Control system and control method of LLC resonant induction heating power supply

Abstract

The invention provides a control system and a control method of an LLC resonance type induction heating power supply, the LLC resonance type induction heating power supply heats a load through a half-bridge inverter circuit, the control system comprises a modulation unit and an odd harmonic control unit, the modulation unit is used for determining a target modulation index and a fundamental wave frequency, and the odd harmonic control unit is used for controlling the modulation index and the fundamental wave frequency. High-frequency alternating-current square waves with the adjustable frequency are output by controlling on-off of all power devices of the half-bridge inverter circuit, and the waveform of the high-frequency alternating-current square waves takes the fundamental wave duration as the period and is of a half-wave symmetrical structure; the odd harmonic control unit is used for predicting and outputting the optimal switching angle combination of each power device under the condition that the odd harmonic suppression target is met, and the modulation unit generates a modulation signal for controlling the switching of each power device based on the optimal switching angle combination. The harmonic suppression effect of the high-frequency induction heating power supply under the dynamic load can be remarkably improved.

Description

Technical Field

[0001] The present application belongs to the technical field of induction heating power supplies, and specifically provides a control system and a control method of an LLC resonant induction heating power supply. Background Art

[0002] Induction heating power supplies are core components of industrial heat treatment systems and are widely used in fields such as heating and metal processing. Their performance directly impacts the efficiency and quality of the heating process. Traditional induction heating power supply systems typically rely on high-frequency resonant circuits to achieve energy conversion. However, in actual operation, power quality degradation often occurs due to nonlinear load characteristics and dynamically changing operating conditions. In particular, the accumulation of harmonic components in the voltage and current waveforms severely impacts system energy efficiency and can cause electromagnetic compatibility issues, thereby interfering with surrounding electronic equipment.

[0003] Furthermore, key components in resonant circuits, such as capacitors and inductors, age due to temperature fluctuations and long-term use, causing their parameters to shift. This shift can lead to resonant point mismatch, which in turn causes unstable power output and may even cause abnormal current increases, potentially damaging power switching devices. Existing protection systems typically rely on static threshold determination methods, lacking the ability to adapt to dynamic changes. They are unable to accurately capture fault characteristics and have slow response times, making it difficult to provide timely protection, increasing the risk of equipment damage.

[0004] Existing technical solutions have certain limitations when dealing with the above problems. Although passive filtering methods can reduce harmonics through multi-stage filtering networks, their effectiveness is limited and they are difficult to adapt to rapid changes under complex working conditions. On the other hand, active control methods based on resonant characteristic point detection, although able to identify resonant mismatches, are easily disturbed by working conditions, resulting in reduced detection accuracy and the risk of misjudgment. In summary, existing technologies have failed to effectively resolve the contradiction between harmonic elimination and maintenance of resonant stability. Therefore, a new method is needed to improve the stability and efficiency of the system, reduce the impact of harmonics, and ensure the reliability of the power supply system. Summary of the Invention

[0005] In order to solve the problems existing in the above-mentioned prior art and precisely control an LLC resonant induction heating power supply, the present application provides a control system for an LLC resonant induction heating power supply through an embodiment. The LLC resonant induction heating power supply heats a load through a half-bridge inverter circuit. The control system includes a modulation unit, which is used to determine a target modulation index and a fundamental frequency, and to output a high-frequency AC square wave with adjustable frequency by controlling the switching of each power device of the half-bridge inverter circuit. The waveform of the high-frequency AC square wave has a half-wave symmetrical structure with a fundamental wave duration as a period.

[0006] The control system also includes an odd harmonic control unit for predicting and outputting the optimal switching angle combination of each power device while meeting the odd harmonic suppression target. The modulation unit generates a modulation signal for controlling the switching of each power device based on the optimal switching angle combination.

[0007] Preferably, the odd harmonic suppression target is:

[0008]

[0009] Where M is the target modulation index, M min 、M max are the lower and upper limits of M respectively, i∈[1,4] is the optimal switching angle combination, 2n+1 is the expression of the order of odd harmonics that need to be suppressed, and N is the upper limit of n.

[0010] Preferably, the odd harmonic control unit uses a trained artificial neural network, takes the target modulation index as input, and predicts and outputs the optimal switching angle combination, wherein the training set for training the artificial neural network is obtained by searching an enhanced particle swarm optimization algorithm based on switching angle sorting constraints and modulation index constraints.

[0011] Preferably, the enhanced particle swarm optimization algorithm adopts a main group-subgroup hierarchical search strategy, which satisfies the preset main group fitness function and subgroup fitness function as the search targets of the main iterative search process and the sub-iterative search process, respectively, and iteratively searches for the optimal switching angle combination corresponding to each modulation index in the switching angle search space. The main group-subgroup hierarchical search strategy is specifically as follows: in each main iterative search process, all search particles are first controlled to execute the main group search strategy to search with the goal of satisfying the modulation index, and then each search particle is controlled to execute the subgroup search strategy at least once in the sub-iterative search process to search with the goal of suppressing each odd harmonic and satisfying the switching angle sorting constraint and the modulation index constraint.

[0012] Preferably, the main group fitness function FF0 is:

[0013]

[0014] The subgroup fitness function FF h for:

[0015]

[0016] Among them, V1 * is the target fundamental amplitude determined based on the target modulation index, V1 is the actual fundamental amplitude; V his the amplitude of the hth harmonic, w0, w h are the weight coefficients corresponding to the fundamental amplitude error and the amplitude error of each odd harmonic, λ1 and λ2 are the penalty factors for violating the angle constraint and modulation index constraint, respectively. violation is the penalty term for the wrong switching angle sequence; P M is the penalty term when the modulation index M exceeds the legal range.

[0017] Preferably, during each iterative search process, each search particle also performs a perturbation update action, and the perturbation update amplitude is determined based on the sinusoidal perturbation model shown in the following formula:

[0018] Δθ i =A·sin(2πf i ×k+φ i ), i∈[1,4],

[0019] Where Δθ i is the angular disturbance of the i-th switching angle, A is the disturbance amplitude, f i 、φ i are the disturbance frequency and initial phase of the i-th switching angle respectively, and k is the number of iterations of the current search.

[0020] Preferably, the control system further comprises: an abnormality detection unit, which performs a real-time monitoring operation on the degree of resonant frequency drift of the LLC resonant induction heating power supply based on the measured values of the secondary side current peak value and the load capacity.

[0021] Furthermore, the real-time monitoring operation monitors the degree of resonant frequency drift by determining whether the measured values of the secondary side current peak and the load capacity exceed the normal operating area, wherein the normal operating area is between the load capacity-secondary side current peak slope corresponding to the ideal resonant frequency and the load capacity-secondary side current peak slope corresponding to the upper limit of the resonant frequency drift.

[0022] Furthermore, the slope of the load capacity-secondary current peak slope corresponding to the upper limit of the resonant frequency drift is K a The slope of the load capacity-secondary current peak value corresponding to the ideal resonant frequency is K b , and K a With K b The ratio is the reciprocal of the ratio of the secondary side current duration a corresponding to the upper limit of the resonant frequency drift under the same load capacity to the secondary side current duration b corresponding to the ideal resonant frequency.

[0023] The present application further provides a control method for an LLC resonant induction heating power supply through an embodiment. The control method uses the aforementioned control system of the LLC resonant induction heating power supply to control the LLC resonant induction heating power supply to heat a load.

[0024] The embodiments of the present application provide a control system and control method for an LLC resonant induction heating power supply. First, the even harmonics are eliminated by rationally constructing a modulation signal waveform. Then, a trained neural network model is introduced to search for the optimal switching angle corresponding to the modulation index, thereby achieving real-time suppression of odd harmonics except the fundamental wave, greatly reducing the real-time calculation burden, and significantly improving the harmonic suppression effect of the high-frequency induction heating power supply under dynamic load.

[0025] Secondly, the training data for the neural network model for suppressing odd harmonics is generated using an enhanced particle swarm optimization algorithm. In the process of searching for the optimal switching angle combination corresponding to each modulation index, a hierarchical search strategy with a "main group-auxiliary group" structure is used to effectively improve the coverage and efficiency of multi-objective optimization, taking into account the special requirements of high-frequency induction heating power supplies for real-time control, switch angle feasibility, and angular periodicity. On this basis, a sorting constraint mechanism and modulation index constraints are introduced to avoid illegal or physically unfeasible switch angle combinations. Penalties are imposed for behaviors such as failure to achieve harmonic suppression goals, overlapping opening angles, and exceeding the modulation index limit, thereby strengthening the optimization algorithm's convergence guidance ability within the legal solution space. In addition, a sinusoidal perturbation function suitable for the periodic structure of the angle space is used to enhance the period matching and jump rationality of the search direction, further improving the algorithm's search efficiency and convergence quality in the switch angle optimization task.

[0026] Again, the control system and control method provided in this application accurately identify the resonance detuning problems caused by load mutation, coil aging or capacitance parameter drift by real-time monitoring of the dynamic relationship between the resonant current peak and the load capacity, thereby effectively improving the safety detection sensitivity of the LLC resonant induction heating power supply, reducing the energy loss and equipment shutdown risk caused by detuning, and extending the life of key components. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a circuit diagram of an LLC resonant induction heating power supply;

[0028] Figure 2 Schematic diagram of the architecture of a control system of an LLC resonant induction heating power supply provided according to some embodiments of the present application;

[0029] Figure 3 A schematic diagram of an implementation of an odd harmonic control unit provided according to some embodiments of the present application;

[0030] Figure 4 A flowchart of an enhanced particle swarm optimization algorithm provided according to some embodiments of the present application;

[0031] Figure 5Schematic diagram of the secondary side voltage waveform before and after suppressing odd harmonics in a specific simulation example;

[0032] Figure 6A FIG1 is a schematic diagram of the measured results of the induced voltage before harmonic suppression of the high-frequency LLC resonant induction heating power supply in a specific embodiment;

[0033] Figure 6B In a specific embodiment, the diagram shows the actual measurement results of the induced voltage after harmonic suppression of a high-frequency LLC resonant induction heating power supply using the control system provided by the present application;

[0034] Figure 7 Schematic diagram of the architecture of a control system of an LLC resonant induction heating power supply provided according to other embodiments of the present application;

[0035] Figure 8 Schematic diagram of the secondary current waveform after the rated resonant frequency and the resonant frequency are offset;

[0036] Figure 9 This is a schematic diagram of the normal operating area of the LLC resonant heating power supply provided according to an embodiment of the present application. DETAILED DESCRIPTION

[0037] Hereinafter, the present application will be further described based on preferred embodiments with reference to the accompanying drawings.

[0038] In the description of the embodiments of the present application, it should be noted that if the terms "upper", "lower", "inner", "outer" and the like indicate an orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or are the orientation or positional relationship in which the products of the embodiments of the present application are usually placed when in use, they are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, in the description of the present application, in order to distinguish different units, words such as first and second are used in this specification, but these are not limited by the order of manufacture, nor can they be understood as indicating or implying relative importance. Their names may be different in the detailed description and claims of the present application.

[0039] The vocabulary in this specification is used to illustrate the embodiments of the present application, but is not intended to limit the present application. It should also be noted that, unless otherwise clearly specified and limited, the terms "disposed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, an indirect connection through an intermediate medium, or a communication between the two components. For those skilled in the art, the specific meanings of the above terms in this application can be specifically understood.

[0040] Figure 1 This is a circuit diagram of an existing LLC resonant induction heating power supply, such as Figure 1 As shown, the LLC resonant induction heating circuit primarily consists of a rectifier, a half-bridge inverter circuit, and a load. The rectifier receives three-phase AC power from the industrial grid and converts it into a DC bus voltage Vdc via a three-phase uncontrolled rectifier bridge. The half-bridge inverter circuit comprises two power devices (e.g., IGBT switches) S1 and S2, and two equal-capacity voltage-divider capacitors C1 and C2. By sending a frequency-modulated signal with a duty cycle of approximately 50% to the gates of S1 and S2, respectively, it controls the switching of S1 and S2, generating a high-frequency square wave with adjustable frequency (to effectively heat the workpiece, the frequency can reach tens of kHz in some high-frequency induction heating circuits).

[0041] The high-frequency square wave is coupled to the secondary coil through the primary coil to achieve voltage conversion and electrical isolation, and then output to the load part. The load part adopts an LLC resonant topology structure, including a series resonant inductor Ls, a parallel resonant capacitor Cr, and a load equivalent inductor Lr and a load equivalent resistor R. The resonant network can generate a high-frequency current close to a sine wave, ultimately achieving effective induction heating of the workpiece.

[0042] The working process of the LLC resonant induction heating power supply is as follows:

[0043] 1) Initial state: At the initial moment, assuming that S1 and S2 are both in the off state, C1 and C2 are charged through the load so that the voltage across them is half of the power supply voltage, that is, Vc1 = Vc2 = Vdc / 2;

[0044] 2) S1 is turned on and S2 is turned off: When the control signal turns on S1, C1 discharges through S1 and its voltage gradually decreases. At the same time, since S1 is turned on, the power supply voltage Vdc charges C2 through S1, causing the voltage across C2 to gradually increase. In this process, the voltage on the load is part of the positive half-cycle waveform, and the specific voltage value depends on the charge and discharge status of C1 and C2;

[0045] 3) Both S1 and S2 are off: When the control signal of S1 disappears, S1 changes from the on state to the off state. At this time, due to the presence of inductance (usually the primary of a transformer or other inductive load), the current in the load cannot immediately reach zero, but gradually decreases. During this process, the current in the load continues to flow, but in the opposite direction to before, causing C1 to be charged and C2 to be discharged. Finally, when the current in the load drops to zero, the voltage across C1 returns to Vdc / 2, and the voltage across C2 also returns to Vdc / 2, and the system returns to its initial state.

[0046] 4) S2 is turned on and S1 is turned off: When the control signal turns on S2, the process is similar to the above, but in the opposite direction. C2 discharges through S2, and its voltage gradually decreases. At the same time, the power supply voltage Vdc charges C1 through S2, causing the voltage across C1 to gradually increase. In this process, the voltage on the load is part of the negative half-cycle waveform.

[0047] During the heating process of the workpiece, the above four states are continuously repeated, so that an alternating voltage is obtained on the load, thereby realizing power output, wherein the frequency and amplitude of the alternating voltage loaded on the load end can be adjusted by changing the modulation signals of S1 and S2. In order to characterize the modulation signal of the power device, in an embodiment of the present application, the angle (i.e., phase) corresponding to the opening or closing of each power device in a complete cycle is defined as the switching angle θ. In the process of modulating and controlling the half-bridge inverter circuit, in order to avoid the two power devices being turned on at the same time, it is generally necessary to set a dead time so that the modulation signals of the two power devices are offset to a certain extent on the basis of mutual complementarity. Therefore, the control parameters of each power device need to be characterized by two switching angles, and the switching angles of the two power devices need to satisfy a specific order and are not completely complementary. Therefore, the power output state of the half-bridge inverter circuit can be described by a set of four switching angles θ1~θ4.

[0048] In addition to the fundamental current that can heat the workpiece, the current output by the above-mentioned half-bridge inverter circuit often includes various high-order harmonic currents. Harmonic currents increase the power loss of the equipment, causing overheating of components such as transformers and inductors, and at the same time increase reactive power, thereby reducing power supply efficiency. Therefore, it is necessary to suppress the various harmonics by optimizing the switching angle combination θ1 to θ4, so that the waveform loaded on the load part reaches the desired target.

[0049] In order to effectively suppress the harmonic currents, some embodiments of the present application provide a control system for an LLC resonant induction heating power supply, referring to Figure 2 , the control system includes a modulation unit and an odd harmonic control unit.

[0050] The modulation unit is used to determine the target modulation index M and the fundamental frequency, and to realize a high-frequency AC square wave with adjustable output frequency by controlling the switching of each power device S1 and S2 of the half-bridge inverter circuit. In the embodiment of the present application, the waveform of the high-frequency AC square wave is based on the fundamental wave duration as a period and has a half-wave symmetrical structure, that is, within a complete control cycle of 0 to 2π, the switching angles of S1 and S2 are defined in the region of 0 to π, and the switching angles in the region of π to 2π are generated by a reverse mirroring method, so that the output waveform within the complete cycle satisfies the half-wave symmetry condition. Since when a periodic signal has half-wave symmetry, all even harmonics (including 2nd, 4th, 6th, 8th, etc.) in its spectrum will be automatically eliminated and no longer appear in the output voltage. Therefore, through this modulation signal waveform control method, there is no need to consider suppressing even harmonics, and only odd harmonics such as 3rd, 5th, 7th, and 9th need to be selectively suppressed, thereby significantly reducing the complexity of system control while achieving harmonic suppression.

[0051] In the embodiment of the present application, the odd harmonic control unit is used to predict and output the optimal switching angle combination of each power device under the condition of meeting the odd harmonic suppression target. i∈[1,4], the predicted optimal switching angle combination is output to the modulation unit, which then generates a modulation signal output to the gates of the power devices S1 and S2 based on the optimal switching angle combination, combined with the odd harmonic frequency and the half-wave symmetry characteristics that the high-frequency AC square wave should have.

[0052] The Fourier analysis equation can be used to calculate the relationship between each harmonic component and the output signal. Fourier analysis decomposes the periodic signal into multiple harmonics of different frequencies. Through Fourier series expansion, the amplitude and phase of each harmonic can be clearly obtained. Therefore, the output voltage of the half-bridge inverter circuit can be characterized and calculated by the Fourier analysis method, thereby providing a quantitative basis for selective harmonic elimination.

[0053] The high-frequency AC square wave output by the half-bridge inverter circuit can be expanded using the Fourier series. When its waveform has a half-wave symmetrical structure and the DC component is 0, its fundamental wave and each odd harmonic can be expressed as (1) and (2):

[0054]

[0055]

[0056] Here, 2n+1 represents the order of odd harmonics that need to be suppressed, and N represents the upper limit of n. For example, when N is equal to 4, the values of n are 1, 2, 3, and 4, indicating that the 3rd, 5th, 7th, and 9th harmonics need to be suppressed.

[0057] Obviously, the ideal output waveform for heating the workpiece should ensure that V1 and each odd harmonic V3...V 2N+1 The larger the ratio, the better, that is, the optimal switching angle combination i∈[1,4] should satisfy the odd harmonic suppression target as shown in formula (3):

[0058]

[0059] Formula (3) indicates that when the four switching angles of the modulation signal are in the optimal switching angle combination, the four switching angles The sum of the cosine functions of the four switching angles is a non-zero value M, and the sum of the cosine functions of the odd multiples of the four switching angles is zero.

[0060] Equation (3) not only gives the conditions that each switching angle needs to meet when each odd harmonic is suppressed, but also gives the amplitude characteristics of the fundamental wave when the conditions are met, that is, In this application, M is defined as the target modulation index.

[0061] The target modulation index M characterizes the proportional relationship between the fundamental amplitude and the DC bus voltage under the premise that each harmonic is well suppressed. Therefore, it can be used to evaluate the utilization rate of the input electrical energy while ensuring the harmonic suppression effect. Generally, by increasing the value of M, the heating efficiency of the workpiece can be effectively improved. However, in the high-frequency induction heating process, M that is too high may produce adverse effects: First, M that is too large will cause serious distortion of the output waveform, increase the unsuppressed higher-order harmonic components, and weaken the harmonic suppression effect; second, too high a fundamental amplitude may cause overvoltage in the inverter circuit devices, increasing the risk of device damage; third, in the process of selective harmonic elimination, when M approaches or even reaches 1, there may be a situation where there is no feasible solution for the switching angle combination or an extreme switching angle configuration is required, making the optimization solution difficult and the control unstable. Therefore, in some preferred embodiments of the present application, the target modulation index needs to be at the lower limit M min and upper limit M max Between, that is, M∈[M min ,M max ], in order to take into account the power control accuracy, harmonic optimization effect and system operation reliability, among which M min Preferably not less than 0.35, M max Preferably not higher than 0.7.

[0062] Figure 3 FIG. 1 shows a schematic diagram of a modulation unit and an odd harmonic control unit cooperatively controlling a half-bridge inverter circuit in some specific embodiments, referring to FIG. Figure 3The modulation unit can estimate the load power capacity that the load part should reach according to the specific requirements of heating the workpiece, and then determine the appropriate fundamental frequency and fundamental amplitude, and determine the target modulation index M in combination with the DC bus voltage. After receiving the target modulation index M to be achieved, the odd harmonic control unit uses the target modulation index as input to predict and output the optimal switching angle combination. i∈[1,4], and then feeds it back to the modulation unit, which generates a modulation signal with the optimal switching angle combination and satisfies half-wave symmetry, and uses the generated modulation signal to control the power devices S1 and S2.

[0063] From the above analysis, we can know that the target modulation index M is based on the workpiece heating demand and input voltage, in the interval [M min ,M max ], therefore, the search for the optimal switch angle combination based on the target modulation index needs to meet the requirements of speed and accuracy. Although the use of a table lookup method can quickly search for the optimal switch angle combination, it can only be quickly searched based on discrete M values. For M that is not in the table, due to the nonlinear characteristics of the switch angle combination, if prediction is made based on interpolation, it is very likely that the ideal switch angle combination cannot be obtained. For this reason, in a preferred embodiment of the present application, Figure 3 As shown, the odd harmonic control unit uses a trained artificial neural network to predict the optimal switching angle combination.

[0064] The artificial neural network can be implemented using various neural network models known to those skilled in the art, such as feedforward neural networks, deep learning networks, etc. In some specific embodiments, the artificial neural network may include an input layer (modulation index M), a hidden layer (4 neurons, Tanh activation) and an output layer (4 neurons, corresponding to switching angles). The artificial neural network can be trained using multiple pre-generated groups (M~optimal switching angle combination). The training process uses the output switching angles to achieve the desired fundamental amplitude and each harmonic amplitude as the optimization goal, and the ability to predict the optimal switching angle combination based on the input modulation index M is obtained through a large number of sample training.

[0065] Since the input of the artificial neural network is the target modulation index M, whose value has a clear physical meaning, the data used to train the artificial neural network needs to meet specific physical constraints. To this end, in a preferred embodiment of the present application, each training data in the training set is obtained by searching through an enhanced particle swarm optimization algorithm based on switching angle sorting constraints and modulation index constraints.

[0066] Specifically, the enhanced particle swarm optimization algorithm adopts a main-group-subgroup hierarchical search strategy, with the preset main-group fitness function and sub-group fitness function as the search objectives for the main and sub-iterative search processes, respectively. It iteratively searches for the optimal switching angle combination corresponding to each modulation index in the switching angle search space. Specifically, the main-group-sub-group hierarchical search strategy is as follows: during each main iterative search process, all search particles are first controlled to execute the main-group search strategy, searching for the desired modulation index. Then, each search particle is controlled to execute the sub-group search strategy at least once during the sub-iterative search process, searching for the desired combination of switching angles while suppressing odd harmonics and satisfying the switching angle ordering constraints and modulation index constraints.

[0067] Figure 4 shows a process for determining training data using enhanced particle swarm optimization algorithm, refer to Figure 4 In each main iterative search process, all search particles are first controlled to use the main group fitness function as the target and execute the main group search strategy. The main group search strategy is used to drive each search particle to move from the current position to the target modulation index direction, so as to ensure that the switch angle combination obtained by the search can meet the requirements of heating the workpiece as much as possible; then, after updating the optimal switch angle combination, the sub-iterative search process is entered, and the sub-group search strategy with the sub-group fitness function as the target is executed in each sub-iterative search. Among them, the sub-group search strategy comprehensively considers the requirements for odd harmonic suppression near the current modulation index value and the constraints on the switching angle sequence and modulation index exceeding the limit, so as to ensure that the search result meets the constraints on the physical conditions of the power device switch while achieving the modulation index and harmonic suppression targets.

[0068] In some specific embodiments, the main group fitness function FF0 and the subgroup fitness function FF1 are respectively shown as formula (4) and formula (5):

[0069]

[0070]

[0071] Among them, V1 * is the target fundamental amplitude determined based on the target modulation index, V1 is the actual fundamental amplitude; V h is the amplitude of the hth harmonic, w0, w h are the weight coefficients corresponding to the fundamental amplitude error and the amplitude error of each odd harmonic, λ1 and λ2 are the penalty factors for violating the angle constraint and modulation index constraint, respectively. violation is the penalty term for the wrong switching angle sequence; P M is the penalty term when the modulation index M exceeds the legal range.

[0072] In some optional embodiments, P MAs shown in formula (6):

[0073]

[0074] Wherein, Penalty is a preset constant used to penalize illegal M value search results.

[0075] In some preferred embodiments, during each iterative search process, each search particle also performs a perturbation update action, and the amplitude of the perturbation update action is determined by the sinusoidal perturbation model shown in formula (7):

[0076] Δθ i =A·sin(2πf i ×k+φ i ), i∈[1,4] (7),

[0077] Where Δθ i is the angular disturbance of the i-th switching angle, A is the disturbance amplitude, f i 、φ i are the disturbance frequency and initial phase of the i-th switching angle respectively, and k is the number of iterations of the current search.

[0078] It should be noted that the above perturbation update action can be performed in each main iterative search process or in each sub-iterative search process, that is, k can represent the number of iterations of the main iterative search or the number of iterations of the sub-iterative search.

[0079] Figure 5 In a specific simulation example, the voltage waveform output by the induction heating power supply under the control of the above control system is shown. For comparison, the figure also shows the voltage waveform when odd harmonic suppression is not performed. In order to highlight the waveform distortion trend and the change of harmonic content, the vertical axis is represented by normalized voltage, that is, the voltage value at each point is standardized according to the fundamental amplitude to highlight the change trend of waveform distortion and harmonic components, so that the waveform value is limited to between -1 and +1. Figure 5 The simulation results show that without odd harmonic optimization, there are obvious low-order odd harmonics (such as 3rd, 5th, etc.) in the output voltage. After the odd harmonics are suppressed by the odd harmonic control unit, the waveform distortion is significantly reduced, which verifies the effectiveness of the present invention in harmonic suppression and waveform quality improvement.

[0080] Figure 6A Figure 1 shows the measured voltage waveform of an LLC resonant induction heating power supply before harmonic suppression in a specific embodiment. The heating power supply is a high-frequency resonant type. The yellow channel in the figure is the half-bridge drive signal applied to the power device, and the blue channel is the output induced voltage waveform. Figure 6BThis is the measured waveform result after harmonic suppression of the LLC resonant induction heating power supply using the control system provided in this application, where the value of M is 0.6.

[0081] Compare Figure 6A 、 Figure 6B It can be seen that after harmonic suppression by the control system provided in this application, the output signal presents a relatively regular sinusoidal shape, and the main resonant frequency is stabilized at 35.87kHz, indicating that the harmonic control strategy can effectively suppress harmonics in actual high-frequency induction heating power supplies and has good dynamic stability.

[0082] LLC resonant induction heating circuits generally operate in the high-frequency range. Key components in the resonant circuit, such as capacitors and inductors, will age due to temperature fluctuations and long-term use, causing their parameters to shift. This shift will lead to a mismatch in the resonance point (generally, the resonant frequency point will drift toward high frequency), which in turn causes unstable power output and may even cause an abnormal increase in current, thereby damaging the power device.

[0083] Existing LLC resonant induction heating circuit protection systems usually rely on static threshold judgment methods, lack the ability to adapt to dynamic changes, cannot accurately capture fault characteristics, and have a slow response speed, making it difficult to achieve timely protection, thereby increasing the risk of equipment damage.

[0084] In order to solve the above problems, in some preferred embodiments of the present application, the control system provided is as follows: Figure 7 As shown, an abnormality detection unit is added, which can monitor the degree of resonant frequency drift in the LLC resonant induction heating power supply in real time based on the measured values of the secondary side current peak of the half-bridge inverter circuit and the load capacity of the load part.

[0085] refer to Figure 7 The abnormality detection unit can receive real-time measurement results of the voltage detection device and the current detection device arranged on the secondary side of the half-bridge inverter circuit, obtain the load capacity of the load part (generally, it can be expressed by average power) and the secondary side current peak value according to the measurement results, and evaluate the degree of resonant frequency drift of the LLC resonant network by judging whether the measured values of the secondary side current peak value and the load capacity exceed the normal operating area.

[0086] In an embodiment of the present application, the normal operating area is between the load capacity-secondary current peak slope corresponding to the ideal resonant frequency and the load capacity-secondary current peak slope corresponding to the upper limit of the resonant frequency drift.

[0087] The following describes how to determine the load capacity-secondary current peak slope and the normal operating area with reference to the accompanying drawings.

[0088] Figure 8 The figure shows the transformer secondary side current waveform before and after aging of the components in the circuit with the same load capacity (correspondingly, the switching cycle of the power device needs to be ensured to be the same).

[0089] Without loss of generality, a wide and low waveform is used to represent the secondary current waveform corresponding to the ideal resonant frequency that can be achieved by the circuit when the components in the circuit are not aged and the power devices are switched at a set period. This waveform represents the current that the induction heating power supply should theoretically output when it is in normal working condition; a narrow and high waveform is used to represent the secondary current waveform output by the heating power supply after the resonant frequency point drifts upward due to aging of the components in the circuit (generally, device aging will cause the resonant frequency point to shift upward compared to the ideal resonant frequency). Considering that the current has a half-wave symmetry characteristic, only the upper half can be analyzed, such as Figure 8 As shown, the area enclosed by the two waveforms can be expressed by formula (8) and formula (9) respectively:

[0090]

[0091] Where h2 and h1 represent the secondary current peaks at the ideal resonant frequency and after the resonant frequency drifts upward under the same load capacity, respectively. b and a represent the corresponding secondary current durations. When the load capacity is the same and minor effects such as the control dead zone are ignored, it can be assumed that the arched areas enclosed by the two different current waveforms in the figure should be consistent, that is:

[0092]

[0093] From formula (10), it can be seen that after the resonant frequency drifts upward, compared with the ideal resonant frequency, the ratio of the secondary side peak current and the ratio of the current duration are inversely proportional.

[0094] Using the above relationship, we can calculate the ideal secondary side peak current corresponding to each load capacity, and then connect the points to get Figure 9 The expression of the slash B in the figure is shown in formula (11):

[0095]

[0096] Then, according to formula (11), we can directly obtain the upward drift of the resonant frequency relative to the ideal resonant frequency (the ratio is times) the corresponding slope K a ,and When the upper limit of the allowed upward drift of the resonant frequency is set, K aWhen setting (for example, setting the upper limit of the resonant frequency drift to 120% of the ideal resonant frequency according to the component specifications of the resonant capacitor), you can get Figure 9 The load capacity corresponding to the upper limit of the resonant frequency drift - the secondary side current peak slope A. Obviously, the normal operating range of the induction heating power supply is between the slope B and the slope A.

[0097] In some specific embodiments, the abnormality detection unit continuously collects the load capacity and the secondary side peak current, and then when it detects that the secondary side current peak exceeds Figure 9 When the modulation unit is outside the normal working range, a warning message is sent to the modulation unit, and the modulation unit stops the phase power device from sending the drive signal for a period of time and cuts off the input and output; further, if the modulation unit receives more than a limited number of warning messages within the set time interval, it further sends a serious fault signal to the upper computer and other devices, and the upper computer and other devices or through manual operation completely cut off the power supply.

[0098] Compared with traditional spectrum analysis methods, the above-mentioned anomaly detection method has a simple, efficient and accurate calculation and analysis process. It has the advantages of adapting to complex working conditions, high sensitivity and low computational complexity, is easy to implement in real time in embedded systems, and has good adaptability to resonant frequency drift. It can quickly warn in the early stages of faults and improve the reliability and safety of the system.

[0099] In some specific embodiments, the above-mentioned modulation unit, odd harmonic control unit and abnormality detection unit can all be implemented by devices such as a digital signal processor (DSP), a microcontroller unit (MCU), a field programmable gate array (FPGA), an embedded system based on Linux or RTOS, etc., which have been written with corresponding functional programs or can execute corresponding algorithms. In addition, the above-mentioned devices also communicate with a host computer, which can be a desktop computer, a laptop computer, a tablet computer, a mobile phone or other device, which is equipped with an interactive operation interface, and can realize operations such as control parameter setting and adjustment, and real-time acquisition and processing of abnormal information.

[0100] Some embodiments of the present application also provide a control method for an LLC resonant induction heating power supply. The control method uses the aforementioned control system of the LLC resonant induction heating power supply to control the LLC resonant induction heating power supply to heat a load. The specific implementation of the above method has been described in detail in the previous description of the control system and will not be repeated here.

[0101] The above is a detailed introduction to the specific implementation methods of the present application. For those skilled in the art, several improvements and modifications can be made to the present application without departing from the principles of the present application. These improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A control system for an LLC resonant induction heating power supply, wherein the LLC resonant induction heating power supply heats a load via a half-bridge inverter circuit, comprising a modulation unit configured to determine a target modulation index and a fundamental frequency, and to output a high-frequency AC square wave with adjustable frequency by controlling the switching of each power device of the half-bridge inverter circuit, wherein: The waveform of the high-frequency AC square wave has a half-wave symmetrical structure with the fundamental wave duration as the period; The control system also includes an odd harmonic control unit for predicting and outputting the optimal switching angle combination of each power device while meeting the odd harmonic suppression target. The modulation unit generates a modulation signal for controlling the switching of each power device based on the optimal switching angle combination.

2. The control system of the LLC resonant induction heating power supply according to claim 1, characterized in that: The odd harmonic suppression objectives are: Where M is the target modulation index, M min 、M max are the lower and upper limits of M respectively, is the optimal switching angle combination, 2n+1 is the expression of the order of odd harmonics that need to be suppressed, and N is the upper limit of n.

3. The control system of the LLC resonant induction heating power supply according to claim 1, characterized in that: The odd harmonic control unit uses a trained artificial neural network, takes the target modulation index as input, and predicts and outputs the optimal switching angle combination, wherein the training set for training the artificial neural network is obtained by searching through an enhanced particle swarm optimization algorithm based on switching angle sorting constraints and modulation index constraints.

4. The control system of the LLC resonant induction heating power supply according to claim 3, characterized in that: The enhanced particle swarm optimization algorithm adopts a main group-subgroup hierarchical search strategy, which satisfies the preset main group fitness function and subgroup fitness function as the search objectives of the main iterative search process and the sub-iterative search process, respectively, and iteratively searches for the optimal switching angle combination corresponding to each modulation index in the switching angle search space. The main group-subgroup hierarchical search strategy is specifically as follows: In each main iterative search process, all search particles are first controlled to execute the main group search strategy to search with the goal of satisfying the modulation index. Then, each search particle is controlled to execute the subgroup search strategy at least once in the sub-iterative search process to search with the goal of suppressing each odd harmonic and satisfying the switching angle sorting constraint and the modulation index constraint.

5. The control system of the LLC resonant induction heating power supply according to claim 4, characterized in that: The main group fitness function FF0 is: The subgroup fitness function FF h for: in, is the target fundamental amplitude determined based on the target modulation index, V1 is the actual fundamental amplitude; V h is the amplitude of the hth harmonic, w0, w h are the weight coefficients corresponding to the fundamental amplitude error and the amplitude error of each odd harmonic, λ1 and λ2 are the penalty factors for violating the angle constraint and modulation index constraint, respectively. violation is the penalty term for the wrong switching angle sequence; P M is the penalty term when the modulation index M exceeds the legal range.

6. The control system of the LLC resonant induction heating power supply according to claim 4 or 5, characterized in that: During each iterative search process, each search particle also performs a perturbation update action, and the perturbation update amplitude is determined based on the sinusoidal perturbation model shown in the following formula: Dth i =A sin(2πf i ×k+φ i ), i∈[1,4], Where Δθ i is the angular disturbance of the i-th switching angle, A is the disturbance amplitude, f i 、φ i are the disturbance frequency and initial phase of the i-th switching angle respectively, and k is the number of iterations of the current search.

7. The control system of the LLC resonant induction heating power supply according to claim 1, characterized in that: Also includes: The abnormality detection unit performs real-time monitoring of the resonant frequency drift of the LLC resonant induction heating power supply based on the measured values of the secondary side current peak value and the load capacity.

8. The control system of the LLC resonant induction heating power supply according to claim 7, characterized in that: The real-time monitoring operation monitors the degree of resonant frequency drift by determining whether the measured values of the secondary side current peak and the load capacity exceed the normal operating range, wherein the normal operating range is between the load capacity-secondary side current peak slope corresponding to the ideal resonant frequency and the load capacity-secondary side current peak slope corresponding to the upper limit of the resonant frequency drift.

9. The control system of the LLC resonant induction heating power supply according to claim 8, characterized in that: The slope of the load capacity-secondary current peak slope corresponding to the upper limit of the resonant frequency drift is K a The slope of the load capacity-secondary current peak slope corresponding to the ideal resonant frequency is K b , and K a With K b The ratio is the reciprocal of the ratio of the secondary side current duration a corresponding to the upper limit of the resonant frequency drift under the same load capacity to the secondary side current duration b corresponding to the ideal resonant frequency.

10. A control method for an LLC resonant induction heating power supply, characterized in that: The control system of the LLC resonant induction heating power supply according to claim 1 is used to control the LLC resonant induction heating power supply to heat a load.

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