Constant temperature control method and system for intermediate ladle electromagnetic heating system

Abstract

The application discloses a kind of intermediate ladle electromagnetic heating system constant temperature control method and system, fast iterative repetitive control is introduced, by utilizing the key variable of historical control period, iterative correction is carried out, the precise closed-loop regulation of temperature and current is realized, control precision and the adaptability of system are significantly improved and complex parameter adjustment is not needed.The application combines delay compensator to carry out forward-looking compensation to the delay effect caused by repetitive control link, by prediction and correction to lag link, the uncertainty caused by system delay is maximally reduced, so that the transient response and steady-state performance of system are significantly improved.The application can realize the fast response and stability improvement of temperature control system by accurate temperature and output current real-time tracking control, greatly optimize the dynamic adjustment capability in high-voltage cascade intermediate ladle electromagnetic heating process, and have certain robustness when coping with high load and temperature fluctuation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of intelligent electromagnetic metallurgy, and particularly to a constant temperature control method and system for an electromagnetic heating system of a tundish. BACKGROUND

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

[0003] Although existing high-pressure cascade tundish electromagnetic heating systems have made significant progress in the field of molten steel heating, due to external disturbances and complex working conditions, the temperature control system often faces significant stability challenges. 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 in a changing heating environment. SUMMARY

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

[0005] To solve the above technical problems, the technical solution adopted by the present application is as follows: a constant temperature control method for a tundish electromagnetic heating system, comprising the following steps:

[0006] collecting a load output voltage , a load output current , and a molten steel load temperature;

[0007] taking the molten steel load temperature error correction value M(k) at time k as the input of the temperature regulator G1 to obtain a load constant temperature control current reference value ;

[0008] calculating the output current given effective value corresponding to the load power demand from the relationship between the load power and the output current ;

[0009] superimposing the load constant temperature control current reference value and the output current given effective value , get the load output current given value ;

[0010] from the load output current given value and the load output current difference to obtain the output current correction value N (k) at k time, 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 intermediate package electromagnetic heating system full-bridge inverter , the output voltage is PWM modulated to obtain the switching pulse signal of the full-bridge inverter power device.

[0011] The present application improves the temperature ring based on the fast iterative repetitive algorithm, and the compensation correction of the data current deviation calculated in the previous control period is utilized, so that the control quality is effectively improved and the control precision is improved. Combined with the delay compensator, the system delay link is fully considered and compensated, and the fast iterative repetitive control is realized.

[0012] The expression of the molten steel load temperature error correction value M (k) at k time is: ; M (k-1) is the temperature error correction value at k-1 time, M (k-2) is the temperature error correction value at k-2 time, is a forgetting factor, T s is a control period, e T (k) is a temperature error value.

[0013] The acquisition process of the temperature error value e T (k) includes: subtracting the load temperature reference value from the molten steel load temperature obtained by sampling at the current time k, and subtracting the output △M (k) of the delay compensator from the difference value, to obtain the temperature error value e T (k); the acquisition process of △M (k) includes: passing the molten steel load temperature error correction value M (k) at k time through the delay module , to obtain the molten steel load temperature error correction value M (k-1) at k-1 time, and subtracting M (k) from M (k-1) to obtain the output △M (k) of the delay compensator; τ is the control system delay.

[0014] The expression of the output current correction value N (k) at k time is: ; N (k-1) is the output current correction value at k-1 time, N (k-2) is the output current correction value at k-2 time, is a forgetting factor of current, is a current error value.

[0015] The acquisition process of the current error value includes: subtracting the load output current given value Subtract the current sampled at the current moment i0, and then subtract the difference from the output ΔN(k) of the delay compensator to obtain the current error value. The process of obtaining the output ΔN(k) of the delay compensator includes: passing the output current correction value N(k) at time k through the delay module. We obtain N(k-1), and the difference between N(k) and N(k-1) is the output ΔN(k) of the delay compensator.

[0016] In this invention, .

[0017] As an inventive concept, this invention also provides a method for constant temperature control of an intermediate drum electromagnetic heating system, comprising a front-stage three-phase rectifier control section and a rear-stage full-bridge inverter control section; wherein,

[0018] The control section of the front-end three-phase rectifier includes the following steps:

[0019] The grid current input via the transfer transformer is collected from the electromagnetic heating power supply of the high-voltage cascade intermediate package. Grid voltage DC side voltage x = a, b, c;

[0020] DC side voltage command signal DC side voltage value The difference is calculated, and the difference is used as the input to the first PI controller to obtain the DC-side current reference value. ;

[0021] Power of load The formula relating input current to load power is used to calculate the input current command amplitude corresponding to the load power. ;

[0022] Accumulated DC side current reference value With input current command amplitude The final reference value of the grid input current is obtained. ;

[0023] The final grid input current reference value d-axis components q-axis components Corresponding to the grid current respectively d-axis components q-axis components By subtracting the input currents, we obtain the input current error in the two-phase rotating coordinate system. , ;

[0024] The input current error in the two-phase rotating coordinate system 、 The voltage output by the second PI controller is PWM modulated to obtain a switching pulse signal, which controls the on-off of the power switching device of the three-phase rectifier of the intermediate package electromagnetic heating system;

[0025] The post-stage full-bridge inverter control part includes the following steps:

[0026] Collecting the load output voltage , the load output current , and the molten steel load temperature;

[0027] The load temperature reference value is subtracted from the current k time temperature T obtained by sampling, and the output ΔM(k) of the delay compensator is subtracted to obtain the temperature error value ;

[0028] The molten steel load temperature error correction value M(k) at k time is passed through a delay module to obtain M(k-1), and M(k-1) is subtracted from M(k) to obtain the output ΔM(k) of the delay compensator; τ is the delay of the control system;

[0029] The value after the temperature error value is corrected is obtained by using the following formula: ; M(k) is the temperature error correction value of the current control period; M(k-1) is the temperature error correction value of the previous control period; M(k-2) is the temperature error correction value of the previous two control periods; is a forgetting factor; is a control period;

[0030] M(k) is taken as the input of the temperature regulator G1 to obtain the load constant temperature control current reference value ;

[0031] The output current given effective value corresponding to the load power demand is calculated from the relationship between the load power and the output current ;

[0032] The load constant temperature control current reference value and the output current given effective value are superimposed to obtain the load output current given value ;

[0033] The load output current given value is subtracted from the output current sampled at the current time , and the output ΔN(k) of the delay compensator is subtracted to obtain the current error value ; the output ΔN(k) of the delay compensator includes: passing the output current correction value N(k) through a delay module , and the output of the delay compensator is obtained by subtracting N(k-1) from N(k);

[0034] The current error value after correction is obtained by using the following formula: ; N(k) is the output current correction value of the current control period, N(k-1) is the output current correction value of the previous control period, N(k-2) is the output current correction value of the previous two control periods, is the forgetting factor of the current, ;

[0035] N(k) is input into the current G2, and the output of the current regulator G2 is added to the load output voltage , to obtain the output voltage of the full-bridge inverter of the intermediate package electromagnetic heating system, and the output voltage is PWM modulated to obtain the switching pulse signal of the full-bridge inverter power device.

[0036] , wherein, is the effective value of the three-phase rectifier AC input voltage.

[0037] ; wherein, is the load impedance, is the angular velocity corresponding to the power frequency, and the value is 100π.

[0038] Different from the traditional high-voltage multi-level cascade electromagnetic heating power supply system adopting the structure of a front-stage PWM rectifier and a rear-stage full-bridge inverter, the current loop and the temperature loop are improved based on the fast iterative repetitive algorithm, the temperature and current deviation are compensated and corrected by using the data calculated in the previous control period, so that the control quality is effectively improved and the control precision is improved. Combined with the delay compensator, the system delay link is fully considered and compensated, and fast iterative repetitive control is realized. At the same time, the present application avoids the complex parameter adjustment process commonly used in traditional controllers, and does not need a large number of parameter designs to adapt to different working environments, thereby simplifying the debugging and maintenance work of the system.

[0039] As an inventive concept, the present application also provides a constant temperature control system for an intermediate package electromagnetic heating system, comprising a memory, a processor and a computer program stored in the memory; the processor executes the computer program on the memory to realize the steps of the above method.

[0040] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention improves the current and temperature loops based on a fast iterative repetitive algorithm. By utilizing data calculated from previous control cycles, it achieves compensation and correction of temperature and current deviations, thereby effectively improving control quality and accuracy. Combined with a delay compensator, it fully considers and compensates for system delays, achieving fast iterative repetitive control. Simultaneously, this invention avoids the complex parameter tuning process common in traditional controllers, eliminating the need for extensive parameter design to adapt to different working environments, and simplifying system debugging and maintenance. Attached Figure Description

[0041] Figure 1 This is a topology diagram of a high-voltage cascaded intermediate tundish electromagnetic heating power supply according to an embodiment of the present invention;

[0042] Figure 2 This is an overall control block diagram of the electromagnetic heating power supply in an embodiment of the present invention;

[0043] Figures 3(a) and 3(b) are control block diagrams of sub-modules in an embodiment of the present invention; Figure 3(a) shows the control of the front-end three-phase rectifier, and Figure 3(b) shows the control of the rear-end full-bridge inverter. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] like Figure 1 The diagram shows the topology of a high-voltage cascaded intermediate-load electromagnetic heating system according to an embodiment of the present invention. The system includes a 10kV power grid, a 10 / 0.4kVA multi-winding shifting transformer, six AC / DC / AC power sub-modules, and a temperature control system. The six AC / DC / AC power sub-modules are connected in parallel on the power grid input side and in series on the load output side. Each AC / DC / AC power sub-module mainly consists of 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, which are fed back to the temperature control system. These represent the AC input voltage and current, respectively. L is the inductor connected to the AC input side, and C1 and C2 are the series capacitors on the rectifier side. The input voltage is used to isolate the grid side from the rectifier side through a transformer; and V and I are output voltage and current respectively, the latter single-phase cascade multilevel inverter circuit takes full-bridge sub-module as power unit, cascades 6 power unit modules, adopts carrier phase-shifted modulation strategy, assuming that single sub-module voltage is uc, single sub-module can output-uc, 0, uc three levels, cascade system can output-13uc~13uc 27 levels.

[0046] Embodiment 1

[0047] The embodiment provides a constant temperature control method of an intermediate ladle electromagnetic heating system, and comprises the following steps:

[0048] Collecting load output voltage , load output current and molten steel load temperature;

[0049] Subtracting the load temperature reference value from the current k moment temperature T obtained by sampling, and then subtracting the output ΔM(k) of the delay compensator to obtain a temperature error value ;

[0050] The molten steel load temperature error correction value M(k) at the k moment is input into a delay module to obtain M(k-1), and the difference between M(k-1) and M(k) is obtained to obtain the output ΔM(k) of the delay compensator; τ is the delay of the control system;

[0051] The value after the temperature error value is corrected is obtained by using the following formula: ; M(k) is the temperature error correction value of the current control period, M(k-1) is the temperature error correction value of the previous control period, M(k-2) is the temperature error correction value of the previous two control periods, is a forgetting factor, is a control period.

[0052] M(k) is taken as the input of the temperature regulator G1 to obtain a load constant temperature control current reference value ;

[0053] , are the proportional coefficient and the integral coefficient of the temperature regulator G1 respectively.

[0054] The output current given effective value corresponding to the load power demand is calculated according to the relationship between the load power and the output current ;

[0055] The load constant temperature control current reference value and the output current given effective value are superimposed to obtain a load output current given value ;

[0056] The load output current is given a value Subtract the output current obtained by sampling at the current moment , and then subtract the output ΔN(k) of the delay compensator to obtain the error value of the current The process of obtaining the output ΔN(k) of the delay compensator includes: passing the output current correction value N(k) through a delay module , to obtain N(k-1), and then subtracting N(k) and N(k-1) to obtain the output ΔN(k) of the delay compensator;

[0057] The value of the current error value after correction is obtained by the following formula: N(k) is the output current correction value of the current control period, N(k-1) is the output current correction value of the previous control period, and N(k-2) is the output current correction value of the two previous control periods, is the forgetting factor of the current, ;

[0058] Pass N(k) through the current regulator G2, and add the output voltage of the load to the output of the current regulator G2 to obtain the output voltage of the intermediate package electromagnetic heating system full-bridge inverter, and perform PWM modulation on the output voltage to obtain the switching pulse signal of the full-bridge inverter power device.

[0059] Embodiment 2

[0060] Another intermediate package electromagnetic heating system constant temperature control method is provided, which includes 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:

[0061] Collect the grid current i sx , grid voltage , and DC side voltage input to the high-voltage cascade intermediate package electromagnetic heating power supply via a moving transformer;

[0062] Subtract the DC side voltage value from the DC side voltage instruction signal , and the difference is taken as the input of the first PI controller to obtain the DC side current reference value ;

[0063] Calculate the input current instruction amplitude corresponding to the load power from the relationship between the load power and the input current ;

[0064] Accumulate the DC side current reference value and the input current instruction amplitude The final reference value of the grid input current is obtained. ;

[0065] The final grid input current reference value d-axis components q-axis components Corresponding to the grid current respectively d-axis components q-axis components By subtracting the input currents, we obtain the input current error in the two-phase rotating coordinate system. , ;

[0066] Input current error in a two-phase rotating coordinate system , As the input to the second PI controller, the voltage output by the second PI controller is modulated by PWM to obtain a switching pulse signal, which controls the on / off state of the power switching devices of the three-phase rectifier of the intermediate drum electromagnetic heating system.

[0067] The control section of the subsequent full-bridge inverter is the same as in Example 1, and will not be described again here.

[0068] Figure 2 Figure 3(a) and Figure 3(b) show the overall control block diagram, while Figure 3(b) shows the control block diagrams for the sub-modules. At the beginning of each sampling cycle, the grid current input through the shifting transformer of the high-voltage cascaded multi-level electromagnetic metallurgical frequency converter is collected. Grid voltage DC side voltage Load output voltage Load output current The molten steel load temperature T is converted by an AD converter and then transmitted to the DSP controller for processing; the DC side voltage is given. and DC side voltage value The difference is used to generate the DC-side current given by the DC voltage closed-loop output through the PI controller. ; Add the power input current calculated from the power input current relationship The reference value of the grid input current can then be obtained. This eliminates harmonic components in the input current, enabling tracking control of the input current. Specifically:

[0069] ;

[0070] In the formula, This is the reference value for the power feedforward current. This is the reference value for the DC-side current. The integral coefficient of the voltage PI controller. The load power, The effective value of the AC input voltage of the rectifier.

[0071] As shown in Fig. 3 (b), the time delay of the system is eliminated by using a time delay compensator, and the temperature error correction value M (k) passes through the time delay module M (k-1) is obtained, and the difference between M (k) and M (k-1) is the output ΔM (k) of the time delay compensator. After the difference with the temperature given value, the correction value of the temperature error amount is obtained by using the iterative repetitive algorithm in the s domain, which can be represented as:

[0072] ;

[0073] M (k) is 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 satisfying the load power calculated by the relationship between the load power and the output current is added to obtain the final current reference value . After subtracting the output current i obtained by sampling at the current time of the gear period, and after the difference with the output of the time delay compensator, the current error correction value N (k) is obtained by correcting through the iterative repetitive algorithm, which can be represented as:

[0074] ;

[0075] N (k) is the input of the current regulator, and the output of the current regulator G2 is the output voltage reference value , and the output voltage is added to obtain the final full-bridge inverter output voltage given . The corresponding gate-level pulse signal is generated by the PWM modulation technology, and the control of the system is completed.

[0076] ; wherein, are the proportional coefficient and the integral coefficient of the current regulator G2, respectively.

[0077] The relationship between the load power and the input current is , wherein is the effective value of the AC input voltage of the rectifier.

[0078] The relationship between the load power and the output current is .

[0079] Embodiment 3

[0080] The embodiment 2 of the present application provides a system corresponding to the above-mentioned embodiment 1 or embodiment 2, which comprises a memory, a processor and a computer program stored on the memory; the processor executes the computer program on the memory to realize the steps of the method of the above-mentioned embodiment 1.

[0081] In some implementations, the memory can be a high-speed random access memory (RAM), and can also include a non-volatile memory, such as at least one disk memory.

[0082] In some implementations, the processor can be a central processing unit (CPU), a digital signal processor (DSP), or other types of general purpose processors, without limitation.

[0083] Although preferred embodiments of the application have been described herein, changes and modifications can be suggested to one skilled in the art and are intended to be encompassed within the scope of the application. It is the intent, therefore, to be limited only as indicated by the scope of the claims appended hereto.

[0084] Obviously, numerous modifications and variations of the present application are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

Claims

1. A tundish electromagnetic heating system thermostat control method, characterized by, The method comprises the following steps: Collecting load output voltage u o Load output current i o and molten steel load temperature; Will k The steel load temperature error correction value M(k) at any given time is used as the input to the temperature regulator G1 to obtain the reference value of the load constant temperature control current. i T_ref ; The output current corresponding to the load power demand is calculated by the relationship between the load power and the output current i op_ref ; Superimposed load constant temperature control current reference value i T_ref And output current given effective value i op_ref , get load output current given value i o_ref ; The load output current is given a value i o_ref The load output current is given a value i o The difference between the output current at time k and the output current at time k-1 is obtained to obtain the output current correction value N(k), and N(k) is passed through a current regulator G2, and the output of the current regulator G2 is added to the load output voltage u o The difference between the output current at time k and the output current at time k-1 is obtained to obtain the output current correction value N(k), and N(k) is passed through a current regulator G2, and the output of the current regulator G2 is added to the load output voltage u ro The output voltage is PWM modulated to obtain a switching pulse signal of the full-bridge inverter power device k The expression of the molten steel load temperature error correction value M(k) at the moment is: M(k-1) is the temperature error correction value at k-1 moment, M(k-2) is the temperature error correction value at k-2 moment, is a forgetting factor, T s is a control period, e T (k) is a temperature error value; Temperature error value e T The process of obtaining (k) includes: taking the load temperature reference value T ref Compared with the current time obtained by sampling k The temperature difference between the molten steel load temperature and the output ΔM(k) of the delay compensator is subtracted from the difference to obtain the temperature error value e. T (k); The process of obtaining △M(k) includes: k The steel load temperature error correction value M(k) at time t is processed by the delay module. ,get k- The steel load temperature error correction value M(k-1) at time 1, the difference between M(k) and M(k-1) is used to obtain the output ΔM(k) of the delay compensator; τ is the delay of the control system; 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 a forgetting factor of the current, is an error value of the current; Error value of current The obtaining process of the error value of current includes: setting the load output current to a given value i o_ref Subtracting the output current i0 sampled at the current moment, and the difference value is subtracted from the output ΔN(k) of the delay compensator to obtain the error value of current The obtaining process of the output ΔN(k) of the delay compensator includes: passing the output current correction value N(k) at the k moment through a delay module to obtain N(k-1), and the difference between N(k) and N(k-1) is obtained to obtain the output ΔN(k) of the delay compensator.

2. The tundish electromagnetic heating system thermostat control method according to claim 1, wherein 。 3. A tundish electromagnetic heating system thermostat control method, characterized by, The method comprises a front-stage three-phase rectifier control part and a rear-stage full-bridge inverter control part; wherein, The front-stage three-phase rectifier control part comprises the following steps: Collecting high-voltage cascade tundish electromagnetic heating power via grid current input to moving transformer i sx , grid voltage u sx , DC side voltage u dc ; x = a, b, c; The direct current side voltage instruction signal u dc_ref The direct current side voltage value u dc The difference is taken, and the difference value is taken as the input of the first PI controller to obtain the direct current side current reference value i dc_ref ; By load power P n The relationship between the input current and the load power, the input current command amplitude corresponding to the load power is calculated i sp_ref ; accumulated dc side current reference value i dc_ref with the input current command amplitude i sp_ref to obtain the final grid input side current reference value i sx_ref ; the final grid input side current reference value i sx_ref the d axis component i sd_ref , q axis component i sq_ref correspond respectively to the grid current i sx the d axis component i sd , q axis component i sq difference, get two-phase rotating coordinate system under the input current error Δi sd , Δ i sq ; The input current error in the two-phase rotating coordinate system is calculated Δi sd , Δi sq The output voltage correction value is obtained as an input of the second PI controller Δu sd , Δu sq ; Grid voltage d , q Axial components u sd , u sq respectively with Δu sd , Δu sq Subtracting them gives the output voltage. d , q Axial components u od , u oq ; Output voltage d , q Axial components u od , u oq After coordinate transformation, a switching pulse signal is obtained through PWM modulation to control the on / off state of the power switching devices of the three-phase rectifier in the intermediate drum electromagnetic heating system; The rear-stage full-bridge inverter control part is realized by the method in claim 1 or 2.

4. The method of claim 3, wherein the temperature of the molten steel in the tundish is controlled to be constant. wherein, is the effective value of the three-phase rectifier AC input voltage.

5. The method of claim 3, wherein the temperature of the molten steel in the tundish is controlled to be constant. ; wherein, is the load impedance, is the angular velocity corresponding to the power frequency.

6. A tundish electromagnetic heating system thermostat control system comprising a memory, a processor and a computer program stored on the memory; characterized in that, The processor executes a computer program on the memory to realize the steps of the method in claim 1 or 2; or the processor executes a computer program on the memory to realize the steps of the method in any one of claims 3-5.

Images