阅读说明：本技术 一种电磁开关高频吸持噪声自适应抑制方法 (Self-adaptive suppression method for high-frequency holding noise of electromagnetic switch ) 是由 汤龙飞 庄剑雄 于 2019-12-05 设计创作，主要内容包括：本发明涉及一种电磁开关高频吸持噪声自适应抑制方法,控制策略：开关管操作频率为18kHz及以上,电磁开关在稳定吸持状态下进行励磁状态与续流状态之间切换控制,分断过程通过前期吸持阶段电容所储能量给线圈加负压,快速退磁；控制算法：通过继电反馈自整定技术对PID控制参数进行在线自整定,通过电流监测环切换机制对采样线圈电流与设定保持参考电流的误差进行在线监测,当误差超出所设阈值范围电流监测环升级成电流闭环,待误差降至阈值范围内电流闭环退化为电流监测环,自动计算当前工况下的输出占空比平均值并固定该平均值为最佳占空比输出给PWM发生器,重复上述自适应切换控制过程。本发明实现电磁开关在宽电压范围内节能、无声运行的控制效果。(The invention relates to a self-adaptive suppression method for high-frequency holding noise of an electromagnetic switch, which comprises the following control strategies: the operating frequency of the switching tube is 18kHz and above, the electromagnetic switch is switched and controlled between an excitation state and a follow current state under a stable holding state, and the breaking process applies negative pressure to the coil through the energy stored in the capacitor in the earlier holding stage and demagnetizes rapidly; and (3) a control algorithm: the method comprises the steps of carrying out online self-setting on PID control parameters through a relay feedback self-setting technology, carrying out online monitoring on errors between sampling coil current and set and maintained reference current through a current monitoring ring switching mechanism, upgrading the current monitoring ring into a current closed ring when the errors exceed a set threshold range, degrading the current closed ring into the current monitoring ring when the errors fall into the threshold range, automatically calculating an average value of output duty ratios under the current working condition, fixing the average value as an optimal duty ratio, outputting the optimal duty ratio to a PWM generator, and repeating the self-adaptive switching control process. The invention realizes the control effect of the energy-saving and silent operation of the electromagnetic switch in a wide voltage range.)

1. A self-adaptive suppression method for high-frequency holding noise of an electromagnetic switch is characterized by comprising the following steps: the method comprises the following steps:

step S1: providing a coil driving circuit, operating a coil of an electromagnetic switch in the high-frequency excitation control mode driving circuit to switch and control the coil between an excitation state and a follow current state in a stable holding state, and applying negative pressure to the coil through energy stored in a capacitor in a holding stage in a breaking process to rapidly demagnetize;

step S2: PID control parameter K through relay feedback self-tuning technology_p、T_i、T_dAnd performing on-line self-setting, calculating an output duty ratio through a current monitoring loop switching mechanism, and fixing the output duty ratio so as to shift the frequency band of the generated high-frequency holding noise out of the range of the audible noise frequency band of the human ears.

2. The adaptive suppression method for high-frequency holding noise of an electromagnetic switch according to claim 1, characterized in that: the coil drive circuit comprises a rectification circuit, a capacitor C and a first switching tube S₁A second switch tube S₄A first fast recovery diode D₂A second fast recovery diode D₃Coil equivalent resistance R_coilAnd coil equivalent inductance L_coil(ii) a The coil equivalent resistance R_coilAnd coil equivalent inductance L_coilAre connected in series to form a coil; the input end of the rectifying circuit is connected with an external AC/DC input control power supply, the AC/DC input control power supply obtains direct current after being rectified and filtered by the rectifying circuit and the capacitor C, and the direct current passes through a first switching tube S₁A second switch tube S₄Applying an excitation voltage to the coil R_coilAnd L_coilAre connected in series at two ends.

3. The adaptive suppression method for high-frequency holding noise of an electromagnetic switch according to claim 2, characterized in that: the specific content of step S1 is: setting the first switch tube S₁And a second switching tube S₄The operating frequency is more than or equal to 18 kHz; when the first switch tube S₁And a second switching tube S₄When the coil is conducted, the coil driving circuit is in an excitation state, and the coil voltage is positive left and negative right; when the first switch tube S₁Cut-off, the second switching tube S₄When the transformer is conducted, the coil driving circuit is in a follow current state, the voltage drop of the tube is ignored, and the voltage at the two ends of the coil is zero; the second switch tube S is arranged at the stage from attraction to attraction of the electromagnetic switch₄Always gives high level conduction to the first switch tube S₁Modulating to make the coil driving circuit in the exciting state and the follow current state for switching control to obtain required coil starting current and holding current; in the breaking stage, the first switch tube S₁And a second switching tube S₄And meanwhile, the switch is switched to a demagnetization state, and because the voltage at two ends of the coil is negative, the current of the coil is rapidly reduced to zero, the electromagnetic attraction is reduced, and the rapid demagnetization and opening of the electromagnetic switch are realized.

4. The adaptive suppression method for high-frequency holding noise of an electromagnetic switch according to claim 1, characterized in that: the step S2 specifically includes the following steps:

step S21: detecting coil current by current sensor, comparing with set reference current to generate error value, and sampling coil current i in real time by current monitoring loop switching mechanism_coilAnd setting the holding reference current i_refE (t) is monitored online; the current monitoring loop is described by the following formula:

step S22: judging whether the error e (t) exceeds a set threshold value epsilon range, if the error e (t) exceeds the set threshold value epsilon range, upgrading the current monitoring ring into a current closed ring, performing PID control parameter on-line self-setting through a relay feedback self-setting PID controller, and quickly adjusting the coil current to a reference current value; after the error e (t) is reduced to the range of the threshold value epsilon, the current closed loop is degenerated into a current monitoring loop, and the average value of the output duty ratio under the current working condition is automatically calculated in the current monitoring loop

where D represents the output duty cycle and N represents the number of cycles.

5. The adaptive suppression method for high-frequency holding noise of an electromagnetic switch according to claim 4, characterized in that: the specific content of online self-tuning of the PID control parameters is as follows: the self-setting process is divided into two stages, wherein the first stage is a relay feedback self-setting adjusting process, and the second stage is a PID control process;

when the self-tuning PID control system is in constant amplitude oscillation, the relay output characteristic is that when the error e (t) is greater than 0, the relay amplitude d is output; when e (t) is less than 0, outputting relay amplitude-d, wherein the output mathematical expression of the relay characteristic is as follows:

in the formula: d is the output relay amplitude, e (t) is the error between the reference current value and the actual current value, i.e. e (t) ═ i_ref-i_coil；

t₀-t₁The time interval is the initial stage of signal input, the signal is input, when the self-tuning PID control system is disturbed, the | e (t) | is not equal to 0, and therefore the output i_coilDeviating from the original equilibrium state, then increasing the equivalent gain of the relay characteristic due to the reduction of | e (t) |, and i_coilIs presented in i_refNearby high frequency small amplitude oscillations;

t₁-t₂in the period of time, namely the steady state stage, when the self-tuning PID control system enters the steady state and is in periodic constant amplitude oscillation, the nonlinear link input signal e (T) is a sine signal, namely e (T) is A sin (ω T), and at the moment, the constant amplitude oscillation periodic oscillation amplitude a of the self-tuning PID control system is measured and the critical period T is calculated_uThe nonlinear link relay output signal u (t) is a periodic square wave signal, and a Fourier series expression is as follows:

in the formula, A₀Is a direct current component; a. the_n、B_nThe fundamental and subharmonic component amplitudes, respectively, are described by the following equation:

the nonlinear relay description function is defined as that under the action of a sine input signal, the complex ratio of a first harmonic component in steady-state output of a nonlinear link and the input signal is a description function of the nonlinear link, and is expressed by N (A):

since most inertial systems can act as a low-pass filter, the fourier expression of the relay output obtained by ignoring higher harmonics is:

in the formula:

the simplified relay characteristic description function is:

and substituting the measured constant amplitude oscillation period oscillation amplitude a into a simplified relay characteristic description function to obtain:

according to the control theory, the conditions for generating limit ring oscillation by the closed-loop system are as follows:

1+N(A)G(jω)＝0

arg G(jω)＝-π

wherein, ω is 2 pi/T, and G (j ω) is a controlled object;

substituting the simplified relay characteristic description function into a closed loop system to generate a limit loop condition to obtain an estimated value of the frequency response at an oscillation frequency point:

in the formula, ω_u＝2π/T_u

Due to G (j omega)_u) Is zero, so that this frequency is the final frequency ω of the measurement process_uConsidering the measurement noise level, the process variable noise interference n is added to obtain the final critical gain:

utilizing a PID setting table to obtain the final critical gain K_uAnd a final critical period T_uSubstituting the PID setting table setting control parameter to obtain a PID control parameter K_p、T_i、T_dA value;

t₂and then, in a self-setting finishing stage, the PID control parameters based on the relay feedback are self-set and finished, the set control parameters are input to a standard PID controller to carry out a PID control process, and the output duty ratio D of a PWM signal is determined through a standard PID algorithm so as to realize the coil current closed-loop control of the PID control parameters under the condition of wide voltage input.

6. The adaptive suppression method for high-frequency holding noise of an electromagnetic switch according to claim 3, characterized in that: the pair of first switch tubes S₁Modulating to drive the coil at the circuitThe specific contents of switching control between the excitation state and the freewheeling state are as follows: a second switch tube S₄Always gives high level conduction to the first switch tube S₁Modulating at a set operating frequency, S₁When the transformer is conducted, the coil driving circuit is in an excitation state, and the coil voltage is positive left and negative right; s₁When the current-voltage-drop transformer is cut off, the coil driving circuit is in a follow current state, the voltage at two ends of the coil is zero by neglecting the voltage drop of the tube, and the coil driving circuit is switched and controlled between an excitation state and the follow current state.

Technical Field

The invention relates to the field of electromagnetic switch control, in particular to a self-adaptive suppression method for high-frequency holding noise of an electromagnetic switch.

Background

An electromagnetic switch is an electrical appliance which utilizes the electromagnetic force generated by electrifying a coil to control a load, and is widely applied to various industrial automatic control systems and civil electrical appliances. The conventional ac electromagnetic switch has two reasons for noise generation: firstly, a silicon steel sheet ferromagnetic material generates vibration caused by magnetostriction under the action of an alternating magnetic field; and secondly, when the alternating current electromagnetic attraction force borne by the armature is smaller than the closing position counter force, the periodic vibration of the armature is caused. The alternating current electromagnetic switch generally adopts a method of additionally mounting a sub-magnetic ring on an electromagnetic mechanism, so that the electromagnetic attraction force synthesized inside and outside the sub-magnetic ring is larger than the spring counter force to reduce the vibration between a moving iron core and a static iron core, and further reduce the noise. However, the alternating current electromagnetic switch still has the defects of narrow working voltage range, easy breakage of the sub-magnetic ring, large power consumption, difficulty in optimization control and the like. In order to achieve a good control effect, the direct current control of the electromagnetic switch is generally adopted at present, wherein the pulse width modulation control technology becomes one of the main control modes of the electromagnetic switch due to the advantages of mature control principle, flexible drive topology and the like.

The following schemes are mainly used for controlling the pulse width modulation of the electromagnetic switch based on feedback: firstly, the coil current is used as a feedback quantity, and the coil excitation voltage is controlled by dynamically adjusting the PWM duty ratio, so that the purpose of adjusting the coil current is achieved. And secondly, the average value of the coil voltage is used as a feedback quantity, the PWM duty ratio is also adjusted to adjust the coil excitation voltage, and then the closed-loop control is carried out on the effective value of the excitation voltage. And thirdly, the current loop is used as an inner loop, the displacement of the movable iron core of the electromagnetic switch is estimated in real time by adopting a displacement estimation technology, and the displacement is used as an outer loop feedback quantity to realize displacement closed-loop control. Compared with the control schemes, the control method of closed-loop regulation by taking the coil current as the feedback quantity directly influences the electromagnetic attraction, can quickly and directly regulate the excitation state of the electromagnetic system, and is convenient for optimization control. However, the electromagnetic switch under the current closed loop PWM control mode is influenced by high-frequency excitation voltage, and a new noise problem is generated in the holding process. Compared with the traditional electromagnetic switch excited in a power frequency alternating current mode, in the stable holding process of the electromagnetic switch excited by the high-frequency square wave, due to the strong inductive action of the electromagnetic mechanism, coil current spikes can be generated at the rising edge and the falling edge of the high-frequency square wave voltage under the influence of distributed capacitance of the coil, and the electromagnetic mechanism can generate more harsh high-frequency noise due to the ripple wave inherent to the coil current under the control of PWM. Meanwhile, the high-frequency coil voltage amplitude, the holding current magnitude and the switching tube operating frequency also affect the frequency spectrum distribution of the high-frequency holding noise. Therefore, it is necessary to effectively control the holding noise of the electromagnetic switch under high-frequency excitation control and wide-voltage range operation.

Disclosure of Invention

In view of the above, the present invention provides a self-adaptive suppression method for high-frequency holding noise of an electromagnetic switch, which aims at the problem of high-frequency holding noise caused by the operation of the electromagnetic switch in high-frequency square wave excitation control and a wide voltage range, and realizes energy-saving and silent operation of the holding process of the electromagnetic switch.

The invention is realized by adopting the following scheme: a self-adaptive suppression method for high-frequency holding noise of an electromagnetic switch comprises the following steps:

step S1: providing a coil driving circuit, operating a coil of an electromagnetic switch in the high-frequency excitation control mode driving circuit to switch and control the coil between an excitation state and a follow current state in a stable holding state, and applying negative pressure to the coil through energy stored in a capacitor in a holding stage in a breaking process to rapidly demagnetize;

step S2: PID control parameter K through relay feedback self-tuning technology_p、T_i、T_dAnd performing on-line self-setting, calculating an output duty ratio through a current monitoring loop switching mechanism, and fixing the output duty ratio so as to shift the frequency band of the generated high-frequency holding noise out of the range of the audible noise frequency band of the human ears.

Further, the coil driving circuit comprises a rectifying circuit, a capacitor C and a first switching tube S₁A second switch tube S₄A first fast recovery diode D₂A second fast recovery diode D₃Coil equivalent resistance R_coilAnd coil equivalent inductance L_coil(ii) a The coil equivalent resistance R_coilAnd coil equivalent inductance L_coilAre connected in series to form a coil; the input end of the rectification circuit is connected with an external AC/DC input control power supply, the AC/DC input control power supply obtains direct current after being rectified and filtered by the rectification circuit and the capacitor C, and the direct current passes through the rectification circuit and the capacitor CFirst switch tube S₁A second switch tube S₄Applying an excitation voltage to the coil R_coilAnd L_coilAre connected in series at two ends.

Further, the specific content of step S1 is: setting the first switch tube S₁And a second switching tube S₄The operating frequency is more than or equal to 18 kHz; when the first switch tube S₁And a second switching tube S₄When the coil is conducted, the coil driving circuit is in an excitation state, and the coil voltage is positive left and negative right; when the first switch tube S₁Cut-off, the second switching tube S₄When the transformer is conducted, the coil driving circuit is in a follow current state, the voltage drop of the tube is ignored, and the voltage at the two ends of the coil is zero; the second switch tube S is arranged at the stage from attraction to attraction of the electromagnetic switch₄Always gives high level conduction to the first switch tube S₁Modulating to make the coil driving circuit in the exciting state and the follow current state for switching control to obtain required coil starting current and holding current; in the breaking stage, the first switch tube S₁And a second switching tube S₄And meanwhile, the switch is switched to a demagnetization state, and because the voltage at two ends of the coil is negative, the current of the coil is rapidly reduced to zero, the electromagnetic attraction is reduced, and the rapid demagnetization and opening of the electromagnetic switch are realized.

Further, the step S2 specifically includes the following steps:

step S21: detecting coil current by current sensor, comparing with set reference current to generate error value, and sampling coil current i in real time by current monitoring loop switching mechanism_coilAnd setting the holding reference current i_refE (t) is monitored online; the current monitoring loop is described by the following formula:

step S22: judging whether the error e (t) exceeds the set threshold epsilon range, if the error e (t) exceeds the set threshold epsilon range, upgrading the current monitoring ring into a current closed ring, carrying out PID control parameter on-line self-setting through a relay feedback self-setting PID controller, and rapidly adjusting the coil currentUntil the reference current value is maintained; after the error e (t) is reduced to the range of the threshold value epsilon, the current closed loop is degenerated into a current monitoring loop, and the average value of the output duty ratio under the current working condition is automatically calculated in the current monitoring loop

And fixing the average value of duty ratio

Outputting the optimal duty ratio to a PWM generator to shift the frequency band of the generated high-frequency holding noise out of the range of the audible noise frequency band of the human ear;

where D represents the output duty cycle and N represents the number of cycles.

Further, the specific content of performing online self-tuning of the PID control parameter is as follows: the self-setting process is divided into two stages, wherein the first stage is a relay feedback self-setting adjusting process, and the second stage is a PID control process;

when the self-tuning PID control system is in constant amplitude oscillation, the relay output characteristic is that when the error e (t) is greater than 0, the relay amplitude d is output; when e (t) is less than 0, outputting relay amplitude-d, wherein the output mathematical expression of the relay characteristic is as follows:

in the formula: d is the output relay amplitude, e (t) is the error between the reference current value and the actual current value, i.e. e (t) ═ i_ref-i_coil；

t₀-t₁The time interval is the initial stage of signal input, the signal is input, when the self-tuning PID control system is disturbed, the | e (t) | is not equal to 0, and therefore the output i_coilDeviating from the original equilibrium state, then increasing the equivalent gain of the relay characteristic due to the reduction of | e (t) |, and i_coilIs presented in i_refNearby high frequency small amplitude oscillations;

t₁-t₂in the period of time, namely the steady state stage, when the self-tuning PID control system enters the steady state and is in periodic constant amplitude oscillation, the nonlinear link input signal e (T) is a sinusoidal signal, namely e (T) Asin (ω T), and at the moment, the constant amplitude oscillation periodic oscillation amplitude a of the self-tuning PID control system is measured and the critical period T is calculated_uThe nonlinear link relay output signal u (t) is a periodic square wave signal, and a Fourier series expression is as follows:

in the formula, A₀Is a direct current component; a. the_n、B_nThe fundamental and subharmonic component amplitudes, respectively, are described by the following equation:

the nonlinear relay description function is defined as that under the action of a sine input signal, the complex ratio of a first harmonic component in steady-state output of a nonlinear link and the input signal is a description function of the nonlinear link, and is expressed by N (A):

since most inertial systems can act as a low-pass filter, the fourier expression of the relay output obtained by ignoring higher harmonics is:

in the formula:

the simplified relay characteristic description function is:

and substituting the measured constant amplitude oscillation period oscillation amplitude a into a simplified relay characteristic description function to obtain:

according to the control theory, the conditions for generating limit ring oscillation by the closed-loop system are as follows:

1+N(A)G(jω)＝0

argG(jω)＝-π

wherein, ω is 2 pi/T, and G (j ω) is a controlled object;

substituting the simplified relay characteristic description function into a closed loop system to generate a limit loop condition to obtain an estimated value of the frequency response at an oscillation frequency point:

in the formula, ω_u＝2π/T_u

Due to G (j omega)_u) Is zero, so that this frequency is the final frequency ω of the measurement process_uConsidering the measurement noise level, the process variable noise interference n is added to obtain the final critical gain:

utilizing a PID setting table to obtain the final critical gain K_uAnd a final critical period T_uSubstituting the PID setting table setting control parameter to obtain a PID control parameter K_p、T_i、T_dA value;

t₂and then, in a self-setting finishing stage, the PID control parameters based on the relay feedback are self-set and finished, the set control parameters are input to a standard PID controller to carry out a PID control process, and the output duty ratio D of a PWM signal is determined through a standard PID algorithm so as to realize the coil current closed-loop control of the PID control parameters under the condition of wide voltage input.

Further, the pair of first switch tubes S₁The specific content of modulating and controlling the coil driving circuit to be switched between the excitation state and the follow current state is as follows: a second switch tube S₄Always gives high level conduction to the first switch tube S₁Modulating at a set operating frequency, S₁When the transformer is conducted, the coil driving circuit is in an excitation state, and the coil voltage is positive left and negative right; s₁When the current-voltage-drop transformer is cut off, the coil driving circuit is in a follow current state, the voltage at two ends of the coil is zero by neglecting the voltage drop of the tube, and the coil driving circuit is switched and controlled between an excitation state and the follow current state.

Compared with the prior art, the invention has the following beneficial effects:

(1) the control parameters of the traditional PID controller need to be manually set, certain experience is needed by engineering personnel, the set control parameters are not optimal, and the relay feedback self-setting PID controller automatically sets the control parameters without the parameter setting experience of the engineering personnel.

(2) The traditional PID controller does not change after setting the preset offline control parameters and cannot adapt to the time-varying operation state of the electromagnetic switch.

(3) The invention can move the audible noise frequency band out of the audible sound frequency band range of human ears by control strategy and algorithm, thus effectively inhibiting high-frequency holding noise and even soundless operation.

Drawings

Fig. 1 is a schematic diagram of an electromagnetic switch adaptive switching control method according to an embodiment of the present invention.

Fig. 2 is a diagram of a relay output corresponding to a signal input according to an embodiment of the present invention.

Detailed Description

The invention is further explained below with reference to the drawings and the embodiments.

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The embodiment provides a self-adaptive suppression method for high-frequency holding noise of an electromagnetic switch, which comprises the following steps:

step S1: providing a coil driving circuit, operating a coil of an electromagnetic switch in the high-frequency excitation control mode driving circuit to enable the coil to be switched and controlled between an excitation state and a follow current state in a stable holding state, and applying negative pressure to the coil through energy stored in a capacitor in an earlier holding stage in a breaking process to rapidly demagnetize;

step S2: PID control parameter K through relay feedback self-tuning technology_p、Ti、T_d(proportional coefficient, integral time constant and differential time constant) is self-tuned on line, the operating frequency of a switching tube is set to be 18kHz or above, the output duty ratio is calculated and fixed through a current monitoring ring switching mechanism, and the high-frequency holding noise frequency band is shifted out of the audible noise frequency band of human ears to be generatedSegment ranges. The specific operation is as follows:

the control parameters of the PID are subjected to online self-setting through a relay feedback self-setting technology, the error between the current of the real-time sampling coil and the set holding reference current is monitored online through a current monitoring ring switching mechanism, when the error exceeds the set threshold range, the current monitoring ring is upgraded into a current closed ring, the coil current is rapidly adjusted to a current reference value through a self-setting PID controller, after the error is reduced to the threshold range, the current closed ring is degraded into a current monitoring ring, the average value of the output duty ratio under the current working condition is automatically calculated at the moment, the average value is fixed to be the optimal duty ratio and is output to a PWM generator, and the frequency band generating the high-frequency holding noise is moved out of the range of the audible noise frequency band of a human ear.

As shown in fig. 1, in the present embodiment, the coil driving circuit includes a rectifying circuit, a capacitor C, and a first switch tube S₁A second switch tube S₄A first fast recovery diode D₂A second fast recovery diode D₃Coil equivalent resistance R_coilAnd coil equivalent inductance L_coil(ii) a The coil equivalent resistance R_coilAnd coil equivalent inductance L_coilAre connected in series to form a coil; the input end of the rectifying circuit is connected with an external AC/DC input control power supply, the AC/DC input control power supply obtains direct current after being rectified and filtered by the rectifying circuit and the capacitor C, and the direct current passes through a first switching tube S₁A second switch tube S₄Applying an excitation voltage to the coil R_coilAnd L_coilAre connected in series at two ends. Wherein C is a capacitor, U_CThe capacitor voltage is used, d is a set relay amplitude value, a coil is formed by connecting an equivalent resistor and an equivalent inductor in series, R_coilIs the coil equivalent resistance, L_coilIs a coil equivalent inductance, S₁、S₄To switch tubes, D₂、D₃For fast recovery diodes, i_coilFor real-time sampling of current values, i_refFor the reference current value, a is the amplitude of the stable constant amplitude oscillation generated by the system, T_uCritical period, K_uIs the critical gain, D is the output duty cycle,output duty cycle average, K_pIs a proportionality coefficient, T_iTo integrate the time constant, T_dThe differential time constant is used, n is an interference signal, N (a) is a relay description function, u (t) is a square wave signal output by a relay experiment, and e (t) is the deviation of a real-time sampling current value and a reference current value.

In this embodiment, the specific content of step S1 is: in the control strategy, the electromagnetic mechanism adopts a high-frequency excitation control mode drive circuit, AC/DC is input into a control power supply, relatively straight direct current is obtained after rectification and filtering, and excitation voltage is applied to a coil R through a modulation switch tube_coilAnd L_coilAre connected in series at two ends. Setting the first switch tube S₁And a second switching tube S₄The operating frequency is more than or equal to 18 kHz; when the first switch tube S₁And a second switching tube S₄When the coil is conducted, the coil driving circuit is in an excitation state, and the coil voltage is positive left and negative right; when the first switch tube S₁Cut-off, the second switching tube S₄When the transformer is conducted, the coil driving circuit is in a follow current state, the voltage drop of the tube is ignored, and the voltage at the two ends of the coil is zero; when switching tube S₁、S₄At the same time, when the coil is cut off, the coil current can not be reduced to zero immediately due to the inductance resistance characteristic of the coil, and the capacitor voltage U_CAnd the voltage is applied to two ends of the coil, the voltage at the two ends of the coil is positive right and negative left at the moment, the magnetic energy of the electromagnetic mechanism is rapidly absorbed, the current of the coil is rapidly reduced, and the coil driving topology is in a demagnetization state. In this embodiment, in order to reduce the ripple of the coil current and the micro-vibration of the coil winding, the second switch tube S is used during the period from the attraction stage to the attraction stage of the electromagnetic switch₄Always gives high level conduction to the first switch tube S₁Modulating to make the coil driving circuit in the exciting state and the follow current state for switching control to obtain required coil starting current and holding current; in the breaking stage, the magnetic energy of the coil is directly related to the holding current, the larger the holding current is, the larger the magnetic energy of the coil is, and the breaking time is prolonged, so that in the breaking stage, the first switching tube S is₁And a second switching tube S₄At the same time, the coil is cut off and switched to a demagnetizing state, and because the voltage at two ends of the coil is negative, the coilThe current is rapidly reduced to zero, the electromagnetic attraction is reduced, and the rapid demagnetization and brake opening of the electromagnetic switch are realized.

In this embodiment, the step S2 specifically includes the following steps:

step S21: detecting coil current by current sensor, comparing with set reference current to generate error value, and sampling coil current i in real time by current monitoring loop switching mechanism_coilAnd setting the holding reference current i_refE (t) is monitored online; the current monitoring loop is described by the following formula:

step S22: judging whether the error e (t) exceeds a set threshold value epsilon range (the threshold value epsilon is 0.02-0.04), if the error e (t) exceeds the set threshold value epsilon range, upgrading a current monitoring ring into a current closed ring, performing PID control parameter on-line self-setting through a relay feedback self-setting PID controller, and quickly adjusting the coil current to a reference current value; after the error e (t) is reduced to the range of the threshold value epsilon, the current closed loop is degenerated into a current monitoring loop, and the average value of the output duty ratio under the current working condition is automatically calculated in the current monitoring loop

And fixing the average value of duty ratio

Outputting the optimal duty ratio to a PWM generator to shift the frequency band of the generated high-frequency holding noise out of the range of the audible noise frequency band of the human ear;

where D represents the output duty cycle and N represents the number of cycles.

In the embodiment, on the basis of a control algorithm, under the condition that an electromagnetic switch is stably held, a coil driving circuit is in switching control between an excitation state and a follow current state, a coil current is detected by a current sensor and compared with a holding reference current to generate an error value, the error value is sent to a relay feedback self-setting PID controller to perform PID control parameter online self-setting, the self-setting process is divided into two stages, the first stage is a relay feedback self-setting adjusting process, and the second stage is a PID control process.

As shown in fig. 2, when the self-tuning PID control system is in constant amplitude oscillation, the relay output characteristic is that when the error e (t) >0, the relay amplitude d is output; when e (t) is less than 0, outputting relay amplitude-d, wherein the output mathematical expression of the relay characteristic is as follows:

in the formula: d is the output relay amplitude, e (t) is the error between the reference current value and the actual current value, i.e. e (t) ═ i_ref-i_coil；

t₀-t₁The time interval is the initial stage of signal input, the signal input is known by the equivalent gain of the relay characteristic, and when the self-tuning PID control system is disturbed, the | e (t) | is not equal to 0, so that the output i_co_ilDeviating from the original balance state, then increasing the equivalent gain of the relay characteristic due to the reduction of | e (t) |, and in the process of trying to return the output to the original balance state, i is a certain switching speed of the relay characteristic in the actual system_coilIs presented in i_refNearby high frequency small amplitude oscillations;

t₁-t₂in the period of time, namely the steady state stage, when the self-tuning PID control system enters the steady state and is in periodic constant amplitude oscillation, the nonlinear link input signal e (T) is a sinusoidal signal, namely e (T) Asin (ω T), and at the moment, the constant amplitude oscillation periodic oscillation amplitude a of the self-tuning PID control system is measured and the critical period T is calculated_uThe nonlinear link relay output signal u (t) is a periodic square wave signal, and a Fourier series expression is as follows:

in the formula (I), the compound is shown in the specification,A₀is a direct current component; a. the_n、B_nThe fundamental and subharmonic component amplitudes, respectively, are described by the following equation:

the relay characteristic often causes the system to generate oscillation phenomenon, so the nonlinear system is analyzed by using a descriptive function method. The nonlinear relay description function is defined as that under the action of a sine input signal, the complex ratio of a first harmonic component in steady-state output of a nonlinear link and the input signal is a description function of the nonlinear link, and is expressed by N (A):

since most inertial systems can act as a low-pass filter, the fourier expression of the relay output obtained by ignoring higher harmonics is:

in the formula:

the simplified relay characteristic description function is:

and substituting the measured constant amplitude oscillation period oscillation amplitude a into a simplified relay characteristic description function to obtain:

according to the control theory, the conditions for generating limit ring oscillation by the closed-loop system are as follows:

1+N(A)G(jω)＝0

argG(jω)＝-π

wherein, ω is 2 pi/T, and G (j ω) is a controlled object;

substituting the simplified relay characteristic description function into a closed loop system to generate a limit loop condition to obtain an estimated value of the frequency response at an oscillation frequency point:

in the formula, ω_u＝2π/T_u

Due to G (j omega)_u) Is zero, so that this frequency is the final frequency ω of the measurement process_uConsidering the measurement noise level, the process variable noise interference n is added to obtain the final critical gain:

utilizing the PID tuning table of Table 1 to obtain the final critical gain K_uAnd a final critical period T_uSubstituting the PID setting table setting control parameter to obtain a PID control parameter K_p、T_i、T_dA value;

TABLE 1 PID tuning Table

t₂Then, namely, in the self-setting completion stage, the PID control parameters based on the relay feedback are self-set and completed, and the setting is carried outAnd the good control parameters are input to a standard PID controller to carry out a PID control process, and the output duty ratio D of the PWM signal is determined by a standard PID algorithm so as to realize the coil current closed-loop control of the PID control parameters under the condition of wide voltage input.

In this embodiment, the pair of first switch tubes S₁The specific content of modulating and controlling the coil driving circuit to be switched between the excitation state and the follow current state is as follows: a second switch tube S₄Always gives high level conduction to the first switch tube S₁Modulating at a set operating frequency, S₁When the transformer is conducted, the coil driving circuit is in an excitation state, and the coil voltage is positive left and negative right; s₁When the current-voltage-drop transformer is cut off, the coil driving circuit is in a follow current state, the voltage at two ends of the coil is zero by neglecting the voltage drop of the tube, and the coil driving circuit is switched and controlled between an excitation state and the follow current state.

The current monitoring loop is described by the following formula:

the current monitoring ring switching mechanism is expressed as that the error between the coil real-time sampling current and the holding reference current is monitored on line, when the absolute value of the coil current error exceeds a set threshold epsilon, the current monitoring ring is upgraded into a current closed ring, PID control of control parameter on-line self-setting is carried out, and the coil current is quickly adjusted to the reference current value; when the absolute value of the current error of the regulated coil is within the set threshold range, the current closed loop retreats to the current monitoring loop, and the average value of the duty ratio under the current working condition is automatically calculated

And fixing the average value as the optimal duty ratio and outputting the optimal duty ratio to a PWM generator, and combining the control strategy provided by the previous step, wherein the original audible high-frequency holding noise frequency band is shifted out of the range of the audible noise frequency band of human ears, thereby showing the silent operation effect to the outside.

Preferably, in the embodiment, aiming at the problem of high-frequency holding noise of the electromagnetic switch under the closed-loop control of wide-voltage input current, in a control strategy, the operating frequency of the switching tube is set to be 18kHz or more, the electromagnetic switch is switched and controlled between an excitation state and a follow current state in a stable holding state, and the coil is subjected to negative pressure and rapid demagnetization through energy stored in a capacitor in an early holding stage in a breaking process; in the control algorithm, online self-setting is carried out on control parameters of PID through a relay feedback self-setting technology, online monitoring is carried out on errors of real-time sampling coil current and set and maintained reference current through a designed current monitoring ring switching mechanism, when the errors exceed a set threshold range, the current monitoring ring is upgraded into a current closed loop, the coil current is rapidly adjusted to a current reference value through a self-setting PID controller, after the errors are reduced to the threshold range, the current closed loop is degraded into a current monitoring ring, at the moment, an average value of output duty ratios under the current working condition is automatically calculated and fixed to be an optimal duty ratio to be output to a PWM generator, the frequency band generating high-frequency holding noise is shifted out of the range of the audible noise frequency band of a human ear, and the self-adaptive switching control process is repeated. Finally, the control effect of the electromagnetic switch on energy-saving and silent operation in a wide voltage range is realized.

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.