A three-wire fan compound control system and control method based on feedforward lookup table and PI feedback

Abstract

The application discloses a three-wire fan compound control system based on feedforward lookup table and PI feedback, wherein a target setting and error generation module is used for receiving a target rotating speed instruction of an MCU, comparing the target rotating speed instruction with filtered rotating speed, and calculating a real-time rotating speed error; a signal acquisition and processing module is used for collecting a three-wire fan operation pulse signal in real time, an MCU records a pulse interval time, and a real-time rotating speed is calculated according to a preset "pulse frequency-rotating speed" mapping relationship; a compound control amount calculation module generates a control amount by using a compound algorithm combining feedforward and proportional-integral feedback; a synthetic output module superimposes a basic duty cycle obtained by the compound control amount calculation module and a duty cycle adjustment amount, obtains a target PWM duty cycle, and performs output limiting; a driving execution module converts the target PWM duty cycle into a corresponding pulse width signal, and outputs the pulse width signal to a fan speed regulation driving circuit, so that accurate rotating speed control is realized by adjusting an average voltage on a power supply line, and the fan can be ensured to stably operate at a target rotating speed.

Description

Technical Field

[0001] This invention relates to a three-wire fan composite control system and control method based on feedforward lookup table and PI feedback, which belongs to the field of compressor refrigeration control systems for refrigerators, freezers and other similar devices. Background Technology

[0002] In refrigerator refrigeration systems, the fan, as a core component for air circulation, directly impacts product performance and user experience due to its control precision and operating noise. Currently, the industry primarily uses three solutions: two-wire fans, three-wire fans, and four-wire PWM fans. Four-wire fans can precisely control speed via PWM lines, but require an additional wiring route inside the refrigerator and a terminal block on the cabinet. Three-wire fans regulate speed through voltage control; while the feedback pin can indicate the current speed, most manufacturers only use it for fault diagnosis and employ traditional open-loop control. Two-wire fans lack a speed feedback pin and also use open-loop control. Therefore, to avoid potential start-up failures, both two-wire and three-wire fans start at higher speeds, resulting in higher noise levels and negatively impacting the user experience.

[0003] Therefore, it is indeed necessary to improve existing technologies to address their shortcomings. Summary of the Invention

[0004] The present invention provides a three-wire fan composite control system and control method based on feedforward lookup table and PI feedback to solve the problems existing in the prior art.

[0005] The present invention adopts the following technical solution: a three-wire wind turbine composite control system based on feedforward lookup table and PI feedback, including a signal acquisition and processing module, a target setting and error generation module, a composite control quantity calculation module, a synthetic output module, and a drive execution module;

[0006] The target setting and error generation module is used to receive the target speed command from the MCU, compare it with the filtered speed, and calculate the real-time speed error.

[0007] The signal acquisition and processing module acquires the operating pulse signal of the three-wire fan in real time through the feedback line. The MCU records the pulse interval time and calculates the real-time speed according to the preset "pulse frequency-speed" mapping relationship.

[0008] The composite control quantity calculation module uses a composite algorithm combining feedforward and proportional-integral feedback to generate control quantities.

[0009] The synthetic output module superimposes the base duty cycle obtained by the composite control quantity calculation module with the duty cycle adjustment quantity to obtain the target PWM duty cycle and performs output limiting;

[0010] The drive execution module converts the target PWM duty cycle into a corresponding pulse width signal and outputs it to the fan speed control drive circuit. By adjusting the average voltage on the power line, the speed is precisely controlled to ensure that the fan runs stably at the target speed.

[0011] Furthermore, in the signal acquisition and processing module, a digital filtering algorithm is used to suppress noise interference in the operating pulse signal of the three-wire fan, and output a stable and reliable speed value.

[0012] Furthermore, the fan speed control drive circuit is an LC filter circuit composed of capacitors, inductors, and transistors.

[0013] Furthermore, the adjustable voltage of the fan speed control drive circuit is 0~12V.

[0014] The present invention also adopts the following technical solution: a control method for a three-wire wind turbine composite control system based on feedforward lookup table and PI feedback, specifically including the following steps:

[0015] Step 1: Initialize the system after startup;

[0016] Step 2: The signal acquisition and processing module acquires the operating pulse signal of the three-wire fan in real time through the feedback line. The MCU records the pulse interval time and calculates the real-time speed according to the preset "pulse frequency-speed" mapping relationship.

[0017] Step 3: Suppress noise interference in the operating pulse signal of the three-wire fan using a digital filtering algorithm to output a stable and reliable filtered speed value;

[0018] Step 4: The target setting and error generation module reads the target speed command, compares it with the filtered speed value, and calculates the real-time speed error;

[0019] Step 5: Determine whether the absolute value of the real-time speed error is less than the dead zone threshold. If it is less than the dead zone threshold, pause the integration operation. If it is greater than or equal to the dead zone threshold, perform the PI operation and limit the integration.

[0020] Step 6: The composite control quantity calculation module uses a composite algorithm combining feedforward and proportional-integral feedback to generate the basic duty cycle and duty cycle adjustment.

[0021] Step 7: The composite output module superimposes the base duty cycle obtained from the composite control quantity calculation module with the duty cycle adjustment quantity to obtain the target PWM duty cycle and performs output limiting;

[0022] Step 8: The drive execution module converts the target PWM duty cycle into a corresponding PWM signal and outputs it to the fan speed control drive circuit. By adjusting the average voltage on the power line, the speed is precisely controlled to ensure that the fan runs stably at the target speed.

[0023] Furthermore, step six specifically includes the following:

[0024] 6.1 Feedforward control: An experimental lookup table of "target speed - base duty cycle" covering the working range of the fan was established. The fan speed corresponding to different duty cycles was measured and recorded. Then, the base duty cycle was quickly obtained by linear interpolation based on the current target speed.

[0025] 6.2 PI Feedback Control: Based on the feedforward duty cycle obtained in 6.1, PI calculation is performed based on the speed error (u(t) = Kp×e(t) + Ki×∫e(τ)dτ).

[0026] Where: u(t): control output, that is, the real-time control quantity calculated by the system based on the error;

[0027] Kp: Scale factor, used to amplify the effect of the current error e(t) to achieve a rapid response to changes in error. The output of the scale term is Kp×e(t).

[0028] Ki: Integral coefficient, which determines the strength of the integral action. It eliminates steady-state deviation by accumulating historical errors. The output of the integral term is Ki×∫e(τ)dτ.

[0029] e(t): Error signal, that is, the difference between the target value and the actual value. e(t) = target value - feedback value, which is the core input driving the controller's action;

[0030] ∫e(τ)dτ: Integral term, which refers to the cumulative error from the initial time to the current time.

[0031] Furthermore, the basic duty cycle is quickly obtained through linear interpolation, specifically as follows: (For the target speed target_rpm, interpolation is performed between two adjacent data points (duty1, rpm1) and (duty2, rpm2), calculated as follows: proportional coefficient = (target_rpm - rpm1) / (rpm2 - rpm1), duty cycle = duty1 + (duty2 -duty1) × proportional coefficient.)

[0032] The present invention has the following beneficial effects:

[0033] (1) Significantly reduce the starting noise of the three-line fan - With the help of closed-loop control, the need for the fan to start at high speed can be avoided, allowing it to start smoothly at a lower speed;

[0034] (2) Significantly improves speed control accuracy. Even under conditions of load fluctuation and power supply voltage fluctuation, the speed deviation can still be controlled within ±30 rpm, reaching the control level of a four-line fan.

[0035] (3) Without increasing hardware costs, high-performance control is achieved through algorithm optimization. Compared with the four-line fan solution, it not only reduces system costs but also achieves better control accuracy. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the three-line fan composite control system based on feedforward lookup table and PI feedback according to the present invention.

[0037] Figure 2 This is a flowchart of the control method for the three-line fan composite control system based on feedforward lookup table and PI feedback according to the present invention. Detailed Implementation

[0038] The invention will now be further described with reference to the accompanying drawings.

[0039] This invention relates to a three-wire wind turbine composite control system based on feedforward lookup table and PI feedback, comprising a signal acquisition and processing module, a target setting and error generation module, a composite control quantity calculation module, a synthetic output module, and a drive execution module.

[0040] The target setting and error generation module is used to receive the target speed command from the MCU, compare it with the filtered speed, and calculate the real-time speed error.

[0041] The signal acquisition and processing module acquires the operating pulse signal of the three-wire fan in real time through the feedback line. The MCU records the pulse interval time and calculates the real-time speed according to the preset "pulse frequency-speed" mapping relationship (such as pulse frequency × 30). The noise interference in the operating pulse signal of the three-wire fan is suppressed by digital filtering algorithm (such as first-order low-pass filter) to output a stable and reliable speed value.

[0042] The composite control quantity calculation module uses a composite algorithm that combines feedforward and proportional-integral (PI) feedback to generate control quantities.

[0043] The composite output module superimposes the base duty cycle obtained by the composite control quantity calculation module with the duty cycle adjustment quantity to obtain the target PWM (pulse width modulation) duty cycle and performs output limiting (0%-100%).

[0044] The drive execution module converts the target PWM duty cycle into a corresponding pulse width signal and outputs it to the fan speed control drive circuit (an LC filter circuit composed of capacitors, inductors, and transistors with adjustable voltage from 0 to 12V). By adjusting the average voltage on the power line, the speed is precisely controlled to ensure that the fan runs stably at the target speed.

[0045] The present invention provides a control method for a three-wire fan composite control system based on feedforward lookup table and PI feedback, which specifically includes the following steps:

[0046] Step 1: Initialize the system after startup;

[0047] Step 2: The signal acquisition and processing module acquires the operating pulse signal of the three-wire fan in real time through the feedback line. The MCU records the pulse interval time and calculates the real-time speed according to the preset "pulse frequency-speed" mapping relationship (such as pulse frequency × 30).

[0048] Step 3: Suppress noise interference in the operating pulse signal of the three-wire fan by using a digital filtering algorithm (such as a first-order low-pass filter) to output a stable and reliable filtered speed value;

[0049] Step 4: The target setting and error generation module reads the target speed command, compares it with the filtered speed value, and calculates the real-time speed error;

[0050] Step 5: Determine if the absolute value of the real-time speed error is less than the dead zone threshold (e.g., ±30 rpm). If it is less than the dead zone threshold, pause the integration operation, i.e., stop calculating u(t) = Kp×e(t) + Ki×∫e(τ)dτ, keeping the Ki×∫e(τ)dτ term unchanged; if it is greater than or equal to the dead zone threshold, perform the PI operation and apply integration limiting.

[0051] Step Six: The composite control quantity calculation module uses a composite algorithm combining feedforward and proportional-integral (PI) feedback to generate the basic duty cycle and duty cycle adjustment.

[0052] Step 7: The composite output module superimposes the base duty cycle obtained by the composite control quantity calculation module with the duty cycle adjustment to obtain the target PWM (pulse width modulation) duty cycle and performs output limiting (0%-100%).

[0053] Step 8: The drive execution module converts the target PWM duty cycle into a corresponding PWM signal and outputs it to the fan speed control drive circuit (an LC filter circuit composed of capacitors, inductors, and transistors with adjustable voltage from 0 to 12V). By adjusting the average voltage on the power line, the speed is precisely controlled to ensure that the fan runs stably at the target speed.

[0054] Step six specifically includes the following:

[0055] 6.1 Feedforward Control: An experimental lookup table covering the fan's operating range, representing the "target speed - base duty cycle," was established. The specific method is as follows: The fan speed corresponding to different duty cycles was measured and recorded. For example, when the output duty cycle was 30%, the current fan speed was recorded; when the output duty cycle was 40%, the corresponding speed was recorded, and so on until the speed corresponding to 100% duty cycle. Then, based on the current target speed, the base duty cycle was quickly obtained through linear interpolation (for the target speed target_rpm, interpolation needs to be performed between two adjacent data points (duty1, rpm1) and (duty2, rpm2). The calculation method is: proportional coefficient = (target_rpm - rpm1) / (rpm2 - rpm1), duty cycle = duty1 + (duty2 - duty1) × proportional coefficient), thus enabling the system to quickly approach the target operating point.

[0056] 6.2 PI Feedback Control: Based on the feedforward duty cycle obtained in 6.1, PI calculation is performed based on the speed error (u(t) = Kp×e(t) + Ki×∫e(τ)dτ).

[0057] Where: u(t): control output, that is, the real-time control quantity (PWM duty cycle) calculated by the system based on the error.

[0058] Kp: Scale factor, used to amplify the effect of the current error e(t) to achieve a rapid response to changes in error. The output of the scale term is Kp×e(t).

[0059] Ki: Integral coefficient, which determines the strength of the integral action. It eliminates steady-state deviation by accumulating historical errors. The output of the integral term is Ki×∫e(τ)dτ.

[0060] e(t): Error signal, that is, the difference between the target value and the actual value (e(t) = target value - feedback value), which is the core input for driving the controller's action;

[0061] ∫e(τ)dτ: The integral term refers to the cumulative error from the initial moment to the current moment. Its physical meaning is to eliminate static error through continuous correction and achieve error-free regulation. The final output duty cycle adjustment is prevented by integral limiting and a speed error dead zone is set (integration is paused when the error is less than the threshold) to reduce steady-state fluctuations.

[0062] This invention presents a composite control system and method for a three-wire wind turbine based on feedforward lookup table and PI feedback. It innovatively proposes a composite control architecture combining feedforward lookup table and PI feedback. A fast dynamic response is achieved through an experimentally modeled "target speed - basic duty cycle" lookup table, while steady-state accuracy correction is achieved through PI feedback, overcoming the shortcomings of slow response or large overshoot in traditional single control algorithms. This invention also pioneers a closed-loop speed control scheme based on the fault feedback pin of the three-wire wind turbine. Accurate speed measurement is achieved through pulse signal acquisition and digital filtering algorithms (such as first-order low-pass filtering), breaking through the technical bottleneck of open-loop control only being possible for three-wire wind turbines. Furthermore, this invention designs a coordinated control strategy of integral limiting and error dead zone. When the speed error is less than a threshold (±30 rpm), the integral action is paused, avoiding integral saturation and reducing steady-state fluctuations, thus improving system robustness.

[0063] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A three-wire fan composite control system based on feedforward lookup table and PI feedback, characterized in that: It includes a signal acquisition and processing module, a target setting and error generation module, a composite control quantity calculation module, a synthetic output module, and a drive execution module; The target setting and error generation module is used to receive the target speed command from the MCU, compare it with the filtered speed, and calculate the real-time speed error. The signal acquisition and processing module acquires the operating pulse signal of the three-wire fan in real time through the feedback line. The MCU records the pulse interval time and calculates the real-time speed according to the preset "pulse frequency-speed" mapping relationship. The composite control quantity calculation module uses a composite algorithm combining feedforward and proportional-integral feedback to generate control quantities. The synthetic output module superimposes the base duty cycle obtained by the composite control quantity calculation module with the duty cycle adjustment quantity to obtain the target PWM duty cycle and performs output limiting; The drive execution module converts the target PWM duty cycle into a corresponding pulse width signal and outputs it to the fan speed control drive circuit. By adjusting the average voltage on the power line, the speed is precisely controlled to ensure that the fan runs stably at the target speed.

2. The three-wire fan composite control system based on feedforward lookup table and PI feedback as described in claim 1, characterized in that: In the signal acquisition and processing module, noise interference in the operating pulse signal of the three-line fan is suppressed by a digital filtering algorithm, and a stable and reliable speed value is output.

3. The three-wire fan composite control system based on feedforward lookup table and PI feedback as described in claim 2, characterized in that: The fan speed control drive circuit is an LC filter circuit composed of capacitors, inductors, and transistors.

4. The three-wire fan composite control system based on feedforward lookup table and PI feedback as described in claim 3, characterized in that: The adjustable voltage of the fan speed control drive circuit is 0~12V.

5. A control method for a three-wire fan composite control system based on feedforward lookup table and PI feedback, characterized in that: Specifically, the steps include the following: Step 1: Initialize the system after startup; Step 2: The signal acquisition and processing module acquires the operating pulse signal of the three-wire fan in real time through the feedback line. The MCU records the pulse interval time and calculates the real-time speed according to the preset "pulse frequency-speed" mapping relationship. Step 3: Suppress noise interference in the operating pulse signal of the three-wire fan using a digital filtering algorithm to output a stable and reliable filtered speed value; Step 4: The target setting and error generation module reads the target speed command, compares it with the filtered speed value, and calculates the real-time speed error; Step 5: Determine whether the absolute value of the real-time speed error is less than the dead zone threshold. If it is less than the dead zone threshold, pause the integration operation. If it is greater than or equal to the dead zone threshold, perform the PI operation and limit the integration. Step 6: The composite control quantity calculation module uses a composite algorithm combining feedforward and proportional-integral feedback to generate the basic duty cycle and duty cycle adjustment. Step 7: The composite output module superimposes the base duty cycle obtained from the composite control quantity calculation module with the duty cycle adjustment quantity to obtain the target PWM duty cycle and performs output limiting; Step 8: The drive execution module converts the target PWM duty cycle into a corresponding PWM signal and outputs it to the fan speed control drive circuit. By adjusting the average voltage on the power line, the speed is precisely controlled to ensure that the fan runs stably at the target speed.

6. The control method for a three-wire fan composite control system based on feedforward lookup table and PI feedback as described in claim 5, characterized in that: Step six specifically includes the following: 6.1 Feedforward control: An experimental "target speed - base duty cycle" lookup table covering the working range of the fan was established. The fan speed corresponding to different duty cycles was measured and recorded. Then, the base duty cycle was quickly obtained by linear interpolation based on the current target speed. 6.2 PI Feedback Control: Based on the feedforward duty cycle obtained in 6.1, PI calculation is performed based on the speed error (u(t) = Kp×e(t) + Ki×∫e(τ)dτ). Where: u(t): control output, that is, the real-time control quantity calculated by the system based on the error; Kp: Scale factor, used to amplify the effect of the current error e(t) to achieve a rapid response to changes in error. The output of the scale term is Kp×e(t). Ki: Integral coefficient, which determines the strength of the integral action. It eliminates steady-state deviation by accumulating historical errors. The output of the integral term is Ki×∫e(τ)dτ. e(t): Error signal, that is, the difference between the target value and the actual value. e(t) = target value - feedback value, which is the core input driving the controller's action; ∫e(τ)dτ: Integral term, which refers to the cumulative error from the initial time to the current time.

7. The control method for a three-wire fan composite control system based on feedforward lookup table and PI feedback as described in claim 6, characterized in that: The basic duty cycle can be quickly obtained by linear interpolation, specifically as follows: (For the target speed target_rpm, interpolation is performed between two adjacent data points (duty1, rpm1) and (duty2, rpm2). The calculation method is: proportional coefficient = (target_rpm - rpm1) / (rpm2 - rpm1), duty cycle = duty1 + (duty2 - duty1) × proportional coefficient.

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