Multi-magnetic field induction heating device

Abstract

A multi-magnetic field induction heating device relates to the technical field of induction heating devices and comprises an induction heating power supply, a load matching slot circuit and an induction coil. The induction heating power supply comprises a three-phase rectifier bridge, a direct-current chopper circuit and a multi-cascade full-bridge inverter circuit; the three-phase rectifier bridge converts alternating current commercial power into direct current, and the direct current chopper circuit changes direct current output voltage rectified by the three-phase rectifier bridge and then inputs the direct current output voltage into the multi-cascade full-bridge inverter circuit; the multi-cascade full-bridge inverter circuit comprises 2n solid-state switches VT1-VT2n which form m bridge arms and provide output current for the (n-1) induction coils at the same time, and n, m # imgabs0 # 2; the induction heating power supply and the induction coil are subjected to optimal impedance matching by adjusting a load matching slot circuit; according to the utility model, simultaneous output of the plurality of induction coils is realized to heat a workpiece, power instability caused by coupling among the plurality of coils is effectively reduced, and stable control of the heating temperature of the workpiece is realized.

Description

Technical Field

[0001] The utility model relates to the technical field of induction heating devices, in particular to a multi-magnetic field induction heating device. Background Art

[0002] In the field of modern induction heating applications, due to the different requirements of induction heating process in different environments and different materials, the heating method of one power supply corresponding to one induction coil can no longer meet the needs. Therefore, a method of using one induction heating power supply corresponding to multiple induction coils, or using multiple induction heating power supplies corresponding to multiple induction coils, is derived to achieve uniform heating, gradient heating or zone heating of the workpiece;

[0003] However, when multiple induction coils heat a workpiece at the same time, there is magnetic field coupling between the coils, which causes coupling of the output power of each coil, making it difficult to accurately control the coil output power, causing large fluctuations in the workpiece temperature, and difficult to achieve independent regulation; at the same time, due to changes in factors such as temperature and environment, parameters such as load impedance will change, so load impedance matching is required. The load impedance matching problem will directly affect the power output, efficiency and safety of each coil, and determine the production quality of the product and the optimal use of energy; therefore, designing an induction heating device that can achieve multiple coil outputs and eliminate coupling between magnetic fields, achieve rapid matching of load impedance, and solve the problem of slow response of nonlinear time-varying systems when multiple coils are heated simultaneously is an urgent problem to be solved by personnel in this technical field;

[0004] A Chinese patent (publication number: CN114423104A) discloses an induction heating power supply for a multi-temperature zone crystal furnace; the induction heating power supply of the patent includes an inverter and a resonant tank circuit, and the resonant tank circuit includes a matching transformer T, a resonant capacitor C and an induction coil L, wherein the primary coil of the matching transformer T is connected to the inverter, and the two ends of the secondary coil are respectively connected to the resonant capacitor C and the induction coil L; the patent enables multiple induction heating power supplies to adjust power independently, solving the problem of mutual inductance interference between two adjacent inductors in multi-temperature zone induction heating applications in the prior art, but it cannot be used for a heating method in which one induction heating power supply corresponds to multiple induction coils. Utility Model Content

[0005] In order to overcome the deficiencies in the background technology, the utility model discloses a multi-magnetic field induction heating device.

[0006] In order to achieve the above utility model purpose, the utility model adopts the following technical solutions:

[0007] A multi-magnetic field induction heating device comprises an induction heating power supply, a load matching slot and an induction coil; the induction heating power supply comprises a three-phase rectifier bridge, a DC chopper circuit and a multi-cascade full-bridge inverter circuit; the three-phase rectifier bridge converts AC mains into DC power, the DC chopper circuit changes the DC output voltage after rectification by the three-phase rectifier bridge and then inputs it into the multi-cascade full-bridge inverter circuit; the multi-cascade full-bridge inverter circuit comprises 2n solid-state switches VT1-VT2n, constituting m bridge arms and providing output current for n-1 induction coils at the same time, wherein n,m 2. The induction heating power supply and the induction coil are optimally impedance matched by adjusting the load matching slot.

[0008] Preferably, the three-phase rectifier bridge is composed of 6 diodes D1-D6 and a filter capacitor Cp, the input end of the three-phase rectifier bridge is connected to the AC mains, the AC power is converted into stable DC power after rectification and filtering by the three-phase rectifier bridge, and the output end of the three-phase rectifier bridge is connected to the DC chopper circuit; the DC chopper circuit is composed of a solid-state switch tube Q1, a diode Da, an output inductor Ls and an output capacitor Cs; the collector of the solid-state switch tube Q1 is connected to the output positive electrode of the three-phase rectifier bridge, the emitter is connected to the cathode of the diode Da and then connected to the output inductor Ls, the anode of the diode Da is connected to the output negative electrode of the three-phase rectifier bridge, one end of the output capacitor Cs is connected to the output inductor Ls, and the other end is connected to the output negative electrode of the three-phase rectifier bridge.

[0009] Preferably, the multi-cascade full-bridge inverter circuit includes 8 solid-state switches VT1-VT8, forming 4 bridge arms; VT1 and VT2 form the first bridge arm called the reference arm; VT3 and VT4 form the second bridge arm; VT5 and VT6 form the third bridge arm; and VT7 and VT8 form the fourth bridge arm.

[0010] Preferably, the load matching tank circuit includes a resonant capacitor Cn and a resonant inductor Ln, the input end of the load matching tank circuit is connected to the output end of the induction heating power inverter circuit, and the output end is connected to the induction coil.

[0011] Preferably, there are multiple induction coils; the induction coils include multi-strand windings and a coil frame, and the multi-strand windings are wound and connected with the insulating coil frame.

[0012] Preferably, it also includes a fuzzy controller, a PID controller, an inverter drive circuit and a current feedback circuit.

[0013] Due to the adoption of the above-mentioned technical solution, the utility model has the following beneficial effects:

[0014] The utility model discloses a multi-magnetic field induction heating device with a simple structure, which realizes the simultaneous output of multiple induction coils to heat the workpiece, effectively reduces the power instability caused by the coupling between the multiple coils, and realizes the stable control of the heating temperature of the workpiece; meets the requirements of modern induction heating for uniform heating, gradient heating or zoned heating of multiple workpieces; realizes the precise control of the current of the multiple induction coils, reduces the magnetic field coupling of the multiple coils, has no influence on the circuit and the coil structure, and ensures the stability and reliability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the overall structure diagram of the utility model;

[0016] Figure 2 This is the topological circuit diagram of the induction heating power supply of the utility model;

[0017] Figure 3 This is the principle diagram of the current closed-loop fuzzy controller of the utility model;

[0018] Figure 4 This is a pulse phase driving diagram of the pulse density modulation method of the utility model. DETAILED DESCRIPTION

[0019] The present invention can be explained in detail through the following embodiments. The purpose of disclosing the present invention is to protect all technical improvements within the scope of the present invention. In the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "front", "back", "left", "right", etc. indicating directions or positional relationships, they only correspond to the drawings of the present application for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific direction.

[0020] Embodiment 1, in combination with Figures 1-2 , a multi-magnetic field induction heating device, an induction heating power supply, a load matching slot, and an induction coil; the induction heating power supply is mainly composed of a three-phase rectifier bridge, a DC chopper circuit, and a multi-cascade full-bridge inverter circuit; the three-phase rectifier bridge converts AC mains into DC power, which is modulated by the DC chopper circuit and input into the multi-cascade full-bridge inverter circuit for inversion processing, and the required high-frequency AC power is obtained and then transmitted to the next-level load matching slot for modulation and matching; adjusting the load matching slot can achieve the best impedance matching between the induction heating power supply and the induction coil, so that the device can output with the best power; the induction coil transmits high-frequency current to generate a changing magnetic field. When a workpiece is in this changing magnetic field, an induced current is generated, thereby induction heating the workpiece.

[0021] The induction heating power supply includes a three-phase rectifier bridge, a DC chopper circuit and a multi-cascade full-bridge inverter circuit; the three-phase rectifier bridge is composed of 6 diodes D1-D6 and a filter capacitor Cp, the input end of the three-phase rectifier bridge is connected to the AC mains, the AC power is converted into stable DC power after rectification and filtering by the three-phase rectifier bridge, and the output end of the three-phase rectifier bridge is connected to the DC chopper circuit; the three-phase rectifier bridge converts the AC mains into DC power, which is modulated by the DC chopper circuit and then input into the multi-cascade full-bridge inverter circuit for inverter processing, and the required high-frequency AC power is obtained and then transmitted to the next-level load matching slot for modulation and matching.

[0022] The DC chopper circuit is composed of a solid-state switch tube Q1, a diode Da, an output inductor Ls and an output capacitor Cs; the collector of the solid-state switch tube Q1 is connected to the output positive electrode of the three-phase rectifier bridge, the emitter is connected to the cathode of the diode Da and then connected to the output inductor Ls, the anode of the diode Da is connected to the output negative electrode of the three-phase rectifier bridge, one end of the output capacitor Cs is connected to the output inductor Ls, and the other end is connected to the output negative electrode of the three-phase rectifier bridge; the DC chopper circuit can change the DC output voltage after rectification of the three-phase rectifier bridge and then input it into the multi-cascade full-bridge inverter circuit.

[0023] The multi-cascade full-bridge inverter circuit includes 2n solid-state switches VT1-VT2n, which form m bridge arms and provide output current for n-1 induction coils at the same time, where n, m 2;

[0024] The multi-cascade full-bridge inverter circuit is specifically described with the number of solid-state switch tubes n and the number of bridge arms m being equal to 4; VT1 and VT2 constitute the first bridge arm called the reference arm; VT3 and VT4 constitute the second bridge arm; VT5 and VT6 constitute the third bridge arm; VT7 and VT8 constitute the fourth bridge arm; the bridge arm 1 simultaneously participates in the operation of each level of the full-bridge inverter circuit; the second bridge arm cooperates with the first bridge arm to constitute the first-level full-bridge inverter circuit, providing the output current I1 for the induction coils R1 and Lr1; similarly, the third and fourth bridge arms cooperate with the first bridge arm to respectively constitute the second-level and third-level full-bridge inverter circuits; the second-level full-bridge inverter circuit provides the output current I2 for the induction coils R2 and Lr2, and the third-level full-bridge inverter circuit provides the output current I3 for the induction coils R3 and Lr3; the multi-cascade full-bridge inverter circuit outputs multiple magnetic fields through the coordinated operation of each group of solid-state switches, thereby realizing the simultaneous operation of multiple induction coils, and realizing uniform heating, gradient heating or zoned heating of the workpiece.

[0025] The load matching tank circuit includes a resonant capacitor Cn and a resonant inductor Ln; the load matching tank circuit is connected to the induction coil to form an LLC type load;

[0026] The input end of the load matching slot is connected to the output end of the induction heating power inverter circuit, and the output end is connected to the induction coil; by adjusting the load matching slot, the impedance matching of the induction heating coil can be adjusted to maximize the power transmission to the coil, thereby adjusting the heating effect and meeting the requirements of different heating processes;

[0027] The load of this embodiment includes an induction coil and a workpiece. The induction coil is composed of multiple windings and is wound on an insulating coil frame. When working, the induction coil will be placed around the heated object. According to different heating process requirements and needs, multiple currents can be output to multiple induction coils at the same time to meet heating scenarios with multiple output requirements.

[0028] It should be noted that if the induction heating power supply only needs a single output, there is no electromagnetic coupling between adjacent induction coils, and decoupling control is not required.

[0029] like Figure 2 As shown, when the output is greater than or equal to two or more paths, the magnetic fields generated between multiple adjacent induction coils will couple with each other to generate mutual inductance M. At this time, the output impedance between each stage will change, causing the output power to change, and the temperature cannot be accurately controlled. At this time, it is necessary to compensate or reduce the current changes caused by the magnetic fields to maintain accurate temperature control.

[0030] Embodiment 2: It is found in actual use that the existing PID control method cannot perform closed-loop control on the current of the output coil, resulting in the inability to ensure accurate control of the heating of the workpiece. To solve this technical problem, this embodiment is further improved;

[0031] Combined with Figures 1 to 4 , a multi-magnetic field induction heating device, based on Example 1, its control system includes a fuzzy controller, a PID controller, an inverter drive circuit and a current feedback circuit; the fuzzy controller schematic diagram is as follows Figure 3 As shown, the specific working process is as follows: according to the expected current value The actual current value Compare and get the deviation value Deviation change rate Input into the fuzzy controller for fuzzification; defuzzification based on the pre-set fuzzy rule base leads to the derivation of the three required tuning parameters , , Then it enters the PID controller for parameter adjustment, and obtains the pulse signal required to be output to the inverter drive circuit. The inverter drive circuit drives the switch tube of the corresponding inverter to realize closed-loop control of the output current.

[0032] The fuzzy rule base is set according to the existing PID controller control law, for example Parameters are set by fuzzy rules. The value you choose depends on the system's response speed: increasing It can improve the response speed and reduce the steady-state deviation; however, Too large a value will cause a large overshoot and even make the system unstable. It can reduce overshoot and improve stability, but Too small will slow down the response speed and prolong the adjustment time; therefore, a larger value should be appropriately selected in the initial stage of adjustment. value to improve the response speed, and in the mid-adjustment period, Then take a smaller value to make the system have a smaller overshoot and ensure a certain response speed; and in the later stage of the adjustment process, The value is adjusted to a larger value to reduce the static error and improve the control accuracy; the principle of the fuzzy rule base is that when the error is large or large, the control amount is selected to eliminate the error as quickly as possible; when the error is small, the control amount should pay attention to preventing overshoot and focus on the stability of the system. , Fuzzy rules are also formulated based on the above control logic.

[0033] By using the fuzzy controller to perform online real-time tuning and rapid processing of PID parameters, stable control of the current of each coil is achieved; at this time, the power instability caused by the coupling between multiple coils is effectively reduced, stable control of the heating temperature of the workpiece is achieved, and the overall heating efficiency of the device is improved as well as the large capacity of induction heating.

[0034] When the load workpiece resonates with the power supply, the phase difference between the inverter voltage and the inverter current is 0°, and the overall output power of the system is at its maximum efficiency at this time. By adjusting the matching values ​​of the resonant inductor Ln and the resonant capacitor Cn of each load matching slot, the phase relationship of the output current and voltage of each full-bridge inverter circuit is kept in a resonant state at all times. At the same time, the synchronous controller and the feedback controller are used to monitor the output of each coil in real time, and the output of the inverter is adjusted as needed to maintain the same frequency and phase, so as to achieve the same frequency and phase of the output current and voltage of the load coil and maximize the output power.

[0035] Each inverter stage is powered by pulse density modulation while achieving independent power regulation and ensuring that the output current is always at the same frequency and phase. Within a fixed cycle, the corresponding output power is changed by adjusting the number of pulses in each power regulation cycle.

[0036] Under the pulse density modulation mode, the frequency-phase relationship of the driving pulse remains almost unchanged, and the frequency-phase relationship of the corresponding load coil output current and voltage remains unchanged. Under the premise of meeting the precise power regulation, the same frequency and phase relationship of multiple coil currents can be maintained.

[0037] Pulse density modulation pulse phase drive diagram Figure 4 As shown, M pulse cycles are selected as the total power regulation cycle. The multi-stage full-bridge inverter circuit has a bridge arm of one in a power regulation cycle. The upper bridge arm switch tube driving pulse phase of each subsequent bridge arm is consistent with the bridge arm VT2 phase signal, and the lower bridge arm switch tube driving pulse phase is consistent with the bridge arm VT1. The upper and lower switch tube driving signal phases of the same bridge arm are complementary. By adjusting a heating cycle The number of driving pulses corresponding to the bridge arm of each full-bridge inverter circuit can respectively realize the adjustment of the output power of multiple loads; Figure 4 As shown, the number of trigger pulses of the second, third and fourth bridge arms are i, j, and k respectively. By adjusting the values ​​of i, j, and k, the output power of coils Lr1, Lr2, and Lr3 can be adjusted respectively. At this time, the output power of each inverter level is basically proportional to the pulse density modulation ratio.

[0038] It realizes uniform heating of multiple coils, improves heating efficiency and heating quality, can adapt to workpieces of different shapes and sizes, has a wider range of applications, improves energy utilization and reduces energy loss, and meets the purpose of uniform heating, gradient heating or zone heating of the workpiece.

[0039] The parts of the present invention that are not described in detail are prior art. It is obvious to those skilled in the art that the present invention is not limited to the details of the above-mentioned exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive, and it is intended that all changes that fall within the meaning and scope of equivalent elements are included in the present invention.

Claims

1. A multi-magnetic field induction heating device, characterized in that: The invention comprises an induction heating power supply, a load matching slot and an induction coil; the induction heating power supply comprises a three-phase rectifier bridge, a DC chopper circuit and a multi-cascade full-bridge inverter circuit; the three-phase rectifier bridge converts the AC mains into DC power, and the DC chopper circuit changes the DC output voltage after rectification by the three-phase rectifier bridge and inputs it into the multi-cascade full-bridge inverter circuit; the multi-cascade full-bridge inverter circuit comprises 2n solid-state switches VT1-VT2n, constituting m bridge arms and providing output current for n-1 induction coils at the same time, wherein n,m 2. The induction heating power supply and the induction coil are optimally impedance matched by adjusting the load matching slot.

2. The multi-magnetic field induction heating device according to claim 1, characterized in that: The three-phase rectifier bridge is composed of 6 diodes D1-D6 and a filter capacitor Cp. The input end of the three-phase rectifier bridge is connected to the AC mains, and the AC power is converted into stable DC power after rectification and filtering by the three-phase rectifier bridge. The output end of the three-phase rectifier bridge is connected to the DC chopper circuit; the DC chopper circuit is composed of a solid-state switch tube Q1, a diode Da, an output inductor Ls and an output capacitor Cs; the collector of the solid-state switch tube Q1 is connected to the output positive electrode of the three-phase rectifier bridge, the emitter is connected to the cathode of the diode Da and then connected to the output inductor Ls, the anode of the diode Da is connected to the output negative electrode of the three-phase rectifier bridge, one end of the output capacitor Cs is connected to the output inductor Ls, and the other end is connected to the output negative electrode of the three-phase rectifier bridge.

3. The multi-magnetic field induction heating device according to claim 1 or 2, characterized in that: The multi-cascade full-bridge inverter circuit includes 8 solid-state switches VT1-VT8, which constitute 4 bridge arms; VT1 and VT2 constitute the first bridge arm called the reference arm; VT3 and VT4 constitute the second bridge arm; VT5 and VT6 constitute the third bridge arm; and VT7 and VT8 constitute the fourth bridge arm.

4. The multi-magnetic field induction heating device according to claim 1, characterized in that: The load matching tank circuit includes a resonant capacitor Cn and a resonant inductor Ln. The input end of the load matching tank circuit is connected to the output end of the induction heating power inverter circuit, and the output end is connected to the induction coil.

5. The multi-magnetic field induction heating device according to claim 1, characterized in that: There are multiple induction coils; the induction coils include multiple windings and a coil frame, and the multiple windings are wound and connected with the insulating coil frame.

6. The multi-magnetic field induction heating device according to claim 1, characterized in that: It also includes a fuzzy controller, a PID controller, an inverter drive circuit and a current feedback circuit.

Images