An electromagnetic pump flow control method based on double duty cycle and current feedback compensation

Abstract

The application discloses a kind of electromagnetic pump flow control methods based on double duty ratio and current feedback compensation, it is related to flow control field, the electromagnetic pump flow control method based on double duty ratio and current feedback compensation includes: step S1, generates double duty ratio pulse width modulation signal, wherein first level PWM signal defines electromagnetic pump's macroscopic on-off timing to adjust the number of times of work per unit time, the beneficial effects of the present application are: the present application generates double duty ratio PWM signal, to first level coarse adjustment unit time work frequency and according to interval distribution on half wave, inhibit the low-frequency flow pulsation of traditional zero-crossing power regulation;By real-time acquisition coil current and closed-loop correction second level PWM duty cycle, effectively compensate the flow drift caused by coil temperature rise and voltage fluctuation;By querying nonlinear correction lookup table to obtain the optimized combination of first and second duty cycles, overcome the low-duty-cycle driving dead zone and high-duty-cycle magnetic circuit saturation nonlinearity.

Description

Technical Field

[0001] This invention relates to the field of flow control, specifically to an electromagnetic pump flow control method based on dual duty cycles and current feedback compensation. Background Technology

[0002] Electromagnetic pumps (especially plunger-type electromagnetic pumps) are widely used in coffee machines, water dispensers, steam mops, and automatic detergent dispensing systems due to their simple structure, low cost, and long lifespan. The flow control accuracy of electromagnetic pumps directly affects the performance of end products—such as the extraction flavor of coffee machines and the detergent dispensing accuracy of home appliances.

[0003] In the existing technology, electromagnetic pump flow control mainly suffers from the following technical defects: 1. Open-loop PWM control suffers from flow drift issues. Most electromagnetic pumps employ open-loop PWM frequency modulation control. However, electromagnetic pumps are strongly coupled nonlinear systems, and their flow rate is affected by multiple factors such as coil temperature, supply voltage fluctuations, and back voltage changes. Experiments show that after 5 minutes of continuous operation, the coil temperature rises by 40-60°C, the coil resistance increases by 15-25%, and under the same duty cycle, the electromagnetic force decreases, resulting in a flow rate reduction of over 20%. Existing solutions lack effective online compensation mechanisms.

[0004] 2. Single-stage PWM modulation exhibits poor linearity in the low-flow region. In a single-stage PWM control scheme, when the duty cycle is below 20%, the electromagnetic force is insufficient to overcome the spring preload, and the plunger cannot fully engage, resulting in a "creeping" or "jittering" state, and the flow rate exhibits severe nonlinearity with the duty cycle. When the duty cycle is above 80%, the magnetic circuit tends to saturate, and the flow regulation sensitivity decreases. The effective linear regulation range is narrow, which cannot meet the requirements for wide-range precise distribution.

[0005] 3. The zero-adjustment solution had large flow fluctuations. For AC electromagnetic pumps, existing zero-over-power adjustment solutions regulate flow by changing the number of conduction half-waves per unit time. However, at low flow settings, the conduction and off cycles are relatively long (e.g., 4-second cycles), resulting in large instantaneous flow pulsations and "pulsating jets" of liquid output, which affects the user experience.

[0006] In summary, existing electromagnetic pump flow control is affected by temperature rise, nonlinearity, and pulsation, making it difficult to achieve accurate and stable delivery over a wide range, and improvements are needed. Summary of the Invention

[0007] The purpose of this invention is to provide an electromagnetic pump flow control method based on dual duty cycle and current feedback compensation, so as to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: An electromagnetic pump flow control method based on dual duty cycle and current feedback compensation includes the following steps: Step S1: Generate a dual duty cycle pulse width modulation signal, wherein the first-level PWM signal defines the macroscopic turn-on and turn-off timing of the electromagnetic pump to coarsely adjust the number of times it works per unit time, and the second-level PWM signal is superimposed on the turn-on period of the first-level PWM signal to finely adjust the single drive intensity. Step S2: Collect the instantaneous current value of the electromagnetic pump coil during the conduction period of the second-stage PWM signal, extract the characteristic parameters, and correct the duty cycle of the second-stage PWM signal in a closed-loop manner based on the deviation between the characteristic parameters and the pre-stored reference current-flow relationship curve to solve the flow temperature drift problem. Step S3: Query the nonlinear correction lookup table according to the target flow rate value to obtain the optimized combination of the first duty cycle of the first-stage PWM signal and the second duty cycle of the second-stage PWM signal, and compensate for the drive dead zone of the electromagnetic pump in the low duty cycle range (such as duty cycle below 20%) and the magnetic circuit saturation nonlinearity in the high duty cycle range (such as duty cycle above 80%).

[0009] As a further aspect of the present invention: in step S1, a fixed number of power frequency half-wave cycles are used as a complete cycle of the first-level PWM signal, the first duty cycle is calculated according to the ratio of the target flow rate to the rated flow rate, and the position of the conducting half-wave is determined according to the principle of equal interval allocation.

[0010] As a further aspect of the present invention: in step S1, the second duty cycle of the second-level PWM signal operates in the linear adjustment range, which is 20% to 80%.

[0011] As a further aspect of the present invention: in step S2, the specific method for correcting the duty cycle of the second-stage PWM signal is as follows: Step S21: Calculate the current deviation ΔI between the real-time characteristic parameters and the calibrated characteristic parameters under the reference operating conditions; Step S22: Generate the second duty cycle correction ΔD2 according to the proportional-integral control law based on ΔI; Step S23: The target second duty cycle is superimposed with ΔD2 to obtain the corrected second duty cycle, and the corrected second duty cycle is limited to the linear adjustment range.

[0012] As a further aspect of the present invention: in step S2, the characteristic parameters include peak current, average current, current rise rate and current overshoot amplitude.

[0013] As a further aspect of the present invention: in step S3, the nonlinear correction lookup table is obtained in the following way: Step S31: Under the reference operating conditions, the first duty cycle of the first-stage PWM signal is sequentially fixed at multiple preset levels; Step S32: For each fixed first duty cycle position, traverse the second duty cycle of the second-level PWM signal from 10% to 90%, and record the measured flow rate value of the electromagnetic pump with a predetermined step size to form the second duty cycle-flow rate characteristic curve under the first duty cycle position. Step S33: Identify the linear adjustment range of the second duty cycle in each characteristic curve, and construct a nonlinear mapping relationship by the data set (first duty cycle, second duty cycle, measured flow rate value) corresponding to when the second duty cycle falls into the nonlinear dead zone or saturation zone, as well as the equivalent second duty cycle value required at different first duty cycle levels to achieve the same flow rate, and obtain a nonlinear correction lookup table.

[0014] As a further aspect of the present invention: the strategy for obtaining the optimal combination in step S3 is as follows: When the second duty cycle corresponding to the target flow value is lower than the preset lower threshold or higher than the preset upper threshold, the nonlinear correction lookup table is queried to obtain an optimized combination (e.g., first duty cycle 50%, second duty cycle 90%) that produces the same flow and whose second duty cycle is within the linear adjustment range. The first duty cycle and the second duty cycle are then updated with this optimized combination.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention generates a dual duty cycle PWM signal, uses the first stage to coarsely adjust the number of working times per unit time and distributes the conduction half-waves at equal intervals, thereby suppressing the low-frequency flow pulsation of traditional zero-crossing power adjustment; by real-time acquisition of coil current and closed-loop correction of the second stage PWM duty cycle, the flow drift caused by coil temperature rise and voltage fluctuation is effectively compensated; by querying the nonlinear correction lookup table to obtain the optimized combination of the first and second duty cycles, the dead zone of low duty cycle drive and the saturation nonlinearity of high duty cycle magnetic circuit are overcome, thereby realizing wide-range, low-pulsation, and high-precision sensorless flow control of electromagnetic pumps. Attached Figure Description

[0016] Figure 1 The waveforms are for a first duty cycle of 50% and a second duty cycle of 100%.

[0017] Figure 2 Waveforms with a first duty cycle of 50% and a second duty cycle of 50%. Figure 3 The waveforms are for the first duty cycle of 33.3% and the second duty cycle of 100%. Figure 4 The waveforms show the first duty cycle at 33.3% and the second duty cycle at 80%. Figure 5The waveforms are shown with a first duty cycle of 33.3% and a second duty cycle of 50%. Figure 6 This is a flowchart illustrating an electromagnetic pump flow control method based on dual duty cycle and current feedback compensation.

[0018] Figure 7 This is a circuit diagram illustrating an electromagnetic pump flow control method based on dual duty cycle and current feedback compensation. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 6 A flow control method for an electromagnetic pump based on dual duty cycle and current feedback compensation includes the following steps: Step S1: Generate a dual duty cycle pulse width modulation signal, wherein the first-level PWM signal defines the macroscopic turn-on and turn-off timing of the electromagnetic pump to coarsely adjust the number of times it works per unit time, and the second-level PWM signal is superimposed on the turn-on period of the first-level PWM signal to finely adjust the single drive intensity. Step S2: Collect the instantaneous current value of the electromagnetic pump coil during the conduction period of the second-stage PWM signal, extract the characteristic parameters, and correct the duty cycle of the second-stage PWM signal in a closed-loop manner based on the deviation between the characteristic parameters and the pre-stored reference current-flow relationship curve to solve the flow temperature drift problem. Step S3: Query the nonlinear correction lookup table according to the target flow rate value to obtain the optimized combination of the first duty cycle of the first-stage PWM signal and the second duty cycle of the second-stage PWM signal, and compensate for the drive dead zone of the electromagnetic pump in the low duty cycle range (such as duty cycle below 20%) and the magnetic circuit saturation nonlinearity in the high duty cycle range (such as duty cycle above 80%).

[0021] In this embodiment: Please refer to Figures 1 to 5 In step S1, a fixed number of power frequency half-wave cycles are used as a complete cycle of the first-level PWM signal. The first duty cycle is calculated based on the ratio of the target flow rate to the rated flow rate, and the position of the conducting half-wave is determined according to the principle of equal interval allocation.

[0022] The electromagnetic pump is powered by mains electricity (50Hz or 60Hz AC). The control circuit typically uses a thyristor to conduct at the voltage zero-crossing point to achieve power regulation. Each half-wave of the mains frequency (half a cycle of a sine wave) is the smallest energy unit driving the electromagnetic pump. Discretizing the continuous operating time into fixed-length "large cycles" facilitates switching control in units of integer numbers of half-waves. The fixed number can be 250. This number ensures that the large cycles are long enough (4-5 seconds) to cover the entire flow regulation range, and is also divisible by various duty cycles, facilitating evenly spaced distribution.

[0023] The first duty cycle D1 is defined as follows: D1 = (Number of half-waves conducting within the large cycle) / (Total number of half-waves within the large cycle) The flow rate is approximately proportional to the number of conduction half-waves (assuming the drive strength is the same for each conduction). Therefore: D1 = Target flow rate / Rated flow rate For example, with 250 half-waves of power frequency as one cycle, the cycle is 20 milliseconds × 250 = 5 seconds when the mains power is 50Hz, and the cycle is 16 milliseconds × 250 = 4 seconds when the mains power is 60Hz.

[0024] Assuming the target traffic is 50% of the rated traffic, this means 250 × 0.5 = 125 half-waves need to be activated. Following the principle of equal intervals, one half-wave needs to be activated for every two half-waves. Figure 1 , 2 As shown.

[0025] Assuming the target traffic is 33% of the rated traffic, this means 250 × 0.33 = 82 half-waves need to be activated. Following an equal-interval allocation principle, one half-wave needs to be activated for every three half-waves. Figure 3 , 4 As shown in Figure 5.

[0026] In this embodiment: In step S1, the second duty cycle of the second-level PWM signal operates in the linear adjustment range, which is 20% to 80%.

[0027] The linear adjustment range is set to 20% to 80% because when the duty cycle is below 20%, the PWM pulse energy is insufficient to overcome the preload of the plunger spring, causing the electromagnetic pump to only vibrate and not pump effectively. When the duty cycle is above 80%, the magnetic circuit tends to saturate, and increasing the duty cycle hardly increases the electromagnetic force, resulting in a significant decrease in flow regulation sensitivity.

[0028] In this embodiment: In step S2, the specific method for correcting the duty cycle of the second-stage PWM signal is as follows: Step S21: Calculate the current deviation ΔI between the real-time characteristic parameters and the calibrated characteristic parameters under the reference operating conditions; Step S22: Generate the second duty cycle correction ΔD2 according to the proportional-integral control law based on ΔI; Step S23: The target second duty cycle is superimposed with ΔD2 to obtain the corrected second duty cycle, and the corrected second duty cycle is limited to the linear adjustment range.

[0029] Flow drift compensation algorithm: (1) Based on the factory calibration data, under the reference operating conditions (25℃, rated voltage, clean water, zero back pressure), establish the reference current-reference flow rate relationship curve: Q_base=f(I_base); Q_base is the reference flow rate, and I_base is the reference current.

[0030] (2) Obtain the actual current I_act by sampling in real time, and calculate the current deviation ΔI=I_base-I_act; (3) If ΔI is positive (current decreases), it indicates that the electromagnetic force is weakened due to the temperature rise or voltage drop of the coil, and the driving strength needs to be increased: ΔD2=Kp×ΔI+Ki×∫ΔIdt; Kp and Ki are constants; (4) Corrected second duty cycle: D2_corrected=D2_target+ΔD2, and limited to the range of [20%,80%]; D2_corrected is the corrected second duty cycle, and D2_target is the target second duty cycle.

[0031] (5) If D2_corrected reaches the upper limit of 80% and still cannot compensate for the flow deviation, the first duty cycle D1 will be automatically increased to increase the number of times it works per unit time and maintain the total flow target.

[0032] In this embodiment: In step S2, the characteristic parameters include peak current, average current, current rise rate and current overshoot amplitude.

[0033] In this embodiment: In step S3, the nonlinear correction lookup table is obtained as follows: Step S31: Under the reference operating conditions, the first duty cycle of the first-stage PWM signal is sequentially fixed at multiple preset levels; Step S32: For each fixed first duty cycle position, traverse the second duty cycle of the second-level PWM signal from 10% to 90%, and record the measured flow rate value of the electromagnetic pump with a predetermined step size to form the second duty cycle-flow rate characteristic curve under the first duty cycle position. Step S33: Identify the linear adjustment range of the second duty cycle in each characteristic curve, and construct a nonlinear mapping relationship by the data set (first duty cycle, second duty cycle, measured flow rate value) corresponding to when the second duty cycle falls into the nonlinear dead zone or saturation zone, as well as the equivalent second duty cycle value required at different first duty cycle levels to achieve the same flow rate, and obtain a nonlinear correction lookup table.

[0034] For example, in a production line or laboratory environment, a fully automated calibration process can be performed: Set the first duty cycle to 50% (to ensure there are enough driving windows); Traverse the second duty cycle = 10%~90%, step size 2%, and record the actual flow rate value measured by the flow meter; Identify the linear range (e.g., 20%~80%) of the second duty cycle-flow curve to obtain both linear and non-linear data; Repeatedly adjust the value of the first duty cycle to obtain multiple sets of linear and non-linear data. Based on the magnitude of the flow rate, obtain the linear data corresponding to the non-linear data. For example, if the first duty cycle is 50% and the second duty cycle is 90%, the flow rate of the non-linear data is the same as that of the linear data set with the first duty cycle of 60% and the second duty cycle of 70%.

[0035] In this embodiment: the strategy for obtaining the optimal combination in step S3 is: When the second duty cycle corresponding to the target flow value is lower than the preset lower threshold or higher than the preset upper threshold, the nonlinear correction lookup table is queried to obtain an optimized combination (e.g., first duty cycle 50%, second duty cycle 90%) that produces the same flow and whose second duty cycle is within the linear adjustment range. The first duty cycle and the second duty cycle are then updated with this optimized combination.

[0036] For the target traffic value set by the user, first determine whether the first duty cycle needs to be adjusted: If the second duty cycle operating point corresponding to the target traffic is within the linear range, then keep the first duty cycle = 50% and only adjust the second duty cycle; If the target traffic is small, and maintaining the first duty cycle = 50% would cause the second duty cycle to be <20%, then reduce the first duty cycle (for example, reduce it to 30%) to make the second duty cycle rise back to about 40%; If the target traffic is large, and maintaining the first duty cycle = 50% would cause the second duty cycle to be >80%, then increase the first duty cycle (for example, increase it to 70%) to make the second duty cycle fall back to about 60%.

[0037] Please see Figure 7The circuit is powered by the positive terminal of ACL and the negative terminal of GND. First, the Zero_Cross zero-crossing detection circuit composed of R9, R10, R11, D3, and C3 collects the zero-crossing signal of the mains sinusoidal wave and sends it to the external interrupt of the MCU, providing a timing reference for the generation of the first-stage PWM signal. Based on this, the MCU allocates the conduction half-wave at equal intervals and determines the first duty cycle to coarsely adjust the number of times the electromagnetic pump works per unit time. At the same time, the PUMP_Current current detection circuit composed of R1, R7, R8, D1, and C1 collects the instantaneous current of the electromagnetic pump coil during the conduction period of the second-stage PWM and sends it to the MCU ADC pin. After the MCU extracts the current characteristic parameters, it calculates the deviation by comparing it with the reference current-flow relationship, generates a correction amount according to the PI control law, and adjusts the duty cycle of the second-stage PWM in a closed loop to compensate for coil temperature rise and voltage fluctuation. The resulting flow drift is addressed by the MCU outputting a fixed 4kHz PWM drive signal via the Pump_Drive pin. This signal is superimposed with dual duty cycle control logic to control transistor Q1, which in turn drives the thyristor TR1 to turn on and off, achieving two-stage drive control with coarse adjustment of the first duty cycle and fine adjustment of the second duty cycle. The MCU also queries a nonlinear correction lookup table based on the target flow rate. When the second duty cycle exceeds the 20%-80% linear range, it automatically adjusts the first duty cycle and pulls the second duty cycle back into the linear range to compensate for the low duty cycle drive dead zone and the high duty cycle magnetic circuit saturation nonlinearity. In addition, C2 in the circuit can stop the thyristor TR1 from conducting in time when the MCU is stuck or the Pump_Drive signal is lost, realizing electromagnetic pump runaway protection. Finally, the flow control method of dual duty cycle regulation and current feedback compensation is fully implemented.

[0038] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and not restrictive.

[0039] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A flow control method for an electromagnetic pump based on dual duty cycle and current feedback compensation, characterized in that, The electromagnetic pump flow control method based on dual duty cycle and current feedback compensation includes: Step S1: Generate a dual duty cycle pulse width modulation signal, wherein the first-level PWM signal defines the macroscopic turn-on and turn-off timing of the electromagnetic pump to coarsely adjust the number of times it works per unit time, and the second-level PWM signal is superimposed on the turn-on period of the first-level PWM signal to finely adjust the single drive intensity. Step S2: Collect the instantaneous current value of the electromagnetic pump coil during the conduction period of the second-stage PWM signal, extract the characteristic parameters, and correct the duty cycle of the second-stage PWM signal in a closed-loop manner based on the deviation between the characteristic parameters and the pre-stored reference current-flow relationship curve to solve the flow temperature drift problem. Step S3: Query the nonlinear correction lookup table according to the target flow rate value to obtain the optimized combination of the first duty cycle of the first-stage PWM signal and the second duty cycle of the second-stage PWM signal, and compensate for the drive dead zone of the electromagnetic pump in the low duty cycle range and the magnetic circuit saturation nonlinearity in the high duty cycle range.

2. The electromagnetic pump flow control method based on dual duty cycle and current feedback compensation according to claim 1, characterized in that, In step S1, a fixed number of power frequency half-wave cycles are used as a complete cycle of the first-level PWM signal. The first duty cycle is calculated based on the ratio of the target flow rate to the rated flow rate, and the position of the conducting half-wave is determined according to the principle of equal interval allocation.

3. The electromagnetic pump flow control method based on dual duty cycle and current feedback compensation according to claim 1, characterized in that, In step S1, the second duty cycle of the second-level PWM signal operates in the linear adjustment range, which is 20% to 80%.

4. The electromagnetic pump flow control method based on dual duty cycle and current feedback compensation according to claim 1, characterized in that, In step S2, the specific method for correcting the duty cycle of the second-stage PWM signal is as follows: Step S21: Calculate the current deviation ΔI between the real-time characteristic parameters and the calibrated characteristic parameters under the reference operating conditions; Step S22: Generate the second duty cycle correction ΔD2 according to the proportional-integral control law based on ΔI; Step S23: The target second duty cycle is superimposed with ΔD2 to obtain the corrected second duty cycle, and the corrected second duty cycle is limited to the linear adjustment range.

5. The electromagnetic pump flow control method based on dual duty cycle and current feedback compensation according to claim 1 or 4, characterized in that, In step S2, the characteristic parameters include peak current, average current, current rise rate, and current overshoot amplitude.

6. The electromagnetic pump flow control method based on dual duty cycle and current feedback compensation according to claim 1, characterized in that, In step S3, the nonlinear correction lookup table is obtained as follows: Step S31: Under the reference operating conditions, the first duty cycle of the first-stage PWM signal is sequentially fixed at multiple preset levels; Step S32: For each fixed first duty cycle position, traverse the second duty cycle of the second-level PWM signal from 10% to 90%, and record the measured flow rate value of the electromagnetic pump with a predetermined step size to form the second duty cycle-flow rate characteristic curve under the first duty cycle position. Step S33: Identify the linear adjustment range of the second duty cycle in each characteristic curve, construct a nonlinear mapping relationship by the data set corresponding to when the second duty cycle falls into the nonlinear dead zone or saturation zone, and the equivalent second duty cycle value required at different first duty cycle levels to achieve the same flow rate, and obtain a nonlinear correction lookup table.

7. The electromagnetic pump flow control method based on dual duty cycle and current feedback compensation according to claim 6, characterized in that, The strategy for obtaining the optimal combination in step S3 is as follows: When the second duty cycle corresponding to the target flow value is lower than the preset lower threshold or higher than the preset upper threshold, the nonlinear correction lookup table is queried to obtain an optimized combination that produces the same flow as the current combination and whose second duty cycle is within the linear adjustment range. The first duty cycle and the second duty cycle are then updated with this optimized combination.

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