LLC architecture induction heating circuit control method and system based on SPWM drive

Abstract

The present invention proposes a control method and system for an LLC-based induction heating circuit based on SPWM drive. The method comprises: using the voltage output value of the inverter circuit switching devices in the induction heating circuit as the voltage feedback value in the voltage outer loop control; processing the voltage input value and the voltage feedback value of the inverter circuit switching devices using PI control and outputting the processed values; using the current output value of the inverter circuit switching devices in the induction heating circuit as the current feedback value in the current inner loop control; modulating the SPWM waveform based on the output processed by PI control and the current feedback value, and using the modulated SPWM waveform to control the on and off of each switching device in the inverter circuit in the induction heating circuit. Using the modulated SPWM waveform to control the on and off of the inverter circuit switching devices in the induction heating circuit effectively suppresses high-order harmonics, promptly responds to current fluctuations caused by external system factors, accelerates the system current response speed, facilitates power regulation, and achieves the same frequency and phase of the coil currents through fine-tuning of the fundamental frequency.

Description

Technical Field

[0001] The present invention belongs to the technical field related to induction circuit control, and in particular relates to a control method and system for an LLC architecture induction heating circuit based on SPWM drive. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Induction heating technology has been used in industry since the early 20th century. With over a century of development, it has achieved significant economic and social benefits. Compared with traditional heating methods, induction heating offers higher efficiency and faster heating speeds, thereby reducing surface oxidation on workpieces. Induction heating is a non-contact method that prevents the infiltration of impurities during the heating process.

[0004] The development of induction heating technology is closely linked to the advancement of semiconductor devices and power electronics. Current induction heating equipment consists of three main components: a rectifier, an inverter, a load resonant structure, and a control unit. The rectifier module converts AC input into a DC source, which serves as the input for the inverter. The inverter module utilizes the principle of electromagnetic induction to heat the workpiece through a resonant load circuit.

[0005] Traditional induction heating power supplies use a series or parallel LC resonant load structure. To meet power output requirements, a medium-frequency transformer is added to the traditional IGBT series resonant full-bridge inverter to achieve impedance matching. However, the LLC resonant load structure omits the medium-frequency transformer. Compared with the LC resonant load structure, the LLC resonant load structure has a simpler structure, more flexible design, strong system robustness, low cost, and high efficiency, which has great advantages.

[0006] However, when using the LCC resonant load structure: 1. The system uses medium-frequency square waves to drive and control the on and off of the switching devices in the inverter circuit, which will cause the inverter output current to contain more third harmonics; 2. The medium-frequency square wave can only adjust the inverter switch once in one cycle. If the system has a sudden change in current due to electric sparks, short circuits, etc., such as a large current spike problem in the system, it exceeds the rated range of the medium-frequency square wave control and cannot respond in time within one cycle for dynamic suppression, and can only passively shut down for protection. Summary of the Invention

[0007] To overcome the deficiencies of the above-mentioned prior art, the present invention provides a control method and system for an LLC-based induction heating circuit based on SPWM drive. The SPWM wave is modulated based on the output current of the inverter circuit, and the modulated SPWM waveform is used to control the on and off of the inverter circuit switching devices in the induction heating circuit. This method can effectively suppress high-order harmonics and promptly respond to current fluctuations caused by external factors of the system. SPWM adjusts power through modulation index and achieves the same frequency and phase of the coil current by fine-tuning the frequency of the SPWM fundamental wave (modulation wave).

[0008] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions: a method for controlling an LLC architecture induction heating circuit based on SPWM drive, comprising:

[0009] The voltage output value of the inverter circuit switching device in the induction heating circuit is used as the voltage feedback value in the voltage outer loop control; the voltage input value and the voltage feedback value of the inverter circuit switching device are processed and outputted by using PI control;

[0010] The current output value of the inverter circuit switch device in the induction heating circuit is used as the current feedback value of the current inner loop control;

[0011] The SPWM wave is modulated according to the output after PI control processing and the current feedback value, and the modulated SPWM wave is used to control the on and off of each switching device of the inverter circuit in the induction heating circuit.

[0012] A second aspect of the present invention provides an LLC architecture induction heating circuit control system based on SPWM drive, comprising:

[0013] Voltage outer loop control module: uses the voltage output value of the inverter circuit switching device in the induction heating circuit as the voltage feedback value in the voltage outer loop control; uses PI control to process the voltage input value and voltage feedback value of the inverter circuit switching device and then outputs them;

[0014] Current inner loop control module: uses the current output value of the inverter circuit switching device in the induction heating circuit as the current feedback value of the current inner loop control;

[0015] Waveform modulation module: modulates the SPWM wave according to the output after PI control processing and the current feedback value, and uses the modulated SPWM wave to control the on and off of each switching device in the inverter circuit in the induction heating circuit.

[0016] The third aspect of the present invention provides a computer device, comprising: a processor, a memory and a bus, wherein the memory stores machine-readable instructions executable by the processor. When the computer device is running, the processor and the memory communicate via the bus, and when the machine-readable instructions are executed by the processor, a method for controlling an LLC architecture induction heating circuit based on SPWM drive is performed.

[0017] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, a method for controlling an LLC architecture induction heating circuit based on SPWM drive is executed.

[0018] One or more of the above technical solutions have the following beneficial effects:

[0019] The present invention utilizes a voltage outer loop and current inner loop control method. When the output current of the inverter circuit is distorted in the current inner loop, the SPWM wave is modulated and the modulated SPWM waveform is used to control the on / off switching of the inverter circuit switching devices in the induction heating circuit. This effectively suppresses higher harmonics, promptly responds to current fluctuations caused by external factors in the system, and accelerates the system current response speed. SPWM allows for convenient modulation to adjust power, while square wave inversion can only be triggered by phase shifting, resulting in increased harmonics. When multiple power supply heating coils are connected in parallel to heat the same workpiece, the fundamental (modulation) frequency of the SPWM can be adjusted to adjust the phase of the coil current, thereby achieving the same frequency and phase of the heating coil currents.

[0020] Advantages of additional aspects of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0022] Figure 1 This is the structure diagram of the existing induction heating power supply;

[0023] Figure 2 This is a simplified diagram of the LLC resonant circuit;

[0024] Figure 3 It is the equivalent circuit diagram of single-phase bridge SPWM inverter;

[0025] Figure 4 In the first embodiment, a pulse sequence is used instead of a sine wave;

[0026] Figure 5This is the SPWM wave modulation process in the first embodiment;

[0027] Figure 6 This is a schematic diagram of the current and voltage inner and outer dual-loop control in the first embodiment;

[0028] Figure 7 This is a diagram of the LCC simulation model in the first embodiment;

[0029] FIG8( a ) is a diagram of an SPWM wave driving signal in the first embodiment;

[0030] FIG8( b ) is a medium frequency square wave driving signal in the first embodiment;

[0031] Figure 9 This is the inverter output current waveform diagram in the first embodiment;

[0032] Figure 10 1 is a current waveform diagram of the parallel compensation capacitor in the first embodiment. DETAILED DESCRIPTION

[0033] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0034] It should be noted that the terms used herein are for describing particular embodiments only and are not intended to limit the exemplary embodiments according to the present invention.

[0035] In the absence of conflict, the embodiments of the present invention and the features thereof may be combined with each other.

[0036] Example 1

[0037] This embodiment discloses a control method for an LLC architecture induction heating circuit based on SPWM drive, including:

[0038] The voltage output value of the inverter circuit switching device in the induction heating circuit is used as the voltage feedback value in the voltage outer loop control; the voltage input value and the voltage feedback value of the inverter circuit switching device are processed and outputted by using PI control;

[0039] The current output value of the inverter circuit switch device in the induction heating circuit is used as the current feedback value of the current inner loop control;

[0040] The SPWM wave is modulated according to the output after PI control processing and the current feedback value, and the modulated SPWM wave is used to control the on and off of each switching device of the inverter circuit in the induction heating circuit.

[0041] like Figure 1The figure shows the main components of the current induction heating equipment. The rectifier module converts the AC input into a DC source as the input of the inverter. The inverter module uses the principle of electromagnetic induction to heat the workpiece through a resonant load circuit.

[0042] The SPWM method is a relatively mature and widely used PWM method. When narrow pulses of equal impulse but different shapes are applied to a link with inertia, the effect is essentially the same. The SPWM method, based on this theory, replaces the traditional LLC medium-frequency square-wave drive mode with a sine-wave-equivalent PWM waveform using the resonant frequency as the fundamental frequency, a higher switching frequency (e.g., 5 kHz) as the carrier frequency, and a sinusoidal pulse width. This SPWM waveform controls the on and off of switching devices in the inverter circuit.

[0043] like Figure 6 As shown, in this embodiment, an inner and outer dual-loop control mode of a voltage outer loop and a current inner loop is adopted. The basic principle of this control method is to control the output voltage of the inverter circuit through the voltage outer loop, and then control the output current of the inverter circuit through the current inner loop, thereby achieving stable control of the system.

[0044] When the inner loop current feedback circuit detects distortion in the inverter circuit's output current, it adjusts the intersection of the modulation wave and the carrier wave downward, thereby changing the pulse width of the SPWM wave and reducing the inverter circuit's output current spikes to suppress the distorted current moment, preventing current distortion from damaging and interfering with resonant components and the system. When multiple heating coils are connected in series, the SPWM modulation wave frequency can be adjusted to adjust the coil current phase, achieving the same frequency and phase as the coil currents.

[0045] The SPWM wave is composed of n pulse sequences within one cycle. When the current feedback circuit detects that the inverter current is distorted or has a tendency to be distorted, it adjusts the intersection point of the modulation wave and the carrier wave downward, thereby changing the pulse width of the subsequent SPWM wave and the time interval of each pulse width. This can achieve the response adjustment of current distortion within one cycle of the modulation wave, thereby accelerating the system current response speed.

[0046] Specifically, the PI controller of the voltage outer loop calculates the result based on the deviation between the actual voltage and the set voltage as the given value of the inner current loop. The inner loop feedback is calculated based on the switching circuit measurement value and the given value calculated by the voltage outer loop, and the SPWM wave is modulated according to the calculation result.

[0047] like Figure 3 As shown, the single-phase bridge PWM inverter circuit using IGBT as the switching device includes the input voltage U d , which forms the four switching tubes V1-V4 of the single-phase bridge, where the input voltage U dIn parallel with the single-phase bridge, the switch tubes V1 and V2 are connected in series to form a first bridge arm, and the switch tubes V3 and V4 are connected in series to form a second bridge arm.

[0048] Switch tube V1 and diode V T1 In parallel, the collector of the switch tube V1 is connected to the diode V T1 The negative pole is connected to the input voltage U d The positive pole of the switch tube V2 is connected to the diode V T2 In parallel, the emitter of switch tube V2 is connected to diode V T2 The positive pole is connected to the input voltage U d The negative pole of the switch tube V3 is connected to the diode V T3 In parallel, the collector of the switch tube V3 is connected to the diode V T3 The negative pole is connected to the input voltage U d The positive pole of the switch tube V4 is connected to the diode V T4 In parallel, the emitter of switch tube V4 is connected to diode V T4 The positive pole is connected to the input voltage U d A resistor R is connected between the emitter of the switch tube V1 and the collector of the switch tube V2, and an inductor L is connected between the emitter of the switch tube V3 and the collector of the switch tube V4. The resistor R and the inductor L are connected in series.

[0049] When the system is working, the on-off states of V1 and V2 complement each other, and the on-off states of V3 and V4 complement each other. The specific control rules are as follows: in the positive half cycle of the output voltage u, let V1 remain in the on state, V2 remain in the off state, and V3 and V4 alternately turn on and off. Because the current lags behind the voltage, in the positive half cycle of the voltage, the current has a positive interval and a negative interval. In the interval where the load current is positive, when V1 and V4 are on, the voltage u is equal to the DC voltage U d When V4 is turned off, the load current flows through V1 and V T3 Freewheeling, u o = 0. In the negative load current range, when V1 and V4 are still conducting, o is negative, so i o In fact, from V3 and V T1 Flows through, and there is still u=U d ; After V4 is turned off and V3 is turned on, i o From V3 and V T1 Freewheeling, u o = 0. Thus, u o You can always get U d and zero. Similarly, at u o In the negative half cycle, V2 is kept on, V1 is kept off, V3 and V4 are switched on and off alternately, and the load voltage u o You can get -U dThe SPWM waveform output by the modulation circuit is as follows: Figure 4 shown.

[0050] like Figure 5 As shown, this embodiment is based on the single-phase bridge PWM inverter circuit, and the absolute value of the waveform of the modulation wave and the carrier is taken. Therefore, the generated SPWM waveform has only two levels: 0 and 1 (when the level is 0, the inverter switch is open, and when the level is 1, the inverter switch is closed). The modulation circuit (modulation ratio is less than 1, The intersection of the sine wave (modulating wave) and the carrier sawtooth wave determines the required duration of the final SPWM pulse output, ultimately generating the SPWM wave. Therefore, using an SPWM wave to control the inverter allows for n adjustments per cycle (n being the number of intersections between the modulating wave and the carrier wave within one cycle).

[0051] In this embodiment, an LLC resonant induction heating equivalent circuit is constructed based on field tests, and the inverter output current waveforms under the SPWM wave driving mode and the medium frequency square wave signal driving mode are compared.

[0052] like Figure 2 As shown, this embodiment adopts a voltage-type inverter, and the equivalent DC power supply U DC =800V, resonant inductor L1 = 75μF, resonant capacitor C = 18740μF, heating coil inductor L2 = 45μF, equivalent resistance R = 0.0045Ω, signal wave frequency uses LLC resonant frequency of 260Hz, carrier frequency is 5kHz. Among them, A and C are modulated by a sine wave with an amplitude of 1 and a frequency of 5kHz and an amplitude of 0.9 and a frequency of 260Hz; B and D are modulated by a sine wave with an amplitude of 0 and a frequency of 5kHz and an amplitude of 0.9 and a frequency of 260Hz (equivalent to a square wave signal with a 50% duty cycle).

[0053] like Figure 3 As shown, based on the operating principle of an inverter circuit, the on-off states of switches V1 and V2 in this embodiment are complementary, as are the on-off states of switches V3 and V4. Furthermore, V1 and V4 are simultaneously on and off, and V2 and V3 are simultaneously on and off. Because the sinusoidal modulation waveform takes its absolute value as input, the period is half of the original period, resulting in an on-off time of approximately 0.00192 seconds for both V3 and V4. Because V1 and V2 are controlled by the SPWM waveform, they each switch on and off eight times within a 0.00192 second period.

[0054] according to Figure 2 The LCC equivalent circuit shown in the figure is constructed using MATLAB software to build a simulation experimental model. Figure 7 shown.

[0055] Among them, A, B, C, and D are the driving modules that control the on and off of the inverter switching devices, and the SPWM waveform output by the equivalent modulation circuit. The signal driving waveform is as follows Figures 8(a)-8(b) As shown, Figure 8(a) shows that A, B, C, and D are SPWM drive signal waveforms (arranged from top to bottom); Figure 8(b) shows that A, B, C, and D are medium-frequency square wave drive waveforms with a duty cycle of 50%.

[0056] Figure 9 Figure 8 shows the simulated waveform of the inverter's output current. As shown in Figure 8, the output current of the inverter controlled by an intermediate-frequency square wave drive contains a significant number of third harmonics, resulting in significant distortion of the output current waveform. The peak output current is higher than that produced by the SPWM-driven inverter. Furthermore, the output current waveform of the SPWM-driven inverter approaches a sine wave, demonstrating that the third harmonic content is significantly reduced compared to the output current of the inverter controlled by an intermediate-frequency square wave drive.

[0057] Figure 10 is the parallel compensation capacitor C in the LLC resonant topology p The current waveform simulation results on Figure 9 It can be seen that when the SPWM wave is used to drive the inverter output, the current on the resonant load structure is well suppressed, ensuring the normal operation of the system.

[0058] Example 2

[0059] The purpose of this embodiment is to provide an LLC architecture induction heating circuit control system based on SPWM drive, including:

[0060] Voltage outer loop control module: uses the voltage output value of the inverter circuit switching device in the induction heating circuit as the voltage feedback value in the voltage outer loop control; uses PI control to process the voltage input value and voltage feedback value of the inverter circuit switching device and then outputs them;

[0061] Current inner loop control module: uses the current output value of the inverter circuit switching device in the induction heating circuit as the current feedback value of the current inner loop control;

[0062] Waveform modulation module: modulates the SPWM wave according to the output after PI control processing and the current feedback value, and uses the modulated SPWM wave to control the on and off of each switching device in the inverter circuit in the induction heating circuit.

[0063] Example 3

[0064] The purpose of this embodiment is to provide a computing device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the steps of the above method are implemented when the processor executes the program.

[0065] Example 4

[0066] The purpose of this embodiment is to provide a computer-readable storage medium.

[0067] A computer-readable storage medium stores a computer program, which, when executed by a processor, performs the steps of the above method.

[0068] The steps involved in the apparatuses of Examples 2, 3, and 4 above correspond to those of Method Example 1. For detailed implementations, please refer to the relevant description of Example 1. The term "computer-readable storage medium" should be understood to mean a single medium or multiple media containing one or more instruction sets; it should also be understood to include any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and causing the processor to perform any method of the present invention.

[0069] Those skilled in the art will appreciate that the modules or steps of the present invention described above can be implemented using a general-purpose computer device. Alternatively, they can be implemented using program code executable by a computing device, which can then be stored in a storage device and executed by the computing device. Alternatively, they can be fabricated into separate integrated circuit modules, or multiple modules or steps can be fabricated into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0070] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A control method for an LLC architecture induction heating circuit based on SPWM drive, characterized in that: include: The voltage output value of the inverter circuit switch device in the induction heating circuit is used as the voltage feedback value in the voltage outer loop control; The voltage input value and voltage feedback value of the inverter circuit switching device are processed and output using PI control; The current output value of the inverter circuit switch device in the induction heating circuit is used as the current feedback value of the current inner loop control; Modulating the SPWM wave according to the output after PI control processing and the current feedback value, and using the modulated SPWM wave to control the on and off of each switching device in the inverter circuit in the induction heating circuit; In one cycle of the SPWM wave, the number of times the switching device of the inverter circuit in the induction heating circuit is adjusted is determined according to the number of intersections between the modulation wave and the carrier wave.

2. The LLC architecture induction heating circuit control method based on SPWM drive according to claim 1, characterized in that: According to the output after PI control processing and the current feedback value, the intersection of the modulation wave and the carrier is adjusted to change the pulse width of the SPWM wave and the time interval of each pulse width; the system heating power is adjusted by changing the modulation wave of the SPWM and the modulation degree of the carrier; when multiple heating coils work in series, the phase of the heating coil current is adjusted by adjusting the modulation wave frequency of the SPWM to achieve the same frequency and phase of the heating coil current.

3. The LLC architecture induction heating circuit control method based on SPWM drive according to claim 2, characterized in that: Taking the absolute values ​​of the waveforms of the modulation wave and the carrier wave, the generated SPWM wave has two levels, 0 and 1. At level 0, the switching device in the inverter circuit is disconnected, and at level 1, the switching device in the inverter circuit is closed.

4. The LLC architecture induction heating circuit control method based on SPWM drive according to claim 1, characterized in that: The modulation ratio is the ratio of the carrier amplitude to the modulating wave amplitude.

5. LLC architecture induction heating circuit control system based on SPWM drive, characterized by: include: Voltage outer loop control module: uses the voltage output value of the inverter circuit switching device in the induction heating circuit as the voltage feedback value in the voltage outer loop control; uses PI control to process the voltage input value and voltage feedback value of the inverter circuit switching device and then outputs them; Current inner loop control module: uses the current output value of the inverter circuit switching device in the induction heating circuit as the current feedback value of the current inner loop control; Waveform modulation module: modulates the SPWM wave according to the output after PI control processing and the current feedback value, and uses the modulated SPWM wave to control the on and off of each switching device in the inverter circuit in the induction heating circuit; In the waveform modulation module, within one cycle of the SPWM wave, the number of times the switching device of the inverter circuit in the induction heating circuit is adjusted is determined according to the number of intersections between the modulation wave and the carrier wave.

6. The LLC architecture induction heating circuit control system based on SPWM drive according to claim 5, characterized in that: In the waveform modulation module, the intersection of the modulation wave and the carrier is adjusted according to the output after PI control processing and the current feedback value, thereby changing the pulse width of the SPWM wave and the time interval of each pulse width; the frequency of the SPWM modulation wave is adjusted to change the phase of the heating coil current.

7. A computer device, characterized in that: include: A processor, a memory, and a bus, wherein the memory stores machine-readable instructions executable by the processor. When the computer device is running, the processor and the memory communicate via the bus. When the machine-readable instructions are executed by the processor, an LLC architecture induction heating circuit control method based on SPWM drive is performed as described in any one of claims 1 to 4.

8. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the control method of an LLC architecture induction heating circuit based on SPWM drive according to any one of claims 1 to 4 is executed.

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