阅读说明：本技术 电磁感应加热温度控制方法 (Electromagnetic induction heating temperature control method ) 是由 刘进志 林凯恩 张阳 李莺歌 于 2019-10-30 设计创作，主要内容包括：本发明涉及一种电磁感应加热温度控制方法,属于温度控制技术领域。本发明包括如下步骤：步骤一：热惯性估计：要提高精确控温的效果,被加热对象的热惯性估计不可或缺；若无热惯性估计加热系统将不能快速锁定合适平衡功率数值,在热惯性小的应用场合中加热初期将造成较大的温度震荡；步骤二：功率控制与调节：基于工艺曲线加热过程中温度是提前设定的,即每一个时刻的理想温度值都通过推算而获知；步骤三：工艺曲线的温控实现：工艺曲线的升温,降温过程相对独立,保温阶段都包含于升温与降温过程之中。本发明以精确实现按工艺曲线的设定进行加热；控温精确,控温方式灵活,其应用不局限于电磁感应加热方式,适用任何按工艺曲线进行加热的系统。(The invention relates to an electromagnetic induction heating temperature control method, and belongs to the technical field of temperature control. The invention comprises the following steps: the method comprises the following steps: thermal inertia estimation: in order to improve the effect of accurate temperature control, the thermal inertia estimation of a heated object is indispensable; if the heating system is estimated without thermal inertia, the heating system cannot quickly lock a proper balance power value, and large temperature oscillation is caused in the initial heating stage in an application occasion with small thermal inertia; step two: power control and regulation: the temperature is set in advance in the heating process based on the process curve, namely the ideal temperature value at each moment is obtained by calculation; step three: the temperature control of the process curve is realized: the temperature rising and temperature lowering processes of the process curve are relatively independent, and the heat preservation stage is included in the temperature rising and temperature lowering processes. The invention can accurately realize heating according to the setting of the process curve; the temperature control is accurate, the temperature control mode is flexible, the application is not limited to an electromagnetic induction heating mode, and the method is suitable for any system which carries out heating according to a process curve.)

1. An electromagnetic induction heating temperature control method is characterized by comprising the following steps:

the method comprises the following steps: thermal inertia estimation: in order to improve the effect of accurate temperature control, the thermal inertia estimation of a heated object is indispensable; if the heating system is estimated without thermal inertia, the heating system cannot quickly lock a proper balance power value, and large temperature oscillation is caused in the initial heating stage in an application occasion with small thermal inertia;

the thermal inertia estimation method of the heated object is simple and effective, and the thermal inertia and the size parameters of the workpiece do not need to be set in advance;

IniEst＝T_1.5degree-T_initial-T_delay(1)

in the formula: IniEst is thermal inertia estimation;

T_1，5degreetime at 1.5 degrees difference in temperature;

T_initialis the time when the process starts;

T_delaytransmitting a delay time for the system power;

the temperature rise was estimated using the following formula:

Pb(0)＝k_r*P_iniital*Slop*IniEst (2)

and (3) during cooling, calculating the balance power by using the following formula:

Pb(0)＝k_fP_iniital/(Slop(IniEst) (3)

in the formula: p_iniitalFor initial output power, literThe rated output power can be set to 70% when the temperature is high, and the rated output power can be set to 1% when the temperature is low;

slop is the heating or cooling rate set in the process curve;

IniEst is a thermal inertia estimated value;

pb (0) is a balance power value at the initial moment;

k_r，k_fis a proportionality coefficient and is a constant;

step two: power control and regulation: the temperature is set in advance in the heating process based on the process curve, namely the ideal temperature value at each moment is obtained by calculation;

therefore, the real-time power value of the power supply is set to:

P(t)＝P_b(t)+K(d)*(T_realt(t)-T_ideal(t)) (4)

in the formula: t is_realt(t)The real-time temperature of the workpiece at the moment t;

T_ideal(t) is the ideal temperature of the workpiece at the moment t;

k (d) is a non-linear scaling factor, where d ═ T_realt(t)-T_ideal(t)), K (d) is non-linear with d;

p (t) is the output power at time t;

P_b(t) is the equilibrium power at time t;

by continuously regulating P_b(t) to achieve a balance between power supply power and actual power required by the workpiece, the adjustment algorithm is as follows:

in the formula: p_b(t0) is the balanced power value at the last moment;

K_pis a scale-down factor;

by continuous calibration of P_b(t) so that a balance is achieved between the power output of the power supply and the power required by heating the workpiece, thereby achieving accurate temperature control, namely:

T_realt(t)≈T_ideal(t)。

2. the electromagnetic induction heating temperature control method according to claim 1, wherein in the first step, the temperature increase and decrease control program supports online switching, wherein:

initializing parameters after the temperature rise is started, heating with initialization power and recording the starting time, adjusting the power of a power supply at two moments I and II in the heating process, infinitely approaching the ideal heating temperature of the power supply within the range within reach of resolution, and entering a heat preservation stage after the heating reaches a target temperature;

the temperature reduction process is similar to the temperature rise process, and after the temperature reduction is started, parameters are initialized, the temperature is reduced by the initialization power, and the starting time is recorded; the power supply adjusts the power at two moments I and II in the cooling process; and entering a heat preservation stage when the temperature is reduced to reach the target temperature.

3. The method of claim 2, wherein in the first step, during the heating process, when the temperature rises to 1.5 degrees, inertia estimation of the heating system is performed and proper initial equilibrium power is derived, and then the heating system enters a normal heating state.

4. The method of claim 2, wherein in the first step, during the cooling process, when the temperature reaches 1.5 degrees, inertia estimation of the cooling system is performed and proper initial equilibrium power is derived, and then the normal cooling state is entered.

5. The temperature control method of claim 1, wherein in the second step, in the formula (4), k (d) and d have a non-linear relationship, and the non-linearity is related to the thermal inertia of the workpiece to be heated.

6. The electromagnetic induction heating temperature control method according to claim 1, wherein in the second step, P is_bThe calibration of (t) occurs at two times:

time I:

when ① T_realt(t)＞T_ideal(t)，②Slop_config＝Slop_realt，③(Slop_realt) ' > 0 when three conditions are simultaneously satisfied;

when ① T_realt(t)＜T_ideal(t)，②Slop_config＝Slop_realt，③(Slop_realt) ' < 0 when three conditions are satisfied simultaneously; in the formula: slop_configThe temperature is 0 when the temperature is kept for the set temperature rising or reducing rate;

Slop_realtthe heating or cooling rate of the workpiece is real-time;

(Slop_realt) ' is the real-time temperature curve second derivative;

and time II:

at fixed time intervals, P_b(t) adjustment.

7. The electromagnetic induction heating temperature control method according to claim 6, characterized by the subsequent step in the second step:

step three: the temperature control of the process curve is realized: the temperature rising and temperature lowering processes of the process curve are relatively independent, and the heat preservation stage is included in the temperature rising and temperature lowering processes.

Technical Field

The invention relates to an electromagnetic induction heating temperature control method, and belongs to the technical field of temperature control.

Background

Important components, special materials and special parts in the industry are welded, and workpieces are required to be preheated; in order to reduce or eliminate the residual stress of the welded joint, prevent cracks and improve the structure and the performance of the weld joint and the heat affected zone metal, corresponding heat treatment is carried out after welding. The electromagnetic induction heating is used as a novel heating method, has the characteristics of environmental protection, safety, high efficiency and the like, and gradually replaces the traditional ceramic chip heating mode. Electromagnetic induction heating can also be used for temperature control of crystal growth furnaces.

In the above application occasions, it is often necessary to achieve temperature increase and heat preservation at a certain rate, and temperature decrease at a certain rate. The requirement on the precision of the temperature is high. However, the heating system, especially for heating large workpieces, has the characteristics of large hysteresis and large inertia, and the conventional PID control algorithm widely used is difficult to obtain a satisfactory control effect. The control algorithm based on the neural network has high complexity, high requirements on hardware platform resources and high implementation difficulty.

The traditional PID algorithm has the defects of large deviation between heating temperature and actual temperature in the heating and cooling processes, large temperature overshoot after heating to reach the target temperature, unstable control and the like.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides an electromagnetic induction heating temperature control method, which has high control precision and low complexity of an algorithm; the control platform based on the STM32F427 is realized and applied.

The electromagnetic induction heating temperature control method comprises the following steps:

the method comprises the following steps: thermal inertia estimation: in order to improve the effect of accurate temperature control, the thermal inertia estimation of a heated object is indispensable; if the heating system is estimated without thermal inertia, the heating system cannot quickly lock a proper balance power value, and large temperature oscillation is caused in the initial heating stage in an application occasion with small thermal inertia;

the thermal inertia estimation method of the heated object is simple and effective, and the thermal inertia and the size parameters of the workpiece do not need to be set in advance;

IniEst＝T_1.5degree-T_initial-T_delay(1)

in the formula: IniEst is thermal inertia estimation;

T_1.5degreetime at 1.5 degrees difference in temperature;

T_initialis the time when the process starts;

T_delaytransmitting a delay time for the system power;

the temperature rise was estimated using the following formula:

Pb(0)＝k_r*P_iniital*Slop*IniEst (2)

and (3) during cooling, calculating the balance power by using the following formula:

Pb(0)＝k_fP_iniital/(Slop*IniEst) (3)

in the formula: p_iniitalThe power is initial output power, and can be set as 70% rated output power when the temperature is raised, and can be set as 1% rated output power when the temperature is lowered;

slop is the heating or cooling rate set in the process curve;

IniEst is a thermal inertia estimated value;

pb (0) is a balance power value at the initial moment;

k_r，k_fis a proportionality coefficient and is a constant;

step two: power control and regulation: the temperature is set in advance in the heating process based on the process curve, namely the ideal temperature value at each moment is obtained by calculation;

therefore, the real-time power value of the power supply is set to:

P(t)＝P_b(t)+K(d)*(T_realt(t)-T_ideal(t)) (4)

in the formula: t is_realt(t) is the real-time temperature of the workpiece at time t;

T_ideal(t) is the ideal temperature of the workpiece at the moment t;

k (d) is a non-linear scaling factor, where d ═ T_realt(t)-T_ideal(t)), K (d) is non-linear with d;

p (t) is the output power at time t;

P_b(t) is the equilibrium power at time t;

by continuously regulating P_b(t) to achieve a balance between power supply power and actual power required by the workpiece, the adjustment algorithm is as follows:

in the formula: p_b(t0) is the balanced power value at the last moment;

K_pis a scale-down factor;

a power deviation value derived for the most recent N temperature deviations recorded;

by continuous calibration of P_b(t) so that a balance is achieved between the power output of the power supply and the power required by heating the workpiece, thereby achieving accurate temperature control, namely:

T_realt(t)≈T_ideal(t)。

preferably, in the first step, the temperature raising and lowering control program supports online switching, wherein:

initializing parameters after the temperature rise is started, heating with initialization power and recording the starting time, adjusting the power of a power supply at two moments of I and II in the heating process, infinitely approaching the ideal heating temperature of the power supply within the range within reach of resolution, and entering a heat preservation stage after the heating reaches a target temperature;

the temperature reduction process is similar to the temperature rise process, and after the temperature reduction is started, parameters are initialized, the temperature is reduced by the initialization power, and the starting time is recorded; the power supply adjusts the power at two moments I and II in the cooling process; and entering a heat preservation stage when the temperature is reduced to reach the target temperature.

Preferably, in the first step, during the temperature rise, when the temperature rise reaches 1.5 degrees, inertia estimation of the heating system is performed and a proper initialization balance power is derived, and then a normal heating state is entered.

Preferably, in the first step, in the cooling process, when the temperature reaches 1.5 degrees, inertia estimation of the cooling system is performed and a proper initialization balance power is derived, and then a normal cooling state is entered.

Preferably, in the second step, in the formula (4), k (d) and d have a non-linear relationship, and the non-linearity is related to the thermal inertia of the heated workpiece.

Preferably, in said step two, P_bThe calibration of (t) occurs at two times:

time I:

when ① T_realt(t)＞T_ideal(t)，②Slop_config＝Slop_realt，③(Slop_realt) ' > 0 when three conditions are simultaneously satisfied;

when ① T_realt(t)＜T_ideal(t)，②Slop_config＝Slop_realt，③(Slop_realt) ' < 0 when three conditions are satisfied simultaneously;

in the formula: slop_configThe temperature is 0 when the temperature is kept for the set temperature rising or reducing rate;

Slop_realtthe heating or cooling rate of the workpiece is real-time;

(Slop_realt) ' is the real-time temperature curve second derivative;

time II:

at fixed time intervals, P_b(t) adjustment.

Preferably, the subsequent step in step two is:

step three: the temperature control of the process curve is realized: the temperature rising and temperature lowering processes of the process curve are relatively independent, and the heat preservation stage is included in the temperature rising and temperature lowering processes.

The invention has the beneficial effects that: the electromagnetic induction heating temperature control method of the invention can accurately realize heating according to the setting of the process curve; the heating control program realized based on the algorithm has accurate temperature control and flexible temperature control mode; the invention is realized and verified based on electromagnetic induction heating, is not limited to an electromagnetic induction heating mode in application, and is suitable for any system for heating according to a process curve.

Drawings

FIG. 1 is a schematic diagram of the temperature ramp process control of the present invention.

FIG. 2 is a schematic diagram of the cooling control process of the present invention.

Fig. 3 is a temperature profile of the present invention.

Fig. 4 is a temperature control graph of a conventional PID.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.