Electronic control method of a flow proportional valve of a fluid delivery circuit

Abstract

The present application belongs to the technical field of fluid delivery control, and particularly relates to an electronic control method for a flow proportional valve of a fluid delivery pipeline, comprising: collecting multi-source sensor monitoring data including flow, pressure, coil voltage and coil current, and obtaining pretreated monitoring data after smoothing processing; obtaining a fluid resistance response coefficient based on the pressure monitoring value and the flow monitoring value in the pretreated monitoring data; obtaining a heating loss correction amount based on the coil voltage monitoring value and the coil current monitoring value; dynamically obtaining a duty cycle of a control signal of the flow proportional valve in combination with a flow target value, a flow monitoring value, the fluid resistance response coefficient and the heating loss correction amount; generating a pulse voltage based on the duty cycle of the control signal and driving the flow proportional valve to correct the displacement amount of a valve core of the flow proportional valve under a complex pressure and thermal environment. The present application solves the problem of control inaccuracy caused by pressure fluctuation and thermal attenuation of an actuator.

Description

Technical Field

[0001] This invention relates to the field of fluid transport control technology. More specifically, this invention relates to an electronic control method for a flow proportional valve in a fluid transport pipeline. Background Technology

[0002] In the power system of heavy-duty diesel engines, the operating status of fluid delivery pipelines directly determines the accuracy of fuel and various functional fluid distribution, which plays a decisive role in improving engine combustion efficiency and emission performance. Currently, in the field of fluid delivery pipeline control, the control model based on standard proportional-integral-derivative logic is commonly used. The operation of this model is based on real-time acquisition of flow monitoring values ​​and comparison with preset flow target values, and the action of the actuator is adjusted according to the magnitude of the linear deviation between the two.

[0003] However, in actual engineering applications, the severe mechanical vibrations and complex electromagnetic fields generated by heavy-duty diesel engines can significantly interfere with the original signals output by sensors, resulting in a large amount of high-frequency noise coupled into the signals. If these fluctuating signals are directly used for calculation, it will cause the actuator to frequently produce small reciprocating vibrations. After long-term operation, this will lead to severe mechanical fatigue of the internal components of the flow proportional valve. In addition, the fluid pressure distribution inside the fluid delivery pipeline is not constant. Under different load conditions, the pressure monitoring values ​​inside the pipeline will exhibit a strong non-proportional change characteristic, and the viscosity of the fluid will also have a significant hysteresis effect with temperature fluctuations. This causes a deviation between the response capability of the flow proportional valve and the actual requirements.

[0004] Traditional control logic often overlooks the constraint effect of uneven pressure distribution on flow regulation. When there is a sudden and drastic fluctuation in the internal pressure of the pipeline, the adjustment amount of the control system often cannot keep up with the rate of pressure change in time, resulting in obvious overshoot or continuous oscillation of the flow proportional valve during the regulation process. At the same time, the power source of the flow proportional valve comes from the internal electromagnetic coil. During long-term continuous regulation tasks, the current passing through the wire will generate heat accumulation, and the resistance value of the coil will drift with the increase of temperature. This directly weakens the magnetic force that the coil can generate under the same control signal, resulting in a slower valve core movement speed and inaccurate position control of the flow proportional valve.

[0005] Existing linear compensation technology is insufficient to fully cover the dynamic characteristics evolution caused by heat accumulation, resulting in insufficient control accuracy and operational stability of fluid transport pipelines under complex working conditions. In particular, under the intertwined influence of pressure transients and coil thermal state changes, flow control failure or regulation failure is likely to occur. Summary of the Invention

[0006] To address the technical problems of inaccurate flow control and unstable dynamic response in fluid delivery pipelines under complex pressure conditions and actuator thermal accumulation effects, this invention provides an electronic control method for a flow proportional valve in a fluid delivery pipeline. The method includes: acquiring and smoothing multi-source sensor monitoring data; acquiring pre-processed monitoring data, including flow monitoring values, pressure monitoring values, coil voltage monitoring values, and coil current monitoring values; obtaining a fluid resistance response coefficient based on the pressure and flow monitoring values ​​in the pre-processed monitoring data; obtaining a heat loss correction amount based on the coil voltage and coil current monitoring values ​​in the pre-processed monitoring data; obtaining a control signal duty cycle based on the target flow value, flow monitoring values, fluid resistance response coefficient, and heat loss correction amount; and generating a pulse voltage based on the control signal duty cycle and applying it to the flow proportional valve to achieve electronic control of the flow proportional valve in the fluid delivery pipeline.

[0007] This invention acquires and smooths multi-source sensor monitoring data including flow rate, pressure, coil voltage, and coil current, and combines the fluid resistance response coefficient and heat loss correction to dynamically obtain the duty cycle of the control signal, thereby generating a pulse voltage to drive the flow proportional valve. This reduces the flow control inaccuracy that occurs in the fluid delivery pipeline of heavy-duty diesel engines under complex pressure conditions and the combined effects of coil thermal attenuation.

[0008] Preferably, the smoothing process to obtain preprocessed monitoring data includes: using a filter to denoise the flow monitoring values ​​and pressure monitoring values, and using a preset cutoff frequency to filter out characteristic noise.

[0009] This invention uses a filter to denoise the flow and pressure monitoring values. It uses a preset cutoff frequency to filter out characteristic noise of a specific frequency to obtain pre-processed monitoring data, thereby reducing the frequent reciprocating jitter of the flow proportional valve actuator caused by high-frequency noise in the original sensor signal and the resulting mechanical fatigue of internal components.

[0010] Preferably, the fluid resistance response coefficient satisfies the expression: In the formula, express The fluid resistance response coefficient at time t. express Pressure monitoring values ​​at any time express Traffic flow monitoring values ​​at any given time This represents the resistance adjustment constant. Represents the gradient operator. The norm operator is used to represent the norm. Represents the differential symbol. Represents the absolute value symbol.

[0011] This invention obtains the fluid resistance response coefficient by using the gradient operator norm of the pressure monitoring value and the differential absolute value of the flow monitoring value, and evaluates the coupling effect of the spatial distribution and time change of fluid pressure on the flow resistance, thereby reducing the decrease in the flow proportional valve regulation efficiency or system oscillation caused by uneven pressure distribution inside the fluid delivery pipeline.

[0012] Preferably, the resistance adjustment constant is obtained by: conducting a steady flow test on the fluid transport pipeline, collecting flow deviation observations under different pressure gradients, performing third-order polynomial regression fitting using the least squares method to obtain a function curve reflecting the relationship between pressure gradient and flow deviation, and using the first derivative of this function curve at the rated operating point as the resistance adjustment constant.

[0013] This invention utilizes constant flow rate experiments and fitting methods to determine the slope of the correlation between pressure changes and flow fluctuations to obtain the resistance adjustment constant. This enables the fluid resistance response coefficient to accurately reflect the physical characteristics of a specific fluid transport pipeline under hardware conditions, thereby improving the system's adaptability when evaluating the contribution ratio of pressure fluctuations.

[0014] Preferably, the heat loss correction amount satisfies the expression: In the formula, express The amount of heat loss correction at any given time; express The coil voltage monitoring value at that moment; express The coil current monitoring value at any given time; Indicates the energy-affected parameter; This represents the integral variable.

[0015] This invention obtains the heat loss correction by integrating the product of the coil voltage monitoring value and the coil current monitoring value over time, assesses the electromagnetic characteristic drift caused by the continuous conversion of electrical energy into heat energy, and reduces the response lag of the flow proportional valve caused by the change in resistance value due to the increase in coil temperature during continuous regulation.

[0016] Preferably, the energy influence parameter is obtained by applying a continuous load to the flow proportional valve under constant ambient temperature, monitoring the relationship between temperature rise and electromagnetic force attenuation, fitting the correlation between energy input and response deviation using the least squares method, and using the fitted proportional constant as the energy influence parameter.

[0017] This invention obtains energy influence parameters by monitoring the correspondence between load and electromagnetic force attenuation under constant ambient temperature, and uses the least squares method to fit the correlation between energy input and response deviation, thereby improving the evaluation accuracy of heat loss correction in describing the influence of heat accumulation on electromagnetic induction intensity.

[0018] Preferably, the duty cycle of the control signal satisfies the expression: In the formula, express The duty cycle of the control signal at any given time. express The target flow rate at any given time. express Traffic flow monitoring values ​​at any given time express The fluid resistance response coefficient at time t. express Correction amount for heat loss at any given time. This represents the comprehensive control coefficient. Represents the symbol for the exponential function. The square root symbol is used to represent the square root.

[0019] This invention combines the results of the exponential function of flow deviation, fluid resistance response coefficient, and heat loss correction to calculate the control signal duty cycle by taking the square root. This achieves dynamic compensation for fluid-side resistance fluctuations and actuator-side heat drift, thereby enhancing the control stability of the fluid delivery pipeline system under complex operating conditions.

[0020] Preferably, the method for obtaining the comprehensive control coefficient is as follows: under standard operating conditions, response data under different flow gradients are collected, the stability gain of the system is calculated using a state estimation algorithm, and the extracted gain value is used as the comprehensive control coefficient.

[0021] This invention utilizes a state estimation algorithm to calculate the system's stable gain under different flow gradients to obtain the comprehensive control coefficient, effectively converting composite physical characteristics into corresponding electrical signal proportions, thereby improving the response consistency of the flow proportional valve electronic control system under standard and variable operating conditions.

[0022] Preferably, the step of generating a pulse voltage based on the duty cycle of the control signal and applying it to the flow proportional valve includes: the electronic control unit controlling the pulse width modulation drive module to generate a pulse voltage based on the duty cycle of the control signal according to the duty cycle of the control signal.

[0023] This invention uses an electronic control unit to control a pulse width modulation drive module to generate pulse voltage based on the duty cycle of the control signal. This precisely converts the control logic into a physical drive signal, reducing the displacement deviation of the flow proportional valve core in fluid delivery pipelines due to insufficient driving force under complex pressure and heating environments.

[0024] Preferably, generating a pulse voltage and applying it to the flow proportional valve includes: using the pulse voltage to adjust the current inside the coil to correct the displacement of the valve core of the flow proportional valve under pressure and heating conditions.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention introduces a fluid resistance response coefficient and a heat loss correction factor to achieve simultaneous evaluation and composite compensation of fluid pressure transients and actuator heat accumulation effects, thereby reducing the technical problem of inaccurate flow regulation in fluid delivery pipelines under complex operating environments.

[0027] This invention utilizes filters to smooth multi-source sensor data and filter out specific characteristic noise, reducing hardware fatigue caused by signal fluctuations due to mechanical vibration and electromagnetic interference from heavy-duty diesel engines on the flow proportional valve, and extending the service life of the actuator.

[0028] This invention obtains various correction parameters and control coefficients by fitting experimental data and state estimation algorithms, and transforms the flow target deviation and multi-field coupling physical characteristics into precise pulse voltage signals, thereby reducing the overshoot and oscillation phenomena that occur in the flow proportional valve during the adjustment process and improving the dynamic response stability of the system. Attached Figure Description

[0029] Figure 1 This schematically illustrates a flowchart of an electronic control method for a flow proportional valve in a fluid delivery pipeline according to the present invention.

[0030] Figure 2 A schematic diagram illustrating the fluid resistance response characteristics is shown.

[0031] Figure 3 A schematic diagram illustrating the heat loss correction characteristics is shown.

[0032] Figure 4 This diagram illustrates the effect of traffic target tracking. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0035] This invention discloses an electronic control method for a flow proportional valve in a fluid delivery pipeline, referring to... Figure 1 This includes steps S1 to S5:

[0036] S1. Acquire multi-source sensor monitoring data and perform smoothing processing. The pre-processed monitoring data includes flow monitoring value, pressure monitoring value, coil voltage monitoring value and coil current monitoring value.

[0037] It should be noted that due to the severe mechanical vibrations and electromagnetic interference generated by heavy-duty diesel engines during operation, the raw signals output by sensors installed on fluid delivery pipelines often contain a large amount of random noise. Directly using these noisy signals for control calculations would lead to frequent fluctuations in the output control commands, thereby causing hardware fatigue in the flow proportional valve. To eliminate interference from non-operating conditions, this invention requires smoothing the monitoring data from multiple sensors to provide a clean data foundation for subsequent calculations.

[0038] Specifically, the present invention utilizes flow sensors, pressure sensors, and voltage and current monitoring modules installed on fluid delivery pipelines to collect multi-source sensor monitoring data in real time; the multi-source sensor monitoring data includes flow monitoring values, pressure monitoring values, coil voltage monitoring values, and coil current monitoring values; the present invention also combines the flow target value issued by the electronic control unit.

[0039] Furthermore, the present invention employs a filter to denoise the flow monitoring values ​​and pressure monitoring values, using a preset cutoff frequency to filter out characteristic noise of a specific frequency, and outputs pre-processed monitoring data.

[0040] S2. Obtain the fluid resistance response coefficient based on the pressure and flow monitoring values ​​in the preprocessed monitoring data.

[0041] It should be noted that the flow response within a fluid delivery pipeline depends not only on the opening degree of the proportional flow valve but also on the spatial distribution of fluid pressure. Traditional control methods neglect the impact of pressure changes on the regulating efficiency of the proportional flow valve, resulting in insufficient control accuracy under unstable pressure conditions. Therefore, this invention proposes a fluid resistance response coefficient, which assesses the influence of fluid resistance on the flow response by introducing pressure gradient changes.

[0042] Specifically, the present invention calculates the fluid resistance response coefficient inside the fluid delivery pipeline based on the pressure monitoring value and flow monitoring value in the preprocessed monitoring data.

[0043] The fluid resistance response coefficient satisfies the following expression:

[0044]

[0045] In the formula, express The fluid resistance response coefficient at time t; express Pressure monitoring values ​​at any given time; express Traffic flow monitoring values ​​at any given time; This represents the resistance adjustment constant; Represents the gradient operator; Norm operator; Represents the differential symbol; Represents the absolute value symbol.

[0046] In the formula, when the pressure monitoring value Drastic changes in the pipeline space can cause the gradient term in the formula to increase in value; simultaneously, if the flow monitoring value... An increased rate of change over time will cause the value within the parentheses to rise; the combined effect of these two factors will affect the overall fluid resistance response coefficient. The value shows an increasing trend. The larger the value, the stronger the fluctuation in fluid resistance inside the fluid delivery pipeline, and the more the system needs to improve its perception of the current environment.

[0047] It should be further added that the resistance adjustment constant in this invention is used to determine the contribution ratio of pressure change to flow response. The resistance adjustment constant is obtained by conducting a steady flow test on the fluid delivery pipeline, collecting flow deviation observations under different pressure gradients, and using the least squares method to perform third-order polynomial regression fitting to obtain a function curve reflecting the relationship between pressure gradient and flow deviation. The first derivative of this function curve at the rated operating point is used as the resistance adjustment constant.

[0048] For example, Figure 2 This is a schematic diagram of fluid resistance response characteristics, showing the changes in the monitored pressure value and fluid resistance response coefficient within the fluid delivery pipeline over time. When the monitored pressure value experiences a sharp, pulsating fluctuation within a four- to five-second timeframe, the fluid resistance response coefficient rapidly increases, demonstrating the system's high sensitivity to changes in the external fluid resistance environment, thus providing a data foundation for subsequent control compensation.

[0049] S3. Obtain the heat loss correction amount based on the coil voltage monitoring value and coil current monitoring value in the preprocessed monitoring data.

[0050] It should be noted that the actuator of the flow proportional valve is driven by an electromagnetic coil. During continuous adjustment, the heat generated by the coil causes its resistance value to drift, thereby altering the magnetic output characteristics. Traditional control strategies cannot compensate for this response lag caused by heat accumulation. Therefore, this invention evaluates the degree of change in the electromagnetic characteristics of the flow proportional valve by calculating the cumulative effect of energy consumption.

[0051] Specifically, the present invention utilizes the coil voltage monitoring value and coil current monitoring value in the preprocessed monitoring data to obtain the heat loss correction amount of the flow proportional valve in real time.

[0052] The heat loss correction satisfies the following expression:

[0053]

[0054] In the formula, express The amount of heat loss correction at any given time; express The coil voltage monitoring value at that moment; express The coil current monitoring value at any given time; Indicates the energy-affected parameter; This represents the integral variable.

[0055] In the formula, when the coil voltage monitoring value With coil current monitoring value As the product of these terms accumulates over time, it indicates that the electrical energy consumed by the flow proportional valve is continuously converted into heat energy. This causes the integral term to increase continuously, resulting in an overall correction for heat loss. It exhibits a monotonically increasing trend. The larger this value, the more severe the internal heating of the flow proportional valve, and the more significant the decrease in execution efficiency.

[0056] It should be further noted that the energy influence parameter in this invention is used to describe the proportional effect of heat accumulation on the electromagnetic induction intensity. The energy influence parameter is obtained as follows: under constant ambient temperature, a continuous load is applied to the flow proportional valve, the relationship between temperature rise and electromagnetic force attenuation is monitored, and the correlation between energy input and response deviation is fitted using the least squares method. The fitted proportionality constant is then used as the energy influence parameter.

[0057] For example, Figure 3 This is a schematic diagram of the heat loss correction characteristics. The diagram shows the changing trend of the heat loss correction and the duty cycle of the control signal during continuous operation of the flow proportional valve. As time goes on, the energy consumption of the coil accumulates, causing the heat loss correction to show a monotonically increasing trend. Based on this, the system dynamically adjusts the duty cycle of the control signal, and compensates for the attenuation of electromagnetic force caused by coil heating by increasing the proportion of the drive current.

[0058] S4. Obtain the control signal duty cycle based on the target flow value, the monitored flow value, the fluid resistance response coefficient, and the heat loss correction.

[0059] It should be noted that the control command ultimately applied to the flow proportional valve must simultaneously consider the resistance fluctuations on the fluid side and the heat drift on the actuator side. If simple linear superposition is used for compensation, control inaccuracies can easily occur under complex operating conditions. Therefore, this invention proposes a method for obtaining the control signal duty cycle, which involves a composite calculation of the fluid resistance response coefficient and the heat loss correction amount.

[0060] Specifically, the present invention combines the target flow rate, the flow rate monitoring value in the preprocessed monitoring data, the fluid resistance response coefficient, and the heat loss correction amount to generate the final control signal duty cycle of the flow proportional valve.

[0061] The duty cycle of the control signal satisfies the expression:

[0062]

[0063] In the formula, express Duty cycle of the control signal at any given time; express The target flow rate at any given time; express Traffic flow monitoring values ​​at any given time; express The fluid resistance response coefficient at time t; express The amount of heat loss correction at any given time; Indicates the comprehensive control coefficient; Indicates the symbol for the exponential function; The square root symbol is used to represent the square root.

[0064] In the formula, when the target flow value With flow monitoring values When the deviation between them increases, it directly leads to a larger calculated value; at the same time, due to the correction amount for heat loss... The fluid resistance response coefficient is affected by the exponential term. This causes the value within the square root to increase due to the compensation effect when the coil heats up severely. These factors collectively influence the duty cycle of the control signal. The trend is increasing. The larger this value, the stronger the regulation force applied by the system to the flow proportional valve, thereby overcoming the dual effects of resistance and heat generation.

[0065] It should be further noted that the integrated control coefficient in this invention is used to convert composite physical characteristic quantities into corresponding electrical signal ratios. The integrated control coefficient is obtained as follows: response data under different flow gradients are collected under standard operating conditions; the stability gain of the system is calculated using a state estimation algorithm; and the extracted gain value is used as the integrated control coefficient.

[0066] For example, Figure 4 This is a schematic diagram illustrating the flow target tracking effect, showing the real-time tracking of the flow monitoring value to the flow target value under the multi-field coupling correction. Despite the significant pressure fluctuations and continuous heat accumulation effects experienced by the system, the flow monitoring value was still able to smoothly and accurately lock onto the flow target value, without any obvious overshoot or violent oscillations during the step response and steady-state maintenance.

[0067] S5. A pulse voltage is generated based on the duty cycle of the control signal and applied to the flow proportional valve to realize the flow proportional valve of the electronically controlled fluid delivery pipeline.

[0068] It should be noted that the calculated control signal duty cycle needs to be converted into a specific physical action through the underlying circuitry. Because the valve core of the proportional flow valve exhibits friction, directly outputting the original calculated value may not overcome the movement obstacles caused by static friction. This step is responsible for converting the control signal duty cycle into an adjustable pulse signal to drive the proportional flow valve to perform its action.

[0069] Specifically, the electronic control unit controls the pulse width modulation drive module to generate a pulse voltage based on the calculated duty cycle of the control signal, according to the calculated duty cycle of the control signal.

[0070] Furthermore, the present invention generates a pulse voltage and applies it to the electromagnetic coil of the flow proportional valve, adjusts the current inside the coil, thereby correcting the displacement of the valve core of the flow proportional valve under complex pressure and heating environments, and ultimately achieves accurate tracking of the target flow value in the fluid delivery pipeline.

Claims

1. An electronic control method for a flow proportional valve in a fluid delivery pipeline, characterized in that, include: Acquire multi-source sensor monitoring data and perform smoothing processing to obtain pre-processed monitoring data. The multi-source sensor monitoring data includes flow monitoring values, pressure monitoring values, coil voltage monitoring values, and coil current monitoring values. The fluid resistance response coefficient is obtained based on the pressure and flow monitoring values ​​from the preprocessed monitoring data. In the formula, express The fluid resistance response coefficient at time t. express Pressure monitoring values ​​at any time express Traffic flow monitoring values ​​at any given time This represents the resistance adjustment constant. Represents the gradient operator. The norm operator is used to represent the norm. Represents the differential symbol. Indicates the absolute value symbol; The heat loss correction amount is obtained based on the coil voltage and coil current monitoring values ​​in the preprocessed monitoring data. In the formula, express The amount of heat loss correction at any given time; express The coil voltage monitoring value at that moment; express The coil current monitoring value at any given time; Indicates the energy-affected parameter; Represents the integral variable; The duty cycle of the control signal is obtained based on the target flow rate, the monitored flow rate, the fluid resistance response coefficient, and the heat loss correction. ; In the formula, express The duty cycle of the control signal at any given time. express The target flow rate at any given time. This represents the comprehensive control coefficient. Represents the symbol for the exponential function. Represents the square root symbol; A pulse voltage is generated based on the duty cycle of the control signal and applied to the flow proportional valve to realize the flow proportional valve of the electronically controlled fluid delivery pipeline.

2. The method for electronic control of a flow proportional valve in a fluid transport pipeline according to claim 1, characterized in that, The smoothing process, which obtains preprocessed monitoring data, includes: A filter is used to denoise the flow and pressure monitoring values, and the characteristic noise is filtered out using a preset cutoff frequency.

3. The method for electronic control of a flow proportional valve in a fluid transport pipeline according to claim 1, characterized in that, The method for obtaining the resistance adjustment constant is as follows: A steady flow test was conducted on the fluid transport pipeline, and the flow deviation was observed under different pressure gradients. The least squares method was used to perform third-order polynomial regression fitting to obtain a function curve reflecting the relationship between pressure gradient and flow deviation. The first derivative of this function curve at the rated operating point was used as the resistance adjustment constant.

4. The method for electronic control of a flow proportional valve in a fluid transport pipeline according to claim 1, characterized in that, The energy influence parameters are obtained as follows: At a constant ambient temperature, a continuous load is applied to the flow proportional valve, and the relationship between temperature rise and electromagnetic force decay is monitored. The correlation between energy input and response deviation is fitted using the least squares method, and the fitted proportional constant is used as the energy influence parameter.

5. The method for electronic control of a flow proportional valve in a fluid transport pipeline according to claim 1, characterized in that, The method for obtaining the comprehensive control coefficient is as follows: Response data under different flow gradients are collected under standard operating conditions. The stability gain of the system is calculated using a state estimation algorithm, and the extracted gain value is used as the comprehensive control coefficient.

6. The method for electronic control of a flow proportional valve in a fluid transport pipeline according to claim 1, characterized in that, The step of generating a pulse voltage based on the duty cycle of a control signal and applying it to the flow proportional valve includes: The electronic control unit controls the pulse width modulation drive module to generate pulse voltages based on the duty cycle of the control signal, according to the duty cycle of the control signal.

7. The method for electronic control of a flow proportional valve in a fluid transport pipeline according to claim 6, characterized in that, The generation of pulse voltage and its application to the flow proportional valve includes: The displacement of the valve core of the flow proportional valve under pressure and heat environments is corrected by adjusting the current inside the coil using pulse voltage.

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