Ultra-silence direct-current brushless outer rotor motor driving system and design method

Abstract

The invention provides an ultra-silence direct-current brushless outer rotor motor driving system and a design method. Aiming at the problems of large low-speed vibration, high-frequency howling, sudden load change, sharp noise increase and the like of a household motor, electromagnetic-structure-control triple collaborative optimization is provided: a harmonic-efficiency model is constructed in an electromagnetic side design, and a Halbach array and fractional slot winding design is combined, so that the proportion of a high-efficiency region is greater than or equal to 85%, and the force wave amplitude is reduced by 40%; a heat dissipation path is innovatively designed on the structure side through a thermal resistance equation, G1 is in dynamic balance (residual unbalance lt; 15 mg.mm / kg), the vibration acceleration is reduced to 0.3 m / s < 2 >; the control side HFI / SMO smooth switching (angle error lt; the dynamic PWM frequency modulation avoids the sensitive frequency band, and the load abrupt change responds to the lt; and 10ms. According to the invention, noise at 3000rpm is less than or equal to 32dB, and working condition fluctuation at 60 DEG C is achieved; the ultra-silence high-reliability motor is especially suitable for the requirements of household appliances such as a washing machine and the like on ultra-silence and high-reliability motors.

Description

Technical Field

[0001] This invention relates to the field of motor drive technology, specifically to an ultra-quiet DC brushless external rotor motor drive system and its design method. Background Technology

[0002] Currently, the integration of Field-Oriented Control (FOC) vector control and mechanical vibration damping is widely adopted as the mainstream approach for noise reduction technology in external rotor motors in the home appliance industry. The core of this approach is to optimize torque ripple through a Field-Oriented Control (FOC) algorithm (typically represented by TI's MCT8316A / MCF8316A drivers), combined with a mechanical vibration damping design using silicone rubber seals to connect the shaft and the iron core. The technical path is as follows: the FOC algorithm generates a sinusoidal current output to suppress electromagnetic noise; the silicone rubber damping structure can reduce mechanical vibration noise by 2-4 dB; and the ROHM sinusoidal wave driver IC is used to suppress coil current distortion. However, this solution has inherent flaws in electronic control, mechanical structure, and system integration: In terms of electronic control, the FOC algorithm at low speeds (<1000rpm) generates audible electromagnetic noise and noticeable torque pulsation at 50-200Hz due to a ±5° position detection error in the Hall sensor; simultaneously, the fixed PWM carrier frequency (16-20kHz) causes sudden changes in switching voltage (dV / dt), inducing magnetostriction of the stator core and generating a high-frequency howling of 35-45dB (8-12kHz). In terms of mechanical structure, the external rotor dynamic balancing process only reaches the G2.5 standard; when the residual imbalance is >50mg·mm / kg, it will excite 100Hz and harmonic mechanical vibration noise, significantly weakening the vibration damping effect of the silicone rubber.

[0003] Furthermore, system integration defects exacerbate the problem: fixed-parameter PID controllers cannot respond to sudden load changes (transient noise spikes by 5-8 dB when inertia changes by >30%, typically as the "whirring" sound of a clogged vacuum cleaner); while strategies to reduce noise by lowering the rotation speed result in a 15-20°C increase in temperature, and a 0.5% decrease in permanent magnet flux at 60°C, creating a vicious cycle of "noise reduction → overheating → performance degradation." These defects collectively restrict the demand for ultra-quiet, highly reliable motors in household appliances (especially washing machines).

[0004] Chinese patent document CN113708587A discloses a "DC brushless external rotor motor with fractional slots," comprising a stator, a rotor, and a shaft. The rotor is disposed inside the stator and coaxially with it. The stator consists of stator teeth, stator slots, and windings wound on the stator teeth. A plurality of neodymium iron boron (NdFeB) permanent magnets are surface-mounted on the outer circumferential surface of the rotor core, arranged in a Halebeck array. The surface-mounted NdFeB permanent magnets on the rotor core, arranged in a Halebeck array, effectively improve the motor's power density and permanent magnet utilization. The number of slots per pole of the NdFeB permanent magnets is an irreducible true fraction, reducing the number of virtual unit motors and thus reducing motor pulsation. A carbon fiber magnet fixing layer is provided on the outer surface of the NdFeB permanent magnets, which counteracts the centrifugal force of the magnets during high-speed operation, improving motor stability and service life. Although the above technical solutions use Hellbeck arrays and fractional slots (such as 12 slots and 10 poles) to reduce torque ripple, they rely only on static magnetic circuit design and do not establish a quantitative correlation model between efficiency and vibration force; moreover, their vibration and heat dissipation are not fundamentally solved, and they do not have the ability to suppress noise under all operating conditions. Summary of the Invention

[0005] This invention proposes an ultra-quiet DC brushless external rotor motor drive system and design method. Addressing the problems of high vibration at low speeds, high-frequency howling, and sudden noise increases due to load changes in household motors, it achieves a fundamental breakthrough through a triple synergistic optimization of electromagnetics, structure, and control: It develops fractional-slot winding technology for the external rotor stator and applies the Hellbeck array to the external rotor motor, effectively improving the motor's power density and permanent magnet utilization; it optimizes the external rotor DC brushless motor drive design to improve motor operating efficiency, reduce vibration, and lower noise; and it applies new technologies and methods to collect noise, systematically constructing noise source, noise propagation channel, and heat conduction analysis models, working synergistically from material selection, product structure design, and process planning to reduce noise.

[0006] The invention also aims to achieve the following breakthroughs: On the electromagnetic side, a novel harmonic-efficiency model is developed, coupling efficiency with vibration suppression targets to reduce force wave amplitude at the source; on the structural side, the magnetic circuit design is constrained by the thermal resistance equation, combined with G1 dynamic balancing (residual amount <15mg·mm / kg) and a composite damping layer to resolve the contradiction between heat dissipation and vibration; on the control side, an HFI / SMO smooth switching algorithm and dynamic PWM frequency modulation are developed to achieve full-condition quiet operation (≤32dB), high reliability (60℃ fluctuation <±2dB), and fast response (load sudden change <10ms).

[0007] To achieve the above objectives, this invention proposes an ultra-quiet DC brushless external rotor motor drive system, including an electromagnetic optimization module, a control execution module, and a structural design module. The electromagnetic optimization module generates an efficiency map and magnetic field topology analysis results, which are output to the structural design module and the control execution module. The structural design module designs a heat dissipation structure and achieves G1 dynamic balance, while simultaneously transmitting physical constraint parameters to the control execution module. The control execution module performs wide-speed control and operating condition partitioning, implements a howling suppression strategy, and feeds back actual operating data to the electromagnetic optimization module. The three modules achieve a triple collaborative innovation of electromagnetic, mechanical, and control through bidirectional data interaction.

[0008] Preferably, the electromagnetic optimization module includes: Fractional slot winding unit, IPM topology selected and Halbach array combined with fractional slot winding collaborative design; The harmonic-efficiency model unit establishes a harmonic-efficiency model for joint optimization and performs iterative calculation of the harmonic-efficiency quantization relationship function. The efficiency map generation unit outputs a speed-efficiency map with a high efficiency zone ratio of ≥85% through finite element simulation.

[0009] Preferably, the harmonic-efficiency quantification function is a quantification function of the order of radial electromagnetic force waves and efficiency, specifically expressed as the sum of the basic efficiency part affected by the force wave and the efficiency compensation part caused by magnetic flux density distortion; by finite element iterative collaborative optimization of motor efficiency and vibration noise performance, the 0th and 2nd order radial electromagnetic force waves are suppressed and the air gap magnetic flux density distortion rate is controlled, thereby improving motor efficiency.

[0010] Preferably, the structural design module includes: The thermal resistance equation design unit designs the stator slot shape according to the hot spot-stress joint criterion, calculates the optimal heat dissipation path through the thermal resistance equation, increases the heat dissipation area by 30% and achieves a magnetic flux utilization rate of >92%. The high thermal conductivity potting compound filling unit uses high thermal conductivity potting compound to fill the gaps (thermal conductivity ≥5W / m·K) to reduce the contact thermal resistance between the stator and the housing, and optimizes the topology of the housing heat dissipation fins to make the hot spot temperature difference <8K. The G1 dynamic balance calibration unit performs G1-level dynamic balance calibration on the rotor assembly through a laser-assisted counterweight system.

[0011] The aforementioned hotspot-stress joint criterion is as follows: In the electromagnetic-thermal coupling model, the magnetic circuit design is constrained by the thermal resistance equation: thermal resistance value ≤ potting compound thickness / (thermal conductivity × heat dissipation area); where, the potting compound thickness is the vertical dimension of the colloid layer filling the stator slot; the thermal conductivity is the thermal conductivity of the potting compound material; the heat dissipation area is the effective heat exchange area between the stator slot and the housing; at the same time, the magnetic circuit design must strictly meet the electromagnetic performance requirement of magnetic flux density ≥ 1.45T.

[0012] Preferably, the control execution module includes: The wide-speed control unit uses high-frequency injection (HFI) zero-speed start in the low-speed range and switches to improved sliding mode observer (SMO) control in the medium and high-speed ranges. The operating condition zoning unit implements maximum torque-to-current ratio (MTPA) control in the constant torque region and field weakening control and voltage limit regulation in the constant power region. The howling suppression unit integrates an adaptive notch filter and a dynamic PWM frequency modulation linkage howling suppression strategy; when a 2-4kHz resonance is detected, the PWM carrier frequency is increased and the notch filter is activated.

[0013] The wide-speed control unit of the above-mentioned control execution module includes: In the low-speed range (0-200rpm), the high-frequency injection method (HFI) is used to achieve zero-speed start through magnetic saturation effect; In the medium-to-high speed range (>200 rpm), a sliding mode observer (SMO) improved with a sigmoid function is used, with an angle error of <±1°; the HFI to SMO switching is realized based on the adaptive weighting function of the speed error, and the switching threshold is set to speed error <5%.

[0014] Preferably, the howling suppression strategy is as follows: The 2-4kHz resonant frequency band was identified by acoustic power waterfall plots, and the source of the howling was located by electromagnetic-structural coupling simulation. An adaptive notch filter is embedded in the control loop to track and suppress the resonant frequency in real time. By combining frequency shifting technology, the PWM carrier frequency is dynamically adjusted to avoid sensitive frequency bands by ±200Hz; When the temperature is >60℃, the PWM carrier frequency is increased to >22kHz according to the temperature rise model to reduce magnetostrictive noise.

[0015] Preferably, the two-way data interaction includes: The electromagnetic optimization module outputs the equivalent circuit parameters of the motor to the control execution module, and the control execution module feeds back the actual operating temperature rise curve to the electromagnetic optimization module. The electromagnetic optimization module outputs an efficiency map and magnetic field topology analysis results to the structural design module, while the structural design module feeds back mechanical feasibility constraints to the electromagnetic optimization module. The structural design module transmits thermal resistance parameters and resonant frequency bands to the control execution module, while the control execution module feeds back dynamic load changes to the structural design module.

[0016] This invention also proposes a design method for an ultra-quiet DC brushless external rotor motor drive system, which includes the following steps: Modeling and experimentation were conducted on the target motor based on finite element analysis to clarify the performance gap between the target and the optimization target. The magnetic field topology of the external rotor motor was screened, and an efficiency map was generated by combining the air gap harmonic influence analysis to select the optimal electromagnetic design. A temperature rise model was established to analyze the temperature distribution of various components of the motor under different operating conditions in order to optimize the magnetic circuit and structure. By optimizing pole slot matching, winding and magnetic poles, the radial / axial electromagnetic force of the motor is suppressed, and the vibration and noise compliance scheme is determined by combining the sound power waterfall diagram and vibration mode analysis. A wide-speed control block diagram was constructed and the operating range was divided, and the switching mode of the range was studied; the operating range is the constant torque range (0-500rpm) and the constant power range (500-1500rpm); A strategy combining frequency shifting and notch control was designed to solve the whistling problem during the speed increase process, while a sensorless control algorithm was developed to achieve stable operation across the entire speed range. The drive system was built and the prototype was tested, and core vibration and noise data were collected.

[0017] Preferably, the sensorless control algorithm includes: In the low-speed stage, the rotor position is detected by high-frequency injection HFI, and zero-speed start is achieved through magnetic saturation effect; In the medium-to-high speed stage, an improved sliding mode observer (SMO) is used, and its switching function is replaced with a sigmoid function to suppress chattering. The switching logic is based on an adaptive weighting function designed for speed error. When the speed error is less than 5%, the SMO algorithm is enabled, and an online parameter identification module is introduced to compensate for changes in inductor parameters in real time.

[0018] Preferably, the system test indicators include: The angular error of the rotor position in the low-speed range is <±1°; G1 dynamic balancing calibration residual unbalance <15mg·mm / kg, vibration acceleration ≤0.3m / s² 2 @100Hz; In the dedicated control mode for washing machines, the total harmonic distortion (THD) in the constant torque region is <3%, and the efficiency in the constant power region is >92%. When the load changes abruptly, the system switches to constant torque mode based on a predictive model, with a response time of <10ms. Noise fluctuation at 60℃ is <±2dB, and noise remains at a silent level of 34dB. 39@500rpm≤Noise test data dB≤32dB@3000rpm.

[0019] When the load changes abruptly, the system switches to constant torque mode based on a prediction model. The load prediction model includes: identifying the rate of change of load inertia based on the motor current ripple spectrum; when the load inertia change is >30%, a switching command is triggered and the PID parameters are adjusted.

[0020] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: 1) Breakthrough suppression of vibration and noise: 100Hz vibration acceleration reduced from 0.8m / s² 2 Reduced to 0.3 m / s 2 (62.5% decrease), noise at 3000 rpm decreased from 38 dB to 32 dB (15.8% decrease), and howling at 2-4 kHz was <40 dB (11.1% decrease). The root cause is the harmonic-efficiency model suppressing low-order force waves and the dynamic carrier frequency shift dispersing harmonic energy. 2) Coordinated optimization of energy efficiency and temperature rise: The proportion of high-efficiency zone (efficiency > 90%) increased from 72% to ≥ 85%, and the efficiency reached 91.5% at 60℃ (88% in traditional solution). The hot spot temperature difference was < 8K (15K in traditional solution), thanks to the optimization of heat dissipation path by thermal resistance equation and filling with high thermal conductivity potting compound (≥ 5W / m·K). 3) Leap in dynamic response performance: Zero-speed start-up angle error <±1° (traditional ±5°), load change response <10ms (traditional 30ms), load change noise fluctuation <±2dB (traditional ±8dB), and noise remains at a silent level of 34dB at a high temperature of 60℃, thanks to HFI / SMO adaptive switching and load inertia spectrum identification. Attached Figure Description

[0021] Figure 1 This is a block diagram of an ultra-quiet DC brushless external rotor motor drive system provided in Embodiment 1 of the present invention.

[0022] Figure 2 This is a flowchart of a design method for an ultra-quiet DC brushless external rotor motor drive provided in Embodiment 2 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only one preferred embodiment of the present invention and are only used to explain the technical solutions of the present invention. They do not limit the scope of protection 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.

[0024] Example 1: This invention provides an ultra-quiet DC brushless external rotor motor drive system, which consists of an electromagnetic optimization module, a structural design module, and a control execution module; The electromagnetic optimization module generates an efficiency map and magnetic field topology analysis results through a harmonic-efficiency model, and outputs them to the structural design module and the control execution module. The structural design module receives the efficiency map and the magnetic field topology analysis results, designs a heat dissipation structure based on the thermal resistance equation and achieves G1 dynamic balance, and transmits physical constraint parameters to the control execution module. The control execution module receives the efficiency map and physical constraint parameters, executes wide speed control, operating condition zoning and howling suppression strategies, and feeds back the actual operating data to the electromagnetic optimization module. Among them, the three major modules achieve triple collaborative innovation of electromagnetic, mechanical and control through two-way data interaction.

[0025] The electromagnetic optimization module includes: Fractional slot winding unit, IPM topology selected and Halbach array combined with fractional slot winding collaborative design; The harmonic-efficiency model unit establishes a harmonic-efficiency model for joint optimization and performs iterative calculation of the harmonic-efficiency quantization relationship function. The efficiency map generation unit outputs a speed-efficiency map with a high efficiency zone ratio of ≥85% through finite element simulation.

[0026] The harmonic-efficiency quantification function is a quantification function of the order of radial electromagnetic force waves and efficiency, specifically expressed as the sum of the basic efficiency part affected by the force wave and the efficiency compensation part caused by magnetic flux density distortion; by finite element iterative collaborative optimization of motor efficiency and vibration noise performance, the 0th and 2nd order radial electromagnetic force waves are suppressed and the air gap magnetic flux density distortion rate is controlled, thereby improving motor efficiency.

[0027] The structural design module includes: The thermal resistance equation design unit designs the stator slot shape according to the hot spot-stress joint criterion, calculates the optimal heat dissipation path through the thermal resistance equation, increases the heat dissipation area by 30% and achieves a magnetic flux utilization rate of >92%. The high thermal conductivity potting compound filling unit uses high thermal conductivity potting compound to fill the gaps (thermal conductivity ≥5W / m·K) to reduce the contact thermal resistance between the stator and the housing, and optimizes the topology of the housing heat dissipation fins to make the hot spot temperature difference <8K. The G1 dynamic balance calibration unit performs G1-level dynamic balance calibration on the rotor assembly through a laser-assisted counterweight system.

[0028] The aforementioned hotspot-stress joint criterion is as follows: In the electromagnetic-thermal coupling model, the magnetic circuit design is constrained by the thermal resistance equation: thermal resistance value ≤ potting compound thickness / (thermal conductivity × heat dissipation area); where, the potting compound thickness is the vertical dimension of the colloid layer filling the stator slot; the thermal conductivity is the thermal conductivity of the potting compound material; the heat dissipation area is the effective heat exchange area between the stator slot and the housing; at the same time, the magnetic circuit design must strictly meet the electromagnetic performance requirement of magnetic flux density ≥ 1.45T.

[0029] The control execution module includes: The wide-speed control unit uses high-frequency injection (HFI) zero-speed start in the low-speed range and switches to improved sliding mode observer (SMO) control in the medium and high-speed ranges. The operating condition zoning unit implements maximum torque-to-current ratio (MTPA) control in the constant torque region and field weakening control and voltage limit regulation in the constant power region. The howling suppression unit integrates an adaptive notch filter and a dynamic PWM frequency modulation linkage howling suppression strategy; when a 2-4kHz resonance is detected, the PWM carrier frequency is increased and the notch filter is activated.

[0030] The wide-speed control unit of the above-mentioned control execution module includes: In the low-speed range (0-200rpm), the high-frequency injection method (HFI) is used to achieve zero-speed start through magnetic saturation effect; In the medium-to-high speed range (>200 rpm), a sliding mode observer (SMO) improved with a sigmoid function is used, with an angle error of <±1°; the HFI to SMO switching is realized based on the adaptive weighting function of the speed error, and the switching threshold is set to speed error <5%.

[0031] The howling suppression strategy is as follows: The 2-4kHz resonant frequency band was identified by acoustic power waterfall plots, and the source of the howling was located by electromagnetic-structural coupling simulation. An adaptive notch filter is embedded in the control loop to track and suppress the resonant frequency in real time. By combining frequency shifting technology, the PWM carrier frequency is dynamically adjusted to avoid sensitive frequency bands by ±200Hz; When the temperature is >60℃, the PWM carrier frequency is increased to >22kHz according to the temperature rise model to reduce magnetostrictive noise.

[0032] Figure 1The block diagram of the ultra-quiet DC brushless external rotor motor drive system is shown. Its core lies in the three-dimensional collaborative architecture of the electromagnetic optimization module, the structural design module, and the control execution module.

[0033] As the design hub of the system, the electromagnetic optimization module first generates an initial magnetic field topology based on a fractional-slot winding scheme (such as a 60-slot-8-pole combination). Its integrated harmonic-efficiency model dynamically correlates motor efficiency with two key physical quantities through quantification: first, the amplitude of radial electromagnetic force waves, such as the 0th-order uniform expansion force F0 and the 2nd-order elliptic deformation force F2; and second, the uniformity index of the air gap magnetic flux density distribution. This model, combined with finite element simulation data, outputs two key parameters: first, an efficiency map, marking the distribution of the high-efficiency region (efficiency > 90%) within the 0-1800 rpm speed range; and second, motor equivalent circuit parameters, including the direct and quadrature-axis inductances and back electromotive force constants. These parameters are transmitted to the control execution module via a real-time data bus, providing the theoretical basis for its control algorithm design. Meanwhile, the electromagnetic module receives mechanical process constraints from the structural design module (such as minimum slot width ≥ 0.5mm, magnetic pole segmentation process tolerance) and actual operating data fed back by the control module (such as winding temperature rise curve, load sudden change spectrum) to dynamically correct model parameters; for example, when the temperature rise rate is abnormal, the weights of the force wave loss coefficients α and β in the model are automatically adjusted to ensure the matching between theoretical design and actual working conditions.

[0034] The structural design module is responsible for both physical implementation and reliability assurance. It receives efficiency maps and magnetic field force wave analysis results from the electromagnetic module, calculates the optimal heat dissipation path using the thermal resistance equation, with key parameters including potting compound thickness, thermal conductivity, and heat dissipation area. Based on this equation, the module performs triple optimization: first, it designs an asymmetric stator slot shape, significantly increasing the heat dissipation area by 30% while ensuring a magnetic flux density B ≥ 1.45T; second, it uses a high thermal conductivity nanocomposite potting compound to fill the slots, reducing the heat transfer resistance between the stator and the housing; and third, it performs G1-level dynamic balancing calibration of the rotor assembly using a laser-assisted counterweight system, ensuring a residual imbalance of <15 mg·mm / kg. This module outputs two types of physical constraints to the control execution module: thermal management parameters (such as a hot spot temperature rise threshold of 60℃) and mechanical resonance frequency band characteristics (2-4kHz range). Simultaneously, it receives dynamic load signals from the control module (such as a sudden load spectrum) to verify whether the potting compound damping characteristics meet the requirements of sudden operating conditions and the effectiveness and reliability of the mechanical damping design.

[0035] The control execution module is the dynamic adjustment center of the system, and its design relies entirely on the output data of the first two modules. In the wide-speed control unit: in the low-speed range (0-200rpm), the high-frequency injection method HFI is used to achieve zero-speed start-up. By injecting a specific voltage signal into the stator winding, the rotor position is detected by the change in inductance caused by the magnetic saturation effect; in the medium-to-high speed range (>200rpm), the control switches to the sliding mode observer (SMO) control with an improved Sigmoid function, replacing the traditional switching function with a smooth transition function to suppress control chattering (angle error <±1°); seamless switching between the two is achieved through an adaptive weighting mechanism, with the weighting coefficient changing with the speed error (SMO is activated when the error is <5%). The operating condition partitioning unit divides the control strategy according to the efficiency map of the electromagnetic module: in the constant torque range (0-500rpm), the maximum torque-to-current ratio (MTPA) control is used to maintain the current harmonic distortion (THD) rate <3%; in the constant power range (500-1500rpm), field weakening control and voltage limit loop regulation are combined, with an efficiency >92%, ensuring high-efficiency operation. The whistling suppression unit directly responds to the resonant frequency band data of the structural module: a frequency-adjustable adaptive notch filter with a center frequency of 2-4kHz is embedded in the control loop, and dynamic PWM carrier frequency adjustment technology is used in conjunction with it (with a ±200Hz offset to avoid the 16-20kHz sensitive band of the human ear); when the temperature sensor detects an overheating risk, the switching frequency is automatically increased to reduce magnetostrictive noise. In addition, the load prediction switching submodule identifies load changes by analyzing the current ripple characteristics in real time, and switches to constant torque mode at the moment of change (response time <10ms), suppressing noise fluctuations <±2dB. This module receives the optimal operating point data of the electromagnetic module and feeds back the operating status to other modules in real time to form a closed loop.

[0036] The entire system's collaborative closed loop is achieved through bidirectional data flow interaction: the electromagnetic optimization module outputs motor equivalent circuit parameters to the control execution module, while the control execution module feeds back the actual operating temperature rise curve to the electromagnetic optimization module; the electromagnetic optimization module outputs efficiency maps and magnetic field topology analysis results to the structural design module, while the structural design module feeds back mechanical feasibility constraints to the electromagnetic optimization module; the structural design module transmits thermal resistance parameters and resonant frequency bands to the control execution module, while the control execution module feeds back dynamic load changes to the structural design module. Specifically, the efficiency map from the electromagnetic module provides the control module with the basis for operating condition zoning boundaries, and the control module's operating status data (such as the temperature rise curve) drives the electromagnetic model correction in reverse; the mechanical resonance parameters from the structural module directly configure the control module's filter center frequency, while the load mutation signal from the control module verifies the effectiveness of the structural damping design.

[0037] The final system output parameters are strictly limited to the safe thresholds for vibration and noise: vibration acceleration at 100Hz ≤ 0.3m / s². 2 Noise level ≤32dB at 3000rpm.

[0038] Example 2: Reference Figure 2 This flowchart systematically describes the design method for an ultra-quiet DC brushless external rotor motor drive provided by this invention. Based on the ultra-quiet DC brushless external rotor motor drive system, this invention adopts an "electromagnetic-control-verification" closed-loop design process, strictly following the following three-stage steps to achieve triple collaborative optimization: Step 1, Electromagnetic-Structure Joint Optimization Stage: S1: Based on finite element analysis, theoretical modeling and experiments are conducted on the target motor to obtain the performance gap with the optimization target; S2: Screen the magnetic field topology of the external rotor motor, combine the influence analysis of air gap harmonics on electromagnetic force, generate different topology efficiency maps and select the optimal design that meets the electromagnetic performance of the motor. S3: Establish a temperature rise model, analyze the temperature distribution of various components of the motor under different operating conditions, and optimize the magnetic circuit and structure; S4: By optimizing pole slot matching, winding design and magnetic poles, the radial / axial electromagnetic force of the motor is suppressed, and the vibration and noise compliance scheme is determined by combining the sound power waterfall diagram and vibration mode analysis. Step 2, Control Algorithm Development Phase: S5: Construct a wide-speed control block diagram, divide it into a constant torque region (0-500rpm) and a constant power region (500-1500rpm), and study the region switching mode; S6: To address the whistling issue during speed increase, a strategy combining frequency shifting and notch filtering is designed to dynamically adjust the PWM carrier frequency to avoid sensitive frequency bands; simultaneously, a sensorless control algorithm is developed to achieve stable operation across the entire speed range. Step 3, System Verification Phase: S7: Build the drive system and deploy the control program, test the prototype on the experimental platform, and collect core vibration and noise data.

[0039] The design process begins with the electromagnetic-structural joint optimization phase. First, a benchmark motor is modeled using finite element software (such as ANSYS Maxwell), and multi-condition simulations (rated load, stall, sudden unloading, etc.) are performed. Vibration (100Hz), noise (3000rpm), and temperature rise data of the benchmark prototype are then measured on an experimental bench, and compared with the target performance parameters (efficiency >90%, vibration <0.3m / s²). 2The system identifies discrepancies and outputs a report. Next, based on the characteristics of the external rotor structure, it filters magnetic field topologies (embedded permanent magnet IPM / surface permanent magnet SPM / permanent magnet shunt PMFS): For the special operating conditions of household appliances, such as the load characteristics of washing machines (frequent starts and stops, wide speed range), the surface permanent magnet (SPM) scheme is excluded (insufficient high-speed field weakening capability), and the embedded permanent magnet IPM scheme is selected, employing a fractional-slot winding with specific pole-slot combinations (e.g., 60 slots - 8 poles) to reduce cogging torque. Subsequently, a core harmonic-efficiency model is constructed to analyze the impact of air gap harmonics on radial electromagnetic force (F0 / F2), generating efficiency maps for different topologies. This model decomposes motor efficiency into three parts: basic efficiency, force wave loss efficiency component, and magnetic flux density distortion compensation term; the model parameters must meet strict force wave amplitude limits and magnetic flux density uniformity requirements (F0≤0.08N / m). 2 F2≤0.05N / m 2 If △B < 3% - If the standard is not met, adjust the pole-slot combination (e.g., change to 72 slots - 10 poles) or increase the skew angle (5° → 7°) and iterate again. Finally, select the optimal design that meets the electromagnetic performance of the motor: the high-efficiency zone (>90%) accounts for ≥85%.

[0040] After completing the electromagnetic model optimization, the thermal management design sub-process begins: A temperature rise model is established, stator copper loss and rotor iron loss data are input, and the temperature field distribution under different loads is simulated. If the hot spot temperature difference exceeds the standard (hot spot temperature difference > 8K), structural parameter optimization is initiated: the layout of the heat dissipation fins on the casing is redesigned (e.g., an asymmetrical layout increases the heat dissipation area by 30%) or the potting compound filling ratio is adjusted (e.g., 60% → 80%). After the thermal design meets the standards (hot spot temperature difference < 8K), the noise and vibration levels are verified through sound power waterfall plots and vibration modal analysis to determine the vibration and noise compliance scheme (100Hz vibration acceleration ≤ 0.3m / s²). 2 Noise level ≤ 32dB at 3000rpm — If acceleration exceeds the limit (> 0.3m / s²), 2 Return to modify the magnetic pole segmentation scheme (e.g., change the 4-segment Halbach array to a 3-segment array).

[0041] After entering the control algorithm development stage, the operating conditions are first divided into zones: the constant torque zone (0-500rpm) uses maximum torque-to-current ratio (MTPA) control, and the constant power zone (500-1500rpm) implements field weakening control and voltage limit regulation. The sensorless control algorithm is designed with a frequency band strategy: in the low-speed zone, a high-frequency injection method (HFI) is deployed to detect the rotor position, and zero-speed start is achieved through magnetic saturation effect. When the motor is stationary, the rotor is positioned by a specific current response envelope; in the medium and high-speed zones, the improved sliding mode observer (SMO) is switched to, and a smoothed sigmoid function is used to replace the traditional switching mechanism to significantly reduce angle jitter. The switching logic is based on adaptive weighting of speed error, with the weighting coefficient changing with the speed error. When the speed error is <5%, the SMO algorithm is activated, and an online parameter identification module is introduced to compensate for inductor parameter changes in real time. The howling suppression strategy combines acoustic test data: if the waterfall plot shows a resonance peak in the 2-4kHz range, a second-order adaptive notch filter is embedded in the control loop, and dynamic random offset technology is used to adjust the PWM carrier frequency to disperse harmonic energy.

[0042] Finally, during the system verification phase, a prototype was built and an experimental platform was constructed. Test items included: Vibration test: Accelerometer collects data at a frequency of 100Hz. If the data exceeds the standard, the source is traced back to the electromagnetic module and the winding is modified. Noise test: Measure the sound pressure level at 3000 rpm in a semi-anechoic chamber. If it exceeds the standard, check the PWM frequency modulation strategy. Temperature rise test: The infrared thermal imager scans the temperature field of the casing. If the noise fluctuation at 60℃ is >±2dB, the stability is insufficient, and the thermal resistance equation is returned to be optimized again. Load mutation test: Simulate real-world mutation scenarios (such as washing machine blockage) to verify switching response time and noise stability.

[0043] The system test metrics include: The angular error of the rotor position in the low-speed range is <±1°; G1 dynamic balancing calibration residual unbalance <15mg·mm / kg, vibration acceleration ≤0.3m / s² 2 @100Hz; In the dedicated control mode for washing machines, the total harmonic distortion (THD) in the constant torque region is <3%, and the efficiency in the constant power region is >92%. When the load changes abruptly, the system switches to constant torque mode based on a predictive model, with a response time of <10ms. Noise fluctuation at 60℃ is <±2dB, and noise remains at a silent level of 34dB. 39@500rpm≤Noise test data dB≤32dB@3000rpm.

[0044] When the load changes abruptly, the system switches to constant torque mode based on a prediction model. The load prediction model includes: identifying the rate of change of load inertia based on the motor current ripple spectrum; when the load inertia change is >30%, a switching command is triggered and the PID parameters are adjusted.

[0045] Once all performance indicators are met, the process moves into mass production, forming a closed-loop system of "electromagnetic design → control development → experimental verification → feedback optimization." The unique value of this process lies in: Deep coupling of electromagnetics and control: the efficiency map directly defines the control partition boundary, and the force wave data drives the configuration of the notch filter; real-time linkage between structure and control: thermal resistance parameters determine the PWM temperature control strategy, and the resonant frequency band activates dynamic frequency modulation; Data closed-loop verification: Prototype test results are used to correct electromagnetic model coefficients (such as α and β) in reverse, enabling continuous optimization and self-iteration of the technical solution.

[0046] In summary, this invention proposes an ultra-quiet DC brushless external rotor motor drive system and its design method. Addressing the problems of high vibration at low speeds, high-frequency howling, and sudden increase in noise due to load changes in household motors, it proposes a triple-coordinated optimization of electromagnetics, structure, and control: On the electromagnetic side, a harmonic-efficiency model is constructed, combined with Halbach array and fractional slot winding design, achieving a high-efficiency zone ratio of ≥85% and reducing force wave amplitude by 40%; on the structural side, an innovative heat dissipation path is designed using thermal resistance equations, and G1 dynamic balancing (residual imbalance <15mg·mm / kg) reduces vibration acceleration to 0.3m / s². 2 The control side features smooth HFI / SMO switching (angle error < ±1°), dynamic PWM frequency modulation avoids sensitive frequency bands, and load change response < 10ms. This invention ultimately achieves a quiet operation with noise ≤ 32dB at 3000rpm and fluctuation < ±2dB at 60℃, making it particularly suitable for household appliances such as washing machines that require ultra-quiet, highly reliable motors.

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. It should be noted that for those skilled in the art, any changes or substitutions that can be easily conceived without departing from the technical principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A super-quiet DC brushless external rotor motor drive system, characterized in that, The system includes an electromagnetic optimization module, a control execution module, and a structural design module. The electromagnetic optimization module generates an efficiency map and magnetic field topology analysis results, which are then output to the structural design module and the control execution module. The structural design module designs a heat dissipation structure and achieves G1 dynamic balance, while simultaneously transmitting physical constraint parameters to the control execution module. The control execution module performs wide-speed control and operating condition zoning, implements a whistling suppression strategy, and feeds back actual operating data to the electromagnetic optimization module. These three modules achieve a triple collaborative innovation of electromagnetic, mechanical, and control systems through bidirectional data interaction.

2. The ultra-quiet DC brushless external rotor motor drive system according to claim 1, characterized in that, The electromagnetic optimization module includes: Fractional slot winding unit, IPM topology selected and Halbach array combined with fractional slot winding collaborative design; The harmonic-efficiency model unit establishes the harmonic-efficiency model and performs iterative calculations of the harmonic-efficiency quantization relationship function. The efficiency map generation unit outputs a speed-efficiency map with an efficient region accounting for ≥85%.

3. The ultra-quiet DC brushless external rotor motor drive system according to claim 2, characterized in that, The harmonic-efficiency quantification function is a quantification function of the order of radial electromagnetic force waves and efficiency, specifically expressed as the sum of the basic efficiency part affected by the force wave and the efficiency compensation part caused by magnetic flux density distortion; by finite element iterative collaborative optimization of motor efficiency and vibration noise performance, the 0th and 2nd order radial electromagnetic force waves are suppressed and the air gap magnetic flux density distortion rate is controlled, thereby improving motor efficiency.

4. The ultra-quiet DC brushless external rotor motor drive system according to claim 1, characterized in that, The structural design module includes: The thermal resistance equation design unit calculates the optimal heat dissipation path using the thermal resistance equation. The high thermal conductivity potting compound filling unit uses high thermal conductivity potting compound to fill the gaps, reducing the contact thermal resistance between the stator and the housing, and optimizing the topology of the housing heat dissipation fins to make the hot spot temperature difference <8K. The G1 dynamic balance calibration unit performs G1-level dynamic balance calibration on the rotor assembly through a laser-assisted counterweight system.

5. The ultra-quiet DC brushless external rotor motor drive system according to claim 1, characterized in that, The control execution module includes: The wide-speed control unit uses high-frequency injection (HFI) zero-speed start in the low-speed range and switches to improved sliding mode observer (SMO) control in the medium and high-speed ranges. The operating condition zoning unit implements maximum torque-to-current ratio (MTPA) control in the constant torque region and field weakening control and voltage limit regulation in the constant power region. The howling suppression unit integrates an adaptive notch filter and a dynamic PWM frequency modulation linkage howling suppression strategy.

6. A super-quiet DC brushless external rotor motor drive system according to claim 1 or 5, characterized in that, The howling suppression strategy is as follows: The 2-4kHz resonant frequency band was identified by acoustic power waterfall plots, and the source of the howling was located by electromagnetic-structural coupling simulation. An adaptive notch filter is embedded in the control loop to track and suppress the resonant frequency in real time. By combining frequency shifting technology, the PWM carrier frequency is dynamically adjusted to avoid sensitive frequency bands; When the temperature is >60℃, the PWM carrier frequency is increased to >22kHz according to the temperature rise model to reduce magnetostrictive noise.

7. The ultra-quiet DC brushless external rotor motor drive system according to claim 1, characterized in that, The two-way data interaction includes: The electromagnetic optimization module outputs the equivalent circuit parameters of the motor to the control execution module, and the control execution module feeds back the actual operating temperature rise curve to the electromagnetic optimization module. The electromagnetic optimization module outputs an efficiency map and magnetic field topology analysis results to the structural design module, while the structural design module feeds back mechanical feasibility constraints to the electromagnetic optimization module. The structural design module transmits thermal resistance parameters and resonant frequency bands to the control execution module, while the control execution module feeds back dynamic load changes to the structural design module.

8. A design method for an ultra-quiet DC brushless external rotor motor drive, based on the ultra-quiet DC brushless external rotor motor drive system according to any one of claims 1 to 7, characterized in that, include: Screen the magnetic field topology of the external rotor motor, generate an efficiency map, and select the optimal electromagnetic design; A temperature rise model was established to analyze the temperature distribution of each component under different operating conditions in order to optimize the magnetic circuit and structure. By optimizing pole slot matching, windings, and magnetic poles, the radial / axial electromagnetic forces of the motor are suppressed, and a vibration and noise compliance solution is determined. Construct a wide-speed control block diagram and divide the operating zone, and study the zone switching mode; A frequency shift and notch control strategy was designed to solve the whistling problem, and a sensorless control algorithm was used to achieve stable operation at all speeds. The drive system was built and tested, and core vibration and noise data were collected.

9. The ultra-quiet DC brushless external rotor motor drive design method according to claim 7, characterized in that, The sensorless control algorithm includes: In the low-speed stage, the rotor position is detected by high-frequency injection HFI, and zero-speed start is achieved through magnetic saturation effect; In the medium-to-high speed stage, an improved sliding mode observer (SMO) is used, and its switching function is replaced with a sigmoid function to suppress chattering. The switching logic is based on an adaptive weighting function designed for speed error. When the speed error is less than 5%, the SMO algorithm is enabled, and an online parameter identification module is introduced to compensate for changes in inductor parameters in real time.

10. The ultra-quiet DC brushless external rotor motor drive design method according to claim 7, characterized in that, The system test metrics include: The angular error of the rotor position in the low-speed range is <±1°; G1 dynamic balancing calibration residual unbalance <15mg·mm / kg, vibration acceleration ≤0.3m / s² 2 @100Hz; In the dedicated control mode for washing machines, the current harmonic distortion rate (THD) in the constant torque zone is <3%, and the efficiency in the constant power zone is >92%. When the load changes abruptly, the system switches to the constant torque zone with a response time of <10ms. Noise fluctuation at 60℃ is <±2dB, and noise remains at a silent level of 34dB. 39@500rpm≤Noise test data dB≤32dB@3000rpm.

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