent to an eCAP module of the DSP for calculation.
In this embodiment, the schematic diagram of the steam generating part is shown in fig. 13, the medium frequency alternating current generated by the above part is sent to the high pressure boiler surrounded by the coil, and the electromagnetic induction law shows that the high speed changing electric field will generate the high speed changing magnetic field, which will generate vortex on the metal surface, and make the boiler raise the temperature rapidly, and make the pressure in the boiler higher than the standard pressure, when the water in the boiler exceeds 100 ℃, it will start to vaporize, and generate steam, and as long as the cut-off of the water inlet and the flow rate of the water entering the high pressure boiler are controlled, it can control whether to generate steam, and the flow rate of the generated steam.

Claims (7)

1. A control device of a steam generator based on an electromagnetic induction heating technology is characterized by comprising the following components: the device comprises a rectification part, a filtering part, a direct-current voltage stabilizing part, an inversion part, a steam generation part, a driving part, a control part and a system power circuit;
the input of the rectification part is three-phase alternating current which is input into the rectification part for rectification; after the rectifying circuit works stably, the rectifying circuit is in short circuit, and the output direct current is filtered by the filtering part; after filtering, the direct-current voltage stabilizing part, namely a chopper circuit is accessed to perform DC-DC chopping conversion; chopping and then switching in the inversion part to perform DC-AC conversion to generate intermediate frequency alternating current; connecting the medium-frequency alternating current generated by the inverter part to a surface coil wound on the steam generating part, i.e. a steam generator;
the control part comprises (1) controlling the chopper circuit; (2) controlling the inversion part; the control part controls the drive circuit to control the on and off of the IGBT in the inverter part on one hand, and controls the over-current, over-voltage and under-voltage protection of the IGBT on the other hand.
2. The control device of the steam generator based on the electromagnetic induction heating technology as claimed in claim 1, wherein the rectification part adopts a three-phase bridge type uncontrollable rectification circuit comprising 6 power diodes, respectively VD1, VD2, VD3, VD4, VD5 and VD 6; VD1, VD3 and VD5 are connected with a common cathode, VD4, VD6 and VD2 are connected with a common anode, the anode of VD1 is connected with the cathode of VD4, the anode of VD3 is connected with the cathode of VD6, and the anode of VD5 is connected with the cathode of VD 2;
when the AC side line voltage UA＞UBWhen the voltage is zero, the diodes VD1 and VD6 are conducted, and the voltage at the direct current side is UAB(ii) a When the AC side line voltage UA＞UCWhen the voltage is zero, the diodes VD1 and VD2 are conducted, and the voltage on the direct current side is UAC(ii) a When the AC side line voltage UB＞UCWhen the voltage is zero, the diodes VD3 and VD2 are conducted, and the voltage on the direct current side is UBC(ii) a Namely, the output direct current voltage is the maximum value of the alternating current side line voltage.
3. The control apparatus of the steam generator based on the electromagnetic induction heating technology according to claim 1, wherein: the filter part is characterized in that two filter capacitors C1 and C2 are connected to a direct-current voltage output end of a three-phase bridge type uncontrollable rectifying circuit, and two resistors R2 and R3 are respectively connected to the C1 and the C2 on the filter capacitors in parallel, so that the voltage sharing effect is achieved, and the voltages applied to two ends of the capacitors C1 and C2 are the same; besides, two voltage dividing resistors R4 and R5 are connected to the direct current voltage output end of the three-phase bridge type uncontrollable rectifying circuit and used for detecting direct current side voltage.
4. The control device of the steam generator based on the electromagnetic induction heating technology according to claim 1, characterized in that the direct current voltage stabilizing part adopts a Sepic chopper circuit to adjust the amplitude of the voltage on the direct current side of the input inversion part, so as to adjust the output power on the direct current side;
the amplitude of the voltage at the direct current side of the input inversion part is adjusted by adjusting the duty ratio alpha of the chopper circuit, and the calculation formula of the alpha is as follows:
Figure FDA0002921395140000021
Figure FDA0002921395140000022
wherein E is the rectified output voltage; u shape0Outputting voltage for the chopper circuit; t is tonAnd toffThe turn-on and turn-off times of the IGBT, respectively.
5. The control apparatus of a steam generator based on electromagnetic induction heating technology as claimed in claim 1, wherein the inverter part employs a single-phase bridge current type inverter circuit, the electromagnetic induction coil for heating is connected in series with the series compensation capacitor C to form a load of the single-phase bridge current type inverter circuit, and the resonant frequency of the control system fluctuates within a set pass band in order to ensure stability of steam generation.
6. The control device of the steam generator based on the electromagnetic induction heating technology according to claim 1, wherein the control part comprises a chopper control circuit, a control circuit of the inverter part, an IGBT driving circuit, a voltage detection circuit, a current detection circuit, a voltage current protection circuit, a reset circuit and an output signal detection circuit;
the output of the chopper control circuit is used as the input of the direct-current chopper circuit to control the on and off of an IGBT in the chopper circuit;
the output of the control circuit of the inversion part is divided into two aspects: on one hand, the output is used as the input of the IGBT driving circuit, the inverter circuit is controlled to complete the inversion process, and the voltage and current protection circuit is controlled to protect the IGBT; on the other hand, the voltage detection circuit and the current detection circuit are controlled to detect the voltage and the current output by the inverter;
the IGBT driving circuit comprises two parts: one part is IGBT drive of a chopper circuit, the other part is IGBT drive of an inverter circuit, the IGBT drive of the chopper circuit is controlled by an SG3525 chip, and the IGBT drive of the inverter circuit is controlled by a DSP;
the IGBT drive, the voltage detection circuit, the current detection circuit, the voltage current protection circuit, the reset circuit and the output signal detection circuit of the inverter circuit are all controlled by a DSP and are all connected with the output of the DSP.
7. The control device of the steam generator based on the electromagnetic induction heating technology as claimed in claim 6, wherein the pin 8 of the SG3525 chip is both the soft start input terminal and the inverting input terminal of the PWM comparator; a soft start capacitor is connected, and because the voltage at two ends of the capacitor can not change suddenly, when the pin 8 is at a low level, the reverse input end of the PWM comparator is also at a low level, the PWM comparator outputs a high level, the output of the PWM latch is also at a high level, and the high level is added to an output transistor through two NAND gates to ensure that the output transistor can not be conducted; when the soft start capacitor is charged to enable the pin 8 of the SG3525 chip to be at a high level, the SG3525 works;
voltage is sent to a pin 1 of SG3525, the pin 1 is the reverse input end of an error amplifier, and a feedback signal is connected to the pin to form closed-loop control; PWM waves generated by SG3525 pass through an isolation driving circuit and then drive an IGBT in a chopper circuit; the reference voltage is connected to the same-direction input end (pin 2) of the error amplifier, and the sampling voltage of the output voltage is added to the reverse input end of the error amplifier; when the output voltage is increased, the output of the error amplifier is reduced, the high level time of PWM output is also prolonged, the on-time of the IGBT tube is shortened, and the steady state is realized.
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