A direct-current axial flow fan adaptive noise reduction speed control method

Abstract

This invention relates to the field of motor control technology and discloses an adaptive noise reduction speed control method for a DC axial fan. The method includes: calculating a theoretical target speed based on the temperature deviation of the heat dissipation object; extracting the effective value of high-frequency ripple in the motor's operating phase current sequence, and establishing the upper and lower boundary speeds of the aerodynamic stall and acoustic resonance sensitive bands based on the abrupt change characteristics of the first derivative of the effective value; when the theoretical target speed is within the interval formed by the upper and lower boundary speeds, comparing the real-time temperature deviation with a safety margin threshold; if the temperature deviation is less than the threshold, executing a vibration damping step, and alternately jumping the output between the boundary speeds according to the target time duty cycle; if the temperature deviation is greater than or equal to the threshold, executing a harmonic step, calculating the target frequency of aerodynamic disturbance, and then generating an anti-phase feedforward compensation harmonic current command for injection output. This invention balances equipment heat dissipation safety and acoustic noise reduction effects.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, specifically to an adaptive noise reduction speed control method for a DC axial fan. Background Technology

[0002] DC axial fans are widely used in the cooling systems of various electronic devices, typically maintaining thermal balance by adjusting the motor speed. However, during actual operation, specific speed ranges can easily trigger aerodynamic stall and acoustic resonance, generating significant structural noise.

[0003] Existing technologies typically use a fixed speed range calibrated at the factory as the vibration isolation blind zone when addressing this problem. However, since the flow field impedance of the equipment in the actual working environment changes with external conditions, the preset fixed boundary is difficult to accurately match the real-time resonance state, resulting in inaccurate identification of the resonance sensitive zone.

[0004] Conventional speed control methods often employ a single speed jump strategy that directly crosses the sensitive range when the target speed falls within it. When heat-generating equipment is under high heat load, this abrupt speed jump causes transient fluctuations in air pressure, leading to a short-term drop in heat dissipation capacity and failing to ensure the thermal safety of core components while suppressing noise. At the underlying control level of the fan drive system, frequent operating condition switching and external interference can also easily cause electrical instability.

[0005] Traditional closed-loop control algorithms are prone to integral term saturation when the target temperature cannot be reached for a long time, resulting in severe speed overshoot when the temperature drops. Furthermore, when the current loop performs high-frequency signal superposition or feedforward compensation, it usually lacks dynamic assessment of the safe output margin of the drive inverter. Directly injected commands can easily cause transient overload or overcurrent in the drive circuit, affecting the overall safety of the motor and hardware circuit. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an adaptive noise reduction speed control method for DC axial fans, which solves the problems that existing fan speed control methods cannot adaptively identify the real-time resonance sensitive zone, and that it is difficult to balance the thermal safety of the heat-generating equipment and the electrical stability of the drive circuit when performing noise reduction adjustment.

[0007] To achieve the above objectives, the present invention provides an adaptive noise reduction speed control method for a DC axial fan, comprising: The theoretical target rotational speed is calculated based on the temperature deviation of the heat dissipation object. Extract the effective value of high-frequency ripple from the motor phase current sequence, and determine the upper and lower boundary speeds of the sensitive bands of aerodynamic stall and acoustic resonance based on the effective value of high-frequency ripple; When the theoretical target speed is within the range formed by the upper limit boundary speed and the lower limit boundary speed, the vibration damping step or the harmonic step is selected to be executed based on the comparison result of the temperature deviation and the safety margin threshold.

[0008] Preferably, the step of calculating the theoretical target rotational speed based on the temperature deviation of the heat dissipation object includes: The real-time temperature data of the heat dissipation object is obtained, and the difference between the actual temperature and the preset target temperature is calculated as the temperature deviation. The temperature deviation is used as the input variable of the outer loop speed controller, and the theoretical target speed required to maintain thermal balance is calculated according to the position-type proportional-integral-derivative control algorithm. A synchronous setting is used to calibrate an integral limit threshold based on the actual thermal volume of the heat dissipation object to prevent the integral term from accumulating indefinitely. When the absolute value of the sum of the temperature deviations within the control cycle exceeds the integral limit threshold, the continued accumulation of the integral term is frozen. When it does not exceed the threshold, the normal accumulation of the integral term is maintained.

[0009] Preferably, the extraction of the effective value of high-frequency ripple in the motor phase current sequence includes: Control the fan motor to execute discrete frequency sweep commands; The phase current of the motor is sampled at high frequency using an analog-to-digital converter to obtain a discrete sequence of the motor phase currents. A high-pass digital filter is used to process the motor phase current sequence to filter out the DC component and the driving fundamental component to obtain a high-frequency current ripple sequence; Within the set calculation window, the effective value of the high-frequency ripple in the high-frequency current ripple sequence is calculated, and the effective value of the high-frequency ripple is associated with the real-time rotational speed corresponding to the discrete frequency sweep command to construct a sequence in which the effective value of the high-frequency ripple changes with the rotational speed.

[0010] Preferably, determining the upper and lower boundary speeds of the aerodynamic stall and acoustic resonance sensitive bands based on the effective value of the high-frequency ripple includes: Calculate the first derivative sequence of the sequence of effective values ​​of the high-frequency ripple as a function of rotational speed; The first derivative sequence obtained by traversing the calculation is used to identify continuous rotational speed ranges where the first derivative undergoes a positive abrupt change and the amplitude exceeds a preset derivative threshold. Verify whether the absolute value of the effective value of the high-frequency ripple corresponding to the positive mutation exceeds the preset ripple reference threshold. The preset derivative threshold and the preset ripple reference threshold are both generated by adding a preset tolerance margin to the ripple data of the fan measured under a standard no-load flow field during the factory manufacturing stage. When the dual over-limit states of the first derivative exceeding the preset derivative threshold and the absolute value of the high-frequency ripple exceeding the preset ripple reference threshold are consistent in at least three adjacent continuous speed test points, the continuous speed range is defined as the aerodynamic stall and acoustic resonance sensitive zone, the lower edge point of the continuous speed range is recorded as the lower limit boundary speed, and the upper edge point is recorded as the upper limit boundary speed.

[0011] Preferably, the step of selecting to perform a vibration damping step or a harmonic damping step based on the comparison result between the temperature deviation and the safety margin threshold includes: The safety margin threshold is calibrated by combining the thermal capacity characteristics of the heat dissipation object and the maximum allowable transient temperature rise rate. The temperature deviation within a continuous period is obtained to form a real-time temperature deviation sequence. A first-order low-pass digital filter is applied to the real-time temperature deviation sequence to obtain a smoothed temperature deviation. The smoothed temperature deviation is compared with the safety margin threshold. When it is determined that the smoothed temperature deviation is less than the safety margin threshold, the vibration damping step is executed, specifically: the running time duty cycle is calculated based on the theoretical target speed, the upper limit boundary speed and the lower limit boundary speed, and the output is alternately jumped; When it is determined that the smoothed temperature deviation is greater than or equal to the safety margin threshold, the harmonic step is executed, specifically: calculating the target aerodynamic disturbance frequency, extracting the amplitude and phase of the phase current at the target aerodynamic disturbance frequency, generating an inverse feedforward compensation harmonic current command based on the amplitude and phase, and outputting it.

[0012] Preferably, the step of alternately jumping outputting the running time duty cycle calculated based on the theoretical target speed, the upper limit boundary speed, and the lower limit boundary speed includes: Based on the similarity law of wind turbines, a time equivalent heat dissipation equation is established. The difference between the cube of the theoretical target speed and the cube of the lower limit speed is divided by the difference between the cube of the upper limit speed and the cube of the lower limit speed to solve for the target time duty cycle as the running time duty cycle. Set a low-frequency scheduling cycle parameter, which is greater than the dynamic step response time of the motor and less than 1 / 10 of the thermal time constant of the heat dissipation object; in the first part of the set low-frequency scheduling cycle, the motor continuously maintains the speed at the upper limit boundary according to the time span corresponding to the duty cycle of the running time; and maintains the speed at the lower limit boundary during the remaining time period.

[0013] Preferably, when the theoretical target speed is within the interval formed by the upper limit boundary speed and the lower limit boundary speed, the determination includes using an interval determination algorithm with hysteresis characteristics, specifically: When the system is currently operating in a normal non-sensitive zone, it is determined to be within the range only if the theoretical target speed enters the absolute range formed by the lower limit boundary speed and the upper limit boundary speed. When the system is already in the sensitive zone control state, the theoretical target speed is limited to cross the extended boundary with an additional fixed speed hysteresis value to determine that it has escaped the aerodynamic stall and acoustic resonance sensitive zone; the fixed speed hysteresis value is established based on the maximum static tracking error range; when it is determined that the theoretical target speed is not within the range, the theoretical target speed command is directly output.

[0014] Preferably, the calculation of the target aerodynamic disturbance frequency includes: Read the actual mechanical speed of the fan and the number of blades pre-stored by the system, convert the mechanical speed into revolutions per second and multiply it by the number of blades to solve for the basic aerodynamic disturbance frequency; The basic aerodynamic disturbance frequency is calculated as a compensated electric angular frequency in the electromagnetic field rotating coordinate system, taking into account the number of pole pairs of the motor, as the target aerodynamic disturbance frequency.

[0015] Preferably, the extraction of the amplitude and phase of the phase current at the target aerodynamic disturbance frequency includes: Perform coordinate transformation on the sampled phase current to obtain the real-time quadrature-axis current feedback value and the current direct-axis current; An adaptive second-order generalized integrator is used to orthogonally decouple the quadrature-axis current feedback value. The target aerodynamic disturbance frequency is used as the input as the resonance parameter, and the output is a direct-axis filter component in phase and a quadrature-axis filter component with a 90° lag. The amplitude of the quadrature current ripple at the corresponding frequency is calculated using the direct-axis filter component and the quadrature-axis filter component, and the corresponding ripple phase is calculated as the phase.

[0016] Preferably, the step of generating and outputting an inverse feedforward compensation harmonic current command based on the amplitude and phase includes: By superimposing the amplitude and the phase with a 180° phase shift, and combining the inherent delay of the system to introduce a phase lead compensation angle, the feedforward compensation harmonic current command is reconstructed using the cosine function and the feedforward compensation coefficient. Injecting the feedforward compensation harmonic current command into the quadrature axis current loop for output includes: superimposing the feedforward compensation harmonic current command onto the original quadrature axis current reference command output by the outer loop speed controller to obtain the synthesized final current command. The square root of the difference between the square of the maximum safe output current of the drive inverter and the square of the current direct-axis current is obtained as the limiting threshold. The limiting threshold is used to perform dynamic limiting verification on the synthesized final current command, and the final current command after limiting protection is output as the setpoint of the inner loop current control.

[0017] This invention provides an adaptive noise reduction speed control method for DC axial fans. It has the following beneficial effects: 1. This invention extracts the effective value of high-frequency ripple in the motor phase current sequence and performs multi-dimensional verification by combining the positive abrupt change characteristics of its first derivative sequence. This can accurately calibrate the upper and lower boundary speeds of the sensitive bands of aerodynamic stall and acoustic resonance, avoiding the fixed estimation error of the resonance interval in traditional methods. This enables the control system to adaptively establish the acoustic boundary according to the actual flow field changes, improving the targeting of noise reduction scheduling.

[0018] 2. This invention dynamically switches between vibration damping and harmonic control strategies based on the comparison results of real-time temperature deviation and safety margin threshold. When the heat load is low, the speed is adjusted by adjusting the duty cycle to allow the speed to jump outside the boundary. When the heat load is high, a constant target speed is maintained and an anti-phase harmonic current is injected to cancel vibration. This suppresses aerodynamic noise in the sensitive zone of the fan while ensuring that the core components do not suffer transient thermal damage.

[0019] 3. In the outer loop speed control stage, the present invention sets an integral limiting threshold to prevent the infinite accumulation of errors, and when injecting feedforward compensation commands in the quadrature axis current loop, it uses the current direct axis current margin to perform dynamic limiting verification, which prevents abnormal speed overshoot and inverter overload and overcurrent under extreme operating conditions, and ensures the operational safety of the fan motor and its drive architecture in complex speed regulation processes. Attached Figure Description

[0020] Figure 1 This is a diagram illustrating the control system architecture and module data flow provided in an embodiment of the present invention. Figure 2 A flowchart of the control method provided in an embodiment of the present invention; Figure 3 The graphs showing the changes in RMS ripple and first derivative during the sensitive band calibration stage provided in this embodiment of the invention are shown, where (a) is the curve showing the change in RMS ripple with mechanical speed, and (b) is the curve showing the change in first derivative with mechanical speed. Figure 4 The diagram shows the state switching and target response curves under dynamic heat load provided in the embodiments of the present invention, wherein (a) is the curve of temperature deviation changing with time, and (b) is the control response curve of target rotation speed changing with time; Figure 5 A frequency domain comparison diagram of current amplitude before and after harmonic control compensation provided in an embodiment of the present invention. Detailed Implementation

[0021] The technical solutions in 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 embodiments of the present invention, and not all embodiments. 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.

[0022] See attached document Figure 1 This invention provides an adaptive noise reduction and speed control system for a DC axial fan, which may include: The module includes a thermal closed-loop module, a sensitive zone calibration module, a state determination module, a vibration damping module, and a harmonic module.

[0023] The control system is deployed in a microcontroller equipped with an analog-to-digital converter peripheral and is electrically connected to the field-oriented control drive circuit. The microcontroller receives thermal load data collected by a temperature sensor and phase current sampling data fed back from the drive circuit. The field-oriented control drive circuit outputs a continuously modulated space vector voltage to the DC axial fan motor according to the instructions of the microcontroller.

[0024] The thermal closed-loop module is used to maintain the thermal balance of the object being cooled. It receives real-time temperature data from a temperature sensor and calculates the deviation between the current actual temperature and a preset target temperature. The module then processes this temperature deviation using a preset control algorithm, calculates the theoretical target rotational speed required for the current heat load, and outputs this theoretical target rotational speed to the status determination module.

[0025] The sensitive band calibration module is used to extract acoustic and aerodynamic boundary parameters under the current flow field environment. Upon initial system power-on or a sudden change in flow field impedance, the sensitive band calibration module controls the fan to execute discrete frequency sweep commands within the basic operating speed range. To ensure heat dissipation safety during calibration triggered mid-operation, the sensitive band calibration module simultaneously sets a minimum guaranteed speed limit to maintain the current basic thermal balance when a flow field impedance change triggers the frequency sweep, and employs a fast step-scan strategy to shorten the time of non-constant heat dissipation. The sensitive band calibration module extracts the effective value of the high-frequency phase current ripple during the frequency sweep process and calculates the first derivative of the effective ripple value with respect to speed. Based on the positive abrupt change characteristic of the first derivative, the sensitive band calibration module establishes the upper and lower boundary speeds of the sensitive bands for aerodynamic stall and acoustic resonance.

[0026] The state determination module comprehensively evaluates data from the thermodynamic closed-loop module and the sensitive zone calibration module to determine the subsequent control flow direction. The state determination module compares the theoretical target speed with the upper and lower boundary speeds of the sensitive zone. When the theoretical target speed falls within the sensitive zone, the state determination module extracts the real-time temperature deviation and applies a low-pass filter to smooth it. Then, it compares the smoothed temperature deviation with a preset safety margin threshold. Based on the comparison result, the state determination module allocates control authority to the vibration damping module or the harmonic distortion module.

[0027] The vibration damping module takes over control when the temperature deviation is less than the safety margin threshold. Based on the principle of equivalent time-averaged heat dissipation, the vibration damping module calculates the time duty cycle corresponding to the theoretical target rotational speed. According to the time duty cycle, the vibration damping module controls the reference rotational speed of the field-oriented control drive circuit to execute low-frequency alternating jump commands between the upper and lower limit boundary speeds.

[0028] The harmonic module takes over control when the temperature deviation is greater than or equal to the safety margin threshold. The harmonic module calculates the target aerodynamic disturbance frequency using the fan's current speed and blade count. It then uses a digital filtering algorithm to extract the amplitude and phase parameters of the phase current at that frequency. Based on the extracted parameters, the harmonic module generates an inverse feedforward compensation harmonic current command, which is then superimposed on the quadrature-axis current reference command of the field-oriented control drive circuit to output a synthesized drive signal.

[0029] See attached document Figure 2 This invention provides an adaptive noise reduction speed control method for a DC axial fan, which may include: The process includes thermal closed-loop steps, sensitive zone calibration steps, state determination steps, vibration isolation steps, and harmonic steps.

[0030] Perform a thermal closed-loop process to acquire real-time temperature data of the object to be cooled, and calculate the temperature deviation between the actual temperature and the target temperature. Based on this temperature deviation, calculate the theoretical target fan speed required for cooling.

[0031] Perform the sensitive band calibration procedure, and control the fan motor to execute discrete frequency sweep commands under preset conditions. Extract the RMS value of high-frequency ripple from the motor phase current sequence, and calculate the first derivative of the RMS value of ripple with respect to speed. Determine the upper and lower boundary speeds of the aerodynamic stall and acoustic resonance sensitive bands based on the abrupt change parameters of the first derivative.

[0032] The execution state determination step compares the theoretical target speed with the aforementioned boundary speeds (or their boundaries after hysteresis extension). When the theoretical target speed falls within the range formed by the upper and lower boundary speeds (specifically, within an absolute or extended range), the temperature deviation (after smoothing) is compared with the safety margin threshold. Based on the comparison result, the system selects to jump to either the vibration damping step or the harmonic damping step. If the theoretical target speed does not fall within this speed range, the system directly outputs the theoretical target speed command.

[0033] When the state determination step determines that the temperature deviation is less than the safety margin threshold, the vibration damping step is executed. The operating time duty cycle is calculated using the theoretical target speed, the upper limit boundary speed, and the lower limit boundary speed. The fan command is controlled according to the calculated time duty cycle to perform low-frequency alternating output between the upper limit boundary speed and the lower limit boundary speed.

[0034] When the state determination step determines that the temperature deviation is greater than or equal to the safety margin threshold, the harmonic step is executed. The target aerodynamic disturbance frequency is calculated based on the actual fan speed and the number of blades. A digital filtering algorithm is used to extract the amplitude and phase of the phase current at this frequency. Based on the amplitude and phase, an inverse feedforward compensation harmonic current command is generated and output. The feedforward compensation harmonic current command is injected into the quadrature-axis current loop for output. Specifically, this includes injecting the feedforward compensation harmonic current command into the quadrature-axis current loop of the field-oriented control architecture for synthesized output.

[0035] The specific process of executing the thermodynamic closed-loop step includes parameter initialization and calculation of the theoretical target rotational speed.

[0036] Execute sub-step S101 to initialize the basic parameters of the control system and the field-oriented control drive architecture. In this embodiment, the system defines the number of pole pairs of the DC axial fan motor as follows: This is used to subsequently map the mechanical rotational speed to an electrical angular frequency; the number of fan blades is defined as... This parameter serves as the structural benchmark for establishing the aerodynamic disturbance frequency model. Based on the system's stability requirements, the pole-log number... With the number of leaves The constants are stored in the microcontroller's non-volatile memory. The system synchronously initializes the microcontroller's analog-to-digital conversion channel and the carrier frequency of the pulse width modulation module. For the initialization parameter configuration of the coordinate transformation module and the duty cycle calculation logic of the space vector pulse width modulation in the field-oriented control architecture, those skilled in the art can calibrate them themselves based on the motor's body parameters. The principles of coordinate transformation and drive signal generation are well-known technologies in this field and will not be elaborated upon here.

[0037] Execute sub-step S102 to obtain the temperature deviation of the object being cooled and calculate the theoretical target rotational speed. The system uses a temperature sensor to obtain real-time temperature data of the surface of the object being cooled. As a preferred method, considering that a single sampling point is highly susceptible to electromagnetic interference from the switching noise of the motor drive circuit, the microcontroller's analog-to-digital conversion channel reads the voltage signal from the sensor, first performs multi-point moving average digital filtering processing, and then maps the smoothed signal to the real-time temperature, denoted as . ,in, This represents a real-time time variable. The system reads the preset target temperature set by the system and denotes it as... In the control principle of thermodynamic systems, temperature deviation directly reflects the dynamic imbalance between the current system's heat dissipation capacity and heat generation. Based on this causal relationship, the temperature deviation is calculated by subtracting the real-time temperature from the preset target temperature, and denoted as . The formula for calculating temperature deviation is as follows: ; The system uses the temperature deviation as the input variable for the outer-loop speed controller. To support the implementation of the control logic, the lower-level features of the outer-loop speed controller include either a position-based proportional-integral-derivative (PI-DI) control algorithm or an incremental PI-DI control algorithm. Taking the position-based PI-DI control algorithm as an example, the system calculates the theoretical target rotational speed required to maintain the current thermal equilibrium based on the temperature deviation, denoted as . The specific formula for calculating the theoretical target rotational speed is as follows: ; In the above formula, This represents the proportional gain coefficient, used to adjust the sensitivity of the speed output to the current temperature deviation; This represents the integral gain coefficient, used to eliminate long-term static temperature errors; This represents the differential gain coefficient, used to suppress speed overshoot caused by the rate of change of temperature deviation; Represents the differential operator; This represents the integral operator. In the actual digital computing environment where the microcontroller operates, the above continuous-time domain equations are discretized, where the integral term is transformed into the sum of historical errors within the control cycle, and the differential term is transformed into the error difference between adjacent sampling cycles.

[0038] To ensure the algorithm's engineering robustness under extreme conditions and prevent the integral term from accumulating infinitely due to the system's inability to reach the preset target temperature for an extended period during equipment startup or under extremely high thermal loads, the system synchronously sets an integral limit threshold for the integral term. When the absolute value of the accumulated error exceeds this integral limit threshold, the control logic freezes the continued accumulation of the integral term to avoid severe speed overshoot when the temperature subsequently drops. If the threshold is not exceeded, normal accumulation of the integral term continues. Regarding the proportional gain coefficient... Integral gain coefficient and differential gain coefficient The specific value can be determined by those skilled in the art based on the commonly used Ziegler-Nichols tuning method in engineering, combined with the actual heat volume of the object being cooled. Its value range is typically normalized based on the motor's maximum rated speed. The calculated theoretical target speed will serve as a reference for subsequent state determination steps and will be directly input to the speed closed-loop point of the field-oriented control drive architecture under normal operating conditions.

[0039] The specific process of performing the sensitive band calibration steps includes the perturbation frequency sweep drive and phase current high-frequency sampling stage, high-frequency ripple RMS value extraction and first derivative mutation verification stage, and sensitive band boundary establishment stage.

[0040] Based on the system's power-on initialization or trigger conditions indicating a steady-state change in the environment, the microcontroller sends a stepped speed scan command to the field-oriented control architecture. The set test speed gradually increases during this period, covering the fan's basic operating range; specifically, when an environmental change is detected during equipment operation, the set test speed range is dynamically truncated to a minimum safe speed limit required for current heat dissipation. For each test speed, once the fan reaches mechanical steady state, the system uses a built-in analog-to-digital converter to continuously sample the phase current of the motor at high frequency. To ensure the capture of aerodynamic characteristic frequencies and avoid spectral aliasing, the sampling frequency of the analog-to-digital converter must strictly adhere to the Nyquist sampling theorem, and its value is forcibly set to be greater than twice the blade passage frequency at the highest rated operating speed. Through the above synchronous acquisition actions, the system obtains a discrete phase current sequence corresponding to the current speed.

[0041] In the fundamental theory of motor control, when the blades of fluid machinery encounter a sudden change in flow channel impedance or enter the aerodynamic stall region, the resulting minute pulsations in the mechanical load will couple to the back electromotive force of the motor, ultimately manifesting in the high-frequency ripple component of the phase current. Based on this causal relationship, in this embodiment, the system uses a high-pass digital filter to process the aforementioned phase current sequence. The cutoff frequency of this digital filter is set above the fundamental electrical frequency corresponding to the minimum allowable operating speed of the fan, thereby filtering out the DC component and the fundamental drive component to obtain the high-frequency current ripple sequence. Within a specified calculation window, the system calculates the effective value of the ripple of this high-frequency current ripple sequence, using the following formula: ; In the above formula, This indicates the currently set test speed. This indicates the RMS value of the ripple at the test speed; This represents the total number of sampling points within the calculation window, which is obtained by multiplying the sampling frequency of the analog-to-digital converter by the set window time span; Indicates the time index number of the discrete sampling point; This indicates the number of high-pass filtered cells. Several high-frequency phase current sampling values ​​were obtained. After acquiring the RMS ripple values ​​at each test speed, in order to capture the signal abrupt change trend caused by the deterioration of aerodynamic impedance, the system further calculated the first derivative sequence of the high-frequency ripple RMS value with respect to speed, as shown in the following formula: ; In the above formula, This represents the first derivative of the RMS value of the ripple with respect to the test rotational speed; This is a differential operator. In the digital computing environment of a microcontroller, since the test rotational speed varies discretely in a step-like manner, the lower-level characteristic of this derivative operation is specifically implemented as the difference between the effective values ​​of the ripple corresponding to two adjacent test rotational speeds divided by the rotational speed step size. Considering the arithmetic constraint that the denominator cannot be zero in the division operation, when the system executes the perturbation sweep frequency instruction, the internal parameter constraints require that the set rotational speed step size must be strictly greater than zero and remain a fixed discrete difference. At the same time, if the underlying computing module detects that the difference between adjacent actual feedback rotational speeds approaches the lower limit of system accuracy, it forcibly sets the current derivative value to zero or discards the current point to avoid register overflow errors caused by division by zero anomalies.

[0042] Establishing the boundaries between aerodynamic stall and acoustic resonance is the core of this control logic. The system iterates through the entire sequence of calculated first derivatives, identifying continuous speed ranges where positive abrupt changes occur and the amplitude exceeds a preset derivative threshold. To avoid single-point misjudgments caused by high-frequency switching noise from the drive circuit or transient fluctuations in the power grid, the system introduces a multi-dimensional judgment logic with dual verification. The system not only requires the first derivative of the test point to exceed the preset derivative threshold, but also verifies whether the absolute value of the RMS ripple at that point exceeds a preset ripple reference threshold. Furthermore, these dual over-limit states must remain consistent across at least three adjacent continuous speed test points.

[0043] As a preferred approach, both the preset derivative threshold and the preset ripple reference threshold are generated by adding a preset tolerance margin to the ripple data measured by the fan under standard no-load flow field during the factory calibration stage, thereby eliminating interference from inherent structural background noise under normal operating conditions. The system defines the continuous speed range that meets the above-mentioned multi-dimensional abrupt change judgment conditions as the aerodynamic stall and acoustic resonance sensitive zone, and records the lower edge point of this range as the lower limit boundary speed and the upper edge point as the upper limit boundary speed. Through this calibration process, the system successfully transforms the invisible aerodynamic boundaries into electromagnetic domain control parameters that can be directly called by the microcontroller, laying the data foundation for subsequent state-based flow separation.

[0044] The specific process of the execution state determination step includes the collision verification of theoretical target speed and sensitive zone boundary, as well as the dynamic heat load margin assessment and multi-scale strategy diversion step.

[0045] During the real-time control cycle of the system operation, the smooth transition of control parameters and the stable switching of the state machine are fundamental to ensuring the reliability of the electromechanical system. In this embodiment, the microcontroller receives the theoretical target speed and temperature deviation from the thermodynamic closed-loop logic, and simultaneously reads the upper and lower limit speeds of the sensitive band calibrated in the previous stage. Considering the inevitable inconsistency in refresh frequency of the multi-source data during task scheduling within the microcontroller, before executing the core state determination, the system forces the discrete execution cycle of the outer loop speed controller in the drive architecture to be used as a unified time reference, and performs timing latch alignment on all input data to ensure that all physical quantities are at the same strictly identical time section during subsequent logic comparisons.

[0046] Execute sub-step S301 to perform a collision check between the theoretical target speed and the sensitive zone boundary. In conventional interval determination logic, if the target speed command experiences a slight disturbance in the white noise of the sensor near the boundary critical point, it can easily trigger frequent jumps in the underlying drive strategy, leading to continuous jitter and abnormal wear of the motor output torque.

[0047] To circumvent this engineering flaw, as a preferred approach, the system's lower-level features employ an interval determination algorithm with hysteresis characteristics. The system compares the theoretical target speed with the lower and upper boundary speeds. The core technology lies in the fact that when the system is currently operating in a normal, non-sensitive zone, the theoretical target speed is determined to be within the interval only if it strictly falls within the absolute range formed by the lower and upper boundary speeds. However, when the system is in a sensitive zone control state, the theoretical target speed must cross an extended boundary with an added fixed speed hysteresis value to be considered out of the aerodynamic stall and acoustic resonance sensitive zone. The specific setting of this speed hysteresis value is determined based on the maximum static tracking error range of the fan's own speed closed-loop system. If it is determined that the target speed has not fallen into the sensitive zone, the control logic directly sends the theoretical target speed as a reference to the underlying drive architecture, maintaining the fan's normal constant-speed closed-loop operation. If it is determined that the target speed has fallen into the sensitive zone, the control flow naturally proceeds to the heat load assessment stage.

[0048] In sub-step S302, dynamic heat load margin assessment and multi-scale control strategy diversion are performed. When the theoretical rotational speed inevitably falls into the aerodynamic stall and acoustic resonance deterioration region, the control system must dynamically balance avoiding acoustic noise and maintaining heat dissipation stability. Based on this multi-objective optimization requirement, the system extracts the real-time temperature deviation and compares it numerically with a preset safety margin threshold. This safety margin threshold is derived by combining the heat capacity characteristics of the object being cooled and the maximum allowable transient temperature rise rate, clearly characterizing the current hardware's tolerance limit to wind pressure fluctuations.

[0049] To prevent high-frequency glitches in the temperature sampling signal from causing misjudgments and abnormal switching of logic branches, the system pre-applies a first-order low-pass digital filter to the real-time temperature deviation sequence before performing numerical comparisons to eliminate high-frequency transient interference. Subsequently, the system directly executes a deterministic strategy for traffic splitting based on the relationship between the smoothed temperature deviation and the safety margin threshold.

[0050] From a technical perspective, when the smoothed temperature deviation is strictly less than the safety margin threshold, it indicates that the current heat load on the heating equipment is at a relatively relaxed level, and the equipment temperature still has sufficient buffer space before reaching the danger threshold. At this point, the system allows for the proactive sacrifice of transient wind pressure stability to achieve a vibration damping effect, thereby avoiding resonance fatigue caused by continuous fan operation within the sensitive zone. Therefore, under this condition, the state determination module transfers full control to the vibration damping step.

[0051] Conversely, if the smoothed temperature deviation is greater than or equal to this safety margin threshold, it indicates that the system is currently facing extremely demanding heat dissipation pressure. At this point, any jump in rotational speed or sudden change in air pressure at any level will cause a transient drop in heat dissipation efficiency, which may lead to irreversible thermal damage to the core components being cooled.

[0052] Based on this rigid safety constraint, the system strictly prohibits speed scheduling and forcibly redirects control authority to the harmonic steps. Through this state-sharing architecture that integrates multi-dimensional data verification and hysteresis anti-disturbance mechanisms, the system achieves adaptive decoupling and smooth transition between thermodynamic rigidity requirements and acoustic suppression flexibility requirements at the underlying logic level.

[0053] The specific process of implementing vibration isolation steps includes the construction of the time equivalent heat dissipation equation based on the wind turbine similarity law, as well as the solution of the vibration isolation operation time duty cycle and the low-frequency discrete alternating scheduling.

[0054] When the state determination module confirms that the current system has a thermal load margin to tolerate transient wind pressure fluctuations, the control system will reconstruct the motor speed output command in the time dimension. Based on the engineering requirement of avoiding aerodynamic resonance, the system no longer allows the fan to operate continuously within the acoustically sensitive zone, but instead adopts a control strategy of jumping to the upper and lower boundaries of the sensitive zone for discrete operation.

[0055] Execute sub-step S401 to construct the time-equivalent heat dissipation equation based on the fan similarity law. In fluid machinery engineering theory, the shaft power of a fan intuitively reflects the system's heat dissipation capacity for the object being cooled. Under the engineering premise that the ambient fluid density remains relatively constant, according to the fan similarity law, the shaft power consumed by the fan is directly proportional to the cube of its rotational speed. To ensure that the time-averaged heat dissipation capacity under discrete alternating operating conditions is strictly consistent with the heat dissipation efficiency expected by the original theoretical target rotational speed, the system establishes an equivalent calculation model using the principle of energy conservation.

[0056] In this embodiment, the system defines the duty cycle for operation at the upper limit boundary speed as follows: The proportion of time spent running at the lower limit boundary speed is naturally derived as follows. Based on this, the system constructs an equivalent heat dissipation equation, the specific equation of which is as follows: ; In the above formula, This indicates the percentage of time the system operates at the upper limit speed within a single low-frequency scheduling cycle; This indicates the upper limit boundary rotational speed established by the sensitive band calibration procedure; Indicates the lower limit boundary speed; This represents the theoretical target rotational speed calculated using thermodynamic closed-loop logic. The technical purpose of this equation is to maintain thermal balance by weighted averaging of discrete high and low speed shaft power in the time domain, making the integral dissipated energy of the system equivalent to the dissipated energy during continuous operation at the theoretical target rotational speed, thereby avoiding frequency resonance.

[0057] Execute sub-step S402 to solve for the runtime duty cycle and perform low-frequency discrete alternating scheduling. The system performs an algebraic transformation on the above equivalent heat dissipation equation to directly solve for the target time duty cycle. The specific duty cycle calculation formula is as follows: ; To ensure the integrity of the microprocessor's underlying arithmetic logic, the system performs a mandatory check on the denominator value before executing the division instruction. Under normal calibration conditions, the upper limit speed is necessarily greater than the lower limit speed. However, to prevent system crashes caused by the denominator approaching zero due to memory single-event flips or abnormal calibration data, a minimum denominator difference protection threshold is set. As a preferred approach, this threshold is set to 5% of the cube of the wind turbine's base operating speed. If the difference between the cube and the two speeds is detected to be less than this threshold, the system will force a duty cycle of 50%. Simultaneously, based on the fact that the theoretical target speed must be between the upper and lower limits, the calculated duty cycle is strictly clamped within the range of 0 and 1.

[0058] After calculating the duty cycle, a low-frequency scheduling cycle parameter is set for the system. To balance the steady-state requirements for flow field establishment with the rigid constraints on device temperature rise, this low-frequency scheduling cycle parameter must simultaneously satisfy two-sided constraints. On the one hand, its value must be strictly greater than the dynamic step response time of the motor speed closed-loop system, typically 5 to 10 times the response time, to ensure that the fan can enter mechanical steady state and establish a stable flow field when switching between two boundary speeds, avoiding additional motor rotor inertia losses and drive heat dissipation caused by frequent acceleration and deceleration. On the other hand, this period value must be less than 1 / 10 of the thermal time constant of the object being cooled, in order to prevent local transient overheating due to insufficient heat dissipation during the duration of the lower speed limit.

[0059] Within each set low-frequency scheduling cycle, the microcontroller sends segmented, alternating reference speed commands to the speed loop of the field-oriented control drive circuit. Specifically, the system controls the fan to maintain its upper limit speed for the time span corresponding to the duty cycle during the early part of the current scheduling cycle; during the remaining time period of the current scheduling cycle, the system controls the fan speed to decrease in a step and maintain its lower limit speed. By using the above-mentioned technique of dividing and allocating different speed operating times on the time axis, the control system cuts off the energy source continuously excited by aerodynamic resonance within the sensitive zone while maintaining a constant overall heat dissipation power, thus achieving the goal of vibration and noise reduction at the surface level.

[0060] This invention provides an adaptive noise reduction control system for DC axial fans based on FOC architecture and multi-scale feature decoupling. Its harmonic steps may include a frequency calculation stage, a feature component extraction stage, and a feedforward compensation injection stage.

[0061] When the system faces stringent heat dissipation requirements and prohibits speed jumps, the microcontroller relies on harmonic steps to maintain a constant speed while counteracting aerodynamic resonance through high-frequency modulation of electromagnetic torque. In this embodiment, the control system directly takes over the theoretical target speed command output by the thermodynamic closed-loop module and uses it as a constant reference operating speed.

[0062] Execute sub-step S501 to establish the mapping relationship between aerodynamic disturbance frequency and electromagnetic frequency. During the operation of fluid machinery, the periodic sweep of blades over the stationary support generates fixed aerodynamic pressure pulsations. Based on this general technical principle, the system reads the actual mechanical speed of the fan and the pre-stored number of blades. The system calculates the basic aerodynamic disturbance frequency by converting the mechanical speed to revolutions per second and multiplying it by the number of blades.

[0063] To unify the disturbance frequency of this mechanical domain into the electrical angular coordinate system of the field-oriented control architecture, the system further calculates the compensated electrical angular frequency in the electromagnetic field rotating coordinate system based on the number of pole pairs of the motor, using this as the target aerodynamic disturbance frequency. This ensures that the extracted center frequency corresponds to the actual alternating component in the electromagnetic field rotating coordinate system. The specific calculation formula is as follows: ; In the above formula, Indicates the compensated electrical angular frequency; This indicates the actual mechanical speed of the fan, as fed back by a position sensor or a sensorless observer. This indicates the number of blades initially cured in the system; Indicates the number of pole pairs of the motor; Pi is a constant. Considering the constraints of division arithmetic, the system mandates that the number of pole pairs used for verification must be a positive integer during initialization to avoid division by zero anomalies. The technical purpose of this calculation process is to lock the specific coordinates of the resonant energy in the stator quadrature-axis current spectrum, providing a dynamic center frequency for subsequent directional filtering.

[0064] In sub-step S502, the amplitude and phase parameters of the quadrature-axis current at the target aerodynamic disturbance frequency are extracted. In the field-oriented control architecture, the quadrature-axis current directly determines the output electromagnetic torque of the motor. Aerodynamic pressure pulsation, as an external load disturbance, reacts to the rotor, inevitably exciting a pulsating component of the same frequency in the quadrature-axis current. To isolate this disturbance component, as a preferred approach, the lower-level system features employ an adaptive second-order generalized integrator to orthogonally decouple the real-time sampled quadrature-axis current feedback value. To prevent timing misalignment of multi-source data, the digital iteration period of this integrator is strictly configured to be synchronized with the current sampling period of the analog-to-digital converter and the carrier period of the pulse width modulation module.

[0065] The second-order generalized integrator uses the input compensated electrical angular frequency as the resonant parameter, outputting a direct-axis filtered component in phase with the input signal and a quadrature-axis filtered component lagging by 90°. Based on this, the system uses these two orthogonal components to calculate the quadrature-axis current ripple amplitude at the corresponding frequency as the amplitude value. The corresponding calculation formula is as follows: ; ; In the above formula, This represents the extracted frequency quadrature-axis current pulsation amplitude; Indicates the corresponding pulsation phase; This represents the in-phase component of the output of the second-order generalized integrator; Indicates orthogonal lag components; This represents the arctangent function. Considering the arithmetic defects of the arctangent function in the division-by-zero case, the system forces the use of underlying logic with quadrant judgment and zero division protection when performing phase calculations inside the microcontroller, thereby ensuring the continuity and safety of phase calculations throughout the entire AC cycle.

[0066] In sub-step S503, an inverted feedforward harmonic compensation current command is generated and injected for synthesis. Based on active noise control theory, injecting an equal-amplitude, inverted excitation into the system can cancel out the original vibration. Based on this principle, the system utilizes the extracted pulsation amplitude and phase, superimposes a 180° phase shift, and incorporates a phase lead compensation angle based on the system's inherent delay to reconstruct the feedforward harmonic compensation current command. The specific reconstruction formula is as follows: ; In the above formula, This indicates the command to generate feedforward compensation harmonic current; Indicates the feedforward compensation coefficient; This represents the extracted pulsation amplitude; Represents the cosine function; Indicates the pulsating phase; Pi is a constant and is used here as a fixed phase offset to achieve antiphase cancellation; This indicates the phase lead compensation angle. This compensation angle is determined based on the inherent phase frequency characteristics of the microcontroller's total computational delay and current loop control bandwidth. Its technical purpose is to eliminate the lag deviation generated during the closed-loop transmission of high-frequency commands.

[0067] As a preferred approach, the feedforward compensation coefficient is set between 0.5 and 0.9. This coefficient is determined to ensure sufficient compensation while avoiding self-oscillations in the control loop caused by signal delay.

[0068] After command reconstruction, the system directly superimposes the feedforward compensation harmonic current command onto the original quadrature-axis current reference command output by the outer-loop speed controller. To prevent the injection of high-frequency compensation signals from causing the total quadrature-axis current reference value to exceed the inverter's linear modulation range, the system performs dynamic limiting verification on the synthesized final current command. The limiting threshold is dynamically calculated based on the vector synthesis margin between the maximum safe output current of the drive inverter and the current direct-axis current. Specifically, the limiting threshold is the square root of the difference between the square of the maximum safe output current of the drive inverter and the square of the current direct-axis current.

[0069] The synthesized drive signal, after being limited and protected, is then input to the inner current loop controller, driving the motor to generate alternating high-frequency compensating torque. Through this electromagnetic torque modulation method, the control system actively absorbs the aerodynamic resonance energy within the sensitive zone without changing the fan's operating state.

[0070] Specific application examples: To aid in understanding the technical solution of this invention, the following description is based on a specific application scenario of a server chassis heat dissipation system.

[0071] Configure the number of pole pairs of the DC axial fan motor used in this server chassis. Number of leaves The maximum rated speed is 6000 RPM. The system's preset target temperature... Based on the thermal capacity characteristics of the server's core CPU, the safety margin threshold is set to 5°C, and the low-frequency scheduling cycle is set to 2 seconds.

[0072] (1) Sensitive band calibration stage: After the device is powered on, the microcontroller controls the fan to perform discrete frequency sweep. The analog-to-digital converter collects the phase current and extracts the effective value of the high-frequency ripple. Combined with Figure 3 It can be seen that, Figure 3 The data changes during the sensitive band calibration phase are shown. Figure 3 (a) is the RMS value curve of ripple (A) in the range of 3000 to 5500 mechanical speed (RPM). In the figure, circles represent data points of the RMS value curve, and pentagrams represent boundary calibration points. Figure 3 (b) shows the curves of the first derivative at the corresponding mechanical rotational speed (RPM), with the threshold for abrupt derivative changes marked by dashed lines. For example... Figure 3 As shown in (a) and (b), after first-order derivative calculation and dual threshold verification, the system identified a continuous interval between 4000 RPM and 4500 RPM where the first-order derivative abruptly changed and the absolute value of the ripple exceeded the limit. Based on this, the system set the lower limit boundary speed. Established at 4000 RPM (i.e. Figure 3 (a) The lower limit (4000) boundary calibration point marked in the figure), and the upper limit boundary speed. Established at 4500 RPM (i.e. Figure 3 (a) The boundary calibration point of the upper limit (4500) marked in the figure.

[0073] (2) Vibration control stage (low heat load): When the server is under medium load, the thermal closed-loop module calculates the theoretical target rotational speed for maintaining thermal balance. RPM. This rotational speed falls within the calibrated sensitivity range (4000-4500 RPM). The status determination module reads the current real-time temperature as 58℃, with a filtered temperature deviation of 3℃. Combined with... Figure 4 It can be seen that, Figure 4 The state switching and target response curves under dynamic heat load are shown, where Figure 4 (a) The horizontal axis represents time (s), the vertical axis represents temperature deviation (°C), and the safety margin threshold (5°C) is marked with a dashed line. Figure 4 (b) The horizontal axis represents time (s), and the vertical axis represents the target rotational speed (RPM). For example... Figure 4 As shown in the 0-5s interval of (a), since 3℃ is less than the safety margin threshold of 5℃, it is in a state below the threshold: a permissible jump state. The system then assigns control authority to the vibration damping module. The vibration damping module operates according to the formula... Calculate the duty cycle and obtain Within a 2-second scheduling cycle, the microcontroller instructs the fan to run at 4500 RPM for 1.14 seconds, then at 4000 RPM for 0.86 seconds, alternating in this cycle. Figure 4 As shown in the 0-5s interval of (b), the system performs vibration damping, with the target rotational speed exhibiting alternating square wave jumps between 4000 RPM and 4500 RPM. The system avoids the resonance point at 4300 RPM while maintaining equivalent heat dissipation power.

[0074] (3) Harmonic control stage (high heat load): As the server suddenly experiences high load operation, the heat generation rises sharply, and the real-time temperature jumps to 62℃. The temperature deviation reaches 7℃, which is greater than the safety margin threshold of 5℃. Figure 4 As shown in the 5-10s interval of (a), due to the temperature deviation exceeding the safety margin threshold (5℃), it is in a state above the threshold: speed jump prohibited. If speed jump continues, the drop in wind pressure during the lower speed limit period may trigger the CPU's frequency reduction protection. The status determination module immediately switches the control authority to the harmonic module. Figure 4 As shown in the 5-10s interval of (b), the system enters the harmonic phase, and the theoretical target speed remains constant at 4300 RPM. The harmonic module calculates the target aerodynamic disturbance frequency. rad / s.

[0075] The second-order generalized integrator extracts the pulsating amplitude and phase of the quadrature-axis current at this frequency, and superimposes a 180° phase shift and the system advance angle to generate a feedforward compensation harmonic current command. After this command is injected into the quadrature-axis current loop, the motor outputs a high-frequency fine-tuning torque containing a cancellation component. While maintaining a constant speed of 4300 RPM (ensuring maximum heat dissipation efficiency), it absorbs aerodynamic resonance energy through electromagnetic modulation.

[0076] Experimental verification and effect comparison: To verify the effectiveness of the present invention, a server chassis heat dissipation test platform was built in a semi-anechoic chamber environment, and data was collected using a multi-channel temperature recorder and a high-precision sound level meter.

[0077] The experiment included three control groups: Control group A: The traditional PID continuous speed control method is used (the speed is not limited by the resonance zone). Control group B: The traditional fixed frequency hopping strategy was adopted (when the target speed enters the preset resonance zone, the speed is forcibly fixed at the lower edge of the resonance zone). Experimental group C: The adaptive noise reduction speed control method provided by this invention is adopted.

[0078] The server heat source was set to a stable medium heat load (requiring a 3°C temperature deviation, corresponding to a target speed of 4300 RPM) and a sudden high heat load (requiring a 7°C temperature deviation, corresponding to a target speed of 4300 RPM). The test data are as follows: Acoustic noise reduction effect verification: Under moderate thermal load (corresponding to the vibration isolation stage of the embodiment), the control group A fan operated continuously at 4300 RPM, generating significant chassis structural resonance, and the weighted sound pressure level of the entire unit A was measured to be 54.2 dBA. Experimental group C performed alternating jumps based on equivalent heat dissipation, avoiding the resonant frequency, and the measured sound pressure level was 46.5 dBA. Control group B, due to forced speed reduction, had a sound pressure level of 45.8 dBA.

[0079] Thermal stability comparison and verification: Under high thermal loads (the harmonic stage of the corresponding embodiment), the system has extremely high requirements for continuous heat dissipation.

[0080] Control group B, due to the adoption of the traditional forced speed reduction and vibration damping strategy, suffered from insufficient air pressure, resulting in a maximum positive overshoot of 6.8℃ in the core temperature of the chassis, which triggered the equipment's temperature rise alarm.

[0081] Control group A, maintaining the target speed, experienced smaller temperature fluctuations with a maximum overshoot of 1.2℃, but the ambient noise reached 54.5 dBA. Experimental group C automatically switched to the harmonic mode, injecting compensating current while maintaining a constant speed of 4300 RPM to ensure airflow supply. Combined with... Figure 5It can be seen that, Figure 5 This demonstrates the relationship between frequency (Hz) and current amplitude (A), comparing the difference in current amplitude before compensation (dark bars) and after compensation (light bars) in harmonic control. Figure 5 As shown, at 50Hz, 100Hz, 150Hz, and 200Hz, the current amplitudes (A) before and after compensation are 0.12 / 0.11, 0.08 / 0.09, 0.07 / 0.06, and 0.05 / 0.04, respectively, with little change. However, at 125Hz (the perturbation frequency), the current amplitude before compensation is as high as 0.95A. After feedforward compensation and harmonic current injection, the current amplitude after compensation decreases to 0.15A. The test results show that the maximum overshoot of the core temperature is only 1.4℃ (comparable to the control group A), and thanks to the aforementioned electromagnetic cancellation effect, the sound pressure level is suppressed to 48.1dBA.

[0082] Data shows that the solution of the present invention achieves a dynamic optimal solution for noise reduction and thermal balance under different operating conditions.

Claims

1. A method for adaptive noise reduction and speed control of a DC axial fan, characterized in that, include: The theoretical target rotational speed is calculated based on the temperature deviation of the heat dissipation object. Extract the effective value of high-frequency ripple from the motor phase current sequence, and determine the upper and lower boundary speeds of the sensitive bands of aerodynamic stall and acoustic resonance based on the effective value of high-frequency ripple; When the theoretical target speed is within the range formed by the upper limit boundary speed and the lower limit boundary speed, the vibration damping step or the harmonic step is selected to be executed based on the comparison result of the temperature deviation and the safety margin threshold.

2. The adaptive noise reduction speed control method for a DC axial fan according to claim 1, characterized in that, The calculation of the theoretical target rotational speed based on the temperature deviation of the heat dissipation object includes: The real-time temperature data of the heat dissipation object is obtained, and the difference between the actual temperature and the preset target temperature is calculated as the temperature deviation. The temperature deviation is used as the input variable of the outer loop speed controller, and the theoretical target speed required to maintain thermal balance is calculated according to the position-type proportional-integral-derivative control algorithm. A synchronous setting is used to calibrate an integral limit threshold based on the actual thermal volume of the heat dissipation object to prevent the integral term from accumulating indefinitely. When the absolute value of the sum of the temperature deviations within the control cycle exceeds the integral limit threshold, the continued accumulation of the integral term is frozen. When it does not exceed the threshold, the normal accumulation of the integral term is maintained.

3. The adaptive noise reduction speed control method for a DC axial fan according to claim 1, characterized in that, The extraction of the high-frequency ripple RMS value from the motor phase current sequence includes: Control the fan motor to execute discrete frequency sweep commands; The phase current of the motor is sampled at high frequency using an analog-to-digital converter to obtain a discrete sequence of the motor phase currents. A high-pass digital filter is used to process the motor phase current sequence to filter out the DC component and the driving fundamental component to obtain a high-frequency current ripple sequence; Within the set calculation window, the effective value of the high-frequency ripple in the high-frequency current ripple sequence is calculated, and the effective value of the high-frequency ripple is associated with the real-time rotational speed corresponding to the discrete frequency sweep command to construct a sequence in which the effective value of the high-frequency ripple changes with the rotational speed.

4. The adaptive noise reduction speed control method for a DC axial fan according to claim 3, characterized in that, The step of determining the upper and lower boundary speeds of the aerodynamic stall and acoustic resonance sensitive bands based on the effective value of the high-frequency ripple includes: Calculate the first derivative sequence of the sequence of effective values ​​of the high-frequency ripple as a function of rotational speed; The first derivative sequence obtained by traversing the calculation is used to identify continuous rotational speed ranges where the first derivative undergoes a positive abrupt change and the amplitude exceeds a preset derivative threshold. Verify whether the absolute value of the effective value of the high-frequency ripple corresponding to the positive mutation exceeds the preset ripple reference threshold. The preset derivative threshold and the preset ripple reference threshold are both generated by adding a preset tolerance margin to the ripple data of the fan measured under a standard no-load flow field during the factory manufacturing stage. When the dual over-limit states of the first derivative exceeding the preset derivative threshold and the absolute value of the high-frequency ripple exceeding the preset ripple reference threshold are consistent in at least three adjacent continuous speed test points, the continuous speed range is defined as the aerodynamic stall and acoustic resonance sensitive zone, the lower edge point of the continuous speed range is recorded as the lower limit boundary speed, and the upper edge point is recorded as the upper limit boundary speed.

5. The adaptive noise reduction speed control method for a DC axial fan according to claim 1, characterized in that, The step of selecting to perform either vibration damping or harmonic damping based on the comparison result between the temperature deviation and the safety margin threshold includes: The safety margin threshold is calibrated by combining the thermal capacity characteristics of the heat dissipation object and the maximum allowable transient temperature rise rate. The temperature deviation within a continuous period is obtained to form a real-time temperature deviation sequence. A first-order low-pass digital filter is applied to the real-time temperature deviation sequence to obtain a smoothed temperature deviation. The smoothed temperature deviation is compared with the safety margin threshold. When it is determined that the smoothed temperature deviation is less than the safety margin threshold, the vibration damping step is executed, specifically: the running time duty cycle is calculated based on the theoretical target speed, the upper limit boundary speed and the lower limit boundary speed, and the output is alternately jumped; When it is determined that the smoothed temperature deviation is greater than or equal to the safety margin threshold, the harmonic step is executed, specifically: calculating the target aerodynamic disturbance frequency, extracting the amplitude and phase of the phase current at the target aerodynamic disturbance frequency, generating an inverse feedforward compensation harmonic current command based on the amplitude and phase, and outputting it.

6. The adaptive noise reduction speed control method for a DC axial fan according to claim 5, characterized in that, The method of alternately jumping outputting the running time duty cycle calculated based on the theoretical target speed, the upper limit boundary speed, and the lower limit boundary speed includes: Based on the similarity law of wind turbines, a time equivalent heat dissipation equation is established. The difference between the cube of the theoretical target speed and the cube of the lower limit speed is divided by the difference between the cube of the upper limit speed and the cube of the lower limit speed to solve for the target time duty cycle as the running time duty cycle. Set a low-frequency scheduling cycle parameter, which is greater than the dynamic step response time of the motor and less than 1 / 10 of the thermal time constant of the heat dissipation object; in the first part of the set low-frequency scheduling cycle, the motor continuously maintains the speed at the upper limit boundary according to the time span corresponding to the duty cycle of the running time; and maintains the speed at the lower limit boundary during the remaining time period.

7. The adaptive noise reduction speed control method for a DC axial fan according to claim 1, characterized in that, When the theoretical target speed is within the interval formed by the upper limit boundary speed and the lower limit boundary speed, the determination includes using an interval determination algorithm with hysteresis characteristics, specifically: When the system is currently operating in a normal non-sensitive zone, it is determined to be within the range only if the theoretical target speed enters the absolute range formed by the lower limit boundary speed and the upper limit boundary speed. When the system is already in the sensitive zone control state, the theoretical target speed is limited to cross the extended boundary with an additional fixed speed hysteresis value to determine that it has escaped the aerodynamic stall and acoustic resonance sensitive zone; the fixed speed hysteresis value is established based on the maximum static tracking error range; when it is determined that the theoretical target speed is not within the range, the theoretical target speed command is directly output.

8. The adaptive noise reduction speed control method for a DC axial fan according to claim 5, characterized in that, The calculation of the target aerodynamic disturbance frequency includes: Read the actual mechanical speed of the fan and the number of blades pre-stored by the system, convert the mechanical speed into revolutions per second and multiply it by the number of blades to solve for the basic aerodynamic disturbance frequency; The basic aerodynamic disturbance frequency is calculated as a compensated electric angular frequency in the electromagnetic field rotating coordinate system, taking into account the number of pole pairs of the motor, as the target aerodynamic disturbance frequency.

9. The adaptive noise reduction speed control method for a DC axial fan according to claim 5, characterized in that, The extraction of the amplitude and phase of the phase current at the target aerodynamic disturbance frequency includes: Perform coordinate transformation on the sampled phase current to obtain the real-time quadrature-axis current feedback value and the current direct-axis current; An adaptive second-order generalized integrator is used to orthogonally decouple the quadrature-axis current feedback value. The target aerodynamic disturbance frequency is used as the input as the resonance parameter, and the output is a direct-axis filter component in phase and a quadrature-axis filter component with a 90° lag. The amplitude of the quadrature current ripple at the corresponding frequency is calculated using the direct-axis filter component and the quadrature-axis filter component, and the corresponding ripple phase is calculated as the phase.

10. The adaptive noise reduction speed control method for a DC axial fan according to claim 9, characterized in that, The step of generating and outputting an inverse feedforward compensation harmonic current command based on the amplitude and phase includes: By superimposing the amplitude and the phase with a 180° phase shift, and combining the inherent delay of the system to introduce a phase lead compensation angle, the feedforward compensation harmonic current command is reconstructed using the cosine function and the feedforward compensation coefficient. Injecting the feedforward compensation harmonic current command into the quadrature axis current loop for output includes: superimposing the feedforward compensation harmonic current command onto the original quadrature axis current reference command output by the outer loop speed controller to obtain the synthesized final current command. The square root of the difference between the square of the maximum safe output current of the drive inverter and the square of the current direct-axis current is obtained as the limiting threshold. The limiting threshold is used to perform dynamic limiting verification on the synthesized final current command, and the final current command after limiting protection is output as the setpoint of the inner loop current control.

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