Power prediction model construction method for resonant inverter of induction heating equipment

Abstract

The present application provides a method for constructing a power prediction model of a resonant inverter of an induction heating device, the method comprising: according to the mutual inductance principle between a primary circuit and a secondary workpiece, the resistance of the secondary workpiece is equivalent to the primary circuit to obtain a resonant load circuit of the primary circuit; a dq-axis equivalent circuit model of the resonant load circuit is constructed, the dq-axis equivalent circuit model comprises a d-axis equivalent circuit model and a q-axis equivalent circuit model, wherein the d-axis equivalent circuit model is the original circuit model of the resonant load circuit, and the q-axis equivalent circuit model is delayed by ninety degrees in phase angle compared with the original circuit model; based on the dq-axis equivalent circuit model and a three-phase control algorithm, a power prediction model of the resonant inverter is constructed, the power prediction model is used to predict the output power and lumped disturbance at the K+1th moment, and the output power at the K+2th moment, based on the compensated inductor current and input voltage of the resonant load circuit at the Kth moment.

Description

Technical Field

[0001] The present application relates to the field of power electronic control technology, and in particular to a method for constructing a power prediction model of a resonant inverter of an induction heating device. Background Art

[0002] As a non-contact heating method, induction heating technology has been widely used in industrial production due to its advantages such as rapid heating and low surface oxidation. However, as China's heavy industry enters the stage of de-capacity, the continuous evolution of market demand has put forward higher requirements for the flexibility of induction heating equipment.

[0003] In induction heating equipment, the control of resonant inverters mostly adopts traditional control methods such as frequency modulation control, PI control, asymmetric voltage elimination control, etc. In the increasingly complex actual working conditions, the heat disturbances and load changes generated by induction heating equipment have caused traditional control to have defects such as large overshoot and poor anti-interference ability, making it difficult to meet the higher requirements of induction heating.

[0004] Due to the market demands of metal processing, energy and power electronics, induction heating equipment is expected to have a wide range of output power according to different process requirements and be able to flexibly heat target loads of different sizes and materials. These requirements set more stringent standards for the robustness, dynamic response capability and control flexibility of induction heating equipment.

[0005] In addition, the induction heating equipment cannot accurately determine the heating status of the target load. When the melting points of the welding material and the base material in the target load are close, the base material will be damaged if the target load changes cannot be observed in time. The resonant inverter has strong nonlinear characteristics, which limits the application of model predictive control (MPC) in high-frequency resonant inverters.

[0006] In view of this, there is an urgent need for a method that can improve the defects of the resonant inverter, such as large overshoot, poor anti-interference ability, poor robustness, poor dynamic response ability and poor control flexibility. Summary of the invention

[0007] The present application provides a power prediction model construction method of a resonant inverter of an induction heating device, a resonant inverter control method of an induction heating device, and related equipment to improve the large overshoot of the resonant inverter, improve anti-interference ability, improve robustness, improve dynamic response ability, and improve poor control flexibility.

[0008] The first aspect of the present application provides a method for constructing a power prediction model of a resonant inverter of an induction heating device, wherein the resonant inverter includes a primary circuit, and the primary circuit is used to provide heat for a secondary workpiece. The method includes: according to the mutual inductance principle between the primary circuit and the secondary workpiece, the resistance of the secondary workpiece is equivalent to the primary circuit to obtain a resonant load circuit of the primary circuit; a dq-axis equivalent circuit model of the resonant load circuit is constructed, and the dq-axis equivalent circuit model includes a d-axis equivalent circuit model and a q-axis equivalent circuit model, wherein the d-axis equivalent circuit model is the original circuit model of the resonant load circuit, and the q-axis equivalent circuit model is delayed by ninety degrees in phase angle compared with the original circuit model; based on the dq-axis equivalent circuit model and a three-phase control algorithm, a power prediction model of the resonant inverter is constructed, and the power prediction model is used to predict the output power and lumped disturbance at the K+1th moment, and the output power at the K+2th moment based on the compensated inductor current and input voltage of the resonant load circuit at the Kth moment.

[0009] In some embodiments of the first aspect, constructing a dq-axis equivalent circuit model of a resonant load circuit includes: constructing an initial d-axis equivalent circuit model and an initial q-axis equivalent circuit model of the resonant load circuit, and combining the initial d-axis equivalent circuit model and the initial q-axis equivalent circuit model into an equivalent circuit model in a rectangular form; and converting the rectangular equivalent circuit model into a rectangular equivalent circuit model in a synchronous coordinate system to obtain a dq-axis equivalent circuit model.

[0010] In some embodiments of the first aspect, a power prediction model of a resonant inverter is constructed based on a dq-axis equivalent circuit model and a three-phase control algorithm, including: constructing an output power model of a resonant load circuit based on the dq-axis equivalent circuit model; constructing an initial power prediction model of the resonant load circuit according to a forward Euler discretization method and the output power model; and obtaining a power prediction model of the resonant inverter according to the three-phase control algorithm and the initial power prediction model.

[0011] In some embodiments of the first aspect, a power prediction model of the resonant inverter is obtained according to a three-phase control algorithm and an initial power prediction model, including: constructing a first-order hyperlocal model of the resonant load circuit based on the initial power prediction model; transforming the output power model into a power differential model according to a preset time interval; and obtaining the power prediction model of the resonant inverter according to the lumped disturbance equality conditions at different times within the control cycle, the power differential model and the first-order hyperlocal model.

[0012] In some embodiments of the first aspect, a power prediction model of the resonant inverter is obtained according to a three-phase control algorithm and an initial power prediction model, including: introducing a linear extended state observer into the initial power prediction model to construct a power prediction model of the resonant inverter.

[0013] A second aspect of the present application provides a resonant inverter control method for an induction heating device, the method comprising: obtaining a compensation inductor current and an input voltage at the Kth moment in a resonant load circuit of a primary circuit of the resonant inverter, and using the obtained compensation inductor current and input voltage as the compensation inductor current and input voltage at the Kth moment; converting the compensation inductor current and input voltage at the Kth moment into a d-axis and q-axis compensation inductor current non-rotating vector and an input voltage non-rotating vector; inputting the d-axis and q-axis compensation inductor current non-rotating vector and the input voltage non-rotating vector into a power prediction model of the resonant inverter, outputting an output power and a lumped disturbance at the K+1th moment, and an output power at the K+2th moment; and controlling the conduction of a switch tube of the primary circuit based on the output power and the lumped disturbance at the K+1th moment and the output power at the K+2th moment.

[0014] In some embodiments of the second aspect of the present application, based on the output power and the lumped disturbance at the K+1th moment and the output power at the K+2th moment, the conduction of the switch tube of the primary circuit is controlled, including: determining whether the square of the difference between the output power at the K+2th moment and the reference output power is less than a preset threshold; if it is greater than or equal to the preset threshold, re-obtaining the compensation inductor current and input voltage of the resonant load circuit as the compensation inductor current and input voltage at the Kth moment until the square is less than the preset threshold; if it is less than the preset threshold, converting the output power and the lumped disturbance at the K+1th moment, the input power and the phase angle into a conversion model, and outputting the phase angle at the K+1th moment; and controlling the conduction of the switch tube of the primary circuit according to the phase angle at the K+1th moment.

[0015] In some embodiments of the second aspect of the present application, the compensated inductor current and input voltage at the Kth moment are converted into the compensated inductor current non-rotating vector and input voltage non-rotating vector of the d-axis and q-axis, including: determining the compensated inductor current and input voltage at the Kth moment as the d-axis inductor current rotating vector and input voltage rotating vector; delaying the compensated inductor current and input voltage at the Kth moment by a phase angle of ninety degrees to obtain the q-axis inductor current rotating vector and input voltage rotating vector; and converting the compensated inductor current rotating vector and input voltage rotating vector of the d-axis and q-axis into the compensated inductor current non-rotating vector and input voltage non-rotating vector of the d-axis and q-axis through a park algorithm.

[0016] According to a third aspect of the present application, there is provided an induction heating device, which includes a resonant inverter and a control unit. The resonant inverter includes a primary circuit, which is used to provide heat for a secondary workpiece. The control unit is used to, according to the mutual inductance principle between the primary circuit and the secondary workpiece, convert the resistance of the secondary workpiece to the primary circuit to obtain a resonant load circuit of the primary circuit; construct a dq-axis equivalent circuit model of the resonant load circuit, the dq-axis equivalent circuit model includes a d-axis equivalent circuit model and a q-axis equivalent circuit model, wherein the d-axis equivalent circuit model is the original circuit model of the resonant load circuit, and the q-axis equivalent circuit model is delayed by ninety degrees in phase angle compared with the original circuit model; based on the dq-axis equivalent circuit model and the three-phase control algorithm, construct a power prediction model of the resonant inverter, the power prediction model is used to predict the output power and lumped disturbance at the K+1th moment, and the output power at the K+2th moment based on the compensated inductor current and input voltage of the resonant load circuit at the Kth moment;

[0017] The control unit is also used to obtain the compensation inductor current and input voltage of the resonant load circuit, and use the obtained compensation inductor current and input voltage as the compensation inductor current and input voltage at the Kth moment; convert the compensation inductor current and input voltage at the Kth moment into the compensation inductor current non-rotating vector and input voltage non-rotating vector of the d-axis and q-axis; input the compensation inductor current non-rotating vector and input voltage non-rotating vector of the d-axis and q-axis into the power prediction model of the resonant inverter, output the output power and lumped disturbance at the K+1th moment, and the output power at the K+2th moment; and control the conduction of the switch tube of the primary circuit based on the output power and lumped disturbance at the K+1th moment and the output power at the K+2th moment.

[0018] In a fourth aspect, the present application provides a control unit for an induction heating device, comprising: a processor and a memory; the memory is coupled to the processor, the memory is used to store computer program code, and the processor calls the computer program code to enable the control unit to execute a method as described in any one of the first aspect or the second aspect.

[0019] The power prediction model construction method of the resonant inverter of the induction heating equipment of the present application, the resonant inverter control method of the induction heating equipment and related equipment, by constructing the d-axis equivalent circuit model and the q-axis equivalent circuit model of the resonant load circuit, obtains the dq-axis equivalent circuit model of the circuit similar to the control system of the three-phase power electronic converter (hereinafter referred to as the three-phase control system), so as to introduce the three-phase control algorithm of the three-phase control system. Compared with the single-phase control algorithm, the three-phase control algorithm makes the resonant inverter smaller and more efficient at the same output power. At the same time, compared with the traditional control algorithm, the three-phase control algorithm can improve the power dynamic response capability, robustness, system anti-interference and conversion efficiency of the resonant inverter.

[0020] Next, based on the dq-axis equivalent circuit model and the three-phase control algorithm, a power prediction model of the resonant inverter is constructed. The power prediction model predicts the output power and lumped disturbance of the resonant load circuit at the K+1th moment, as well as the output power at the K+2th moment, to control the conduction of the switch tube in the primary circuit, thereby improving the heating efficiency of the induction heating equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0022] Figure 1 An application scenario diagram of the induction heating device provided in an embodiment of the present application;

[0023] Figure 2 A schematic diagram of the structure of an induction heating device provided in an embodiment of the present application;

[0024] Figure 3 A schematic diagram of a process of constructing a power prediction model of a resonant inverter of an induction heating device provided in an embodiment of the present application;

[0025] Figure 4 An application scenario diagram of a method for constructing a power prediction model for a resonant inverter of an induction heating device provided in an embodiment of the present application;

[0026] Figure 5 An application scenario diagram of a power prediction model construction method of a resonant inverter of an induction heating device and a resonant inverter control method of an induction heating device provided in an embodiment of the present application;

[0027] Figure 6 An equivalent circuit diagram of a dq-axis equivalent circuit model construction process in a power prediction model construction method for a resonant inverter of an induction heating device provided in an embodiment of the present application;

[0028] Figure 7 An equivalent circuit diagram of a dq-axis equivalent circuit model of a power prediction model of a method for constructing a power prediction model of a resonant inverter of an induction heating device provided in an embodiment of the present application;

[0029] Figure 8 A schematic diagram of a flow chart of a resonant inverter control method for an induction heating device provided in an embodiment of the present application;

[0030] Fig. 9 A schematic diagram of the structure of a control unit of an induction heating device provided in an embodiment of the present application.

[0031] The above drawings have shown clear embodiments of the present application, which will be described in more detail later. These drawings and text descriptions are not intended to limit the scope of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0032] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0033] The terms "first", "second", etc. involved in this application are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0034] See also Figure 1 , Figure 1 The induction heating device 100 is an application scenario diagram of the induction heating device of the present application. According to the resonant inverter control method of the induction heating device provided by the present application, the induction heating device 100 converts the DC power of the DC power supply into AC power with adjustable frequency, so that eddy currents are generated inside the secondary workpiece 200 (target load), thereby generating heat.

[0035] See also Figure 2 , Figure 2 The induction heating device 100 of the present application is a structural diagram. The induction heating device 100 at least includes a resonant inverter 10 and a control unit 20. The resonant inverter 10 includes other components (not shown) and a primary circuit 11. The primary circuit 11 includes a support capacitor C i , full-bridge inverter circuit 12, resonant circuit 13 and heating coil L p The full-bridge inverter circuit 12 includes switch tubes S1 to S4 and reverse diodes D1 to D4 respectively connected in parallel with the switch tubes S1 to S4. The resonant circuit 13 includes a compensation inductor L r and resonant capacitor C p The connection relationship and operation principle of the relevant components in the resonant inverter 10 can refer to the relevant technology. In some embodiments, the induction heating device 100 also includes a DC power supply U DC ( Figure 2 Not shown), or an external DC power supply U DC , DC power supply U DC The two ends are connected to the support capacitor C i Connect both ends.

[0036] The control unit 20 includes a voltage sampling circuit 21, a current sampling circuit 22 and a device power supply (DSP) main control circuit 23. The voltage sampling circuit 21 is used to collect the input voltage V at both ends of the resonant circuit 13. in The current sampling circuit 22 is used to collect the compensation inductor L r The compensation inductor current I r The device power supply main control circuit 23 is used to control the resonant inverter 10 of the induction heating device 100 provided in the present application, and controls the switching tubes S1 to S4 to conduct according to the phase angle, so as to convert the DC power supply U DC The direct current is converted into an alternating current with adjustable power. The alternating current causes the heating coil to generate an alternating magnetic field. The alternating magnetic field causes eddy currents to be generated inside the secondary workpiece 200, thereby generating heat.

[0037] It should be noted that Figure 2 This is only a schematic diagram of a structure provided in the embodiment of the present application. Figure 2 The actual form of the various devices included in the Figure 2 The interaction mode between devices is limited, and in the specific application of the solution, it can be set according to actual needs.

[0038] The present application provides a method for constructing a power prediction model of a resonant inverter of an induction heating device, so as to construct a power prediction model of the resonant inverter. The induction heating device 100 implements a control method for the resonant inverter of the induction heating device according to the power prediction model of the resonant inverter.

[0039] The technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems are described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0040] Please combine Figures 3 to 6 , Figure 3 The present invention provides a flow chart of a method for constructing a power prediction model of a resonant inverter of an induction heating device. The execution subject of the construction method can be a control device, such as a personal computer and a server. It can also be an induction heating device 100, specifically, it can be a control unit 20. Figure 3 As shown, the construction method may include the following steps:

[0041] Step S110: According to the mutual inductance principle between the primary circuit and the secondary workpiece, the resistance of the secondary workpiece is equivalent to the primary circuit to obtain a resonant load circuit of the primary circuit.

[0042] Specifically, the expression of the resistance of the secondary workpiece 200 is as follows:

[0043] (1)

[0044] in, represents the resistance of the secondary workpiece 200, represents the angular frequency of the AC signal of the resonant inverter, Indicates heating coil L p The coil L of the secondary workpiece 200 s The mutual induction, represents the self-inductance of the secondary workpiece 200, Indicates coil L s The self-inductance.

[0045] The resistance of the secondary workpiece 200 After being equivalent to the primary circuit 11, the resonant load circuit 14 of the primary circuit 11 is obtained as follows: Figure 4 shown in (2).

[0046] Step S120: constructing a dq-axis equivalent circuit model of the resonant load circuit.

[0047] Specifically, the construction of the dq axis equivalent circuit model includes the following steps:

[0048] Step S121: constructing an initial d-axis equivalent circuit model and an initial q-axis equivalent circuit model of the resonant load circuit.

[0049] In actual working conditions, the angular frequency of the AC signal will be The resonant frequency of the resonant inverter 10 is set near the resonant frequency point, so that the resonant circuit 13 in the resonant inverter 10 has a higher quality factor, for example, the quality factor is greater than 5. At this time, the AC signal in the secondary workpiece 200 is approximately the fundamental wave, so please combine Figure 5 , the AC signal of the resonant load circuit 14 can be expressed as follows:

[0050] (2)

[0051] in, Indicates the input voltage, Indicates the amplitude of the input voltage, represents the working time of the resonant inverter 10, represents the phase angle of the input voltage, Indicates the output voltage, Indicates the amplitude of the output voltage, represents the phase angle of the output voltage, Indicates the compensation inductor L r The compensation inductor current, represents the amplitude of the compensation inductor current, represents the phase angle of the compensation inductor current, Represents the output current, Indicates the amplitude of the output current, Indicates the phase angle of the output current.

[0052] In this way, the AC signal of the resonant load circuit 14 can be regarded as the AC signal of the initial d-axis equivalent circuit model, and the AC signal with a phase angle delayed by ninety degrees compared with the AC signal of the initial d-axis equivalent circuit model can be regarded as the AC signal of the initial q-axis equivalent circuit model. Thus, the initial d-axis equivalent circuit model and the initial q-axis equivalent circuit model are created based on the resonant load circuit 14. The circuit diagrams of the initial d-axis equivalent circuit model and the initial q-axis equivalent circuit model are as shown in FIG. Figure 6 As shown in (1). In one embodiment, the AC signals of the d-axis equivalent circuit model and the q-axis equivalent circuit model refer to the AC signals when the induction heating device 100 is working in a steady state.

[0053] Step S122: The initial d-axis equivalent circuit model and the initial q-axis equivalent circuit model are combined into a rectangular equivalent circuit model.

[0054] Combined with the Euler formula, the initial d-axis equivalent circuit model and the initial q-axis equivalent circuit model can be used to obtain the initial dq-axis equivalent circuit model. The expression of the AC signal of the initial dq-axis equivalent circuit model is as follows:

[0055] (3)

[0056] in, Indicates that the AC signal is The angular frequency of rotation, Indicates that the AC signal is The angular frequency of rotation, j represents the imaginary expression, represents the rotating vector of the input voltage, represents the rotating vector of the output voltage, represents the rotating vector of the compensation inductor current, Represents the rotating vector of the coil current of the heating coil. represents the non-rotating vector of the input voltage, represents the non-rotating vector of the output voltage, Represents the non-rotating vector of the compensation inductor current. The non-rotating vector of the coil current of the heating coil. The subscript of the AC signal indicates the AC signal of a specific circuit. For example, represents the rotation vector of the input voltage of the initial dq-axis equivalent circuit model, represents the rotation vector of the input voltage of the initial d-axis equivalent circuit model, Represents the rotating vector of the input voltage of the initial q-axis equivalent circuit model.

[0057] The real component of formula (3) can be regarded as the AC signal of the initial d-axis equivalent circuit model, and the imaginary component of formula (3) can be regarded as the AC signal of the initial q-axis equivalent circuit model.

[0058] It can be understood that formula (3) also reflects the equivalent relationship from the rotating vector of the AC signal to the non-rotating vector. Therefore, according to formula (3), the initial d-axis equivalent circuit model and the initial q-axis equivalent circuit model in the initial dq-axis equivalent circuit model can be combined into a rectangular equivalent circuit model in which the AC signal is represented in the form of a non-rotating vector. The rectangular equivalent circuit model is as follows: Figure 6 shown in (2).

[0059] Step S123: converting the rectangular equivalent circuit model into a rectangular equivalent circuit model in a synchronous coordinate system to obtain a dq axis equivalent circuit model.

[0060] Specifically, based on Kirchhoff's Voltage Law (KVL) and the rectangular equivalent circuit model, the expression of the rectangular equivalent circuit model can be obtained as follows:

[0061] (4)

[0062]

[0063] in, Indicates the compensation inductor L r The inductance, Resonance capacitor C p Capacitance.

[0064] Next, multiply both sides of equation (4) by The following equation (5) can be obtained:

[0065] (5)

[0066]

[0067] That is, by multiplying both sides by , the angular frequency rotation of the AC signal can be eliminated, and the AC signal of the rectangular equivalent circuit model can be unified into a non-rotational quantity, that is, the AC signal of the rectangular equivalent circuit model is converted into a rectangular equivalent circuit model in a synchronous coordinate system. The rectangular equivalent circuit model in the synchronous coordinate system is as follows: Figure 6 shown in (3).

[0068] Finally, according to formula (5), it can be split into the following formulas (6) and (7).

[0069] (6)

[0070] (7)

[0071] According to formula (6), the d-axis equivalent circuit model can be obtained, and according to formula (7), the q-axis equivalent circuit model can be obtained. The d-axis equivalent circuit model and the q-axis equivalent circuit model are as follows: Figure 7 That is, the dq-axis equivalent circuit model includes a d-axis equivalent circuit model and a q-axis equivalent circuit model, wherein the d-axis equivalent circuit model is the original circuit model of the resonant load circuit 14, and the q-axis equivalent circuit model is delayed by ninety degrees in phase angle compared with the original circuit model.

[0072] It can be understood that by constructing the d-axis equivalent circuit model and the q-axis equivalent circuit model of the resonant load circuit 14, a dq-axis equivalent circuit model of a circuit similar to a control system of a three-phase power electronic converter (hereinafter referred to as a three-phase control system) is obtained, so as to facilitate the introduction of a three-phase control algorithm. That is, by using the resonant single-phase synchronous dq coordinate system modeling method to establish a cross-coupling model of the resonant circuit 13 in the resonant inverter 10, a circuit model of a dq-axis circuit similar to a three-phase control system can be obtained, so that the control model in the three-phase control system can be applied to the induction heating device 100.

[0073] Compared with the single-phase control algorithm, the three-phase control algorithm can make the resonant inverter 10 smaller and more efficient at the same output power. Compared with the traditional control algorithm, the three-phase control algorithm can improve the power dynamic response capability, robustness, system anti-interference performance and conversion efficiency of the resonant inverter 10, thereby improving the heating efficiency of the induction heating device 100.

[0074] From the d-axis equivalent circuit model and the q-axis equivalent circuit model, it can be seen that there is q-axis current information in the d-axis circuit and there is d-axis current information in the q-axis circuit, showing cross-characteristic coupling, which decomposes the original large signal model into a more accurate signal model.

[0075] Step S130: constructing a power prediction model of the resonant inverter based on the dq-axis equivalent circuit model and the three-phase control algorithm.

[0076] The three-phase control algorithm is an algorithm used to control a three-phase power electronic converter, such as PI decoupling control, model predictive control (MPC), model-free predictive control (MFPC), and disturbance observer.

[0077] According to Figure 7 The dq-axis equivalent circuit model shown, combined with the three-phase control algorithm, can construct a power prediction model for the resonant inverter 10. The power prediction model is used to predict the output power and lumped disturbance at the K+1th moment, and the output power at the K+2th moment based on the compensation inductor current and input voltage of the resonant load circuit 14 at the Kth moment.

[0078] That is, the control unit 20 obtains the compensated inductor current and input voltage of the resonant load circuit, and uses the obtained compensated inductor current and input voltage as the compensated inductor current and input voltage at the Kth moment, transforms the compensated inductor current and input voltage at the Kth moment into the d-axis and q-axis compensated inductor current non-rotating vector and input voltage non-rotating vector, and inputs them into the power prediction model. The power prediction model outputs the output power and lumped disturbance at the K+1th moment, and the output power at the K+2th moment.

[0079] The control unit 20 can control the conduction of the switch tube of the primary circuit 11 based on the output power and the lumped disturbance at the K+1th moment, and the output power at the K+2th moment, and switch the DC power supply U DC The DC power is converted into an adjustable AC power, which makes the heating coil generate L p The alternating magnetic field generates eddy currents inside the secondary workpiece 200, thereby generating heat.

[0080] It can be understood that the above technical solution, by constructing the d-axis equivalent circuit model and the q-axis equivalent circuit model of the resonant load circuit 14, obtains the dq-axis equivalent circuit model of the circuit similar to the control system of the three-phase power electronic converter (hereinafter referred to as the three-phase control system), so as to introduce the three-phase control algorithm, so that the volume of the resonant inverter 10 is smaller and the conversion efficiency is higher. Compared with the traditional control algorithm, the three-phase control algorithm can improve the power dynamic response capability, robustness, system anti-interference of the resonant inverter 10 and the conversion efficiency of the resonant inverter 10.

[0081] Next, based on the dq-axis equivalent circuit model and the three-phase control algorithm, a power prediction model of the resonant inverter 10 is constructed. The power prediction model predicts the output power and lumped disturbance of the resonant load circuit 14 at the K+1th moment and the output power at the K+2th moment to control the conduction of the switch tube of the primary circuit 11, thereby improving the heating efficiency of the induction heating device 100.

[0082] In some embodiments, step S130: constructing a power prediction model of a resonant inverter based on a dq-axis equivalent circuit model and a three-phase control algorithm comprises the following steps:

[0083] Step S131: constructing an output power model of the resonant load circuit based on the dq-axis equivalent circuit model.

[0084] Specifically, based on the dq axis equivalent circuit model, an output power model of the resonant load circuit 14 is constructed, and the formula of the output power model is as follows:

[0085] (8)

[0086] in, represents the output power of the resonant load circuit 14 at the Kth moment, represents the non-rotating vector of the d-axis input voltage at the Kth moment, represents the non-rotating vector of the d-axis compensation inductor current at the Kth moment, represents the non-rotating vector of the q-axis input voltage at the Kth moment, Represents the non-rotating vector of the q-axis compensation inductor current at the Kth moment. Indicates input voltage The effective value of the compensation inductor current It is worth mentioning that the expression of the effective value of the input voltage is:

[0087] , Indicates DC power supply voltage.

[0088] It can be understood that because the output voltage of the resonant load circuit 14 is not a standard sine wave, when calculating the output power, the effective value of the input voltage is introduced to optimize the input voltage.

[0089] Step S132: constructing an initial power prediction model of the resonant load circuit according to the forward Euler discretization method and the output power model.

[0090] Specifically, in a continuous control cycle, the input voltage and the compensation inductor current are continuous, and according to the forward Euler discretization method and the output power model, an initial power prediction model of the resonant load circuit 14 can be obtained. The expression of the initial power prediction model is:

[0091] (9)

[0092] in, represents the output power at the K+1th moment, represents the output power at the K+2th moment, represents the inductive internal resistance of the compensation inductor Lr, represents the control cycle, represents the reactive power at the Kth moment, represents the reactive power at the K+1th moment, Used to refer to the formula following an equation. Calculated according to formula (8).

[0093] Step S133: Obtaining a power prediction model of the resonant inverter according to the three-phase control algorithm and the initial power prediction model.

[0094] In one embodiment, the three-phase control algorithm used is model-free predictive control MFPC, that is, a power prediction model of the resonant inverter 10 is constructed by a super-local model. Specifically, the following steps are included:

[0095] Firstly, based on the initial power prediction model, a first-order super-local model of the resonant load circuit 14 is constructed.

[0096] Specifically, based on the initial power prediction model, an initial first-order super-local model of the resonant load circuit 14 is constructed, and the formula of the initial first-order super-local model is as follows:

[0097] (10)

[0098] in, is the lumped disturbance, is the unknown disturbance term, , Refers to the input gain of the first-order hyperlocal model.

[0099] It can be understood that the hyperlocal model is only related to nonlinear input variables and output variables compared to the model predictive control MPC. Therefore, the output power in formula (9) can be reduced to (that is, compensating the inductor current and input voltage) and Other variables other than the variable are equivalent to lumped disturbances , and we get formula (10).

[0100] Formula (10) is discretized to obtain the first-order hyperlocal model of the resonant load circuit 14. The expression of the first-order hyperlocal model is as follows:

[0101] (11)

[0102] Next, the output power model is transformed into a power difference model according to a preset time interval.

[0103] Specifically, since the resonant inverter adopts phase shift modulation control, the preset time interval refers to the Kth moment , and the K-1th moment That is, define and Under this condition, the output power model is differentiated to obtain the power differential model, which is as follows:

[0104] (12)

[0105] in, denoted by the differential power.

[0106] Finally, the power prediction model of the resonant inverter 10 is obtained according to the lumped disturbance equality conditions at different times, the power difference model and the super-local model.

[0107] It can be understood that when the sampling frequency is high, the aggregate disturbances at different times are equal, that is, The power prediction model of the resonant inverter 10 is as follows:

[0108] (13)

[0109] It can be understood that for this prediction stage (i.e., based on the output power and aggregate disturbance at the Kth moment, the output power and aggregate disturbance at the K+1th moment and the output power at the K+2th moment are predicted), in addition to the output power at the Kth moment is calculated from the sensed value, and Except for the unknown, other variables are preset or obtained from the calculation results of the previous forecasting stage.

[0110] It can be understood that the control unit 20 obtains the compensation inductor current and input voltage at the Kth moment and transforms them into the compensation inductor current non-rotating vector of the d-axis and q-axis , and the input voltage non-rotating vector , After that, the power prediction model (Formula (13)) is input to obtain the output power at the Kth moment. .based on Get the differential power at the Kth moment At the same time, based on the output power Get the output power at the K+1th moment , based on output power and Get the differential power at the K+1th moment Based on differential power and Get the gain at the K+1th moment Based on the gain and differential power Get the lumped disturbance at the K+1th moment .

[0111] Finally, according to the output power and lumped disturbance , and get the output power at the K+2th moment In this way, the power prediction model outputs the output power at the K+1th moment: and lumped disturbance , and the output power at the K+2th moment The output value of the power prediction model of this embodiment also carries To solve formula (20) .

[0112] In another embodiment, the three-phase control algorithm used is a linear extended state observer. That is,

[0113] A linear extended state observer is introduced into the initial power prediction model to construct a power prediction model of the resonant inverter 10 .

[0114] Specifically, a state equation of the resonant load circuit 14 is established, and the formula of the state equation is as follows:

[0115] (14)

[0116] in, Represents the differential of the state quantity of the resonant load circuit, , and Expressed as the system matrix of the resonant load circuit, represents the disturbance gain of the resonant load circuit, represents the system output of the resonant load circuit, Represents the state variable of the resonated load circuit.

[0117] Next, based on the formula of the state equation, a linear extended state observer (LESO) of the resonant load circuit 14 is constructed. The formula of the linear extended state observer is as follows:

[0118] (15)

[0119] It is represented as the output power observation and lumped disturbance observation of the linear extended state observer. represents the gain vector of the linear extended state observer, represents the estimated value of the observed value, It is represented as a system matrix. Represents the system output, Represents the system output after observation compensation.

[0120] According to the Lyapunov stability criterion, the characteristic equation of LESO can be expressed as:

[0121] (16)

[0122] in, is the control bandwidth of the linear extended state observer, represents the characteristic equation, represents the identity matrix, represents the Laplace expression, and Represents the gain factor.

[0123] In order to make the observer stable, the roots of the characteristic equation should all fall on the negative half axis, so the gain coefficient can be designed as:

[0124] (17)

[0125] Combining formula (9) and formula (14) to formula (17), the power prediction model based on the linear extended observer is obtained as follows:

[0126] (18)

[0127] in, Output power With power observation The error between .

[0128] Similarly, the control unit 20 obtains the compensation inductor current and input voltage at the Kth moment and transforms them into the compensation inductor current non-rotating vectors of the d-axis and q-axis , and the input voltage non-rotating vector , After inputting the power prediction model (Formula (18)), the output power observation values ​​at the K+1 and K+2 moments are obtained. , And the aggregate disturbance observation value at the K+1th moment .

[0129] That is, using the output power observation values ​​at the K+1 and K+2 moments , Update the output power at the K+1th and K+2th moments respectively and Then output the lumped disturbance observation value at the K+1th moment As the lumped disturbance at the K+1th moment .

[0130] It is understandable that when the system faces a large disturbance, the accuracy of the dynamic part estimation of the super-local model directly affects the control performance. In actual operation, the system has a large deviation in calculation due to the low sensor accuracy and the large disturbances such as high temperature and electromagnetic interference, which will lead to poor super-local model effect. Therefore, the improvement of MFPC relative to MPC is limited. Therefore, the linear extended state observer is used to perform feedback compensation to the control unit 20 to improve the estimation accuracy of the disturbance and improve the control effect of induction heating.

[0131] It can be understood that the linear expansion observer is introduced to observe the disturbance caused by the resonant inverter 10, so as to observe the heating condition of the secondary workpiece 200. Compared with the linear expansion observer of the traditional PI controller, only a reasonable control bandwidth needs to be set to achieve the effect of fast dynamic response and no overshoot.

[0132] See also Figure 5 and Figure 8 The present application also provides a control method for a resonant inverter 10 of an induction heating device 100. The execution subject of the control method may be the induction heating device 100, specifically, the control unit 20. Figure 8 As shown, the control method may include the following steps:

[0133] Step S210: obtaining the compensation inductor current and input voltage of the resonant load circuit of the primary circuit of the resonant inverter, and using the obtained compensation inductor current and input voltage as the compensation inductor current and input voltage at the Kth moment;

[0134] like Figure 5 As shown, the control unit 20 obtains the compensation inductor current at the Kth moment in the resonant load circuit 14 of the primary circuit 11 of the resonant inverter 10. and input voltage .

[0135] Step S220: converting the compensation inductor current and the input voltage at the Kth moment into a compensation inductor current non-rotating vector and an input voltage non-rotating vector of the d-axis and the q-axis.

[0136] Specifically, the inductor current will be compensated and input voltage According to the determination of the d-axis inductor current rotation vector and the input voltage rotation vector .

[0137] Next, the compensation inductor current and input voltage Delaying the phase angle by ninety degrees, we get the q-axis inductor current rotation vector and the input voltage rotation vector .

[0138] Then, the compensation inductor current of the d-axis and q-axis is rotated into vector , and the input voltage rotation vector , The non-rotating vector of the compensated inductor current converted to the d-axis and q-axis , and the input voltage non-rotating vector , .

[0139] Step S230: input the d-axis and q-axis compensation inductor current non-rotating vector and the input voltage non-rotating vector into the power prediction model of the resonant inverter, and output the output power and lumped disturbance at the K+1th moment, and the output power at the K+2th moment.

[0140] Step S240: Based on the output power and lumped disturbance at the K+1th moment, and the output power at the K+2th moment, control the conduction of the switch tube of the primary circuit 11.

[0141] Specifically, it is determined whether the square of the difference between the output power at the K+2th moment and the reference output power is less than a preset threshold. The formula is as follows:

[0142] (19)

[0143] in, represents the cost function, i.e. the output power at the K+2th moment With reference output power The square of the difference, Indicates the reference output power.

[0144] If it is greater than or equal to the preset threshold, the compensation inductor current and input voltage of the resonant load circuit are reacquired as the compensation inductor current and input voltage at the Kth moment until the square is less than the preset threshold.

[0145] If it is less than the preset threshold, the output power at the K+1th moment is and the lumped disturbance at the K+1th moment , the conversion model of input power and phase angle, output phase angle at the K+1th moment , and according to the phase angle at the K+1th moment Control the conduction of the switch tube of the primary circuit 11.

[0146] The conversion model of input power and phase angle is as follows:

[0147] (20)

[0148] Fig. 9 Schematic diagram of the structure of a control unit 20 of an induction heating device 100 provided in this application. Fig. 9 As shown, the control unit 20 includes:

[0149] Processor 24, memory 25 and bus 26;

[0150] The memory 25 is used to store the computer program code of the processor 24;

[0151] The processor 24 is configured to execute the technical solution of the control method of the phase-shifted full-bridge converter in any of the aforementioned method embodiments by executing the computer program code.

[0152] Optionally, the memory 25 can be independent or integrated with the processor 24.

[0153] The memory 25 is connected to the processor 24 via a bus 26 and implements communication therebetween.

[0154] Optionally, the memory 25 may include a random access memory (RAM), and may also include a non-volatile memory (non-volatile memory), such as at least one disk memory.

[0155] The bus 26 may be a peripheral component interconnect (PCI) bus or an extended industry standard architecture (EISA) bus, etc. The bus may be divided into an address bus, a data bus, a control bus, etc. For ease of representation, only one thick line is used in the figure, but it does not mean that there is only one bus or one type of bus.

[0156] The above-mentioned processor can be a general-purpose processor, including a central processing unit CPU, a network processor (NP), etc.; it can also be a digital signal processor DSP, an application-specific integrated circuit ASIC, a field programmable gate array FPGA or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components.

[0157] The control unit 20 is used to execute the technical solution provided in any of the aforementioned method embodiments, and its implementation principle and technical effect are similar and will not be repeated here.

[0158] Those skilled in the art can understand that all or part of the steps of implementing the above-mentioned method embodiments can be completed by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When the program is executed, the steps of the above-mentioned method embodiments are executed; and the aforementioned storage medium includes: ROM, RAM, disk or optical disk and other media that can store program codes.

[0159] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for constructing a power prediction model of a resonant inverter of an induction heating device, characterized in that: The resonant inverter includes a primary circuit, and the primary circuit is used to provide heat for a secondary workpiece. The method includes: According to the mutual inductance principle between the primary circuit and the secondary workpiece, the resistance of the secondary workpiece is equivalent to the primary circuit to obtain a resonant load circuit of the primary circuit; Constructing a dq-axis equivalent circuit model of the resonant load circuit, wherein the dq-axis equivalent circuit model includes a d-axis equivalent circuit model and a q-axis equivalent circuit model, wherein the d-axis equivalent circuit model is an original circuit model of the resonant load circuit, and the q-axis equivalent circuit model is delayed by ninety degrees in phase angle compared with the original circuit model; Based on the dq-axis equivalent circuit model, construct an output power model of the resonant load circuit; Constructing an initial power prediction model of the resonant load circuit according to the forward Euler discretization method and the output power model; According to the three-phase control algorithm and the initial power prediction model, a power prediction model of the resonant inverter is obtained, wherein the power prediction model is used to predict the output power and the lumped disturbance at the K+1th moment and the output power at the K+2th moment based on the compensation inductor current and the input voltage of the resonant load circuit at the Kth moment; Wherein, the power prediction model of the resonant inverter is obtained according to the three-phase control algorithm and the initial power prediction model, including: Based on the initial power prediction model, constructing a first-order hyperlocal model of the resonant load circuit; According to a preset time interval, transforming the output power model into a power difference model; Obtaining a power prediction model of the resonant inverter according to the lumped disturbance equality conditions at different times, the power difference model and the first-order super-local model; or A linear extended state observer is introduced into the initial power prediction model to construct a power prediction model of the resonant inverter.

2. The method according to claim 1, characterized in that The constructing of the dq-axis equivalent circuit model of the resonant load circuit comprises: constructing an initial d-axis equivalent circuit model and an initial q-axis equivalent circuit model of the resonant load circuit; Combining the initial d-axis equivalent circuit model and the initial q-axis equivalent circuit model into an equivalent circuit model in a rectangular form; The rectangular equivalent circuit model is converted into a rectangular equivalent circuit model in a synchronous coordinate system to obtain the dq-axis equivalent circuit model.

3. A resonant inverter control method for an induction heating device, characterized in that: Methods include: Acquire a compensation inductor current and an input voltage of a resonant load circuit of a primary circuit of the resonant inverter, and use the acquired compensation inductor current and input voltage as the compensation inductor current and input voltage at a Kth moment; Converting the compensation inductor current and the input voltage at the Kth moment into a compensation inductor current non-rotating vector and an input voltage non-rotating vector on the d-axis and the q-axis; Inputting the d-axis and q-axis compensation inductor current non-rotating vectors and the input voltage non-rotating vectors into the power prediction model of the resonant inverter as claimed in any one of claims 1 to 2, and outputting the output power and the lumped disturbance at the K+1th moment, and the output power at the K+2th moment; Based on the output power and the lumped disturbance at the K+1th moment and the output power at the K+2th moment, the conduction of the switch tube of the primary circuit is controlled.

4. The method according to claim 3, characterized in that The controlling the conduction of the switch tube of the primary circuit based on the output power and the lumped disturbance at the K+1th moment and the output power at the K+2th moment includes: Determine whether the square of the difference between the output power at the K+2th moment and the reference output power is less than a preset threshold; If it is greater than or equal to the preset threshold, reacquire the compensation inductor current and input voltage of the resonant load circuit as the compensation inductor current and input voltage at the Kth moment, until the square is less than the preset threshold; If it is less than the preset threshold, the output power and the lumped disturbance at the K+1th moment are input into the conversion model of power and phase angle, and the phase angle at the K+1th moment is output; The conduction of the switch tube of the primary circuit is controlled according to the phase angle at the K+1th moment.

5. The method according to claim 3, characterized in that: The step of converting the compensation inductor current and the input voltage at the Kth moment into a compensation inductor current non-rotating vector and an input voltage non-rotating vector of a d-axis and a q-axis includes: Determine the compensation inductor current and the input voltage at the Kth moment as a d-axis inductor current rotation vector and an input voltage rotation vector; Delaying the compensation inductor current and the input voltage at the Kth moment by a phase angle of ninety degrees to obtain a q-axis inductor current rotation vector and an input voltage rotation vector; The park algorithm converts the d-axis and q-axis compensation inductor current rotating vector and the input voltage rotating vector into the d-axis and q-axis compensation inductor current non-rotating vector and the input voltage non-rotating vector.

6. An induction heating device, characterized in that: The induction heating device comprises a resonant inverter and a control unit, wherein the resonant inverter comprises a primary circuit, wherein the primary circuit is used to provide heat for a secondary workpiece, and the control unit is used to: According to the mutual inductance principle between the primary circuit and the secondary workpiece, the resistance of the secondary workpiece is equivalent to the primary circuit to obtain a resonant load circuit of the primary circuit; Constructing a dq-axis equivalent circuit model of the resonant load circuit, wherein the dq-axis equivalent circuit model includes a d-axis equivalent circuit model and a q-axis equivalent circuit model, wherein the d-axis equivalent circuit model is an original circuit model of the resonant load circuit, and the q-axis equivalent circuit model is delayed by ninety degrees in phase angle compared with the original circuit model; Based on the dq-axis equivalent circuit model, construct an output power model of the resonant load circuit; Constructing an initial power prediction model of the resonant load circuit according to the forward Euler discretization method and the output power model; According to the three-phase control algorithm and the initial power prediction model, a power prediction model of the resonant inverter is obtained, wherein the power prediction model is used to predict the output power and the lumped disturbance at the K+1th moment and the output power at the K+2th moment based on the compensation inductor current and the input voltage of the resonant load circuit at the Kth moment; Wherein, the power prediction model of the resonant inverter is obtained according to the three-phase control algorithm and the initial power prediction model, including: Based on the initial power prediction model, constructing a first-order hyperlocal model of the resonant load circuit; According to a preset time interval, transforming the output power model into a power difference model; Obtaining a power prediction model of the resonant inverter according to the lumped disturbance equality conditions at different times, the power difference model and the first-order super-local model; or Introducing a linear extended state observer into the initial power prediction model to construct a power prediction model of the resonant inverter; The control unit is further used to obtain the compensation inductor current and input voltage of the resonant load circuit, and use the obtained compensation inductor current and input voltage as the compensation inductor current and input voltage at the Kth moment; Converting the compensation inductor current and the input voltage at the Kth moment into a compensation inductor current non-rotating vector and an input voltage non-rotating vector on the d-axis and the q-axis; Inputting the d-axis and q-axis compensation inductor current non-rotating vectors and the input voltage non-rotating vector into the power prediction model of the resonant inverter, and outputting the output power and lumped disturbance at the K+1th moment, and the output power at the K+2th moment; Based on the output power and the lumped disturbance at the K+1th moment and the output power at the K+2th moment, the conduction of the switch tube of the primary circuit is controlled.

7. A control unit for an induction heating device, characterized in that: include: Processor and memory; The memory is coupled to the processor, and the memory is used to store computer program codes. The processor calls the computer program codes to enable the control unit to execute the method according to any one of claims 1 to 2 or 3 to 5.

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