An electromagnetic stirring control method fusing PID control and pulse width modulation technology

Abstract

The application belongs to the field of electromagnetic stirring, and discloses an electromagnetic stirring control method combining PID control and pulse width modulation technology, which comprises the following steps: step 1, stirring initialization; step 2, PWM intervention adjustment; step 3, PID feedback adjustment of PWM duty cycle through speed sensor data; and step 4, PID feedback adjustment of PWM switching frequency through temperature sensor data. The application can generate a high-frequency and smooth-changing magnetic field through PWM technology, so that the stirring speed can be smoothly and quickly adjusted. Meanwhile, the application introduces two PID control algorithms, one of which ensures that the stirring speed of the liquid metal solution can always reach the user-set speed, and the other of which is responsible for real-time adjustment according to whether the current stirring temperature is uniform.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic stirring, and in particular to an electromagnetic stirring control method integrating PID control and pulse width modulation technology. Background Art

[0002] Electromagnetic stirring (EMS) is a technology that stirs liquid metal by inducing eddy currents and generating Lorentz forces. This technology is widely used in metallurgy and materials science, particularly in the casting and processing of metals such as steel and aluminum. Currently, many factories using EMS to stir liquid metal often experience uneven mixing, resulting in poor processing results. Furthermore, the system cannot quickly respond to and adjust the stirring speed or temperature in real time. Summary of the Invention

[0003] The object of the present invention is to provide an electromagnetic stirring control method that integrates PID control and pulse width modulation technology to solve the problems raised in the above background technology.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] An electromagnetic stirring control method integrating PID control and pulse width modulation technology, comprising:

[0006] Step 1: After power-on, perform initialization of the stirring operation;

[0007] Step 2: Initially, the initial duty cycle and switching frequency are used to control the stirring process. Then, two PID controllers are used: one for controlling the uniformity of the stirring temperature and the other for controlling the uniformity of the stirring speed. The PID controller for controlling the uniformity of the stirring speed works first, followed by the PID controller for controlling the uniformity of the stirring temperature.

[0008] Step 3: Use speed sensor data and PID feedback to adjust the PWM duty cycle;

[0009] Step 4: Use temperature sensor data and PID feedback to adjust the PWM switching frequency.

[0010] Furthermore, the step 1 specifically includes:

[0011] Step 1.1, set a stirring speed and stirring temperature deviation value according to the type of liquid metal;

[0012] Step 1.2, set an initial duty cycle. When the power is turned on and the machine starts working, the stirring speed of the liquid metal solution is 0, and the temperature difference of each temperature sensor is also close to 0. At this time, the first PID responsible for controlling the uniformity of the stirring temperature does not intervene in the work, and the output value of the second PID responsible for controlling the stirring speed of the liquid metal solution is superimposed with the initial duty cycle. The specific method is to superimpose the output value of the second PID with the set PWM step limit value ΔD max After division, it is added to the initial duty cycle to achieve precise control. The PWM duty cycle is expressed by the following formula:

[0013]

[0014] Where D represents the duty cycle, t high Represents the time the PWM switch is turned on, and T represents the PWM period;

[0015] In step 1.3, the duty cycle after the second PID feedback adjustment is expressed by the following formula:

[0016]

[0017] Where D final Represents the final duty cycle after the second PID adjustment, D initial Represents the initial duty cycle, PID voutput Represents the output adjustment value of the second PID, ΔD max Represents the step limit value.

[0018] Furthermore, the step 2 specifically includes:

[0019] Step 2.1: When the PWM duty cycle gradually increases, the equivalent current flowing into the electromagnetic coil will also gradually increase. According to the PWM formula, the equivalent current in the electromagnetic coil at this time can be expressed by the following formula:

[0020]

[0021] Where I avg Represents the equivalent current in the electromagnetic coil, D final Represents the duty cycle adopted after the second PID adjustment, V sta represents the PWM standard input voltage, and R represents the resistance value of the electromagnetic coil;

[0022] In step 2.2, the magnetic field generated by the equivalent current in the electromagnetic coil gradually increases, thereby affecting the stirring speed of the liquid metal solution. At this time, the magnitude of the electromagnetic field generated and the magnitude of the Lorentz force on the liquid metal solution are expressed by the following equations:

[0023]

[0024] F l =B×J(5)

[0025] Where I avg represents the equivalent current in the electromagnetic coil, m is the number of turns of the electromagnetic coil, L is the length of the electromagnetic coil, μ0 represents the magnetic permeability in the atmosphere, B represents the magnetic field strength, F l represents the magnitude of the Lorentz force on the liquid metal solution, and J represents the current density inside the liquid metal solution;

[0026] Furthermore, the step 3 specifically includes:

[0027] In step 3.1, the input source of the second PID is determined by the average value of each position speed sensor installed in the stirring container. The control algorithm of the second PID is expressed by the following formula:

[0028]

[0029] Where, e V (t) is the error, that is, the difference between the user's expected speed value and the actual average speed measurement of each different position sensor, K p , K i , K d They are proportional, integral and differential gains respectively, and the output signal u of the second PID v (t) represents the output value of the second PID, V s (t) represents the average value of each speed sensor, V sta Represents the speed expectation set by the user;

[0030] Step 3.2: If the current actual speed is lower than the expected speed value set by the user, the output value of the second PID will increase. However, in order to prevent the PWM step size from changing too much and causing the speed to increase too quickly, thereby affecting the stability of the stirring, the output value of the second PID will be adjusted to the PWM step size limit value ΔD. max After division, add it to the existing control quantity.

[0031] Furthermore, the step 4 specifically includes:

[0032] In step 4.1, the first PID uses the temperature difference of the temperature sensors at different locations as the input source to adjust and control the switching frequency of the PWM duty cycle. The temperature difference of the temperature sensors at different locations is defined by the following formula:

[0033]

[0034] Where ΔTtem represents the input source of the first PID, n represents the number of temperature sensors in the stirring container, and Ttem nRepresents the temperature value of the temperature sensor, Ttem sta Indicates that the value of the temperature sensor is used as the reference temperature value;

[0035] Step 4.2: Since the first PID is not always involved in the mixing process, only the current calculated ΔTtem is greater than the user's set value ΔTtem sta After that, the first PID starts to intervene, so set ΔTtem sta The value of must be greater than 0;

[0036] Step 4.3, if the currently calculated ΔTtem is greater than ΔTtem sta , the first PID immediately intervenes and controls the PWM switching frequency instead of the duty cycle. The PWM switching frequency is obtained by the following formula:

[0037]

[0038] Where T represents the PWM cycle time, and ω represents the PWM switching frequency;

[0039] Step 4.4, when the calculated ΔTtem is greater than ΔTtem sta When it exceeds fifty percent, the output value of the first PID significantly reduces the current PWM switching frequency. PWM has a minimum switching frequency. If the PWM switching frequency adjusted by the first PID is lower than the minimum switching frequency, the minimum switching frequency is used for adjustment.

[0040] Step 4.5, the control equation of the first PID is expressed as follows:

[0041]

[0042] Where, PID ωoutput Represents the output value of the first PID, e ω (t) represents the difference between the actual ΔTtem measured by each temperature sensor and the ΔTtem expected by the user sta The error value, n represents the number of temperature sensors in the stirring container, K p , K i , K d are proportional, integral and differential gains respectively, t is the current time, t' is the time variable of integration, which means the accumulation of past errors;

[0043] Step 4.6: Once the ΔTtem after the first PID adjustment is less than or equal to the expected temperature deviation ΔTtem set by the user during the control process, sta After that, the first PID is immediately disconnected and no longer participates in the electromagnetic stirring work until the next time ΔTtem calculated according to formula 7 is greater than ΔTtemsta After that, the first PID continues to participate in the stirring work.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows: By using the present invention, a high-frequency and smoothly changing magnetic field can be generated through PWM technology, so that the stirring speed can be adjusted smoothly and quickly. At the same time, the present invention introduces a two-way PID control algorithm. One-way PID ensures that the stirring speed of the liquid metal solution can always reach the user-set speed. The other way of PID is responsible for making real-time adjustments according to whether the current stirring temperature is uniform. Description of the Drawings

[0045] Figure 1 is a flow chart of the present invention.

[0046] Figure 2 is a schematic diagram of the effects of different PWM duty cycles in the present invention. In the figure, D1, D2, and D3 represent PWM waveforms with different duty cycles, D1 < D2 < D3, T1, T2, and T3 represent the periods corresponding to different duty cycles, T1 = T2 = T3, V 等效 represents the equivalent voltage of this PWM under different periods.

[0047] Figure 3 is a schematic diagram of PID adjustment according to the average value of speed sensors at different positions in the stirring container in the present invention.

[0048] Figure 4 is a schematic diagram of the effects of different PWM switching frequencies in the present invention. In the figure, W1, W2, and W3 represent PWM waveforms with different switching frequencies of PWM, W1 > W2 > W3, T1, T2, and T3 represent the periods corresponding to different switching frequencies of PWM, T1 < T2 < T3, V 等效 represents the equivalent voltage of this PWM under different switching frequencies.

[0049] Figure 5 is a schematic diagram of PID adjustment according to the temperature sensor difference at different positions in the stirring container in the present invention. Detailed Embodiments

[0050] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0051] Please refer to Figure 1-Figure 5 , an electromagnetic stirring control method integrating PID control and pulse width modulation technology, includes the following steps.

[0052] Step 1: After power-on, perform the initialization operation of the stirring work, which specifically includes the following steps:

[0053] Step 1.1: When starting to stir the liquid metal, the user first needs to set a stirring speed and stirring temperature deviation value according to the type of liquid metal.

[0054] Step 1.2, this control method sets an initial duty cycle. When the power is turned on and the work starts, the stirring speed of the liquid metal solution is 0, and the temperature difference of each temperature sensor is also close to 0. At this time, the first PID responsible for controlling the stirring uniformity (PID based on the difference of the temperature sensors at each position as input) does not intervene in the work, and the second PID responsible for controlling the stirring speed of the liquid metal solution will output a larger value and superimpose it with the initial duty cycle. However, in order to make the stirring speed of the liquid metal solution rise smoothly and linearly, it is necessary to prevent the duty cycle from changing too fast and causing unstable stirring. The present invention compares the output value of the second PID with the step limit value ΔD of the PWM set inside the control method. max After division, the value is added to the initial duty cycle to achieve precise control. The PWM duty cycle can be expressed as follows.

[0055]

[0056] Where D represents the duty cycle, t high Represents the time that the PWM switch is turned on (maintaining a high level), and T represents the PWM period.

[0057] In step 1.3, the duty cycle after PID feedback adjustment can be expressed by the following formula.

[0058]

[0059] Where D final Represents the final duty cycle after the second PID adjustment, D initial Represents the initial duty cycle built into the algorithm, PID voutput Represents the output adjustment value of the second PID, ΔD max Represents the step limit value.

[0060] Step 2: PWM intervention regulation. Initially, the initial duty cycle and switching frequency are used to control the stirring process. Then, there are two PIDs, one responsible for controlling the uniformity of the stirring temperature and the other responsible for controlling the uniformity of the stirring speed. First, the PID responsible for controlling the uniformity of the stirring speed works first, and then the PID responsible for controlling the uniformity of the stirring temperature works. Specifically, the following steps are included:

[0061] Step 2.1: When the duty cycle of PWM is gradually increased, the equivalent current flowing into the electromagnetic coil will also gradually increase. This is achieved by the PWM algorithm, as shown in the schematic diagram. Figure 2 According to the PWM formula, the equivalent current in the electromagnetic coil at this time can be expressed by the following formula.

[0062]

[0063] Where I avg Represents the equivalent current in the electromagnetic coil, D final Represents the duty cycle adopted by the algorithm after the second PID adjustment, V sta represents the PWM standard input voltage, and R represents the resistance value of the electromagnetic coil.

[0064] In step 2.2, the magnetic field generated by the equivalent current in the electromagnetic coil will gradually increase, thereby affecting the stirring speed of the liquid metal solution. The magnitude of the electromagnetic field generated at this time and the magnitude of the Lorentz force on the liquid metal solution can be expressed by the following equations:

[0065]

[0066] F l =B×J(5)

[0067] Where I avg represents the equivalent current in the electromagnetic coil, m is the number of turns of the electromagnetic coil, L is the length of the electromagnetic coil, μ0 represents the magnetic permeability in the atmosphere, and B represents the magnetic field strength. l represents the magnitude of the Lorentz force acting on the liquid metal solution, and J represents the current density inside the liquid metal solution.

[0068] In step 2.3, the above equation shows that, given a constant current within the liquid metal solution, a higher duty cycle results in a greater electromagnetic field generated by the electromagnetic coil, a greater Lorentz force acting on the liquid metal solution, and ultimately a faster rotational speed. The above equation also shows that the stirring speed of the liquid metal solution is closely related to the PWM duty cycle.

[0069] Step 3: Use the speed sensor data and PID feedback to adjust the PWM duty cycle, which specifically includes the following steps:

[0070] In step 3.1, the input source of the second PID is determined by the average value of each position and speed sensor installed in the stirring container. The control algorithm of the second PID can be expressed by the following formula.

[0071]

[0072] Where, e V(t) is the error, that is, the difference between the user's expected speed value and the actual average speed measurement of each different position sensor. K p , K i , K d are proportional, integral and differential gains respectively. The output signal u of the second PID v (t) represents the adjustment amount that needs to be applied to the system. V s (t) represents the average value of each speed sensor, V sta Represents the speed expectation set by the user.

[0073] Step 3.2: If the current actual speed is lower than the expected speed value set by the user, the output value of the second PID will increase. However, in order to prevent the PWM step size from changing too much and causing the speed to increase too quickly, thereby affecting the stability of the stirring, the output value of the second PID will be different from the PWM step size limit value ΔD. max After division, add it to the existing control quantity. The second PID control diagram is as follows Figure 3 shown.

[0074] Step 4: Using temperature sensor data and PID feedback to adjust the PWM switching frequency, specifically including the following steps:

[0075] Step 4.1: During the stirring process, the liquid metal solution itself has a high heat content, and the liquid metal solution particles rub against each other and also against the stirring container, so the temperature of the liquid metal solution will rise. In addition, the more uniform the stirring, the more conducive it is to heat conduction inside the liquid metal solution, and the more uniform the temperature distribution inside the liquid metal solution. Therefore, the first PID uses the temperature difference of the temperature sensors at different positions as the input source to adjust and control the switching frequency of the PWM duty cycle. The temperature difference of the temperature sensors at different positions is defined by the following formula:

[0076]

[0077] Where ΔTtem represents the input source of the first PID (i.e., the difference between the temperature sensors at different locations), n represents the number of temperature sensors in the stirring container, and Ttem n Represents the temperature value of the temperature sensor, Ttem sta Indicates that the value of the temperature sensor is used as the reference temperature value.

[0078] Step 4.2: Since the first PID is not always involved in the mixing process, only the current calculated ΔTtem is greater than the user's set value ΔTtem sta After that, the first PID starts to intervene. It is impossible to ensure that the temperature at each position is absolutely equal during the stirring process, so generally ΔTtem sta The value must be greater than 0.

[0079] Step 4.3, if the ΔTtem calculated by the system is greater than ΔTtem sta , the first PID will immediately intervene. The first PID mainly controls the PWM switching frequency rather than the duty cycle. The PWM switching frequency can be calculated as follows:

[0080]

[0081] Where T represents the PWM cycle time, and ω represents the PWM switching frequency.

[0082] Step 4.4, when the calculated ΔTtem is greater than ΔTtem sta When the value exceeds 50%, the output value of the first PID will significantly reduce the current PWM switching frequency. However, in order to prevent large oscillations during the stirring process, the system will set a minimum PWM switching frequency. If the PWM switching frequency after PID adjustment is lower than this value, the minimum value will be used for adjustment.

[0083] According to formula (8), when the switching frequency of PWM is reduced, when the equivalent current of the same magnitude is output, the period of PWM will become longer, the switching speed of high and low levels will be reduced, and the real-time response capability of PWM will be weakened. Then, the equivalent current output of PWM in one period will no longer be smooth. This will cause a slight oscillation effect in the liquid metal solution during the stirring process, thereby promoting the uniformity of the temperature inside the liquid metal. This will make the viscosity and flow behavior of the liquid metal solution at different positions tend to be consistent, which is conducive to the uniformity of stirring. The schematic diagram of the effect of different PWM switching frequencies is shown in the figure below. Figure 4 shown.

[0084] Step 4.5, the control equation of the first PID can be expressed as follows:

[0085]

[0086] Where, PID ωoutput Represents the first PID output value, e ω (t) represents the difference between the actual ΔTtem measured by each temperature sensor and the ΔTtem expected by the user sta The error value is n. n represents the number of temperature sensors in the stirring vessel. K p , K i , K d are proportional, integral, and differential gains respectively. t is the current time, and t' is the time variable of the integral, which means the accumulation of past errors.

[0087] During the adjustment process, if the PID adjustment value is too large and the PWM switching frequency is reduced to the minimum limit, the system will automatically adopt the minimum limit. This process can be represented by the following code block:

[0088]

[0089] where ω inital Represents the initial PWM switching frequency of the system, ω min Represents the lowest PWM switching frequency set by the system. ω is the final PWM switching frequency used.

[0090] Step 4.6: Once the ΔTtem after the first PID adjustment is less than or equal to the expected temperature deviation ΔTtem set by the user during the control process, sta After that, the first PID is immediately disconnected and no longer participates in the electromagnetic stirring. The working diagram of the first PID is as follows Figure 5 Until the next time ΔTtem calculated according to formula 7 is greater than ΔTtem sta After that, the first PID continues to participate in the stirring work.

[0091] Through the above process, the PWM switching frequency and duty cycle serve as the underlying algorithms that actually influence the stirring effect within the entire control method. The two-way PID control algorithm adjusts the PWM-related variables according to the user's set values. This control method arrangement can better meet stirring requirements, making the entire stirring process highly controllable and improving stirring quality.

[0092] The control method of the present invention includes two parts, the first part is the PWM algorithm. This method extracts the switching frequency and duty cycle of PWM separately, and controls them separately by two PIDs respectively. Adjusting the size of the PWM duty cycle can change the stirring speed of the liquid metal solution. The size of the PWM switching frequency can affect whether slight oscillation occurs during the stirring process. In the stirring work, it is often required to stir evenly and avoid the phenomenon of local excessive temperature causing inconsistent fluidity of the entire liquid metal solution. Therefore, the size of the PWM frequency is adjusted so that the oscillation effect is triggered by artificial control during the stirring process, so as to ensure that the temperature of the entire liquid metal solution tends to be consistent during the stirring process.

[0093] The second major part of the present invention is mainly a two-way PID algorithm, which is mainly designed for the input and output of the two PIDs. The second PID and the PID that performs feedback adjustment on the PWM duty cycle are present throughout the stirring process, and the user's desired stirring speed is met by changing the duty cycle. However, to avoid uncontrollable oscillation effects during operation, this method limits the output of the PID, dividing the output by the step size limit before acting on the system. At the same time, while ensuring that the stirring speed meets the requirements, the stirring is as uniform as possible. Therefore, the input of this PID is the average value of the speed sensors distributed at different positions in the stirring container. The first PID plays a major role in regulating the uniformity of the entire stirring process. By changing the PWM switching frequency through the PID, a slight oscillation phenomenon is artificially induced, thereby promoting the temperature uniformity of the entire liquid metal solution during the stirring process. To better ensure this, the input of this PID is the difference between the temperature sensors at different positions. However, to keep the induced oscillation effect within a controllable range, the output of this PID is compared with the minimum PWM switching frequency set by the system before outputting it.

[0094] This invention simultaneously controls both the PWM switching frequency and duty cycle. Two PID controllers are provided to independently control each. The PID controller for controlling the PWM switching frequency only activates when the temperature difference between the different sensors exceeds a user-set value. Once this difference is met, the controller ceases operation.

[0095] The present invention combines PWM technology with PID control, sets a certain amount of PWM duty cycle step limit value and PWM minimum switching frequency, and then uses two separate PIDs to separately control the PWM duty cycle and switching frequency.

[0096] To ensure that the temperature of the liquid metal solution at different locations is consistent during the stirring process, the present invention uses a separate PID control to control the PWM switching frequency. By reducing the PWM switching frequency, the oscillation effect caused by human control is used to promote the temperature of the liquid metal solution to be consistent during the stirring process.

[0097] The characteristics of the present invention are:

[0098] 1) Combining PWM technology with PID algorithm and introducing it into electromagnetic stirring, PWM can make the current change smoothly at high frequency, thereby generating a high-frequency and smoothly changing magnetic field, which makes the stirring process more stable.

[0099] 2) Two PID controllers are introduced to control the duty cycle and switching frequency of PWM respectively, and are combined with PWM in the electromagnetic stirring algorithm.

[0100] 3) The PWM switching frequency is reduced through PID control, thereby artificially inducing an oscillation effect during the liquid metal stirring process to promote the temperature of the liquid metal solution to be consistent during the stirring process.

[0101] 4) The switching frequency and duty cycle of PWM are extracted separately and controlled by PID, which increases the controllability of the electromagnetic stirring process.

[0102] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. An electromagnetic stirring control method integrating PID control and pulse width modulation technology, characterized in that: include: Step 1: After power-on, perform the initialization operation of the stirring work, including: Step 1.1, set a stirring speed and stirring temperature deviation value according to the type of liquid metal; Step 1.2, set an initial duty cycle. When the power is turned on and the machine starts working, the stirring speed of the liquid metal solution is 0, and the temperature difference of each temperature sensor is also close to 0. At this time, the first PID responsible for controlling the uniformity of the stirring temperature does not intervene in the work, and the output value of the second PID responsible for controlling the stirring speed of the liquid metal solution is superimposed with the initial duty cycle. The specific method is to superimpose the output value of the second PID with the set PWM step limit value ΔD max After division, it is added to the initial duty cycle to achieve precise control. The PWM duty cycle is expressed by the following formula: Where D represents the duty cycle, t high Represents the time the PWM switch is turned on, and T represents the PWM period; In step 1.3, the duty cycle after the second PID feedback adjustment is expressed by the following formula: Where D final Represents the final duty cycle after the second PID adjustment, D initial Represents the initial duty cycle, PID voutput Represents the output adjustment value of the second PID, ΔD max Represents the step limit value; Step 2: Initially, the initial duty cycle and switching frequency are used to control the stirring process. Then, two PID controllers are used: one for controlling the uniformity of the stirring temperature and the other for controlling the uniformity of the stirring speed. The PID controller for controlling the uniformity of the stirring speed works first, followed by the PID controller for controlling the uniformity of the stirring temperature. Step 2.1: When the PWM duty cycle gradually increases, the equivalent current flowing into the electromagnetic coil will also gradually increase. According to the PWM formula, the equivalent current in the electromagnetic coil at this time can be expressed by the following formula: Where I avg Represents the equivalent current in the electromagnetic coil, D final Represents the duty cycle adopted after the second PID adjustment, V sta represents the PWM standard input voltage, and R represents the resistance value of the electromagnetic coil; In step 2.2, the magnetic field generated by the equivalent current in the electromagnetic coil gradually increases, thereby affecting the stirring speed of the liquid metal solution. At this time, the magnitude of the electromagnetic field generated and the magnitude of the Lorentz force on the liquid metal solution are expressed by the following equations: F l =B×J (5) Where I avg represents the equivalent current in the electromagnetic coil, m is the number of turns of the electromagnetic coil, L is the length of the electromagnetic coil, μ0 represents the magnetic permeability in the atmosphere, B represents the magnetic field strength, F l represents the magnitude of the Lorentz force on the liquid metal solution, and J represents the current density inside the liquid metal solution; Step 3: Use speed sensor data and PID feedback to adjust the PWM duty cycle, including: In step 3.1, the input source of the second PID is determined by the average value of each position speed sensor installed in the stirring container. The control algorithm of the second PID is expressed by the following formula: Where, e V (t) is the error, that is, the difference between the user's expected speed value and the actual average speed measurement of each different position sensor, K p , K i , K d They are proportional, integral and differential gains respectively, and the output signal u of the second PID v (t) represents the output value of the second PID, V s (t) represents the average value of each speed sensor, V sta Represents the speed expectation set by the user; Step 3.2: If the current actual speed is lower than the expected speed value set by the user, the output value of the second PID will increase. However, in order to prevent the PWM step size from changing too much and causing the speed to increase too quickly, thereby affecting the stability of the stirring, the output value of the second PID will be adjusted to the PWM step size limit value ΔD. max After dividing, add it to the existing control quantity; Step 4: Use temperature sensor data and PID feedback to adjust the PWM switching frequency.

2. The electromagnetic stirring control method integrating PID control and pulse width modulation technology according to claim 1 is characterized in that: The step 4 specifically includes: In step 4.1, the first PID uses the temperature difference of the temperature sensors at different locations as the input source to adjust and control the switching frequency of the PWM duty cycle. The temperature difference of the temperature sensors at different locations is defined by the following formula: Where ΔTtem represents the input source of the first PID, n represents the number of temperature sensors in the stirring container, and Ttem n Represents the temperature value of the temperature sensor, Ttem sta Indicates that the value of the temperature sensor is used as the reference temperature value; Step 4.2: Since the first PID is not always involved in the mixing process, only the current calculated ΔTtem is greater than the user's set value ΔTtem sta After that, the first PID starts to intervene, so set ΔTtem sta The value of must be greater than 0; Step 4.3, if the currently calculated ΔTtem is greater than ΔTtem sta , the first PID immediately intervenes and controls the PWM switching frequency instead of the duty cycle. The PWM switching frequency is obtained by the following formula: Where T represents the PWM cycle time, and ω represents the PWM switching frequency; Step 4.4, when the calculated ΔTtem is greater than ΔTtem sta When it exceeds fifty percent, the output value of the first PID significantly reduces the current PWM switching frequency. PWM has a minimum switching frequency. If the PWM switching frequency adjusted by the first PID is lower than the minimum switching frequency, the minimum switching frequency is used for adjustment. Step 4.5, the control equation of the first PID is expressed as follows: Where, PID ωoutput Represents the output value of the first PID, e ω (t) represents the difference between the actual ΔTtem measured by each temperature sensor and the ΔTtem expected by the user sta The error value, n represents the number of temperature sensors in the stirring container, K p , K i , K d are proportional, integral and differential gains respectively, t is the current time, t' is the time variable of integration, which means the accumulation of past errors; Step 4.6: Once the ΔTtem after the first PID adjustment is less than or equal to the expected temperature deviation ΔTtem set by the user during the control process, sta After that, the first PID is immediately disconnected and no longer participates in the electromagnetic stirring work until the next time ΔTtem calculated according to formula 7 is greater than ΔTtem sta After that, the first PID continues to participate in the stirring work.

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