Constant temperature control method and system for tundish electromagnetic heating system

Abstract

The invention discloses a constant-temperature control method and system for a tundish electromagnetic heating system, which introduces rapid iterative repetitive control, carries out iterative correction by using key variables of a historical control period, realizes accurate closed-loop adjustment of temperature and current, remarkably improves control precision and adaptability of the system, and does not need complex parameter adjustment. According to the method, the delay compensator is combined to carry out prospective compensation on a delay effect brought by a repetitive control link, and uncertainty caused by system delay is reduced to the greatest extent by predicting and correcting a lagging link, so that transient response and steady-state performance of the system are remarkably improved. According to the invention, through accurate real-time tracking control of the temperature and the output current, rapid response and stability improvement of the temperature control system are realized, the dynamic adjustment capability in the electromagnetic heating process of the high-voltage cascade tundish is greatly optimized, and the method has certain robustness when dealing with high load and temperature fluctuation.

Description

Technical Field

[0001] The invention relates to the field of intelligent electromagnetic metallurgy, and in particular to a constant temperature control method and system for an electromagnetic heating system of a tundish. Background Art

[0002] Electromagnetic induction heating has gradually become the core heating technology in the metallurgical industry due to its high efficiency and precise temperature control characteristics. During the heating of molten steel, the alternating magnetic field excited by high-frequency alternating current induces the current to generate Joule heat in the molten steel, thereby achieving efficient heating. Electromagnetic induction heating does not rely on physical contact, which not only improves the utilization efficiency of thermal energy, but also can accurately control the heating temperature and extend the service life of the equipment. It also has significant energy-saving and environmental protection advantages. During the tundish smelting process, the high-pressure cascade tundish electromagnetic heating system can stably maintain the temperature of the molten steel and ensure the casting quality by efficiently converting electrical energy into thermal energy. Therefore, the application of tundish electromagnetic heating technology in steel production has become more and more extensive, becoming one of the key technologies in the industry.

[0003] Although the existing high-pressure cascade tundish electromagnetic heating system has made significant progress in the field of molten steel heating, the temperature control system often faces great stability challenges due to external disturbances and complex working conditions. The current control strategy has weak anti-interference ability when dealing with disturbances, and the parameter adjustment is complex, making it difficult to maintain precise control under a changing heating environment. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a constant temperature control method and system for an electromagnetic heating system of a tundish in view of the deficiencies in the prior art, so as to effectively improve the stability and control accuracy of the heating process.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for constant temperature control of a tundish electromagnetic heating system, comprising the following steps: Collect load output voltage , load output current and the molten steel load temperature; The molten steel load temperature error correction value M(k) at time k is used as the input of the temperature regulator G1 to obtain the load constant temperature control current reference value ; According to the relationship between load power and output current, the output current corresponding to the load power requirement is calculated to obtain the given effective value ; Reference value of constant temperature control current for superimposed load and the output current given effective value , get the load output current given value ; The load output current given value Output current with load The output current correction value N(k) at time k is obtained by subtraction, and N(k) is passed through the current regulator G2. The output of the current regulator G2 is added to the load output voltage , get the output voltage of the full-bridge inverter of the tundish electromagnetic heating system , PWM modulation is performed on the output voltage to obtain a switching pulse signal of a full-bridge inverter power device.

[0006] The present invention improves the temperature loop based on the fast iterative repetitive algorithm, and effectively improves the control quality and control accuracy by compensating and correcting the data current deviation calculated in the previous control cycle. Combined with the delay compensator, the system delay link is fully considered and compensated to achieve fast iterative repetitive control.

[0007] The expression of the molten steel load temperature error correction value M(k) at time k is: ; M(k-1) is the temperature error correction value at time k-1, M(k-2) is the temperature error correction value at time k-2, is the forgetting factor, T s is the control period, e T (k) is the temperature error value.

[0008] Temperature error value e T The acquisition process of (k) includes: setting the load temperature reference value The temperature error value e is obtained by subtracting the output △M(k) of the delay compensator from the difference value. T (k); the acquisition process of △M(k) includes: passing the molten steel load temperature error correction value M(k) at time k through the delay module , the molten steel load temperature error correction value M(k-1) at time k-1 is obtained, and the output △M(k) of the delay compensator is obtained by subtracting M(k) from M(k-1); τ is the control system delay.

[0009] The expression of the output current correction value N(k) at time k is: ; N(k-1) is the output current correction value at time k-1, N(k-2) is the output current correction value at time k-2, is the forgetting factor of the current, is the current error value.

[0010] Current error The acquisition process includes: setting the load output current given value Subtract the output current i0 sampled at the current moment, and then subtract the difference from the output △N (k) of the delay compensator to obtain the current error value The process of obtaining the output △N(k) of the delay compensator includes: passing the output current correction value N(k) at time k through the delay module , we get N(k-1), and the difference between N(k) and N(k-1) is the output △N(k) of the delay compensator.

[0011] In the present invention, .

[0012] As an inventive concept, the present invention also provides a method for controlling the constant temperature of a tundish electromagnetic heating system, comprising a front-stage three-phase rectifier control part and a rear-stage full-bridge inverter control part; wherein, The front three-phase rectifier control part includes the following steps: Collect the grid current input from the high-voltage cascade tundish electromagnetic heating power supply via the transfer transformer , Grid voltage , DC side voltage ; x = a, b, c; The DC side voltage command signal With DC side voltage value The difference is used as the input of the first PI controller to obtain the DC side current reference value ; By load power The relationship between the input current and the load power is used to calculate the input current command amplitude corresponding to the load power. ; Accumulated DC side current reference value With the input current command amplitude , get the final grid input side current reference value ; The final grid input side current reference value The d-axis component , q-axis component Corresponding to the grid current The d-axis component , q-axis component Make a difference and get the input current error in the two-phase rotating coordinate system , ; The input current error of the two-phase rotating coordinate system , As the input of the second PI controller, the voltage output by the second PI controller is modulated by PWM to obtain a switch pulse signal to control the on and off of the power switch device of the three-phase rectifier of the tundish electromagnetic heating system; The rear full-bridge inverter control section includes the following steps: Collect load output voltage , load output current and the molten steel load temperature; Set the load temperature reference value The temperature error value is obtained by subtracting the output △M(k) of the delay compensator from the current temperature T at the time k obtained by sampling. ; The molten steel load temperature error correction value M(k) at time k is passed through the delay module , we get M(k-1), and we subtract M(k-1) from M(k) to get the output △M(k) of the delay compensator; τ is the control system delay; Use the following formula to get the value after temperature error correction: ; M(k) is the temperature error correction value of the current control cycle; M(k-1) is the temperature error correction value of the previous control cycle; M(k-2) is the temperature error correction value of the previous two control cycles; For the forgetting factor; To control the cycle; Take M(k) as the input of temperature regulator G1 to get the load constant temperature control current reference value ; According to the relationship between load power and output current, the output current corresponding to the load power requirement is calculated to obtain the given effective value ; Reference value of constant temperature control current for superimposed load and the output current given effective value , get the load output current given value ; Set the load output current to a given value Subtract the output current sampled at the current moment , and then subtract it from the output △N (k) of the delay compensator to get the current error value The process of obtaining the output △N(k) of the delay compensator includes: passing the output current correction value N(k) through the delay module , get N(k-1), and the difference between N(k) and N(k-1) is the output △N(k) of the delay compensator; Use the following formula to get the corrected current error value: ; N(k) is the output current correction value of the current control cycle, N(k-1) is the output current correction value of the previous control cycle, and N(k-2) is the output current correction value of the previous two control cycles. is the forgetting factor of the current, ; N(k) passes through current G2, and the output of current regulator G2 is added to the load output voltage , obtain the output voltage of the full-bridge inverter of the intermediate ladle electromagnetic heating system, perform PWM modulation on the output voltage, and obtain the switching pulse signal of the power device of the full-bridge inverter.

[0013] ,in, It is the effective value of the AC input voltage of the three-phase rectifier.

[0014] ;in, is the load impedance, is the angular velocity corresponding to the industrial frequency, and its value is 100π.

[0015] Different from the traditional high-voltage multi-level cascade electromagnetic heating power supply system using the front-stage PWM rectifier and the rear-stage full-bridge inverter structure, the present invention improves the current loop and the temperature loop based on the fast iterative repetitive algorithm, and realizes the compensation correction of the temperature and current deviation by using the data calculated in the previous control cycle, thereby effectively improving the control quality and improving the control accuracy. Combined with the delay compensator, the system delay link is fully considered and compensated to realize fast iterative repetitive control. At the same time, the present invention avoids the complex parameter adjustment process commonly seen in traditional controllers, does not require a large amount of parameter design to adapt to different working environments, and simplifies the debugging and maintenance of the system.

[0016] As an inventive concept, the present invention also provides a constant temperature control system for an intermediate ladle electromagnetic heating system, comprising a memory, a processor and a computer program stored in the memory; the processor executes the computer program in the memory to implement the steps of the above method.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention improves the current loop and the temperature loop based on a fast iterative repetitive algorithm, and realizes compensation correction of temperature and current deviations by using the data calculated in the previous control cycle, thereby effectively improving the control quality and control accuracy. Combined with the delay compensator, the system delay link is fully considered and compensated to achieve fast iterative repetitive control. At the same time, the present invention avoids the complex parameter adjustment process commonly seen in traditional controllers, does not require a large amount of parameter design to adapt to different working environments, and simplifies the debugging and maintenance of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a topological diagram of a high-voltage cascade tundish electromagnetic heating power supply according to an embodiment of the present invention; Figure 2 This is an overall control block diagram of the intermediate package electromagnetic heating power supply in an embodiment of the present invention; FIG3 (a) and FIG3 (b) are control block diagrams of submodules according to an embodiment of the present invention; FIG3 (a) is the control of the front-stage three-phase rectifier, and FIG3 (b) is the control of the rear-stage full-bridge inverter. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] like Figure 1 As shown, the topology diagram of the high-voltage cascaded intermediate ladle electromagnetic heating system of the embodiment structure of the present invention, the high-voltage cascaded intermediate ladle electromagnetic heating system includes a 10kV power grid, a 10 / 0.4kVA multi-winding shift transformer, 6 AC / DC / AC power sub-modules, and a temperature control system. The 6 AC / DC / AC power sub-modules are connected in parallel on the grid input side and in series on the load output side. The AC / DC / AC power sub-module is mainly composed of four parts: a filter circuit, a rectifier circuit, a DC energy storage capacitor, and a full-bridge inverter circuit. The AC output of the inverter circuit is connected to the AC bus to power the electromagnetic heating system. The system is regulated by real-time measurement of the load temperature, output voltage, and output current and feedback to the temperature control system. are the AC input voltage and current respectively, L is the inductor connected to the AC input side, C1 and C2 are the series capacitors on the rectifier side, For input voltage, the grid side and the rectifier side are isolated through a transformer; and They are output voltage and current respectively. The rear-stage single-phase cascade multi-level inverter circuit uses the full-bridge sub-module as the power unit. A total of 6 power unit modules are cascaded. A carrier phase-shift modulation strategy is adopted. Assuming that the voltage of a single sub-module is uc, a single sub-module can output three levels of -uc, 0, and uc. The cascade system can output 27 levels from -13uc to 13uc.

[0021] Example 1 This embodiment provides a method for controlling the constant temperature of a tundish electromagnetic heating system, comprising the following steps: Collect load output voltage , load output current and the molten steel load temperature; Set the load temperature reference value The temperature error value is obtained by subtracting the output △M(k) of the delay compensator from the current temperature T at the time k obtained by sampling. ; The molten steel load temperature error correction value M(k) at time k is passed through the delay module , we get M(k-1), and we subtract M(k-1) from M(k) to get the output △M(k) of the delay compensator; τ is the control system delay; Use the following formula to get the value after temperature error correction: ; M(k) is the temperature error correction value of the current control cycle, M(k-1) is the temperature error correction value of the previous control cycle, and M(k-2) is the temperature error correction value of the previous two control cycles. For the forgetting factor, To control the cycle; Take M(k) as the input of temperature regulator G1 to get the load constant temperature control current reference value ; , They are the proportional coefficient and integral coefficient of the temperature regulator G1 respectively.

[0022] According to the relationship between load power and output current, the output current corresponding to the load power requirement is calculated to obtain the given effective value ; Reference value of constant temperature control current for superimposed load and the output current given effective value , get the load output current given value ; Set the load output current to a given value Subtract the output current sampled at the current moment , and then subtract it from the output △N (k) of the delay compensator to get the current error value The process of obtaining the output △N(k) of the delay compensator includes: passing the output current correction value N(k) through the delay module , get N(k-1), and the difference between N(k) and N(k-1) is the output △N(k) of the delay compensator; Use the following formula to get the corrected current error value: ; N(k) is the output current correction value of the current control cycle, N(k-1) is the output current correction value of the previous control cycle, and N(k-2) is the output current correction value of the previous two control cycles. is the forgetting factor of the current, ; N(k) passes through the current regulator G2, and the output of the current regulator G2 is added to the load output voltage , obtain the output voltage of the full-bridge inverter of the intermediate ladle electromagnetic heating system, perform PWM modulation on the output voltage, and obtain the switching pulse signal of the power device of the full-bridge inverter.

[0023] Example 2 This embodiment provides another method for controlling the constant temperature of a tundish electromagnetic heating system, including a front-stage three-phase rectifier control part and a rear-stage full-bridge inverter control part; the front-stage three-phase rectifier control part includes the following steps: Collect the grid current i input by the high-voltage cascade tundish electromagnetic heating power supply through the transfer transformer sx , Grid voltage , DC side voltage ; x = a, b, c; The DC side voltage command signal With DC side voltage value The difference is used as the input of the first PI controller to obtain the DC side current reference value ; By load power The relationship between the input current and the load power is calculated by ; Accumulated DC side current reference value With the input current command amplitude , get the final grid input side current reference value ; The final grid input side current reference value The d-axis component , q-axis component Corresponding to the grid current The d-axis component , q-axis component Make a difference and get the input current error in the two-phase rotating coordinate system , ; The input current error of the two-phase rotating coordinate system , As the input of the second PI controller, the voltage output by the second PI controller is modulated by PWM to obtain a switching pulse signal to control the on and off of the power switch device of the three-phase rectifier of the intermediate ladle electromagnetic heating system.

[0024] The control part of the rear-stage full-bridge inverter is the same as that of Embodiment 1 and will not be described in detail here.

[0025] Figure 2 Figure 3 (a) and Figure 3 (b) are the overall control block diagrams, and Figure 3 (a) and Figure 3 (b) are the submodule control block diagrams. At the beginning of each sampling cycle, the grid current of the high-voltage cascade multi-level electromagnetic metallurgical frequency conversion power supply input via the transfer transformer is collected. , Grid voltage , DC side voltage , load output voltage , load output current And the molten steel load temperature T, the data is converted by the AD converter and transmitted to the DSP controller for processing; the DC side voltage is given and DC voltage The DC voltage closed loop output DC side current given by PI controller ; Plus the power input current calculated by the relationship The grid input current reference value can be obtained , eliminate the harmonic components in the input current and achieve tracking control of the input current. Among them: ; In the formula, is the power feed-forward current reference value, is the DC side current reference value, is the integral coefficient of the voltage PI controller, is the load power, It is the effective value of the rectifier AC input voltage.

[0026] As shown in Figure 3 (b), the delay compensator is used to eliminate the system delay, and the temperature error correction value M (k) passes through the delay module Get M(k-1), and make a difference between M(k) and M(k-1) to get the output △M(k) of the delay compensator. After making a difference with the given temperature value, use the iterative repetition algorithm in the s domain to get the correction value of the temperature error, which can be expressed as: ; M (k) is used as the input of the temperature controller, and the output of the temperature controller G1 is the current reference value of the load temperature feedforward , and the output current reference value that satisfies the load power calculated by the relationship between load power and output current Add together to get the final current reference value Subtract the output current i at the current time of the period obtained by sampling, and then make a difference with the output after the delay compensator, and then correct it by iterative repetitive algorithm to obtain the current error correction value N (k), which can be expressed as: ; N(k) is the input of the current regulator, and the output of the current regulator G2 is the output voltage reference value , plus the output voltage of the feedforward The final full-bridge inverter output voltage is given The corresponding gate-level pulse signal is generated by PWM modulation technology to complete the control of the system.

[0027] ;in, They are the proportional coefficient and integral coefficient of the current regulator G2 respectively.

[0028] The relationship between load power and input current is: ,in It is the effective value of the rectifier AC input voltage.

[0029] The relationship between load power and output current is: .

[0030] Example 3

[0031] Embodiment 2 of the present invention provides a system corresponding to the above-mentioned embodiment 1 or embodiment 2, including a memory, a processor and a computer program stored in the memory; the processor executes the computer program in the memory to implement the steps of the method in the above-mentioned embodiment 1.

[0032] In some implementations, the memory may be a high-speed random access memory (RAM), and may also include a non-volatile memory, such as at least one disk memory.

[0033] In some other implementations, the processor may be a central processing unit (CPU), a digital signal processor (DSP), or other general-purpose processors of various types, which are not limited herein.

[0034] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0035] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A method for controlling the constant temperature of a tundish electromagnetic heating system, characterized in that: The following steps are involved: Collect load output voltage , load output current and the molten steel load temperature; The molten steel load temperature error correction value M(k) at time k is used as the input of the temperature regulator G1 to obtain the load constant temperature control current reference value ; According to the relationship between load power and output current, the output current corresponding to the load power requirement is calculated to obtain the given effective value ; Superimposed load constant temperature control current reference value i T_ref and the output current given effective value , get the load output current given value ; The load output current given value Output current with load The output current correction value N(k) at time k is obtained by subtraction, and N(k) is passed through the current regulator G2. The output of the current regulator G2 is added to the load output voltage , get the output voltage of the full-bridge inverter of the tundish electromagnetic heating system , PWM modulation is performed on the output voltage to obtain a switching pulse signal of a full-bridge inverter power device.

2. The method for controlling the constant temperature of the tundish electromagnetic heating system according to claim 1, characterized in that: The expression of the molten steel load temperature error correction value M(k) at time k is: ; M(k-1) is the temperature error correction value at time k-1, M(k-2) is the temperature error correction value at time k-2, is the forgetting factor, T s is the control period, e T (k) is the temperature error value.

3. The method for controlling the constant temperature of the tundish electromagnetic heating system according to claim 2, characterized in that: Temperature error value e T The acquisition process of (k) includes: setting the load temperature reference value The temperature error value e is obtained by subtracting the output △M(k) of the delay compensator from the difference value. T (k); the acquisition process of △M(k) includes: passing the molten steel load temperature error correction value M(k) at time k through the delay module , the molten steel load temperature error correction value M(k-1) at time k-1 is obtained, and the output △M(k) of the delay compensator is obtained by subtracting M(k) from M(k-1); τ is the control system delay.

4. The method for controlling the constant temperature of the tundish electromagnetic heating system according to claim 1, characterized in that: The expression of the output current correction value N(k) at time k is: ; N(k-1) is the output current correction value at time k-1, N(k-2) is the output current correction value at time k-2, is the forgetting factor of the current, is the current error value.

5. The method for controlling the constant temperature of the tundish electromagnetic heating system according to claim 4, characterized in that: Current error The acquisition process includes: setting the load output current given value Subtract the output current i0 sampled at the current moment, and then subtract the difference from the output △N (k) of the delay compensator to obtain the current error value The process of obtaining the output △N(k) of the delay compensator includes: passing the output current correction value N(k) at time k through the delay module , we get N(k-1), and the difference between N(k) and N(k-1) is the output △N(k) of the delay compensator.

6. The method for controlling the constant temperature of the tundish electromagnetic heating system according to any one of claims 2 to 5, characterized in that: 。 7. A method for controlling the constant temperature of a tundish electromagnetic heating system, characterized in that: It includes a front-stage three-phase rectifier control part and a rear-stage full-bridge inverter control part; wherein, The front three-phase rectifier control part includes the following steps: Collect the grid current input from the high-voltage cascade tundish electromagnetic heating power supply via the transfer transformer , Grid voltage , DC side voltage ; x = a, b, c; The DC side voltage command signal With DC side voltage value The difference is used as the input of the first PI controller to obtain the DC side current reference value ; By load power The relationship between the input current and the load power is used to calculate the input current command amplitude corresponding to the load power. ; Accumulated DC side current reference value With the input current command amplitude , get the final grid input side current reference value ; The final grid input side current reference value The d-axis component , q-axis component Corresponding to the grid current The d-axis component , q-axis component Make a difference and get the input current error in the two-phase rotating coordinate system , ; The input current error of the two-phase rotating coordinate system , As the input of the second PI controller, the output voltage correction value is obtained , ; d-axis and q-axis components of grid voltage , Respectively , Subtract and get the d and q axis components of the output voltage , ; The d and q axis components of the output voltage , After coordinate transformation, PWM modulation is used to obtain a switch pulse signal to control the on and off of the power switch device of the three-phase rectifier of the tundish electromagnetic heating system; The control part of the rear-stage full-bridge inverter is implemented by the method described in any one of claims 1 to 6.

8. The method for controlling the constant temperature of the tundish electromagnetic heating system according to claim 7, characterized in that: ,in, It is the effective value of the AC input voltage of the three-phase rectifier.

9. The method for controlling the constant temperature of the tundish electromagnetic heating system according to claim 7, characterized in that: ;in, is the load impedance, is the angular velocity corresponding to the industrial frequency.

10. A constant temperature control system for a tundish electromagnetic heating system, comprising a memory, a processor and a computer program stored in the memory; characterized in that: The processor executes the computer program on the memory to implement the steps of the method described in any one of claims 1 to 6; or, the processor executes the computer program on the memory to implement the steps of the method described in any one of claims 7 to 9.

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