Topological structure of power supply main circuit of medium-frequency centerless induction furnace

Abstract

The invention discloses a power supply main circuit topological structure of a medium-frequency centerless induction furnace. The power supply main circuit topological structure comprises a three-phase rectification-chopping step-down circuit, a full-bridge inverter circuit, a voltage-sharing capacitor and a load parallel resonance circuit, the three-phase rectification-chopping step-down circuit comprises a first rectification-chopping step-down module and a second rectification-chopping step-down module; the rectification-chopping step-down module comprises two groups of three-phase six-pulse rectifier bridges with the phase difference of 30 degrees, a positive chopping step-down module, an anti-chopping step-down module and a filter inductor; the full-bridge inverter circuit comprises a first full-bridge inverter module and a second full-bridge inverter module, and the output end of the first full-bridge inverter module is connected with the output end of the second full-bridge inverter module in series. According to the invention, through the filter inductor connected between the three-phase rectifier bridge and the positive and negative chopping step-down module, the six-pulse component output by the three-phase rectifier bridge is weakened with low cost; the full-bridge inverter modules are connected in series, so that the problems of parallel non-uniform current and voltage resistance of semiconductor devices can be solved, and the energy loss of a power transmission line is reduced.

Description

Technical Field

[0001] This application relates to the technical field of medium-frequency induction melting, and particularly to a main circuit topology of a medium-frequency coreless induction furnace power supply. Background Art

[0002] Currently, large-scale medium-frequency coreless induction furnace power supplies basically do not adopt a full-bridge inverter series circuit, but a full-bridge inverter parallel circuit. Besides avoiding the risk of overvoltage of devices caused by uneven voltage in the series circuit, it is also because each single module can be independently controlled, and the dynamic response can be optimized by adjusting the phase and amplitude to adapt to load fluctuations.

[0003] However, in a full-bridge inverter parallel circuit, the output currents of multiple inverters need to be evenly distributed to avoid overload of some branches. Due to parameter differences between inverters, load imbalance, or inconsistent control strategies, there are prone to problems of current sharing in parallel branches and power loss in transmission lines. Summary of the Invention

[0004] The purpose of this application is to provide a main circuit topology of a medium-frequency coreless induction furnace power supply. By connecting the output ends of each full-bridge inverter module in series and then connecting to the load parallel resonance circuit, a better effect than the conventional boost parallel resonance circuit can be achieved; with the help of a filter inductor, the 5th and 7th, 17th and 19th harmonic currents generated by two three-phase 6-pulse rectifier bridges with a phase difference of 30° are weakened, and at the same time, the energy loss of the transmission line is significantly reduced.

[0005] In the first aspect, the invention purpose of this application is achieved by adopting the following technical solution: This application provides a main circuit topology of a medium-frequency coreless induction furnace power supply, including: a three-phase rectification-chopper buck circuit, a full-bridge inverter circuit, a voltage-sharing capacitor, and a load parallel resonance circuit; the three-phase rectification-chopper buck circuit includes a first rectification-chopper buck module and a second rectification-chopper buck module; the rectification-chopper buck module includes two three-phase 6-pulse rectifier bridges with a phase difference of 30°, a positive chopper buck module, a negative chopper buck module, and a filter inductor; the full-bridge inverter circuit includes a first full-bridge inverter module and a second full-bridge inverter module, and the output ends of the first full-bridge inverter module and the second full-bridge inverter module are connected in series to supply power to the load parallel resonance circuit.

[0006] Through the above technical solution, each full-bridge inverter circuit is powered by an independent rectifier chopper module, and the outputs of the full-bridge inverter circuits are in series. In the series structure, the current paths are the same, and naturally, the current unevenness problem of the parallel circuit will not occur. Therefore, by connecting the outputs of the full-bridge inverter circuits in series, the uneven current problem in the parallel structure can be avoided, achieving a better effect than the conventional boost parallel resonant circuit. In addition, since the series structure reduces the current path and charge accumulation, the line resistance loss can be reduced by nearly half; in this application, 24-pulse rectification reduces harmonic interference, and the positive and negative chopper circuits reduce power transmission losses, weakening the 6-pulse components of the rectified output with a 30-degree phase shift of the two three-phase 6-pulse rectifier bridges. The series inverter structure avoids the parallel current sharing problem, and the voltage equalizing capacitor network solves the voltage equalization problem of multiple series-connected inverter bridges, significantly improving the system efficiency and stability, thereby achieving the technical purpose of effectively avoiding the occurrence of parallel current unevenness in the medium-frequency coreless induction furnace power supply circuit and reducing the energy loss of the power transmission line.

[0007] Optionally, the positive chopper buck module and the negative chopper buck module are connected back-to-back, and the input ends are connected to the series output ends of two three-phase 6-pulse rectifier bridges with a phase difference of 30°.

[0008] Through the above technical solution, first, 24-pulse rectification suppresses the input harmonics above 24 times the fundamental frequency, which can reduce the interference to the power grid; in addition, the phase shifts are symmetrically distributed, which helps to balance the three-phase current, reduce the harmonics caused by imbalance, and the positive chopper buck module and the negative chopper buck module are cooperatively controlled. After the inverter outputs are connected in series to form a high-voltage intermediate frequency output, the problem of excessive voltage stress of a single chopper buck module can be avoided.

[0009] Optionally, the positive chopper buck module is composed of a first IGBT half-bridge module and a first filter capacitor, and the negative chopper buck module is composed of a second IGBT half-bridge module and a second filter capacitor. The common connection point of the two filter capacitors is connected to the series connection common point of the two three-phase 6-pulse rectifier bridges through the filter inductor.

[0010] Through the above technical solution, the common point of the filter capacitors is connected to the series connection common point of the three-phase 6-pulse rectifier bridges through the filter inductor. Compared with the conventional cascaded chopper circuit, the number of power transmission lines of the IGBT chopper circuit is reduced, and at the same time, the 6-pulse components of the rectified output with a 30-degree phase shift of the two are weakened, and a clamping voltage is provided for the filter capacitors, reducing the low-frequency filtering pressure of the filter capacitors, and solving the voltage equalization problem of the series-connected IGBT half-bridge modules.

[0011] Optionally, the load parallel resonant circuit includes the induction coil of the medium-frequency coreless induction furnace and a parallel resonant capacitor bank, and the parallel resonant capacitor bank is composed of two series-connected resonant capacitors; a voltage equalizing capacitor is connected across between the series connection point of the output ends of the full-bridge inverter module and the series connection point of the parallel resonant capacitor bank.

[0012] Through the above technical solution, the series connection point of the series capacitors is connected to the series connection point of the full-bridge inverter in the full-bridge inverter series circuit through voltage-sharing capacitors, which is equivalent to connecting large-capacity capacitors in parallel to each inverter bridge, forcing the output voltages of each full-bridge inverter module to be balanced.

[0013] Optionally, the first rectifier-chopper step-down module and the first full-bridge inverter module form a cascade unit, the second rectifier-chopper step-down module and the second full-bridge inverter module form a second cascade unit, the number of cascade units can be extended to N, the parallel resonant capacitor bank is composed of N resonant capacitors connected in series, and voltage-sharing capacitors are respectively connected across the series connection points at the output ends of each full-bridge inverter circuit and the connection points of the corresponding resonant capacitor banks to form N - 1 voltage-sharing branches, where N is an integer greater than or equal to 2.

[0014] Through the above technical solution, by increasing the number of cascade modules, different power levels can be flexibly adapted. At the same time, N - 1 voltage-sharing capacitors can ensure the voltage balance of each inverter bridge after expansion.

[0015] Optionally, two three-phase 6-pulse rectifier bridges with a phase difference of 30° are replaced by two three-phase 12-pulse rectifier bridges with a phase difference of 15°.

[0016] Through the above technical solution, the filter inductor can effectively weaken the 12-pulse component output by two three-phase 12-pulse rectifier bridges with a phase difference of 15°.

[0017] In a second aspect, the invention object of the present application is realized by adopting the following technical solution: A power supply detection method for an intermediate-frequency coreless induction furnace power supply based on the above, the method includes: Establish the forward conversion relationship between the input voltage and the output voltage of the rectifier-chopper step-down module, and the reverse conversion relationship between the output voltage and the input voltage of the full-bridge inverter module; Construct a joint optimization model based on the forward conversion relationship and the reverse conversion relationship, where the joint optimization model includes a loss function for quantifying rectification losses and a constraint function for constraining inverter performance, to realize the collaborative optimization of the rectification and inversion processes; Construct a cascaded detection network including a bottom-layer detection network, a middle-layer detection network, and a top-layer detection network; The bottom-layer detection network extracts the 12-pulse phase-shift angle error of the rectifier-chopper step-down module based on Fourier transform to obtain a phase deviation value for monitoring the rectifier-chopper rectification module; The middle-layer detection network uses Kalman filtering to predict the first inverter voltage distribution coefficient and the second inverter voltage distribution coefficient of the full-bridge inverter module to evaluate the voltage balance of the full-bridge inverter module; The top - layer detection network uses wavelet transform to analyze the frequency deviation value of the load parallel - resonance module for detecting the stability of the resonance frequency; Synchronously collect the three - phase input voltage, DC bus voltage, inverter output current, and resonance capacitor voltage of the medium - frequency coreless induction furnace power supply, and perform time - domain and frequency - domain feature extraction to generate a multi - dimensional detection vector; Execute a circuit closed - loop adjustment strategy based on the multi - dimensional detection vector.

[0018] By adopting the above - mentioned technical solution, a forward / reverse conversion model of the rectification - chopping and inverter modules is constructed. The cascaded detection network integrating the rectification loss function and the inverter constraint function includes three - layer structures: the bottom layer (Fourier phase error), the middle layer (Kalman filter voltage distribution coefficient), and the top layer (wavelet transform frequency deviation); synchronously collect multi - dimensional signals (three - phase voltage, DC bus voltage, inverter current, resonance capacitor voltage) to generate a detection vector; it is beneficial to improve the detection accuracy, enhance the dynamic response ability, reduce the rectification - inverter coupling interference at the same time, and enhance the stability of a medium - frequency coreless induction furnace power supply.

[0019] In a preferred example of the present application: The circuit closed - loop adjustment strategy includes: When the phase deviation value is greater than the preset phase deviation threshold, trigger a rectification phase - shift angle correction instruction, and compensate for the phase deviation through PWM duty - cycle adjustment; When the difference between the distribution coefficients of the first inverter voltage distribution coefficient and the second inverter voltage distribution coefficient is greater than the preset distribution difference threshold, dynamically adjust the voltage distribution weight coefficient of the positive chopping buck module or the reverse chopping buck module to reduce the difference between the distribution coefficients of the first inverter voltage distribution coefficient and the second inverter voltage distribution coefficient; When the frequency deviation value is greater than the preset resonance frequency difference, adjust the inverter trigger angle based on a fuzzy controller.

[0020] By adopting the above - mentioned technical solution, functions of phase deviation correction, voltage distribution adjustment, and resonance frequency compensation are provided. Through the accurate phase - correction control ability, the fuzzy controller suppresses power - grid fluctuations and harmonic interference, optimizes the anti - interference performance of a medium - frequency coreless induction furnace power supply, and reduces the device switching loss through a dynamic adjustment strategy at the same time.

[0021] In summary, by cascading a three - phase rectification - chopping buck circuit and a full - bridge inverter circuit to replace the traditional parallel structure, the current - sharing problem is fundamentally eliminated, and the line loss is reduced; the filter inductor has a low cost and can significantly suppress harmonics; the voltage - equalizing capacitor and the extended architecture support high - voltage output and are suitable for low - voltage - withstand devices. This solution has significant industrial application value in large - scale medium - frequency induction furnaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1It is the circuit diagram of the main circuit topology of the medium-frequency coreless induction furnace power supply in Embodiment 1 of the present application; Figure 2 It is a rectifier - chopper buck module in the prior art; Figure 3 It is the circuit diagram of the topology expansion of the main circuit topology of the medium-frequency coreless induction furnace power supply in Embodiment 1 of the present application; Figure 4 It is the preferred rectifier - chopper buck module in the circuit diagram of the main circuit topology of the medium-frequency coreless induction furnace power supply in Embodiment 2 of the present application; Figure 5 It is the circuit diagram of the main circuit topology of the medium-frequency coreless induction furnace power supply in Embodiment 2 of the present application. Detailed implementation manners

[0023] The following will Figure 1 be combined with Figure 5 the attached drawings to further elaborate on the present application in detail.

[0024] Embodiment 1 The present application provides a main circuit topology of a medium-frequency coreless induction furnace power supply. Refer to Figure 1 , The main circuit topology of the medium-frequency coreless induction furnace power supply includes a three-phase rectifier - chopper buck circuit, a full-bridge inverter circuit, a voltage-sharing capacitor, and a load parallel resonance circuit; the three-phase rectifier - chopper buck circuit includes a first rectifier - chopper buck module and a second rectifier - chopper buck module; the rectifier - chopper buck module includes two three-phase 6-pulse rectifier bridges with a phase difference of 30°, a positive chopper buck module, a negative chopper buck module, and a filter inductor; the full-bridge inverter circuit includes a first full-bridge inverter module and a second full-bridge inverter module, the load parallel resonance circuit includes the induction coil of the medium-frequency coreless induction furnace and a parallel resonance capacitor group, and the parallel resonance capacitor group is composed of two series-connected resonance capacitors; a voltage-sharing capacitor is connected across between the series connection point of the output terminals of the first full-bridge inverter module and the second full-bridge inverter module and the series connection point of the parallel resonance capacitor group.

[0025] As a key industrial equipment, the medium-frequency coreless induction furnace has an irreplaceable position in the metal processing industry. Especially for large-scale application scenarios, how to efficiently solve the problem of current sharing in parallel branches and significantly reduce the energy loss of transmission lines has become one of the core technical challenges. The present invention aims to fundamentally break through the above technical bottleneck by optimizing the design of the main circuit topology.

[0026] The embodiment of the present application provides a main circuit topology for a medium-frequency coreless induction furnace power supply, which mainly includes two cascaded units. The first rectification-chopper step-down module and the first full-bridge inverter module form a cascaded unit, and the second rectification-chopper step-down module and the second full-bridge inverter module form the second cascaded unit. That is, each cascaded unit is composed of a rectification-chopper step-down part and a full-bridge inverter part working together; among them, the rectification-chopper step-down part is responsible for initially processing the received grid power resources and then transmitting them to the adjacent full-bridge inverter part to complete medium-frequency conversion; the outputs of each full-bridge inverter are connected in series to supply power to the load parallel resonance circuit.

[0027] Specifically, each three-phase rectification-chopper step-down circuit independently processes a part of the input power. After the first full-bridge inverter module and the second full-bridge inverter module are connected in series, the output voltages are superimposed, and a higher medium-frequency voltage can be formed. For example, if the two rectification-chopper step-down modules respectively output a 2000V DC bus voltage, then after being connected in series through the full-bridge inverter modules, a medium-frequency AC voltage of about 5200V can be output. Since under the condition of the same power, the doubling of the voltage will cause the current to be halved, and the reduction of the current in the transmission line means that the loss of the transmission line will also be reduced. Therefore, the cascaded topology design proposed in the present application can not only solve the problem of uneven current sharing in the parallel circuit, but also reduce the loss of the transmission line.

[0028] In the embodiment of the present application, the three-phase 24-pulse rectification module includes a phase-shifting rectification transformer and four groups of independent three-phase 6-pulse rectification bridges; the three-phase 6-pulse rectification bridge is also called a three-phase uncontrolled rectification bridge. The phase-shifting rectification transformer includes four groups of phase-shifting windings with phase differences of ±7.5° and ±22.5°. Each group of phase-shifting windings is connected to an independent three-phase 6-pulse rectification bridge, and the DC output terminals of each three-phase 6-pulse rectification bridge are connected in series after passing through the positive chopper step-down module and the negative chopper step-down module; the positive chopper step-down module and the negative chopper step-down module are connected back to back, the input ends are connected to the series output terminals of two three-phase 6-pulse rectification bridges with a phase difference of 30°, and the output ends of the positive chopper step-down module and the negative chopper step-down module are connected in series to form a DC bus.

[0029] In this embodiment, the primary winding of the phase-shifting rectification transformer is connected in a delta or star shape, and the secondary winding includes four groups of zigzag delta phase-shifting windings with phase differences of ±7.5° and ±22.5°, generating four paths of alternating current with a phase difference of 15°. After three-phase uncontrolled rectification, they are superimposed into 24-pulse DC, which can filter out low-order harmonics.

[0030] In addition, the positive chopper step-down module and the negative chopper step-down module respectively process the rectification outputs of two groups with a phase difference of 30°, that is, the positive chopper step-down module processes the rectification output with a phase shift of +7.5°, and the negative chopper step-down module processes the rectification output with a phase shift of -22.5°. The two paths of DC are connected in series to form a DC bus.

[0031] In Embodiment 1 of the present application, the positive chopper step-down module is composed of a first IGBT half-bridge module and a first filter capacitor, and the negative chopper step-down module is composed of a second IGBT half-bridge module and a second filter capacitor. The common connection point of the two groups of filter capacitors is connected to the series connection common point of each three-phase 6-pulse rectifier bridge through a filter inductor.

[0032] Compared with the conventional cascaded chopper circuit, as shown in Figure 2 , the number of transmission lines of the IGBT chopper cascaded circuit is reduced. The filter inductor weakens the 6-pulse component of the rectified output with a 30-degree phase shift between the two, and also provides a clamping voltage for the filter capacitor, that is, the common connection point of the filter capacitor is connected to the midpoint of the rectifier bridge through the filter inductor, and the potential is clamped at the midpoint potential of the DC bus voltage. If the voltage of the series-connected DC bus is , then the voltages of the first filter capacitor and the second filter capacitor are clamped at , forcing the IGBT modules of the positive chopper step-down circuit and the negative chopper step-down circuit to bear equal DC voltages, thus solving the voltage sharing problem of the series connection of the IGBT half-bridge modules.

[0033] In the embodiment of the present application, the first full-bridge inverter module and the second full-bridge inverter module adopt thyristor inverter full bridges, and the first full-bridge inverter module and the second full-bridge inverter module are connected through a series resonance capacitor. When the output voltage of one of the full-bridge inverter modules is too high, the capacitive impedance voltage division effect forces the output voltage of the other full-bridge inverter module to rise synchronously, ensuring the voltage balance of the two full-bridge inverter modules.

[0034] In the embodiment of the present application, the load parallel resonance circuit includes the induction coil of the intermediate frequency coreless induction furnace and a parallel resonance capacitor bank. The parallel resonance capacitor bank is composed of two series-connected resonance capacitors; a voltage sharing capacitor is connected across the series connection point of the output ends of the full-bridge inverter module and the series connection point of the parallel resonance capacitor bank.

[0035] The voltage sharing capacitor is connected across the series midpoint of the first full-bridge inverter module and the second full-bridge inverter module and the series midpoint of the parallel resonance capacitor bank, forming a high-frequency current path, forcing the two node potentials to change synchronously, and dynamically balancing the voltage difference between the inverter bridge and the resonance capacitor. When the load changes and causes the midpoint potential to shift, the voltage sharing capacitor can quickly balance the voltage through high-frequency charge and discharge, preventing adverse effects on the circuit caused by voltage mutations due to trigger asymmetry or differences in semiconductor device performance parameters.

[0036] In another embodiment, in order to adapt to the operation of induction furnaces with different powers, the number of cascaded units can also be expanded to N. Correspondingly, the parallel resonance capacitor bank will also be composed of N series-connected resonance capacitors. Similarly, voltage sharing capacitors are respectively connected across the series connection points of the output ends of each full-bridge inverter circuit and the connection points of the corresponding resonance capacitor bank, forming N - 1 voltage sharing branches, where N is an integer greater than or equal to 2.

[0037] After the cascaded unit is expanded, the total output voltage is the sum of the voltages of each full-bridge inverter circuit, which can adapt to higher-power loads. By adjusting the number of cascaded units, different-power-level loads can be flexibly adapted. For example, see Figure 3 , when the number of cascaded units is 3, the resonant capacitor bank is composed of three resonant capacitors connected in series. Equalizing capacitors are respectively connected across the connection points between the series connection points at the output ends of each full-bridge inverter circuit and the connection points of the corresponding resonant capacitor bank, forming two equalizing branches to cover all series nodes and ensure the voltage balance of each full-bridge inverter module after expansion.

[0038] Embodiment 2 See Figure 4 and Figure 5 , the difference between this embodiment and Embodiment 1 is that in the three-phase rectifier-chopper buck circuit, the two three-phase 6-pulse rectifier bridges with a phase difference of 30° in Embodiment 1 are replaced by two three-phase 12-pulse rectifier bridges with a phase difference of 15° in Embodiment 2; the phase difference of 15° enables the two 12-pulse current harmonics to be weakened by the filter inductor.

[0039] The embodiments of this specific implementation manner are all preferred embodiments of this application, and do not limit the protection scope of this application accordingly. Therefore, all equivalent changes made according to the principles of this application should be covered within the protection scope of this application.

[0040] In one embodiment, a power detection method for a medium-frequency coreless induction furnace power supply is provided. This power detection method for a medium-frequency coreless induction furnace power supply is applied to a medium-frequency coreless induction furnace power supply. The power detection method for a medium-frequency coreless induction furnace power supply specifically includes the following steps: S1: Establish the forward conversion relationship between the input voltage and the output voltage of the rectifier-chopper buck module, and the reverse conversion relationship between the output voltage and the input voltage of the full-bridge inverter module.

[0041] In this embodiment, the forward conversion relationship refers to the mathematical mapping model (such as a linear equation or a neural network model) between the input voltage (three-phase alternating current) of the rectifier-chopper buck module and the output direct current voltage ( , ); the reverse conversion relationship refers to the mathematical mapping model between the input direct current voltage ( , ) of the full-bridge inverter module and the output alternating current voltage (induction coil voltage).

[0042] S2: Construct a joint optimization model based on the forward conversion relationship and the reverse conversion relationship. The joint optimization model includes a loss function for quantifying the rectification loss and a constraint function for constraining the inverter performance, so as to realize the collaborative optimization of the rectification and inversion processes.

[0043] In this embodiment, the loss function is used to quantify the efficiency loss of the rectification module (such as THD, switching loss and conduction loss ); THD reflects the quality of the input current waveform, the switching loss is the energy loss of the IGBT device during the chopping process, and the conduction loss is the conduction voltage drop loss when the rectifier bridge arm conducts; the constraint function refers to the performance index that restricts the voltage distribution error, resonance frequency deviation, and output voltage amplitude constraint of the inverter module; the joint optimization model simultaneously minimizes the loss function and satisfies the constraint conditions through an optimization algorithm to achieve the global optimum of rectification-inversion.

[0044] Specifically, the loss function for quantifying rectification loss , where , , are weight coefficients, calibrated according to the actual working conditions.

[0045] The calculation of THD is based on the harmonic components of the Fourier transform ; where is the amplitude of the nth harmonic; is the fundamental wave amplitude; N is the total number of harmonics.

[0046] Switching loss is calculated through the device switching frequency and voltage and current stresses: ; where, , are the voltage and current stresses of the ith IGBT, is the conduction time; the number of switching operations M varies with the load (e.g., M decreases under light load). Conduction loss The calculation formula is ; where, is the DC bus current; is the equivalent conduction resistance, related to the corresponding rectifier bridge voltage drop.

[0047] Specifically, the constraint function of the inverter module for constraining the inverter performance includes a voltage distribution error constraint (for restricting the difference in voltage distribution coefficients between the two inverter modules), a resonance frequency deviation constraint (ensuring that the resonance frequency is stable near the target value), and an output voltage amplitude constraint (preventing overvoltage or undervoltage); The manifestation form of is ; where, is the first voltage distribution coefficient; is the second voltage distribution coefficient; is the resonance frequency deviation, i.e., the frequency offset value; is the minimum constraint value of the output voltage of the full-bridge inverter module, which can be set to 0.9 times the nominal output voltage; is the output voltage of the full-bridge inverter module; is the maximum constraint value of the output voltage of the full-bridge inverter module, which can be set to 1.1 times the nominal output voltage.

[0048] Further, the mathematical form of the joint optimization model is: optimization objective function - minimize , where the optimization variables are (DC output voltage of the rectifier module), voltage distribution coefficient of the inverter module and , resonant frequency value of the resonant capacitor voltage ; adopting a weighted constraint optimization strategy, converting the constraint conditions into penalty terms and adding them to the objective function ; where , are penalty factors, such as = 100, = 50, and the set solution method is the gradient descent method: by performing continuous adjustable parameter optimization on and , using the Adam optimizer to accelerate convergence, such as performing discrete search on the voltage distribution coefficients and (such as taking a step size of 0.1); when performing data synchronization operations, using a GPS timing module to achieve μs-level synchronous sampling of three-phase voltage, DC bus voltage, current, and resonant capacitor voltage, and when performing data calibration, every time a data synchronization period (such as 100 hours) is run, the weight coefficients of the loss function are updated based on the LSTM neural network. This application combines multi-objective collaboration, real-time guarantee, and self-adaptability. It can not only cover the full-link states of rectification, inversion, and resonance through time-frequency domain feature fusion, but also balance efficiency and stability through a weighted constraint strategy, combine gradient descent and integer programming to meet the ms-level control period, and adapt to load mutation scenarios (such as the moment of charging an induction furnace) based on online learning-based parameter dynamic adjustment. Practice has proved that the joint optimization model improves the rectification efficiency by 2% and the inverter voltage balance error ≤ 1%.

[0049] S3: Construct a cascaded detection network including a bottom-layer detection network, a middle-layer detection network, and a top-layer detection network; the bottom-layer detection network extracts the 12-pulse phase-shift angle error of the rectifier-chopper buck module based on Fourier transform to obtain the phase deviation value for monitoring the rectifier-chopper rectifier module; the middle-layer detection network uses Kalman filtering to predict the first and second inverter voltage distribution coefficients of the full-bridge inverter module to evaluate the voltage balance of the full-bridge inverter module; the top-layer detection network uses wavelet transform to analyze the frequency deviation value of the load parallel resonance module to detect the stability of the resonant frequency.

[0050] In this embodiment, the bottom-layer detection network extracts the 12-pulse phase-shift angle error of the rectifier bridge of the rectifier-chop buck module based on the Fourier transform, and is used to monitor the phase synchronization accuracy of the rectifier bridge; the middle-layer detection network predicts the voltage distribution coefficient of the full-bridge inverter module through Kalman filtering, and is used to evaluate the voltage balance of the full-bridge inverter module; the top-layer detection network analyzes the frequency deviation value of the resonant capacitor voltage adopted in the load parallel resonance module by using wavelet transform to detect the stability of the load resonance frequency.

[0051] Specifically, a Hall voltage sensor is used to collect the three-phase input voltage, the DC bus voltage, and the resonant capacitor voltage; a Rogowski coil is used to collect the inverter output current; the bottom-layer detection network performs a fast Fourier transform (FFT) on the rectified output voltage to calculate the fundamental wave phase 、 ; the phase deviation value (assuming the theoretical phase difference is 30°). The middle-layer detection network uses Kalman filtering to predict the relationship between the inverter input voltage 、 and the output voltage . The first voltage distribution coefficient is equal to the ratio of to the output voltage . The second voltage distribution coefficient is equal to the ratio of to the output voltage . The top-layer detection network extracts the frequency-domain components of the resonant capacitor voltage by wavelet transform (db4 wavelet, 3-layer decomposition), and the frequency deviation value , where is the resonant frequency value of the resonant capacitor voltage detected currently, and 500 Hz is set as the target resonant frequency (the specific value of the target resonant frequency can be adaptively modified according to the actual circuit structure).

[0052] S4: Synchronously collect the three-phase input voltage, the DC bus voltage, the inverter output current, and the resonant capacitor voltage of the medium-frequency coreless induction furnace power supply, and perform time-domain and frequency-domain feature extraction to generate a multi-dimensional detection vector.

[0053] In this embodiment, the time-domain features include the mean value and the variance; the frequency-domain features include the harmonic components and the frequency deviation; the multi-dimensional detection vector is a comprehensive feature vector used to reflect the system state.

[0054] S5: Execute the circuit closed-loop adjustment strategy based on the multi-dimensional detection vector.

[0055] In this embodiment, the circuit closed-loop adjustment strategy refers to triggering corresponding correction measures according to the abnormal indicators (phase deviation, voltage distribution error, frequency deviation) in the detection vector.

[0056] Exemplarily, the model initialization step of the joint optimization model includes: the nominal voltage of the rectification module ( = 1000V), the nominal voltage of the full-bridge inverter module ( = 500V); the thresholds are set as: the phase deviation threshold = 2°, the voltage distribution difference threshold = 5%, and the frequency deviation threshold = 1%.

[0057] Model loading includes: a pre-trained Kalman filter (covariance matrix Q = 0.01I, R = 0.1) and wavelet thresholds; real-time data is collected based on a preset sampling frequency and data preprocessing is performed, including digital filtering and a de-mean preprocessing content for eliminating DC bias.

[0058] The circuit closed-loop adjustment strategy includes: When the phase deviation value is greater than the preset phase deviation threshold, a rectification phase-shift angle correction instruction is triggered, and the phase deviation is compensated by adjusting the PWM duty cycle; when the difference between the first inverter voltage distribution coefficient and the second inverter voltage distribution coefficient is greater than the preset distribution difference threshold, the voltage distribution weight coefficient of the positive chopper buck module or the negative chopper buck module is dynamically adjusted to reduce the difference between the first inverter voltage distribution coefficient and the second inverter voltage distribution coefficient; when the frequency deviation value is greater than the preset resonance frequency difference, the inverter trigger angle is adjusted based on a fuzzy controller.

[0059] Specifically, if the phase deviation value is greater than the preset phase deviation threshold , PWM duty cycle adjustment is triggered: that is, the correction amount is calculated, (where ), and the duty cycle of the IGBT drive signal is updated, and the new duty cycle is equal to the sum of the original duty cycle and the correction amount.

[0060] The difference between the first inverter voltage distribution coefficient and the second inverter voltage distribution coefficient is reduced by adopting a voltage equalization adjustment method: if the absolute value of the difference between the first voltage distribution coefficient and the second voltage distribution coefficient is greater than the voltage distribution difference threshold, the voltage weight coefficient of the chopper module is dynamically adjusted: ( = 0.1), where is the adjusted voltage weight coefficient, is the voltage weight coefficient before adjustment, and by adjusting the output voltage of the chopper module, is forced.

[0061] The resonance compensation strategy includes: if the frequency deviation value , based on the conditional inverse trigger angle of the fuzzy controller , an example of the control rule base of the fuzzy controller: ; ; By changing the trigger angle, the inverse output frequency is adjusted to relock the resonance point.

[0062] It should be understood that the sequence numbers of the steps in the above embodiments do not mean the order of execution, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

Claims

1. A main circuit topology of a medium-frequency coreless induction furnace power supply, characterized in that, Comprising: A three-phase rectifier-chopper buck circuit, a full-bridge inverter circuit, a voltage-sharing capacitor, and a load parallel resonance circuit; the three-phase rectifier-chopper buck circuit includes a first rectifier-chopper buck module and a second rectifier-chopper buck module; the rectifier-chopper buck module includes two three-phase 6-pulse rectifier bridges with a phase difference of 30°, a positive chopper buck module, a negative chopper buck module, and a filter inductor; the full-bridge inverter circuit includes a first full-bridge inverter module and a second full-bridge inverter module, and the output ends of the first full-bridge inverter module and the second full-bridge inverter module are connected in series to supply power to the load parallel resonance circuit.

2. The main circuit topology of the medium-frequency coreless induction furnace power supply according to claim 1, wherein The positive chopper buck module and the negative chopper buck module are connected back-to-back, and the input ends are connected to the series output end of two three-phase 6-pulse rectifier bridges with a phase difference of 30°.

3. The main circuit topology of the medium-frequency coreless induction furnace power supply according to claim 2, characterized in that The positive chopper buck module is composed of a first IGBT half-bridge module and a first filter capacitor, the negative chopper buck module is composed of a second IGBT half-bridge module and a second filter capacitor, and the common connection point of the two filter capacitors is connected to the common connection point of the series connection of the two three-phase 6-pulse rectifier bridges through the filter inductor.

4. The main circuit topology of the medium-frequency coreless induction furnace power supply according to claim 1, characterized in that, The first full-bridge inverter module and the second full-bridge inverter module adopt a thyristor inverter full bridge.

5. The main circuit topology of an intermediate frequency coreless induction furnace power supply according to claim 1, characterized in that, The load parallel resonance circuit includes the induction coil of an intermediate-frequency coreless induction furnace and a parallel resonance capacitor bank, and the parallel resonance capacitor bank is composed of two series-connected resonance capacitors; a voltage-sharing capacitor is connected across between the series connection point of the output ends of the full-bridge inverter module and the series connection point of the parallel resonance capacitor bank.

6. The main circuit topology of the medium-frequency coreless induction furnace power supply according to claim 5, characterized in that, The first rectifier-chopper buck module and the first full-bridge inverter module form a cascaded unit, the second rectifier-chopper buck module and the second full-bridge inverter module form a second cascaded unit, the number of cascaded units can be extended to N, the parallel resonance capacitor bank is composed of N series-connected resonance capacitors, and a voltage-sharing capacitor is respectively connected across between the series connection point of the output end of each full-bridge inverter circuit and the connection point of the corresponding resonance capacitor bank, forming N - 1 voltage-sharing branches, where N is an integer greater than or equal to 2.

7. A main circuit topology of a medium-frequency coreless induction furnace power supply according to claim 1, characterized in that, Two three-phase 6-pulse rectifier bridges with a phase difference of 30° are replaced by two three-phase 12-pulse rectifier bridges with a phase difference of 15°.

8. A power supply detection method for a main circuit topology of a medium-frequency coreless induction furnace power supply according to any one of claims 1-7, characterized in that, The method includes: Establishing the forward conversion relationship between the input voltage and the output voltage of the rectifier-chopper buck module, and the reverse conversion relationship between the output voltage and the input voltage of the full-bridge inverter module; Constructing a joint optimization model based on the forward conversion relationship and the reverse conversion relationship, where the joint optimization model includes a loss function for quantifying rectification losses and a constraint function for constraining inverter performance, to achieve the collaborative optimization of the rectification and inversion processes; Constructing a cascaded detection network including a bottom detection network, a middle detection network, and a top detection network; The bottom detection network extracts the 12-pulse phase-shift angle error of the rectifier-chopper buck module based on Fourier transform to obtain the phase deviation value for monitoring the rectifier-chopper rectifier module; The middle detection network uses Kalman filtering to predict the first inverter voltage distribution coefficient and the second inverter voltage distribution coefficient of the full-bridge inverter module to evaluate the voltage balance of the full-bridge inverter module; The top - layer detection network uses wavelet transform to analyze the frequency deviation value of the load parallel resonance module for detecting the stability of the resonance frequency; Synchronously collect the three - phase input voltage, DC bus voltage, inverter output current, and resonance capacitor voltage of the medium - frequency coreless induction furnace power supply, and perform time - domain and frequency - domain feature extraction to generate a multi - dimensional detection vector; Execute a circuit closed - loop adjustment strategy based on the multi - dimensional detection vector.

9. The power supply detection method for the main circuit topology of the intermediate frequency coreless induction furnace power supply according to claim 8, characterized in that, The circuit closed - loop adjustment strategy includes: When the phase deviation value is greater than a preset phase deviation threshold, trigger a rectifier phase - shift angle correction instruction and compensate for the phase deviation through PWM duty - cycle adjustment; When the difference between the distribution coefficients of the first inverter voltage distribution coefficient and the second inverter voltage distribution coefficient is greater than a preset distribution difference threshold, dynamically adjust the voltage distribution weight coefficient of the positive chopper buck module or the negative chopper buck module to reduce the difference between the distribution coefficients of the first inverter voltage distribution coefficient and the second inverter voltage distribution coefficient; When the frequency deviation value is greater than a preset resonance frequency difference, adjust the inverter trigger angle based on a fuzzy controller.

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